Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/spacedig/V16_3/V16NO362.ZIP/V16NO362

Internet Message Format | 1993-07-13 | 32KB

Date: Thu, 25 Mar 93 05:19:28
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #362
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu, 25 Mar 93       Volume 16 : Issue 362

Today's Topics:
                     Artificial Gravity (2 msgs)
                         Canada Space Program
              Can we still build the Saturn V? (2 msgs)
                            CRAF's budget
                                 DC-X
                               gravity
                          How to cool Venus
                       Inflatable lunar habitat
                          Life in the Galaxy
          Rocket clones: reduce risk of introducing new tech
                       See Grechko is possible
           Simple atmosphere calculations (was Re: gravity)
            Skintight suits (was: Re: Water Simulations...
                        STS-55 launch aborted
                      temperature of Lunar soil
                        Uplink/downlink rates
    Water Simulations (Was Re: Response to various attacks on SSF)

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

Date: 24 Mar 93 15:34:18 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Artificial Gravity
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (neil storey) writes:
>
>
>Since the film "2001" every school-boy has known that the
>solution to the problem is simple (at least in principle). One
>simply constructs a space station in the form of a torus
>and then spins it at an appropriate rate such that
>the centrifugal force (caused by the centripetal acceleration)
>is equivalent to the force of gravity on earth. The force
>experienced is proportional to the product of the radius of
>the toroid and the square of its angular velocity.
[delete]
>Many people have pointed out the
>impracticability of attempting to build such a large torus in
>space when every piece must be shuttled from earth. However
>this argument overlooks two important points: firstly that it
>is not necessary to recreate full earth gravity in space, even
>a fraction of this value would be of great benefit; and
>secondly, it is not necessary to construct the complete torus
>to simulate gravity, two small spacecraft linked by a cable
>would have the same effect. The planned Russian mission to
>mars would/will consist of two spacecraft. If these where joined
>together by a cable and the resultant binary spun, both craft would
>experience artificial gravity.
[delete]
>Since it seems inconceivable that no-one has thought of this
>idea before, it would seem obvious that there must be some reason why
>this approach to artificial gravity is unusable! I would be
>very grateful to any readers who could throw some light on
>this problem.

The physiological effects of gravity, simulated or otherwise, are
fairly well understood due to our long experience right here on
Earth. Thus the majority of experiments in space have dealt with
the novel effects of microgravity. Since most everything launched
into space is an experiment intended to discover the problems and
advantages of the space environment, duplicating earthly conditions
has not been a high priority since we already have a large experience
base with earthlike conditions. Long term microgravity exposure in
LEO is intended to find answers to the question of whether spun
or despun structures and craft are better for long term or semi-
permanent use. It may be that we can manage the problem in less
costly or complex ways than by spinning our structures. Many things
we'd like to do are easier in despun structures, so the cost of
spinning is more than just the cost of rigging a cable.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

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

Date: 24 Mar 93 16:35:09 GMT
From: Steve Willner <[e-mail]>
Subject: Artificial Gravity
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (neil
storey) writes:
> secondly, it is not necessary to construct the complete torus
> to simulate gravity, two small spacecraft linked by a cable
> would have the same effect.

Research has been proceeding, but on a very slow track.  The recent
tether experiment was supposed (among other things) to answer the
first-order question of whether a line could be unreeled and then
reeled in again without something unpleasant happening.  There appear
to be no show stoppers, but there is a lot still to be learned.
--
Steve Willner            Phone [phone]         Bitnet:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]
  member, League for Programming Freedom; contact [e-mail]

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

Date: Wed, 24 Mar 93 00:47:57 CST
From: "Norman P. Paterson" <[e-mail]>
Subject: Canada Space Program
Newsgroups: sci.space

[e-mail] writes:

> In article <[e-mail]>, [e-mail] (Joel Sem
> > I need information about the Canadian Space program.  Does anybody know whe
> > I can obtain information pertaining to jobs in the space program.  If anyon
> > has any information that they can give me about who or where I can contact
> > would really appreciate it.  Thanks.
> >
> > Joel Semeniuk
> > Computer Science III
> > University of Manitoba
> > Winnipeg, MB.
> >
> >
>
> Read the latest issue of "FINAL FRONTIER"  There is a whole article on the
> Canadian Space Program.
>

