This would make several of the Solar System's moons 'planets', then.
This is actually not a problem. "Moon" is an auxilliary category, like "dwarf," is all.
It is rather radical, but it does have some logic behind it.
Moons are even easier to define IMHO. They're in Orbit around a planet, with the barycentre existing inside the parent planet.
Of course, then you have to separate them into their own individual categories, but that should be "relatively" simple.
Exactly. It's just that using my scheme also provides for a quick discriminant between large, generally active moons, and smaller, inactive ones.
This Pluto discussion show the actual problem between scientists and citizens
for Scientist, we have catalogue of "Planetary" objects in space (see Bahamut-255 post 938)
While most people see in Sky: the Moon, Sun, stars and the rest are "Planets"
for Scientist, we have catalogue of "Planetary" objects in space (see Bahamut-255 post 938)
While most people see in Sky: the Moon, Sun, stars and the rest are "Planets"
Part II: Post 12: Comet probes: Helios-Encke and The Halley Armada: Newton/Kirchhoff, Gallei 1/2 and Suisei/Sakigake
Well, it's that time again. Last week, we followed the Voyager probes as they made their final flybys of the outer systems planets (and Pluto, whose status I see spurs some debate even among our commentators) then proceeded past into the deep dark. While one mission was ending, though, others were beginning, and this week we're focusing on a couple of those, this time on the comet explorations of the 1980s.947 replies 114528 views
Eyes Turned Skyward, Part II: Post #12
Asteroids and comets--what astronomers term "primitive bodies" due to their low rates of chemical and thermal modification relative to larger bodies--have long fascinated and sometimes terrified human observers. Nevertheless, in the first half of the 20th century they did not attract much regard from professional astronomers, being viewed more as irritating interruptions to observations of distant stars and galaxies than highly interesting objects in their own right. As with the rest of the Sun's offspring, that began to change with the advent of spaceflight. Now offered the chance not merely to observe them through a telescope's lens but to actually visit these "vermin," if only via robotic emissaries, astronomers gained a certain level of regard for the objects. Slowly, proposals to send probes to not just the planets but also these flying mountains or dirty snowballs were developed. The most well-known of the targets proposed was undoubtedly Halley's Comet, the famously clockwork object whose passages near the Sun had been recorded for centuries. In a fortuitous coincidence, the practical development of spaceflight had occurred roughly halfway through Halley's 76-year orbit, some thirty years before its second passage during the 20th century. This offered plenty of time to think about and develop the methods by which a probe could be dispatched to study it, the brightest and most active of the periodic comets. The early concepts were almost invariably rendezvous missions, in which either a Jupiter swingby or a low-thrust propulsion system (both ion propulsion and, briefly, a solar sail were considered) would allow a probe to slowly meet with Halley and stay nearby for months or even years, intensively observing the coma and nucleus throughout its closest passage to the Sun. However, while certainly scientifically attractive, the Halley mission suffered from the long lead time needed to conduct the mission, since it needed to be launched no later than 1982 to successfully rendezvous; high costs (estimated to be comparable to Viking, Voyager, or Galileo); and a surplus of competing projects, particularly the expensive Voyager and Galileo missions to the outer planets. Therefore, when budgetary approval was not obtained for the probe in the FY 1979 budget, the entire mission plan had to be abandoned.
Nevertheless, American scientists had not given up on Halley; trajectory analysis showed that an electrically propelled spacecraft launched in 1985 could make a flyby of Halley that November and then go on to rendezvous with another comet, with Encke and Tempel 2 being the most seriously considered candidates. Such a spacecraft would be lower cost than the Halley rendezvous probe, as it would demand a much shorter endurance and would need to venture much less far out from the Sun, and could carry a small "nucleus probe" to more closely explore the vicinity of Halley's nucleus while the main spacecraft stayed at a safe (and dust-free) distance. A lack of interest by American scientists, together with long-standing European involvement in cometary science and the high interest at the time for "international" missions, led this parasite probe, named "Newton," being supplied by the European Space Agency rather than NASA itself. Attempts to convince Japan to supply a distant "tail probe" were unfortunately less successful, as it would not be possible to accommodate a tail probe as well as a nucleus probe aboard the primary spacecraft, and political constraints required both that Japan launch any such probe itself and that it make an encounter after perihelion[1]. Unfortunately, the Comet Rendezvous/Comet Flyby spacecraft had to encounter Halley before perihelion for the rendezvous, and the purpose of a tail probe was lost if it flew through the comet at a different time than the main spacecraft. The Japanese would therefore launch a pair of probes, virtually identical in all respects, to make a distant encounter with the comet at the best post-perihelion opportunity. In this, they would have good company from the Soviet Union, which planned to send a pair of "Gallei" probes to make a close flyby of Halley, although not as close as Newton. As a result, a regular flotilla of probes was forming to visit the comet, representing all of the major space-faring countries except China. Despite this, and despite the hot Cold War rhetoric passing between the United States and the Soviet Union, Halley exploration was leading to a burst of international cooperation, at least for Halley exploration. Data from the US and European probes would be passed to the Soviets, who would use the refined ephemerides generated by CR/CF and intense observations from telescopes around the world (including Hubble) to more precisely target their own probes. The results of the probes would also be widely shared, giving a more detailed image of how Halley changed over time than would be possible from ground instruments alone. Altogether, the international effort engendered by Halley would give an unprecedented level of data on how comets changed both over time and over their surface.
