Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_5/V13_579.TXT

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Subject: SPACE Digest V13 #579

SPACE Digest                                     Volume 13 : Issue 579

Today's Topics:
          Re: SPACE STATION FREEDOM WOUNDED
         Re: New Subject--Solar Collectors/Antimatter
               Re: Saturn V and the ALS
     Re: Re: Ethics of Terraforming (was Re: Terraforming Venus)
             Re: Space Station Cancelled
          Re: Tethers (was Re: Gas Guns and Tethers
         Re: If no Freedom, what comes next?
              Re: Why the space station?
                BITFTP Demise

Administrivia:

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

Date: 16 May 91 12:56:18 GMT
From: iggy.GW.Vitalink.COM!widener!hela![e-mail]  (Allen W. Sherzer)
Subject: Re: SPACE STATION FREEDOM WOUNDED

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

>NEWS FLASH!  NEWS FLASH!  Spending $120,000,000,000 will
>REDUCE COSTS!!!  Pictures at 11!

Gee Nick I thought you understood finances better than that. I would
say the computer and electronics industry has spent well over that
much over the last 30 years to develop markets, processes, and products.
I think has reduced costs. Don't you agree?

   Allen
--
+---------------------------------------------------------------------------+
|Allen W. Sherzer |        Allen's tactics are too tricky to deal with      |
|   [e-mail]   |             -- Harel Barzilai                           |
+---------------------------------------------------------------------------+

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

Date: 16 May 91 07:35:15 GMT
From: att!emory!wa4mei!ke4zv![e-mail]  (Gary Coffman)
Subject: Re: New Subject--Solar Collectors/Antimatter

In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>
>My question regards the efficiency of solar collectors.  Now, obviously,
>technology will change and improve during the next few centuries, but based
>on what we know today about such solar power cells...

I've conducted some naive experiments with solar cells. My answers are
based on those experiments and my limited understanding of how photovoltac
cells work.

>   1) Given a solar cell that will produce 10 kilowatts in Earth orbit,
>would the same cell (i.e., the same mass of finished product) produce more
>power if it was moved to Venus orbit, where it would be getting more than
>twice as much energy from sunlight?  (If power is the wrong word, I
>apologize; you know what I mean, though.)  Will it produce 20+ kilowatts
>now?  Do the cells have a limit on how much electricity they will produce,
>or will they just keep giving you more power if you increase the solar
>energy per square meter?

The more light applied to the cell, the more electricity generated. A
limit case would be when the bulk conductivity of the cell is inadequate
to transport the electrons across the cell. A practical limit is reached
much quicker. That is the point where the waste heat breaks down the
semiconductor doping and destroys the photovoltac ability of the cell.
This point is below the melting point of the cell. Solar cells are
quantum devices. Certain wavelengths of light don't have enough energy
to liberate an electron, others have much more than is needed. As I
understand it, there is no method to cause two or more photons of
inadequate energy to combine to liberate an electron. Therefore all
photons below the critical energy generate heat only in the cell. On
the other end of the energy scale, a photon with too much energy, above
the critical energy needed to liberate an electron, will release the
excess as kinetic energy in the freed electron. Much of this excess energy
will degrade to device heating, some will knock other electrons into the
freed state. So with device conversion efficiency in the 15% range, 85%
of the energy must be removed from the device as waste heat, or limited
from striking the device in the first place. Using a concentrating lens,
the best improvement I have obtained is about a fourfold increase in
cell current before the cell overheated. Several cooling/filtering
approaches were tried. I tried operating the cells immersed in a bath
of deionized water. I tried various photographic filters in the hopes
of removing the ineffective wavelengths. I tried the special "heat filters"
used in movie projectors. None of these approaches improved efficiency
much above that of the plain cell and a concentrating lens of about 4X used
alone. I have read of special surface coatings that can be applied to cells
to reflect undesired wavelengths. These may do better than my crude approaches.
I also tried forced air cooling, and using chilled water running through
a metal plate with the cell cemented to the plate. These approaches helped,
but the net energy gain was small once the energy used to cool the cells
was taken into consideration.


