Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/spacedig/V16_1/V16NO161.ZIP/V16NO161

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Date: Fri, 12 Feb 93 18:21:16
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #161
To: Space Digest Readers
Precedence: bulk


Space Digest                Fri, 12 Feb 93       Volume 16 : Issue 161

Today's Topics:
                   Book Computers/AI in Shuttle-SSF
                    hardware on the moon (2 msgs)
     Honorary Names (was: Today in 1986-Remember the Challenger)
                          HST repair mission
                 Ideal fuel for 'anti-matter' engine
                Insurance/Liability slush Fun/Dividend
                        kerosene/peroxide SSTO
   Launching in a Winter Wonderland (was Re: Polar Orbit) (2 msgs)
                           NASA Space Plane
                       New russian solar sail+
                     Orbital Mechanics--Careers?
                     Payload Hit For Polar Orbit
                         Polar Orbit (2 msgs)
            Pt 1/2: FREE-ENERGY TECHNOLOGY For Spacecraft
                 Russian Solar Sail experiments ends
                          Sabatier Reactors.
                    Space Station Freedom Fighters
                   Using Off the shelf/incase them!

    Welcome to the Space Digest!!  Please send your messages to
    "[e-mail]", and (un)subscription requests of the form
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    (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle
    (THENET), or [e-mail] (Internet).
----------------------------------------------------------------------

Date: 9 Feb 93 06:23:52 GMT
From: [e-mail]
Subject: Book Computers/AI in Shuttle-SSF
Newsgroups: sci.space

That is an idea.. Design the parts of the SSF as cargo spaces..
BAsically have the parts of the new space station as parts of the rocket to
refuel other projects.. once the feul tank is in orbit and empty then use it
as part of SSF!!

Other idea if there is a sattellite that is currently in orbit
and is about to die, maybe try to send it up to an orbit where SSF can
retrieve it and use its parts and such.. One way to learn about space
metallurgy and such.

I had an idea that is in the future.. Maybe give astronauts a book computer,
have an internal modem where it sends info to the main shuttle/Station computer
so that all info that the astronaut wants or can give is put into the
computer..Make the book/hand held a writable one where the astronauts can take
notes. It might have to be able to handle space walks(?).. Make the Shuttle
Computer a AI or a node for a earth bound AI..


Michael Adams
Alias: Morgoth/Ghost Wheel
[e-mail]


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

Date: Tue, 9 Feb 1993 01:28:57 GMT
From: Bill Goffe <[e-mail]>
Subject: hardware on the moon
Newsgroups: sci.space

[e-mail] (Henry Spencer) writes in response to an earlier
question:

>The later lunar modules were deliberately crashed on the lunar surface
>for the benefit of the lunar-surface seismometer network.  One or two
>of the early ones weren't; I forget whether they were just abandoned
>in lunar orbit (from which they almost certainly would have crashed
>by now) [further material deleted]

Why would they have crashed? With no atmosphere, wouldn't the orbit
have been stable? Further, I'd think any orbit would be close to the
moon, so it'd be relatively free of perturbations from the earth or sun.

Not a big point, just curious what I might be missing.

Bill Goffe
[e-mail]

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

Date: Tue, 9 Feb 1993 02:43:50 GMT
From: Dave Michelson <[e-mail]>
Subject: hardware on the moon
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Bill Goffe) writes:
>
>Why would they have crashed? With no atmosphere, wouldn't the orbit
>have been stable? Further, I'd think any orbit would be close to the
>moon, so it'd be relatively free of perturbations from the earth or sun.
>
>Not a big point, just curious what I might be missing.

The mascons which lie underneath the lunar maria perturb low altitude orbits
rather badly.

After a number of years, the probability that the perturbed orbit will
intersect the lunar surface is apparently rather high.

---
Dave Michelson                             University of British Columbia
[e-mail]                                  Antenna Laboratory

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

Date: Tue, 9 Feb 1993 01:33:56 GMT
From: Mary Shafer <[e-mail]>
Subject: Honorary Names (was: Today in 1986-Remember the Challenger)
Newsgroups: sci.space,sci.space.shuttle

They renamed 10th St East, the street they used to tow the Shuttles
between Palmdale and Edwards, Challenger Way.

There's also a very nice painting of Dick Scobee in the Test Pilot
School auditorium and I think it's now the Scobee Auditorium.

