Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_1/V10_180.TXT

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Subject: SPACE Digest V10 #180

SPACE Digest                                     Volume 10 : Issue 180

Today's Topics:
         NASA Headline News for 10/24/89 (Forwarded)
    Re: Balloon Launch attempt of a High Power Rocket (40 Miles).
             Re: PowerSat Options
             Re: Exhaust velocity
             Re: Galileo Schedule
           Re: "Terraforming", so-called...
           Re: "Terraforming", so-called...
           Re: "Terraforming", so-called...
             Re: PowerSat Options
             Re: PowerSat Options
    Re: Balloon Launch attempt of a High Power Rocket (40 Miles).
             Re: PowerSat Options
             Re: Galileo boost from Venus
----------------------------------------------------------------------

Date: 24 Oct 89 18:24:42 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: NASA Headline News for 10/24/89 (Forwarded)

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Tuesday, Oct. 24, 1989                       Audio:  202/755-1788
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This is NASA Headline News for Tuesday, October 24th......

The space shuttle Atlantis and its crew...Commander Donald
Williams, Co-pilot Michael McCulley and Franklin Chang-diaz,
Shannon Lucid and Ellen Baker...landed safely yesterday morning
at Edwards Air Force Base.  The landing occurred two orbits
earlier than originally planned because of predicted high winds
on the desert lake bed later in the afternoon.

William Lenoir, Acting Associate Administrator for Space Flight,
said "the vehicle looks amazingly clean.  We did not see, with a
quick inspection, any significant tile damage--a little nick here
and a nick there."

The schedule calls for Atlantis to ride back to Kennedy Space
Center aboard the 747-carrier transport jet over the weekend.


Meanwhile, technicians at KSC plan to roll out the space shuttle
Discovery to launch pad 39-B, beginning at 12:01 A.M. Wednesday.
Its crew...Commander Frederick Gregory, Co-pilot John Blaha and
Manley Carter, Story Musgrave and Kathryn Thornton...plan to fly
to KSC this weekend, and board the orbiter on Monday for a
dress-rehearsal countdown at the launch pad.  Discovery is
scheduled to fly a classified DoD mission later in November.

The schedule currently calls for the orbiter Columbia to be moved
to launch pad 39-A on November 22, for a planned night time
launch around December 18.  Its crew...Commander Daniel
Brandenstein, Co-pilot James Weatherbee and Bonnie Dunbar, David
Low and Marsha Ivins plan to spend 10-days in orbit to deploy a
military communications satellite and retrieve the Long Duration
Exposure Facility (LDEF).

"The next two launches look like they're pretty much on
schedule," Lenoir said.  "There's a very good likelihood that the
next two missions will be in the air over the two upcoming
holidays, Thanksgiving and Christmas."



                      *************








-----------------------------------------------------------------
Here's the broadcast schedule for public affairs events on NASA
Select television.  All times are Eastern.

Thursday, Oct. 26......

     11:30 A.M.        NASA Update will be transmitted.

All events and times are subject to change without notice.
-----------------------------------------------------------------
These reports are filed daily, Monday through Friday, at 12 noon,
Eastern time.
-----------------------------------------------------------------
A service of the Internal Communications Branch (LPC), NASA
Headquarters, Washington, D.C.

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

Date: 24 Oct 89 18:18:58 GMT
From: cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!utgpu!watmath!looking![e-mail]  (Brad Templeton)
Subject: Re: Balloon Launch attempt of a High Power Rocket (40 Miles).

But what good is a baloon rocket launch?  When it comes to getting into
orbit, 90% of the problem is gaining horizontal velocity, not going through
the atmosphere or gaining altitude.
--
Brad Templeton, ClariNet Communications Corp. -- Waterloo, Ontario 519/884-7473

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

Date: 25 Oct 89 05:28:00 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: PowerSat Options

The two sexiest powersat approaches I'd heard of last time I pinched
myself awake long enough to sit through a discussion on the topic, were
maser pumping to a ground antenna field and superfuel generation
on-orbit for batch re-entry to earth.  I know there were frightful
environmental concerns associated with all those masers zorching down
through the atmosphere at an economically viable number of locations.
Chemical fuel delivery was more exotic but bore the potential for a
clean cycle.

