Solar System Exploration Subcommittee Findings and Reccommendations

Status Report From: NASA HQ
Posted: Monday, November 27, 2000

Office of the Head and Director
Department of Planetary Sciences
Lunar and Planetary Laboratory
University of Arizona
PO Box 210092
Tucson Arizona 85721-0092
Tel: (520) 621-6962
Fax: (520) 626-6647

November 27, 2000

Dr. Jay Bergstralh
Code S
NASA Headquarters
Washington, D.C. 20546

Dear Jay:

The Solar System Exploration Subcommittee (SSES) of the Space Science Advisory Committee (SScAC) met on October 30 and 31, 2000 in Pasadena, California. The purpose of this letter is to summarize the findings and recommendations of that meeting.

Mars Exploration

The SSES received reports from Scott Hubbard, Jim Garvin, and Farouz Naderi. It is clear to the SSES that NASA has put its "A Team" in charge of the Mars Exploration Program, and overwhelmingly endorses the missions set laboriously constructed after consultations with a wide range of constituencies. Given budget constraints, the team has done an excellent job. A minority view felt the plan was "timid" in that it did not obviously engage enough public support and may be inconsistent with a possible future decision to send humans to Mars in the next decade.

Antarctic Meteorites

The SSES noted that one way to increase access to Martian samples for fairly low cost is to increase the recovery rate of Martian Meteorites. Currently, Martian Meteorites from Antarctica account for approximately 1 in 2000 Antarctic meteorite specimens, or a recovery rate of about 1 every 4 years. For an investment of ~$400K - $450K per year (or 0.02% of the currently projected cost of a Mars sample return mission), predominantly for field logistics and curation support, the rate of Antarctic meteorite recovery could be approximately doubled. This would be accomplished by putting a second field team on the ice each season, either in a reconnaissance mode (investigating new regions to assess their suitability for future collecting seasons) or collecting mode (systematic searching for meteorites in one or more areas). The consensus of the SSES is that this moderate investment from the Mars Program budget could go a long waay to preparing us to handle and analyze returned Martian samples, but should not be construed as a substitute for returning a scientifically selected suite of samples from Mars in the near future. The SSES recommends that investment in increasing the recovery rate of Martian meteorites be made.

Outer Planets

The highest priority outer planet missions, Pluto-Kuiper Express (PKE) and Europa Orbiter (EO), have received strong endorsements in previous considerations by COMPLEX and SSES. Recent developments in our understanding of the solar system have strengthened the case for both of these missions as a compelling and essential part of NASA's planetary program. This is documented below. There is no compelling scientific basis for a program that places EO ahead of PKE in importance. An orderly and timely program that accomplishes these missions takes advantage of the 2004 launch opportunity for PKE. The likely delay in EO that is implied by this choice is unfortunate but vastly preferable to the alternative of a long delay and possible associated degraded science of PKE. Given the difficulty in solving EO engineering problems before 2006 at the earliest, it is logical to consider flying PKE first. EO would still return data first.

PKE is a pioneering mission. It takes us to examples of an important and little understood class of bodies, the small icy objects that populate the Kuiper Belt. In our developing understanding of these bodies, we have come to recognize that they are essential to our understanding of how planets form and what materials go into habitable planets, including Earth. The giant planets define the architecture of our solar system, define the inner edge of the Kuiper belt, and probably determined the delivery of much of the most volatile materials including water to planet Earth. In the Kuiper belt bodies, the largest known example of which is the planet Pluto, we have repositories of volatile and organic matter and information on the mass and distribution of materials dating back to solar system origin. We need to learn about compositions, and about the population of bodies expressed through impact cratering of the surfaces of these bodies. These goals are central aspects of NASA's Origins Program.

We must go there. The information needed is mostly unobtainable from telescopic observations, even allowing for future improvements. Though small, Pluto has an atmosphere and is expected to have internal dynamic processes. The Pluto-Charon binary planet system has no other solar system analog in its tidal evolution except possibly Earth and our companion the Moon. The images from the Pluto encounter, collected over an extended period, are likely to fascinate the public. From our perspective close in to the Sun, this is a mission to the frontier of the solar system, an appealing aspect to both scientists and the public.

The scientific justification for EO remains strong. Galileo results have strengthened the case for a water ocean but have led to no consensus about ice thickness or the conditions beneath the thin, outermost brittle layer of very cold ice. A well-instrumented EO should be designed to answer with certainty the issue of whether there is an ocean and identify some aspects of the nature of this subsurface environment that might support life. An orderly approach to Europa exploration calls for an orbiter before a lander. However, there is no aspect of our developing view of Europa that would compel us to place its importance above that of the science addressed by PKE.

