I'm back from the Europa Focus Group meeting... Options

[Guest_BruceMoomaw_*]

...which I decided to attend literally at the last possible minute, which is why I didn't alert you guys in advance. Very interesting -- both the discussions about the likely design of the mission (and how to retrieve it from cancellation), and many of the actual science presentations (which aren't on the Web yet, although they probably soon will be). I'll give you some more information tomorrow -- although I can't resist telling Alex that Tom Spilker's subgroup took my ideas about a Europa penetrator, and the printed information I gave them on the subject, seriously enough to recommend making further inquiries to NASA HQ on it. (And without my browbeating them, either. Nyaah.) The case for it, however, is still extremely far from certain.

As I say, more tomorrow.

[Guest_BruceMoomaw_*]

One advantage of a penetrator is precisely that it provides better seismic coupling -- although, in the case of Europa, this is probably the least of its fringe benefits. More important is that it:

(1) Is the only conceivable type of lightweight hard lander that can punch down below Europa's radiation-scrambled surface layer to reach possible recognizable biological remains.

(2) Can use the ice itself to shield itself from Jupiter's radiation for a fairly long lifetime.

(3) Is much lighter than a full-fledged soft lander -- or even an airbag hard lander.

(4) Can land on rough surfaces.

The big catch with a penetrator, however, is whether it can (1) point itself nose downward accurately enough without an atmosphere to avoid hitting the surface with its nose pointed at a slew ("angle of attack"), and (2) deal properly with hitting a sloping surface ("incidence angle"). Europa seems to have a very rugged surface; its AVERAGE surface slope seems to be about 12 degrees. This was the continuing point of dispute at the conference -- quite rightly -- and it remains uncertain to me, too (although it turns out that the Deep Space 2 probes were designed explicitly to deal with this problem, and their solution might work at Europa too).

Anyway, more on all this shortly. As I say, it was a VERY interesting conference, with a definite sprinkling of new scientific news (notably on Europan surface composition) -- and it seems to have reached some genuine initial conclusions about the feasibility, purpose and design of any lightweight piggyback lander that might possibly be carried on the Europa Orbiter.

[ugordan]

The big catch with a penetrator, however, is whether it can (1) point itself nose downward accurately enough without an atmosphere to avoid hitting the surface with its nose pointed at a slew ("angle of attack"), and (2) deal properly with hitting a sloping surface ("incidence angle"). Europa seems to have a very rugged surface; its AVERAGE surface slope seems to be about 12 degrees.

IIRC, someone recently mentioned that (2) is not an issue at all. A penetrator could survive a wide range of incidence angles as long as point (1) held, that is -- the axis of the penetrator is precisely aligned with its velocity vector.
Whether or not the surface impact is at an oblique angle is apparently much less of a factor.