The First Europa Lander, What can be done first, cheapest & best? Options

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I think that many people in this forum would agree that somebody's going to have to land on Europa someday before the rather elaborate schemes to penetrate the outer ice layer will ever fly, if for no other reason than to get some relevant ground truth before committing to such an elaborate, expensive, and risky mission.

EO seems to have ruled out any surface science package for that mission (though it would be nice to change their minds! ), but I think that there is a valid requirement at some point to directly assess the surface properties of Europa in an inexpensive yet creative way. Some candidate instrument payloads might be:

1. A sonar transducer/receiver set embedded within a penetrometer to determine crust density and examine the uniformity of the ice layer within the operational radius of the instrument (looking for cracks and holes, in other words).

2. A conductivity sensor again embedded inside a penetrometer to measure the native salinity of the surrounding material and possibly derive some constraints on the composition of metallic salts in the European crust (saltiness has a major effect on ice properties, in addition to the obvious need to derive the salt content of any underlying ocean).

3. A seismometer for all sorts of reasons.


How does this sound? Any critiques, additions, or subtractions? I omitted a surface imager not only because of bandwidth/extra complexity considerations but also because it seems desirable to penetrate the crust in order to minimize as much as possible reading any contaminants from Io during surface measurements. The orbiter data could be used to sense and subtract this from the penetrometer readings.

[Guest_BruceMoomaw_*]

Uh-uh. An object that short would take weeks -- and maybe months -- to align itself, and then it would point itself straight downward instead of in the direction of motion. There is no simple solution to this problem.

As for a smaller lander to provide ground truth for the later bigger ones, there are two possible ways in which this could be useful -- but there are cheaper alternatives to both. First, of course, we need really high-resolution pictures of Europa's surface to see what kinds of landing hazards exist -- especially since the data we have up to now suggests that the surface may be extremely rugged, laced with crevasses and small ridges. But Europa Orbiter is now virtually certain to carry a big MGS-type camera for very high-res photos of some patches of the surface from orbit.

Second, it might be wise to get a measure of the salt content of the ice before sending a big lander that would probably obtain its data by releasing a short-distance Cryobot to melt its way 100 meters or more into the surface. (We want to be sure of getting below the upper layer of radiation-modified surface material -- which may have been gardened by impacts a fair distance into the surface if we're unlucky -- and Chris Chyba has also pointed out that a Cryobot may be the only way of gathering and filtering enough meltwater to have a good chance of detecting small amounts of biochemicals.) But high salt content might jam up a Cryobot by causing it to build up more and more concentrated brine in front of its nose until you had a block of salt which it could not melt through -- so it may be necessary to add a mechanical grinding head to chew down through this at the same time that you melt the ice. However, EO is virtually certain to carry a good near-IR spectrometer -- and a mass spectrometer to analyze the molecules of Europa's surface sputtered into the space above it by Jupiter's intense radiation -- and these together should be able to answer that question. (They may even add an X-ray spectrometer for direct element measurements.)

I've wondered, though, if it might be worthwhile to put a small sterilized impactor on EO, equipped with a camera, to be released during the last flyby of Europa which the craft will make to almost match orbits with the moon before it finally fires its rocket engine on the next pass to enter orbit around it. This could provide us with very close-up pre-impact photos that might provide more data on surface roughness -- and the Orbiter might be able to fly through the cloud of debris thrown up by the impact (Ice Clipper-style) to do a better mass spectrometric analysis of Europa's main surface constituents. And such an impactor would of course be much lighter than a flat-out lander, especially since EO wouldn't need to carry the fuel to brake its mass into Europa orbit. I still imagine the data from this would not be worth the monetary and mass cost, but I DO intend to ask the mission's designers about the possibility.

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Hmm. How about a "semi-hard" lander al a Ranger instead? (...without the balsa wood, of course!)

Seriously, if the velocity differential is small enough during the final flyby, maybe something like a minature version of the MER EDL system without chutes but augmented by a retro could drop a nice little instrument suite on the surface with a high probability of success.