Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v15_0/v15no006.txt

Internet Message Format | 1993-07-13 | 7KB

Date: Thu, 16 Jul 92 05:09:53
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #006
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu, 16 Jul 92       Volume 15 : Issue 006

Today's Topics:

                  Chemical unit operations in space
                 Interplanetary communications relays

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Date: Thu, 16 Jul 92 10:38 N
From: <[e-mail]>
Subject:

Could somebody tell me if there exists a LIST which deals with subjects, related
 to the HUBBLE-Space telescope?

Thank you very much!
Greetings,  Dirk Niestadt

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Date: 16 Jul 92 03:07:27 GMT
From: Jonathan Burns <[e-mail]>
Subject: Chemical unit operations in space
Newsgroups: rec.arts.sf.science,sci.space

In article <[e-mail]>
 [e-mail] (Thomas Koenig)writes:

> 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.

[...]

> 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?


Not much - splendidly practical and timely. But let me throw in a
twist or two.

    v^2 = r * a

    v = tangent velocity
    r = radius
    a = centripetal acceleration

Suppose our factory is swinging at the end of a long line. Kinetic
energy is about constant. Let out the line, gravity decreases; reel
in the line, gravity increases.

Vibration of the factory is either self-generated, or transmitted
along the line. I bet the problem of damping the latter is tractable.
Also, rotation about the line as axis is probably well controllable
with gyroscopes.

Perhaps micro-gravity has been over-emphasized. The big win might
be _variable_ gravity. Boiling, convection and sedimentation can
have the g-knob turned up or down. Seems very suitable for the
comet-slush extraction problem.

Can there be any problem in hanging a 100-meter column from a
10-kilometer cable? The longer the cable the more uniform the
gravity.

To turn the column over, let it out to maximum, turn it, pull it
in again. How easy is that to do on Earth for a 50-m tube?


I have a toy at home: two glass plates with water between, and two
grades of coloured sand. Turn it over and mix them up; let them
settle for a few minutes. Makes the prettiest marbled strata.


The mechanical handling problems are still brutal, and need a lot
of engineering practice in space itself. We might rethink robotics
with blood-flow and digestion as models, perhaps?


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jonathan Burns        |  you mean twenty years of doctor who serials
[e-mail]|  havent taught you not to trust characters
Computer Science Dept |  with names like intel & zilog
La Trobe University   |                          - archy's core dump
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

Date: 16 Jul 92 02:19:25 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Interplanetary communications relays
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:
>
>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).

True, but I would like to belabor the obvious for just a while longer.
A relay at Jupiter orbit for a Saturn mission would still require a
DSN type setup on Earth, *and* would need DSN style receiving and
*transmitting* capabilities on the relay sat. Instead of one difficult
communications path, you now have two only slightly easier paths spanning
the same distance. And the key element is now in space where support and
maintenance are difficult to impossible. Inverse square loss is a killer
because it doesn't take a lot of distance, on the interplanetary scale, to
make reception difficult. If it takes extraordinary reception equipment
anyway, it's often cheaper and more reliable to simply use one set of
extra-extraordinary equipment that can be maintained instead of two sets
of merely extraordinary equipment, one of which can't be serviced.

>*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?

Galileo was supposed to *be* the relay for the atmospheric probe, and

still will be at a lower data rate. It's once again a *reliability* issue.
The more complex the *required* system, the more likely it is to fail.
Additional complexity is a benefit only if it adds *redundancy* to the
system. That usually costs money.

Gary

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End of Space Digest Volume 15 : Issue 006
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