After NASA announced its cancellation last summer because of cost overruns, a campaign by the scientific community (including a forceful recommendation by NASA's own advisory Solar System Exploration Subcommittee) and the general public led to NASA's tentative revival of the Pluto mission in a new form.

Rather than assigning the Jet Propulsion Laboratory the job of designing the probe using new, expensive and potentially unnecessary advanced technologies, NASA in December issued an Announcement of Opportunity similar to those issued for its Discovery Program of inner Solar System missions.

NASA invited individual teams of scientists and engineers to propose their own designs for the mission, which would be limited to a total mission cost of $500 million, and would then be appraised by a review board to see whether any of them looked feasible.

No sooner did this happen, however, than the Bush Administration entered office and responded to the steadily growing cost overruns of the International Space Station by placing a limit on NASA's overall spending levels.

Adding further pressure to funding exploration of the outer planets was the decision to boost funding to the Mars exploration program, and cover any cost overruns in other space science areas, by dumping the Pluto mission and deferring the proposed Solar Probe to the next decade.

NASA therefore announced cancellation of the process for collecting Pluto mission proposals.

Within two days of this, however, the House and Senate Appropriations Committees responded in turn to this by issuing statements forcefully criticizing the Administration for inadequate spending in space science as a whole, and ordering NASA to continue collecting and appraising Pluto proposals until Congress itself ordered it to stop -- and so the collection process was on again.

Since then, in early April, Congress has made another important move: both the House and the Senate, in their budget resolutions, favored adding a considerable amount to Bush's budget for America's "General Science, Space and Technology" outlays in Fiscal Year 2002 -- which includes all the funding of NASA, the National Science Foundation, and the Department of Energy's science programs.

The House favored adding $883 million, while the Senate favored adding fully $1.481 billion.

This has not yet been divvied up among individual programs -- but, while there is great uncertainty as to just how much Congress will end up increasing NASA's FY 2002 Space Science budget, it suggests that it will be increased by somewhere between $80 million and $150 million.

This may allow correction of several smaller problems in NASA's new Space Science budget.

For example, it may mean correction of the recent one-year delay in the flight of the next Discovery mission to be selected (which, given planetary launch windows, would actually have delayed two of the three finalists -- a low-cost Jupiter orbiter and a mission to survey the main asteroid belt in detail -- from 2005 to 2007).

And it would also greatly increase the odds that the $1 million dollars or so needed to allow the Galileo probe to photograph Io during its last flyby of that volcanic world in January 2002 would be available.

But the main impact of that new money is on the Pluto-Kuiper probe, which will suddenly come alive again as a serious possibility if most of the added Space Science money goes to it -- especially if Congress can be persuaded to add a modest additional amount to Space Science funding.

The April 6 deadline for presenting mission proposals has now passed, and five of them have been officially offered.

From several sources, TerraDaily has learned that one of these proposals involves an effort by JPL and Lockheed Martin to redesign a copy of the "Stardust" comet dust sample-return mission to fly by Pluto.

Another -- also involving the reworking of an existing spacecraft design -- connects the Southwest Research Institute (always intensely interested in Pluto) and the Johns Hopkins Applied Physics Laboratory, which has just completed the highly successful "NEAR" mission to the asteroid Eros and is already working on a low-cost mission to orbit Mercury in 2004 (which APL director Stamatios Krimigis describes as being considerably harder than a Pluto flyby).

A third may involve collaboration between JPL and the TRW company, while another is rumored to involve Malin Space Science Systems (which has built most of the main cameras carried on America's recent Mars probes), and the fifth -- surprisingly -- involves a proposal by Russia's IKI space science agency, the first Russian proposal ever for a probe to the outer Solar System.

SpaceDaily's sources also say that several of these proposals look genuinely promising.

Most of them -- like the Lockheed Martin proposal -- involve low-cost reworking of various existing spacecraft designs (as this writer also proposed last summer).

They don't require the development of any radical new technology -- which was the problem with JPL's original Pluto-Kuiper Express proposal -- but they are lightweight enough to be launched on the coming new generation of moderately powerful boosters such as Delta 4 and Atlas 5.

Indeed, some of them may be lightweight enough to be launched on the Atlas 3, which has already completed a totally successful first flight.

On top of this, they seem to use these developed technologies in ways ingenious enough that their science payloads may be somewhat bigger than originally thought.

The minimum science package for the Pluto-Kuiper mission involves a camera for closeup photos of Pluto and somewhat more distant views of its big moon Charon, a mapping near-IR spectrometer to analyze the different ices covering their surfaces, and a UV spectrometer that would analyze Pluto's faint but very interesting atmosphere and look for any around Charon.

At least three miniature integrated camera-spectrometer packages have already been designed that could make all these studies with a total instrument weight of only about 10 kg.

But it's possible that the Pluto probe could also make some of the lower-priority "Category 2 and 3" studies -- such as using a mass spectrometer to analyze Pluto's atmosphere in more detail, or using fields and particles sensors to look for any Plutonian magnetic field and map the precise way in which the solar wind streaming past Pluto sweeps some of that thin atmosphere away with it (a process which affected all the planets during the Solar System's earliest days -- especially Mars -- but is now unique to Pluto).

It should also be kept in mind that such a probe would study other targets besides Pluto and Charon.