However, Halley would not be the first comet encountered by a space probe, nor would either the Americans or the Soviets gain that distinction. Instead, a European probe, Helios-Encke, would win the race, in so doing also setting the first European first of the space age, however little noted it may have been. The outgrowth of the highly successful German-American Helios solar observation program, Helios-Encke was originally an effort to extend the observations of Helios 1 and 2 by using spare Helios C hardware to launch another probe in the late 1970s or early 1980s during the next solar maximum, ensuring optimal coverage of what was expected to be an important moment for heliophysics. Shortly after this original proposal was made, trajectory planners noted that if launched in August 1980 the probe would be able to make a close encounter with the periodic comet Encke that December; in fact, it would be possible to shape the probe's subsequent orbit to encounter Encke again in 1984 (if the probe had not failed from its close solar passages by that time). To return useful data from the encounter would require significant modifications to the existing Helios C hardware, driving up costs, which led NASA to reject proposals of collaboration with Germany on the mission in favor of spending on more crucial planetary and human programs. However, the European Space Research Organisation found the mission scientifically attractive enough to be worth pursuing, and began funding for development in 1974, shortly before it transformed into the ESA. With ESRO involvement, NASA agreed to procure the Titan IIIE needed to launch the Helios spacecraft in 1975, in exchange for ESRO producing a set of experimental equipment for Spacelab. While modification of the Helios C hardware proved more expensive and time-consuming than expected, the significant time margin available ensured that technical delays did not significantly affect the launch date, just as cost overruns were dismissed as the product of inexperience. The tenth and final Titan IIIE hurtled into the air from Cape Canaveral carrying Helios-Encke along with it August 1980. Although not as complex or active as Halley, Encke still provided a number of surprises to the scientists behind Helios-Encke that December, showing a body which was at once less and more active than anticipated. Less surprisingly, it provided a resounding yes for the long-favored "dirty snowball" model of comets, although its data seemed to indicate that the proper description would be more "icy dirtball" instead, with relatively high levels of rocky compounds and materials detected. Despite several scars, Helios-Encke survived its passage, surprising some scientists who had expected intense dust fluxes to shatter the spacecraft, score its imaging systems into uselessness, or otherwise disable it. In fact, the spacecraft was in such good condition that there was no trouble approving the second flyby, and after occupying itself observing the Sun in conjunction with a growing fleet of Earth-orbiting spacecraft Helios-Encke had its second date with the comet in late March 1984. This time, Helios penetrated much deeper into the cometary coma, into regions where Encke was not so gentle. Buffeted by increasingly intense particle fluxes, Helios-Encke returned considerable amounts of data about how the comet had changed since its last perihelion before being blown away by dust grains too large and energetic for its particle shielding to block.
Thus, by 1985, European scientists had gained not just theoretical but actual practical knowledge of the dynamics of comet encounters and the conditions near cometary nuclei. Their Newton was, as a result, perhaps the proportionately best-equipped spacecraft of the entire flotilla, sporting thick protective armor against Halley's expected much more intense gas and dust jets, along with a suite of instruments based on those developed for Helios-Encke. Its parent, now named "Kirchhoff" after the wide-ranging 19th century German physicist responsible not only for the eponymous circuit laws but also for important research into solar radiation, was lifted into the heavens by a Saturn-Centaur in late July 1985, to the sounds of cheering later in the day as normal functioning of the crucial ion drive was confirmed. Four months later and just two weeks before meeting Halley, continuous thrusting had driven Kirchoff to the point where it could release Newton, before adjusting its course to pass well sunward of the energetically active comet. For now, Kirchhoff would only observe its cometary partner at a distance, waiting for the probe to close in and begin its survey. Two hours before closest encounter, a timer that had been counting down since Newton departed Earth finally reached zero, fully activating the scientific payload. Although several of the lower-power experiments had been intermittently collecting data since separation, and key systems such as the communications antennas beaming data to Kirchhoff and Earth had been checked out, most of the probe's systems had been powered down since launch, waiting for just this moment. As the probe streaked in towards the errant comet, it encountered an increasing storm of cometary gas and dust, sleeting against the multilayered shields intended to armor it against the sort of damage Helios-Encke had taken. All the while, it was furiously collecting and beaming back every possible scrap of data about its environment, detecting not only the rate and size of dust impacts, but also the composition of the gas and dust surrounding the probe and the electrical and magnetic behavior of that gas and dust. By far the most sophisticated instrument on board, however, was the camera, able to take stable and unblurred photographs of objects moving, like the comet's nucleus, at an astounding 60 kilometers per second--or 135,000 miles per hour--relative to the camera itself, with a resolution of several hundred meters[3]. As the probe streaked by just under 1000 kilometers from the comet's nucleus[4], this camera took a single complete high-resolution image of the nucleus, and part of a second, revealing details only a few hundred meters across. Much like Encke, this photo revealed a craggy and coal-black surface to the potato-shaped rock, with jets of gas and dust erupting from numerous locations, showing that even in their diversity comets are much alike and further supporting the theory of a common origin in the Kuiper Belt or Oort Cloud. As with Helios-Encke before it, however, Newton would not emerge intact from its cometary partner, as it encountered a particularly dense stream of cometary material just twenty minutes after closest approach, perhaps directly emanating from one of the jets seen on the nucleus. The frequency and size of impacts rapidly increased under the stream's influence before all telemetry abruptly cut off, probably the result of a particularly large and energetic fragment hitting the probe. Although it had not been given good odds to survive Halley, the premature destruction of the probe nevertheless saddened the team members who had spent years developing and building the little vehicle.
