Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_4/V10_413.TXT

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Subject: SPACE Digest V10 #413

SPACE Digest                                     Volume 10 : Issue 413

Today's Topics:
       Re: March 1990 ANALOG article on self-refueling vehicles
     Cosmonauts successfully install star sensors on Mir
              Greenhouse effect
            ADDITION TO SUBSCRIPTION LIST
            Re: Nuclear Reactors in Space
             NSS' DIAL-A-SHUTTLE
            Standardized payloads
         Re: Red Shifts through Random Media
               Re: Mars rovers
----------------------------------------------------------------------

Date: 10 Jan 90 19:32:39 GMT
From: frooz![e-mail]  (Steve Willner, OIR)
Subject: Re: March 1990 ANALOG article on self-refueling vehicles

> In article <[e-mail]> [e-mail] () writes:
>>I don't see what difference it makes that the reactor is not operational
>>until after departure,

From article <[e-mail]>, by
[e-mail] (Paul Dietz):
> The halflife of U-235 is eight million times the halflife of Pu-238
> (the stuff used in RTGs), so, pound for pound, it is about 8 million
> times less radioactive.

Uranium also lacks plutonium's tendency to accumulate in the blood
forming tissues (i.e., bone marrow and such), so the radiation from
uranium isotopes is on average delivered to less vulnerable targets.
Also, uranium is less chemically poisonous than plutonium, though
chemical toxicity is probably not much of an issue in this context.
-------------------------------------------------------------------------
Steve Willner            Phone [phone]         Bitnet:   willner@cfa
60 Garden St.            FTS:      830-7123           UUCP:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]

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

Date: Wed, 10 Jan 90 19:17:53 EST
From: <@ll-vlsi.arpa:glenn@vdd> (Glenn Chapman)
To: [e-mail], [e-mail],
        [e-mail], [e-mail],
        [e-mail], [e-mail]
Subject: Cosmonauts successfully install star sensors on Mir

     This year's major space activities on board the Russia's Mir space
station have begun with cosmonauts Alexander Viktorenko and Alexander
Serebrov making a space walk.  On Jan 8th they opened the hatch at 23:23
Moscow time (15:23 EST), about one hour latter than intended.  They then
brought out two 80 Kg (176 lbs.) stellar sensors which were attached to
Kvant 1's scientific equipment sections (the astrophysical module at the
back end of Mir).  These star sensors will enable more accurate orientation
of the station which has been made more difficult with the addition of the
Kvant 2 module to the side docking port.  These transducers were mounted
in place and the electrical connections made to the stations external
signal bus.  In addition the Viktorenko and Serebrov retrieved some samples
left on the hull in earlier walk.  Which EVA started that experiment was as
not stated but my records show that on Dec. 9, 1988 Alexander Volkov and
Jean-Loup Chretien (the French visitor) placed some French samples on Mir's
surface originally intended to be retrieved some in six months (June '89).
However, Mir had been closed down on Apr. 27 '89 so the decision must have
been made to leave the samples until now, about 13 months later.  Distance
traveled from the hatch in this EVA was about 35 meter (114 ft.).  It was
not stated in the announcements which airlock which airlock was used, the
older one on Mir or the new larger system on Kvant 2.  However, 35 meters
would be about the distance from the end of Kvant 2 to the Kvant 1 section.
Also the TASS announcement made a point of calling this the longest
distance traveled away from the airlock on the outside of the station, and
many cosmonauts have walked up to the Kvant 1 section from Mir's port. The
total time for this space walk was 2 hours 56 min.  Rather surprisingly the
next EVA is scheduled for Thursday Jan 11 (no time released as of yet).  An
additional 3 more space walks are planed for before Feb. 24th, when
Viktorenko and Serebrov will be replaced on Mir with a new crew.
     A least this decade begins with a manned space station in orbit,
something the 70' and 80's did not.  Hopefully the turn of the century will
show zero G facilities from two or more nations/organizations permanently
manned.


                                             Glenn Chapman
                                             MIT Lincoln Lab

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

Date: Wed, 10 Jan 90 20:27:17 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Greenhouse effect


>From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
>Subject: NASA Headline News for 12/22/89 (Forwarded)

>The Washington Post reports that scientists have scaled back
>predictions of a significant sea level rise in the next 100 years
>because of global warming.  The latest prediction is based on a
>noticeable accumulation of snow and ice in Greenland and
>Antarctica.  Data from Greenland was gathered by scientists at
>NASA's Goddard Space Flight Center using satellites.  A
>University of Wisconsin polar research center study indicated
>similar snow and ice accumulation in Antarctica.

