Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_1/V11_138.TXT

Internet Message Format | 1991-07-08 | 18KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/8Zyo4I200VcJQ7105C>;
          Mon, 12 Mar 90 01:26:28 -0500 (EST)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Mon, 12 Mar 90 01:26:01 -0500 (EST)
Subject: SPACE Digest V11 #138

SPACE Digest                                     Volume 11 : Issue 138

Today's Topics:
            Re: Artificial Gravity
           Re: Solar System Questions from a Novice
              Space Probe Communications
              Artificial Gravity
           Re: Artificial Gravity rephrased
          Re: Spacecraft drives and fuel efficiency
              Re: Challenger Last Words
         Information on planetary atmospheres
             Artificial Gravity rephrased
              Re: Saturn's Rings
                  Re: SR-71
----------------------------------------------------------------------

Date: 12 Mar 90 00:09:37 GMT
From: cs.utexas.edu!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Artificial Gravity

In article <[e-mail]> [e-mail] (Zaphod Beeblebrox) writes:
>How realistic is the idea that if a spaceship had a section revolving that
>the astronauts could just hang around in there and experience 'gravity'
>i.e. like in the movie 2001. . .wouldn't the spinning section have to keep
>accelerating to have the this effect???
>
   But it does keep accelerating. Remember, acceleration is the time rate
of change of the velocity vector (speed or direction or both). A point on
the rim of a hoop of radius 'r' rotating at a constant angular velocity 'w'
experiences an acceleration of r*w*w. This is a measure of the force needed
to keep pushing the object in a circular path, when it would really rather
move in a straight line.
   If you make a space ship with a large circular cross-section, and stand
on the inside surface after it has been spun up, your body would like to
move straight out through the skin of the space ship, but it can't. Your
feet can't pass through the ship, which exerts a force on your feet. The
physiological effect of this rotational gravity is almost the same as that
of a planet. The larger the radius of the cylinder, the closer it will
approximate a planet's gravity field.


--
 Christopher Neufeld....Just a graduate student  | "I always think there's
 [e-mail]              | a band."
 [e-mail]                    |   Prof. Harold Hill
 "Don't edit reality for the sake of simplicity" |   (The Music Man)

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

Date: 12 Mar 90 00:29:22 GMT
From: mailrus!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Solar System Questions from a Novice

In article <[e-mail]> [e-mail] (Lori + 8/9) writes:
>
>I just bought an old poster of our solar system from a swap meet last
>weekend, and some of the facts on it are really intriguing.
>
   It's got some out of date information, must be quite old.

>Can someone answer a few questions about Mercury?  Its temperature is
>hundreds of degrees F on the sunny side, and (fewer) hundreds of degrees F
>below zero on the dark side.  The poster also says that it 88 days to
>rotate.  What would Mercury's climate be like if it rotated as fast
>as the earth?  How fast would it have to rotate to produce a moderate
>or life-supporting climate, at least at certain latitudes (longitudes?)?
>
   No. This used to be assumed, because it was thought that the extremely
short distance to the Sun would force Mercury to be tidally locked to face
the Sun. Mercury's sidereal day is 58.6462 Earth days. The climate on
Mercury would be too harsh for any Earth-based life to exist no matter what
the rotational rate of the planet.

>Also, the earth's atmosphere is very different from all the other
>planets.  (In fact, they all seem unique.)  Could someone explain why?
>
   This is a long question. For the inner planets, Mercury has essentially
no atmosphere, being too light to hold onto one. Venus has a very heavy
atmosphere consisting of 96% carbon dioxide, and is likely the result of a
lack of water and an absence of life. Earth's atmosphere evolved from
reducing to oxidizing when early anaerobic bacteria produced oxygen as a
waste product (and poisoned the planet against them). Mars was also too
light to hold onto its atmosphere, though evidence is that it had a denser
atmosphere earlier in its history.
   To get a more complete answer to this question, look for an appropriate
book in your library. I'll post a reference as soon as I get to my
bibliographic notes.

>Are there dual-sun solar systems?  This poster didn't seem to
>think so (but hey, it's pretty old).  If there are, how do the suns
>revolve around each other?  Would the bigger sun tend to draw the
>smaller one toward it?
>
   There are binary stars, but the presence of solar systems other than our
own has not been demonstrated. A planet could orbit one of two suns, or
their centroid if they were very close together (orbiting them both). The
suns would revolve around each other the same way that the Moon and Earth
revolve around each other. The bigger sun would draw the smaller one toward
it, but only enough to maintain the orbit (if it didn't draw the smaller
one toward it, the two suns would go their separate ways). The smaller sun
would also draw the bigger sun toward it (action-reaction). The suns would
not spiral in and collide in a small number of billions of years.
   Last I heard, a planet could not do a figure-eight around two suns,
because such an orbit would be unstable. Maybe somebody else has more
recent information on this, though.