I remain concerned that regardless of how lily-white the generation
methods, if we keep increasing power generation and consumption on this
ball we'll melt the icecaps and drown in waste heat.
--
"Take off your engineering hat   | "The filter has      | Tom Neff
and put on your management hat." | discreting sources." | [e-mail]

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

Date: 24 Oct 89 19:08:00 GMT
From: telesoft![e-mail]  (Roger Arnold @prodigal)
Subject: Re: Exhaust velocity

[e-mail] (Conor O'Neill) writes:
> [e-mail] (Henry Spencer) writes:
> >In general, correct.  For one thing, it's easier to build solid motors
> >in large sizes (i.e. high thrusts).  For another, the average molecular
> >weight of the exhaust is higher, which is bad for getting maximum velocity
> >but good for getting maximum thrust.
>
> I've seen this said before (many times) but never with a simple explanation.
> My school physics seemed to imply that it is exhaust momentum which matters,
> not simply velocity nor molecular weight. Could someone please elaborate.
>
> --
> Conor O'Neill, Software Group, INMOS Ltd., UK.
> UK: [e-mail]        US: [e-mail]

You're correct that it's exhaust momentum which matters.  Momentum is
mass times velocity; energy, however, is proportional to mass times
velocity *squared*.  For a given amount of power (energy per second),
you can increase the thrust (momentum per second) by increasing the
mass flow and reducing the exhaust velocity.

The tradeoff between thrust and exhaust velocity is most relevant in
optimizing the performance of ion engines for interplanetary missions.
In that case, you're dealing with an external power source, as opposed
to using the energy in the fuel itself.  Henry's example for solid
fuel rockets is a little misleading.  Power, in a solid fuel rocket,
is a function of the burn rate, and that's controlled by things like
the fuel composition, the exposed surface area, and the grain size.
It's pretty easy to design for the maximum burn rate, and hence thrust,
that the rocket casings will take.  There's no reason to deliberately
reduce exhaust velocity in a solid fuel rocket; you want whatever the
most energetic combination of solid fuel and oxidizer you can manage
to develop will deliver.

- Roger Arnold                ucsd!telesoft!roger

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

Date: 25 Oct 89 15:36:00 GMT
From: gem.mps.ohio-state.edu!rpi!plato.rdrc.rpi.edu![e-mail]  (George Kyriazis)
Subject: Re: Galileo Schedule

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Rod Stephens) writes:
>>What is "Venus Data Playback?" Why is it so long after the Venus flyby?
>
>Galileo can't deploy its high-gain antenna until it's far enough out from
>the Sun to get rid of its sunshades.  (Remember that Galileo was designed
>to go straight Earth->Jupiter, and wasn't built to go in closer to the Sun.)
>And the data rate from the low-gain antennas isn't anything wonderful at
>long range......

My question is:  How much memory does Galileo have?  If it plays back
the pictures from Venus after it gets rid of its influence, it must
be some time, and assuming that it takes several pictures, where does
it store all this information?

That brings the question of the resolution of the pictures, and how
many primary colors (if any) are there for each picture.  Can anybody
answer that?


  George Kyriazis
  [e-mail]
  [e-mail]
------------------------------

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

Date: 25 Oct 89 04:30:08 GMT
From: munnari.oz.au!murtoa.cs.mu.oz.au!ditmela!yarra!melba![e-mail]  (Gregory N. Bond)
Subject: Re: "Terraforming", so-called...

In article <[e-mail]> [e-mail] (Henry Spencer) writes:

   Unfortunately, it's difficult.  Even if we could wave a magic wand and
   turn all of Venus's CO2 into oxygen, there is far too *much* of it.  We
   have to get rid of about 99% of the atmosphere somehow, perhaps by
   reacting the oxygen with iron extracted from rocks.  (The surface rock
   itself would probably absorb some, once free oxygen became available in
   the atmosphere, but almost certainly not enough.)

Can anyone explain why Venus, which is smaller and with weaker gravity
than Earth, has an atmosphere 100x more dense?  Why didn't it just
escape?  (Conversly, why is Earth's atmosphere so thin?)

Greg.
--
Gregory Bond, Burdett Buckeridge & Young Ltd, Melbourne, Australia
Internet: [e-mail]    non-MX: [e-mail]
Uucp: {uunet,pyramid,ubc-cs,ukc,mcvax,prlb2,nttlab...}!munnari!melba.bby.oz!gnb

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

Date: 25 Oct 89 13:08:13 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: "Terraforming", so-called...

In article <[e-mail]> [e-mail] (Gregory N. Bond) writes:

>Can anyone explain why Venus, which is smaller and with weaker gravity
>than Earth, has an atmosphere 100x more dense?  Why didn't it just
>escape?  (Conversly, why is Earth's atmosphere so thin?)

The earth has as much carbon as Venus, it's just locked up in carbonate
rocks.  However, the reaction

    silicate + CO2 --> carbonate + SiO2

while exothermic, requires liquid water to proceed.  On Earth, I
understand that the presence of life also accelerates the reaction.