Ha! I knew it! Everybody's worried about the greenhouse effect, and we
could be heading for another ice age! Here in Maryland, our last two
summers were significantly cooler than usual (though nobody but the
meteorologists believe it), and this past December was the coldest on record.
(Purely by coincidence, I greatly prefer hot weather to cold weather, and
live ~600 feet above sea level. :-)

Just think how bad it would have been if we had stopped burning coal and
used nuclear reactors for power generation. :-)
                         John Roberts
                         [e-mail]

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

Date:    Wed, 10 Jan 90 12:44 CST
From: [e-mail]
To: <[e-mail]>
Subject: ADDITION TO SUBSCRIPTION LIST

Could you please add <[e-mail]> to
your mailing list of space digest.

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

Date: 10 Jan 90 22:53:35 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: Nuclear Reactors in Space

In article <[e-mail]> [e-mail] (Neal Woodall) writes:

>Sure, there is a fundamental similarity: both use nuclear processes to "store"
>their energy (as opposed to chemical proceses in a battery). Beyond this, they
>are dissimilar.

Wrong; both also convert heat to electricity.

>1) The reactor uses a fissionable form of Plutonium which emits fast neutrons
>and is capable of sustaining a nuclear reaction,

As far as I know, all space reactor designs will use U-235, not
plutonium.

> while the RTG uses a non-
>fisionable form of plutonium which emits only (I believe) beta particles.....

Alpha particles.

>which you you rather be hit by, a bunch of fast neutrons or a bunch of beta
>particles?

Of course, if the reactor breaks up, it *stops* making neutrons.  The
RTG continues to emit alpha particles even if it disintegrated down
to component atoms.

>2) The nuclear reactor gets its power from a sutained nuclear reaction, and
>as such has the potential to get out of hand, while the RTG gets its power
>strictly from nuclear decay...no chance of a runaway chain reaction here.

Runaway chain reactions are not a problem.  If the chain reaction uses
thermal neutrons, the most a runaway reaction can do is disperse the core
with about the energy yield of the same mass of chemical explosives.

> 3) Because the nuclear reactor actually has a sustained nuclear
> reaction going on inside of it, it needs active control systems to
> dampen the reaction....thus, it is much more complex.

A properly engineered reactor has inherent negative feedback.  As
the core heats up, the thermal neutrons get hotter, and the chance
a neutron will cause a fission goes down.  You do need to adjust
for buildup of neutron poisons (xenon, for example), but this is
a slow process.

>In all, the RTG is an excellent trade-off of safety and power: because it uses
>nuclear fuel, it has a very high energy density....much higher than chemical
>batteries. However, because the fuel is not fissionable, it is much safer.
>Also, because there is no nuclear chain reaction, it is safer than a reactor.

Not safer.  A reactor contains much less radioactivity before it is turned
on.  An RTG is already radioactive at launch time.

    Paul F. Dietz
    [e-mail]

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

Date: 10 Jan 90 22:45:24 GMT
From: [e-mail]  (Eric William Tilenius)
Subject: NSS' DIAL-A-SHUTTLE


                          DIAL-A-SHUTTLE

                          1-900-909-NASA

Listen to the astronauts!  Plus updates and features, 24 hours a day, from
Launch to Landing.  Sponsored by the National Space Society.

($2.00 first minute; $.45 each additional minute.)

                    CALL  1-900-909-NASA

- ERIC -

         (__)         Eric W. Tilenius
         (oo)
  /-------\/          President, Princeton Planetary Society
 / |     ||
*  ||----||           609-734-7677  //  [e-mail]

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

Date: Wed, 10 Jan 90 20:51:00 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Standardized payloads


>From: ibmpa![e-mail]  (Nick Szabo)
>Subject: Cargo: costs and standards

>>In article <[e-mail]> [e-mail] (Nick Szabo) writes:
>>>Unmanned strikes again!  Delta launches cost probably one-fifth to
>>>one-tenth of a Shuttle launch, depending on whose accounting you want
>>>to believe.

>Of course, I was talking about absolute cost, not cost per pound.
>Delta launch versus Shuttle launch, is what I said.

Therefore, obviously, the Shuttle should not be used to launch small
payloads that do not require human presence. This is the "window of
opportunity" being used by the startup launch companies - very small
payloads at a low price, so "medium-sized" organizations can afford to
buy launch services.

>Hopefully, we will soon have a set of standards for space cargo.  In fact, I
>can foresee somebody like AMROC making a "Delta clone": a launch vehicle with
>the same exact cargo hold as the Delta, with the same lift capability, but
>using the new AMROC engine technology.  That way, satellite makers can
>design their satellites for the standard without have to commit to any
>specific launch vehicle.  Also, implementers of new technologies like
>EML or laser-launch would be well-advised to scale the machines to
>existing payloads.

So I should design my payload so that it can be blasted into space at
~10000G, or wafted gently upward at ~5-10G, depending on which service
is the cheapest at the time, and that will save money? :-) I agree with
Henry, who pointed out that exotic new launch services will probably be
most useful (at least at first) in entirely new applications.

