Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_6/V13_664.TXT

Internet Message Format | 1991-06-19 | 18KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from hogtown.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/AcLjiUK00WBwI3DE5Y>;
          Wed, 19 Jun 91 02:37:20 -0400 (EDT)
Message-ID: <[e-mail]>
Precedence: junk
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Wed, 19 Jun 91 02:37:15 -0400 (EDT)
Subject: SPACE Digest V13 #664

SPACE Digest                                     Volume 13 : Issue 664

Today's Topics:
Re: Phil has too much to drink, flames me for uncomfortable facts, no huhu
        Re: Tethers (was Re: Laser launchers)
         Trustworthy NASA and BITFTP at Ames
        Re: Tethers (was Re: Laser launchers)
Re: The Reasons for a Station? Was Re: Rational next station design...

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
  [e-mail].  Other mail, esp. [un]subscription requests,
  should be sent to [e-mail], or, if urgent, to
             [e-mail]

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

Date: 1 Jun 91 23:08:25 GMT
From: agate!headcrash.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Phil has too much to drink, flames me for uncomfortable facts, no huhu

In article <[e-mail]> [e-mail] writes:
>BTW, Skylab had neither:
>
>* Satellite refueling equipment
>* OMV
>* A lifetime of 30 years
>
>All of which are required to create a refueling infrastructure in the
>bizarre manner suggested.  _Furthermore_, I didn't include the cost of
>redesigning the satellites for refueling, which itself would probably
>cost more than $30 million per pop for the actual market of one per year.
>
My station concept was not to refuel satellites. I had suggested refueling
s in an earlier post, and the general oppinion was that it could be done,
e.g. for profit, but only by a single-use "orbital tug" launched on a
or rather, that a single-use orbital tug could be used to raise the orbit of
the intended satellite. The station concept was to repair/maintain/unstick
e.g. for profit, but only by a single-use "orbital tug" launched on a
jammed parts. This would require 2 EMU (spacesuits) assorted hand tools
e.g. for profit, but only by a single-use "orbital tug" launched on a
(which NASA has already developed or is developing for the space station)
and a remote mechanical arm (similar to the one on the shuttle). There is,
therefore, no new equipment needed for the actual repairs. In connection to
my suggested station concept, YOU are the only one to say anything about a
30 year lifetime. This is NOT part of my concept.

And, yes, an OMV would be required. But alot of design work has already
gone into one. The work was done by, I believe, Lockheed. By the way, does
anyone have any information on how far this design got before it was cut from
the budget? Also anything on its operational parameters? (I have assumed
in my cost estimates, a 5-tonne OMV with a 3000 m/s exhaust velocity.)

As far as re-designing the satellite, the repairs I have assumed are the
replacement of failed components. This would require only that the parts
are accessable to an astronaut. There exist NOW a number of so designed
satellites (Solar Max, Hubble, etc...) The job would be even easier if the
satellite were designed with easily removable component boxes (as US
military hardware is designed.) but this is neither necessary or difficult
to design.

By the way, when you refer to the "actual market" of one repair per year,
what do you base this on? From your earlier post, you guessed that there
were 50 satellites in low earth orbit, guessed that only 5 would be close
enough to the station to make the OMV transfer feasible, and again guessed
that only one of these five would need repairs in any given year. If this
is, in fact how you got your figure for the "actual market," I think you
misunderstand the meaning of the word "actual."

                        Frank Crary

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

Date: 27 May 91 05:01:39 GMT
From: swrinde!zaphod.mps.ohio-state.edu!rpi!news-server.csri.toronto.edu!helios.physics.utoronto.ca!aurora.physics.utoronto.ca![e-mail]  (Christopher Neufeld)
Subject: Re: Tethers (was Re: Laser launchers)

In article <[e-mail]> [e-mail] (Walter Dnes    ) writes:
>
>[e-mail] (Christopher Neufeld) and
>[e-mail] (Earl A. Hubbell)
>
>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...
>
   I take up the gauntlet. Challenge is lawfully accepted.

