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Date: Thu, 31 May 1990 02:30:48 -0400 (EDT)
Subject: SPACE Digest V11 #470

SPACE Digest                                     Volume 11 : Issue 470

Today's Topics:
    Re: Terraforming Venus (was: Manned mission to Venus)
             Re: Problems of missing mass
     Soviet Soyuz TM-9 problems not a risk to cosmonauts
             shuttle reliability
                Re: Radiation
----------------------------------------------------------------------

Date: 30 May 90 22:33:35 GMT
From: zephyr.ens.tek.com!wrgate!mrloog![e-mail]  (Dan Tilque)
Subject: Re: Terraforming Venus (was: Manned mission to Venus)

[e-mail] (Christopher Neufeld) writes:
>   One question about intercepting and deflecting comets: how does the
>force from the vapour jets outgassing compare to the force which a human
>thrust unit could impart on the comet? Might it be necessary to shroud
>the comet in a reflective sheet to prevent the outgassing from swamping
>the steering thrust?

My understanding of the celestial mechanics of comets is that there's
always a fairly large uncertainty in their orbits when compared to the
orbits of asteroids and planets.  Sometimes the error in the time of
perihelion can be several days.

I think that vapor jets make the largest contribution to this
uncertainty, although I imagine that loss of mass is also significant
in the long run.

>   Maybe it would be possible to put a rigid cover on
>the comet with a hole at one end as a reaction jet, and use a heater to
>drive the steam.

You'd probably only need a rigid cover in the region around the jets.
The rest of the comet could probably be covered with mylar.  A rigid
cover around a 20 km diameter comet sounds expensive.

---
Dan Tilque    --    [e-mail]

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

Date: 31 May 90 01:09:12 GMT
From: zaphod.mps.ohio-state.edu!uwm.edu!csd4.csd.uwm.edu![e-mail]  (Mark William Hopkins)
Subject: Re: Problems of missing mass

In article <[e-mail]> [e-mail] (Pavlos Papageorgiou) writes:
>  It was recently posted in this group that the large number of
>small dark bodies postulated to exist in the inter-stellar region and
>constituting a great part of the mass of galaxies, be the result of
>ejections from solar systems rather than independent formation.

Actually, it was that some people recently misinterpreted the original article
this way.  Nothing of the like was ever said, but that's how the rumor got
started...

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

Date: Thu, 31 May 90 01:27:59 -0400
From: Glenn Chapman <[e-mail]>
To: [e-mail], [e-mail], [e-mail],
        [e-mail], [e-mail],
        [e-mail], [e-mail]
Subject: Soviet Soyuz TM-9 problems not a risk to cosmonauts

     A number of news reports have been issued in the past week concerning
the damage to the Soyuz TM-9 capsule currently at the Russian's Mir space
station.  An article in the May 21 Aviation Week and Space Technology
prompted the reports, carrying the title "Damaged Soyuz Spacecraft Puts
Cosmonauts at Risk."  The interesting thing is that almost all of the
information discussed has been public knowledge since Soyuz TM-8 came down
on Feb. 14th (and even my postings contained them several months ago).  The
truth, as far as I have been able to obtain, is far less lurid.  The facts
are as follows.  During its launch on Feb. 11th Soyuz TM-9 appears to have
developed a problem when the aerodynamic shroud surrounding the capsule
separated.  Three strips of the dark green thermal insulating blankets
which cover the descent section tore loose, and are now floating outward
from the craft, like petals from a flower (note the Soyuz consists of three
sections: a nearly spherical orbital section at the front, a bell shaped
descent module in the center, and a cylindrical support section with two
solar wings at the rear - only the center section returns to earth).  There
are two areas of concern, the first being that thermal stress on the
capsule instrumentation will be increased possibly leading to a system
failure.  The most probably danger here is the build up of water or ice if
the module gets too cold. To prevent this the Soviets have been restricting
the orientation of Mir itself to keep the craft at a moderate temperature.
Note though that these blankets are not as important as the highly
reflective gold foil covering most US space craft, their dark green colour
indicates that (neither black to radiate heat, or reflective to reject it).
The second worry is that the flapping of the blankets during movement may
disturb the horizon sensors at the reentry rocket ignition.  This flapping
was clearly seen during the Moscow Vermya TV tapes of the Soyuz TM-9
movement to the front (ball end) of Mir in February.  The blankets could be
seen being moved by maneuvering jets.  TV reports at the time mentioned the
difficulty and said there was no treat to the cosmonauts.
     Since this hit the news there have been articles in Isvestia (as
reported on the BBC), and announcements by TASS.  All repeated the points
above, stated there was no danger and spokesman noted that the blankets
played only a subsidiary role in the capsule temperature maintenance.
Finally some discussion of the needed repairs was made.  When the Progress
42 cargo craft docked May 8th it brought up some of the repair materials,
but most will be in the 20 Tonne Krystall expansion module for Mir, planed
for a May 31 launch.  Cosmonauts Anatoly Solyov and Alexander Balandin will
then take a space walk to reattach the blankets by first exiting the Kvant
2 airlock from the module sitting on the side of Mir.  Then an extendible
lander will be set up between Kvant 2 and Soyuz TM-9 (docked to the front
ball port axis) which the space walker will move along.  He will either
reattach the insulation or cut it off.  (AW&ST May 20, BBC May 20, TASS May
22)
     Two other points here.  On May 22 the Progress 42 tanker craft was
used to refuel Mir, then separated from it on May 27th, and reentered on the
28th.  The Solyov and Balandin then moved Soyuz TM-9 from the front to the
rear port in preparation for Krystall's launch.  As the Russians have
always been very conservative with their long duration capsules this
suggests they had little worry about this one.  Once they separated the
capsule from the station they would have real problems if there was a
failure in the Soyuz.  Secondly if there was significant concern all they
would likely do is send up a new unmanned capsule for the crew to use.  At
worst, if there was no spare on the ground (unlikely as that is), they
could cancel the Soyuz TM-10 mission set for July and use it.  The Soviets
have done this before: in Apr. '79 Soyuz 33 failed to dock with their
earlier Salyut 6 station, leaving the Soyuz 32 crew with a capsule that had
exceeded the 90 day orbital rating in force at that time.  All they did was
launch Soyuz 34 unmanned in Jun. '79, return the Soyuz 33 unmanned, and
bring the crew down in the new capsule (incidentally setting the desired
space endurance record of 175 days at that time).  Reports on TV here
talking about a NASA rescue ignore that, the difficulty of putting the
shuttle in the right orbit without flying a special mission, and the fact
that long before any US flight could occur the USSR could launch its own
rescue craft.
     In summary these reports seemed so strange that I wished to confirm
that no new information had come out before I posted this note.  What it
shows most is how a sensational report, even when not put in the proper
prospective, can generate lots of coverage of a space event.
Unfortunately, many reporters are even more uneducated on Soviet programs
then they are on Western programs.
     Currently cosmonauts Solovyov and Balandin, who have spent 109 days in
orbit, are preparing for the arrival of the Krystall expansion module,
scheduled for a May 31 launch according to TASS.  However, note that at
this time (late May 30th) there has been no mention of this launch for
several days.  They will be returning on July 29th after the Soyuz TM-10
crew arrives.