I agree that coming up with several discrete classes of standardized
payloads is probably a good idea.
                              John Roberts
                              [e-mail]

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

Date: 11 Jan 90 01:39:00 GMT
From: shelby![e-mail]  (Anthony E. Siegman)
Subject: Re: Red Shifts through Random Media

The work is by Professor Emil Wolf at the University of Rochester and
you should be able to find it by looking through the indexes of the
various journals of the Optical Society of America for the past
several years.  (At least I think this is what you're referring to.)
Might look into Phys. Rev. Letters also.

I don't think you'll find the discussion awfully understandable,
however.  In my opinion, the essence of Wolf's work is not that the
light gets red-shifted, but that when a broad light spectrum passes
through certain scattering processes a greater fraction of the red end
of the spectrum (and a lesser fraction of the blue end) gets scattered
toward the observer, with the result that the light received by the
observer appears red-shifted compared to the original light spectrum
before scattering.

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

Date: Wed, 10 Jan 90 22:17:46 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Re: Mars rovers


>From: zephyr.ens.tek.com!tektronix!percy!parsely!bucket![e-mail]  (Leonard Erickson)
>Subject: Re: Mars rovers

>[long argument for getting around the time-lag and AI problems of
>a Mars rover by slowing it down deleted]

>Fine, the rover is creeping along at the feet feet per hour that you
>suggest is safe. Now something unexpected happens. The surface shifts.
>(loose rocks hidden by dust, a dust pocket, whatever]

>The rover *must* make a real time response. If it isn't autonomous, it
>can't. You can handle some things be designing in recovery gear (like
>those levers for righting it that you mentioned) but the odds are
>against you. What do you do it it manages to "high center" itself?
>or if it is traversing a slope and starts to slip?

Autonomy and real-time control are good as far as it goes, but they are not
sufficient. Suppose the rover moves out over a thin-shelled volcanic bubble,
which suddenly collapses. Or suppose the rover travels halfway down a slope
of loose rubble, then triggers an avalanche. In either case, even an
immediate response is far too late, and the rover will be destroyed.

That's where the propagation of information backward in time comes into
play. (The technique is described in the novel Thrice upon a Time, by James
P. Hogan.) If the rover receives continual status updates from a future
version of itself, say over a 5-10 minute span, then it will perceive upcoming
dangers, and thus avoid the bubble or the unstable slope. This approach is
clearly so vital to the safety of the rover, that we must hold off rover
deployment until this technology has been perfected. :-)

(Disclaimer: OK, maybe I'm being a little sarcastic, but I'm trying to make
a point.)

In the message I posted 1-2 months ago, it should not be construed that I
was promoting remote control as a *goal* - I suggested it merely as an
*expediency*. (This is comparable to the popular misconception of RISC
computer design - that reducing the instruction set somehow improves
performance. In fact, the goal is to improve the performance of the
individual instructions, which usually means that the instruction set has to
be trimmed down to limit chip complexity.) Sure, feel free to include as
much local autonomy as you can manage, but I feel it is counterproductive
to deliberately hold up deployment for many years while searching for a
perfect "fully" autonomous control algorithm. This greatly increases the
complexity and cost of the project, as well as the time before the first
rover data is obtained.

The rover design proposal that I have been most impressed by is the CMU
rover, which uses a laser rangefinder to build up a model of its
surroundings, and walks on pivoting legs. It will supposedly be "mostly"
autonomous. Note that the proposed rate of motion (a few centimeters per
second) is not much faster than the rate at which I think a "more remote-
controlled" rover would be able to move, given local feedback and the
ability to follow a fairly complex set of instructions. (In either case,
maximum safe speed will be affected by the "roughness" of the terrain.)
I think that autonomous land rovers that can bound along at 40 miles per
hour are several decades away.

In the case of the CMU rover, I suspect that the hardware will be done
before the software is perfected. If that turns out to be the case, I
would recommend that the project push for launch as soon as possible,
based on the following argument:
  It is not necessary that the rover be "fully" autonomous before it can
  be useful. At worst, it can operate under close human supervision, and while
  its rate of travel will be reduced, it can still collect a considerable
  amount of data. In the meantime, development of autonomous control software
  can proceed at essentially the same rate that it would if the rover were
  sitting back on earth doing nothing. When this development is complete,
  the internal program of the rover can be updated. Moreover, software
  development can continue over the ~2-year trip from Earth to Mars. There
  are precedents for this situation. The hardware of the Space Telescope
  was essentially complete long before the control software was ready.
  The control algorithms of the Voyager spacecraft were considerably
  enhanced years after they had been launched.

I agree with your contention that the first target for local autonomy
should be in safety systems, such as avoidance of large rocks and holes,
slip detection, and antenna pointing. Once these systems are in place, it
is time to concentrate on performance enhancement.

The arguments about interruptions in communications and bandwidth required
must also be considered.
                       John Roberts
                       [e-mail]

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

End of SPACE Digest V10 #413
*******************