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.
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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)