>     - select a tether-length; minimum 250 km, maximum infinity

   OK, I select 500 km tether running radially out from the space
shuttle in a 300 km altitude orbit.

>     - select the "optimum" taper function

   Done, A(x) is almost a gaussian, save for a term like 1/(1-x) in the
exponent.

>     - select an appropriate material

   All right, HP-PE.

>     - select a useful load, presumably at least several tonnes
>
   A twenty ton object at the end of the tether.

>     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...
>
   Right. Well, I don't feel like doing the integral, so I'll evaluate
an upper bound for this situation, taking the mass of the tether if it
were a uniform cylinder of area equal to the maximal area of the ideal
tether. This isn't too harsh an approximation since the taper for HP-PE
is only 1.09. Now, in order to hold that twenty ton object the tether has
to be able to support a tension of about thirty kilonewtons (putting in
a factor of about 20% for safety).  This requires an HP-PE cable with
diameter 3.4 mm at the mass. A total volume of about five cubic metres.
Total mass is roughly 4.8 tons.

>     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...
>
   0.0000048 *MILLION* tonnes of HP-PE.

>        a) a massive storage drum for the tether

   OK, say another ton, or 0.000001 *MILLION* tons, if you prefer.

>        b) a motor with the power to reel/unreel the whole mess
>        c) a power supply for the motor
>
   Let me lump these in with the ton from (a), since we're not talking
about a huge system here.

>     2) How many *THOUSAND* flights (Atlas II or whatever) will
>        it take to get it all up there ?
>
   I don't have the figures for an Atlas. For the shuttle, about 0.0002
*THOUSAND* shuttle flights (you could carry four or five up in one
flight).

>     3) How many *DECADES* will launching those flights take ?
>
   With the shuttle, who knows? Say between one and two *DECADES*.

>     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 ?
>
   One.

>     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 ?
>
   I don't know. Check with the company which makes the stuff over in
Holland. I doubt very much that it is a significant fraction of the
yearly production of that material. If it's a problem, use Kevlar. In
this case the mass roughly triples. Now, the Olympic Stadium in Montreal
has a roof made out of the stuff, so it can't be that hard to get in
bulk.

>     6) How many *TRILLION* dollars is this going to cost ?
>
   Don't know. At 0.0005 *TRILLION* dollars per shuttle flight, roughly,
and putting in an equal cost for the HP-PE, about 0.001 *TRILLION*
dollars.

>     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 ?
>
   I'll leave the politics out of this posting. It doesn't look too
silly to think that somebody might pay for this.

>     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.
>
   Right. So, do you object to my assumptions? I can rewrite them to new
parameters if necessary.
   For perspective, a few shuttle loads of tapered nylon could make a
useful lunar synchronous tether reaching to L1 from the surface of the
Moon.

>Walter Dnes
>[e-mail]


--
 Christopher Neufeld....Just a graduate student  | There no place like $FC58
 [e-mail]    Ad astra! | They're $FF69-ing my
 cneufeld@{pnet91,pro-cco}.cts.com               | every word! Send for a
 "Don't edit reality for the sake of simplicity" | free $A56E.

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

Date: 27 May 91 10:50 +0100
From: Andreas Moehn <[e-mail]>
Subject: Trustworthy NASA and BITFTP at Ames

>This may not be a "short term sacrifice" The ESA and Japan treat the inter-
>national agreement to develop and operate Freedom as an legal treaty with
>another nation, and that it is a binding international law. Of all the
>nations contributing to Freedom, only the US feels that they can freely
>change the design (or trash it) whenever they please. If we do dump
>Freedom (as opposed to orbiting something that still meets our agreement
>with ESA/NASDA/etc...) then we may NEVER be able to enter into another
>jont venture with anyone. By dumping Freedom, we FORCE these parties to
>"squander billions" themselves, without even warning them...

