Part II: Post 23: Mission to the Asteroids: NASA NEAP, ESA Piazzi and Soviet “Grand Tour” program
Hello everyone! I'm posting this week from my re-vivified laptop, with all programs now re-installed and performing nominally! With that done, we'll be returning to the ongoing construction of Mir and Freedom here in a couple weeks. However, this week, we're following up on last week's post about probes to comets (including the second half of the Kirchoff mission) by looking at the other primitive bodies of the solar system: asteroids. 1161 replies, 142335 views
Eyes Turned Skyward, Part II: Post #23:
Comets were not the only type of primitive body attracting new scrutiny from astronomers and planetary scientists during the 1980s. Even as early as the 1960s, NASA had drawn up plans for a "Main Belt Tour" where a spacecraft would traverse the entire main asteroid belt, from inner to outer edge, using a Pioneer-type spacecraft. Due to limited funding and the absence of any particular asteroid flybys on the mission schedule, the mission failed to gain approval, but the idea of exploring the asteroids did not die with it. Again, though, NASA would not be the first to dispatch a mission to the asteroid belt, and again that honor would instead fall to the Europeans. In the early 1980s, ESA approved two new major robotic missions for development and launch in the next decade; first, the International Infrared Observatory, or IIO, in collaboration with Japan, and second the Piazzi mission, named after the Italian astronomer responsible for discovering the first asteroid, Ceres, in 1801. Like NASA's Main Belt Tour, this would visit the main asteroid belt, lying between the orbits of Mars and Jupiter. However, rather than simply be thrown into a belt-crossing orbit by its launch vehicle, Piazzi would use ion thrusters to constantly modify its orbit, allowing it to visit and orbit several asteroids during its tour of the belt, all of different types.[1] While Ceres would unfortunately not be among them, Piazzi would still be able to thoroughly investigate several different asteroids of varying spectral types while also flying by several other bodies in between these longer encounters. Encountering "C" and "S" spectral type asteroids was a particularly high scientific priority, as bodies of the former type appeared to be more primitive, and therefore more similar to "original" Solar System material than other asteroids, while objects of the latter type seemed similar to a large number of meteorites found on Earth.[2] Also of interest were the "M"-type asteroids, which appeared to be more metallic than others and might therefore be the remnants of protoplanetary cores, and the unique "V"-type Vesta, which seemed to have undergone differentiation and volcanic activity much like Earth or Mars. Since there were an abundance of possible targets, dependent on launch date, multiple possible tour options were drawn up, addressing possible launch dates, from scheduled to optimistic to contingency.
At the same time, the Soviets were beginning what they were calling the "Grand Tour" program. Like the American Grand Tour of the 1970s, this would use a series of gravitational assists to visit a wide range of targets which otherwise would have been far more difficult and time-consuming to reach. Unlike the American program, which planned to visit the giant planets and Pluto, "Grand Tour" planned to visit the near-Earth asteroids, with help from Venus and Earth. After launch, it would fly by Venus, whose gravity would redirect it to fly by one of the Aten asteroids, a class of asteroids that pass only just outside Earth's orbit at their greatest distance from the Sun, then dive into the hotter realms below. After this encounter, the probe would ascend back towards Earth orbit, where it could either flyby Earth--increasing its energy and allowing another asteroid flyby--or conduct a deep-space maneuver for the same purpose. This pattern of gravity assists allowing asteroid encounters could continue for several orbits around the Sun, allowing the probe to conduct a detailed survey of at least the Aten asteroids, and possibly some of the also Earth-orbit crossing Apollo asteroids, clarifying many of their bulk properties and providing "ground truth" for radar and spectroscopic studies. This would not be a solely Soviet endeavor, either, as they reached out to the French and German space agencies to participate in the mission. This early international involvement would prove to be prescient, as "Grand Tour" was buffered to some extent against the political and budgetary issues that gradually grew to consume the Soviet space program over the next half-decade. With the French and Germans already heavily involved and unwilling to simply abandon their investment, the Russians could count on outside financial support for the ambitious mission even as their own ability to fund it withered away.[3]
In response to these actions from the Europeans and Soviets, the United States began its own Near Earth Asteroid Pioneer program in 1987. Unlike Piazzi and Grand Tour, NEAP would rendezvous with a near-Earth body, then intensively investigate it from a nearby vantage point. Besides complementing their observations, especially Grand Tour, which would give brief glimpses of a wide range of objects, NEAP would show that NASA and the United States were just as capable as anyone else of dispatching missions to asteroids. Managed by Ames Research Center and based on their ongoing Lunar Reconnaissance and Mars Reconnaissance Pioneers, the development of NEAP played second fiddle to those already established spacecraft. Nevertheless, the identification and solution of problems in both the LRP and MRP spacecraft greatly assisted the design of NEAP, despite the modifications needed not only to adapt it for a different target than either but also to a different launch vehicle. In a major victory, Lockheed had won some of the first competitively awarded US government launch contracts, including that for the Near Earth Asteroid Pioneer. Fortunately, the degree of modification needed for the probe due to the very different environments of its target to that of Mars or the Moon meant that modifications for the differing launch environment were relatively simple to accommodate within the overall program. In late May 1992, NEAP left Earth for its final destination, an Amor-type asteroid with a diameter of 2.3 kilometers called 1943 Anteros.[4] While small, it was hoped this target would be relatively representative of other near-Earth bodies, and frequent launch windows raised hopes that future missions might be dispatched to the same asteroid, perhaps to return samples of Anteros to Earth.
After a voyage of over a year, NEAP finally reached Anteros in late August 1993, where it executed a burn providing nearly a kilometer per second of delta-V to put itself in orbit around the asteroid. From there, it quickly set out to thoroughly investigate Anteros, mapping it in high resolution, determining its surface composition, and producing a global shape profile via a laser rangefinder/altimeter. Careful tracking of NEAP’s signals on Earth provided estimates of Aneteros’ gravitational field, as well, although not to the precision necessary to probe its internal structure. For nearly two years, during the entire period of the asteroid’s orbit around the Sun, NEAP observed the asteroid, creating the first complete record of the seasonal changes to such an airless body in such an elliptical orbit, greatly exceeding its design mission in the process. Finally, in April 1995, with NEAP having completed its full extended mission, controllers decided to attempt a final experiment: repeating the successes of Kirchhoff and Mars 12, and landing NEAP on Anteros. Over a period of about a month, NEAP slowly lowered its orbit until it was passing within a few hundred meters of Anteros’ surface, before finally putting itself on a trajectory that would intersect the asteroid’s surface. To the delight of controllers, who had thought that NEAP’s low propellant reserves might cause the probe to be destroyed during the landing, NEAP soon checked in from its landing point, apparently a stretch of rocky ground near the rim of the crater Big Dip (so-named by the imaging team as one of the largest craters on Anteros). NEAP had, nevertheless, suffered significant damage during the landing, and the hostile thermal environment of Anteros’ surface ended the probe only a few days after touchdown, though not before it was able to take extremely close range spectroscopic data from the surface.
Even as NEAP marched easily towards launch, Piazzi was struggling to get off the ground. Developmental difficulties related to its challenging environment and novel form of propulsion caused repeated delays and budget overruns in the probe, which gradually grew to dominate ESA's science programs as other spacecraft suffered less serious problems. These issues were compounded by related overruns and problems with the series of "minor" missions that ESA had become involved in, ranging from the Newton comet probe to the Mars Surface Elements of the Mars 12/13 mission. To fill the gaps, ESA tended to raid Piazzi's funding, reasoning that the probe was so far over budget and behind schedule that it would matter little. Having already slipped from a planned 1990 launch date into 1991, the final blow came with German reunification and the related collapse of the Soviet Union. With ESA member states, especially Germany, reducing their allocations, all programs of ESA had to suffer. Although plans to convert the Minotaur logistics vehicle to carry humans bore the brunt of the cuts, Piazzi was not spared, slipping to 1992 and then 1993 as a result. The only thing that spared it from outright cancellation was the fact that significant flight hardware had been procured, and it would be more expensive to cancel it and dispose of the otherwise useless remains then to finish and fly the mission after all. When it finally launched in February of 1993, the scientists involved were happy that it had at last gotten off of the ground, almost regardless of which asteroids it would be visiting. Insertion into a heliocentric orbit, followed by startup of the probe's ion engines (a more advanced and capable design than those used on Kirchhoff) proceeded smoothly, and Piazzi began its voyage to the asteroids. A year and a half after launch, Piazzi reached its first target, the 46 kilometer SX-type asteroid 113 Amalthea (not to be confused with the Jovian moon). Although it sped by Amalthea at 3 kilometers per second, Piazzi was nevertheless able to image the asteroid and collect remote-sensing data about its surface, together with determining its mass and rotational period to a greater precision than possible from Earth.
In June 1995, Piazzi at last reached the first of its rendezvous targets, 4 Vesta, in so doing becoming the first spacecraft to rendezvous with and orbit a main-belt asteroid. The third largest of the asteroids with a diameter of 576 kilometers and the only one sometimes visible to the naked eye from Earth, Vesta was of particular interest due to the processes of differentiation and vulcanism it seemed to have gone through, unlike most other asteroids. Since Vesta is so much smaller than other bodies that have gone through the same evolution, like Earth or the Moon, it therefore offered a unique chance to see such a body frozen in mid-stride, so to speak, before it could really get going. Besides that, comparison with other asteroidal bodies, particularly those of relatively similar composition, might allow a better understanding of what conditions were needed for differentiation, a key step in the formation of planets and other large bodies, to occur. The world that was revealed to Piazzi's instruments met all of those expectations and more, possessing just as much geological diversity as any planet or moon elsewhere in the Solar system. The most prominent feature on Vesta’s battered surface was a massive impact basin occupying much of the southern hemisphere, itself overlying another giant crater, probably the source of much of the material in the asteroid belt observed to originate from Vesta. These impacts seemed to have created a system of massive troughs and cliffs elsewhere on the surface from seismic waves, giving Vesta a rough, textured appearance together with the ubiquitous impact craters. Finally, data returned by the probe showed that the interior of Vesta appeared to be much more similar to that of Earth, Mars, or other terrestrial planets than any previously explored asteroid, with clearly separate core, mantle, and crust regions.[5] Unfortunately, the probe’s exploratory mission had to be ended after only three months probing Vesta[6], as the window for its departure to its second destination, the 90 kilometer wide S-type asteroid 17 Thetis opened in late September 1995.
