Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_3/V15NO360.TXT

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Date: Sat, 31 Oct 92 05:01:34
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #360
To: Space Digest Readers
Precedence: bulk


Space Digest                Sat, 31 Oct 92       Volume 15 : Issue 360

Today's Topics:
                       Comet Collision (6 msgs)
                      Galileo High Gain Antenna
           Geo Bush: Claiming revelance , getting phasered
                        HRMS for ETI (2 msgs)
                             lunar phases
                      Magellan Update - 10/30/92
                 pocket satellite receivers (was Re:
                      Query Re: pluto direct/ o
               Re:Swift-Tuttle Comet a threat to earth?
                   REPOST!  UN Space/Moon Treaty?!
              Strategy for new generation of telescopes
      Surveyor landings (was Re: QUESTIONS: Apollo, Earth, Moon)
                Swift-Tuttle Comet a threat to earth?

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Date: 30 Oct 92 15:14:00 GMT
From: Dave Jones <[e-mail]>
Subject: Comet Collision
Newsgroups: sci.space,alt.sci.planetary

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John Black ([e-mail]) wrote:
> Maybe a near comet approach could be a good thing. I did a rough calculation
> and estimated that there must be something of the order of 10 to the power 11
> metric tonnes of water. Maybe in 130 years time somewhere on the Earth could do
> with some water, eg the interior of large continents affected by drought. I
> know that one of the effects of the greenhouse effect is to make sea levels
> rise, but that is salt water, no good for crops, and still would be hundreds of
> miles from a continental desert region. The comet presumably is almost pure
> water and therefore would be ideal for crops, drinking etc.
>
OK, I'll bite.  10^11 tonnes of water is a lake about 30km on a side and
1 meter deep.  I imagine Lake Eyre, in Australia, has about that much, when
it has any water at all, and it evaporates PDQ.  Not much help.

> So if in 130 years technology is sufficiently advanced, it could be possible
> to alter the orbit of the comet so that it goes into a stable orbit around the
> Earth. The trick then would be to "chip" bits off the comet and "land' them
> in the appropriate region of the Earth. This would be the most difficult bit
> since viz the probable cause of the Tunguska event (see previous article on
> comet hitting Earth) you would end up doing the equivalent of nuking the region
> The comet could also be an almost infinite supply of water for lunar bases if
> there are any by then.
>
Notwithstanding other comments about linear-vs-exponential-vs-synergistic
change, the fact is that if you have the ability to do 45 mi/s velocity
changes on comets, then you also have the ability to do other things closer
to home: like moving icebergs bodily into the Sahara, excavating artificial
inland seas etc.  Or just plain replanting all the flora that were lost to
desertification in the first place.....

--
||)))))))))))))))))))))))))))))))))))))|Puff the Magic Dragon
||)))))))))))))))))))))))))))))))))))))|Lived by the sea
||Dave Jones ([e-mail])|Who knows what's in the autumn mists
||Eastman Kodak Co. Rochester, NY      |In the mind of Yadallee?

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

Date: 30 Oct 92 15:31:03 GMT
From: Dave Jones <[e-mail]>
Subject: Comet Collision
Newsgroups: sci.space,alt.sci.planetary

Dave Jones ([e-mail]) wrote:
> John Black ([e-mail]) wrote:
> > Maybe a near comet approach could be a good thing. I did a rough calculation
> > and estimated that there must be something of the order of 10 to the power 11
> > metric tonnes of water. Maybe in 130 years time somewhere on the Earth could do
> > with some water, eg the interior of large continents affected by drought. I
> > know that one of the effects of the greenhouse effect is to make sea levels
> > rise, but that is salt water, no good for crops, and still would be hundreds of
> > miles from a continental desert region. The comet presumably is almost pure
> > water and therefore would be ideal for crops, drinking etc.
> >
> OK, I'll bite.  10^11 tonnes of water is a lake about 30km on a side and
> 1 meter deep.  I imagine Lake Eyre, in Australia, has about that much, when
> it has any water at all, and it evaporates PDQ.  Not much help.
>
Whoops!  Make that 316 km on a side and 1 m. deep.  Still not a lot by most
standards: try 100km on a side and 10m deep, and compare with the Great Salt
Lake, though Lake Eyre may still be good....  Anyway, neither blooms the
desert, except on a strictly local basis.