>Here's a pretty dum question, I'm sure....Does our sun rotate?  Which way?
>Does the whole solar system rotate with it?
>
   Not a dumb question.
   The Sun rotates the same way as the solar system does, counter-clockwise
as viewed from a point far above the Earth's North pole. Almost everything
in the solar system has this north rotation, the planets around the sun and
around their own axes, and the moons around the planets. There are a few
notable exceptions, such as the rotation of Venus around its own axis, and
some of the smaller outer moons, which are probably captured. This
uniformity of rotation is a consequence of the original north rotation of
the cloud out of which the whole solar system condensed.

>
>...lori


--
 Christopher Neufeld....Just a graduate student  | "I always think there's
 [e-mail]              | a band."
 [e-mail]                    |   Prof. Harold Hill
 "Don't edit reality for the sake of simplicity" |   (The Music Man)

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

Date: Sun, 11 Mar 90 20:53 EST
From: Chuck Rothauser <[e-mail]>
Subject: Space Probe Communications

Greetings,

I am taking a graduate course in Telecommunication Networks and recently
had a problem using an idealized 'Go-Back-N' (GBN) model to determine the
optimum data frame size when communicating with a space probe.  Communication
over VERY long distances implies that many frames can be in transit between
the transmitter and the receiver.

The bit error probability was given as 1/10000....... is this reasonable?
Seems to me that there is a lot of 'noise' out there, resulting in many
requests for retransmission of data frames.  Perhaps higher power trans-
mitterrs, lower temperature receivers, and larger antennas overcome the
requirement to retransmit many data frames?

Chuck Rothauser
United Technologies Research Center

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

Date: 11 Mar 90 20:26:34 GMT
From: psuvm![e-mail]  (Zaphod Beeblebrox)
Subject: Artificial Gravity

How realistic is the idea that if a spaceship had a section revolving that
the astronauts could just hang around in there and experience 'gravity'
i.e. like in the movie 2001. . .wouldn't the spinning section have to keep
accelerating to have the this effect???

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

Date: 12 Mar 90 05:23:54 GMT
From: sdcc6!sdcc3![e-mail]  (Sir Six)
Subject: Re: Artificial Gravity rephrased


     There's an interesting scene in _2001_ when Commander Poole (or
was it Bowman?  hmm.  whatever) jogs around the spinning carousel.
I was just thinking, would he get a better workout by jogging in the
same direction as the spinning of the carousel than be jogging in
the opposite direction?  (My thinking is that one would effectively
increase the angular velocity while the other would effectively
decrease it, and therefore that one would increase the centrifugal
force while the other would decrease it.)  eh?

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

Date: 11 Mar 90 19:52:55 GMT
From: mailrus!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Spacecraft drives and fuel efficiency

In article <[e-mail]> [e-mail] (Brian or James) writes:
>
> I think perhaps Mr. Ryan is incorrect in his statements about energy contents
>of high exhaust velocity boosters. It's true that mass ratios go down as
>Ve increases, but the energy tied up in getting the reaction mass to Ve goes
>up exponentially (E~V*e2).
>
   Actually, that's quadratically. Exponential growth is well defined, and
this isn't it.

>A pure 'photon-drive' style booster would be one
>hell of good light show before your eyes ran down your face, and would be a
>good way to drive a mohole at the same time (My texts are inaccessable
>right now.
>Could someone post the power output of a hundred ton launch vehicle boosting
>at 4ish gs propelled by a pure annihilation booster?).
>Not that anyone advocatedusing these extreme approach, of course.
>
   For a pure photon drive, accelerating upwards at 3g (so that the
occupants experience 4g), a hundred ton vehicle would annihilate 13.1g per
second. This would slag a medium sized state and would cost more in terms
of energy than any modern launchers.

>  Whem I said that the detonation of an annhilation  energised booster  would
>be survivable at short ranges, I meant on the order of 1000 meters or so, and
>I assumed a launch mass of only a few hundred tonnes using a couple of mg of
>antimatter. Mr. Maroney advocates only producing this stuff in space (Lunar
>Farside, anyone?). The problem with that is the current lack of well developed
>power generating systems in space (OK, there's one *big* fusion generator, but
>it's currently hard to get a direct feed cheaply). If you put the am source
>on Earth, you can use the powergeneration systems in place now. If prudence
>dictates a remote location like Farside, then I suspect that antimatter is
>unlikely to contribute anything useful for a long time.
>                                                          JDN

   In order for an annihilation explosion on the Moon to dissipate a power
flux at the Earth equal to that the sun puts out, it would have to be
converting 30 tons of matter to energy every second. In other words, a
nearside antimatter containment facility is perfectly safe for any but
absurd antimatter requirements.
   For an object in Clarke orbit, the mass-energy equivalent is 250kg per
second to match solar flux. There seems no reason to stockpile more than
grams in any one place (assuming 1mg for a shuttle launch, and mere grams
for a continuous burn flight to Mars).
   If you were serious about an antimatter-fuelled space program, you might
put solar collectors on Mercury to manufacture the fuel, and shuttle it to
Earth vicinity regularly in gram amounts. This might or might not be more
economical than using fission or fusion reactors on the moon or in Earth
orbit.
   Most economical, of course, would be to do it on the Earth, but there
are political difficulties with this approach.