The SSES received a presentation from Lockheed-Martin which suggested that different PKE concepts could possibly achieve scientific objectives at lower cost than the current PKE baseline mission.

The consensus of the SSES is that JPL should be given until approximately the end of November 2000 to formulate a plan that achieves Europa Orbiter and Pluto-Kuiper Express within the current budget. If they are unable to come up with a solution PKE and, possibly, Europa Orbiter should be put out for competitive bidding through an appropriate process.

If such a plan is followed and JPL is unable to come with a viable plan, the recommended boundary conditions are:

c. NASA announce selections of the PKE and EO science payloads by January 2001 from those that have been proposed in response to the September 10, 1999 AO (AO-99-OSS-04).
d. AO solicitation be issued by NASA on or before 1/15/01, requesting proposals that include the totality of the OP program, a la Discovery, and accommodate the NASA-selected science payloads. Responses should be requested by 4/15, with intended NASA selection by 6/1/01.
e. Simultaneously with the issuance of the AO, NASA should proceed to begin manufacture of an appropriately-sized RTG (e.g. RTG9), with currently existing hardware. Also, NASA should initiate processes for regulatory approval of a PKE launch no earlier than December 2004.

The above recommendations will accomplish a number of Outer Planets science and programmatic objectives. These include: timely launch of a PKE mission to take advantage of the unprecedented opportunity in the 2004 launch window, within a possibly affordable budget; continued development of EO technology for a launch in the 2005-2010 timeframe that will result in returned science data from Europa long before the PKE flyby of the Pluto-Charon system; and likely implementation of the program within NASA budgetary guidelines, with appropriate adjustments.

Attached Payloads

The SSES considered the problem of the suborbital/attached payloads program that has found itself fitted within the Planetary Atmospheres program as an unfunded mandate. For FY00 that amount is $300K out of the $8M Planetary Atmospheres budget. It was widely agreed that level of funding is far below any reasonable support level for the program and that the mandate must necessarily grow to 450K in FY01 and 600K in FY02. The consensus of the SSES is that if that program support remains within Planetary Atmospheres, it should continue to be separated by a firewall from the rest of Planetary Atmospheres. The two programs are distinctly different in terms of their average grant size (about a factor of two) and in their objectives (basic investigator science vs. flight missions, technology development, space hardware training). The SSES sees as the most important objective to find a natural home for the planetary suborbital/attached payloads program, perhaps as a new, free standing Research and Analysis Program for suborbital/attached payloads that cuts across themes. This would allow SSE proposals to compete more directly with their naturally complementary counterparts from other themes. The financial support at the current or projected level from the SSE suborbital grants would be contributed to this program. This kind of cross-theme program is not unprecedented. Such a program currently exists in the Flight Information Systems area. The SSES recommends that the SScAC review the suborbital/attached payloads issue to advise on the possibility of creating a cross-theme program. The availability of the Space Shuttle and the International Space Station should not be overlooked by the Solar System Exploration Program.


The failure to account adequately for the Doppler shift between Cassini and the Huygens probe was discussed. It appears that there are solutions related to mission operations that can compensate for this oversight. The SSES recommends that any solution maximizes overall mission science return, even if it involves delaying deployment of the Huygens probe.

Deep Space Network (DSN)

The SSES received a briefing which points to a significant overload of DSN capabilities in 2004 and beyond, but that measures are being followed to mitigate this problem. The Solar System Exploration Division should nevertheless remain concerned that an adequate solution is achieved.

Planetary Data System (PDS)

It appears the PDS is underfunded by about $2M per year. The Solar System Exploration Program needs to address this issue.


MUSES-CN is a Japanese mission to an asteroid to carry out in situ science and return samples to Earth. The SSES concurs in NASA's decision to terminate its involvement in the rover program. It is critical, however, that NASA assures access to samples for U.S. scientists.

With kindest regards.


Michael J. Drake, Chair
Solar System Exploration Subcommittee

c. Dr. Jay Bergstralh, Director, Solar System Exploration
Dr. Scott Hubbard, Mars Program Office
Dr. Ed Weiler, Associate Administrator for Space Science
Dr. Steve Squyres, Chair, Space Science Advisory Committee
Solar System Exploration Subcommittee

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