Read the Globe and Mail daily, I've seen many positions posted for the
Canadian Aerospace/Space industry these last few months.
Too, you may want to contact Spar and Bristol Aerospace; as they are
active in the exploration of space.
Also, contact the department of Industry, Science & Technology; they have
comprehensive directories of Canadian firms involved in Space Exploration
and also an online database of the same.  The database service known as
"BOSS" is offered as a service to Canadian taxpayers for free.  Simply
tell them the type of company you are seeking and they will provide a
print-out or dBase compatible format on disk; instantiously.
        It may be an idea to also contact the NRC, Defense Department,
and the Canadian Space Program Headquarters.

[e-mail]
The Inquiring Mind BBS, Winnipeg, Manitoba  204 488-1607

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

Date: 24 Mar 93 14:49:57 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Can we still build the Saturn V?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (David Drumheller) writes:
>
>   It always appeared to me that for boosting large payloads (e.g. a space
>station or portion thereof) the shuttle is far too expensive.  Therefore,
>people have suggested the `big dumb booster.'  Yet others have said the
>development of such a booster would be expensive.
>
>   My counter argument to this is to dust off the old blueprints for the
>Saturn series and start building them again.  The technology may be close
>to 30 years old, but so what?  They worked.  And there would be almost no
>development cost.
>
>   However, a friend of mine said that NASA (and/or the contractors) lost
>the blueprints?  Is this true?  Have other's suggested the use of the
>Saturn series, and then found that the plans have been lost?

The Saturn plans are still at Huntsville. However, the contractor
infrastructure is gone, many subassemblies were farmed out to
small shops that are either out of business or who have long since
discarded the necessary tooling. It's estimated it would cost at
least $16 billion to retool to produce Saturns to the old plans.

It should also be noted that Saturn didn't have very many flights,
so reliability statistics are not available. This is a similar
problem to that facing Energia. Many NASA and contractor engineers
believe we were incredibly lucky with the Apollo program and that
if it had continued we would have inevitably lost missions. Also
Saturn launches were expensive.  They cost about $550 million in
*1967* dollars. A 1993 dollar is worth 12.5 cents in 1967 dollars
so multiply costs by 8 to get current pricing.

In reality you wouldn't want to reproduce Saturn in any event. There
have been sufficient advances in most of the flight systems since
Saturn was designed that a clean sheet of paper approach would be
better. It wouldn't be possible to get the avionics components used,
they are no longer made. So new flight systems would be required.
The F1 engine could be resurrected fairly cheaply, but better engine
designs exist. And tankage is pretty much tankage, though the pogoing
problem of Saturn was never really solved. Saturn was designed in
the days of slide rules and drafting boards. With today's advanced
design tools, CAD and CADCAM, finite structural analysis, etc, a
lighter, stronger version could be designed with considerable
confidence that it would work to near spec.

The Big Dumb Booster idea is a good one. There are many possible
missions that could be flown using heavy lift, though none are
planned because we don't have heavy lift anymore. The only current
programatic need for heavy lift that exists is for a possible rescoped
Freedom. The current Freedom design does not require heavy lift by
design since only Shuttle is available. The rescope of Freedom now
underway probably will not use heavy lift either, since we don't
have heavy lift. It's chicken and egg. Freedom was based on in space
assembly since we don't have heavy lift. Now with fears of in space
assembly, and still no heavy lift, the New Freedom will probably
consist of small docked cans, like MIR, if it's built at all.
Meanwhile, the Russians are going ahead with MIR II which will use
a truss design, and many other features of old Freedom. They have
the option of heavy lift if needed, and they aren't afraid to try
major in space assembly as their next baby step into space. They've
already done docked cans so there's no need to repeat that experiment.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

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

Date: 24 Mar 93 18:28:25 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Can we still build the Saturn V?
Newsgroups: sci.space

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

>>However, it would cost $16 billion to begin production again and

>$16 BILLION?  Not $16 million?