However dramatic Newton's flyby may have been, though, it was only the first member of the Halley Armada to reach the comet. By early March of the next year, the Japanese and Soviet members of the Halley armada were closing in on the comet. While the Japanese, undertaking their first deep-space mission, cautiously aimed their probes at a distant flyby, providing more prestige and engineering feedback than scientific value, the Soviets had ambitiously chosen to aim at a near flyby; not quite so near as Newton, but still close enough to pose significant risk to their Gallei probes. The first flashed by a few days after the Japanese probes made their closest approach, passing about 10,000 kilometers from the nucleus and showing (among other things) that the coma environment had changed significantly from Newton's encounter the previous year. A week later, Gallei 2, relying on updated navigational data from its sister probe dove into the coma, passing less than 5000 kilometers from the nucleus. Like Newton, it photographed the comet's core, showing that it had significantly changed from the earlier encounter. Although matching surface features was admittedly difficult, it appeared that many of the jets and vents previously detected by Newton were no longer active, and there was some evidence of other surface changes as well. Unlike Newton, however, Gallei managed to survive its encounter with Halley, successfully passing through the coma and beyond, back into interplanetary space. After three further weeks of increasingly distant observations, both Gallei probes were shut down to divert resources to preparations for the Mars 12/13 mission scheduled for 1988. Both Japanese probes continued to operate for several months, but although using gravity assists to divert one or the other to new targets was suggested, excessive propellant consumption and a feeling that the pair had limited scientific value led to them also being shut down by the end of the year. Only Kirchhoff remained, slowly adjusting its orbit farther and farther away from Earth's.
[1] This is to avoid scaring the fish. No, this is not a joke; OTL, until 2010 (!) launches from Tanegashima were restricted to only certain months of the year on behalf of the local fishing lobby. This constraint prevented Japan from launching its probes to the pre-perihelion opportunity OTL and forced them to use the post-perihelion opportunity[2]. Since Japanese politics have not significantly departed from OTL in TTL...
[2] An object which is moving in a highly elliptical and inclined orbit, like Halley, will offer two minimum-energy flyby opportunities during its close passage around its central body, one for each time it passes through the plane of the ecliptic. One will therefore proceed and the other follow periapsis (as can be seen if you picture the geometry and think about it a little). IOTL, all the flybys were conducted at the post-perihelion opportunity. The Japanese were constrained by politics, the Soviets by the position of Venus, and the Europeans by the presence of the Vegas (their data was used to refine the ephemerides used for Giotto's navigation), although the post-perihelion opportunity did require a slightly smaller delta-V than the pre-perihelion opportunity. Here, however, the geometry of the Tempel 2 rendezvous restricts the US flyby to the pre-perihelion opportunity, and with Newton clinging to Kirchoff that meant the Europeans must go along. The Japanese are restricted by the same politics, and the Soviets choose the later opportunity to avoid being compared to the Europeans and Americans as much as possible (European instruments or no). Plus, that allows some more interesting science than everyone going by simultaneously would.
[3] I actually mathematically worked out what this camera could do; it could resolve, accurately, the weapons mounted on an F-15E flying by at Mach 5 and an altitude of 9000 feet (well, obviously not an actual F-15E, but something the same rough size--the F-15E would appear to be about the size of Halley's Comet at 1000 kilometers). In fact, most US aircraft weapons are quite a bit larger than the resolution goal! The minimum size of viewed objects would be closer to a baseball or cricket bat, but strike aircraft don't typically carry those mounted on the outside.
