Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v15_0/v15no003.txt

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Date: Wed, 15 Jul 92 05:01:02
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Subject: Space Digest V15 #003
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Space Digest                Wed, 15 Jul 92       Volume 15 : Issue 003

Today's Topics:
                  Chemical unit operations in space
            Interplanetary communications relays (2 msgs)
                       Need Lunar closeup image
                     SSRT/SSTO Comments (1 of 2)

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Date: Wed, 15 Jul 1992 06:56:17 GMT
From: Thomas Koenig <[e-mail]>
Subject: Chemical unit operations in space
Newsgroups: rec.arts.sf.science,sci.space

I've been wondering a bit about how a chemical plant would look
like in space.

If you assume microgravity conditions, there are going to be severe
difficulties in separating two phases, which affects just about
everything.  Some examples:

- Distillation columns.  These rely on counterflow of gas and liquid
  and on a large surface between the two, both provided for by gravity
  and geometry (either plates, with bubbles rising/spray descending
  or packed columns with liquid drops coming down and gas going
  up).

- Liquid - liquid extraction also relies on gravity

- Gas / liquid chemical reactors (see above)

- Sedimentation, obviously, is not going to work

- After separating solids from liquid or gas, most conventional filters/
  centrifuges/whatever rely on the stuff actually falling down after-
  wards.

- Transportation of solids on conveyer belts is not going to work

- Getting solids out of a silo will require additional effort

- Boiling will also require an extra step of two - phase separation;
  the fact that bubbles will not rise on their own will also
  make things rather different.

... and so on... just take a look at Perry's Chemical Engineering
Handbook and figure which unit operations rely on gravity.

Most of the workarounds I can think of rely on centrifugal force, which
would wreck micro - g conditions, as anyone who has ever watched a
centrifuge vibrate on its foundations will probably tell you.

Using a different gravity level, such as on the moon, is also going to
affect some operations quite a lot.  All the experiments done here
on Earth have Earth's gravity constant wired into them; this is
particularly nasty in areas which have been just barely understood,
such as two - phase flow.

Conclusions: to build a chemical factory in orbit, build a rotating one
with about 10 m/s^2 of acceleration (but make it big, current distillation
columns are up to 50 m high); if you want to build something like that
on the moon, build a couple of universities there first and let the
people study things there for about a decade.

Anything wrong with the above?
--
Thomas Koenig, [e-mail], [e-mail]
The joy of engineering is to find a straight line on a double logarithmic
diagram.

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

Date: 15 Jul 92 02:11:01 GMT
From: John Roberts <[e-mail]>
Subject: Interplanetary communications relays
Newsgroups: sci.space

-From: [e-mail] (Gary Coffman)
-Subject: Re: Interplanetary communications relays
-Date: 13 Jul 92 14:51:24 GMT
-Organization: Gannett Technologies Group

-In article <[e-mail]> [e-mail] (John Roberts) writes:
->I realize that it's possible to get too ambitious on the capabilities of
->the relay probes, so that they would be too expensive for practical
->consideration, and making them too complex might reduce reliability.
->That's why such a proposal must be carefully considered, and why I haven't
->formally presented it yet. I would appreciate input from the readers of
->sci.space.

-You really should do some (simple) link budget calculations. To be
-useful, the relay satellites would require really large arrays with
-superb pointing accuracy and really sophisticated receiving equipment
-backed by a lot of computer processing power. Inverse square loss
-really is a killer over interplanetary distances.

I think I understand what you're saying, but now I disagree with the way
you say it. Inverse square loss isn't the main problem, otherwise the
relays would have a strong advantage. The problem is that the receivers/
transmitters on the ground are so much better than anything we can put in
space with current technology, that even with inverse square loss, space
relays can't compete over long distances. So if your scientific probe is at
Saturn, then a relay at the orbit of Jupiter can't communicate with it as
well as a DSN station, despite the much shorter distance. So we should drop
the idea of long-distance space relays until the technology improves, or
until such devices are going to be put out there anyway (i.e. for radio
astronomy).

That still leaves the possibility of close-up relays. As Nick says, if you
want to send a *lot* of scientific probes to Mars or Jupiter, then having a
relay in orbit around the planet could possibly save the expense of putting
a powerful high-gain system on every one of those probes. The decision on
whether to do it this way depends on the number of probes planned, the
relative cost, and the bandwidth needed. (I believe the Viking landers
used orbital relays, though they could also communicate directly.)

I wasn't really thinking of any spectacularly high bandwidth for a minimal
system - 10000-100000 bits per second would be fine, and 1000 bps would
perhaps still be useful.

*If* the decision had been made to send a relay probe to Jupiter to help
Galileo, what sort of bandwidth might we have reasonably expected?

