From: anita@astro.as.utexas.edu (Anita Cochran)
Subject: Re: Mariner Mark II vs smaller missions
Organization: Univ. of Texas McDonald Observatory
Date: Wed, 30 Sep 1992 23:56:50 GMT

In article <mikew.717692440@kpc.com>, mikew@kpc.com (Mike Wexler) writes:
> anita@astro.as.utexas.edu (Anita Cochran) writes:
> 
> It goes with out saying that A single-purpose craft won't be able to 
> study the systematics as well as a more expensive multipurpose craft.
> I think the more important question is whether several simple, quick &
> dirty craft are more cost effective than a single expensive craft.
> 
> >Well, if we agree that we want to study the system as a whole, this
> >puts certain requirements on the instrument complement.  It suggests
> >one needs an imaging instrument, IR and UV spectrometers, and
> >fields and particle experiments.  A probe for Titan's atmosphere
> >is a nice thing to have too, once you have a spacecraft going that
> >way.  So, add these together and what do you have?  You have
> >a Mariner Mark II class mission.  And once the spacecraft is going,
> >you might as well send a full spacecraft.
> 
> Imagine instead of a Mariner Mark II class mission you have a series of
> missions starting with a relay satellite and following up with separate
> craft with imagine, IR, UV and fields and particle instruments. And with
> the quick turn around you can send updated instruments based on knowledge
> gained by early instruments. You can afford to try more risky techniques
> like ion propulsion and aerobraking. 
> 


This still does not allow for the systematic studies.  Systematic studies
require that you study the various components at the same time.  We know
that Saturn is temporally variable -- look at the Saturnian storms
this last year.  And it is not sufficient to study part of the problem
without the other problems.  If you put the fields and particles experiments
in orbit, you really should have the UV spectrometer since much of
the fields phenomena like aurorae and sub-storms have a UV signature.
And you really would like an image to put the conditions in the atmosphere
in context.  So now you are talking UVS, imaging and fields and particles.
That is NOT a small mission any more.  Now, you say we will study the
surfaces so we would like to do some spectral work so we send VIMS
(visual and Infrared Mapping Spectrometer) and maybe cover the thermal
IR.  But we would like to have things in context and want to study
the geomorphology  so you have to send
a camera.  This is also NOT a small mission.  Now you want to study the
atmosphere.  Well, you need the UV spectrometer and probably CIRS (Cassini
IR spectrometer) and, guess what, you need imaging to put things in context
and to study the dynamics.  None of these are small missions.
And by the time you have now sent 3 moderate missions  and they should
all go at the same time (see the temporal issue above) you are back to
a big mission so let's fly Cassini.

Now, if you  don't want systematics, the smaller missions are fine but if
you concede that you want to study the systematics, you  have
to have a big mission.

And new technology does not only mean ion drives and solar sails.  The
CIRS is THE MOST SOPHISTICATED IR spectrometer we have yet built for
space.  Its PI expressed the opinion last week at a Goddard meeting that
it probably is the most sophisticated which will ever fly since you cannot
do it smaller (this has nothing to do with detectors or electronics but
the need for big optics).  And the Ion Mass Spectrometers are getting
more and more sophisticated.  And the CCDs which were developed for
CRAF and Cassini opened up a whole new world in CCDs and resulted in
the new WF/PC II cameras on HST.  So you see, these missions are cutting
edge in their own way.  Yes, they are expensive.  And there is where
you must make the decision of what are your priorities and what kinds
of questions you want to answer.  There is no absolute path but
Cassini is NOT old-fashioned technology.
-- 
 Anita Cochran  uucp:  !utastro!anita
                arpa:  anita@astro.as.utexas.edu  
                snail: Astronomy Dept., The Univ. of Texas, Austin, TX, 78712
                at&t:  (512) 471-1471
Newsgroups: sci.space,sci.astro