[4] This is actually rather farther away from the nucleus than Giotto OTL managed; it benefited from the Vegas getting very nearby and transmitting updated ephemerides a few days earlier, as noted in [2]. ITTL, although capable Kirchhoff is never coming closer than 130,000 kilometers to Halley (the Vegas reached about 9000), and in any case releases the probe (which has no real method of correcting its trajectory) around two weeks before encounter, further limiting the possible accuracy. Nevertheless, this is towards the edge of the 3-sigma dispersion ellipse estimated at the start of the project, so it's still not a great performance.
Also, you may wonder whether the International Comet Probe (aka ISEE-3) exists ITTL. Well, as ISEE-3 it does, but as ICE...not so much. With a flagship-class comet mission coming down the line, even the relatively cheap ICE proposal would just be such an obvious waste of money that Farquhar would probably not even propose it in the first place.
Eyes Turned Skyward, Part II: Post #12
Asteroids and comets--what astronomers term "primitive bodies" due to their low rates of chemical and thermal modification relative to larger bodies--have long fascinated and sometimes terrified human observers. Nevertheless, in the first half of the 20th century they did not attract much regard from professional astronomers, being viewed more as irritating interruptions to observations of distant stars and galaxies than highly interesting objects in their own right. As with the rest of the Sun's offspring, that began to change with the advent of spaceflight. Now offered the chance not merely to observe them through a telescope's lens but to actually visit these "vermin," if only via robotic emissaries, astronomers gained a certain level of regard for the objects. Slowly, proposals to send probes to not just the planets but also these flying mountains or dirty snowballs were developed. The most well-known of the targets proposed was undoubtedly Halley's Comet, the famously clockwork object whose passages near the Sun had been recorded for centuries. In a fortuitous coincidence, the practical development of spaceflight had occurred roughly halfway through Halley's 76-year orbit, some thirty years before its second passage during the 20th century. This offered plenty of time to think about and develop the methods by which a probe could be dispatched to study it, the brightest and most active of the periodic comets. The early concepts were almost invariably rendezvous missions, in which either a Jupiter swingby or a low-thrust propulsion system (both ion propulsion and, briefly, a solar sail were considered) would allow a probe to slowly meet with Halley and stay nearby for months or even years, intensively observing the coma and nucleus throughout its closest passage to the Sun. However, while certainly scientifically attractive, the Halley mission suffered from the long lead time needed to conduct the mission, since it needed to be launched no later than 1982 to successfully rendezvous; high costs (estimated to be comparable to Viking, Voyager, or Galileo); and a surplus of competing projects, particularly the expensive Voyager and Galileo missions to the outer planets. Therefore, when budgetary approval was not obtained for the probe in the FY 1979 budget, the entire mission plan had to be abandoned.
Nevertheless, American scientists had not given up on Halley; trajectory analysis showed that an electrically propelled spacecraft launched in 1985 could make a flyby of Halley that November and then go on to rendezvous with another comet, with Encke and Tempel 2 being the most seriously considered candidates. Such a spacecraft would be lower cost than the Halley rendezvous probe, as it would demand a much shorter endurance and would need to venture much less far out from the Sun, and could carry a small "nucleus probe" to more closely explore the vicinity of Halley's nucleus while the main spacecraft stayed at a safe (and dust-free) distance. A lack of interest by American scientists, together with long-standing European involvement in cometary science and the high interest at the time for "international" missions, led this parasite probe, named "Newton," being supplied by the European Space Agency rather than NASA itself. Attempts to convince Japan to supply a distant "tail probe" were unfortunately less successful, as it would not be possible to accommodate a tail probe as well as a nucleus probe aboard the primary spacecraft, and political constraints required both that Japan launch any such probe itself and that it make an encounter after perihelion[1]. Unfortunately, the Comet Rendezvous/Comet Flyby spacecraft had to encounter Halley before perihelion for the rendezvous, and the purpose of a tail probe was lost if it flew through the comet at a different time than the main spacecraft. The Japanese would therefore launch a pair of probes, virtually identical in all respects, to make a distant encounter with the comet at the best post-perihelion opportunity. In this, they would have good company from the Soviet Union, which planned to send a pair of "Gallei" probes to make a close flyby of Halley, although not as close as Newton. As a result, a regular flotilla of probes was forming to visit the comet, representing all of the major space-faring countries except China. Despite this, and despite the hot Cold War rhetoric passing between the United States and the Soviet Union, Halley exploration was leading to a burst of international cooperation, at least for Halley exploration. Data from the US and European probes would be passed to the Soviets, who would use the refined ephemerides generated by CR/CF and intense observations from telescopes around the world (including Hubble) to more precisely target their own probes. The results of the probes would also be widely shared, giving a more detailed image of how Halley changed over time than would be possible from ground instruments alone. Altogether, the international effort engendered by Halley would give an unprecedented level of data on how comets changed both over time and over their surface.