One day, I'm going to sit down and work out if Asimov's Martian Way really
would have worked....soft land a chunk of Saturns Rings on Mars, when just
getting into Earth orbit takes 90% of your starting mass?  Hmmm.......


--
||)))))))))))))))))))))))))))))))))))))|Puff the Magic Dragon
||)))))))))))))))))))))))))))))))))))))|Lived by the sea
||Dave Jones ([e-mail])|Who knows what's in the autumn mists
||Eastman Kodak Co. Rochester, NY      |In the mind of Yadallee?

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

Date: 30 Oct 92 18:16:16 GMT
From: Ken Arromdee <[e-mail]>
Subject: Comet Collision
Newsgroups: sci.space,sci.misc,rec.arts.sf.science

In article <[e-mail]> [e-mail] writes:
>You are guilty of the classic fallacies of extrapolation. The first
>fallacy is an overestimate of short term advance. The second is the
>underestimate of the long term. Both are due, in part, to linear
>thinking, straight line extrapolation. Technological capabilities and
>knowledge are accumulating exponententially. If you make a linear
>extrapolation in a particular field, you will tend to "draw a line"
>of some slope that seems "reasonable". But the problems invariably
>turn out to be more difficult in your field than you actually
>believed.  So the exponential will for some period of time grow
>slower (lesser slope) than your line, but when it finally does cross
>it...

There was a non-fiction article in Analog (a science fiction magazine) around
1960.  The author pointed out exactly what you do here: lots of ideas about the
future are extrapolated linearly.  He graphed the maximum speed that human
beings could travel at, as an example, and showed that it increased faster than
even an exponential.

The curve also showed, however, that (by extrapolation) humanity would surpass
the speed of light by the year 1985.

I believe that in the 1980's he (or someone, anyway) wrote another article
recognizing the existence of S-shaped curves that eventually level off.

The moral is that some barriers can't be found by extrapolation from points
before the barriers have any significant effect.  It's legitimate to argue that
advances require solving a difficult or impossible problem; just noting that
you can graph past that point is not an answer.

(How do you conclude that technological capabilities are accumulating
exponentially, anyway?)
--
"the bogosity in a field equals the bogosity imported from related areas, plus
the bogosity generated internally, minus the bogosity expelled or otherwise
disposed of."  -- K. Eric Drexler

Ken Arromdee (UUCP: ....!jhunix!arromdee; BITNET: arromdee@jhuvm;
     INTERNET: [e-mail])

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

Date: 30 Oct 92 18:15:47 GMT
From: Doug Mohney <[e-mail]>
Subject: Comet Collision
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] writes:
>
>The capabilities of 130 years from now are really and truly outside
>the realm of science fiction. We can't extrapolate that far ahead at
>the current rate of advance. The exponential is rising so fast now
>that knowledgeable projection and hard science fiction are almost
>indistinquishable and cover the same time frame: no more than 30-50
>years in the future.

>
>In 2126 we'll be able to do just about anything we care to do with
>that oversized snowball. As to what that might be, I fear my crystal
>ball is bit cloudy today.

Dateline: O'Neill News Service, October 31, 2125

Subject:  Szabo Asteroid Miners, LunaOne Space Resources race to claim comet.

            :-)

                 Play in the intelluctual sandbox of Usenet

  -- >                  [e-mail]                        < --

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

Date: 30 Oct 92 17:49:06 GMT
From: Mark Evans <[e-mail]>
Subject: Comet Collision
Newsgroups: sci.space

[e-mail] (Mark 'Henry' Komarinski) writes:
:
: There is a greater change of dying from a train wreck or a car accident than
: getting plowed by the comet.
: Another thing to consider:  How big is this comet?  It doesn't have to hit
: us to do some major damage.  YOOGE tidal waves, earthquakes, knocking
: the earth out of it's orbit, etc.  Y'know...minor worldwide disaters.

And what do you think it is made of (neutronium???) the gravity produced
from a 10km iceberg is minimal.

--
-------------------------------------------------------------------------
Mark Evans                                   |[e-mail]
+(44) 21 565 1979 (Home)                     |[e-mail]
+(44) 21 359 6531 x4039 (Office)             |

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

Date: 30 Oct 1992 12:51 PST
From: SCOTT I CHASE <[e-mail]>
Subject: Comet Collision
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Mark Evans) writes...
>[e-mail] (Mark 'Henry' Komarinski) writes:
>:
>: There is a greater change of dying from a train wreck or a car accident than
>: getting plowed by the comet.
>: Another thing to consider:  How big is this comet?  It doesn't have to hit
>: us to do some major damage.  YOOGE tidal waves, earthquakes, knocking
>: the earth out of it's orbit, etc.  Y'know...minor worldwide disaters.