(Los Angeles County made a park called Apollo Park out by Fox Field
and named the three ponds Armstrong, Aldrin, and Collins, but it's a
dubious distinction since they're filled with recycled water from
the nearby sewage plant.)
--
Mary Shafer  DoD #0362 KotFR NASA Dryden Flight Research Facility, Edwards, CA
[e-mail]                    Of course I don't speak for NASA
 "A MiG at your six is better than no MiG at all."  Unknown US fighter pilot

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

Date: Mon, 8 Feb 1993 23:45:34 GMT
From: "Paul A. Scowen" <[e-mail]>
Subject: HST repair mission
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Steinn Sigurdsson) writes:
|> There's a faint rumour that the "return-to-Earth" option
|> for the HST mission has been re-opened and that a committee [sic]
|> has been set up to look at that option [again].
|>
|> Anyone know whatsup? Are there new concerns over the EVA
|> schedule or is this out of the blue.

This rumour apparently came from the recent Users Committee meeting at Goddard.
I heard that Goldin is being pressured by some Space Station types to minimise
the EVA role in the repair mission, because they fear a drop in credibility
with the Hill if the mission goes awry.

The ST people I've spoken too think that if it does come down it almost
certainly won't go back up, because that would be an excellent way to massively
reduce the MONDA, wouldn't it (re: Goldin's AAS speech)?

Anyway, most people in the know seem to think that it's a pretty ludicrous
idea and are hoping that sanity will prevail, especially since we've come this
far down the repair mission path.

--
-------------------------------------------------------------------------------
Paul A. Scowen                INTERNET: [e-mail]
Department of Physics & Astronomy          [e-mail]
Arizona State University        Tel:      [phone]
Box 871504                FAX:      [phone]
Tempe, AZ 85287-1504
-------------------------------------------------------------------------------

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

Date: Tue, 9 Feb 1993 06:43:35 GMT
From: Adrian Hassall Lewis <[e-mail]>
Subject: Ideal fuel for 'anti-matter' engine
Newsgroups: sci.space

[e-mail] (fred j mccall 575-3539) writes:

>The subject pretty much says it all.  If you had close to unlimited
>energy for input to the fuel (say from anti-matter reactions) as you
>exhausted it, what would be the best fuel to carry from a performance
>standpoint?  Would you go for something relatively dense like mercury
>and superheat it to a plasma, do something like a buckyball
>massdriver, or still go for the light-weight atoms like hydrogen for
>maximum exhaust velocity?


>--
>"Insisting on perfect safety is for people who don't have the balls to live
> in the real world."   -- Mary Shafer, NASA Ames Dryden
>------------------------------------------------------------------------------
>[e-mail] - I don't speak for others and they don't speak for me.

This doesn't really answer your question.  But you may like to look up the
following reference -

Electrostatic propulsion using C60 molecules
S. D. Leifer, D. Rapp, and W. A. Saunders
Journal of Propulsion and Power
Vol.8, no.6, Nov-Dec 1992, pp1297-1300.

ajax

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

Date: 9 Feb 93 06:47:33 GMT
From: [e-mail]
Subject: Insurance/Liability slush Fun/Dividend
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Edward V. Wright) writes:
> In <[e-mail]> [e-mail] writes:
>
>>Maybe the US can start their own
>>Lloyds for space related projects..
>>Use the money left over in the "Insurance"
>>fund for the next year..
>
> Uh, what money left over?  The record of the space-insurance
> industry is that they pay out more money than they take in.

I mean take a few million and put it in a fund, use most for "insurance"
the rest for investments and take the money left over each year (yes if there
is any) and use it to fund next years Insurance.. Kind of liek the permenant
fund here in Alaska.. Maybe also take the inventions that have been made or so
some said by NASA and the shuttle and sell them for royalties,. Take the
royalties and invent them and use part of the interest/dividends for
"insurance"... Maybe make NASA into a semi-money making project.. It can still
be a government agency, but it is tiem the US sold the inventions made at
government labs and such.. They the labs are government property and such, but
that does not mean they can't support themselves andf save the tax payers
money..
Why must the big corps make big money on products given them for "free" and
then sell them to us the population for high prices and run the medical cost up
with them..