After departing Vesta, Piazzi’s ion thrusters smoothly functioned through the voyage to Thetis, marked only by the flyby of the 96 kilometer C-type asteroid 313 Chaldaea in March 1996. As an S-type asteroid, Thetis was spectroscopically similar to the important class of meteorites called the ordinary chondrites, promising possible breakthroughs in the understanding of the origins of these meteorites. Therefore, in October 1996 Piazzi slowly slid into orbit around Thetis, hoping to catch a better look than had been available from Earth. It was richly rewarded, as a world far smaller but with just as much history to explore passed under its cameras. Like Vesta, or for that matter the Moon, Thetis proved to be pockmarked with craters and other evidence of impact at all scales visible to Piazzi's cameras, from the most minute to the very largest. Furthermore, several ordinary chondrites in fact proved to be from Thetis, or at least to be near-perfect spectroscopic matches for regions of Thetis visible to Piazzi[7], effectively making them some of the first samples returned from a known asteroid, only slightly beaten by the vast collection of Howardite-Eucrite-Diogenite meteorites from Vesta. As with every other body ever visited by space probes, from Charon to Mercury, Thetis also proved to have a rich geological history, with evidence, curious in light of the asteroid's evident lack of differentiation and therefore of significant internal heating, of flows of rock through the asteroid and other internal activity. The four months of observation Piazza was allowed by orbital mechanics before departing Thetis for good only opened up more questions on the part of the mission team, but the probe once again had to frustrate any desires for a more in-depth investigation.
Piazzi's last stop would be the 86 kilometer C-type 449 Hamburga. While the asteroids 313 Chaldaea and 415 Palatia, which it had flown by in March 1996 and June 1997, respectively, had both been C-types, the brief encounters Piazzi had been limited to had only whetted the appetites of asteroid scientists for the more detailed look waiting at the end of the line. If Piazzi would cooperate, at least, for the aging probe was becoming increasingly cranky and difficult for European ground controllers to manage. Several of the ion thrusters had developed problems which, while not mission-ending, nevertheless required careful attention to allow proper operation, while power output had decreased more than anticipated from radiation exposure and panel damage. Nevertheless, in September of 1998 the probe was able to push itself into orbit around Hamburga, finally giving scientists the view they had been waiting for since launch. Once again, Piazzi's imagery revealed a world battered by impacts, a familiar scene throughout
the solar system by now, and once again evidence of internal activity, perhaps similar to that within the icy moons of the outer system. However, it was in spectroscopic analysis that Hamburga's differences with Vesta and Thetis shone through, with a rich surface chemistry revealed to these probing appendages[8]. A fantastically complex mélange of organic and inorganic chemicals seemed to coat Hamburga's surface, transforming every square centimeter into the equivalent of a chemical factory. Energetic solar radiation, together with whatever internal heat Hamburga had once possessed and perhaps the occasional impact seemed to have catalyzed an amazing range of surface chemistry, despite the lack of water, air, or any other fluid medium for chemical reaction. There was even some evidence that extremely simple chains of amino acids and nucleotides seemed to have formed on Hamburga's surface, something which proved to have a significant effect on later theories of abiogenesis. With no future destinations in mind--in any case, Piazzi had virtually exhausted its ion propellant stocks upon reaching Hamburga--the scientific team could take as long as they liked examining and reexamining Hamburga’s surface, limited only by the probe’s inevitable failure or the ending of operational funding. Finally, in early 2000 Piazzi stopped responding to commands from Earth, ending Europe’s first completely independent and highly successful planetary science mission.
[1]: This is based on the AGORA mission. You may have noted that ITTL things are a bit friendlier to planetary exploration across the board; this is another expression of that tendency. IOTL, ESA tended to fund more telescopes.
[2]: This is my understanding, anyways.
[3]: The fate of this probe will not be revealed. Yet.
[4]: This was a common target for asteroid missions during the 1980s IOTL, along with 4660 Nereus and 433 Eros, because it is relatively easy to reach and has frequent (roughly once every other year) launch windows.
[5]: This is all as per Dawn--go Dawn!
[6]: Alas, time and windows wait for no probe.
[7]: As far as I know, this is plausible speculation, but the sources of most if not all ordinary chondrites are not actually known.
[8]: Again, I believe this and the following to be plausible speculation based on carbonaceous chondrites (which correspond to “C”-type asteroids, sort of).
Eyes Turned Skyward, Part II: Post #23:
Comets were not the only type of primitive body attracting new scrutiny from astronomers and planetary scientists during the 1980s. Even as early as the 1960s, NASA had drawn up plans for a "Main Belt Tour" where a spacecraft would traverse the entire main asteroid belt, from inner to outer edge, using a Pioneer-type spacecraft. Due to limited funding and the absence of any particular asteroid flybys on the mission schedule, the mission failed to gain approval, but the idea of exploring the asteroids did not die with it. Again, though, NASA would not be the first to dispatch a mission to the asteroid belt, and again that honor would instead fall to the Europeans. In the early 1980s, ESA approved two new major robotic missions for development and launch in the next decade; first, the International Infrared Observatory, or IIO, in collaboration with Japan, and second the Piazzi mission, named after the Italian astronomer responsible for discovering the first asteroid, Ceres, in 1801. Like NASA's Main Belt Tour, this would visit the main asteroid belt, lying between the orbits of Mars and Jupiter. However, rather than simply be thrown into a belt-crossing orbit by its launch vehicle, Piazzi would use ion thrusters to constantly modify its orbit, allowing it to visit and orbit several asteroids during its tour of the belt, all of different types.[1] While Ceres would unfortunately not be among them, Piazzi would still be able to thoroughly investigate several different asteroids of varying spectral types while also flying by several other bodies in between these longer encounters. Encountering "C" and "S" spectral type asteroids was a particularly high scientific priority, as bodies of the former type appeared to be more primitive, and therefore more similar to "original" Solar System material than other asteroids, while objects of the latter type seemed similar to a large number of meteorites found on Earth.[2] Also of interest were the "M"-type asteroids, which appeared to be more metallic than others and might therefore be the remnants of protoplanetary cores, and the unique "V"-type Vesta, which seemed to have undergone differentiation and volcanic activity much like Earth or Mars. Since there were an abundance of possible targets, dependent on launch date, multiple possible tour options were drawn up, addressing possible launch dates, from scheduled to optimistic to contingency.
At the same time, the Soviets were beginning what they were calling the "Grand Tour" program. Like the American Grand Tour of the 1970s, this would use a series of gravitational assists to visit a wide range of targets which otherwise would have been far more difficult and time-consuming to reach. Unlike the American program, which planned to visit the giant planets and Pluto, "Grand Tour" planned to visit the near-Earth asteroids, with help from Venus and Earth. After launch, it would fly by Venus, whose gravity would redirect it to fly by one of the Aten asteroids, a class of asteroids that pass only just outside Earth's orbit at their greatest distance from the Sun, then dive into the hotter realms below. After this encounter, the probe would ascend back towards Earth orbit, where it could either flyby Earth--increasing its energy and allowing another asteroid flyby--or conduct a deep-space maneuver for the same purpose. This pattern of gravity assists allowing asteroid encounters could continue for several orbits around the Sun, allowing the probe to conduct a detailed survey of at least the Aten asteroids, and possibly some of the also Earth-orbit crossing Apollo asteroids, clarifying many of their bulk properties and providing "ground truth" for radar and spectroscopic studies. This would not be a solely Soviet endeavor, either, as they reached out to the French and German space agencies to participate in the mission. This early international involvement would prove to be prescient, as "Grand Tour" was buffered to some extent against the political and budgetary issues that gradually grew to consume the Soviet space program over the next half-decade. With the French and Germans already heavily involved and unwilling to simply abandon their investment, the Russians could count on outside financial support for the ambitious mission even as their own ability to fund it withered away.[3]
In response to these actions from the Europeans and Soviets, the United States began its own Near Earth Asteroid Pioneer program in 1987. Unlike Piazzi and Grand Tour, NEAP would rendezvous with a near-Earth body, then intensively investigate it from a nearby vantage point. Besides complementing their observations, especially Grand Tour, which would give brief glimpses of a wide range of objects, NEAP would show that NASA and the United States were just as capable as anyone else of dispatching missions to asteroids. Managed by Ames Research Center and based on their ongoing Lunar Reconnaissance and Mars Reconnaissance Pioneers, the development of NEAP played second fiddle to those already established spacecraft. Nevertheless, the identification and solution of problems in both the LRP and MRP spacecraft greatly assisted the design of NEAP, despite the modifications needed not only to adapt it for a different target than either but also to a different launch vehicle. In a major victory, Lockheed had won some of the first competitively awarded US government launch contracts, including that for the Near Earth Asteroid Pioneer. Fortunately, the degree of modification needed for the probe due to the very different environments of its target to that of Mars or the Moon meant that modifications for the differing launch environment were relatively simple to accommodate within the overall program. In late May 1992, NEAP left Earth for its final destination, an Amor-type asteroid with a diameter of 2.3 kilometers called 1943 Anteros.[4] While small, it was hoped this target would be relatively representative of other near-Earth bodies, and frequent launch windows raised hopes that future missions might be dispatched to the same asteroid, perhaps to return samples of Anteros to Earth.
After a voyage of over a year, NEAP finally reached Anteros in late August 1993, where it executed a burn providing nearly a kilometer per second of delta-V to put itself in orbit around the asteroid. From there, it quickly set out to thoroughly investigate Anteros, mapping it in high resolution, determining its surface composition, and producing a global shape profile via a laser rangefinder/altimeter. Careful tracking of NEAP’s signals on Earth provided estimates of Aneteros’ gravitational field, as well, although not to the precision necessary to probe its internal structure. For nearly two years, during the entire period of the asteroid’s orbit around the Sun, NEAP observed the asteroid, creating the first complete record of the seasonal changes to such an airless body in such an elliptical orbit, greatly exceeding its design mission in the process. Finally, in April 1995, with NEAP having completed its full extended mission, controllers decided to attempt a final experiment: repeating the successes of Kirchhoff and Mars 12, and landing NEAP on Anteros. Over a period of about a month, NEAP slowly lowered its orbit until it was passing within a few hundred meters of Anteros’ surface, before finally putting itself on a trajectory that would intersect the asteroid’s surface. To the delight of controllers, who had thought that NEAP’s low propellant reserves might cause the probe to be destroyed during the landing, NEAP soon checked in from its landing point, apparently a stretch of rocky ground near the rim of the crater Big Dip (so-named by the imaging team as one of the largest craters on Anteros). NEAP had, nevertheless, suffered significant damage during the landing, and the hostile thermal environment of Anteros’ surface ended the probe only a few days after touchdown, though not before it was able to take extremely close range spectroscopic data from the surface.
Even as NEAP marched easily towards launch, Piazzi was struggling to get off the ground. Developmental difficulties related to its challenging environment and novel form of propulsion caused repeated delays and budget overruns in the probe, which gradually grew to dominate ESA's science programs as other spacecraft suffered less serious problems. These issues were compounded by related overruns and problems with the series of "minor" missions that ESA had become involved in, ranging from the Newton comet probe to the Mars Surface Elements of the Mars 12/13 mission. To fill the gaps, ESA tended to raid Piazzi's funding, reasoning that the probe was so far over budget and behind schedule that it would matter little. Having already slipped from a planned 1990 launch date into 1991, the final blow came with German reunification and the related collapse of the Soviet Union. With ESA member states, especially Germany, reducing their allocations, all programs of ESA had to suffer. Although plans to convert the Minotaur logistics vehicle to carry humans bore the brunt of the cuts, Piazzi was not spared, slipping to 1992 and then 1993 as a result. The only thing that spared it from outright cancellation was the fact that significant flight hardware had been procured, and it would be more expensive to cancel it and dispose of the otherwise useless remains then to finish and fly the mission after all. When it finally launched in February of 1993, the scientists involved were happy that it had at last gotten off of the ground, almost regardless of which asteroids it would be visiting. Insertion into a heliocentric orbit, followed by startup of the probe's ion engines (a more advanced and capable design than those used on Kirchhoff) proceeded smoothly, and Piazzi began its voyage to the asteroids. A year and a half after launch, Piazzi reached its first target, the 46 kilometer SX-type asteroid 113 Amalthea (not to be confused with the Jovian moon). Although it sped by Amalthea at 3 kilometers per second, Piazzi was nevertheless able to image the asteroid and collect remote-sensing data about its surface, together with determining its mass and rotational period to a greater precision than possible from Earth.
