The result is that a big section of the planetary science community is in a state of restrained panic, with interest groups such as the Planetary Society launching a campaign to persuade NASA and Congress to provide extra funds in order to save the 2004 Pluto mission. But their success is highly doubtful.

Is the situation hopeless? Possibly not, as there many be an alternative way to rescue this mission: namely, cutting it loose from the rest of the Outer Planets/Solar Probe program, and flying it not by developing a revolutionary new spacecraft, but by making only slight modifications in an already-existing Solar System exploration spacecraft in order to fly a copy of that craft to Pluto with an absolute minimum of development costs.

The Pluto-Kuiper Express has suffered seriously from the effects of a still-unexplained NASA decision in Feb. 1998. Originally, NASA's Solar System Exploration Subcommittee had urged that it be launched before the Europa Orbiter, which requires much more sophisticated technologies.

The electronics of the Europa probe must endure radiation levels dozens of times greater than those which must be endured by a Pluto probe during its brief flight through Jupiter's intense radiation belts.

Furthermore, the maneuvering requirements of the Europa Orbiter are huge -- 2.5 km/sec -- which means that over half its weight must consist simply of propellant, which in turn means that the Orbiter's dry weight must be cut to an absolute minimum in order to make the whole spacecraft light enough to be launched to Jupiter with an acceptably small and cheap launch vehicle.

In its Fiscal Year 1999 budget request to Congress, NASA unexpectedly announced that it would nevertheless try to launch the Europa Orbiter first, in 2003.

Given NASA Administrator Dan Goldin's interest in astrobiology, his belief that the general public shares that interest, and his repeated willingness to single-handedly make sudden and risky changes in the U.S. Mars program in order to try and make its investigations of the possibility of Mars life faster and more spectacular, it is possible that the Europa Orbiter decision may also have been his personal idea.

Europa is after all, the second possible place for past or present life elsewhere in the Solar System -- and the Europa Orbiter is directly linked to that search, since it will try to determine both whether there is still a liquid-water ocean capable of supporting life underneath Europa's outer ice shell, and where the thinnest parts of that shell are located so that future landers may be able to melt through the ice layer and reach it.

For whatever reason this decision was made, its effect on Pluto Express has been disastrous. The new plan was to save money on the Pluto probe by making it a near-duplicate of the Europa Orbiter except for the elimination of that craft's huge propellant tanks, in the confidence that the Europa vehicle would be ready for launch in 2003 and so naturally its simpler Pluto Express clone could be launched in 2004. But, as I say, the technologies for either craft simply won't be ready even by 2004.

But the irony is that those technologies aren't needed at all just for a Pluto mission. We've flown similar missions into the outer Solar System, using Jupiter flybys, for a quarter-century.

The single most important requirements for the Pluto Express spacecraft are that it must last 8 to 14 years -- which is no problem -- and that it must be fairly lightweight: about 420 kg or less, so that an acceptably small (and cheap) booster can hurl it to Pluto in an acceptably short time.

The heavier Europa Orbiter virtually requires one of the new EELV boosters -- but the Atlas 3 booster, which has already been successfully flown, could send a 350-kg craft to Pluto in 9-3/4 years, and a 400-kg craft in a still-acceptable 11-1/2 years.

Are there any already-developed Solar System spacecraft that can meet these requirements? There are two.

In fact, one of them -- the "Stardust" probe designed to fly by a comet and collect a tiny sample of its dust and gas for later return to Earth -- has been on the way to its target for the past 18 months, and is working extremely well.

Its mission will last 6 years, so increasing its reliability for that longer Pluto flight should be relatively straightforward. In fact, one group of scientists has already suggested that a very slightly modified version of it -- the "Europa Ice Clipper" -- should be used to fly by Jupiter and return to Earth with a tiny sample of orbiting dust from the surface of Europa, a mission which would take 12 years.

The other spacecraft -- "Contour" -- is planned to fly by three different comets over a period of 6 years (without returning to Earth), and may well have its mission extended to 12 years to make further comet flybys.

It is still being built, for launch in July 2002. But it uses only already-developed and very reliable systems and technologies (greatly cutting its cost), and there is no reason to think that a copy of it could not be built in time for a Pluto-bound launched in 2004.

