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_*]

The tether idea, alas, would work about as well as one of Wile E.'s schemes (but would be a lot more costly -- after all, he always survives somehow). The moment the lower end of the tether brushes the surface, the penetrator gets flung downwards -- in an entirely uncontrolled way -- on the top end.

As for the Bowling Ball's instrumentation: it would unfold nothing. What it would have on its surface is a number of little camera ports and patch antennas, and about half a dozen little sharp-edged "sample cups" that could scoop up surface samples as a result of the impact itself -- after which electrodes in the cups would analyze the ice's pH, salinity and redox content, and a fiber-optic lead from the cups to an onboard Raman spectrometer would provide further composition analysis. Add an onboard short-lived seismometer or geophone, and that's the total instrument payload of the current model (although an active pulse generator might allow the geophone to double as a simple sonar system to help measure the rock content of the ice, as Spilker thinks is wise).

I'm starting to think that the biggest problem with a penetrator might be not its impact angle, but its remaining horizontal drift on landing -- which a broad surface-contact foreplate couldn't correct on impact, especially if the edge of the plate in the direction of the horizontal motion was also tilted slightly downwards. That is, the penetrator might "trip" and thus "flip". It may be that the only way to solve that problem is to absolutely minimize remaining horizontal motion during the deorbit burn -- which, in turn, might require a forward-facing Doppler radar sensor. (The Bowling Ball, by contrast, has tremendously more tolerance for horizontal landing velocity.)

It starts to look as though the only question is whether the possibility of getting some astrobiological data on the very first landing -- using a sample from a still quite shallow depth, and involving the analysis of a very small amount of ice collected by the penetrator -- would be worth the considerably increased complexity of the Penetrator as opposed to the Bowling Ball. In short, I'm starting to acquire new serious doubts about my Brilliant Idea.