Yep.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------84 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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

Date: 24 Mar 93 15:11:35 GMT
From: Gary Coffman <ke4zv!gary>
Subject: CRAF's budget
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>Few NASA projects, manned or unmanned, would survive to fly if they had
>firm budget limits.  Overruns are a way of life for NASA space projects.

And it's not just NASA projects. Most "design by committee" projects
suffer from creeping featuritis when they are uncoupled from a firm
deadline and a firm budget cap. See most any military procurement
program, or look at the work of standard operating systems or languages
committees. It's the nature of the bureaucratic beast. When schedules,
objectives, and budgets are continually and arbitrarily changed by outside
agencies, the programs become totally out of control.

Even mundane things like skyscrapers can fall to this problem. The
PBS program _Skyscraper_ outlined how seemingly minor changes can
balloon program costs via an escalating series of change orders in
order to accomodate the origninal minor alteration.

Gary

--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

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

Date: 24 Mar 1993 08:32:57 -0500
From: Pat <[e-mail]>
Subject: DC-X
Newsgroups: sci.space

 There is a picture of DC-X in this weeks Space News.
It's still missing the skin,  so it looks more like a cream
separation plant then a spaceship.   I'd hav enever thought
it was meant to fly, if the caption hadn't told me what it was.

pat

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

Date: Wed, 24 Mar 1993 15:13:19 GMT
From: Joe Cain <[e-mail]>
Subject: gravity
Newsgroups: alt.sci.planetary,sci.astro,sci.space

In article <[e-mail]> [e-mail] (Jim Baker) writes:
>
>Acknowledging the fact that the earth has enough fravity to hold an
>atmosphere in place, and the moon (with approximately 1/6 of earth's
>gravity) does not, how much gravity does it take to hold an
>atmosphere?

See figure 11.10 in the text "Exploration of the Universe" by Abel,
Morrison, and Wolff (my copy has it on p. 193 and is the 1991 edition
from Saunders Publishing).

It combines the formula for molecular speeds as a function of
temperature and molecular weight of the gas with that for the escape
speed, which depends on gravity. The rate of escape depends on the
ratio of average speed to escape speed.

(I suppose the rate might also depend on the abilility of solar uv to
get to the gas and break apart molecules)

Thus the giant planets can hold most any gas, whereas a hot small
bodies like Mercury or the Moon have a hard time hanging on to
anything.

Joseph Cain        [e-mail]
[e-mail]        scri::cain
[phone]        FAX [phone] or -0098

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

Date: 24 Mar 93 14:16:13 GMT
From: Gary Coffman <ke4zv!gary>
Subject: How to cool Venus
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>
>> Rather than too much of the atmosphere being blown away, I suspect
>> the reverse would be the problem. It would take some *really* big
>> nuclear bombs to blow off 90% of the atmosphere. Certainly bigger
>> than anything we have a clue about building. Maybe some sort of
>> anti-matter bomb would work.
>
>
>Actually, thermonuclear explosives should be *easier* to engineer as
>they get larger.  The reason is fundamental.  The rate of reaction in
>a plasma of a given composition and temperature is proportional to the
>density.  The time available for the reaction to proceed, on the other
>hand, is proportional to the linear dimensions of the plasma.  What
>this means is that in small devices the fusion fuel must be highly
>compressed (laser fusion plans are for fuel to be compressed to 1000x
>its normal density).  In larger devices, lower compressions work; in
>very large devices, no compression at all would be needed, just
>heating to fusion temperatures.
>
>The biggest fusion bomb ever detonated was 60 MT (a Soviet test).
>This would be sufficient to ignite a large amount of uncompressed
>fuel.

I think you're wrong about this, in practice if not in principle.
And I'd point to the same Soviet test as a counter argument. It's
been reported that the Soviet test was intended to be a 100 MT
device, but that their hydrocodes weren't advanced enough to
allow them to make a bomb that big that wouldn't disassemble
itself prematurely. Of course a star is a perfect counterexample
as well. Fusion only occurs in the core areas where both compression
and temperature are extremely high. Trying for an intermediate
yield, between the Soviet bomb and the Sun, presents formidable
technical challenges.