However, Halley would not be the first comet encountered by a space probe, nor would either the Americans or the Soviets gain that distinction. Instead, a European probe, Helios-Encke, would win the race, in so doing also setting the first European first of the space age, however little noted it may have been. The outgrowth of the highly successful German-American Helios solar observation program, Helios-Encke was originally an effort to extend the observations of Helios 1 and 2 by using spare Helios C hardware to launch another probe in the late 1970s or early 1980s during the next solar maximum, ensuring optimal coverage of what was expected to be an important moment for heliophysics. Shortly after this original proposal was made, trajectory planners noted that if launched in August 1980 the probe would be able to make a close encounter with the periodic comet Encke that December; in fact, it would be possible to shape the probe's subsequent orbit to encounter Encke again in 1984 (if the probe had not failed from its close solar passages by that time). To return useful data from the encounter would require significant modifications to the existing Helios C hardware, driving up costs, which led NASA to reject proposals of collaboration with Germany on the mission in favor of spending on more crucial planetary and human programs. However, the European Space Research Organisation found the mission scientifically attractive enough to be worth pursuing, and began funding for development in 1974, shortly before it transformed into the ESA. With ESRO involvement, NASA agreed to procure the Titan IIIE needed to launch the Helios spacecraft in 1975, in exchange for ESRO producing a set of experimental equipment for Spacelab. While modification of the Helios C hardware proved more expensive and time-consuming than expected, the significant time margin available ensured that technical delays did not significantly affect the launch date, just as cost overruns were dismissed as the product of inexperience. The tenth and final Titan IIIE hurtled into the air from Cape Canaveral carrying Helios-Encke along with it August 1980. Although not as complex or active as Halley, Encke still provided a number of surprises to the scientists behind Helios-Encke that December, showing a body which was at once less and more active than anticipated. Less surprisingly, it provided a resounding yes for the long-favored "dirty snowball" model of comets, although its data seemed to indicate that the proper description would be more "icy dirtball" instead, with relatively high levels of rocky compounds and materials detected. Despite several scars, Helios-Encke survived its passage, surprising some scientists who had expected intense dust fluxes to shatter the spacecraft, score its imaging systems into uselessness, or otherwise disable it. In fact, the spacecraft was in such good condition that there was no trouble approving the second flyby, and after occupying itself observing the Sun in conjunction with a growing fleet of Earth-orbiting spacecraft Helios-Encke had its second date with the comet in late March 1984. This time, Helios penetrated much deeper into the cometary coma, into regions where Encke was not so gentle. Buffeted by increasingly intense particle fluxes, Helios-Encke returned considerable amounts of data about how the comet had changed since its last perihelion before being blown away by dust grains too large and energetic for its particle shielding to block.
Thus, by 1985, European scientists had gained not just theoretical but actual practical knowledge of the dynamics of comet encounters and the conditions near cometary nuclei. Their Newton was, as a result, perhaps the proportionately best-equipped spacecraft of the entire flotilla, sporting thick protective armor against Halley's expected much more intense gas and dust jets, along with a suite of instruments based on those developed for Helios-Encke. Its parent, now named "Kirchhoff" after the wide-ranging 19th century German physicist responsible not only for the eponymous circuit laws but also for important research into solar radiation, was lifted into the heavens by a Saturn-Centaur in late July 1985, to the sounds of cheering later in the day as normal functioning of the crucial ion drive was confirmed. Four months later and just two weeks before meeting Halley, continuous thrusting had driven Kirchoff to the point where it could release Newton, before adjusting its course to pass well sunward of the energetically active comet. For now, Kirchhoff would only observe its cometary partner at a distance, waiting for the probe to close in and begin its survey. Two hours before closest encounter, a timer that had been counting down since Newton departed Earth finally reached zero, fully activating the scientific payload. Although several of the lower-power experiments had been intermittently collecting data since separation, and key systems such as the communications antennas beaming data to Kirchhoff and Earth had been checked out, most of the probe's systems had been powered down since launch, waiting for just this moment. As the probe streaked in towards the errant comet, it encountered an increasing storm of cometary gas and dust, sleeting against the multilayered shields intended to armor it against the sort of damage Helios-Encke had taken. All the while, it was furiously collecting and beaming back every possible scrap of data about its environment, detecting not only the rate and size of dust impacts, but also the composition of the gas and dust surrounding the probe and the electrical and magnetic behavior of that gas and dust. By far the most sophisticated instrument on board, however, was the camera, able to take stable and unblurred photographs of objects moving, like the comet's nucleus, at an astounding 60 kilometers per second--or 135,000 miles per hour--relative to the camera itself, with a resolution of several hundred meters[3]. As the probe streaked by just under 1000 kilometers from the comet's nucleus[4], this camera took a single complete high-resolution image of the nucleus, and part of a second, revealing details only a few hundred meters across. Much like Encke, this photo revealed a craggy and coal-black surface to the potato-shaped rock, with jets of gas and dust erupting from numerous locations, showing that even in their diversity comets are much alike and further supporting the theory of a common origin in the Kuiper Belt or Oort Cloud. As with Helios-Encke before it, however, Newton would not emerge intact from its cometary partner, as it encountered a particularly dense stream of cometary material just twenty minutes after closest approach, perhaps directly emanating from one of the jets seen on the nucleus. The frequency and size of impacts rapidly increased under the stream's influence before all telemetry abruptly cut off, probably the result of a particularly large and energetic fragment hitting the probe. Although it had not been given good odds to survive Halley, the premature destruction of the probe nevertheless saddened the team members who had spent years developing and building the little vehicle.