Actually, I think that if you just average the deaths per year over 100
millions years or so, the odds of getting killed by a comet or meteor
is several times higher than the annual odds of dying in a car crash.
NASA recently reported such a calculation.  Of course, the difference is
that a meteor kills billions of people all at once, but only once every few
10 million years or so.

-Scott
--------------------
Scott I. Chase            "It is not a simple life to be a single cell,
[e-mail]         although I have no right to say so, having
                 been a single cell so long ago myself that I
                 have no memory at all of that stage of my
                 life." - Lewis Thomas

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

Date: 30 Oct 1992 11:54 PST
From: SCOTT I CHASE <[e-mail]>
Subject: Galileo High Gain Antenna
Newsgroups: sci.space,sci.astro

In article <[e-mail]>, [e-mail] writes...
>
>>  and 2) would this help the engineers at all?
>
>Very doubtful.  They know what the problem is, they just can't find any
>way to fix it.

That's too strong a statement, I believe.  They certainly have a model
of the problem which they are using to try to fix it.  But I don't think
that it's possible to do more than go with a likely candidate.  There is
little doubt that the HGA failed to open.  But *why* is didn't open -
what got it stuck - is a matter of some speculation.  That's why it is not
possible to say with any confidence whether the various attempts to
fix it will work or not.

-Scott
--------------------
Scott I. Chase            "It is not a simple life to be a single cell,
[e-mail]         although I have no right to say so, having
                 been a single cell so long ago myself that I
                 have no memory at all of that stage of my
                 life." - Lewis Thomas

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

Date: Fri, 30 Oct 92 18:24:07 -0600
From: [e-mail] (Phil G. Fraering)
Subject: Geo Bush: Claiming revelance , getting phasered

In article <[e-mail]>, Clinton for President <[e-mail]> writes:
|>
|>  FOR IMMEDIATE RELEASE
|>  October 20, 1992
|>
|>       GEORGE BUSH'S DRUG WAR: CLAIMING VICTORY, COVERING UP LOSSES
|>        [Statement by Bob Boorstin, Deputy Communications Director]
|>
|>  George Bush just doesn't get it.  He's shown time and time again he
|>  doesn't understand America's economic problems.  Now he's showing
|>  again he doesn't understand America's drug problem.

>etc.

|>  Bill Clinton will lead a national and international crusade against
|>  drugs.  He knows we have to tackle both demand for drugs and the
|>  supply of drugs.  He sees the drug problem from a personal
|>  perspective, not a political one.  And he knows we can do better than
|>  George Bush's cynical, failed drug war and attempted coverup.

>Let's beam George Bush into a wall.

Actually, Bush understands it about as well as Clinton, who hasn't
really said what he'd do besides "get tougher." I sorta wonder what
that means with the Bill of Rights in the state it's in today.

Thankfully the only Ferengi in the race has made sounds about how
it's obsolete, and if it's in the way, change it!

In short, dudes, I feel nothing but contempt for all of this
non-space-related political arguing, so haul it off of sci.space
before I get nasty with the photon torpedoes.

Besides, everyone knows these coersive states are not the way of
the _true_ Klingons...

--
Phil Fraering [e-mail] where the x is a number from 1-5.
Phone: [phone] SnailMail: 2408 Blue Haven Dr., New Iberia, La. 70560
---------------------
Disclaimer: Some reasonably forseeable events may exceed this
message's capability to protect from severe injury, death, widespread
disaster, astronomically significant volumes of space approaching a
state of markedly increaced entropy, or taxes.

    The world will end tomorrow.
    NASA scientists note that this was the way the system was
    designed to operate.

    - From the Nov. Focus in Sky and Telescope, on a hypothetical
      NASA press release on something hitting the Earth...

