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Subject: SPACE Digest V13 #644

SPACE Digest                                     Volume 13 : Issue 644

Today's Topics:
           Re: Rational next station design process
           Re: Rational next station design process
         Galileo Antenna (was Re: Amputation)
          Re: Expedition to the stars (hypothetical)
         Re: Self-sustaining infrastructures
        Re: Tethers (was Re: Laser launchers)
         Re: Self-sustaining infrastructures

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

Date: 27 May 91 01:08:12 GMT
From: agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Rational next station design process

In article <[e-mail]> [e-mail] (Nick Janow) writes:
>[e-mail] (Frank Crary) writes:
>> No, the way it sounds to me is: "This is the way they do things, lets try to
>> do SOMETHING, rather than fight with the government over administrative/legal
>> details."

>Do you mean that it is better to throw billions of dollars away, ruining the
>chance for other present or future programs, than to not pursue a manned space
>program right now?

No on several counts: First _I_ did not say that. My post, as I recall, was
in response to YOUR interpertation of a post by George Herbert. Try to get
you citations correct, please. Second, what I believe George Herbert was
saying is that IF a manned program can be done WITHOUT fighting with the
Federal government over administration/legal details, it should be done.

>> The question posed by assessing the value of the missions is, as I phrased
>> it, "Is it worth the costs to build a space station?" While you seem to want
>> to study the question, "What would the best way to satisfy these missions?"
>> While your question is more generally useful, mine is more practicle. By
>> limiting the scope of the problem, I make it easier to answer. Only space
>> station designs need to be considered. There are far fewer station designs
>> than "alternate" designs.

>This sounds like, "I want a space station, so let's put on our blinders so we
>don't have to consider any non-station proposals that might actually provide a
>greater scientific/technological value."  Sure it's easier to to narrow the
>scope, but narrowing the scope of your study doesn't narrow the scope of
>reality.

I admit, and did admit in my origional posting, that my system is less
"generally useful." You are correct. It WILL miss other possibilities.
However, if we study ALL the possibilities, we will be doing a decade of
paper studies before we actually DO anything. My idea will, at least,
assure a positive "scientific/technological value" (e.g. will be in the
black.) and might actually produce a flight article before the end of the
century. The problem with a study of ALL alternatives is that you must
WASTE a large ammount of time and effort. Will my study produce a perfect
solution? No, it will not. Will the "perfect" solution be so much better,
that it will justify the longer design studies? Again I think not. For
example, the soviets made no effort to design a perfect space station. They
simply build the first, good design they thought of. Based on experience
using it, they improved the design and corrected its imperfections. The
result is that they NOW have a very capable station AND almost 20 years
of results from their station.

>Let's take one of your justifications for the space station:
>
>> Since a lot of money goes into replacing these satellites, I think the
>> ability to refuel a satellite in orbit could easily pay for itself.

This is NOT my "justification for the space station." I offered this as
a way in which "space infrastructure" might be able to make a profit. I
said nothing about space stations, and as my more recient post to Henry
Spence says, I am not thinking only of MANNED refueling of satellites.
Please do not quote me out of context.

                      Frank Crary

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

Date: 24 May 91 22:43:10 GMT
From: van-bc!rsoft!mindlink![e-mail]  (Nick Janow)
Subject: Re: Rational next station design process

[e-mail] (Frank Crary) writes:

> No, the way it sounds to me is: "This is the way they do things, lets try to
> do SOMETHING, rather than fight with the government over administrative/legal
> details."

Do you mean that it is better to throw billions of dollars away, ruining the
chance for other present or future programs, than to not pursue a manned space
program right now?


> The question posed by assessing the value of the missions is, as I phrased
> it, "Is it worth the costs to build a space station?" While you seem to want
> to study the question, "What would the best way to satisfy these missions?"
> While your question is more generally useful, mine is more practicle. By
> limiting the scope of the problem, I make it easier to answer. Only space
> station designs need to be considered. There are far fewer station designs
> than "alternate" designs.

This sounds like, "I want a space station, so let's put on our blinders so we
don't have to consider any non-station proposals that might actually provide a
greater scientific/technological value."  Sure it's easier to to narrow the
scope, but narrowing the scope of your study doesn't narrow the scope of
reality.  You could narrow the problem of automobile safety to the issue of
preventing fuel tank ruptures, but if you reject factors beyond your narrow
scope, such as _passenger_ safety, your study has little meaning in the real
world.

Let's take one of your justifications for the space station:

> Since a lot of money goes into replacing these satellites, I think the
> ability to refuel a satellite in orbit could easily pay for itself.