Michael Adams
Alias: Morgoth/Ghost Wheel
[e-mail]

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

Date: 8 Feb 93 19:57:24 GMT
From: Craig Meyer <[e-mail]>
Subject: kerosene/peroxide SSTO
Newsgroups: sci.space

> Also of note were the peroxide monopropellant rocket engines used in the
> NF-104 rocket-boosted aircraft flown by NASA and the USAF, which worked
> quite well and were serviced and fuelled by ordinary USAF technicians.

I, the space-dunce, would like to know how H2O2 could serve as a monopropellant
when the decomposition of H2O2 is an endothermic reaction (takes up energy).

Could someone please explain the chemical reaction?

> As mentioned elsewhere, Mitch went so far as to sketch out a design for
> a pressure-fed reusable SSTO, although Bruce Dunn has cast some serious
> doubts on Mitch's weight estimates for pressurization gas.

The space-dunce's instincts say that eliminating a mechanical fuel-delivery
system would greatly simplify a launch vehicle.  Thicker tanks SEEM to be worth
it, but I don't know the numbers.

--
       Craig Meyer                 [e-mail]
       Indiana Academy for Science, Mathematics, and Humaities.
       Muncie, IN  47306                          317-285-7433

       Opinions expressed are mine alone, and not necessarily
       shared by the Indiana Academy.

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

Date: Mon, 8 Feb 1993 23:47:59 GMT
From: [e-mail]
Subject: Launching in a Winter Wonderland (was Re: Polar Orbit)
Newsgroups: sci.space

[e-mail] wrote:
: In article <[e-mail]>, [e-mail] (Gregory N. Bond) writes:
: > And did you hear that researchers in Fairbanks, Alaska have developed
: > room-temperature superconductors?

: I have not heard that.. I will check it out.. Unles this is a hoax?

It's a joke, son.  Think about it.

Of course, we don't get winter here in Houston.  It just rains a little
more.

My wife has Renault's Syndrome [sp?], a problem with blood flow to the
hands which gives her perpetually cold fingers.  Her doctor back in
Illinois told her to move someplace warm.  It's a darned good thing
that most of the space program is located where it's warm -- Texas,
California, Florida, Alabama (not in any particular order).  It's be
hell on her to live in Alaska.

-- Ken Jenks, NASA/JSC/GM2, Space Shuttle Program Office
      [e-mail]  [phone]

     "We choose to go to the moon not because it is easy,
      but because it is fun."
    -- John F. Kennedy, as [mis]quoted by
             Scott Brigham, [e-mail],
             in alt.folklore.urban

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

Date: Tue, 9 Feb 1993 01:04:33 GMT
From: Leigh Palmer <[e-mail]>
Subject: Launching in a Winter Wonderland (was Re: Polar Orbit)
Newsgroups: sci.space

In article <[e-mail]> ,
[e-mail] writes:

>My wife has Renault's Syndrome [sp?], a problem with blood flow to the
>hands which gives her perpetually cold fingers.

I think that's Reynaud's Syndrome (but I'm not sure, either); it is not
uncommon. I've got it, too.

Renault's Syndrome is indicated when an otherwise sane person suddenly
buys a French car.

Leigh

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

Date: 9 Feb 93 06:48:00 GMT
From: Avatar <[e-mail]>
Subject: NASA Space Plane
Newsgroups: sci.space

Dear friends,

    What is the present status of the NASA Space Plane?

    I am aware that the NASA Space Plane is designed to use some sort of
scramjet/ramjet (?) propulsion system in the atmosphere, but what sort of
propulsion system is it designed to use in space?

                                       .
                                     .'|`.
___________________________________.'-{*}-`.____________________________________
Zerxes M. Bhagalia                '----|----` INT: [e-mail]
State University of New York   .---------------.    [e-mail]
  at Buffalo                 .'                 `.  News Director, WFFT 104.9 FM
Political Science          .'                     `. Justice, SA Judiciary (SWJ)
Computer Science         .'________MDCCLXXVI________`. Computer Consultant (UCS)
---------------------N O V U S   O R D O   S E C L O R U M----------------------

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

Date: 9 Feb 93 06:09:33 GMT
From: [e-mail]
Subject: New russian solar sail+
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Keith Stein) writes:
> The separation of the sail and PROGRESS was a scheduled event. They both
> will reenter and burnup very soon I heard.
>
Any idea when they will burn up and where should we watch?(I know Im out of the
pale, but others might liek to know)...
==
Michael Adams alias Ghost Wheel/Morgoth [e-mail]