And what bandwidth can Galileo get over the low gain antenna during an Earth
flyby?

John Roberts
[e-mail]

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

Date: 15 Jul 92 04:01:43 GMT
From: John Roberts <[e-mail]>
Subject: Interplanetary communications relays
Newsgroups: sci.space

-From: [e-mail] (Nick Szabo)
-Subject: Re: Interplanetary communications relays
-Date: 14 Jul 92 08:59:49 GMT

-Interesting ideas; some points to ponder:

-* The data still has to come down to Earth.  The space-based antenna
-  only reduces the requirement for ground facilities, it does not
-  replace them.  If the relay is in Earth orbit the ground receiver
-  can be small, and the relay provides better scheduling flexibility
-  with a 24-hour view period.  If the relay is itself in deep space the
-  savings comes primarily from operations with large numbers of space
-  probes (eg Martian comsat for rover network); the ground antenna is
-  still constrained to c. 10 hour view periods.

I hadn't thought of that application - interesting point.

-* Good deep-space relay locations may be Sun/Earth LaGrange points,
-  which are much closer to planets in opposition.

That reminds me - I saw a good article on natural objects in LaGrangian
orbits - their behavior isn't exactly what one might think. I'll try to
find the article again, but it may take a long time.

-* The main benefit comes when we can deploy or assemble large
-  (eg 70-100m) antennas in orbit for less cost than building
-  gravity-constrained receivers on the ground.

Definitely!

As long as we can dream about the future, what would be *really* handy
is a vast array of relay spacecraft, arranged in concentric rings,
and linked together in an enormous switching network! (Very useful for
radio astronomy, too.) All we have to do is get the cost down to a few
million dollars per spacecraft (mass production might help), or cancel the
next three or four savings and loan scandals. :-)  :-)

John Roberts
[e-mail]

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

Date: 15 Jul 92 04:08:17 GMT
From: "Guy B. Purcell" <[e-mail]>
Subject: Need Lunar closeup image
Newsgroups: sci.space

Hi,
    A friend of mine is doing a thesis on image processing and needs
an image of good relief to test his ideas on.  He thinks one of the Apollo
Lunar cluseups ought to just do the trick.  I've looked on ames.arc.nasa.gov,
but the image names aren't very helpful.  If someone knows from where I
could ftp such an image in some standard format, please let me know (or
just email the image if you have it -- it can be small since he can't
display more than 256x256 in high resolution mode).  Thanks.

Guy ([e-mail])

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

Date: Tue, 14 Jul 92 17:49:34 PST
From: Michael Wallis <[e-mail]>
Subject: SSRT/SSTO Comments (1 of 2)
Newsgroups: sci.space

[e-mail] (Edward V. Wright) writes:

> A sucessful flight of DCX will repudiate the report, but it's too
> early to say if that will make much difference.  The accomplishments
> of engineers who actually bend the metal and make it work often account
> for far less than the opinions of the professional "analysts" who have
> often never built any hardware in their lives but know their way around
> inside Washington.

Couldn't have said it better. Hope it happens that way.

------------------------------------------------------------------------------
[e-mail] - Michael Wallis

"College isn't the place to go for ideas." - HELEN KELLER

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

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Newsgroups: sci.space
Subject: Documentation/instructions
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Date: 15 Jul 92 01:51:02 GMT
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-From: [e-mail] (Gary Coffman)
-Subject: Re: exploding NASA equipment
-Date: 13 Jul 92 14:31:39 GMT
-Organization: Gannett Technologies Group

-In article <[e-mail]> [e-mail] (John Roberts) writes:
->I've recently been trying to put several times the normal amount of
->documentation into my designs - it's already started to pay off.

-I strongly applaud your design documentation efforts. I would note,
-however, that the cardinal rule of electronics is "When all else
-fails, read the instructions." The requirement for *operating*
-instructions should be minimal in a well designed system.

-I noted with some disgust the necessity of the ground based investigator
-for DPM having to repeatedly walk the payload specialist through the
-baroque touch screen menus of the experiment.

A good point. Even for a complicated piece of equipment, there should be a
simple set of instructions to use a "default setting" that will at least do
the basic task. For more complex uses, there should be plenty of examples,
well-explained. If touch screens are really necessary, they should be as
self-explanatory as possible (even to the point of having help menus that are
really helpful).

We have a logic analyzer that came with about a foot and a half of
instructions, and you have to read most of them even for a very simple
application. Naturally, nobody uses it any more than absolutely necessary.
(We didn't select it, by the way - we inherited it. Having it around has
made us *very* picky about the complexity of any new equipment we buy.)

John Roberts
[e-mail]

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

End of Space Digest Volume 15 : Issue 003
------------------------------