In June 1995, Piazzi at last reached the first of its rendezvous targets, 4 Vesta, in so doing becoming the first spacecraft to rendezvous with and orbit a main-belt asteroid. The third largest of the asteroids with a diameter of 576 kilometers and the only one sometimes visible to the naked eye from Earth, Vesta was of particular interest due to the processes of differentiation and vulcanism it seemed to have gone through, unlike most other asteroids. Since Vesta is so much smaller than other bodies that have gone through the same evolution, like Earth or the Moon, it therefore offered a unique chance to see such a body frozen in mid-stride, so to speak, before it could really get going. Besides that, comparison with other asteroidal bodies, particularly those of relatively similar composition, might allow a better understanding of what conditions were needed for differentiation, a key step in the formation of planets and other large bodies, to occur. The world that was revealed to Piazzi's instruments met all of those expectations and more, possessing just as much geological diversity as any planet or moon elsewhere in the Solar system. The most prominent feature on Vesta’s battered surface was a massive impact basin occupying much of the southern hemisphere, itself overlying another giant crater, probably the source of much of the material in the asteroid belt observed to originate from Vesta. These impacts seemed to have created a system of massive troughs and cliffs elsewhere on the surface from seismic waves, giving Vesta a rough, textured appearance together with the ubiquitous impact craters. Finally, data returned by the probe showed that the interior of Vesta appeared to be much more similar to that of Earth, Mars, or other terrestrial planets than any previously explored asteroid, with clearly separate core, mantle, and crust regions.[5] Unfortunately, the probe’s exploratory mission had to be ended after only three months probing Vesta[6], as the window for its departure to its second destination, the 90 kilometer wide S-type asteroid 17 Thetis opened in late September 1995.
After departing Vesta, Piazzi’s ion thrusters smoothly functioned through the voyage to Thetis, marked only by the flyby of the 96 kilometer C-type asteroid 313 Chaldaea in March 1996. As an S-type asteroid, Thetis was spectroscopically similar to the important class of meteorites called the ordinary chondrites, promising possible breakthroughs in the understanding of the origins of these meteorites. Therefore, in October 1996 Piazzi slowly slid into orbit around Thetis, hoping to catch a better look than had been available from Earth. It was richly rewarded, as a world far smaller but with just as much history to explore passed under its cameras. Like Vesta, or for that matter the Moon, Thetis proved to be pockmarked with craters and other evidence of impact at all scales visible to Piazzi's cameras, from the most minute to the very largest. Furthermore, several ordinary chondrites in fact proved to be from Thetis, or at least to be near-perfect spectroscopic matches for regions of Thetis visible to Piazzi[7], effectively making them some of the first samples returned from a known asteroid, only slightly beaten by the vast collection of Howardite-Eucrite-Diogenite meteorites from Vesta. As with every other body ever visited by space probes, from Charon to Mercury, Thetis also proved to have a rich geological history, with evidence, curious in light of the asteroid's evident lack of differentiation and therefore of significant internal heating, of flows of rock through the asteroid and other internal activity. The four months of observation Piazza was allowed by orbital mechanics before departing Thetis for good only opened up more questions on the part of the mission team, but the probe once again had to frustrate any desires for a more in-depth investigation.
Piazzi's last stop would be the 86 kilometer C-type 449 Hamburga. While the asteroids 313 Chaldaea and 415 Palatia, which it had flown by in March 1996 and June 1997, respectively, had both been C-types, the brief encounters Piazzi had been limited to had only whetted the appetites of asteroid scientists for the more detailed look waiting at the end of the line. If Piazzi would cooperate, at least, for the aging probe was becoming increasingly cranky and difficult for European ground controllers to manage. Several of the ion thrusters had developed problems which, while not mission-ending, nevertheless required careful attention to allow proper operation, while power output had decreased more than anticipated from radiation exposure and panel damage. Nevertheless, in September of 1998 the probe was able to push itself into orbit around Hamburga, finally giving scientists the view they had been waiting for since launch. Once again, Piazzi's imagery revealed a world battered by impacts, a familiar scene throughout
the solar system by now, and once again evidence of internal activity, perhaps similar to that within the icy moons of the outer system. However, it was in spectroscopic analysis that Hamburga's differences with Vesta and Thetis shone through, with a rich surface chemistry revealed to these probing appendages[8]. A fantastically complex mélange of organic and inorganic chemicals seemed to coat Hamburga's surface, transforming every square centimeter into the equivalent of a chemical factory. Energetic solar radiation, together with whatever internal heat Hamburga had once possessed and perhaps the occasional impact seemed to have catalyzed an amazing range of surface chemistry, despite the lack of water, air, or any other fluid medium for chemical reaction. There was even some evidence that extremely simple chains of amino acids and nucleotides seemed to have formed on Hamburga's surface, something which proved to have a significant effect on later theories of abiogenesis. With no future destinations in mind--in any case, Piazzi had virtually exhausted its ion propellant stocks upon reaching Hamburga--the scientific team could take as long as they liked examining and reexamining Hamburga’s surface, limited only by the probe’s inevitable failure or the ending of operational funding. Finally, in early 2000 Piazzi stopped responding to commands from Earth, ending Europe’s first completely independent and highly successful planetary science mission.
[1]: This is based on the AGORA mission. You may have noted that ITTL things are a bit friendlier to planetary exploration across the board; this is another expression of that tendency. IOTL, ESA tended to fund more telescopes.
[2]: This is my understanding, anyways.
[3]: The fate of this probe will not be revealed. Yet.
[4]: This was a common target for asteroid missions during the 1980s IOTL, along with 4660 Nereus and 433 Eros, because it is relatively easy to reach and has frequent (roughly once every other year) launch windows.
[5]: This is all as per Dawn--go Dawn!
[6]: Alas, time and windows wait for no probe.
[7]: As far as I know, this is plausible speculation, but the sources of most if not all ordinary chondrites are not actually known.
[8]: Again, I believe this and the following to be plausible speculation based on carbonaceous chondrites (which correspond to “C”-type asteroids, sort of).
Small wonder, these probes are often referred to as the Unsung Heroes of Space Exploration - if my understanding is correct. The immense wealth of data that they can provide, for a far lower expenditure than any Manned Programme. And it would appear that the various Space Agencies have all aimed for separate items of interest here. Understandable, given that it would be expected that they'd still have at least some co-operation, even in the bleakest of times, to negate duplication of efforts.
For the ESA portion of this update, having stated that it was completely independent, I would believe that that means a variant of the Europa III LV was used for the launch - I'd wager one of the forms that has the LOX/LH2 Stages 2 & 3 - which quite simply means that it's ability to send probes on BEO Missions has been demonstrated.
And again, landing probes on Asteroids/Comets when they were never really designed to do such a thing. Goes to show that they were built to last - but then they'd have to be built that way, wouldn't they?
And congrats on getting that computer fixed! Now we can finally get the Freedom/Mir segments of TTL! Can't even begin to say how much I've been wanting to see it.
For the ESA portion of this update, having stated that it was completely independent, I would believe that that means a variant of the Europa III LV was used for the launch - I'd wager one of the forms that has the LOX/LH2 Stages 2 & 3 - which quite simply means that it's ability to send probes on BEO Missions has been demonstrated.
And again, landing probes on Asteroids/Comets when they were never really designed to do such a thing. Goes to show that they were built to last - but then they'd have to be built that way, wouldn't they?
And congrats on getting that computer fixed! Now we can finally get the Freedom/Mir segments of TTL!
Can't even begin to say how much I've been wanting to see it.Yeah, it's on a Europa 4 of one variant or another. Probably either a E40a or a E42, but maybe an E42a--depends on the kick it needs to get going and the precise mass of the spacecraft. It's well within the family's capability, though. (EDIT: did a bit more poking about in our notes and some OTL stuff--it's probably an E40a.)
I've been looking forward to it a lot, too-part of why I want to make sure it gets done right.And congrats on getting that computer fixed! Now we can finally get the Freedom/Mir segments of TTL!
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What for nice twist,
i had expected that NASA would launch the backup of Kirchhoff probe and ESA launch Hayabusa type mission.
but this here is Better, With Kirchhoff visit to Comet Temple 2 and Mars 12 landing, making a ESA Rosetta type mission become unlikely.
So Piazzi is excellent choice.
so we have allot of probe of 1990s and 2000, already flow in 1980s begin 1990s.
so what left to do ?
A Mercury, Saturn, Uranus, Neptun orbiters.(with lander probe).
Sample return mission from a Asteroid (Hayabusa) or Mars surface.
Radar orbiter to Jupiter Moon Europa and Saturn moon Titan
already there indication for next post:
Ames Research Center and their ongoing Lunar Reconnaissance and Mars Reconnaissance Pioneers,
i had expected that NASA would launch the backup of Kirchhoff probe and ESA launch Hayabusa type mission.
but this here is Better, With Kirchhoff visit to Comet Temple 2 and Mars 12 landing, making a ESA Rosetta type mission become unlikely.
So Piazzi is excellent choice.
so we have allot of probe of 1990s and 2000, already flow in 1980s begin 1990s.
so what left to do ?
A Mercury, Saturn, Uranus, Neptun orbiters.(with lander probe).
Sample return mission from a Asteroid (Hayabusa) or Mars surface.
Radar orbiter to Jupiter Moon Europa and Saturn moon Titan
already there indication for next post:
Ames Research Center and their ongoing Lunar Reconnaissance and Mars Reconnaissance Pioneers,
MRP was already discussed in detail in Post 9, LRP uses a similar bus, but is aimed at the moon (similar timescale--about a 1990 launch). We'll be picking that mission up in more detail in Part III. I wonder why we might feel that'd fit better there?
With Germany, reducing their allocations in ESA, because the Germans reunification cost.
will this be raise of France to more power inside ESA ?
or will Great Britain under Margaret Thatcher increase there grip on ESA ?
will this be raise of France to more power inside ESA ?
or will Great Britain under Margaret Thatcher increase there grip on ESA ?
By the time German Reunification came into effect IOTL, Margaret Thatcher had already left No.10. The UK might attempt to bolster it's holdings in ESA, but in the 1990s, Europhobia was making itself known - and wrecked the Conservatives in the process.
Dam, that put Labor party (with Tony Blair as MP?) back in power, poor ESA ...
Just did. The info would suggest that the Apollo 4 Flight used a Block I Apollo CSM. Likely since it was an Unmanned All-Up Test Flight of the Saturn V. Which is news to me.