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

Date: Mon, 1 Feb 1993 22:51:33 GMT
From: " John O. Bell II " <[e-mail]>
Subject: Orbital Mechanics--Careers?
Newsgroups: sci.aeronautics,sci.research.careers,sci.space,soc.college.grad

>In <[e-mail]> [e-mail] (Srinivas Bettadpur) writes:
>
>>    * I know of UT-Austin, MIT, Stanford, UC-Boulder, VPISU, U. Mich-Ann
>>Arbor, U. Ill.-UC, Purdue, Auburn U. as offering any significant
         ^^^^^^^^^^
>>graduate programs in CM in the US.

If you ever get the chance, take a very close look at the Aero Engineering
grad program at the U of Illinois... especially for concentration in the
field of Orbital/Celestial Mechanics. The university is getting gobs of
money poured into it, the dean (Prof. Solomon) is on a mission to make it
the top AAE grad school in the country, and if you're lucky and say your
prayers :-) you'll get to work with either Prof. J. E. Prussing or
Prof. B. A. Conway, both highly respected contributors to the field and
quite pleasurable to work with.

I know, I know, my check's in the mail... :-)
(but believe me, they are _excellent_ teachers at an excellent school).

John Bell
Applied Computing Devices, Inc.
[e-mail]

P.S. Yes, I graduated from U of I with a degree in Aeronautical Engineering
     (how did you _ever_ guess :-) ).

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

Date: Tue, 09 Feb 1993 03:00:26 GMT
From: Dave Rickel <[e-mail]>
Subject: Payload Hit For Polar Orbit
Newsgroups: sci.space

In article <[e-mail]>, "UTADNX::UTDSSA::GREER"@utspan.span.nasa.gov writes:
|> We know that kinetic energy varies with the square of the velocity.  Orbital
|> velocity at 300 km altitude is about 7700 meters/second, while the velocity of
|> the surface of the Earth at the equator is about 460 m/s...

OK, what is important is delta-V.  Using your numbers:

Equator launch - equatorial orbit    7240 m/s
Equator launch - retrograde equ. orbit    8160 m/s
Equator launch - polar orbit        7714 m/s
Pole launch - polar orbit        7700 m/s

Pretty clearly, the differences in velocity needed for polar orbit from the
equator or polar orbit from a pole are pretty insignificant.  Anyway,
plucking numbers out of the air, let's assume that you always need an
additional 1.5 km/sec to make orbit (atmospheric effects), and that your
effective exhaust velocity is 4.4 km/sec.

So the table now goes

Launch        delta V        effective    required
type        (km/sec)    delta V        mass ratio
                (km/sec)

E - E        7.24        8.74        7.29
E - RE        8.16        9.56        8.78
E - P        7.714        9.214        8.12
P - P        7.7        9.2        8.09

Using these numbers, the penalty for equatorial launch into polar orbit vs
polar launch into polar orbit is on the order of 0.4%.


david rickel
[e-mail]

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

Date: 9 Feb 93 02:34:23 GMT
From: "David M. Faubert" <[e-mail]>
Subject: Polar Orbit
Newsgroups: sci.space

>"In projecting a satellite into Earth orbit, the launch vehicle is invariably
>tilted after liftoff in an easterly direction.  Launching to the east is done
>to take advantage of the Earth's eastward surface velocity.  This rotational
>surface velocity is about 1500 feet (450 metres) per second at the equator and
>1370 feet (400 metres) per second at the latitude of Cape Kennedy.  It would be
>perfectly possible to launch a satellite on a westerly orbit, but an additional
>2000 feet (600 metres) per second would be required for an orbit of the same
>altitude compared with an easterly one.
>     If the satellite is launched in a northerly or southerly direction, a polar
>orbit is obtained.  The easterly surface velocity launch advantage is lost"
>It's just a guess, but I think it would be more advantageous to look for a high
>mountain from which to launch rather than a northerly latitude.  That way you'd
>have less of that thick air to punch through.
>Chris Jones    [e-mail]

OK, I'm not a space scientist or an academic but an engineer with a reasonable
background in physics. Agreeing with the Brittanica excerpt, I ask you: Since
polar orbits have no "easterly" or "westerly" velocity, wouldn't it be most
advantageous to launch near one of the poles? If you launch an object from the
equator, say, you would have to lose all of that "easterly" velocity in order
to put the thing in a polar orbit at all. Ideally, launching from one of the
poles, all of your delta-v would go into the orbit and not into compensating
for the rotation of the earth.

