Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v13_2/v13_221.txt

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Subject: SPACE Digest V13 #221

SPACE Digest                                     Volume 13 : Issue 221

Today's Topics:
              Magellan Update - 03/01/91
           Re: chimps in space -- question
             Re: Terraforming, sun shield
          Re: NASA Prediction Bulletins ftp site ??
         Re: Whither Lunar Observer in FY92?
          Thrust  (was Re: Terraforming, sun shield)
       Intro and request for comments on sci.space FAQ
                  Re: Thrust

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
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----------------------------------------------------------------------

Date: 2 Mar 91 01:08:36 GMT
From: elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov![e-mail]  (Ron Baalke)
Subject: Magellan Update - 03/01/91


                         MAGELLAN STATUS REPORT
                            March 1, 1991

     The Magellan spacecraft and its radar system are performing nominally.
All STARCALS (star calibrations) and DESATS (desaturations) during the past
24 hours were successful, with the attitude updates averaging less than 0.04
degree.

     The command sequence update being sent to the spacecraft later today
will remove the 10 minute early turn from mapping and restore the full 37
minute mapping swaths.  DMS-A (Data Management Subsystem) Test #3, the playback
of tape recorded data patterns, has been completed and the playbacks are being
studied.

     The spacecraft is now in a period of periapsis occultations where the
orbit passes through the shadow of Venus during the low part of the orbit.
This results in added cooling for the spacecraft components.  When the
periapsis occultations end in mid-April, however, a temperature control
strategy will have to be implemented again.

     The strategy which will be used is called "Two Hide," denoting two 8 to
12 minute segments in each orbit when the spacecraft is positioned to hide the
electronic compartments in the shade of the High Gain Antenna.   It is
expected that this strategy will require a period of four weeks at the end of
the primary mission.  Since the time in hiding will deduct from the mapping
pass, the strategy will result in image losses amounting to about 2% of the
surface area of Venus.
      ___    _____     ___
     /_ /|  /____/ \  /_ /|      Ron Baalke         | [e-mail]
     | | | |  __ \ /| | | |      Jet Propulsion Lab | Is it mind over matter,
  ___| | | | |__) |/  | | |___   M/S 301-355        | or matter over mind?
 /___| | | |  ___/    | |/__ /|  Pasadena, CA 91109 | Never mind.
 |_____|/  |_|/       |_____|/                      | It doesn't matter.

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

Date: 1 Mar 91 19:08:36 GMT
From: uokmax![e-mail]
Subject: Re: chimps in space -- question

[e-mail] (Eddie A. McCreary) writes:

>In article <[e-mail]>, [e-mail] (Elijah Millgram) writes:
>> Can anyone tell me about instances of chimpanzees
>> being sent into space (name and date of mission,
>> purpose and results of mission, name of chimp, etc.)?
>>
>> And a subsidiary question:  does anyone know of movies
>> in which chimps are sent into space?

>Here you go...

>Mission        Date    Occupant    Duration    Objective
>MA-5        12/29/61 Eros (C)    3:20:59        Three orbit test of
>                            life support system

     I always thought his name was Enos...

>Also, Sputnik 2 carried two dogs, Stelka and Belka and Sputnik 3 carried
>another two dogs, Pchelka and Mushka.  Theses were launched on Aug. 20 and
>Dec 1, 1957 respectively.

     Uh... Sputnik 1 wasn't launched until October 4, 1957, so Sputnik 2
was some time after.  I don't have a source with the date handy.  Also,
Sputnik 2 carried only one dog.  I think her original given name was
Strelka, but she has since become known almost universally as Laika.
Sputnik 3 was a scientific instrument platform and carried no dogs.
--------
[e-mail]

"I'm with you, LEM, though it's a shame that it had to be you.
 The mother ship is just a blip from your train made for two.
 I'm with you, boys, so please employ just a little extra care.
 It's on my mind, I'm left behind when I should have been there."
                      --Jethro Tull, "For Michael Collins, Jeffrey, and Me"

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

Date: 28 Feb 91 18:36:06 GMT
From: mcsun!ukc!tcdcs!maths.tcd.ie![e-mail]  (Fergal Toomey)
Subject: Re: Terraforming, sun shield

[e-mail] (Henry Spencer) writes:

>The real problem with terraforming Venus, far more significant
>than the shortage of water or the nearness to the Sun, is the need to get
>rid of most of the atmosphere somehow.