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

Date: 30 Oct 92 18:18:25 GMT
From: Stanley Friesen <[e-mail]>
Subject: HRMS for ETI
Newsgroups: sci.space,sci.bio

In article <[e-mail]> [e-mail] (Paul Dietz) writes:
|In article <[e-mail]> [e-mail] (Stanley Friesen) writes:
|
|> This last is an extremely unlikely requirement.  The basic upshot of the
|> Urey experiment and its follow-ups is that organics form spontaneously
|> under most non-oxidizing 'medium-energy' conditions.  The presence of
|> organics in interstellar dust clouds just confirms this basic ubiquity.
|
|The Miller-Urey experiment is widely acknowledged to be irrelevant,
|as it assumed an atmosphere that likely bears little resemblance
|to the early earth.  Specifically, methane and ammonia are unlikely
|to have been abundant in the early atmosphere, as they are destroyed
|within centuries by UV light.

That is why I specified 'and follow-ups'.  Almost every variant atmosphere
that was either reducing or 'neutral' has yielded organics.  The results
do *not* depend particularly on the exact original chemistry - though the
exact set of organics produced does vary with the initial conditions.

|When performed with more reasonable gas mixtures, the experiments have
|much lower yields.  And, in any case, all that these experiments
|indicate is that some of the basic molecules of life are rather stable
|(and, importantly, that others are not), not that a particular source
|is where they first came from.

They show them to be formed under a wide variety of conditions, so they are
liekly to be present on most otherwise suitable planets - perhaps from
*multiple* sources.  In short, it is more *lack* of organics is more
extraordinary, and thus more unlikely, than thier presence.

|The unstated assumption here is that life would *not* have had a hard
|time originating back then.  We simply don't know enough about how
|life started to say this.

Not really, the all I was talking about here was the fact that our
oxidizing atmosphere destroys all unprotected organics.
|
|Au contraire!  Our ignorance about origin of life is profound, and
|very little progress has been made in dispelling it.  There is no
|really plausible model for the origin of life.  We're missing at least
|one, and possibly several, fundamental ideas.
|
Have you read Cairns-Smith's "Seven Clues to the Origin of Life"?
I consider that to be an extremely plausible model (though the best
reasons are not in that, now out-of-date, book).

Also, one could argue, based on the usual defnitions of life, that the
recently produced self-replicatinf RNA molecule *is* alive, and thus
we *have* made life in the laboratory. (Of course the exact definition
of life in the boundry cases is decidedly difficult, so one could also
make a case that it is not alive).
--
[e-mail]            (formerly tdatirv!sarima)
  or
[e-mail]

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

Date: Fri, 30 Oct 1992 19:51:02 GMT
From: Paul Dietz <[e-mail]>
Subject: HRMS for ETI
Newsgroups: sci.space,sci.bio

In article <[e-mail]> [e-mail] (Stanley Friesen) writes:

 >|Au contraire!  Our ignorance about origin of life is profound, and
 >|very little progress has been made in dispelling it.  There is no
 >|really plausible model for the origin of life.  We're missing at least
 >|one, and possibly several, fundamental ideas.

 > Have you read Cairns-Smith's "Seven Clues to the Origin of Life"?
 > I consider that to be an extremely plausible model (though the best
 > reasons are not in that, now out-of-date, book).

Cairns-Smith's ideas are very imaginative, but are supported by almost
no evidence.  In particular, no one has ever demonstrated that clays
-- or any other crystals -- can propagate genetic information.  The
fact that such speculations are taken seriously shows how blocked the
field has become.

 > Also, one could argue, based on the usual defnitions of life, that the
 > recently produced self-replicatinf RNA molecule *is* alive, and thus
 > we *have* made life in the laboratory. (Of course the exact definition
 > of life in the boundry cases is decidedly difficult, so one could also
 > make a case that it is not alive).

Sure, we've made RNAs in the laboratory -- using purified, chiral
tri(?)phosphorylated nucleotides, which (correct me if I'm wrong)
are extracted from biological sources.  Prebiotic Miller-Urey type
experiments have not, to my knowledge, ever produced nucleotides, nor
have they produced anything but racemic mixtures of mostly
biologically irrelevant molecules.  The monomers of RNA are
sufficiently complicated that it is quite implausible they could have
arisen without some prior evolution.

    Paul F. Dietz
    [e-mail]

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

Date: Fri, 30 Oct 1992 10:23:49 GMT
From: Jan Spitzkowsky <[e-mail]>
Subject: lunar phases
Newsgroups: sci.space

Please help,

I need an algorithm for calculating the lunar phases.
I need it for computing the red letter days, most of them
depend on the moon like Easter.