And damn. ETS never won the Turtledove Award.
...
And damn. ETS never won the Turtledove Award.
I too say
and also ; it's not for lack of my vote, last year and this one.I have my own questions regarding the update to the Technical Data.
According to the Wikipedia page on the Apollo CSM the all-up mass of the two modules mated was 30.332 tonnes, of which 18.41 tonnes were SPS propellants and 3 were the main engine. Your tech data are consistent if I assume we are talking dry mass for the Block II.
However the Block III is just one tonne less, dry!
I'd have thought it would be a lot smaller, since the heavy main engine has been replaced by a much-downsized one more suitable for orbital maneuvering and also much more compact, saving on other structural masses to mate the CSM to the rocket. And the propellent is vastly reduced, since the Block II was designed to brake an entire LM-CSM stack to Lunar orbit, then later propel the CSM into a Trans-Earth Injection; most of the fuel mass, which was 60 percent of the total fueled CSM for Lunar missions, is needed for these purposes and not needed for missions involving shuttling around between low Earth orbits and deorbiting burns.
For the post-Lunar missions using Block II, I guess they just scanted the fuel load a whole lot, and I even seem to recall that the large fuel bay volumes freed up then were filled with extra supplies, oxygen and water and the like. This, plus extra tankage for the extra fluids, might have brought to the total SM launch mass back up to the old Lunar mission ballpark and by the way justified using the otherwise horribly oversized legacy main engine, which among other things served as an escape engine once the main lauch escape rocket tower was discarded shortly after first stage burnout; in case of catastrophic failure of the second (or third, on Lunar missions using a Saturn V) stage, the SM main engine would use its full thrust to boost the CSM to safety. This is still feasible with the Block II with scanted fuel load, indeed more feasible unless the extra supplies added into the SM in lieu of fuel actually massed more than the omitted fuel, which seems unlikely.
But then we go over ITTL to block III and I am wondering why it doesn't mass any less, dry. For one thing I think you said sometime last year it would mass a lot less, citing both the smaller escape tower and the smaller main engine, and in the pictures, the module is quite obviously a lot shorter than the Block II SM. Obviously the fuel tanks are designed to be a lot smaller. OTOH the mission of all Block III ships is to go to a space station, and clearly supplies are of great use, at least if there is some means of getting them transferred from the SM to the station!. They might easily want a mass and volume of supplies that would tend to bring the length of the SM back up toward the Block II standards.
Since the updated page shows the Block III CSM as just one tonne less massive than the Block II, whereas deleting the old main engine alone would lower the mass by 3 tonnes (offset of course by the mass of the less powerful replacement engine, but that's not going to be 2 tonnes, is it?) it seems that rather than going for something ultralight to just accomplish the orbital maneuvering mission, the Block III designers did indeed use the SM as a major supply locker. This means having to use a bit more fuel, to accomplish the same necessary delta-vs on a bigger mass.
And so it would seem the Block III SM is not really a lot smaller than the Block II. A little, but not a lot; the difference is, it is now much less of a fuel tank and much more of a supply locker and location of mission instruments and equipment.
I like this, since going over to Block III+, which basically shifts the equipment and supplies over to the MM, will require more propellant and I was wondering where it went.
The main drawback, from the point of view of the thread, is that all your artwork shows the Block III and III+ SM as radically smaller, much shorter that is, than the Block II. It seems to me now that this must be incorrect; they'll have much smaller main engines and be a little bit shorter but not a lot.
I tried to look over the respective capacities of the Saturn 1B and 1C; it is hard to compare them directly because the orbits given for the given payloads are all different! The 1B has a 16 tonne capacity to a low orbit, whereas two capacities, for a high-inclination and low-inclination, orbit are given for the 1C at a much higher altitude. This led me to seach the posts for a definitive statement of what Spacelab's orbit is. I guess the high-inclination (because the first Spacelab missions involved Soviet cooperation) and high altitude orbits for which the 1C can deliver a bit over 20 tonnes is it, 430 km, 51.6 degrees inclination. (And now I note with some surprise the payload to the same altitude and a much lower inclination, 28.5 degrees, which I suspect is actually Cape Canaveral's latitude, is actually 5 tonnes lower? Shouldn't it be higher, since an inclination equal to launch latitude is easiest of all?)
Anyway, taking the 1C as the workhorse launcher, and assuming all missions go to Spacelab at 430 km up and 51.6 inclination, we have for Block III--Well, looking at post 426, almost a year ago, where figures were given for the Block III+, it seems the fuel load for these missions was just 1600 kg, presumably that or less would do just fine for a Block III. All up CSM mass given as 12800, the escape tower system mass was 3500, that gives 16300 kg at launch, whereas the 1C can deliver 20150 to what I presume is Spacelab, so that is a margin of nearly 4 tonnes that can be filled in with supplies of various kinds--again, if we can get them into the space station from the SM!. And I think it's more than that because the Launch Escape system doesn't fully count, being discarded early in the burn.
Recalling that a Block II SM was designed to take on 18 tonnes of propellant and here we want less than a tenth of that, we'd have to have a volume equivalent to 16 tonnes of the storable hypergolics to justify the CM being the same volume. Well, it isn't, but it's reduced by just one tonne--and since we've replaced the 3 tonne engine with something much lighter, it would seem that actually the structural mass must have been increased for some reason!
Anyway we have apparently a boost capability of about 4 tonnes or more to be used for supplies which can only go one place, that is, inside the SM. The fact that we might want supplies that pack a lot less densely than the dense hypergolic fluids mean the volume left by omitting more than 16 tonnes of it might be filled better than we might guess by 4 tonnes of other stuff plus packaging, deployment systems etc. And we can probably get more than 4 tonnes in there, considering that the escape system doesn't really deduct over 3 tonnes from the orbit mass, and that the dry mass of the SM really ought to be somewhat lower still.It really is not clear to me what NASA was doing with those 4-6 tonnes of launch capacity to Spacelab orbit that seem unaccounted for, until going over to Block III+ just lately. The MM absorbs the mass surplus just fine and allows me to visualize the compact SM you illustrated, but on Block III missons I can't imagine what was done, short of deliberately scanting fuel on the upper stage of the 1C to give it somewhat less capability than cited!
Or there's another possibility, which is that you are dramatically over-estimating the mass of the Block II engine. The Apollo Block 1/2 SPS was based around an AJ-10 variant. This is a different, slightly lower thrust variant, but it indicates a mass of >100 kg, and a T/W for the engine alone of 45. Scaling this to Apollo's AJ-10-137 variant and its 97 kN gives a mass of 219 kg for the Apollo's main engine--far, far less than 3,000 kg!
I went to check this out myself, but it looks like truth is life saw what you were talking about and already got that fixed--looks like the wrong numbers got copied from a planning doc.
Basically, the reason here is that we didn't pin down the performance of the Saturn IC early enough, our early calculations didn't properly account for the lower mass of the first stage. The end result was we basically designed Block III to fit on a Saturn IB before we realized how much more capable Saturn IC would be. Rather than retconning this, we're instead saying that they designed Block III to be capable of being launched on Saturn IB in case IC development dragged on or was cancelled (recall, they'd just had Shuttle cancelled and had barely gotten authorization for Spacelab, they were probably a bit paranoid). Once it became clear it was a success, they do Block III+ to use up the margin.
What I did there was accept the 3000 kg mass given for the AJ10-137 in the Wikipedia page on the CSM uncritically. In my defense, look at the huge size of it, the engine bell being nearly 4 meters long! So I didn't balk at 3 tonnes.
Also in my defense--it's not easy to get an alternate statement of the mass of that particular engine. You'd think it would be worth mentioning in the Wiki article the engine's name links to but no, that's an article on the whole AJ-10 series, and gives an example of an engine of half the thrust--and only 100 kg dry weight.
Here's the one link I found that stops beating around the bush and simply states a weight for the thing--"650~ lbs (approximately)"(!) And cites the Apollo Operations Handbook: Block II Spacecraft (SM2A-03-Block II) (15 April 1969).
650 lbs is of course just the size range you indicate and 1/10 the mass claimed in Wikipedia; evidently someone typed an extra zero.
And it isn't easy to check.
I am quite amazed an engine of that sheer linear size can be made massing a lot less than a compact car, though admittedly 3 tonnes would be on the ridiculously heavy side.
Aha, you don't have the actual specs for the thing handy either! Not that you need them exactly, you've moved on to a new ship that has an even lighter engine.
If we can believe the "alternatewars" page, then you are underestimating a bit; this excerpt from NASA's Remembering the Giants suggests why; it's chapter 5, Aerojet engineer Clay Boyce reminisces on the development of the AJ10-137--he mentions that they made it pressure-fed to avoid using pumps, and this made it heavier. It would have been about 290 kg.
That makes perfect sense, and I do note that Block III+ is the version to use with 1C, and Block IV will presumably be finalized when the M02 demonstrates its actual capabilities in tests, allowing an exact calibration of each MM to each launch, to various orbits.
But it means that the Block III missions have been launched with a very wide margin for error. I suppose that the launch stages were filled up all the way but the boost of the second stage was always cut off well before it ran out of propellent, once the target orbital velocities had been reached?
That likely includes the whole engine system mass, not just the engine per se. Or, as you say later, it's a simple typo.
No, it's being designed to the M02's specs (and most of the changes are in the SM, anyways, because it needs to be able to move large Freedom components, and are independently determined). If M02 underperforms, then a very frantic weight-saving process will be carried out (see: Orion OTL with Ares I constantly reducing estimate performance). If it overperforms, then there will be wasted capability.
Well, the S-IE and S-IVB are not Atlases or Centaurs with pressure-stabilized tanks, they don't need propellant to stay in shape. So they probably just short fuel them and launch them partially empty for the Block III flights.
To elaborate on how Block IV can be adapted based on final M02 performance, part of redesigning the MM for Block IV is adding extra volume for almost 2.5 tons of cargo. This represents margin for an up to 10% performance performance shortfall on the M02--and given that the performance of the F-1A and J-2S are well-characterized by their extensive history on Saturn IC, they can be pretty sure any shortfall won't be that bad. Any performance overshoots (should a miracle result in one) can similarly be eaten by adding another few hundred kg of cargo without cramping the habitable volume of the MM too badly.
Also, a side note, but this marks 1,175 posts on this thread. At this point, that's enough to move Eyes Turned Skyward into the top 30 threads of all time by replies on the Post 1900 section. That's amazing, folks, and you've been what's made this all possible: your comments, and your support. We may not have won the Turtledoves this year, but there's always next year. In the meantime, thanks for making the top 30 happen.
According the NASA Apollo [CSM] Operation Handbook for Astronauts
the SPS engine has weight of 650 lb or 295 kg.
because it's a light weigh space Engine with a radiatively cooled nozzle.
and yes it was design to blast of the heavy CSM Block II from Saturn V, if it's S-II or S-IVB had "serious malfunction", specially if translunar injection goes wrong.
but Bock III and III+ are launch not to Moon but in low orbit, in case of "serious malfunction" on S-IVB
here the CSM has sufficed engine power to jettison from the S-IVB and get the CM suborbital to earth !
now in Bock III the SPS is replaced by TRW TR-201 the descend engine of Lunar module.