I was recently at the ESA facilty in Kiruna, Sweden at 68 degrees north
latitude. One of the selling points of this sight for future development
is the relative ease with which satellites can be launched into polar orbits.

Dave Faubert
.

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

Date: Tue, 9 Feb 1993 05:10:20 GMT
From: Dave Michelson <[e-mail]>
Subject: Polar Orbit
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (David M. Faubert) writes:
>
>OK, I'm not a space scientist or an academic but an engineer with a reasonable
>background in physics. Agreeing with the Brittanica excerpt, I ask you: Since
>polar orbits have no "easterly" or "westerly" velocity, wouldn't it be most
>advantageous to launch near one of the poles? If you launch an object from the
>equator, say, you would have to lose all of that "easterly" velocity in order
>to put the thing in a polar orbit at all. Ideally, launching from one of the
>poles, all of your delta-v would go into the orbit and not into compensating
>for the rotation of the earth.

Try working out the math.  The penalty for launching from the equator
appears to be fairly small because the velocity that you're trying to kill
is both fairly small and at right angles to the desired velocity.  Unless
I'm missing something.

>I was recently at the ESA facilty in Kiruna, Sweden at 68 degrees north
>latitude. One of the selling points of this sight for future development
>is the relative ease with which satellites can be launched into polar orbits.

It certainly appears to be a commonly held belief...

---
Dave Michelson                             University of British Columbia
[e-mail]                                  Antenna Laboratory

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

Date: Sat, 06 Feb 1993 13:17:01
From: Bogdan Eremia <[e-mail]>
Subject: Pt 1/2: FREE-ENERGY TECHNOLOGY For Spacecraft
Newsgroups: sci.space

 mm>               One other energy source should be mentioned
 mm>here,
 mm>          despite the fact that it does not fit the
 mm>definition of Free
 mm>          Energy.  A Bulgarian-born American Physicist named
 mm>Joseph
 mm>          Maglich has invented and partially developed an atomic FUSION
 mm>          reactor which he calls 'Migma', which uses  NON-radioactive
 mm>          deuterium as a fuel [available in nearly UNLIMITED quantities
 mm>          from sea water], does NOT produce radioactive waste, can be
 mm>          converted DIRECTLY into electricity (with-OUT energy-wasting
 mm>          steam turbines), and can be constructed small enough to power
 mm>          a house or large enough to power a city.  And UNLIKE the
 mm>          "Tokamaks" and laser fusion MONSTROSITIES that we read about,
 mm>          Migma WORKS, already producing at least three watts of power
 mm>          for every watt put in.  ["New Times" (U.S.


    Just one question....why aren't we using these already?

 * Origin: Empire BBS [phone] (3 lines) (3:635/550)

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

Date: Tue, 9 Feb 1993 04:24:29 GMT
From: Glenn Chapman <[e-mail]>
Subject: Russian Solar Sail experiments ends
Newsgroups: sci.space

     The Russian solar sail Znamya experiment ended yesterday (Sunday,
Feb. 7th) when the sail entered the atmosphere.  Current reports indicate
that initial results went well after it was deployed from the Progress TM-15
cargo craft at the Mir space station about 4 am UTC (11 pm PST) Feb. 4th.
The solar sail illumined several areas in Europe, especially in Toulouse
France.  Apparently in that southern French city, near the Spanish boarder,
the streets were noticeably brighter during the pass as seen by several town
people.  Shortly after it crossed the day/night terminator in Europe the
solar sail was released from the Progress.  Observations here in Vancouver
suggested that it fell about 95 Km (60 mi) to about 300 km altitude in just
about 30 hours, by Friday (Feb. 5th) morning.  Since such orbital decays would
increase rapidly so it would seem that by Feb. 6th it would have been down to
a 200 km orbit, and renter shortly there after on Feb. 7th as reported.  This
is not unreasonable for a 20 metre (85 ft) diameter very light sail.  Some
reports indicate that the Znamya was set free after the rotation which was to
stabilized its shape caused problems with the Progress' guidance.  However,
note that the original experimental plan called for only about 3 days of
flight, consistent with this same time frame.  Until more reports come out it
is not possible to tell which was the reason for the release.  Dr. Leigh
Palmer here observed the Mir space station on Feb. 7th, but the Progress was
no longer near it, so that has probably deorbited by now as well.  That would
be consistent with standard operations.  (Radio Moscow, BBC, CBC)
     Certainly this ranks as one of the more noticed Russian/CIS space
experiments in recent years.