However dramatic Newton's flyby may have been, though, it was only the first member of the Halley Armada to reach the comet. By early March of the next year, the Japanese and Soviet members of the Halley armada were closing in on the comet. While the Japanese, undertaking their first deep-space mission, cautiously aimed their probes at a distant flyby, providing more prestige and engineering feedback than scientific value, the Soviets had ambitiously chosen to aim at a near flyby; not quite so near as Newton, but still close enough to pose significant risk to their Gallei probes. The first flashed by a few days after the Japanese probes made their closest approach, passing about 10,000 kilometers from the nucleus and showing (among other things) that the coma environment had changed significantly from Newton's encounter the previous year. A week later, Gallei 2, relying on updated navigational data from its sister probe dove into the coma, passing less than 5000 kilometers from the nucleus. Like Newton, it photographed the comet's core, showing that it had significantly changed from the earlier encounter. Although matching surface features was admittedly difficult, it appeared that many of the jets and vents previously detected by Newton were no longer active, and there was some evidence of other surface changes as well. Unlike Newton, however, Gallei managed to survive its encounter with Halley, successfully passing through the coma and beyond, back into interplanetary space. After three further weeks of increasingly distant observations, both Gallei probes were shut down to divert resources to preparations for the Mars 12/13 mission scheduled for 1988. Both Japanese probes continued to operate for several months, but although using gravity assists to divert one or the other to new targets was suggested, excessive propellant consumption and a feeling that the pair had limited scientific value led to them also being shut down by the end of the year. Only Kirchhoff remained, slowly adjusting its orbit farther and farther away from Earth's.
[1] This is to avoid scaring the fish. No, this is not a joke; OTL, until 2010 (!) launches from Tanegashima were restricted to only certain months of the year on behalf of the local fishing lobby. This constraint prevented Japan from launching its probes to the pre-perihelion opportunity OTL and forced them to use the post-perihelion opportunity[2]. Since Japanese politics have not significantly departed from OTL in TTL...
[2] An object which is moving in a highly elliptical and inclined orbit, like Halley, will offer two minimum-energy flyby opportunities during its close passage around its central body, one for each time it passes through the plane of the ecliptic. One will therefore proceed and the other follow periapsis (as can be seen if you picture the geometry and think about it a little). IOTL, all the flybys were conducted at the post-perihelion opportunity. The Japanese were constrained by politics, the Soviets by the position of Venus, and the Europeans by the presence of the Vegas (their data was used to refine the ephemerides used for Giotto's navigation), although the post-perihelion opportunity did require a slightly smaller delta-V than the pre-perihelion opportunity. Here, however, the geometry of the Tempel 2 rendezvous restricts the US flyby to the pre-perihelion opportunity, and with Newton clinging to Kirchoff that meant the Europeans must go along. The Japanese are restricted by the same politics, and the Soviets choose the later opportunity to avoid being compared to the Europeans and Americans as much as possible (European instruments or no). Plus, that allows some more interesting science than everyone going by simultaneously would.
[3] I actually mathematically worked out what this camera could do; it could resolve, accurately, the weapons mounted on an F-15E flying by at Mach 5 and an altitude of 9000 feet (well, obviously not an actual F-15E, but something the same rough size--the F-15E would appear to be about the size of Halley's Comet at 1000 kilometers). In fact, most US aircraft weapons are quite a bit larger than the resolution goal! The minimum size of viewed objects would be closer to a baseball or cricket bat, but strike aircraft don't typically carry those mounted on the outside.
[4] This is actually rather farther away from the nucleus than Giotto OTL managed; it benefited from the Vegas getting very nearby and transmitting updated ephemerides a few days earlier, as noted in [2]. ITTL, although capable Kirchhoff is never coming closer than 130,000 kilometers to Halley (the Vegas reached about 9000), and in any case releases the probe (which has no real method of correcting its trajectory) around two weeks before encounter, further limiting the possible accuracy. Nevertheless, this is towards the edge of the 3-sigma dispersion ellipse estimated at the start of the project, so it's still not a great performance.