According the TRW TR-201 handbook, it's weight is 394 lb or 179 kg
were do he find that stuff, you ask ?
a part i buy it at Up-Ship.com
or i plundering the NASA technical Report Server
the SPS engine has weight of 650 lb or 295 kg.
because it's a light weigh space Engine with a radiatively cooled nozzle.
and yes it was design to blast of the heavy CSM Block II from Saturn V, if it's S-II or S-IVB had "serious malfunction", specially if translunar injection goes wrong.
but Bock III and III+ are launch not to Moon but in low orbit, in case of "serious malfunction" on S-IVB
here the CSM has sufficed engine power to jettison from the S-IVB and get the CM suborbital to earth !
now in Bock III the SPS is replaced by TRW TR-201 the descend engine of Lunar module.
According the TRW TR-201 handbook, it's weight is 394 lb or 179 kg
were do he find that stuff, you ask ?
a part i buy it at Up-Ship.com
or i plundering the NASA technical Report Server
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Not as lightweight as it might have been if it had been pump-fed instead of pressure-fed using helium, I gather from the remark by Clay Boyce I mentioned above. But yes, 290 kg--which is indeed for the engine itself and not auxiliary stuff like its bearings, gimbals, etc--is quite a reasonably light engine to drive a 45 tonne mass (LM-CSM on approach to the Moon, braking to Lunar orbit)!
Actually, the critical mission this engine was designed for was for boosting the whole CSM--30 tonnes, though in the early design stages they might have optimistically thought it would be less--off the Moon and directly into trans-Earth trajectory after a direct mission to the Moon landed the whole thing on Luna. Then NASA decided to go for LOR instead, but the engine design was well along and it was adopted anyway for that mission, which note required it to brake a still greater mass to Lunar orbit, then days later shove the (somewhat lightened!) CSM back to Earth from there. Despite a 50 percent increase in mass for lunar orbit injection, I think they clearly could have gone with something lighter, but as y'all point out a 300 kg engine is not really worth fighting too hard to reduce.
And it was more than adequate to serve as second stage escape system too. Though I think the critical thing there is, not just to achieve a survivable trajectory should the second or third stage fail, but also to have enough acceleration to escape the worst-case explosion of the second stage (the third stage is much smaller and would be blowing up in vacuum). Evidently it could handle that too, another benefit of letting a system designed originally for a much more demanding task ride.
The TR-201 as used for Apollo LEM has a bit under half the thrust of the SPS, while the launch mass of the Block III CSM is well under half the 30-tonne Block II mass, so there is no problem I can see with the escape mode.
This means the system is still overpowered from a strictly economizing point of view, but the costs involved are small and offset considerably by using off-the shelf man-rated hardware that proved itself repeatedly in very critical situations more severe than anticipated for the Block III and later block orbital missions.
Well, I might wind up having to purchase from Up-Ship myself, but meanwhile I did decide to go to the source at NASA too and see what contemporary NASA documents told me. Unfortunately they remain something of a crazy-quilt. I downloaded a section of SM2A-03-Block II-(1) Apollo Operations Handbook, the section labeled the systems data for the SPS, hoping to find a table of all component masses, grouped by system. No such luck; buried in there it is possible to confirm the SPS engine itself weighed 650 pounds--approximately!
Similarly, you'd think an element like the propellent tanks (a main and sump tank for oxidant and reactant, 4 total) would merit quoting a weight. But no!
However, the helium pressurization tanks, which were much smaller in volume but operated at very high initial pressure, do have a cited weight--393 pounds each, no "approximately" here! There were two of them, for redundancy I suppose. The main propellent tanks they pressurize do not have a cited weight but I could compare the volumes, take the 2/3 root to estimate areas, and note that the lower pressure allowed much thinner-walled tanks--the thicknesses in inches are given--and thus estimate that the propellent system tankage (which note, is part of the "engine" in that the helium provides the pressure to drive it) added up to something like 660 kg--approximately!But although you don't have a functioning SPS without the pressurization, the masses would scale with fuel volume, not engine thrust. I don't know enough about the TR-201 to be sure it used a similar pressure-driven system--if it used pumps instead (this seems very unlikely to me!) the tankage can be even lighter--but with the Block III we use less than 1/10 the propellent of the Block II, so the tankage mass should be well under 70 kilograms, maybe under 50.
So altogether, dry, we have the SPS for Block II massing 950 kilograms--no 3 tonnes, but almost a third of that, but that includes the tankage--versus 250 or so for the Block III TR-201 based system, assuming a similar pressure fed system and again including the tankage.
And if we want to double the tankage, that's another 50-70 kg at worst--to contain another 1600 kg of propellant.
We clearly don't need that in Block III missions, and possibly not in Block III+. But I suspect we might want to kick the propellant capacity up from 1600 kg, if not double it, for future Block IV.
Even bearing in mind that beyond the tankage itself, the overall structure of the SM must also be stretched for bigger tanks (unless we just move other stuff formerly kept in the SM to the MM to open up more volume for fuel) it ought to cost less than 100 kg of structure mass to allow a doubling of propellant, which is probably more than would ever be needed.
I'm still confused by what is making up the total mass of the Block III SM though; we don't save thousands of kg but we do clearly save 750, 3/4 of a tonne, by simply switching engines and downsizing tankage to accomodate just 1.6 tonnes of propellant. The unreliable Wikipedia gave the "structural mass" of the SM as just 2 tonnes, so knocking 250 off that would only shorten it by 1/8, whereas the pictures all show it something like half the length of the OTL SM--the all-up dry weight of the CSM should still be lower than 11 tonnes, I think. Which frees up mass that could be stored in the large volumes deleting over 90 percent of the Block II propellent requirements free up, even when we discard half that freed volume by compacting the module.
That's why I rather hope the Block III SM was actually overdesigned, or conservatively downsized, to leave considerable room for expansion--those larger fuel tanks possibly needed for M02 launched Block IV missions for instance.
Another possibility is, the Block III SM's are relatively heavily built with the haunting experience of Apollo 13 in mind; by using a heavier structure there is hope that if some other unforseen explosion takes place only the items in that system's bay will be damaged, with the rest protected, leaving the SM with some kind of partial functionality.
Considering that the Block III+ MM was not planned when Block III was designed, and that the notion I had that the MM should be viewed as an auxiliary spacecraft/lifeboat in case something fails in the SM was dismissed on the grounds that there wasn't a lot of mass margin--I hope that since the Apollo designers are putting all their eggs, even on the later Blocks with MMs, in the one basket of the SM, without which the astronauts are dead meat, that the are very closely indeed watching that basket.
Part II: Post 24: Telescopes Beyond Hubble
Well, it's that time once again, everyone! This week, we're turning our attention back once more to the field of astronomy, and taking a look at the other non Hubble telescopes of the 80s and early 90s. This is another one of truth is life's excellent posts, and I hope everyone will enjoy it as much as I did. 1178 replies 144536 views
Eyes Turned Skyward, Part II: Post #24:
However impressive Hubble was, it was not and never had been the be-all and end-all of space observatories, nor was the United States the only player in space astronomy. Even as Hubble began the long process of definition in the early 1970s, the newly constituted ESA had selected a pair of British-led astronomical satellites, the UltraViolet Astronomical Satellite and the InfraRed Astronomical Satellite, or UVAS and IRAS, to form its first scientific satellite program. While UVAS was essentially a descoped version of the Large Astronomical Satellite that had long been under consideration at ESRO, and was essentially similar to the Orbiting Astronomical Observatories of NASA, IRAS was something new, taking advantage of the rapid development of infrared astronomy over the previous decade to launch a cryogenically cooled infrared telescope into space, where it would use the lack of atmosphere to allow observations of a potentially much broader range of wavelengths than possible from the ground.[1] Both IRAS and UVAS would have participation from NASA, although in a novel turn of events as a junior partner rather than a senior. The projects would be led and managed by ESA, with NASA providing certain technical elements. Although novel, in many ways the IRAS proposal was a simple extrapolation of existing trends, with infrared telescopes having been flown on airplanes, built on mountains, and lifted by balloons during the 1960s to allow observations through a smaller and smaller air column. As with x-ray or ultraviolet observations before, putting a telescope into space would be a mere logical extension to its absolute limit of this movement. While the development of its sister vehicle, UVAS, proceeded relatively smoothly up to its eventual 1978 launch, IRAS proved to have a more difficult and protracted development program due to the challenges associated with the containment and management of a large amount of cryogenic liquid helium over a relatively long period of time in a microgravity environment. Although it was intended to be launched at about the same time as UVAS, problems with the relatively novel cryogenic systems and infrared detectors, European inexperience in space activities, and the higher priority of UVAS led it to slip significantly behind. Nevertheless, work never stopped on the project, and in 1980 it was lifted from Kourou into a low Earth orbit by a boosted Europa 2, some two years behind its sister satellite.
Once it was in orbit, however, IRAS lived up to expectations, producing a detailed map of the sky at infrared wavelengths, particularly those inaccessible to ground-based telescopes due to atmospheric absorption. In the course of this effort, it made several significant discoveries, including the debris disks around other stars, warm dust called infrared cirrus pervading interstellar space, and intense infrared emissions from colliding galaxies.[2] In a more minor sidenote, it also discovered several lost or previously unseen comets and asteroids, taking advantage of their greater visibility in infrared relative to visible frequencies. The greatest accomplishment of IRAS, however, was merely in proving that a cryogenically cooled space-based infrared telescope was possible and practical, and with its success European astronomers almost immediately began to look forward to the next logical step, a larger, higher resolution imaging infrared telescope, tentatively termed the Advanced Infrared Space Observatory, or AISO. Meanwhile, senior managers at ESA had long been dissatisfied with the degree of control they actually possessed over the continent’s space program, both from bureaucratic self-interest and perhaps from a degree of latent pan-Europeanism. Of the various ESA programs, only the Europa launch vehicle program and ESA’s human spaceflight program were truly European endeavours; the remainder were largely vehicles for individual national programs to promote their projects and missions at continental expense, with little in the way of a common European program. For example, ESA’s planetary science program was dominated by German involvement in Helios-Encke and the forthcoming Newton comet probe, while the astronomy program had conversely been dominated through the 1970s by the British-led UVAS and IRAS satellites. Moreover, all of the member states routinely cut deals with outside countries, often the superpowers, to partake in other projects, such as the Franco-Soviet Eos Venus balloon probe. To counter these tendencies, ESA management induced the European Science Foundation to consider space science programs in the early 1980s, seeking to have them draw up a list of continent-wide priorities, both for native European projects and for collaboration with other countries, particularly the United States and the Soviet Union but also the rising space program of Japan.[3] As part of this program, the European Science Foundation initiated a series of high-level contacts between its own members and the members of the National Academy of Sciences, the Soviet Academy of Sciences, and the Japan Academy, to communicate about what programs would be of greatest interest to the scientists of each country.