Solving the water problem, creating large oceans along the way, would also
at least partly solve the atmosphere problem, since water absorbs large
amounts of O2 and CO2. In fact, the balance between atmospheric and oceanic
CO2 on Earth is believed to be responsible for many of the long term climate
variations.

>--
>"Read the OSI protocol specifications?  | Henry Spencer @ U of Toronto Zoology
>I can't even *lift* them!"              |  [e-mail]  utzoo!henry

Fergal Toomey. TCD.

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

Date: 1 Mar 91 20:52:46 GMT
From: sdd.hp.com!caen!sol.ctr.columbia.edu!src.honeywell.com!msi.umn.edu!cs.umn.edu!uc!nachos.SSESCO.com![e-mail]  (Chris Elmquist)
Subject: Re: NASA Prediction Bulletins ftp site ??

In article <[e-mail]> [e-mail] (Steve Masters) writes:
>
>Can someone please send me (or post here) an ftp site for the NASA orbital
>prediction bulletins.  I realize they are posted here periodically but I
>would also like to know an ftp site if I need a copy quickly.  I tried
>"nachos.sseco.com" today via the Princeton FTP server but the site was
>unknown.  I have retrieved the bulletins from this site in the past.

As far as I know-- we are still on the net (at least I hope we are!!)
Perhaps you dropped an 's' in our name.  It's  SSESCO.  So, the
system name is   nachos.ssesco.com
and the address is   [192.55.187.18]

I posted Kelso's elements last Friday and expect to again this
evening.

Let me know if you are still having trouble.

Chris

--
Chris Elmquist, N0JCF
Internet: [e-mail]
   AMPRN: [e-mail]
 BellNet: [phone]

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

Date: Fri, 1 Mar 91 08:46:08 -0500
From: "Allen W. Sherzer" <[e-mail]>
Subject: Re: Whither Lunar Observer in FY92?
Newsgroups: sci.space
Cc:

In article <[e-mail]>:
>>If LLNL gets the go ahead within the next two years they just might have
>>a base on the moon before Lunar Observer is even launched.

>And we'll all enjoy the nice exports of green cheese.  :-)

Why Nick, I suprised at you. Don't you know that the moon isn't made
of green cheese?  The manned space program established that over 20
years ago. Looks like the unmanned results you are looking at aren't
very good. :-)

  Allen
--
+-----------------------------------------------------------------------------+
|Allen Sherzer |A MESSAGE FROM THE ANTI-WAR MOVEMENT TO THE PEOPLE OF KUWAIT: |
|[e-mail]   |       "If rape is inevitable, enjoy it!"                     |
+-----------------------------------------------------------------------------+

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

Date: 1 Mar 91 15:58:06 GMT
From: agate!bionet!uwm.edu!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!aurora.physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Thrust  (was Re: Terraforming, sun shield)

In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>
>But who says habitats have to be space slums.  Once a society becomes
>wealthy enough (and I have a feeling that self-replicating machinery, even
>if it was controlled by governments and corporations, would make societies
>very wealthy in terms of material, and fusion and solar and anti-matter
>power will make them wealthy in terms of energy) habitats could be spacious
>and pleasant, truly microworlds, instead of "habitats."
>
   Just a quick note. Antimatter is not a "power" system. It's a storage
system. You might just as well say that we'll have a lot more
electrical energy now that we can make such efficient batteries.

