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SPACE SCIENCE
Will Funding Europa Bust The Bank

Despite much talk about a "Cryobot" submersible that would melt its way down through kilometers of ice into Europa's ocean itself, this would be a tremendously difficult project.
by Bruce Moomaw
Cameron Park - March 7, 2001
The funding issue now facing a Pluto flyby is only one aspect of a bigger problem to which NASA's Solar System Exploration Subcommittee devoted much time at its meeting last week. Michael Drake, the committee's chair, described the situation to SpaceDaily as a "Reality Check" -- adding that it's now quite clear that NASA simply has no way to fly most of the sophisticated Solar System missions it had planned over the next 15 years at the funding levels that it can now reasonably expect to be available.

Another aspect of this problem is the Europa Orbiter. It has major propulsion requirements, since it must not only brake into orbit around Jupiter, but must then brake itself further into a low circular orbit around its final destination: the Jovian moon Europa. This will require that the spacecraft's payloads be highly miniaturized in order to leave room for its very large fuel load.

And the Orbiter, during this mission, must also survive very high radiation levels from Jupiter's radiation belts without a major weight in shielding, by using radiation-hardened electronics which are yet to be developed.

Although the "induced magnetic field" measurements that the Galileo spacecraft conducted in 2000 have now essentially proven that Europa has a large liquid-water ocean beneath its surface ice -- which was a key question to be answered by the Europa Orbiter -- the SSES still agrees that an Europa Orbiter will be crucial in finding the optimum landing sites for future Europa landers that will look for evidence of life.

To do that, we still need to locate the places where liquid water is closest to the surface.

Despite much talk about a "Cryobot" submersible that would melt its way down through kilometers of ice into Europa's ocean itself, this would be a tremendously difficult project.

Drake went so far as to say he thinks it will never be done - and while this may be overly pessimistic, it is certainly decades away.

But a growing number of planetary scientists specializing in Europan studies now think it likely that there are crevasses and other pockets of liquid water within a few hundred meters or less of the surface. Moreover, there is a growing belief that Jupiter's radiation may itself manufacture -- in the uppermost layers of Europa's ice -- large amounts of the chemical nutrients that would be critical for any microbial life on Europa.

While looking for near-surface liquid water, the Europa Orbiter could also help identify other chemical substances mixed in with Europa's ice - anything from salts and acids to organic compounds - and map the locations where they are most concentrated.

There is no doubt that - even more so than on Mars - we must try hard to locate the best possible scientific landing spots for any future Europan landers, since any landing on Europa would be very expensive, and in the next half-century no more than a few may ever fly.

To find the right landing spots on Europa, a spacecraft must orbit Europa itself -- since a Jupiter-orbiting spacecraft that made repeated close flybys of Europa, while needing less fuel, could only map a few percent of Europa's surface.

Therefore we need to find every possible way to make a Europa Orbiter cost-effective -- such as finding cheaper routes to Jupiter by using inner-planet gravity assists or ion engines -- and to make its science payload as lightweight as possible while still being effective at its given tasks.

The same problems also plague many other Solar System missions high on NASA's wish list, including Mars sample return missions. The truth is that there is just no inexpensive way to fly missions to the outer planets or sophisticated missions to Mars.

With this in mind, the SSES has created two subcommittees that will make a major effort to find out how to get the biggest possible scientific bang for NASA's limited bucks.

One subcommittee will carefully reexamine NASA's current strategy for outer Solar System exploration.

The current plan calls for the next such mission, after the Europa and Pluto missions, to be a Comet Nucleus Sample Return spacecraft which would rendezvous with a comet using ion engines, and then either land on the nucleus and pick up core samples itself, or orbit the nucleus and dispatch a small lander to pick up core samples from its surface and then return to rendezvous and dock with the main spacecraft.

In either case the main spacecraft would then return to Earth with its highly prized samples, which are believed to represent pristine material from the original protoplanetary disk that the Solar System condensed from.

Again this would be a very complex and expensive mission, and Drake wonders whether it should definitely be the next priority.

In particular, Drake wonders if the coming examination of the Saturn system (and especially Titan) by the Cassini spacecraft in 2004-08 may not lead us to radically upgrade the importance of a return visit to Titan - about which we currently know very little, except that it must be the repository of extremely complex organic chemistry which could tell us a lot about the way in which organic chemicals evolved into life on early Earth.

These are the questions which the Outer Solar System subcommittee will examine - along with the general problem of making outer Solar System missions as cost-effective as they possibly can be.

Part Two: Life's Hell Then There's Venus

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