Japanese astronomers had, at the same time, been nurturing a growing interest in space astronomy, fueled by the successful Hakucho and Hinotori missions and the growing Japanese economy. While the Japanese were naturally aware of European success in not only x-ray but also infrared and ultraviolet space astronomy, they had not been particularly privy to intimate details nor had they entertained much thought of collaboration with their trans-Eurasian counterparts. The meetings spurred by ESA between European and Japanese scientists changed that, as a new conduit opened to allow information to flow between the two programs. Scientists on both sides saw the advances their compatriots had made and the programs they were interested in in more detail, and were able to converse more freely and deeply about their common areas of interest than they otherwise would. Japanese astronomers interested in expanding their program beyond the admittedly highly successful x-ray program quickly latched on to the budding AISO program as an attractive method of broadening their horizons. Japan could usefully make a number of contributions to the program, allowing it to gain experience in the necessary technology and operational techniques for a future Japanese infrared telescope, without the risks or expense associated with beginning their own infrared observatory program. As a result of Japanese interest in the project, the AISO had developed into the International Infrared Observatory, or IIO, by the time the project was approved along with the Piazzi asteroid probe in 1983.
The International Infrared Observatory would consist of a telescope generally similar to IRAS, of about the same aperture and still using detectors cryogenically cooled with liquid helium, one of which would be built by Japan. Despite these similarities, however, IIO would depart significantly from IRAS in two major ways. First, it would be launched into a heliocentric orbit, rather than Earth orbit.[4] By placing it into solar orbit, a number of advantages could be realized, most obviously that of Earth and the Moon no longer being present to block large parts of the sky at any given time. The heat flux on the telescope would also be drastically reduced, vastly increasing the amount of time a given amount of liquid helium could chill the telescope to its cryogenic operating temperature. The principal disadvantage was that communications would be more difficult than with an Earth-orbiting probe, although the construction of European and Japanese deep-space communications facilities for planned future projects helped mitigate this difficulty substantially. [5] For a telescope intended to provide a vast leap over IRAS in terms of sensitivity and resolution--to take on the task of detailed imaging of the sources IRAS had mapped out--the advantages of the heliocentric orbit more than outweighed the disadvantages. Second, IIO would take full advantage of major advances in detector technology that had taken place since IRAS was designed, particularly the rapidly advancing state-of-the-art in charge-coupled devices (especially sensitive to “red” radiation) to provide greatly improved resolution and sensitivity. Unlike IRAS, which had been designed as a survey telescope, one which mapped out sources from the entire sky, albeit at a relatively low resolution, IIO would be an imaging telescope, one which observed a relatively narrow area of a the sky, but at relatively high resolution and sensitivity. Data from IRAS could be used to “aim” IIO, allowing it to focus on the strangest and most interesting sources in the sky, without having to waste time finding those sources in the first place.
As with its counterpart Piazzi, development of IIO proceeded more slowly than anticipated, hampered not only by the growing diversity of ESA’s programs, but also by the technical difficulties of the project.[6] While by virtue of their construction of IRAS and Hubble’s Long Wavelength/Planetary Camera Europeans had more experience in infrared space astronomy than any other group in the world, scientists wanted to push the boundaries of technology even further to achieve pointing stability and accuracy, cryogenic lifetime, resolution, and sensitivity much superior to IRAS’ capabilities. By the time construction of the observatory could start, the financial challenges posed by the crumbling Soviet empire of Eastern Europe, especially the costs being borne by the Federal Republic of Germany after its reunification with the German Democratic Republic in 1989, served as a further block to development. As with Piazzi, this led to IIO’s launch being delayed several years, from the initially envisioned late 1992 to early 1995. By the time it launched, the rapidly advancing state of the art in ground-based infrared telescopes and increasing NASA interest in launching a Large Infrared Space Telescope[7] to replace Hubble in the next decade had made IIO seem less groundbreaking than in 1983, but it would still be a worthy and capable telescope by itself, and available considerably earlier than NASA’s larger offering. Its successful launch into an escape trajectory by a Europa 42 was quickly followed by Japanese and European confirmation of proper operation of all the spacecraft’s systems.
Over the next several years, until the depletion of its liquid helium supply, IIO remained the world’s premier facility for infrared astronomy. In its primary mission, providing high-resolution infrared imaging of a variety of galactic and extragalactic targets, it succeeded magnificently, entirely confirming the hopes of astronomers who wanted to use infrared observations to penetrate veils of interstellar dust. It also extended IRAS’ observations of extrasolar debris disks and performed a large number of spectroscopic observations, taking advantage of the position of spectral lines for many important chemical species in infrared frequencies. Some consideration was even given towards attempting to image newly discovered extrasolar planets with IIO, but the telescope lacked an occultation disk and was otherwise poorly suited for the task, so the idea was dropped. Even after its cryogenic supply ran out in late 2000 and the telescope was shut down, the accumulated archives of data IIO had gathered continued to power scientific research for years.
European high-energy astronomers were dismayed by ESA’s selection of UVAS and IRAS to be its first astronomical (or, indeed, scientific) satellites. For several years, inspired by the success of x-ray and gamma-ray observations using American satellites, as well as balloons and rockets, they had been pressing ESRO to build a European x-ray or gamma-ray observatory, while in the meantime participating in American observations (particularly Italian astronomers, through the Small Astronomical Satellites program). Although these attempts at gaining a native capability had, for the moment at least, borne no fruit, they had hardly given up. On the one hand, they continued their attempts to persuade the agency to develop such an observatory, even a small and inexpensive one, while on the other they sought out other ways of furthering their scientific interests. French astronomers collaborated with the Soviet Union in a series of programs, including observations via Soyuz and Salyut flights, before joining in the construction of the large Gamma space telescope at the end of the decade, while German and Italian astronomers found partnership in each other. Under Italian leadership, and with mostly Italian funding (due to the expense of developing the mostly German Helios-Encke, among others, at the same time), Germany and Italy began a project to build and launch a small x-ray astronomy satellite, name RoSat, for Röntgen Satellite, after the discoverer of x-rays and first Nobel physics laureate. As with the simultaneous Japanese, Soviet, and Indian[8] programs, few truly fundamental breakthroughs originated from RoSat, but nevertheless the project was an important step forwards for European high-energy astronomy.
In the United States, meanwhile, despite the overwhelming focus on Hubble among many members of the astronomical community, American astronomers had been working hard on a series of smaller space telescopes exploring a diverse range of wavelengths and targets. Even as Hubble had been approved, American high-energy astronomers had been pushing for a larger and more capable set of follow-on missions to those earlier efforts, the High-Energy Astronomical Observatories, or HEAOs. These would extend the observations of the Orbiting Astronomical Observatories, sounding rocket and balloon flights, and other satellites like Uhuru through a series of similar relatively large satellites carrying a range of instruments in the x-ray, gamma ray, and cosmic ray energy regions. Each HEAO would be specialized to attack one particular problem, rather than carrying a large number of instruments itself, allowing larger experiments, such as a proposed x-ray telescope, to be carried than was possible on earlier observatories. While budget cuts and new programs such as Hubble and the UVAS and IRAS projects forced a reduction in the scale of the program, even in their reduced form the HEAOs would offer a substantial leap forwards from previous generation high-energy observatories.
While all three HEAOs offered the opportunity for important astronomical research, the most important of the three would be the second, the “Einstein Observatory,” as it would carry the most novel instrument of the series, the x-ray telescope. Previous spacecraft had simply carried their detectors placed around the outside of the spacecraft, an arrangement that had been effective enough but made it difficult to focus on the emissions of a single source, for example to conduct spectroscopy or form images. As with optical and radio astronomy, a telescope was the logical next step, some method of concentrating x-rays emitted from a single source into a small area. Such a device had actually been developed over the past several two decades by the efforts of Riccardo Giacconi and his colleagues at American Science and Engineering. Because of the high energy of x-rays compared to visible or even ultraviolet light, conventional parabolic or hyperbolic mirrors cannot be used to concentrate x-ray radiation; instead, with the photons striking the material of the mirror head-on, they would simply pass through or be absorbed, something which was quickly discovered when AS&E began working on x-ray telescopes in the early 1960s. Additionally, such a mirror would be very poor optically, with significant distortion of the image outside of a very small central region. Fortunately, early in the previous decade the German physicist Hans Wolter had worked out several possible designs for x-ray reflectors which relied instead on the principle of grazing incidence reflection and consisted of nested conic sections.[9] These would allow a much larger field of view and higher quality image than a simple parabolic or hyperbolic mirror, but were also considerably more complex to design and build. However, Giacconi and the engineers and scientists of AS&E were able over the next several years to work out the kinks in the design and launch the first x-ray telescope aboard a sounding rocket in the mid-1960s.
The logical next step would of course be to place a telescope in orbit, where it could continuously perform observations rather than be limited to a few minutes outside the atmosphere like a sounding rocket-based model. Indeed, Giacconi and other x-ray astronomers had proposed doing just that several times before and after the first successful telescope, laying out a plan that would lead to a major Earth-orbiting x-ray observatory being launched in the 1970s after a precursor mission. However, the higher budgets and greater oversight associated with space programs as opposed to cheap, quick sounding rockets slowed any implementation of this concept. AS&E could not simply go out and develop their own x-ray satellite and arrange for it to be launched; they would have to pursue and maintain the favor of NASA and the astronomical community while developing a much larger and more complex telescope than they had demonstrated in flight previously. At this juncture, the HEAO program came along at just the right time to support such a mission, and Giacconi’s team quickly latched on to the concept as a method of moving their project forwards. Construction of the telescope, while, as with all space projects, not easy, had nevertheless not been marred by the political and technical difficulties experienced by Hubble, and by the assigned launch date of late 1978 what would be dubbed the Einstein Observatory was more than ready for launch. As expected, it had a significant effect on x-ray astronomy. At last, many diffuse sources could be resolved into point components, and other sources imaged in fine detail. X-ray sources in distant galaxies could be resolved, providing some of the first evidence for supermassive black holes at the center of those galaxies (in the form of large, energetic jets of gas being emitted from their nuclei), and spectroscopic measurements of many sources were taken for the first time.[10]
As the High Energy Astronomical Observatories launched, attention was finally beginning to turn towards what, if any, large scale projects should succeed the Hubble Space Telescope as a priority for the late 1980s and early 1990s, as Hubble would be hitting its stride. Given the success of the High Energy Astronomical Observatories over the last few years, the obvious choice, confirmed by the astronomy decadal survey completed in 1982[11], was a follow-on to that program. As envisioned by the decadal survey, such a follow-on would consist of two “Advanced High Energy Observatories,” one a gamma-ray satellite equipped with a range of instruments and the other a large imaging x-ray telescope, as had been proposed some time ago to succeed HEAO-2. Although NASA had been studying both for several years, under the rubrics of the “Large Gamma-Ray Observatory,” or LGO, and the “Advanced X-Ray Telescope,” or AXT, respectively, the funding requirements of other major programs had prevented more than conceptual work from being completed. Combined with the Vulkan Panic and the recent launch of a large Soviet gamma-ray observatory named, unimaginatively, “Gamma,” the decadal survey’s endorsement provided the impulse necessary to move from paper studies to actual program. As the AXT and LGO would be closer in size and therefore budget to Hubble rather than the smaller HEAOs or even earlier telescopes, it would be infeasible to develop them simultaneously even with the expanded budgets made available in the wake of the Vulkan Panic. The natural choice for prioritization was AXT. Besides the fact that the Einstein Observatory had only just demonstrated the ability to operate an x-ray telescope to begin with, such an observatory would require advanced (and therefore impressive) technology, something fitting in well with the environment of the Panic. While work on the AXT was therefore started almost immediately, with a launch planned for perhaps shortly after Hubble’s slated demise, work on the LGO was put off until after AXT’s launch, meaning that it could not be completed before the late 1990s or early 2000s.