>I
>have heard that fusion and anti-matter are good candidates, because of
>the high Isp, but that they suffer from "low thrust."
>
>My questions are as follows.  1) What is meant by "low thrust"?  One
>tenth of a gee as the max. you could get?  Less?  2) With this "low
>thrust," what kind of Isp are you talking about for fusion and/or
>antimatter drives?  3) Assuming that the basic laws of the universe
>are unchanged, but that we have extensive technological advances
>(the stories are set in the far future), could the problem of low
>thrust be solved--it seems to me that "low thrust" simply means a
>lousy efficiency of the engine, you need a big engine to get a certain
>amount of thrust, which means you have that much more mass to push
>around.
>
   Low thrust means that the actual force in Newtons exerted by the
engine is low compared to other engines. Isp is essentially a measure of
the ratio of the momentum of propellant to its mass. A high Isp implies
that you're throwing things out very quickly.
   So, you have situations like this:
a) low thrust, low Isp       A catapult on a skateboard
b) high thrust, low Isp      A modern chemical rocket
c) low thrust, high Isp      An ion engine, solar sail, etc.
d) high thrust, high Isp     A futuristic fusion or
                             antimatter/propellant drive.
   Most modern systems with very high exhaust velocity don't throw much
matter out per second. An ion engine has very high exhaust velocity, but
a 1 ton engine/powerplant can't pour out a ton of propellant per second.
A high Isp, low thrust engine can deliver a very large delta-v, but it
takes a lot longer than a low Isp, high thrust engine. The low Isp
engine, though, uses a lot more propellant to achieve the same delta-v.
A solar sail, for example, has an infinite Isp (it carries no
propellant), but it has a thrust limited to no more than 1E-5 Newtons
per square metre of sail area at Earth orbit, and that in a
configuration which is not really useful for interplanetary
trajectories. Given long enough, a solar sail can put itself into any
solar orbit, unlike many chemical launchers. No chemical launcher
nowadays could put ten tons into a polar solar orbit. A solar sail could
do it, but it might take decades.
   It's not really a question of efficiency, so much as engine capacity.
A high Isp engine can be very efficient, but at the moment it just
doesn't process enough matter per second to move very quickly. By
comparison, you can imagine that I make a car engine which burns less
than a litre of gasoline per hundred kilometres it travels, but is, by
its design, incapable of burning fuel faster than one cubic centimetre
per hour. It's very efficient, but you won't win any drag races in it.
   There are no physical laws which prevent an ion or fusion engine from
achieving much higher thrusts. There are also no physical laws which
forbid a hydroelectric dam from weighing one hundredth of what they do
now. It's an engineering challenge.


--
 Christopher Neufeld....Just a graduate student  | Note: new host.
 [e-mail]    Ad astra! | helios will still
 cneufeld@{pnet91,pro-cco}.cts.com               | forward my mail to
 "Don't edit reality for the sake of simplicity" | me on aurora.

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

Date: 1 Mar 91 18:45:17 GMT
From: borg!vangogh![e-mail]
Subject: Intro and request for comments on sci.space FAQ


    Inspired by Eugene Miya's suggestion, I've been gathering and editing
material for new Frequently Asked Questions, and a variety of material that
is not so frequently asked, but is (IMO) worth preserving. Eugene is in the
process of handing his FAQ material over to me for inclusion in my list, as
he is inactive on sci.space at present. It will be included in the next
revision, and help keep down the bewildering variety of informative
postings.

    I was planning on doing some more editing work, but there seems to be an
near blizzard of requests for databases and such recently, so I'm posting
the draft copy now. I'd appreciate assistance from net readers offering
corrections, advice, new material, etc. for the FAQ list.

    Because a number of these questions are relevant to both sci.space and
sci.astro, I'm crossposting the FAQ to both lists and expect to continue
doing so unless there's significant objection.