Also, you may wonder whether the International Comet Probe (aka ISEE-3) exists ITTL. Well, as ISEE-3 it does, but as ICE...not so much. With a flagship-class comet mission coming down the line, even the relatively cheap ICE proposal would just be such an obvious waste of money that Farquhar would probably not even propose it in the first place.
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Also, in reviewing this post, I did see that due to a slight shuffling in post order earlier in the production process, Saturn-Centaur has ended up being used before being introduced. This is a Saturn 1C being used with a new third stage, the Centaur-E, an enlarged Centaur similar to the OTL Centaur-G which is developed specifically for use as an EDS for interplanetary missions launched on Saturn 1C. It'll also be available for Multibody and as an optional swap-out for Centaur-D on the SRB-assisted upper end of the Delta 4000 range.
So if I read it right. This means you've used the Saturn/Centaur before you released the post that covered it.
As for the comets. Interesting for ESA to finally score it's first with regards to space exploration, some 24 years after the first one that made Global News. Although given everything else that's happened, I'm not surprised it isn't so well known.
Can't say I know the comet probes that well though, even so, quite a few interesting details here. Especially in that the ESA Helios-Encke probe was the reason that the Titan IIIE managed to get a flight rate that entered double digits ITTL - if only just. But given that they don't have an equivalent capacity insofar as LV performance is concerned, that's going to remain the case for some years to come.
Nice to see Halley studied in some serious detail anyways.
As for the comets. Interesting for ESA to finally score it's first with regards to space exploration, some 24 years after the first one that made Global News. Although given everything else that's happened, I'm not surprised it isn't so well known.
Can't say I know the comet probes that well though, even so, quite a few interesting details here. Especially in that the ESA Helios-Encke probe was the reason that the Titan IIIE managed to get a flight rate that entered double digits ITTL - if only just. But given that they don't have an equivalent capacity insofar as LV performance is concerned, that's going to remain the case for some years to come.
Nice to see Halley studied in some serious detail anyways.
Yeah, truth is life finished the Galileo post before this one, and thus wrote the introduction of the Saturn-Centaur combination in the Galileo material instead of this comets update. However, when we sat down to put together the post list into an order for posting, Helios-Enke and Kirchhoff ended up fitting the outline better here, while Galileo got slotted in as Post 19.
the post #12 is so beautiful
but open question:
Is Helios-Encke equipped with a camera ?
do Soviet Gallei make fly by at venus and drop probes like VEGA mission ?
have Kirchhoff solar or nuclear power system ?
by the way
Tanegashima launch restriction, thanks to the local fishing lobby were no joke...
but open question:
Is Helios-Encke equipped with a camera ?
do Soviet Gallei make fly by at venus and drop probes like VEGA mission ?
have Kirchhoff solar or nuclear power system ?
by the way
Tanegashima launch restriction, thanks to the local fishing lobby were no joke...
i forgot to mention the name of OTL Japanese Halley probes
ISAS has the habit to use first project name, until successful launch. then rename them
MS-T5 became Sakigake (means Pioneer)
Planet-A became Suisei (means comet)
ISAS has the habit to use first project name, until successful launch. then rename them
MS-T5 became Sakigake (means Pioneer)
Planet-A became Suisei (means comet)
Yes. There was a similar proposal OTL (but the Germans couldn't get ESRO or US support). It would have had a camera.
No. You will see why
Solar-powered. Like Helios-Encke, this was an OTL proposal, although the names were different (unfortunately, I can't recall right now exactly what it was called). If you have Paolo Ulivi and David Harland's book, Volume 2, it's right near the beginning.
A fine and exciting post, dear authors e and truth!
When I was a kid in the mid-70s, with ambitions of becoming a scientist, I looked forward to 1986 as the year of the comet and being involved in the encounter missions. I miscalculated a bit as I'd still only be a junior, just starting my senior year toward the end of it, and I didn't understand then the timescale of the postgraduate ladder to PhD. Still if I were properly qualified to take advantage, the place I wound up misspending my first take at college years was uniquely well suited to a truly talented and driven and crafty young scientist or engineer on the make. Sadly that didn't truly describe me, and anyway the dang Shuttle blew up.
Basket, meet broken eggs.But I suppose this all has something to do with why this particular unmanned system exploration post has taken me by storm. Thanks!
Now it's time to give something back to the ETS community, after a couple years of whiny wishing and taking, I present--a relevant graphic image of my own creation!
You see...Indeed not. Nor does anyone's strike aircraft proceed at Mach 5, certainly not at a mere 9000 feet, that's well under 3 kilometers altitude!
At that altitude the FAA doesn't even require passenger planes to provide either pressurization or oxygen supplements; that rule kicks in at 10,000 feet/3 kilometers. The air 9000 feet up is pretty much as dense as at sea level, well, about 75 percent anyway.
