Space Studies Board Annual Report 1994 (1995) / Chapter Skim
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On the Space Infrared Telescope Facility and the Stratospheric Observatory for Infrared Astronomy
On the Space Infrared Telescope Facility and the Stratospheric Observatory for Infrared Astronomy
Pages 68-78
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From page 68... ...
REPORT OF THE TASK GROUP ON THE SPACE INFRARED TELESCOPE FACILITY AND THE STRATOSPHERIC OBSERVATORY FOR INFRARED ASTRONOMY I INTRODUCTION In the 1991 National Research Council report, The Decade of Discovery in Astronomy and Astrophysics, the Astronomy and Astrophysics Survey Committee characterized the 1990s as "the Decade of the Infrared." The Bahcall report (after the Committee Chair, John Bahcall)
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and the Stratospheric Observatory for Infrared Astronomy (SOFIA) missions remain responsive to the principal scientific objectives identified in the report The Decade of Discovery in Astronomy and Astrophysics (the Bahcall report)
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Liquid helium requirements are much lower because of the improved thermal environment in solar orbit, the significant improvements in telescope and instrument power dissipation, and a decrease in planned facility lifetime from 5 to 2.5 years. Moreover, the telescope will be launched warm, with a potential for cost savings not only in dewar design and fabrication but file:///C|/SSB_old_web/sirtfsofialtr.htm (3 of 12)
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D Scientific Instruments The redefined SIRTF scientific instrument payload incorporates 11 larger-format detector arrays (down from 19 in the previous concept)
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Cooled instrument volume 0.8 m3 0.2 m3 Cryogenic mechanisms 23 1 Number of detector arrays 19 11 Cryogenic instrument mass 200 kg 50 kg Cryogenic instrument 17 mW 10 mW heat dissipation Warm electronics (mass/volume/power) 97 kg/0.5 m3/150 W 75 kg/0.08 m3/75 W Fine guidance Internal External The simplification has been achieved through significant reduction in capabilities.
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TABLE 3 Changes in SIRTF Capabilities Improved SIRTF Capabilities Deleted SIRTF Capabilities Availability of Si:Sb arrays-improved quantum efficiency, larger format in the 20- to 40- m range Greater reliability through simplified hardware Solar orbit instead of high Earth orbit results in a. greater observing efficiency-shorter life b.
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From page 74... ...
However, the reduced data rate and shorter lifetime demand careful approaches to planning and executing the science program in order to maximize scientific productivity while assuring community involvement. The traditional "observatory" paradigm originally envisaged for SIRTF, in which scientific programs evolve as a wide spectrum of users learn and test the capabilities of the system, is no longer applicable.
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The relative astronomical capability is a figure of merit combining point-source sensitivity, array size, facility lifetime, and efficiency in the following relation: (facility lifetime) x (number of array pixels)
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It appears to the TGSS that the proposed Key Projects program is an excellent way of involving the whole astronomical community in SIRTF. This program and other mechanisms for promoting and coordinating participation by a broad user community are essential for maximizing scientific returns from a shorter mission.
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From page 77... ...
to a position between the wing and tail section, allowing important simplifications in the required aircraft modifications. An aft location requires construction of only one new pressure bulkhead, rather than two, and far fewer of the aircraft control systems have to be rerouted around the telescope cavity door.
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The TGSS concludes that SOFIA, with frequent flight opportunities for a broad range of state-of-the-art instrumentation programs, remains a uniquely powerful facility for science and continues the airborne program's role of developing technology for future space missions, for training experimentalists, and for educational outreach, as envisaged in the Bahcall report. 1The CAA is a joint activity of the National Research Council's Space Studies Board and the Board on Physics and Astronomy.
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