Yes, refueling satellites could provide some income for a manned station.
However, this task doesn't require humans.  It should be possible to have
automated refueling systems.  Launch a refueling pod on a cheap, unmanned
booster, match orbits with a satellite using an ion drive (speed isn't
critical), mate with a refueling port (built in on new satellites), replenish
the satellite, undock and go on to the next satellite.

Such an automated system might have a comparable R&D cost, but IMO, it would
have a much greater value.  The same technology could be used to
repair/resupply satellites around Uranus, and you must admit, that would be a
pretty expensive service call for a human gas pump attendant.  :)

Yes, we could probably have men flying around Earth orbit doing the refueling,
but considering the risks (radiation, debris, breakdowns) should we?

The question of "should a small space station be built now" must be viewed in a
much wider scope, including other space science/R&D, future possibilities, a
long-term space program, etc.

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

Date: 26 May 91 13:19:16 GMT
From: agate!bionet!uwm.edu!zaphod.mps.ohio-state.edu!rpi!news-server.csri.toronto.edu!qucis![e-mail]  (Richard Akerman)
Subject: Galileo Antenna (was Re: Amputation)

In article <[e-mail]> [e-mail] (Doug Mohney) writes:
>In article <[e-mail]>, [e-mail] (Jim Bowery) writes:
>>2) was damaged because by insisting on everything flying on Shuttle,
>>JSC ensured Galileo would have to take a trajectory it was never
>>designed for -- one which damaged it,
>
>You are implying that Galileo's antenna deployment problems are a direct
>result of the trajectory. or that flying it on Shuttle damaged it. Could you
>please produce some direct evidence of this? I wasn't aware that JPL had
>figured out why the antenna was gorked.
>
>Could be just a part which failed. Could be a lot of things. I'm sure both sci.
>space and JPL would appreciate the documentation of failure and why.

Well, certainly the high-gain antenna cover was necessary because of the Venus
flyby, but I guess the question is whether the "umbrella" design of the
HG antenna was used because of the flyby or if it had been intended for the
spacecraft even if it had been launched by a Centaur upper stage from the
shuttle.  Anyone know?

Richard Akerman
Incompetent Physics Graduate Student

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

Date: 26 May 91 14:52:10 GMT
From: mcsun!hp4nl!dutrun2![e-mail]  (Arthur van der Harg)
Subject: Re: Expedition to the stars (hypothetical)

In article <[e-mail]> [e-mail] (Eric Olson) writes:
"If a team of explorers were to hop a ship to a nearby star, what
"should they take and why?

"         [...]

"Mostly what I'm looking for are things you might look for on a planet
"you found at that star; for example, you could take some "spy"
"satellites to assist in mapping it, surveying equipment to look for
"valuable resources and determine the general structure, and so forth.
"
"Any suggestions?
"
"Eric Olson <[e-mail]> Gryphon Gang Fairbanks AK 99775

The first and most important things everybody should have on this
mission don't take much space, but are absolutely necessary:

a) An open mind.
b) A lot of self-control, or respect for the planet they are surveying.

One messed-up spaceball (Earth) is enough. One cannot be sure there
isn't life on that planet (in whatever form, with whatever inteligence),
and I don't think we humans should start out interstellar life as
"planet-strippers".

I am not looking forward to a flame-war about the existence of life on
other planets. I want to bring home that unthoughtful exploration of
natural resources is what brought us the current environmental crisis.

Arthur
--
             | [e-mail] (Arthur van der Harg)
Yet another message from |
             | this remote end of the world
* * ** * ** * ** * ** * ** * ** * ** * ** * ** * *  *

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

Date: 27 May 91 02:44:13 GMT
From: world!ksr![e-mail]  (Chris Jones)
Subject: Re: Self-sustaining infrastructures

In article <[e-mail]>, fiddler@concertina (Steve Hix) writes:
>
>Btw, would it make sense to build Clarke-orbit comsats with gravity-gradient
>stabilization?  Or do they *really* have to have station-holding capability?
>

Both, I'd say.  Gravity-gradient stabilization could reduce the need for
attitude control fuel, but without small corrections, the satellite simply
isn't going to hold its geosynchronous position.  The ability to change orbits
is also useful for relocating the position of the satellites, something that
seems to be done somewhat often to cover for failures.

--
Chris Jones    [e-mail]    {uunet,harvard,world}!ksr!clj

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

Date: 26 May 91 00:49:49 GMT
From: agate!bionet!uwm.edu!rpi!news-server.csri.toronto.edu!utgpu!utzoo!utdoe!torag!w-dnes![e-mail]  (Walter Dnes )
Subject: Re: Tethers (was Re: Laser launchers)


[e-mail] (Christopher Neufeld) and
[e-mail] (Earl A. Hubbell)

     have both responded to a previous posting of mine. They point
out that tethers work better if tapered, rather than a uniform
thickness (my example assumed a uniform thickness). However, as
Earl Hubbell has pointed out...