Thanks in advance
                       Jan

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

Date: Sat, 31 Oct 1992 05:57:26 GMT
From: Ron Baalke <[e-mail]>
Subject: Magellan Update - 10/30/92
Newsgroups: sci.space,sci.astro,alt.sci.planetary

Fowarded from the Magellan Project

                    MAGELLAN STATUS REPORT
                       October 30, 1992

1.  Magellan continues to operate normally, performing a
    starcal (star calibration) and desat (desaturation of
    the reaction wheels) on each orbit and transmitting a
    carrier plus 40 bps X-band signal.

2.  No commanding of the spacecraft is planned for today or
    the weekend.  Magellan continues to pass through the
    shadow of Venus during the apoapsis portion of each orbit.

3.  The craft has completed 5982 orbits of Venus, just 18
    orbits from the 6000 mark.  346 orbits have been completed
    in Cycle 4.  Since the science requirement is to collect
    gravity data on at least one out of every four orbits, we
    have about 86 orbits of gravity.  This represents about 70
    degrees of longitude out of the 360 degree coverage
    planned.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | If God had wanted us to
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | have elections, he would
|_____|/  |_|/       |_____|/                     | have given us candidates.

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

Date: 30 Oct 92 09:52:22 GMT
From: John C Sager <[e-mail]>
Subject: pocket satellite receivers (was Re:
Newsgroups: comp.sys.hp48,comp.sys.palmtops,sci.space

I got some information on the GESSA device. It appears that they use the
NavCore V GPS receiver module from Rockwell-Collins.

John C Sager                    Mail:    B67 G18, BT Labs
Email:    [e-mail]                Martlesham Heath
Tel:    [phone]                    IPSWICH  IP5 7RE
Fax:    [phone]                    England

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

Date: Fri, 30 Oct 1992 17:53:59 GMT
From: Henry Spencer <[e-mail]>
Subject: Query Re: pluto direct/ o
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Ian Taylor) writes:
>>... aerobraking at Pluto.
>
>How about aerobraking at Neptune first?

For the Nth time, folks, Neptune is nowhere near Pluto.  Nothing of any
useful size is anywhere near Pluto.  Any braking done must be done at
Pluto; otherwise the trip times are simply too long.

>While I'm here, anyone know if a gravity assist trajectory can be used to
>*reduce* speed?

Yes... but a gravity assist around *what*?
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

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

Date: 30 Oct 92 16:34:20 GMT
From: Erik Max Francis <[e-mail]>
Subject: Re:Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

[e-mail] (Robert Sheaffer) writes:

> I should think that, given that a comet consists largely of ice and
> other volatiles, even one good-sized H-bomb placed directly into the
> nucleus would pretty much eliminate any "threat to earth". Seems it
> would be mostly vaporized and scattered.

Splitting it up might not help, if those chunks still hit the Earth.  A
million million-kilogram chunks of ice and rock isn't very much less
dangerous than a single trillion-kilogram chunk.  It would have to be
separate into considerably small pieces so that any pieces that _do_
still hit the Earth burn up in the atmosphere with little surface damage.
The best bet is to use a device to _nudge_ it out of the way, not to blow
it to bits.  That just isn't practical.

----------
Erik Max Francis   Omnia quia sunt, lumina sunt.  Coming soon:  UNIVERSE _ | _
USmail:  1070 Oakmont Dr. #1 San Jose CA 95117  ICBM:  37 20 N  121 53 W _>|<_
UUCP:  ..!apple!uuwest!max   Usenet:  [e-mail]   464E4F5244   |

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

Date: Fri, 30 Oct 1992 17:50:12 GMT
From: Henry Spencer <[e-mail]>
Subject: REPOST!  UN Space/Moon Treaty?!
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
>I am looking for information concerning the "Moon Treaty" or some sort
>of treaty drafted by the UN dealing with "...the Use of the Moon
>and Other Celestial Bodies".