Moreover, both spacecraft are clearly lightweight enough for the Pluto mission. Stardust weighs 386 kg; Contour (without an attached solid kick motor that isn't needed for a Pluto mission) is 414 kg. And both craft, for their comet missions, carry about 80 kg of hydrazine fuel so that they can make 360 meters/sec worth of maneuvers -- but NASA's official requirement for the Pluto Express is only 90 meters/sec, which means that about 60 kg of hydrazine could be removed from their Pluto versions.

Alternatively, some of that extra propellant could be retained -- slightly slowing the probe's flight to Pluto, but raising the chances that its trajectory could be changed after the Pluto flyby to allow it to make additional flybys of one or two more small Kuiper Belt objects.

The number of changes that would have to be made in either craft to carry out the Pluto mission is surprisingly small. The main ones are a much larger, lightweight high-gain antenna dish some two meters across, and the replacement of their solar panel power source by an "RTG" (the currently used type of radioisotope power generator). And both spacecraft already have a perfect mounting place for that RTG.

On Contour, the RTG could be mounted where the unneeded solid kick motor is currently attached; while on Stardust, the RTG could be mounted where the 25-kg sample return capsule for parachuting the comet-dust samples back to Earth when the craft returns here is currently located.

In both cases, that big high-gain antenna dish would go on the craft's other end, just as is planned for the current Pluto Express spacecraft.

The Contour and Stardust buses also have another built-in advantage. The Pluto Express mission would hurtle past Pluto and its equally interesting moon Charon at 65,000 km/hour -- and since both worlds are small, it will have to slew its camera's viewfield around rapidly to observe them without having that speed blur its photos.

For this reason, many scientists feel that the craft will also end up having to carry a small tiltable mirror to allow it to swivel its camera's viewfield fast -- but since spacecraft on comet flyby missions have an even more serious version of the same problem, both Stardust and Contour already include a tiltable mirror in their payload kits.

Contour has another advantage: it's already designed to save operations money by spending fully 94 percent of its long space cruise time in "hibernation mode", rotating to stabilize itself and only communicating occasionally with Earth.

The current Stardust probe can't do that -- it must keep its solar panels continuously pointed at the Sun -- but without those panels, it could easily be adapted to the same spinning hibernation mode, which is ideal to save money for the long cruise to Pluto, and is in fact planned for the current Pluto Express spacecraft.

Finally, Stardust may have yet another advantage. Because, unlike Contour, it has already undergone extensive testing in space, a similar spacecraft bus for a Pluto flyby would have a good chance of being developed in time to take advantage of the earlier Nov. 2003 Jupiter launch window, which is better than the 2004 one -- for that launch date, an Atlas 3 could send a 400-kg probe to Pluto in only 9-1/4 years, and a 350-kg one in only 8-1/2 years.

In any case, the financial benefits of such a move would be huge. The original Fiscal Year 2001 NASA budget included $113 million to develop the new technologies needed for the Europa Orbiter and the Pluto Express (and described by NASA as "revolutionary").

Since then, that figure has ballooned -- but the cost of adapting the existing Stardust or Contour spacecraft for a Pluto mission, using absolutely no new technologies, would be minimal: possibly as little as $40 million or so spread out over several years.

The new "X2000" technologies that really are needed to carry out the Europa Orbiter and Solar Probe missions could then be developed in a more leisurely way, since both those missions can tolerate launch delays with absolutely no loss of science or increase in mission cost.

If NASA and the planetary science community really want to save this mission -- and sharply cut its cost in the process -- a "Keep It Simple, Stupid" approach, whereby Stardust or Contour is adapted for a Pluto flyby, may be the only way to get to Pluto before its atmosphere freezes out for another 200 years.

Back To Part One

WAY OUT THERE
Pluto's 25 Degree Difference In Bloody Cold
Paris - May 29, 2000 - A team from the Observatoire de Paris using ESA's infrared space telescope ISO has measured variations in the thermal flux of the Pluto-Charon system, which prove that the temperature of Pluto's surface is not uniform.

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