                                                Glenn Chapman
                                                MIT Lincoln Lab

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

Date: 31 May 90 03:48:34 GMT
From: clyde.concordia.ca!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: shuttle reliability

I finally got around to digging out my copy of the OTA report "Round Trip
To Orbit", which talks about future manned-spaceflight alternatives for
the US.  Although this is generally an interesting report, the real hot
spot is the comments on shuttle reliability...

- NASA's objective was a 97% probability of an orbiter lasting 100 flights.
    It's hard to say how well this has been achieved, since NASA makes
    little attempt at quantitative estimation of reliability.

- However, if reliability had been that high (equating to 99.97% chance of
    completing each mission successfully), the odds against Challenger
    being lost would have been 130:1.  It seems very likely that the
    reliability isn't that good.

- The best guess at reliability from the observed success rate is 96%.

- Shuttle launches to date provide only 50% confidence that the reliability
    is at least 94.3%.

- If reliability is now 94.3%, there is a better than even chance of losing
    at least one orbiter on the next 12 flights.  [These estimates will
    have improved a bit, as the report was written only four flights
    after Challenger.]

- If post-Challenger reliability is 98% -- there is little confidence of
    this in an objective statistical sense -- there is a 50% chance
    of losing another orbiter within 34 flights (about three years
    at planned near-term launch rates).

- At 98%, the chance of having four orbiters available for space station
    construction start is 28%.  The chance of having all four still
    operational at the end of station construction is 12%.

- At 98%, there is a 30-40% chance [reading off the graph, they don't cite
    a number for this one] that another orbiter will be lost before
    Endeavour is finished.

The report draws a number of conclusions about possible approaches to
take -- OTA tends to list alternatives rather than making recommendations --
but they say, loud and clear, that an ongoing shuttle fleet absolutely
requires ongoing orbiter construction.  And the decision to build the
next one will have to be made in the next year or two.

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

Date: 31 May 90 05:38:18 GMT
From: usc!zaphod.mps.ohio-state.edu!rpi!uupsi!uhasun![e-mail]  (Jon Bloom)
Subject: Re: Radiation

In article <[e-mail]>, [e-mail] (Ralph Reid) writes:
>
> An Amateur Radio satellite (perhaps it is OSCAR 11?) is currently in
> a low orbit because the kick motor which was supposed to push it into
> its proper orbit after it left the launch vehicle failed.  As I

It was AMSAT-OSCAR 10 (launched in 1984, I think it was), and it's not
in a low orbit (apogee ~34,500 km), but it _is_ in an orbit with a
lower than expected inclination (~26 degrees) because of kick motor
problems.

> understand the story, radiation continued to damage the main memory
> of the onboard computer.  To compensate for this problem, the control
> program was modified to fit into the smaller space, until there was
> no undamaged memory left to work with.  The satellite now operates in
> only one communication mode, and only when the batteries have been
> sufficiently charged.  Because the computer can no longer be operated,
> no telemetery is transmitted by the satellite.  More information

That's right.  The satellite does not have rad-hard memories because
of the cost.  (Hams have to work from donated funds--the entire cost
of the satellite was only a few hundred thousand dollars, in part
thanks to some donated materials.)  The OSCAR-13 satellite, launched
in 1988 and occupying the design orbit (~57 degree inclination, 37,000
km apogee) _does_ have rad-hard memories that were donated by Harris Corp.

Also, the University of Surrey recently launched two satellites into
LEO that include experiments for the measurement of radiation effects
on memory.  Unfortunately, one of the two satellites hasn't been
heard from since shortly after separation.  I don't know offhand the
mix of the experiments, so I'm not sure if the working satellite has
radiation experiments or not.  I could find out if anyone is dying to
know.

Jon

--
Jon Bloom, KE3Z                              | American Radio Relay League
Internet: [e-mail]         |
Snail:    225 Main St., Newington, CT 06111  | "I have no opinions."

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

End of SPACE Digest V11 #470
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