Fortunately, for reasons that would make me look like even more of a doofus than I generally do here, I happen to possess a model of an F-16 that sort of halfway survived a major house fire. I present the Acme-modified Mach 5 F-16XS, test pilot one Lt. Col W. E. Coyote:
On behalf of truth and myself, I'm glad you enjoyed it. I think one of my favorite parts of being an author on this is that I get to read these probe posts as turth finishes them under the guise of "editing" and "continuity checks."
For those of you who enjoyed this post, it's worth noting that Kirchhoff's still got half it's mission ahead of it--it's only completed the "CF" part of CR/CF (Comet Rendezvous, Comet Flyby). It'll be back in about Post 24.Also, on that note, I feel like I should point out that the "I" in this bit is truth, not me, though I posted the final product. On this post, I merely bask in reflected glories.
truth is life said:
As for that plane...sheesh, Shevek. It looks nice enough, but that tail and wing layout gives me serious worries about the roll stability.
Hello gents,
More excellent work. Clearly, the road not taken was a much better one, in so many ways...
And having satiated my desire for info on the robotic programs (where we've gotten the most bang for our buck in either timeline since 1972), I'm keen to hear the next installments on Saturn Multibody/Centaur and Vulkan, and, of course, the details on the next generation space stations each side is preparing to loft...
It occurs to me just how lucky a break the Russians got from the U.S. inability to get its own station up and running before the collapse of the Soviet Union. With Freedom under advanced construction by 1991, there's no easy way to work in Mir II (or whatever they call it in this timeline) to the new U.S.-EU-Japan station. My guess: ROSCOSMOS tries to string out Mir as long as possible and tease European some cooperation to fill the funding shortfall, no easy task with Columbus already being integrated into Freedom, and a more robust ESA launcher and supply system coming into being. And when Plan A runs out, they're going to be left begging for a spot on Freedom, or an alliance with China. Neither an attractive possibility.
P.S. One thing that might be helpful would be a timeline of missions to date, if you all have the time to do it.
More excellent work. Clearly, the road not taken was a much better one, in so many ways...
And having satiated my desire for info on the robotic programs (where we've gotten the most bang for our buck in either timeline since 1972), I'm keen to hear the next installments on Saturn Multibody/Centaur and Vulkan, and, of course, the details on the next generation space stations each side is preparing to loft...
It occurs to me just how lucky a break the Russians got from the U.S. inability to get its own station up and running before the collapse of the Soviet Union. With Freedom under advanced construction by 1991, there's no easy way to work in Mir II (or whatever they call it in this timeline) to the new U.S.-EU-Japan station. My guess: ROSCOSMOS tries to string out Mir as long as possible and tease European some cooperation to fill the funding shortfall, no easy task with Columbus already being integrated into Freedom, and a more robust ESA launcher and supply system coming into being. And when Plan A runs out, they're going to be left begging for a spot on Freedom, or an alliance with China. Neither an attractive possibility.
P.S. One thing that might be helpful would be a timeline of missions to date, if you all have the time to do it.
Good point. IIRC, NASA began meeting the cost of supporting Mir IOTL in the mid-1990s. With the larger, and more capable Freedom ITTL, that's just not gonna happen. They won't want to lose it though, so I'd guess they try to find the money to keep it up and running, even at the cost of losing most of the rest of their programme - which all but happened IOTL.
But it is being called Mir here. What they have up now is a transitional station named Salyut 7.
Nice idea. Either here or on the Wiki page.
i found Data about original Helios-C
OTL they wanted to use the third probe for 1980 launch (backup and Test Model, today a Museum piece in Munich)
after some author, they even planned to build a new probe
but German Minister of research and technology, Hans Matthöfer was against the project,
Probable because Helios-C was not part of Helios A/B Join-Venture deal between USA and Germany.
this would make the Helios-C program very expensive for the Germans: around 559 million US dollar (2012 value)
OTL they wanted to use the third probe for 1980 launch (backup and Test Model, today a Museum piece in Munich)
after some author, they even planned to build a new probe
but German Minister of research and technology, Hans Matthöfer was against the project,
Probable because Helios-C was not part of Helios A/B Join-Venture deal between USA and Germany.
this would make the Helios-C program very expensive for the Germans: around 559 million US dollar (2012 value)
It's basically convergent with OTL through the mid '80s: Thanks to converted ballistic missiles, they've got the capability to launch their own (small) satellites and recover film and stuff from orbit, which is certainly "space-faring." However, they're not really in any position to send anything to Halley (or really anywhere other than LEO), and they're stalled on HSF and heavy lift (even on the 70s-era scale of "more than a few tons). We'll come back to them later in a whole post devoted to their program, and they'll become a bigger player as we move into Part III.