A proposed mission to Pluto, recently endorsed by an independent scientific panel, will undergo a key test this week in its effort to obtain funding for the project.

An artist's concept of the New Horizons spacecraft. Photo: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

A subcommittee of the US Senate's Appropriations Committee is scheduled to meet this week to "mark up", or revise and approve, the proposed 2003 budget for NASA. Among the key issues in the proposed budget is whether to add or transfer funding for a Pluto mission NASA did not provide any money for in its proposal.

New Horizons, a proposed Pluto mission selected by NASA last year, requires $122 million in the fiscal year 2003 budget in order to continue work and meet a 2006 launch deadline. However, NASA added no funding for the mission in its proposed budget, released earlier this year, electing instead to fund advanced propulsion technologies that agency officials said could allow for faster, more efficient exploration of Pluto and the outer solar system in the future.

However, there have been efforts to persuade Congress to add funding to the budget for a Pluto mission. Such a move would not be unprecedented: last year Congress added $30 million to NASA's 2002 budget for a Pluto mission, after NASA cancelled the previous Pluto-Kuiper Belt mission and attempted to stop a request for proposals for a new Pluto mission. One of the leaders of that effort was Sen. Barbara Mikulski, who is chairperson of the Senate Appropriations Committee subcommittee that handles NASA's budget. Mikulski has spoken out in favor of a Pluto mission on several occasions; moreover, the Johns Hopkins University Applied Physics Laboratory, where the New Horizons spacecraft would be built, is located in Mikulski's home state of Maryland.

This week's Senate hearing comes less than two weeks after the release of a report by the National Research Council that prioritized planetary science spacecraft missions for the next decade. That report ranked a mission to Pluto and the Kuiper Belt as the highest priority among medium-sized missions, with total mission costs less than $650 million. The report also concluded that such a mission would have "clear advantages" over the highest-ranked high-cost mission, a Europa orbiter, in terms of technology.

A mission to Pluto also has a great degree of interest among the general public, based on reactions after past attempts to cancel such missions. PlutoMission.com, a web site established in 2000 by then-high school student Ted Nichols II, got thousands of people to sign a petition asking NASA and Congress to support a Pluto mission. In June Nichols sent a hard copy version of the petition - in the form of three books, each with over 500 pages - to NASA Administrator Sean O'Keefe, President George W. Bush, and Senator Mikulski.

The Planetary Society has also been asking its members to contact Congress and ask them to support funding for both the New Horizons Pluto mission as well as a Europa orbiter. "The Pluto/Kuiper Belt mission is especially urgent," wrote Planetary Society president Wesley Huntress, a former associate administrator of NASA, in a letter to Congress. "If NASA misses the 2006 launch opportunity that enables a gravitational boost from Jupiter, then the encounter with Pluto and multiple Kuiper Belt objects will be delayed at least a decade. If there are any delays to its development, the 2006 launch will not be possible."

However, planetary scientists are not willing to fund a Pluto mission at all costs. A statement released Sunday by the Division for Planetary Sciences (DPS) of the American Astronomical Society cautioned Congress not to take money from other space science programs in order to fund a Pluto mission. "Any [budget] augmentation less than this amount [$122 million], coupled with the need to meet a 2006 launch date, would require sacrificing other important NASA programs," the DPS statement noted. "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."

The statement noted that one of the claims of Pluto mission proponents - that the planet's tenuous atmosphere might freeze out if a mission is delayed - may not be true, based on some atmospheric models. However, it is still important to get there in the near future as the planet's high orbital tilt is putting an increasing fraction of the planet's surface in perpetual shadow: from 7% of the surface now up to a peak of 23% in 2029.

In an ironic twist, the DPS statement noted that either chemical or electric propulsion systems, like the one used on Deep Space One, could make up for missing a Jupiter flyby if the mission is launched after 2006. "A statement this week that missing the 2006 launch window will result in a delay of 'at least a decade' overlooks these known opportunities," the statement noted. The statement was signed by several key officers of the DPS, including its chair, Wesley Huntress, the same person who signed the Planetary Society letter that made that claim last week.