--
 Christopher Neufeld....Just a graduate student  | "I always think there's
 [e-mail]              | a band."
 [e-mail]                    |   Prof. Harold Hill
 "Don't edit reality for the sake of simplicity" |   (The Music Man)

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

Date: 11 Mar 90 19:57:37 GMT
From: rochester!rit!ultb![e-mail]  (C.E. Johnson)
Subject: Re: Challenger Last Words

In article <[e-mail]> [e-mail] (David Messer) writes:
>Yes, the last words recorded were:  "No, I wanted a BUD Light!"  :-)

Not Funny.

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

Date: 12 Mar 90 00:35:34 GMT
From: zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Information on planetary atmospheres


   There's a good book detailing planetary atmosphere's for those
interested. _Planets and Their Atmospheres - Origin and Evolution_ by John
S. Lewis and Ronald G. Prinn  ISBN 0-12-446580-3  (1984).


--
 Christopher Neufeld....Just a graduate student  | "I always think there's
 [e-mail]              | a band."
 [e-mail]                    |   Prof. Harold Hill
 "Don't edit reality for the sake of simplicity" |   (The Music Man)

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

Date: 12 Mar 90 00:11:12 GMT
From: psuvm![e-mail]  (Zaphod Beeblebrox)
Subject: Artificial Gravity rephrased

Before I get majorly flamed here I would like to rephrase my question
about artificial gravity on a ship. . .sure a spinning 'donut' at part
of the ship and the astronauts can jog around or whateven on the inside
circumference experiencing a normal force from the floor. . . and a person
who falls out of an airplane feels 'weightless' (no air resistance) because
there is no normal force exerted on him by the floor, the earth, etc.
but concerning circular motion to induce artificial gravity. . is this same
exact effect as gravity?  Sure the floor is pushing the guy up and he
feels 'heavy' but there is no force say on his arm pulling it down. . .???
Sure his arm is attached to his body and his feet are being pushed 'up' and his
arm comes along for the ride but is this the same exact effect as gravity
pulling equally over his whole mass??  This may be a dumb question. . .
sure on the carnival ride where they drop the floor out you can't pull your
arms off from the wall. . .maybe a better question is what scale would this
have to be attempted say on a trip to Mars. . and how much energy would be
needed to make up for friction on the bearings etc. and would the angular
momentum of such a spinning section make turning the ship more difficult
during the flight etc.. . .hey I only saw the movie. .

Mark. . MXP122 at psuvm.psu.edu

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

Date: 12 Mar 90 00:48:20 GMT
From: cs.utexas.edu!wuarchive!swbatl!texbell!nuchat![e-mail]  (Steve Nuchia)
Subject: Re: Saturn's Rings

In article <[e-mail]> [e-mail] (Stephen Thomas) writes:
[questions about rings]

According to a talk I heard at Rice recently:

>The first query is this: What is the composition of the rings? I have
>read that they are composed of ice and rock, but I would like to
>know a little more about the makeup of the rings.

There was a slide of "what a ring would look like from ~3 meters".
Basically they are very thin, like a few (tens of ?) meters, and
composed of particles ranging from the microscopic up to fist size,
with occasional "boulders" up to a meter or so.

I don't recall the composition any better than "ice and rock", but
would suggest that you read "ice" as whatever compound forms ice
at the planet in question.  For saturn, water basically falls into
the "rock" category and CO2 might be the ice, farther out you may
have methane ice, etc.  This paragraph is deranged speculation.

>The second query: Last I heard, the ring system was maintained by a
>shepherd (sp?) moons arrangement. How delicate is this system? In other
>words, if some of the moons were removed (somehow), what would happen

The word on this is that the estimated lifetime of an unshepherded
ring system is much shorter than the age of the solar system, probably
around 10,000 years.  There were some problematical ring systems
for which the moons had not been found, but the Voyagers seem to
have found moons for all of them.  It is now believed that ring
formation is a normal part of the planet forming process, and that
ring preservation is a fairly common thing when there are enough moons.

--
Steve Nuchia          South Coast Computing Services      [phone]
"You have no scars on your face, and you cannot handle pressure." - Billy Joel

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

Date: 12 Mar 90 03:08:04 GMT
From: crdgw1!sixhub![e-mail]  (Wm E. Davidsen Jr)
Subject: Re: SR-71

In article <[e-mail]> [e-mail] (Kris Chubb) writes:
|
| Someone told me last night that they cheated on the coast to coast
| flight. Seems that the SR-71 flew west about 100 miles, turned around,
| and with a running start and altitude already gained, started being timed
| as it passed over the coast (or Edwards AFB?). Any comment (or clarification)?

  As long as the type of flight is clear, I can't call that cheating.
One record would be for running start and continue past destination,
like the flying mile landspeed records at Bonneville, and the other for
a flight takeoff to landing.
--
bill davidsen - [e-mail] (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc
"Getting old is bad, but it beats the hell out of the alternative" -anon

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

End of SPACE Digest V11 #138
*******************