Why bother?  Nobody's ratified it, and nobody's likely to.  In particular,
US support of it is stone cold dead, thanks entirely to the efforts of the
late lamented L5 Society.
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

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

Date: 30 Oct 92 18:57:02 GMT
From: Garry Holmen <[e-mail]>
Subject: Strategy for new generation of telescopes
Newsgroups: sci.space,sci.image.processing

In article <[e-mail]> [e-mail] (Yossarian Yggy King) writes:
>
>I saw a talk last week by Dr. Geoff Hinton, and he mentioned that he'd
>been involved in some work (though maybe only peripherally, I'm not
>sure) on building neural nets to learn how to correct for optical
>defects in large lenses. I've probably got this wrong, but it was
>something like having the net learn the distortion parameters for each
>point on the lens, which are then corrected with a secondary lens that
>is distorted in real-time as the image is gathered to correct for the
>distortions in the primary lens.
>    He said in passing that the neural-net corrected lenses
>rivaled the resolution of the Hubble scope. Obviously (I think) you
>can only correct for distortions, not attenuations, by the atmosphere
>... once you've lost information you can't get it back.
>--
>Yggy King    | Thinking the world should entertain you leads to boredom
>UBC Comp Sci    | and sloth. Thinking you should entertain the world leads
>B.C., Vancouver    | to bright clothes, odd graffiti and amazing grace in
>Canada        | running for the bus.    -- Ann Herbert

One should note that neural nets are not 100% accurate on the predictions
that they can make. A good net usually has an accuracy somewhere between
80 - 90%. And when a neural network isn't correct the results can vary wildly.
This is the big disadvantage of neural nets.... noone can guarantee error
bounding. So while these new telescopes should be better than existing
telescopes I would be hesitant to compare them to Hubble. Except when it
comes to $$$$ 8).

PS: You should also be able to use neural nets to enhance Hubble images. But
    as a word of caution : Anytime you distort data to achieve results that
    you deem desirable you can lose valuable information outside your interest.


Garry Holmen

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

Date: Sat, 31 Oct 1992 06:03:43 GMT
From: Ron Baalke <[e-mail]>
Subject: Surveyor landings (was Re: QUESTIONS: Apollo, Earth, Moon)
Newsgroups: sci.astro,sci.space

In article <[e-mail]>, [e-mail] (Bill Higgins-- Beam Jockey) writes...
>I've played Lunar Lander (being a relic of the compter dark ages
>beforre Flight Simulator and Sim City), so I can appreciate the
>usefulness of a throttlable engine. So how did Surveyor manage to
>land?  I recall a big solid-fuel motor and small liquid-fuel "vernier"
>engines.  Was there a computer playing Lunar Lander on board?  Was
>there a radar altimeter?  Or did they just get the probe to
>*approximately* zero velocity with the big motor, and build it
>extra-sturdy to survive a drop?  How does this compare with the scheme
>Luna 9 used to land, which I understand was rougher?
>

The Surveyors fired a solid rocket motor at 96 km to cancel most of its
horizontal velocity, causing the spacecraft to descend towards the Moon's
surface.  The solid rocket motor was then ejected, and a radar altimeter was
used to  feed a computer for a closed loop control of three thrusters to
further  reduce the descent velocity.  At 4.3 km above the surface, the
three thrusters were shut off, and the spacecraft simply dropped the
remainder of the way down, landing at a velocity of 11 km/hour.

>(I recall that one of the Surveyors was moved after landing with the
>verniers.)

You are thinking of Surveyor 6 in 1967.  It became the first spacecraft
ever to be launched from the surface of the Moon when it fired its thrusters
for 2.5 seconds, lifting the spacecraft 3 meters high at a slight angle.
It landed 2.5 meters away from its original landing spot.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | If God had wanted us to
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | have elections, he would
|_____|/  |_|/       |_____|/                     | have given us candidates.

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

Date: Fri, 30 Oct 1992 19:04:36 GMT
From: "Stephen F. Schaffner" <[e-mail]>
Subject: Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

In article <[e-mail]>, [e-mail]
(Scott D. Young) writes:
|>
|>    According to the data I have seen (I will try and find the reference),
|>    a comet 1 mile in diameter moving at an averge orbital velocity (what
|>    ever tht means) would cause a crater 40 miles diameter, and destroy
|>    everything for 100 miles. 400 million cubic *miles* of dirt would be
|>    thrown up into the tmosphere, nd stay there for up to 1000 years,
|>    blocking 98% of solar radition. As someone else put it, "You die, I
|>    die, everybody dies".

That seems like rather a lot of dirt.  Unless I'm confused (which I frequently
am), to get it all out of a 40 mile diameter crater you'd need a crater
300,000 miles deep.  Now *that's* a crater I'd like to see (provided I
didn't have to be around while it was being made, of course).

--
Steve Schaffner        [e-mail]
    The opinions expressed may be mine, and may not be those of SLAC,
Stanford University, or the DOE.

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End of Space Digest Volume 15 : Issue 360
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