It would try to continue its mission after Pluto to fly by at least one -- and, with luck, two -- of the smaller Kuiper Belt objects which have turned out to make up an entirely new major section of the Solar System that contains important hints about conditions when the planets were first formed.

And the probe would probably reach Pluto by making a gravity-assist flyby of Jupiter, at a distance that might allow it to make an optional close flyby of Europa to further photograph and map the surface composition of that world.

It might even be able to add a flyby of a small asteroid.

However, the probe's fate still hangs by a thread.

The review board is scheduled to pick one or two finalists on June 1 for $450,000 worth of further studies, with possible final selection of a mission proposal in August.

But there may be a delay of up to a month in that initial winnowing process, and it's quite possible that NASA will end up declaring that no proposal was promising enough to be worthwhile.

There is also a scientific deadline ticking away that is unique to this mission.

Pluto is slowly moving further away from the Sun in its lopsided orbit, which makes it probable (though not certain) that its thin but scientifically important atmosphere will freeze out on its surface by 2020.

And if a probe cannot be launched in December 2004 to take advantage of that Jupiter flyby opportunity, the mission will at once become longer, more expensive and less likely to arrive before the freezeout.

A less efficient Jupiter flyby is possible for a January 2006 launch -- but such a probe wouldn't arrive at Pluto until 2020.

And while the Bush Administration has added $300 million to NASA's budget to study ion drives and other deep-space propulsion techniques that might allow a Pluto probe to be launched directly from Earth to Pluto later while bypassing Jupiter, such a mission would be much more expensive and, even at its best, would take still longer to reach Pluto.

While both scientific and general-public interest in the possibility of life on other worlds remains very strong, there is an increasing feeling -- both among scientists and members of Congress -- that America's current space science budget may be seriously over tilted in that direction.

As it currently stands, the Solar System exploration program consists almost entirely of missions to Mars and one very expensive outer Solar System mission -- the Europa Orbiter -- which is undeniably important but is also difficult and growing steadily in cost.

These two worlds are currently eating up all the rest of the Solar System exploration program, as witness that one or two-year delay even in the inexpensive Discovery missions.

The Pluto-Kuiper probe has several things to recommend it.

It is almost unique among space science missions in its inability to tolerate delay without a genuine and permanent loss in its science output -- Pluto's atmosphere won't thaw out again for 120 years!

Moreover, if NASA can identify a viable mission design among the current proposals, it will represent a whole new forward step in Solar System missions -- the extension to outer Solar System missions of the highly successful philosophy behind the Discovery inner Solar System missions, which so far has done an excellent job of sharply lowering mission cost-effectiveness by pitting competitive teams against each other, rather than allowing one agency (such as JPL) to have a complete monopoly of the program and thus risk becoming inefficient and lazy.

Finally, any spacecraft design usable for this mission can be very easily adapted to a wide variety of other outer Solar System missions.

Not only could it be used with virtually no changes for flyby missions to other small outer Solar System objects such as Chiron, but -- with minimal changes -- it could also be used for follow-up flyby missions to Uranus and Neptune, two giant, important and complex planets which run the risk of being neglected in future space exploration.

There is interest in flying full fledged orbiter missions to both worlds, but these are projects for the fairly distant future -- in order to cut their costs far down below the now unacceptably high levels of Galileo and Cassini, they will have to make use of future weight-cutting technologies which are nowhere near flight ready.

But the Pluto flyby bus, with very few changes, could not only make flybys of Uranus and Neptune with new instruments, but also carry an entry probe to parachute down through the atmosphere of either world as the Galileo probe did at Jupiter, thus studying an entirely distinct type of middle-sized planet while using a heat shield no heavier than that needed for a probe entering the atmospheres of Venus or Earth.

Uranus, in particular, is another of those rare cases of a scientific space target that doesn't tolerate delays very well, because it's "tilted on its side", as are the orbits of its moons.

When Voyager 2 flew by it in 1986, it had one pole pointed toward the Sun -- but if a probe could be launched to it later this decade using a Jupiter gravity-assist, it could fly by Uranus at a time when the planet is presenting its side to the Sun, producing both radically different weather and magnetospheric phenomena but also allowing at least distant photography of both sides of Uranus' moons rather than just one illuminated hemisphere of them.

And Uranus won't move into position for another opportunity to do this for 42 years afterwards.

Such a mission, combined with a Uranus entry probe, might be another example of the usefulness for outer Solar System exploration of the same competitive and extremely flexible mission selection process used by the Discovery program.

At any rate, the window of opportunity is about to close.

NASA will make its decision on which, if any, of the current Pluto probe proposals to consider on June 1 -- and it says that it will make such a selection only if Congress instructs it this month to do so.

If Congress doesn't select a Pluto mission this year, the odds that it will select one capable of reaching Pluto before its atmosphere freezes out will very quickly drop to almost nothing -- and any mission it does select will actually be more expensive.

The House Science Committee is considering holding hearings on the advisability of reactivating the Pluto mission -- and if that authorization committee does so, it will have a major impact on the final decisions of the House and Senate Appropriations Committees.

The Planetary Society is currently conducting another letter-writing drive to try to persuade Congress again of the importance of retaining this mission, and anyone who agrees should definitely visit their website for details -- and to do so quickly.

Related Links
Pluto Mission Campaign at Planetary Society
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