[X] My Assistant

[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.

[djellison]

I'm having difficulty imagining a Europa impactor.

You'd have to have active attitude control, thus either hydrazine thrusters, or perhaps some cold-gas thrusters to maintain attitude for the nose-first impact.

You've not got the budget, I assume, for much delta V to slow the thing down before impact - so we're talking a very VERY fast impact - are we talking straight in from approach, or a deorbit manouver after arrival? The former might be several km/s - the later is going to be a very low angle of impact. ( I assume you want the later so some sort of targetting can be planned from high res imagery )

A 355km Europa Orbit is something like 1.3 km/sec orbital speed.

If you do a deorbit manouver of say, 100m/sec, your impact would be at about 5 degrees and more like 1.5 km/sec

Given that attitude control would require some sort of pressure vessel, be it cold gas or liquid prop, you're going to have an explosion on impact of some sort.

DS2 heritage is 1) not too great because let's not forget, DS2 was a failure for whatever reason. 2) the speed of impact is going to be an order of magnitude higher unless you take some sort of decelleration propulsion, in which case the mass is going to be an order of magnitude higher. 3) DS2 was passively orientated and required no active attitude control for entry or impact.

We're talking RTG (as you mention a long life span) which means a fairly heavy craft before we even think about anything else, and the rtg's going to have to be built like the proverbial brick out house to survive the thing going in. Plus the fact that we're talking about highly sensitive biological experiments - which don't really like hundreds of G.

I'd really really like to see something like this - but I struggle to see how an impactor probe would work out there.

I have to say - it's a very very long shot - the sort of long shot that'd I'd expect you to lambast for being totally outside the realms of sensibility Bruce

If there are specific design details around, I'd love to see some - see how they're proposing this thing.


Doug