>Antimatter would not be sensible, as it would be much too expensive
>to make.

Today. It will continue to be expensive in energy required, but if
the price of energy is sufficiently low, it might become economical.
There are few technical reasons why an anti-matter explosive can't
be any arbitrary size.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

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

Date: Thu, 25 Mar 93 00:18:39 EST
From: John Roberts <[e-mail]>
Subject: Inflatable lunar habitat

NASA Select just played a video of an envisioned inflatable habitat on the
moon. Maybe that aspect of the "Great Exploration" concept isn't entirely
dead. Perhaps the new Administration could be sold on the idea of inflatable
space habitats, on a cost-saving basis.

(The video was produced by JSC.)

John Roberts
[e-mail]

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

Date: 24 Mar 93 16:51:06 GMT
From: Charles Pooley <[e-mail]>
Subject: Life in the Galaxy
Newsgroups: sci.space

For those intersted in life in the galaxy, SETI, etc I reccommend the
book by Stephen Dole,  Habitable Planets for Man, Elsevier Publishing,
1970.   ISBN 0-444-00092-5     L Cong. 71-133445.

Though only 154 pgs, it discusses clearly some of the attributes of stellar
systems which might be conducive to development of live.   Good foundation
for discussing the topic...
--
Charles Pooley                  [e-mail]    GEnie  c.pooley
EE consultant, Los Angeles, CA

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

Date: 24 Mar 93 15:19:47 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Rocket clones: reduce risk of introducing new tech
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>As witness Pegasus, it *is* possible to create a new payload class with
>a new launcher.

Scout, and Ariane multiple satellite launch systems, had already created
the Pegasus payload class. What Pegasus brings to the table is rapid
unscheduled launch from any point on the globe of these payloads, though
at a cost premium over either Scout or Ariane.

Gary

--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

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

Date: 24 Mar 93 17:52:46 GMT
From: Josh Hopkins <[e-mail]>
Subject: See Grechko is possible
Newsgroups: sci.space

[e-mail] writes:

>BH>> Dr. Georgi Grechko, Cosmonaut
> Lecture Tour of the United States
>
>[long grueling itinerary which ends with:]
>Travel to Chicago, IL                       April 6

>Folks, if you have a chance to see Dr. Grechko, don't miss it.
>He visited San Diego a few years, and was one of the more informative
>and entertaining speakers on space I have met.

He visited here last week. I'll try to get around to posting a summary.  I would
unequivocally endorse David's comment.  The tickets were cheap (though I don't
know if that's true everywhere) and he's worth going to see.  Well informed,
funny and he has a lot to talk about.  Seeing as he's been part of everything
from Sputnik to their Moon program he has an interesting perspective.

>He is one of the few former Soviet cosmonauts who will answer
>*any* questions you ask about their space program.

Indeed.  He set aside more than half of his program to answer questions.  I'll
post some of the most interesting stuff soon.

--
Josh Hopkins                                          [e-mail]
          "Tout ce qu'un homme est capable d'imaginer, d'autres hommes
                     seront capable de la realiser"
             -Jules Verne

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

Date: 24 Mar 93 04:04:12 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: Simple atmosphere calculations (was Re: gravity)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Gary Coffman) writes:
> In article <[e-mail]> [e-mail] (Jim Baker) writes:
>>
>>Acknowledging the fact that the earth has enough gravity
>>to hold an atmosphere in place, and the moon (with about 1/6
>>of earth's gravity) does not, how much gravitiy does it take
>>to hold an atmosphere?
>
> The criteria for holding an atmosphere is simple. The mean
> free speed of the atmospheric constituent molecules must be
> below escape velocity.
[...]
> Given atmospheric temperature, and given atmospheric molecular
> mass, the necessary escape velocity is easily determined. Then
> a planetary mass can be calculated to supply that field strength.
> This is complicated somewhat by density considerations. The G
> field gradient is different for a large diameter low density
> world than for a smaller denser world.

Let's give the guy the formulas, shall we?  At least for the simple cases.