    The FAQ size is too large, and I expect that many of the entries will be
reduced to pointers to longer entries available from some net site, probably
Ames. The Ames email server has been having some problems recently, but
Peter Yee tells me he's working on it.

    The FAQ follows this posting. Please send all comments by *email* to
[e-mail] - don't post them back to the net.

    Thanks!
--
    Jon Leech ([e-mail])    __@/
    ``My goodness,'' thought Milo, ``everybody is so terribly sensitive
      about the thing they know best.''
      - Norman Juster, _The Phantom Tollbooth_

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

Date: Fri, 1 Mar 91 18:46:03 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Re: Thrust


>From: [e-mail] (Christopher Neufeld)
>Subject: Thrust  (was Re: Terraforming, sun shield)
>Date: 1 Mar 91 15:58:06 GMT
>Organization: University of Toronto Physics/Astronomy/CITA

>A high Isp, low thrust engine can deliver a very large delta-v, but it
>takes a lot longer than a low Isp, high thrust engine. The low Isp
>engine, though, uses a lot more propellant to achieve the same delta-v.

True. (Assuming, of course, that you are not in a situation such as launch
from a planet, where the actual value of the thrust is critical.)

>A solar sail, for example, has an infinite Isp (it carries no
>propellant),

I'm not sure how a solar sail should be classified, but this statement is
not true for a generic photon drive. For such a drive, Isp is equal to c / g,
or about 30 million. [ Isp = thrust / (g * (mass equivalent propellant flow))
 = (E / c) / (g * (E / c^2)), where E = energy, c = speed of light, g =
acceleration equivalent to one earth gravity.] Since a traditional shiny
solar sail gets up to double the kick from each photon, perhaps for some
calculations it would be useful to double the above figure.

The wonderful thing about solar sails is that if you are willing to wait
long enough, the total energy available for maneuvers is unlimited.

>but it has a thrust limited to no more than 1E-5 Newtons
>per square metre of sail area at Earth orbit, and that in a
>configuration which is not really useful for interplanetary
>trajectories. Given long enough, a solar sail can put itself into any
>solar orbit, unlike many chemical launchers. No chemical launcher
>nowadays could put ten tons into a polar solar orbit. A solar sail could
>do it, but it might take decades.

>   It's not really a question of efficiency, so much as engine capacity.
>A high Isp engine can be very efficient, but at the moment it just
>doesn't process enough matter per second to move very quickly.

High-Isp engines are very efficient in their use of reaction mass. They are
by definition very *inefficient* in their use of energy (in many cases only
a tiny fraction of the efficiency of a typical chemical rocket), so if
you're going to run one, you'd better have plenty of energy available. In
practical terms, that means an exotic power source such as sunlight, a
nuclear reactor (I expect RTGs would not really be practical, due to lower
power density), fusion, or antimatter.

>   Most modern systems with very high exhaust velocity don't throw much
>matter out per second. An ion engine has very high exhaust velocity, but
>a 1 ton engine/powerplant can't pour out a ton of propellant per second.

That's because of trouble handling the vast amounts of power that would be
required due to the very low energy efficiency - cooling becomes impractical,
engines melt or fly apart, and so on. You can get around this by being patient,
and using power at a reasonable rate over the course of weeks to years, or
you can make the choice not to "handle" the power at all - a series of
nuclear explosions in open space, reacting against a suitable plate attached
to the ship has been proposed for trips to nearby stars. :-)

Please don't take any of this to imply that I don't favor the development
of high-Isp drives - they're great, as long as you recognize their limitations
and use them for what they do well. I'm particularly intrigued by the use
of solar power to run an ion drive - has this been studied?

> Christopher Neufeld....Just a graduate student  | Note: new host.
> [e-mail]    Ad astra! | helios will still
> cneufeld@{pnet91,pro-cco}.cts.com               | forward my mail to
> "Don't edit reality for the sake of simplicity" | me on aurora.

       John Roberts
       [e-mail]

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

End of SPACE Digest V13 #221
*******************