I was wrong in suggesting in an earlier article that this might be connected with NASA's sudden decision to launch a second "Athena" rover to Mars in 2003. NASA has decided to take most of the money needed for that added mission out of other parts of the NASA budget, with only $10-20 million per year coming out of other Space Science Programs -- and since the total yearly Space Science budget is $2.4 billion per year, it's clear that the second Mars rover can be funded without taking a cent away from the Pluto mission, and with only relatively small cuts and delays (months or even weeks) in all of NASA's other space science projects.

But the Pluto probe is nevertheless in serious danger, because the "Outer Planets/Solar Probe" program of which it is part requires the development of many advanced new technologies under NASA's "X2000" program -- electronics and other systems which are both extremely lightweight and extremely radiation-proof -- and this is proving harder and more expensive than had been thought.

In particular, NASA had hoped to develop a new kind of radioisotope-fueled power source which would be fully three times more efficient in converting the heat of its plutonium core into electrical power, thus greatly cutting down on the weight of the power generator -- but this is turning out to be a serious problem; the new thermal conversion techniques required do exist, but won't have all the fine technical bugs worked out of them for several years.

Another problem is that the new generation of "Evolved Expendable Launch Vehicles" (EELVs) intended to launch the OPSP program spacecraft -- the Delta 4 and Atlas 5 -- are also proving harder to develop than thought; they will be both later and more expensive than had been hoped.

NASA's plan had been to launch the first OPSP mission -- the Europa Orbiter -- to Jupiter in November 2003, following it with the Pluto Express and the Solar Probe (both of which require Jupiter gravity-assist flybys) in Dec. 2004 and Jan. 2006.

When the development crisis became clear this year, NASA's first move was to delay the Europa mission into 2006 and the Solar Probe to 2007, and then it proposed delaying both of them another year -- all the while keeping the Pluto mission on schedule for Dec. 2004.

But NASA Solar Exploration Exploration Division chief Carl Pilcher has now admitted in a letter to scientists interested in Pluto Express that even this won't be adequate to make up the funding gap. It looks now as though there's simply no way no way for the program to launch Pluto Express in 2004, unless the OPSP program receives a massive new influx of money -- which is doubtful

And the consequences of this are serious. After 2004, Jupiter will not be lined up to provide an effective gravity assist to Pluto for another decade. There are other possible ways of getting the probe to Pluto -- such as skipping Jupiter and instead having it make a whole series of gravity-assist flybys of Venus, or attaching a solar-powered ion engine module to it and using that (along with one or two Venus flybys) to propel it into the outer Solar System at high speed. But, as OPSP deputy project manager Robert Staehle has told SpaceDaily, all these alternate techniques require "much longer and more expensive missions".

Moreover, this mission is virtually unique among space missions in that a delay in reaching Pluto will seriously reduce its science return. Pluto is currently moving farther away from the Sun in its lopsided orbit, and its extremely thin but scientifically interesting atmosphere of nitrogen and other gases is starting to freeze solid onto the surface.

Studying the composition and structure of that atmosphere is one of Pluto Express' most important goals -- but if it doesn't reach Pluto by about 2016, there may be no atmosphere left to study. The result is that a big section of the planetary science community is in a state of restrained panic, and such lobbying groups as the Planetary Society have launched a furious campaign to persuade NASA and Congress to provide extra funds in order to save the 2004 Pluto mission. But their success is highly doubtful.

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