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The Webfooted Astronomer - January 2002
ISS-AT, the Amateur’s Dream Telescope Come True
By Greg Donohue
JUDY Schroeder received her Astronomical League Messier certificate at the beginning of the meeting. Congratulations, Judy!
Our guest speaker for December was Mac Gardiner, retired Boeing employee and president of the Battlepoint Astronomical Association (BPAA). He presented information about the International Space Station Amateur Telescope (ISS-AT) program. Mac is well qualified to speak on the subject; after all, he is the one who came up with the idea in the first place (though he is the modest type, and never mentioned this little fact).
The ISS-AT is just one of four on-going programs at the BPAA. They have just finished a very lightweight 16-inch telescope. Their student-mentoring program currently has students age 11-14 working with robotic Sumo wrestlers. And the association is developing a novel program that uses a fisheye lens to convert a LCD projector into a planetarium projector.
Mac immediately set our minds at ease about whether the ISS-AT was a solid, established program. According to him, “The program is mature. You can always tell that because we have a logo!” The Astronomical League has primary responsibility for developing the ISS-AT, which is currently their dominant project. They take care of the ground operations portion of the ISS-AT project, including funding, staffing, and operating it.
Current plans have the ISS-AT arriving at the Space Station in 2006 aboard an express pallet delivered by the Space Shuttle. The telescope must fit on this pallet, and weigh no more than about 250 kilograms (550 pounds)-on the ground, that is.
The ISS has been in orbit and staffed for about a year and a half. Construction is ongoing, with one of the six planned labs complete. The station is in low earth obit, at a latitude accessible from both Cape Canaveral and the Baikonur Cosmodrome. Though the original plan called for a crew of seven, reviews of consistent and significant cost-overruns may reduce that to as low as three. Even if the full complement of crew is present, the station is a mammoth undertaking for its inhabitants, so almost anything associated with the ISS must be as automatic and autonomous as possible. This means the ISS-AT must be run entirely from the ground, with no intervention by station personnel whatsoever. If you need any of the astronauts’ time, you have to budget it at about $200,000 per person-hour. Many other constraints must be considered in developing a plan for the Amateur Telescope. It must be located along one of the four station trusses. But not only does the station spin about its axis and orbit around the Earth, many of the other parts of the space station move - the solar power panels, for instance. Therefore, one must pick the location carefully to make sure that the telescope's view is not blocked for significant periods of time.
The telescope will be in direct sunlight 50% of the time, and then will abruptly plunge into nearly total darkness for the other 50%. Power (110kW total, 46kW average for research) is also at a premium on the station, with none available for cooling, so the telescope’s temperature must be maintained by non-powered means. An external baffle and sunshade will be employed to maintain the system at its optimum operating temperature of -80 degrees Centigrade (for the CCD cameras).
Vibration from the Station and its components is another challenge for operating a telescope on the ISS. A piezzo-electric panel that senses and counters the vibrations is one way of dealing with this problem. Or the telescope assembly might be attached to the truss by an electromagnetic clamp. It could then be physically disconnected from the station and float free while imaging an object, then reattached when the exposure was complete. Studies of the Station’s mechanical dynamics show that the telescope would need to be about one-tenth of an inch away from the truss to be completely decoupled from the ISS’s normal vibrations. Of course, you might want some sort of tethers for this electromagnetic clamp scenario, just in case.
Since the ISS rotates around its own axis, mounting the telescope in a simple alt-azimuth arrangement results in an equatorial configuration. In this case, the “equator” is not the Earth’s but rather the Station’s. This greatly simplifies the telescope design. The ISS goes around in 90 minutes, and has its own “North Pole.” Also, whereas the Earth’s axis precesses once in 26,000 years, the Space Station’s axis completes its own wobble in about 5 hours.
The ISS-AT will have a 16-inch (about 400mm) aperture, with an 800-inch focal length, f/1.6 system. A rotating mirror would redirect light to four different CCD cameras. The CCDs have a 3000-by-2000 array of 9um pixels. The full field of the planetary camera will be twice the apparent size of Jupiter. It also includes a spectrograph, high-speed photometer, and 3-star guidance system.
The ISS-AT is dedicated for use by amateur astronomers (individuals or groups), and by legitimate astronomical associations. Almost anyone can submit a proposal for telescope time. Those proposed observing programs that require the ISS-AT’s unique capabilities (above the atmosphere, in completely dark skies, with all of the cosmos visible all of the time) have the best chance of being selected.
The observing time will be divided among three programs: a background program of synoptic planetary imaging and imaging of selected deep-sky objects; a foreground program of amateur observing projects (selected by the Astronomical League); and a rapid-response program to acquire images of noteworthy astronomical events (supernovae, gamma ray bursts, comets, planetary events, and other unexpected happenings). All observations will be available on the Internet within 24 hours.
As part of the ISS-AT support system run by the Astronomical League, a series of six ground-based telescopes (½ meter in size) will be built to operate autonomously through the Internet. One such facility is already underway. These ground-based telescopes will be used for those amateur observing requests that do not necessarily require the unique characteristics of the orbiting ISS-AT itself. And the League will also build and operate a single ground-based clone of the ISS-AT, which will be used for troubleshooting and testing of potential system changes/upgrades. For those who would like more information, have an idea for the ISS-AT, or would like to volunteer to help with the project, here are some contacts and sources of information:ISS-AT:
Web site: www.issat.org
Project Coordinator: Orville Brettman
Phone: (815) 923-2419
Mac Gardiner : E-mail:firstname.lastname@example.org
Phone: (206) 842-3717
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