This would not only allow quick sprints to even the most distant planets without waiting for Jupiter to be lined for a gravity-assist flyby; it would then allow the craft to easily brake itself into orbit around its destination planet without the need for aerocapture - and, even after all that, it could have 20 km/second or so of maneuvering capability left, allowing it to cruise virtually anywhere within the planet's system of moons (and repeatedly enter or leave orbit around the moons themselves).

But NEP - quite apart from the fact that its development would take about a billion dollars by itself - has, of course, the huge disadvantage that people do not look fondly on putting large amounts of radioactive material into orbit where it could sooner or later sprinkle down on their heads.

The relatively small amounts of plutonium-238 contained in the electrical generators of present-day outer planet probes produce more than enough unease already, despite NASA's repeated attempts to assure everyone that there is no significant danger of a launch accident or accidental reentry scattering powdered plutonium into the atmosphere.

Actually, though, an NEP craft's reactor could be made much safer than the current-day RTGs. It could be fueled with uranium-235 - which is more expensive than plutonium, but fully a thousand times less radioactive when not piled up into a critical mass.

And such a craft could be launched, unfueled, into a high Earth orbit from which it would virtually never reenter, and only then be loaded with uranium fuel carried in two or more separate unmanned satellites that would automatically dock with it before it lit up its engines and left Earth. Still, NEP is clearly a project for the fairly distant future where NASA is concerned.

At any rate, there was general agreement at the group meetings that, given the extreme importance of these new technologies for a wide variety of missions, NASA needs to considerably increase its spending on a separate program to develop them - an enlarged version of its current "New Millennium" program - rather than trying to fund their development for any single mission.

JPL currently follows the latter strategem of trying to fund their development only when a specific mission first requires them, thus sharply reducing the odds that Congress will approve that particular mission with its high total cost.

But here the really central problem raises its head: limited funding.

At the meeting of the Decadal Survey's Steering Committee, NASA Solar System Exploration Division director Colleen Hartman set forth a model of the wonderful things NASA could do if it had $935 million per year to spend on Solar System exploration not connected with the planet Mars:

- a $360 million Discovery mission every 2 years, - a $640 million Medium-class mission every 4 years, - an $850 million large mission every 5 years - $155 million per year for Research and Data Analysis; - $70 million for development of deep-space propulsion systems such as SEP, NEP and solar sails; - and $200 million a year for other new technology development and maintenance of the Deep Space network.

There's only one tiny problem: NASA doesn't have $935 million a year to spend on these programs. In FY 2002, it will have only about $500 million. And, even in the unlikely event that NASA drastically shrinks its spending on the Space Station - perhaps by turning it from a permanently manned lab into an unmanned one periodically visited by humans - it's very hard to conceive of non-Mars Solar System exploration ever getting more than $600 million per year.

And - until those new technologies allow mission costs to start shrinking again - Solar System missions will continue to show a steady trend toward becoming more expensive, since most of the relatively cheap stuff has already been done.

That being the case, it's a pretty safe bet that for a long time to come, we will see only two Medium to Large class non-Mars Solar System missions per decade, along with several Discovery-class ones.

The clear frontrunners for the Medium to Large missions in the next 10 years are the Pluto flyby - whenever it finally does launch - and Europa Orbiter, with the Comet Nucleus Sample Return as a dark horse.

Still, that by itself allows a very active and productive program, provided the missions are wisely chosen. It will be extremely interesting to see the Decadal Survey's final recommendations for the Solar System exploration program when they're officially released next spring.

One remaining part of NASA's Solar System exploration -- the most important part of all -- will not be directed in detail by the Decadal Survey's report next year. NASA spends as much on the exploration of Mars as on all the rest of the Solar System combined. And a separate report recently issued by "COMPLEX" (the national Academy of Sciences' Committee on Planetary and Lunar Exploration) has already concluded both that that disproportionate chunk of the planetary budget is justified (given Mars unquestioned importance) and that the overall form of the program currently planned looks pretty good (although the COMPLEX committee did recommend some minor changes).

But the Decadal Survey committee does need to mesh its other recommendations with the spending levels and scientific results from the Mars program -- and so, at its November meeting, the Survey's central committee was given a quite detailed description of the U.S. Mars program. In the final part of this series, I'll describe the Mars program as it now exists, and the changes that have recently been made in it.

Back to Part One of this Report

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SPACE SCIENCE

Taking The Medium Class Route To Deep Space
Los Angeles - Nov 29, 2001
The main purpose of the Nov. 14-16 meeting of the Steering Committee for NASA's Solar System Decadal Survey was to decide the best, most scientifically cost-effective sequence of planetary missions for the period 2003 to 2013. Unfortunately the press were kept out of the lengthy "closed sessions" during which it debated the comparative virtues of specific missions. In addition, there will be two more meetings of the Committee before it issues its official report to NASA in late spring.

No Bucks Without ET
Los Angeles - Nov 26, 2001
Other than finding out that the current outer planets program is effectively dead in the water, planetary scientists who gathered Nov 14-16 in Irvine to map out the best plan for the next 10 years for NASA's Solar System exploration program saw discussions center around three critical themes - astrobiology, the need for more terrestrial studies, and the need to start a new line of "Medium-class" planetary missions midway in cost between the small Discovery missions and the billion-dollar behemoths NASA has been fond of in its earlier space science plans.

Out To The Horizon Of Sol
Cameron Park - Dec 10, 2001
The saga of NASA's mission to fly by Pluto and its moon Charon continues as NASA selects a spacecraft for design development while still saying the mission will never be funded, but which many in Congress say will. SpaceDaily's Bruce Moomaw reports that the funding impasse might be solved by a new class of Discovery Plus missions.

Into The Deep Space Of Nowhere
Irvine - Nov 16, 2001
For the past several years, a strange "Pluto-Europa war" has been raging within NASA -- over whether to launch a Pluto flyby mission in the near future (so that it can utilize a gravity-assist flyby of Jupiter to be confident of reaching Pluto before the imminent freeze-out of the planet's thin air as it moves farther away from the Sun on its eccentric orbit ), or to delay it in favor of first launching a much more expensive and technically sophisticated mission to orbit Europa in preparation for later biological studies of that Jovian moon, thus very likely giving up the last chance for 250 years to study Pluto's atmosphere, as well as to see a good deal of its surface which is starting to fall into 125-year-long continual shadow due to the planet's greatly tilted spin axis.

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