>   2) If you can get more energy from solar cells by moving them closer
>to a star, what is the limit?  First, is there a point where the cells
>simply will not put out more energy, no matter how much sunlight they get.
>Also, there is obviously a point where the cells will melt, but where is
>that?  Could we build solar power stations, say, in Mercury orbit, where
>we would be getting more than six times the sunlight we get in Earth orbit?
>
>  (Obviously, it depends on the materials involved.  Also, clearly, solar
>cells are getting better all the time, and we cannot predict what technology
>will be like in the far future, but I would appreciate speculations based
>on existing technology.)

The ultimate limit would be when more photons of the right energy are
arriving than there are electrons available in the cell to receive the
quantum jump. There are 6.023*10^23 atoms in a gram mole of material.
If each atom has one electron available for jumping, doubtful because
it's the doping that makes the cell work and the concentration of the
dopant is much less than the overall number of atoms, then you would
get an Avagadro of electrons out of each gram mole of material. That's
roughly 42,000 amperes per gram mole of cell material. Obviously, we
haven't come anywhere near this absolute limit. Dopant concentration,
the electronic structure of the material, bulk conductivity, and
waste heat transport all establish lower limits.

If anyone has a better grasp of the numbers than this simple minded
approach, please post.

Gary

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

Date: 16 May 91 19:22:14 GMT
From: agate!stanford.edu!snorkelwacker.mit.edu!spool.mu.edu!mips!swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Saturn V and the ALS

In article <[e-mail]> [e-mail] (S. J. Okay) writes:
>BTW, were Fred to ever have a lifeboat capability, why not use the CM capsule?
>If I recall correctly, there was some extra space in the capsule itself that
>might provide room for the 4th seat.

The idea has been suggested, actually, by Rockwell (corporate inheritor of
the CM technology).  Max capacity was actually 5 in the Skylab "rescue"
configuration, because if you assumed less-than-severe-worst-case impact
loads on landing, you could put three astronauts on the floor behind the
couches (with the middle couch removed for access).

You'd need to do some re-engineering, and think about details like retrofire
and the effects of long standby periods in space on materials, but it is a
possibility.
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

Date: 16 May 91 00:25:28 GMT
From: hpfcso![e-mail]  (Mark Luce)
Subject: Re: Re: Ethics of Terraforming (was Re: Terraforming Venus)

/ hpfcso:sci.space / [e-mail] (Lon Stowell) /  5:09 pm  May 10, 1991 /

But what about the face?  (Does anyone else think it sorta looks
like Maggie Thatcher?)

     Nah. It looks like Michael Dukakis wearing a tank helmet. Since the face
was in the news before the 1988 election, it was clearly a warning... :-)

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

Date: Thu, 16 May 91 02:03:05 PDT
From: [e-mail] (Jim Bowery)
To: crash![e-mail]
Subject: Re: Space Station Cancelled

Allen Sherzer writes:
> In article <[e-mail]> [e-mail] (Jim Bowery)
writes:
> >The VA, HUD and Independent Agencies Subcommittee of the House
> >Appropriations Committee canceled Space Station Freedom

>                               ... This was a bit of
> a suprise move for the house and it's likely the Senate will
> move to restore funding. This could be the worst possible scenario:
> low level funding so it limps on for years without dying or
> building anything. The Senate markup will be critical.

Yes, and even if the Senate is reasonable, Bush can still veto the
cancellation.

The battle to save the space program isn't over yet.

Rep. Bob Walker 202/225-6371 needs to be encouraged to lay low during
the floor fight, because his credibility as a space commercialization
advocate will be attacked by certain young gun Dems if he expends his
credibility supporting Fred.  Fred isn't exactly "commerce friendly."
Fred is his Achilles' Heel and he needs to be reminded of that fact.

Speaking of "young gun Dems" who will attack Walker's Achilles' Heel:

Rep. Tim Roemer 202/225-3915 needs to be thanked for showing such
courage and leadership in this fight.  Ask for his staffer John St. Croix.
Remind Mr. Croix to remind Rep. Roemer to personally remind Rep. Walker's
of his socialist Achilles' Heel named Fred.  Rep. Dick Zimmer, although
a Republican, seems to have enough integrity to challenge Walker on
this issue.  Zimmer is at 202/225-5801.  Ask for Chris Hessler.