Kinetic energy of a molecule of ideal gas: 1.5 * kT
k= Boltzmann's constant, 1.381E-23 joules/Kelvin
T= Temperature in Kelvin degrees

Kinetic energy of a molecule is *also* 0.5 * m * v^2
m = mass of molecule in kilograms
v = speed of molecule in meters/second

You can set one of these equal to the other and solve for what you're looking
for (speed, temperature, whatever).

Escape velocity is given by (hmm, I always have to derive this over
again... *scribble scribble*

v = square root of (2GM/R)

where v is escape velocity
G is gravitational constant, 6.67E-11 m^3 kg^(-1) sec^(-2)
M is mass of planet in kilograms
R is radius of planet in meters

Find escape velocity, use it as v in the kinetic energy formula above,
then plug in molecular mass m and solve for T.  If T is colder than
the planet's peak surface temperature, you're likely to have an
atmosphere.  If not, not.

I'll bet you can play with these numbers to learn:

Why does the Earth have free oxygen and nitrogen in its atmosphere,
but not hydrogen or helium?

If the Moon orbited Jupiter, would it be cold enough to hold an oxygen
atmosphere?  How about Pluto?

 ...and many other things.  I haven't done this.

For questions like "How long could the Moon *keep* an atmosphere?" you
need a more complex model.

Bill Higgins, Beam Jockey              | Comet Swift-Tuttle is
Fermi National Accelerator Laboratory  | Mama Nature's way of
Bitnet:           [e-mail]  | saying it's time to
Internet:       [e-mail]  | get off the planet.
SPAN/Hepnet:           43011::HIGGINS  |   --Dale Amon

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

Date: Wed, 24 Mar 1993 15:56:24 GMT
From: "Phil G. Fraering" <[e-mail]>
Subject: Skintight suits (was: Re: Water Simulations...
Newsgroups: sci.space

[e-mail] (George William Herbert) writes:

>In article <1onsgi$[e-mail]> [e-mail] (Pat) writes:
>>I saw some old Air FOrce/ NASA footage on the old skin suits.
>>The fabric looked real hokey,  and the NASA PM for suit technology
>>claimed it could only achieve 1.5 psi, and they needed 5,
>>so it was a triple suit.
>>
>>Now with new spandex,  could a single layer produce between
>>3-5 lbs counterpressure?

>What you don't see in those films are the test subjects getting blood
>blisters and worse, several requiring emergency medical attention.

>Pure fabric pressure suits do poorly in joints, which is where they
>hold the advantage over normal suits (normal suits have difficulty
>bending, while fabric pressure suits can be much easier to move).
>If you get a little crease, suddenly it will start having bad
>things happen to the skin under the crease, etc.

>I have heard it rumored that some of those problems were solved, but
>the suit people I know and have talked to, both the Ames and Johnson
>teams, don't like the idea at all, and not because it's a threat.
>They have all sorts of sh*t land on them if people get hurt trying
>ideas out...

Then why should they be allowed to try out their own style pressure
suits?  After all, there are probably some injuries associated with
the early tests of those (prob. way back in the 40's, though).

Especially look at what happened to Alexi Leonov during the first
spacewalk: he's very lucky he didn't end up with a very damaging
case of the bends. (I don't know if the SU had started selecting
its cosmonaut corps for natural resistance to the bends yet).

Sorry, George, but if past injuries are a reason to stop investigating
a technology, let's stop throwing all those damn billions away on
space to begin with.

I sense a very big double standard here...

Besides, insisting on the "perfect safety" space suit is probably
a sure way of driving suit cost into the launch vehicle range while
producing something you can't do real EVA work in. I wonder how
much of the problems NASA has are due to this suit design philosophy.



--
Phil Fraering         |"...drag them, kicking and screaming,
[e-mail]|into the Century of the Fruitbat." - Terry Pratchett,
                       _Reaper Man_

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

Date: Wed, 24 Mar 1993 12:55:31 GMT
From: "Simon E. Booth" <[e-mail]>
Subject: STS-55 launch aborted
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:
>
>The launch of Columbia was aborted at T-3 seconds, just as the main engines
>were in the process of being ignited. No reason has been given yet, but a
>person watching the launch on NASA Select said that the flame of one of the
>engines didn't look as good as the other two.

