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Date: Fri,  9 Feb 90 01:41:10 -0500 (EST)
Subject: SPACE Digest V11 #25

SPACE Digest                                      Volume 11 : Issue 25

Today's Topics:
              Request for info/opinions
             SPACE Digest V11 #18
             Re: Gravity Assist Mechanism
          Re: Galileo Update - 02/06/90 (Forwarded)
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Date: 8 Feb 90 15:03:09 GMT
From: zaphod.mps.ohio-state.edu!wuarchive!kuhub.cc.ukans.edu![e-mail]
Subject: Request for info/opinions

Fellow netters:
I'm working on an article about the future of U.S. space exploration. There
were a lot of them last year around the 20th anniversary of Apollo 11, but
none of them seemed to cover some of the issues I've seen discussed on the
net. I didn't save copies of a lot of the discussions I saw, and most of
them didn't have a lot of focus, so I was hoping some interested souls
could answer the following questions:

1.  What should the goals of the space program be? Should we be interested
in scientific research? Commercial exploitation? Preparing to build
colonies in space?

2.  How should we reach the broad goals we set? What is the best way to
fulfill these goals? What specific projects would best fulfill scientific
research? What are the most profitable uses of space? How can we best build
a manned presence in space? Should we concentrate on joint ventures with
other countries?

3.  What should the role of man in space be? Although this is a subset of
#2, it has been the focus of enough controversy that it deserves a separate
mention. Can unmanned craft usually perform research more efficiently for
less money? Are the things man can do in space valuable enough to warrant
sending him along?

4.  What should the government's role be in space? Should the government
control all U.S. space flight, as it has until recently? Should commercial
participants be given a larger share of the launch market? Is NASA spending
its money wisely? Should the government get out of the space business
altogether?

5.  What will we get out of the space program? Another frequent chestnut;
but with all the railing against space by the anti-Galileo groups last
year, it may be worth going over again.

A good focus for many of these questions is the proposed mission to Mars.
Is it a worthwhile mission for scientific goals? What would be the best way
to explore Mars--with manned or unmanned craft? Would a so-called "Mars
Rover" really work? What would give the best return (scientific or
otherwise) on the investment? Should we be doing it in conjunction with the
Soviets?

Another focus is the space station. Why should we build it? What will it do
for us? Is it the best way to gain scientific information? To learn and use
manufacturing techniques? Or is putting man in space on a permanent basis
justification enough?

If any of you are interested, please e-mail your responses to the address
below. I can't use the information without a full name, organization, and
position, so if you could include that information as well I'd be grateful.

Thank you in advance for any replies. If there's enough interest, I'll post
the completed article (probably in a month or two, after there's been
enough time for all the responses to get in and for me to write the
article).

Travis Butler                    Argue ideas, not sources.
University of Kansas, Lawrence   [e-mail]

------------------------------

Date:     Thu, 8 Feb 90 11:29:20 MST
From: [e-mail]
Subject:  SPACE Digest V11 #18

Ron Baalke:
 (or whoever else can answer my question...)
   You stated that during the Venus flyby, Galileo will pass 41 degrees south
of the equator.  Wouldn't such a manoeuver propel the craft slightly out of
the ecliptic plane??   Will the two rendezvous with Earth later on compensate
for this effect?
   Very interesting information at any rate...  Thanks for your postings!

Alan Pengelly:
   With regards to your question on how a gravity-assist manoeuver works,
the kinetic energy of the planet is transferred to that of the probe.  (not
the rotational angular momentum).  The manoeuver is often referred to as a
gravitational slingshot effect, for good reason.  When a craft approaches
the trailing edge of a planet, it accelerates towards the planet for a longer
period of time that it decelerates away.  This provides the velocity boost
required.
   A similar but opposite effect of the gravitational slingshot occurs if the
probe approaches the leading side of a planet.  In such a situation, the
acceleration toward the planet has a shorter period than its deceleration
away, and the probe slows down.  It is such a manouever that (I believe)
Galileo will use on approach to Jupiter so it is captured by the planet rather
than continue on its journey as the Voyagers did.
   Hope this helps... (and hope I understand the situation sufficiently so
as to have got it right! :-)
               Dan

------------------------------

Date: 8 Feb 90 17:25:56 GMT
From: mnetor!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Gravity Assist Mechanism

In article <[e-mail]> [e-mail] (alan pengelly) writes:
>Is there anybody out there that has a detailed understanding of gravity
>assist? We would greatly appreciate some enlightenment of this subject.

Gravity assist works like bouncing a ball off a car.  If the car is moving
toward you at high speed (kids, don't try this at home :-)), the ball will
come back a lot faster than you threw it.  The car will be slightly slowed
down in the process, although the disparity in mass is so large that the
effect probably won't be noticeable.

The Galileo Venus gravity assist, for example, accelerates Galileo at the
expense of very slightly decelerating Venus.
--
SVR4:  every feature you ever |     Henry Spencer at U of Toronto Zoology
wanted, and plenty you didn't.| uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date: 8 Feb 90 17:33:31 GMT
From: mnetor!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Galileo Update - 02/06/90 (Forwarded)

In article <[e-mail]> [e-mail] (Jon Binkley) writes:
>>[Galileo's main antenna] was not
>>designed to get too close to the Sun...
>
>When the craft makes its second Earth flyby, will it come close
>enough to the sun that they have to cover up the antenna again,
>or will it remain unfurlled for the rest of its journey?

I forget just when the unfurling happens, but the Venus-encounter leg
is the only part of the mission where there is a heating problem.  Even
in the original mission Galileo would have been in the neighborhood of
the Earth for a little while after launch, so it is designed to be okay
at Earth's distance from the Sun.  Problems occur only when closer in
than that; the first Earth encounter will end the thermally-tricky part
of the mission.
--
SVR4:  every feature you ever |     Henry Spencer at U of Toronto Zoology
wanted, and plenty you didn't.| uunet!attcan!utzoo!henry [e-mail]

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End of SPACE Digest V11 #25
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