> Note that you
> do pay a price for exponential taper - the total mass of your
> cable system goes up >very< fast - a severe consideration for space work.

     Let's look at some of the real-world problems here. I invite
Christopher and/or Earl (or anybody else) to post answers to the
following...

     - select a tether-length; minimum 250 km, maximum infinity
     - select the "optimum" taper function
     - select an appropriate material
     - select a useful load, presumably at least several tonnes

     Okay, now integrate the tether's cross-section area over the
length of the tether, giving the solid volume. Multiply by the
specific gravity of your appropriate material, and we get the mass
of the tether. Now let's get into some interesting questions...

     1) How many *MILLION* tonnes of <whatever> do you have to
        put into orbit ? If you plan to reel/unreel the tether,
        don't forget to include...
        a) a massive storage drum for the tether
        b) a motor with the power to reel/unreel the whole mess
        c) a power supply for the motor

     2) How many *THOUSAND* flights (Atlas II or whatever) will
        it take to get it all up there ?

     3) How many *DECADES* will launching those flights take ?

     4) Item 3 might not be the bottleneck. Given the number of
        pieces to assemble/weld/whatever, how long will assembly
        of the structure take ? How many shuttle missions ?

     5) What is the total annual production of the material
        you've chosen for your tether ? I.e. how many years
        worth of production are you going to use up ?

     6) How many *TRILLION* dollars is this going to cost ?

     7) What are the chances of the world's taxpayers (not to
        mention their political representatives) shelling out all
        that cash over the years, regardless of all the
        cheerleading that the project's proponents might do ?
        (Give me an F...
         give me an R...
         give me an E...
         give me a  D...
        What's that spell ?)

     I've asked Christopher and Earl (or anybody else who wants
to jump in) to pick their parameters, within reason. The only
restrictions I've placed on the four conditions are designed to
eliminate trivial solutions such as very short tethers or very
small load capacities. This time there can be no complaints about
me selecting a non-optimal configuration.

     \/\/ |>

Walter Dnes
-------------------------
[e-mail]
[e-mail]

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

Date: 26 May 91 18:14:42 GMT
From: agate!earthquake.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Self-sustaining infrastructures

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>Kind of dubious, since their useful lifetime usually *is* limited by fuel.
>They need it for precision station-keeping.
>
I had thought component failures were also a major factor in the lifetime
of a geostationary satellite. Is this not, as well as station-keeping fuel,
an issue?

>Another issue here, by the way, is that satellites fuelled by hydrazine also
>suffer from slow degradation of the catalysts they use to break it down in
>their thrusters.  So just refuelling them has limits.
>
I would think this would limit the length of time the fuel could be stored.
A small tank, frequently re-filled, would not be storing the fuel for long.

>>... Can anyone comment on the viability of a
>>for-profit Low Earth orbit infrastructure for the purpose of re-fueling
>>satellites?
>
>Minimal.  It's always in the wrong orbit, since no two low-orbit satellites
>are in exactly the same plane, barring the occasional deliberately-established
>constellation.

Even a one-shot re-boosting craft might be viable, I would think. For
example, a very small craft, launched on a Pegasus booster, could give
a 7-tonne class (e.g. Atlas launched) satellite a roughly 125 m/s boost
While this might not be much, such a one-shot reboost would be much cheaper
than replacing the satellite.
As far as deliberately-established constellations go, it was my impression
that some of these (NavStar/GPS for example) required alot of station keeping
Might a GPS-serving-only reboost/refuel craft be usefull? There are alot of
these satellites up.

>Refuelling geostationary comsats would be much more promising.
>Getting from one side of Clarke orbit to the other is not quick, but it *is*
>relatively cheap, and there usually is plenty of advance warning that a bird
>is running low.  Of course, you'd have to convince the comsat builders to
>start providing for refuelling.
>
Yes there might be a market, but would you not also have the problems of
flying quite close to other communications satellites, when you travel from
one stop to another? I know this is not a problem in LEO (Space is Big...)
but all the geostationary satellites are in almost identical orbits, which
might complicate things...

>I'm unsure about the legal aspects, but it doesn't seem likely to be very
>profitable.  The low-orbit birds are usually specialized, and often would
>be of little value to anyone other than their owners.  You really want to
>get contracts for refuelling them *before* they run out.

I can think of several Soviet generals who would pay alot for close up
photographs of and/or small parts from a salvaged USAF reconisance
satellite. Also, what's wrong with reactivation an abandoned satellite and
selling it back to its owners (assuming no one else wants it?) But I agree
that this is a reletively limited market.

                    Frank Crary

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

End of SPACE Digest V13 #644
*******************