    Paul F. Dietz
    [e-mail]

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

Date: 25 Oct 89 14:09:10 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: "Terraforming", so-called...

In article <[e-mail]> [e-mail] (Gregory N. Bond) writes:
>Can anyone explain why Venus, which is smaller and with weaker gravity
>than Earth, has an atmosphere 100x more dense?  Why didn't it just
>escape?  (Conversly, why is Earth's atmosphere so thin?)

We lost ours courtesy an ecosphere and a big moon.  Venus had no such luck.

--
Knowing *when* to optimize is just   >>>/     Tom Neff
  as important as knowing *how*.       /<<<   [e-mail]

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

Date: 25 Oct 89 15:12:58 GMT
From: cs.utexas.edu![e-mail]  (Donald A. Varvel)
Subject: Re: PowerSat Options

In article <[e-mail]> [e-mail] (S Schaper) writes:
>The CPSU would take a dim view of a 15 megawatt laser in orbit. So would the
>UN. Actually a maser would be better, as it should penetrate cloud cover, I
>think, but it too, has that weapons potential

Actually, anything that has weapons potential also has at least minor
environmental effects.  The earliest proposals suggested microwave
transmission at a power density that would hardly increase the body
temperature of a bird flying through it, and that would pose no risk
to stray airplanes.  Any proposals for increasing the transmitted
power density should take that into consideration.

Last time I looked into this matter, which was admittedly several
years ago, transmission to the ground wasn't viewed as a major problem.
Putting the necessary tonnage in Clarke orbit was.  Solutions would
take the form of more efficient conversion of solar energy and lower
launch costs.

-- Don Varvel ([e-mail])

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

Date: 25 Oct 89 07:45:10 GMT
From: crash!orbit!pnet51![e-mail]  (S Schaper)
Subject: Re: PowerSat Options

The CPSU would take a dim view of a 15 megawatt laser in orbit. So would the
UN. Actually a maser would be better, as it should penetrate cloud cover, I
think, but it too, has that weapons potential

UUCP: {amdahl!bungia, uunet!rosevax, chinet, killer}!orbit!pnet51!schaper
ARPA: crash!orbit!pnet51![e-mail]
INET: [e-mail]

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

Date: 25 Oct 89 12:57:50 GMT
From: ispi![e-mail]  (Jonathan Bayer)
Subject: Re: Balloon Launch attempt of a High Power Rocket (40 Miles).

[e-mail] (Brad Templeton) writes:

>But what good is a baloon rocket launch?  When it comes to getting into
>orbit, 90% of the problem is gaining horizontal velocity, not going through
>the atmosphere or gaining altitude.


Altitude.   The balloon allows the rocket to attain a higher altitude
(which is necessary for certain scientific measurements).


JB
--
Jonathan Bayer        Intelligent Software Products, Inc.
[phone]        500 Oakwood Ave.
[e-mail]        Roselle Park, NJ   07204

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

Date: 25 Oct 89 13:14:05 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: PowerSat Options

In article <[e-mail]> [e-mail] (S Schaper) writes:

>The CPSU would take a dim view of a 15 megawatt laser in orbit. So would the
>UN. Actually a maser would be better, as it should penetrate cloud cover, I
>think, but it too, has that weapons potential

A powersat's aperture would be small, so it could not form an intense
beam at the earth's surface.  The power density would be far lower
than in BMD applications.  This weapons application stuff is a canard.

    Paul F. Dietz
    [e-mail]

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

Date: 25 Oct 89 12:28:33 GMT
From: aoa![e-mail]  (Carl Witthoft)
Subject: Re: Galileo boost from Venus

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
[was about gaining velocity slingshotting around venus...]
>
>I'm indebted to David Navas for this analogy:  if you bounce a ball off a
>car coming towards you at 60 MPH, it comes back a lot harder than if you
>bounce it off a stationary car.  Even though, from inside the car, either
>way the ball bounces back at about the velocity it arrived at.
And, just to avoid silly comebacks like the one I had for 1.5 seconds :=),
this only applies when the momentum of the ball is tiny
compared to the momentum of the car.  That's why it makes a difference
whether you swing a baseball bat (momentum on the order of ball) with
continuous application for force or just "swipe" at the ball. The
ball, or satellite, goes faster so long as it receives rather than
donating momentum.


--
Alix' Dad ( Carl Witthoft @ Adaptive Optics Associates)
{harvard,ima}!bbn!aoa!carl
54 CambridgePark Drive, Cambridge,MA 02140 617-864-0201
"disclaimer? I'm not a doctor, but I do have a Master's Degree in Science!"

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

End of SPACE Digest V10 #180
*******************