Also, Rep. Barbara Boxer 202/225-5161 should be thanked for holding
the first rational hearing on Fred costs/uses in the history of the
program.  Ask for her staffer Tim Morrison.  As with Mr. Croix, Mr.
Walker's Achilles' Heel should be mentioned.  She smells blood...
as well as a Senate seat.

On the Senate side, Mikulski has a bit of a problem because EOS is
threatened if Fred makes it.  I'm sure JSC tried to buy her support
somehow, but with so much money cut from the budget, she's wise enough
to know JSC/MSFC won't let enough go to her district to make up for
the loss of EOS.  Personally, I think Mikulski is bluffing.  I don't
think she supports Fred nearly as much as her appearance of doing so.
Lobby her anyway at 202/224-4654.
-----------------------------------------------------------------------------
Jim Bowery      619/295-3164               The Coalition for
PO Box 1981                                   Science and
La Jolla, CA 92038                             Commerce
-----------------------------------------------------------------------------

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

Date: 16 May 91 08:39:27 GMT
From: att!emory!wa4mei!ke4zv![e-mail]  (Gary Coffman)
Subject: Re: Tethers (was Re: Gas Guns and Tethers

In article <[e-mail]> [e-mail] (Ron Carter) writes:
>
>Walter Dnes writes:
>>     In another reply on this thread, I made a glaring error that
>>would seem to allow this scheme to work. I assumed that a shuttle
>>could be "reeled out". ( Silly me, I'll never graduate to sci.skeptic
>>this way. ) If the shuttle detaches and the main station unreels
>>several thousand miles of tether... you'll merely end up with an
>>atrocious "crowsnest" like no fisherman has ever seen before. The
>>shuttle will tend to remain in the same orbit as the station, *UNLESS
>>IT FIRES ITS ROCKET ENGINES TO DE-ORBIT*. That's what the shuttle has
>>to do right now.
>
>You have two mistaken ideas here.
>
>1.)    You have assumed that the center of mass of the Shuttle
>    orbiter and space station could be in the same place, so
>    that the tidal forces between them would disappear.  This
>    is naive.
>
>2.)    You have assumed that it would take a rocket burn equivalent
>    to an OMS de-orbit burn to get adequate separation to tension
>    a tether.  This is not true.  The tidal and centrifugal
>    acceleration in LEO is roughly .004 m/sec^2/km for a vertical
>    separation.  Assuming that 10 N is required to hold the tether
>    straight, a 100,000 kg mass must be offset only
>    10 N / (1e5 kg * .004 m/sec^2/km) = 10 N / (400 N/km )
>    = >>>25 meters<<< from the center of mass to tension the
>    tether.  A Shuttle can easily back off a kilometer or more
>    using the RCS jets.

Unless I totally screwed up the integration, it would take 11.5 days
for the shuttle to drop 50 km in this system. Is that reasonable?

>Because capturing a Shuttle on the end of a tether would be next to
>impossible, the only real possibilities involve having one rendevous
>with the station and be attached there.  It would then be reeled out
>(and, maybe, back in again).  If it is reeled out in the downward
>direction and then released, three things are accomplished:
>
>1.)    Considerable work is done on the tether reel, which can
>    be used to charge batteries.  (Reeling one out 150 km
>    in LEO would yield roughly 4.5 GJ of work, or 1,250 KWH.)
>
>2.)    The space station is placed in a higher orbit, without any
>    consumption of fuel.  (Orbit-raising fuel is expensive.)
>
>3.)    The Shuttle is placed in a lower orbit, also without any
>    fuel used.  This orbit could be a re-entry orbit if desired.

I'm confused by the energy balances here. It seems you could get
electrical energy *or* you could change the station's orbit. How
are you dividing the energy gain from converting gravitational
potential energy and orbital kinetic energy (I assume) between the
reel and the orbit changing?

