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

[nprev]

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.

[remcook]

Most importantly IMO is the whole uncertainty of the plan: noone knows exactly what happens when you impact Europa. Designing a mission with these enormous uncertainies will give you a mission that is overly robust and thus too heavy and too costly. And that without a good idea if it even works! I'd spend my money on something else...

[algorimancer]

...
noone knows exactly what happens when you impact Europa
....

The nice thing about Europa is that, of all the icy satellites out there, it is the one with the least uncertainty about material composition. Essentially we're looking at a surface which, to considerable depth, and beyond reasonable doubt, is predominantly water ice with contamination from salts and sulfur compounds. Rocky material should be virtually non-existent. This is the sort of material which can be (relatively) neatly modeled in a laboratory or a computer, and engineering feasibility determined with confidence. (yes, I'm simplifying a great deal here)

The implicit tradeoff in this notion is that between the mass of the fuel and hardware needed for traditional deceleration, versus the mass of an impactor and shielding for impact-assisted aerobraking [IAA]. This leaves open a lot of unanswered engineering questions, such as whether it is possible to design an impactor which will do a good job of vaporizing a volume of Europan ice rather than simply fragmenting it (I like the notion of an impactor which splits into many small pieces prior to impact, perhaps a bag of water with a small explosive charge which detonates shortly before impact). If the mass balance tradeoff is in favor of IAA then it might be worth testing a prototype.

Certainly you'd want to test a notion like this prior to sending a full-scale rover. If you're sending several penetrators anyway, why not replace one or two of them with IAA technology demonstrators.

One more thing, any Europa orbiter/lander might benefit from aerobraking at Jupiter prior to arrival at Europa, which could substantially reduce the approach velocity to something like AndyG's figure. The impactor component of an IAA package could do the opposite and use Jupiter for a gravity assist so as to impact Europa with maximum velocity.

Lot's of unanswered questions. I too initially thought the Pathfinder/MER airbag approach was pretty outrageous, but it worked rather well. Heck, they designed a manned vehicle (Orion) designed to be powered by H bombs, and demonstrated a prototype. Just at the moment I think IAA is outrageous but might still work, and I'll leave it at that.