I remember reading that the shuttle could reach orbit on only two engines,
but I thnk that was only if an engine had failed during ascent and not during
launch.

If the SRB's had ignited, we just might have seen either an RTLS abort or
an emergency landing in either Spain or Senegal.

Or a single orbit for a landing in California or at White Sands.

Either one of these situations would have been complicated even more with
the extra weight of the Spacelab, although perhaps the trans-Atlantic
aborts would have been riskier since the runways used would just barely
long enough to handle a fully loaded orbiter landing at 250 mph.

Although I would imagine any payload would be heavy enough to cause some
problems.
                        nical info recently posted to this group on the
Incidentally, in the technicl info recently posted to this group on the
DC spacecraft, it was mentioned that the shuttle program had experience
a 'near crash' on landing.  When was this and which orbiter was involved?
I know there have been problems with the brakes overheating on some landings
but I've never heard of anything more serious than that during a landing.
BTW- Is Spacelab the heaviest payload the shuttle has carried?


Simon

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

Date: Wed, 24 Mar 93 15:48:22 GMT
From: Russ Brown <[e-mail]>
Subject: temperature of Lunar soil
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Russ Brown) writes:
>>Since the measurements were only made in the top few metres of the
>>regolith, and those, of necessity, were all made during transients, the
>>1.3K/m extrapolation is probably of little value.
>
>I agree that the extrapolation is of little value.  Indeed, there are
>hints in the data that the rate of increase is falling as depth increases,
>but it's impossible to be sure with such scanty data.

Agreed.
>
>Note, though, that the measurements were not made "during transients".
>(I'm not quite sure what that is meant to mean, but I suspect the intent
>was "during visits".)  The sensors were part of the ALSEP packages that
>were left on the Moon; the measurements covered a number of months.
>(This is why we can separate day-night variation from steady-state
>temperature.  The day-night variation is zero at the depths in question.)
>--

The measurements above 1.5 m were subject to the constantly changing
surface conditions.

The temp at 1.5 m and lower should be constant; it could be predicted
using heat transfer calculations, including the changing boundary
conditions at the surface.

More data would be required to estimate the variations of temperature
with depth, whatever it is.

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

Date: 24 Mar 93 16:46:40 GMT
From: Steve Willner <[e-mail]>
Subject: Uplink/downlink rates
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Steve
Collins) writes:
> It was pointed out to me that the transmitter power is less factor in the
> differing up and downlink rates than the receiver antenna sensitivity.
> The ground antennas can be very big...

The antenna gains will be the same in both directions as long as the
same antennas are used for transmit and receive.  (They usually are.)

Given a pair of antennas and a distance, data rates will be limited
by transmitter power and receiver noise.  The DSN receivers are the
best that can be built.  Spacecraft receivers are fairly noisy, but
very reliable and lightweight.  They could no doubt be made quieter
if there were a requirement to do so, but uplink does not generally
require high data rates, and even if high rates are required, it's
usually easier to raise the transmitter power.

The real answer, then, is that uplink rates are low because there's
no need to make them higher.
--
Steve Willner            Phone [phone]         Bitnet:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]
  member, League for Programming Freedom; contact [e-mail]

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

Date: 24 Mar 1993 08:30:25 -0500
From: Pat <[e-mail]>
Subject: Water Simulations (Was Re: Response to various attacks on SSF)
Newsgroups: sci.space

References: <1ojede$[e-mail]> <[e-mail]> <1onsgi$[e-mail]> <1op1ou$[e-mail]>
Nntp-Posting-Host: access.digex.com
Sender: [e-mail]
Source-Info:  Sender is really [e-mail]

 What the NASA guy, said, was that at any place where a void can
form, the crotch, the joints,  a gel bag needed to be placed in order
to prevent  air voids.  I was thinking that maybe a gel slurry
kind of like thick jello molded inside the suits and smeared on the astronauts
bodies would provide a similiar protection with less complexity.
it would be a semi-hydraulic fluid protection.

pat

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End of Space Digest Volume 16 : Issue 362
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