Another thing I can't quite picture is the fact that the shuttle,
in dropping to a lower orbit, has got to go faster to stay in that
orbit. It will lead the station by more and more as the cable is
unreeled. Doesn't the shuttle need more energy in order to go faster?
Isn't this the energy gained by the shuttle in dropping to the lower
orbit? Doesn't that mean there is none left over to raise the station's
orbit or generate electricity from turning the reel? Have I completely
misunderstood something?

I just reread what I wrote in the last paragraph. I must be missing
something, *my* questions sound screwy to me. The shuttle can't gain
enough energy from a drop (delta h) to increase it's orbital speed
(delta v) enough to establish a stable orbit. If it did, it wouldn't
drop anymore. What's the real geometry of the situation?

Gary

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

Date: 17 May 91 03:11:41 GMT
From: pasteur!agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: If no Freedom, what comes next?

In article <[e-mail]> [e-mail] (George William Herbert) writes:
>    Long term: look at NDV as a launch platform.  Paradigm shift; how
>do we design a station for $100/lb? (It's a rule of thumb that a space
>vehicle's final cost is usually about twice the launch cost; thus, if the
>NDV flies 10 tons to orbit for a $1 million pricetag, we want 10 ton $1
>million modules...)

I don't think a NASP Derived Vehicle will be able to lift 10 tonnes. 5 might
be a better guess (at this point, guessing on the low side would be good.)
5 tonne elements could make assembly a real pain. While a NDV would be
a good way to transport the crew, and possible to resupply. The actual
structural elements would be better launched on a larger platform. (say
a Titan IV.)

                    Frank Crary
                    UC Berkeley

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

Date: 16 May 91 08:53:11 GMT
From: att!emory!wa4mei!ke4zv![e-mail]  (Gary Coffman)
Subject: Re: Why the space station?

In article <[e-mail]> [e-mail] (Fraering Philip) writes:

Responding to my denigration of a grab and run sampling mission.

>
>Mars will not be as easy to quantify with an Apollo-style sampling
>as the moon was. Anyway, even with HLV, the scale I just described
>would have to be assembled in space or the mission foregone.
>
>Even with HLV's, if assembly and on-site resources are not used,
>you're just going to repeat Apollo.

Amen to that. The Mars mission had better not be another spectatular,
I don't think the space program could stand another one. We need to
build infrastructure step by step so that real exploration can take
place. Whether the return to the Moon, and Mars exploration, winds up
being manned or advanced robotics, smash and grab is not the way to
do it. It's going to take years of surface roving and tons of samples
from representative sites to give us even a token understanding of
another world. We still don't fully understand this world, and we've
been clamoring all over it for milliena.

Gary

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

Date: 16 May 91 17:48:21 GMT
From: voder!nsc!amdahl!JUTS![e-mail]  (Robert Mitchell)
Subject: BITFTP Demise

I successfully retrieved several CDROM documentation files
from Ames.  Now, just when I am getting close, BITFTP
appears to have gone belly-up on me.
This was my last reply from Princeton on 16 May:

13:15:34 > ftp ames.arc.nasa.gov
* * * * * * * * * * * * * * * * * * * * * * * * * * * *
* * BITFTP is no longer able to provide service to  * *
* * nodes that are not directly on EARN or BITNET   * *
* * or NetNorth.  Your node appears to be           * *
* * accessible from BITNET only via a mail-only     * *
* * gateway.  If you believe that your node is      * *
* * directly on BITNET or NetNorth or EARN, please  * *
* * send mail to MAINT@PUCC specifying your         * *
* * BITNET/EARN/NetNorth node name.                 * *
* * * * * * * * * * * * * * * * * * * * * * * * * * * *

Does any other node provide this service, for those of
us unable to directly FTP???

This could be serious...
--
UUCP:  [e-mail]
DDD:   408-746-8491
USPS:  Amdahl Corp.  M/S 205,  1250 E. Arques Av,  Sunnyvale, CA 94086
BIX:   bobmitchell

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

End of SPACE Digest V13 #579
*******************