[1]: These are, of course, similar to the OTL observatories IUE (which was, in fact, essentially a descoped LAS) and IRAS. Note, however, that Europe is taking a lead role in both (largely because Britain, which was heavily involved in both programs OTL, is now a major ESA member), rather than leading from behind, as it were. However, as noted later ESA spending on these two spacecraft precludes their involvement in COROT and x-ray astronomy more generally.
[2]: This is largely following the OTL discoveries of the spacecraft. I don’t see any particular reason why the results of the first orbital infrared telescope wouldn’t be broadly similar, to the level of detail in the post.
[3]: IOTL, in the 1982 period there were meetings between scientists from the European Science Foundation and the National Academy of Sciences to discuss various possibilities for collaboration on planetary science projects, which led by and by to Cassini-Huygens. So far as I am aware, there was no larger goal on the part of the ESF or ESA in those meetings, but I felt the presented idea of a larger series of meetings involving more countries was plausible. You will be hearing more about these and what they led to on the American side in Part III...
[4]: Conceptually, this is similar to a merger of the Infrared Space Observatory and Spitzer; obviously, it has the orbital characteristics of the latter and the nationality (so to speak) of the former. The Europa 4, unlike the Ariane 4, has more than enough power to lift even a large space observatory into heliocentric orbit, and from my reading it seems that such orbits were preferred beginning in about the 1980s because of the cited advantages.
[5]: The “planned future projects” being the various planetary missions previously discussed. Effectively, Usuda plus the European facilities can obtain DSN-type coverage without needing to touch NASA.
[6]: Readers interested in the IIO may find the ISO handbook and ISO scientific publications list interesting.
[7]: Yes, I’m teasing you You’ll have to wait until Part III for more...
[8]: IOTL, the first Indian satellite launched was an x-ray astronomy satellite, Aryabhata. This may or may not have been more successful ITTL.
[9]: More technical details may be found here, at the Goddard web site.
[10]: As with IRAS, I felt the OTL discoveries would be similar to the ITTL discoveries.
[11]: IOTL, the corresponding decadal survey recommended four "large" programs, two of which were space-based. First, there was, essentially, Chandra (then called AXAF). Second, there was a large deployable reflector; think a bigger version of the James Webb optimized for optical wavelengths and deployed from Shuttle.
(Out of interest, the two ground programs were the Very-Long Baseline Array and a large (~15m!) telescope for optical and infrared observations).
It may be noted that they got 2.5/4 of these large projects, albeit Chandra arrived roughly a half-decade after the other one and a half (the VLBA, completed in 1993, and the Keck, which while only 10m does operate in the optical and near-infrared bands, and was also completed in 1993)
1178 replies 144536 viewsEyes Turned Skyward, Part II: Post #24:
However impressive Hubble was, it was not and never had been the be-all and end-all of space observatories, nor was the United States the only player in space astronomy. Even as Hubble began the long process of definition in the early 1970s, the newly constituted ESA had selected a pair of British-led astronomical satellites, the UltraViolet Astronomical Satellite and the InfraRed Astronomical Satellite, or UVAS and IRAS, to form its first scientific satellite program. While UVAS was essentially a descoped version of the Large Astronomical Satellite that had long been under consideration at ESRO, and was essentially similar to the Orbiting Astronomical Observatories of NASA, IRAS was something new, taking advantage of the rapid development of infrared astronomy over the previous decade to launch a cryogenically cooled infrared telescope into space, where it would use the lack of atmosphere to allow observations of a potentially much broader range of wavelengths than possible from the ground.[1] Both IRAS and UVAS would have participation from NASA, although in a novel turn of events as a junior partner rather than a senior. The projects would be led and managed by ESA, with NASA providing certain technical elements. Although novel, in many ways the IRAS proposal was a simple extrapolation of existing trends, with infrared telescopes having been flown on airplanes, built on mountains, and lifted by balloons during the 1960s to allow observations through a smaller and smaller air column. As with x-ray or ultraviolet observations before, putting a telescope into space would be a mere logical extension to its absolute limit of this movement. While the development of its sister vehicle, UVAS, proceeded relatively smoothly up to its eventual 1978 launch, IRAS proved to have a more difficult and protracted development program due to the challenges associated with the containment and management of a large amount of cryogenic liquid helium over a relatively long period of time in a microgravity environment. Although it was intended to be launched at about the same time as UVAS, problems with the relatively novel cryogenic systems and infrared detectors, European inexperience in space activities, and the higher priority of UVAS led it to slip significantly behind. Nevertheless, work never stopped on the project, and in 1980 it was lifted from Kourou into a low Earth orbit by a boosted Europa 2, some two years behind its sister satellite.
Once it was in orbit, however, IRAS lived up to expectations, producing a detailed map of the sky at infrared wavelengths, particularly those inaccessible to ground-based telescopes due to atmospheric absorption. In the course of this effort, it made several significant discoveries, including the debris disks around other stars, warm dust called infrared cirrus pervading interstellar space, and intense infrared emissions from colliding galaxies.[2] In a more minor sidenote, it also discovered several lost or previously unseen comets and asteroids, taking advantage of their greater visibility in infrared relative to visible frequencies. The greatest accomplishment of IRAS, however, was merely in proving that a cryogenically cooled space-based infrared telescope was possible and practical, and with its success European astronomers almost immediately began to look forward to the next logical step, a larger, higher resolution imaging infrared telescope, tentatively termed the Advanced Infrared Space Observatory, or AISO. Meanwhile, senior managers at ESA had long been dissatisfied with the degree of control they actually possessed over the continent’s space program, both from bureaucratic self-interest and perhaps from a degree of latent pan-Europeanism. Of the various ESA programs, only the Europa launch vehicle program and ESA’s human spaceflight program were truly European endeavours; the remainder were largely vehicles for individual national programs to promote their projects and missions at continental expense, with little in the way of a common European program. For example, ESA’s planetary science program was dominated by German involvement in Helios-Encke and the forthcoming Newton comet probe, while the astronomy program had conversely been dominated through the 1970s by the British-led UVAS and IRAS satellites. Moreover, all of the member states routinely cut deals with outside countries, often the superpowers, to partake in other projects, such as the Franco-Soviet Eos Venus balloon probe. To counter these tendencies, ESA management induced the European Science Foundation to consider space science programs in the early 1980s, seeking to have them draw up a list of continent-wide priorities, both for native European projects and for collaboration with other countries, particularly the United States and the Soviet Union but also the rising space program of Japan.[3] As part of this program, the European Science Foundation initiated a series of high-level contacts between its own members and the members of the National Academy of Sciences, the Soviet Academy of Sciences, and the Japan Academy, to communicate about what programs would be of greatest interest to the scientists of each country.
Japanese astronomers had, at the same time, been nurturing a growing interest in space astronomy, fueled by the successful Hakucho and Hinotori missions and the growing Japanese economy. While the Japanese were naturally aware of European success in not only x-ray but also infrared and ultraviolet space astronomy, they had not been particularly privy to intimate details nor had they entertained much thought of collaboration with their trans-Eurasian counterparts. The meetings spurred by ESA between European and Japanese scientists changed that, as a new conduit opened to allow information to flow between the two programs. Scientists on both sides saw the advances their compatriots had made and the programs they were interested in in more detail, and were able to converse more freely and deeply about their common areas of interest than they otherwise would. Japanese astronomers interested in expanding their program beyond the admittedly highly successful x-ray program quickly latched on to the budding AISO program as an attractive method of broadening their horizons. Japan could usefully make a number of contributions to the program, allowing it to gain experience in the necessary technology and operational techniques for a future Japanese infrared telescope, without the risks or expense associated with beginning their own infrared observatory program. As a result of Japanese interest in the project, the AISO had developed into the International Infrared Observatory, or IIO, by the time the project was approved along with the Piazzi asteroid probe in 1983.
The International Infrared Observatory would consist of a telescope generally similar to IRAS, of about the same aperture and still using detectors cryogenically cooled with liquid helium, one of which would be built by Japan. Despite these similarities, however, IIO would depart significantly from IRAS in two major ways. First, it would be launched into a heliocentric orbit, rather than Earth orbit.[4] By placing it into solar orbit, a number of advantages could be realized, most obviously that of Earth and the Moon no longer being present to block large parts of the sky at any given time. The heat flux on the telescope would also be drastically reduced, vastly increasing the amount of time a given amount of liquid helium could chill the telescope to its cryogenic operating temperature. The principal disadvantage was that communications would be more difficult than with an Earth-orbiting probe, although the construction of European and Japanese deep-space communications facilities for planned future projects helped mitigate this difficulty substantially. [5] For a telescope intended to provide a vast leap over IRAS in terms of sensitivity and resolution--to take on the task of detailed imaging of the sources IRAS had mapped out--the advantages of the heliocentric orbit more than outweighed the disadvantages. Second, IIO would take full advantage of major advances in detector technology that had taken place since IRAS was designed, particularly the rapidly advancing state-of-the-art in charge-coupled devices (especially sensitive to “red” radiation) to provide greatly improved resolution and sensitivity. Unlike IRAS, which had been designed as a survey telescope, one which mapped out sources from the entire sky, albeit at a relatively low resolution, IIO would be an imaging telescope, one which observed a relatively narrow area of a the sky, but at relatively high resolution and sensitivity. Data from IRAS could be used to “aim” IIO, allowing it to focus on the strangest and most interesting sources in the sky, without having to waste time finding those sources in the first place.
As with its counterpart Piazzi, development of IIO proceeded more slowly than anticipated, hampered not only by the growing diversity of ESA’s programs, but also by the technical difficulties of the project.[6] While by virtue of their construction of IRAS and Hubble’s Long Wavelength/Planetary Camera Europeans had more experience in infrared space astronomy than any other group in the world, scientists wanted to push the boundaries of technology even further to achieve pointing stability and accuracy, cryogenic lifetime, resolution, and sensitivity much superior to IRAS’ capabilities. By the time construction of the observatory could start, the financial challenges posed by the crumbling Soviet empire of Eastern Europe, especially the costs being borne by the Federal Republic of Germany after its reunification with the German Democratic Republic in 1989, served as a further block to development. As with Piazzi, this led to IIO’s launch being delayed several years, from the initially envisioned late 1992 to early 1995. By the time it launched, the rapidly advancing state of the art in ground-based infrared telescopes and increasing NASA interest in launching a Large Infrared Space Telescope[7] to replace Hubble in the next decade had made IIO seem less groundbreaking than in 1983, but it would still be a worthy and capable telescope by itself, and available considerably earlier than NASA’s larger offering. Its successful launch into an escape trajectory by a Europa 42 was quickly followed by Japanese and European confirmation of proper operation of all the spacecraft’s systems.
