----- Original Message -----
From: "Gary McMurtry" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, October 02, 2001 9:58 PM
Subject: Re: Possible solution to zero-G bone loss problem (and
osteoporosis!)
> BTW, the Europa Focus Group meeting in Flagstaff in early Sept. was
> interesting. Yours truly attended, and made his presence known.
> Basically, there was a push made by myself and others to add a
> lander/rover/corer to the Europa Orbiter Program presently scheduled
> for a 2008 launch. The logic goes like this. The main goal of the
> orbiter is to ascertain "for certain" (1) the presence or absence of
> an ocean (or lakes), (2) crust thicknesses, (3) mantle/seafloor
> depths. Secondary goals are to map the surface ala Galileo but with
> complete coverage and at even higher resolution. The latter should
> better define lander targets. Some of us (me, especially) objected
> to a purely orbiter mission given (a) the almost certain existence of
> an ocean, (b) the nearly-(too mild?) certain evidence for past liquid
> water, and (c) given either a or b, the interesting proposition that
> life may have existed there in the past if not also present, and that
> evidence for it may therefore be trapped in relatively young ice/salt
> near the surface (just below the few decimeters that are blasted by
> Jupiter's ionospheric radiation). Other arguments against the
> orbiter-only mission are: (1) we already have quite a few fairly
> high-res. targets for a lander based upon Galileo (we fussed over
> several at the meeting), (2) adding more targets and more high-res.
> remote sensing will not get us any closer to the more compelling
> questions about the ocean, its composition and prospects for life
> there than we basically are at now, and (3) an orbiter mission
> failure (Heaven forbid) would kick the lander mission so far into the
> future that anyone capable of reading this can forget being around to
> enjoy the outcomes.
>
> If it goes, the rumor is the Europa Orbiter will cost about 1 Billion
> dollars (I now place my little finger in the corner of my mouth ala
> Dr. Evil). An orbiter-lander mission would cost about 50% more, per
> Torrence Johnson. Seems to me 1.5 billion will get us a lot closer
> to the answers we seek. These are big numbers, but I think most of
> you will agree that the science and technology stakes are high, also.
>
> I could comment on lander options as well, but thought I'd get this
> off my chest first.
You, sir, are a godsend. The piece I'm working on right now is on exactly
this subject -- and since I couldn't attend the Focus Group meeting myself,
I've been reduced to reading the various abstracts (most of which weren't
really all that important), and planning to ask Dr. Greeley tomorrow what
conclusions the actual work groups reached as to the best form of future
Europa exploration.
My reasoning is along exactly the same lines as yours -- except that I'll go
one step further, and suggest that we simply skip Europa Orbiter and replace
it with a "Galileo 2" Jupiter orbiter to make dozens of new flybys of all 4
Galilean moons and inspect the entire Jovian system with far better
instruments than Galileo 1's (not to mention an, er, somewhat better data
rate). The data it would get on Europa itself would, of course, be far
inferior to that obtained by a Europa orbiter -- but, for the reasons you
suggest (and Jack Farmer, who once again at the meeting proposed simply
jumping straight to a Europa lander), I'm now strongly inclined to think
that we don't NEED anything better than Galileo 2 as a precursor for a
Europa lander. We already know now(from Galileo's induced magnetic field
data) that the place almost certainly still has a subsurface ocean; and
we've known for a long time that even if it's now frozen completely solid,
it probably had a liquid-water ocean during its early days and the remnants
of any ancient Europan life are likely to be very well-preserved in its ice
(far better than the remains of any ancient Martian life).
The only good remaining argument for Europa Orbiter is that its radar
sounder can locate the places where liquid water is closest to the surface.
But while such a radar sounder on Galileo 2 could sound only a few percent
of Europa's surface, if we arranged for those flybys to be over spots that
we already regard as interesting and promising as future landing sites, we
could both confirm which ones are best and get data to extrapolate what's
probably going on under the other Europan surface features that we didn't
get the chance to radar-sound. (Consider also that near-IR surface
composition mapping -- which isn't even in Europa Orbiter's primary payload
list -- may be almost as important as radar sounding in picking the best
biological landing sites.)
This mission would certainly provide us with far more data to select the
first Europa landing site than if we just used what Galileo 1 has given us
(as Farmer suggests). And the additional scientific dividend from studying
the other Galilean moons (especially Io) and Jupiter itself, over that which
Europa Orbiter could provide on them before entering Europan orbit, would be
enormous. Galileo 2 would both be far cheaper than Europa Orbiter and able
to carry a much bigger payload of science instruments -- and the same
central set of instruments would be very well suited to studying all four of
the Galileans and Jupiter itself. The only "specialized" instrument would
be the radar sounder -- and while its primary target would be Europa, even
it could provide a lot of useful data on the subsurface structures of the
other 3 Galileans.
I made this same suggestion a few months ago, save that I thought Galileo 2
should also carry a small Europa lander. This no longer seems advisable to
me -- it simply complicates the mission too much -- but I still think that
Galileo 2 is the only precursor we need before launching the first Europa
lander. And while its data would be extremely useful in picking the first
Europa landing site, if it did fail it would not be a total show-stopper for
launching Europa Lander based on the data we already have from Galileo.
(After all, one of the goals of last month's Focus Group was to come up with
the first preliminary ranked list of the best landing sites based on the
data we already have.) Any more data you can give me on what went on at
that workshop will be EXTREMELY welcome, Gary.
==
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