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OCR for page 79
On the Advanced X-ray Astrophysics Facility and Cassini Saturn Probe
On the Advanced X-ray Astrophysics
Facility and Cassini Saturn Probe
On July 5, 1994, Space Studies Board Chair Claude R. Canizares and
Board Past-Chair Louis J. Lanzerotti sent the following letter to Presidential
Science Advisor John Gibbons.
Recent developments in outlay allocations to NASA's Senate
appropriations subcommittee are threatening the necessity for very difficult
choices in the FY95 budget. As you know, many of NASA's science missions
have been closely scrutinized for savings over the past few years. In particular,
the two largest space science mission development programs, the Cassini Saturn
probe and the Advanced X-ray Astrophysics Facility (AXAF), have been
subjected by NASA to budget-driven rescopings. Each of these missions has
been accorded the highest priority in its respective discipline.1 On completion of
these rescopings, which significantly reduced total program cost in each case,
the National Research Council (NRC) Space Studies Board was asked to
conduct scientific reviews to determine if the resulting missions remained
scientifically responsive to the opportunities presented by our current state of
knowledge. Copies of the final reports on these two assessment studies are
enclosed, but we would like to summarize their findings briefly here.
With respect to Cassini, on October 19, 1992, the Board's Committee on
Planetary and Lunar Exploration (COMPLEX) stated that:
Although the Cassini spacecraft has undergone considerable revision, it is
COMPLEX's overall opinion that the restructured Cassini mission remains
responsive to the scientific priorities set out in its report, A Strategy for
Exploration of the Outer Planets: 1986-1996. Significant though these changes
are with respect to legitimate individual science objectives, the recommended
modifications do not substantially compromise the primary mission objectives,
which include the intensive study of the saturnian system as a whole.
We also note the significant investment of the European Space Agency in the
Huygens Titan probe, which will perform a pioneering first characterization of
Titan's atmosphere and surface.
With respect to AXAF, the Board created a task group to evaluate the
quality of the program that resulted from AXAF's division into two spacecraft,
AXAF-I (imaging), and AXAF-S (spectroscopy). This task group reported its
findings, with the endorsement of the NRC's Committee on Astronomy and
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OCR for page 80
On the Advanced X-ray Astrophysics Facility and Cassini Saturn Probe
Astrophysics, on April 28, 1993, as follows:
The Task Group on AXAF [TGA] concludes that the revised AXAF program
continues to meet the scientific expectations set forth in previous NRC reports,
which have recommended AXAF as the highest-priority, new, large-scale
program in astronomy. . . . Thus the TGA urges NASA to proceed with the
implementation of the restructured AXAF program and to make every effort to
ensure the launch of both AXAF-I and AXAF-S before the end of this decade.
The subsequent cancellation of the AXAF-S mission, while dismaying, did not impair the scientific
promise of the imaging mission, whose "angular resolution . . . is more than an order of
magnitude better than that offered by any other mission under development or even in the
planning stages."
The enclosed letter reports on the two missions provide the scientific and technical
background that elaborates and substantiates these program reassessments. We realize that
science missions must be balanced within the overall objectives of NASA and priorities of the
federal R&D budget, but cancellation of either AXAF or Cassini would be a serious reverse for
NASA's program of exploration of the solar system and the universe beyond. Please contact us if
you have any further questions about these missions or their importance to U.S. science.
NOTES
1For Cassini, see A Strategy for Exploration of the Outer Planets: 1986-1996 (National Academy
Press (NAP), Washington, D.C., 1986), page 5; for AXAF, see Astronomy and Astrophysics for
the 1980s, Volume 1 (NAP, 1982), page 15; for AXAF, see also The Decade of Discovery in
Astronomy and Astrophysics (NAP, 1991), page 65.
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