Over the next several years, until the depletion of its liquid helium supply, IIO remained the world’s premier facility for infrared astronomy. In its primary mission, providing high-resolution infrared imaging of a variety of galactic and extragalactic targets, it succeeded magnificently, entirely confirming the hopes of astronomers who wanted to use infrared observations to penetrate veils of interstellar dust. It also extended IRAS’ observations of extrasolar debris disks and performed a large number of spectroscopic observations, taking advantage of the position of spectral lines for many important chemical species in infrared frequencies. Some consideration was even given towards attempting to image newly discovered extrasolar planets with IIO, but the telescope lacked an occultation disk and was otherwise poorly suited for the task, so the idea was dropped. Even after its cryogenic supply ran out in late 2000 and the telescope was shut down, the accumulated archives of data IIO had gathered continued to power scientific research for years.
European high-energy astronomers were dismayed by ESA’s selection of UVAS and IRAS to be its first astronomical (or, indeed, scientific) satellites. For several years, inspired by the success of x-ray and gamma-ray observations using American satellites, as well as balloons and rockets, they had been pressing ESRO to build a European x-ray or gamma-ray observatory, while in the meantime participating in American observations (particularly Italian astronomers, through the Small Astronomical Satellites program). Although these attempts at gaining a native capability had, for the moment at least, borne no fruit, they had hardly given up. On the one hand, they continued their attempts to persuade the agency to develop such an observatory, even a small and inexpensive one, while on the other they sought out other ways of furthering their scientific interests. French astronomers collaborated with the Soviet Union in a series of programs, including observations via Soyuz and Salyut flights, before joining in the construction of the large Gamma space telescope at the end of the decade, while German and Italian astronomers found partnership in each other. Under Italian leadership, and with mostly Italian funding (due to the expense of developing the mostly German Helios-Encke, among others, at the same time), Germany and Italy began a project to build and launch a small x-ray astronomy satellite, name RoSat, for Röntgen Satellite, after the discoverer of x-rays and first Nobel physics laureate. As with the simultaneous Japanese, Soviet, and Indian[8] programs, few truly fundamental breakthroughs originated from RoSat, but nevertheless the project was an important step forwards for European high-energy astronomy.
In the United States, meanwhile, despite the overwhelming focus on Hubble among many members of the astronomical community, American astronomers had been working hard on a series of smaller space telescopes exploring a diverse range of wavelengths and targets. Even as Hubble had been approved, American high-energy astronomers had been pushing for a larger and more capable set of follow-on missions to those earlier efforts, the High-Energy Astronomical Observatories, or HEAOs. These would extend the observations of the Orbiting Astronomical Observatories, sounding rocket and balloon flights, and other satellites like Uhuru through a series of similar relatively large satellites carrying a range of instruments in the x-ray, gamma ray, and cosmic ray energy regions. Each HEAO would be specialized to attack one particular problem, rather than carrying a large number of instruments itself, allowing larger experiments, such as a proposed x-ray telescope, to be carried than was possible on earlier observatories. While budget cuts and new programs such as Hubble and the UVAS and IRAS projects forced a reduction in the scale of the program, even in their reduced form the HEAOs would offer a substantial leap forwards from previous generation high-energy observatories.
While all three HEAOs offered the opportunity for important astronomical research, the most important of the three would be the second, the “Einstein Observatory,” as it would carry the most novel instrument of the series, the x-ray telescope. Previous spacecraft had simply carried their detectors placed around the outside of the spacecraft, an arrangement that had been effective enough but made it difficult to focus on the emissions of a single source, for example to conduct spectroscopy or form images. As with optical and radio astronomy, a telescope was the logical next step, some method of concentrating x-rays emitted from a single source into a small area. Such a device had actually been developed over the past several two decades by the efforts of Riccardo Giacconi and his colleagues at American Science and Engineering. Because of the high energy of x-rays compared to visible or even ultraviolet light, conventional parabolic or hyperbolic mirrors cannot be used to concentrate x-ray radiation; instead, with the photons striking the material of the mirror head-on, they would simply pass through or be absorbed, something which was quickly discovered when AS&E began working on x-ray telescopes in the early 1960s. Additionally, such a mirror would be very poor optically, with significant distortion of the image outside of a very small central region. Fortunately, early in the previous decade the German physicist Hans Wolter had worked out several possible designs for x-ray reflectors which relied instead on the principle of grazing incidence reflection and consisted of nested conic sections.[9] These would allow a much larger field of view and higher quality image than a simple parabolic or hyperbolic mirror, but were also considerably more complex to design and build. However, Giacconi and the engineers and scientists of AS&E were able over the next several years to work out the kinks in the design and launch the first x-ray telescope aboard a sounding rocket in the mid-1960s.
The logical next step would of course be to place a telescope in orbit, where it could continuously perform observations rather than be limited to a few minutes outside the atmosphere like a sounding rocket-based model. Indeed, Giacconi and other x-ray astronomers had proposed doing just that several times before and after the first successful telescope, laying out a plan that would lead to a major Earth-orbiting x-ray observatory being launched in the 1970s after a precursor mission. However, the higher budgets and greater oversight associated with space programs as opposed to cheap, quick sounding rockets slowed any implementation of this concept. AS&E could not simply go out and develop their own x-ray satellite and arrange for it to be launched; they would have to pursue and maintain the favor of NASA and the astronomical community while developing a much larger and more complex telescope than they had demonstrated in flight previously. At this juncture, the HEAO program came along at just the right time to support such a mission, and Giacconi’s team quickly latched on to the concept as a method of moving their project forwards. Construction of the telescope, while, as with all space projects, not easy, had nevertheless not been marred by the political and technical difficulties experienced by Hubble, and by the assigned launch date of late 1978 what would be dubbed the Einstein Observatory was more than ready for launch. As expected, it had a significant effect on x-ray astronomy. At last, many diffuse sources could be resolved into point components, and other sources imaged in fine detail. X-ray sources in distant galaxies could be resolved, providing some of the first evidence for supermassive black holes at the center of those galaxies (in the form of large, energetic jets of gas being emitted from their nuclei), and spectroscopic measurements of many sources were taken for the first time.[10]
As the High Energy Astronomical Observatories launched, attention was finally beginning to turn towards what, if any, large scale projects should succeed the Hubble Space Telescope as a priority for the late 1980s and early 1990s, as Hubble would be hitting its stride. Given the success of the High Energy Astronomical Observatories over the last few years, the obvious choice, confirmed by the astronomy decadal survey completed in 1982[11], was a follow-on to that program. As envisioned by the decadal survey, such a follow-on would consist of two “Advanced High Energy Observatories,” one a gamma-ray satellite equipped with a range of instruments and the other a large imaging x-ray telescope, as had been proposed some time ago to succeed HEAO-2. Although NASA had been studying both for several years, under the rubrics of the “Large Gamma-Ray Observatory,” or LGO, and the “Advanced X-Ray Telescope,” or AXT, respectively, the funding requirements of other major programs had prevented more than conceptual work from being completed. Combined with the Vulkan Panic and the recent launch of a large Soviet gamma-ray observatory named, unimaginatively, “Gamma,” the decadal survey’s endorsement provided the impulse necessary to move from paper studies to actual program. As the AXT and LGO would be closer in size and therefore budget to Hubble rather than the smaller HEAOs or even earlier telescopes, it would be infeasible to develop them simultaneously even with the expanded budgets made available in the wake of the Vulkan Panic. The natural choice for prioritization was AXT. Besides the fact that the Einstein Observatory had only just demonstrated the ability to operate an x-ray telescope to begin with, such an observatory would require advanced (and therefore impressive) technology, something fitting in well with the environment of the Panic. While work on the AXT was therefore started almost immediately, with a launch planned for perhaps shortly after Hubble’s slated demise, work on the LGO was put off until after AXT’s launch, meaning that it could not be completed before the late 1990s or early 2000s.
[1]: These are, of course, similar to the OTL observatories IUE (which was, in fact, essentially a descoped LAS) and IRAS. Note, however, that Europe is taking a lead role in both (largely because Britain, which was heavily involved in both programs OTL, is now a major ESA member), rather than leading from behind, as it were. However, as noted later ESA spending on these two spacecraft precludes their involvement in COROT and x-ray astronomy more generally.
[2]: This is largely following the OTL discoveries of the spacecraft. I don’t see any particular reason why the results of the first orbital infrared telescope wouldn’t be broadly similar, to the level of detail in the post.
[3]: IOTL, in the 1982 period there were meetings between scientists from the European Science Foundation and the National Academy of Sciences to discuss various possibilities for collaboration on planetary science projects, which led by and by to Cassini-Huygens. So far as I am aware, there was no larger goal on the part of the ESF or ESA in those meetings, but I felt the presented idea of a larger series of meetings involving more countries was plausible. You will be hearing more about these and what they led to on the American side in Part III...
[4]: Conceptually, this is similar to a merger of the Infrared Space Observatory and Spitzer; obviously, it has the orbital characteristics of the latter and the nationality (so to speak) of the former. The Europa 4, unlike the Ariane 4, has more than enough power to lift even a large space observatory into heliocentric orbit, and from my reading it seems that such orbits were preferred beginning in about the 1980s because of the cited advantages.
[5]: The “planned future projects” being the various planetary missions previously discussed. Effectively, Usuda plus the European facilities can obtain DSN-type coverage without needing to touch NASA.
[6]: Readers interested in the IIO may find the ISO handbook and ISO scientific publications list interesting.
[7]: Yes, I’m teasing you
You’ll have to wait until Part III for more...[8]: IOTL, the first Indian satellite launched was an x-ray astronomy satellite, Aryabhata. This may or may not have been more successful ITTL.
[9]: More technical details may be found here, at the Goddard web site.
[10]: As with IRAS, I felt the OTL discoveries would be similar to the ITTL discoveries.
[11]: IOTL, the corresponding decadal survey recommended four "large" programs, two of which were space-based. First, there was, essentially, Chandra (then called AXAF). Second, there was a large deployable reflector; think a bigger version of the James Webb optimized for optical wavelengths and deployed from Shuttle.
(Out of interest, the two ground programs were the Very-Long Baseline Array and a large (~15m!) telescope for optical and infrared observations).
It may be noted that they got 2.5/4 of these large projects, albeit Chandra arrived roughly a half-decade after the other one and a half (the VLBA, completed in 1993, and the Keck, which while only 10m does operate in the optical and near-infrared bands, and was also completed in 1993)
Oh My God
This IRAS ist bigger! 2110 kg v.s the OTL with 1073 kg.
only one thing is missing, Space radio-telescope
the Soviet had tested radio-telescope on Salut.
and hab launch Sektr-Radioastron
sadly with big delay. Planed in 1989 for 1990 launch, it arrive in orbit 2011
This IRAS ist bigger! 2110 kg v.s the OTL with 1073 kg.
only one thing is missing, Space radio-telescope
the Soviet had tested radio-telescope on Salut.
and hab launch Sektr-Radioastron
sadly with big delay. Planed in 1989 for 1990 launch, it arrive in orbit 2011