                                                        Yours truly
                            Glenn Chapman
                            Simon Fraser U.
                            [e-mail]

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

Date: Mon,  8 Feb 93 17:59:21 PST
From: Brian Stuart Thorn <[e-mail]>
Subject: Sabatier Reactors.
Newsgroups: sci.space

>And the Soviets have had an unmanned resupply craft, launched on a
>cheap, Atlas-class launcher, available for such refullings. As
>far as I know, NASA has no plans to develop such a craft, and as
>a cargo/fuel transport the Shuttle isn't exactly cost-effective...
>By the way, how do they plan to get around the no-liquid-fuel-payload
>requirement imposed on the Shuttle after the Challenger accident?
>
>                                                Frank Crary

    There is no such requirement. What did happen was that Centaur
    was banned from Space Shuttle operations, but this was a case
    of Centaur being too heavy and carrying too much fuel to dump
    in an emergency. Liquid fuels are still okay, but the U.S. has
    no other liquid-fuel upper stages (Agena being dead and gone.)

    Most satellite carried aloft by the Shuttle have liquid fueled
    propulsion systems, such as TDRS, Galileo, Magellan, UARS, and
    EURECA. Also, Shuttle EDO pallets carry a significant amount of
    cyrogenic fuels in the payload bay.

    -Brian

-------------------------------------------------------------------------
Brian S. Thorn                                    "If ignorance is bliss,
[e-mail]                               this must be heaven."
                                                -Diane Chambers, "Cheers"
-------------------------------------------------------------------------

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

Date: Tue, 9 Feb 1993 01:56:00 GMT
From: [e-mail]
Subject: Space Station Freedom Fighters
Newsgroups: sci.space

In article <[e-mail]>,
[e-mail] (tomas o munoz 283-4072) writes:
> This message is posted as a favor to the Space Station Freedom Fighters.

Who will no doubt become known as Space Station Terrorists in unsympathetic
venues...

> Engineers think equations are an approximation of reality.
> Physicists think reality is an approximation of the equations.
> Mathematicians never make the connection.

But only Physicists can assume a bridge and go home.

-Bill Gawne,  Space Telescope Science Institute

 "Forgive him, he is a barbarian, who thinks the customs of his tribe
  are the laws of the universe."                       - G. J. Caesar

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

Date: 9 Feb 93 06:07:33 GMT
From: [e-mail]
Subject: Using Off the shelf/incase them!
Newsgroups: sci.space

Why can't off the shelf items be used in space, you might have to incase them
in soemthing that meets the specs (namely outgassing and such), and have some
form of interface (remember boy in the bottle). So that you can use off the
shelf equipment, you just put them in a position where there dangers are
neutralized..
==
Michael Adams alias Ghost Wheel/Morgoth [e-mail]

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


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From: Henry Spencer <[e-mail]>
Newsgroups: sci.space
Subject: Re: hardware on the moon
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In article <[e-mail]> [e-mail] (Bill Goffe) writes:
>>... early ones weren't; I forget whether they were just abandoned
>>in lunar orbit (from which they almost certainly would have crashed
>>by now) [further material deleted]
>
>Why would they have crashed? With no atmosphere, wouldn't the orbit
>have been stable? Further, I'd think any orbit would be close to the
>moon, so it'd be relatively free of perturbations from the earth or sun.

But not from the Moon itself.  The Moon's gravitational field is very
lumpy, thanks to the mascons (heavy spots in its crust).  It is not
particularly well mapped, but so far as we know there is no such thing
as a stable lunar orbit in the long term.  They all get perturbed enough
to intersect the surface eventually.  Designs for lunar orbiters have
to include quite substantial amounts of orbit-correction fuel.
--
C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology
effect since OS/360.                    |  [e-mail]  utzoo!henry

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

End of Space Digest Volume 16 : Issue 161
------------------------------