The Division for Planetary Sciences of the American Astronomical Society endorses the top priority of a Kuiper Belt Object/Pluto mission in the medium-cost New Frontier mission category, given in the recently released NRC planetary decadal report. The report states that the recently selected New Horizons flyby mission to Pluto satisfies this objective. New Horizons as presently configured uses a Jupiter gravity assist with a launch in 2006 (flyby in 2015/16). Because no funds for a Pluto mission were in the President's 2003 budget request, Congress must augment the NASA budget by $122 million over the President's budget request if that launch date is to be met by the New Horizons mission.
The DPS supports this augmentation. However, any augmentation less than this amount, coupled with the need to meet a 2006 launch date, would require sacrificing other important NASA programs. If the full augmentation is not forthcoming, the DPS strongly urges Congress to relax any specific launch date requirement and give NASA the flexibility to evaluate and choose a development profile and launch date that allows the scientific goals articulated by the decadal study for a KBO/Pluto mission to be realized while preserving other Space Science programs.
Significant effort and money has been invested in the detailed development of a successful Pluto mission, the recent history of which has been marked by controversy and political intervention. Originally a JPL program, it was cancelled in 2000 because of cost overruns. This caused an outcry by supporters in the planetary community and public. Following the model of its successful Discovery program, NASA announced a competition for a Pluto-Kuiper Belt mission that was to be cost-capped at $500 million. Before proposals were due, however, the program was cancelled by the Bush administration. This caused members of Congress to request that NASA proceeds with the initial selection of proposals for technical study, so that Congress could address the issue of the mission in its FY02 budget. Congress subsequently directed NASA to make a final mission selection and appropriated $30 million for its conceptual development phase in FY02. No funds were requested by the Bush administration for the Pluto mission in FY03, with predictable political consequences.
The Pluto mission is timely and possesses no strict deadlines to be of value. It has been suggested in the popular press that a launch in 2006 (or 2007) is our last opportunity in 200 years to visit Pluto before its tenuous atmosphere freezes out as it marches away from the Sun. This is not accurate on two counts. First, future launch opportunities are available using both chemical systems and solar electric propulsion (demonstrated successfully on Deep Space 1), many not requiring a Jupiter gravity assist. A statement this week that missing the 2006 launch window will result in a delay of "at least a decade" overlooks these known opportunities. Second, a recent scientific paper on the subject ("Emissivity and the Fate of Pluto's Atmosphere" by J. Stansberry and R. Yelle, Icarus 41, 299-306, 1999), suggests that Pluto's atmosphere never freezes out. This is but one of many important scientific issues that will be resolved in the course of the mission.
A more demonstrable concern than Pluto's atmosphere is the fact that Pluto's extreme tilt results in an increasingly large fraction of its surface moving into shadow as the Sun climbs to higher latitudes (just like the polar regions on the Earth that are in complete darkness during Winter). Today, 7% of Pluto's surface is always in shadow as it rotates. In subsequent years that fraction grows to 18% (2015), 21% (2020), and a maximum of 23% (2029). Later launches mean later flyby dates and a decrease in the visible fraction of Pluto's (and its moon, Charon's) surface.
Some of these later trajectories also result in higher flyby speeds. This means that there is less time to collect scientific measurements and closeup imagery of Pluto's surface is more difficult to obtain. Perhaps just as important, the inclination of Pluto is rapidly increasing, making it ever more difficult to target other Kuiper Belt objects after the Pluto flyby. In short, the science return is potentially degraded as the arrival date at Pluto is delayed.
Therefore, the DPS endorses the efforts to fully augment the NASA budget in FY03 to allow for a 2006 launch of the New Horizons Pluto/Kuiper Belt mission. However, should a less than full augmentation be enacted, we consider it critical that Congress places no launch date requirement on the mission and allow NASA to determine the funding profile that allows for the soonest practical launch date and the realization of the decadal survey science goals within the resources appropriated.
The DPS is the world's largest professional organization dedicated to the exploration of the Solar System.
Dr. Wesley T. Huntress, Jr.
Dr. Richard P. Binzel
Dr. Mark V. Sykes
DPS Past Chair