Re: Guidance System for Icepick I, and Cryobot thoughts

[JHByrne]

In a message dated 11/1/2002 1:22:24 AM Alaskan Standard Time, [EMAIL PROTECTED] writes:

Actually, it's a rather intereting one, and the mechanism involved wouldn't
have to be nearly as complex as the one you propose.  All you have to do is
arrange for the cryobot, once its descent is complete, to reduce its total
density below that of liquid water -- that is, give it positive buoyancy
like a submarine -- and it would rise to the TOP of any meltwater space it
produced, allowing it to melt its way back up if it had a similar heater on
its top end.  This could be done by having it simply drop ballast (perhaps
its lower end?), with the Cryobot having enough low-density internal space
inside its hull (perhaps filled with a lower-density pressure-compensating
liquid) to give it positive buoyancy afterwards.  But keep in mind that,
just as it will probably take several years to melt its way down to the
bottom of Europa's ice crust, it will take just as long to melt its way back
up.

This is sidestepping the question, of course:  once the Europa cryobot has performed its central function of 1)  tunneling down and collecting data along the way, 2) transmitting data and control information back along transponders, and 3) dropping of a main payload of a submersible capable of exploring a subsurface sea... why would you want the cryobot back?

If it takes several years to go down, and several years to get back up, then by the time it returns to the surface, its utility is presumeably even less... particularly if it found anything interesting, which would have encouraged a superior cryobot to have been dropped in the meantime.

Still, if we really MUST recover it, then as Bruce suggested, and I alluded to, positive buoyancy seems far more efficient than trying to turn a cryobot into a tunnel crawler.  I'd imagine that simply dropping off a water submersible in 'the sunless sea' under the ice of Europa would be the ballast drop that Bruce describes, ie, tunnel down, drop the submersible payload, and once freed of that weight, back it comes to the surface.

-- JHB