That was right the effect we experienced. I remember tha case when NASA
suddenly stopped its participance in an ESA probe for budgetary reasons
so that ESA had to build the other half, too. ESA was pleased. No wonder
that with regard to Freedom a few months ago the Frankfurter Allgemeine,
onc of the largest German newspapers, seriously recommended that ESA
should give up cooperation with NASA at all and concentrate on coworking
with Glavkosmos and NASDA considered more reliable.

>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.

I felt pleased by that, too, and would like to know whether there are other
nodes available.

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

Andreas Moehn
Max-Planck-Institute of Polymer Research
W-6500 Mainz, Germany
[e-mail]

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

Date: 27 May 91 13:17:57 GMT
From: agate!usenet.ins.cwru.edu!magnus.acs.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!jarthur!nntp-server.caltech.edu!hamlet.caltech.edu![e-mail]  (Lydick, Carl)
Subject: Re: Tethers (was Re: Laser launchers)

In article <[e-mail]>, [e-mail] (Walter Dnes    ) writes...
>
>[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.

Afraid not.  You GAIN by using the exponential taper.  The proper exponential
taper is on that has constant tension per unit cross-sectional area for the
entire length of the tether, and you pick that value to be close to the
breaking strain for the material.  Any other geometry is going to require more
material than an exponential taper, for a given strength/weight ratio for your
material.

--------------------------------------------------------------------------------
Carl J Lydick    HEPnet/NSI: SOL1::CARL    Internet: [e-mail]

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

Date: 27 May 91 19:42:52 GMT
From: agate!spool.mu.edu!mips!dimacs.rutgers.edu!morley.rutgers.edu![e-mail]  (Mark Purtill)
Subject: Re: The Reasons for a Station? Was Re: Rational next station design...

[e-mail] (Daniel Fischer) writes:

>In article <[e-mail]> [e-mail] (George William Herbert) writes:
>>Here are the missions that I want to see done that I think can be done only
>>or best by a station:

>>    * Long-term Human studies
>This kind of study is being performed by the Soviets since two decades; they
>have had people up for 1 year and flown a doctor on a 200+ days mission. What
>could be learned by repeating these boring adventures that they don't already
>know and are likely ready to join?
    Well, for one thing, we might actually like to find out what
happens to women for more than a few days.  In case you haven't
noticed, the Russians haven't had any women cosmonauts for some time.
Judging by the comments from various Russians when the British sent a
female cosmonaut (along the lines of "women don't belong in space"), I
don't think it's likely that they'll be giving us any information on
this any time soon.  (I omit pointing out that a year isn't really
very long only because someone else already has).
    Flames that the Russians are right to /dev/null.

>>    * some Microgravity (not all)
>Microgravity reasearchers prefer quick return of their samples and do *not* ask
>for superduper manned stations that can be served only once in a while.
    Microgravity researchs on a space station have very fast turn
around time.

>>    * most Biological science
>What Biological science? Again the Soviets have done all that before,especially
>with the Biosputnik spacecraft where many foreign experiments were flown.
    *All* biological science?  You're kidding, right?  Quick:
what's the effect on bacon production of a pig kept at .15g for it's
entire life?  We don't even have a good understanding of how
microgravity effects conception and birth (in any species), or even
how it effects an animal kept in microgravity for most of it's life).

>Adding up points 1 & 3 one could also ask: why should we be interested at all
>in the response of biological systems to microgravity as all life as we know it
>has developed under 1g conditions? Seems like a lousy circular argument: "We
>need man/animals in space so that we can learn how badly space affects them..."
    If you think that humans will never leave this planet,
certainly studying what happens to people and their animals in space
is not a high priority.  But many of us disagree with that.  ABC just
had a film on about colonizing the moon -- they must think someone's
interested!
    In any case, "biological science" does not mean just "studying
how microgravity effects (animals,people,plants)."  For instance,
protein crystals can only be grown in microgravity and an American
company has done this on Mir (in a project that involved some activity
by the cosmonauts, although not much).  Studying calcium loss in space
could help determine how to prevent it in older people on earth.  (I'm
not saying it will, that's just an example).  Studying how people and
animals are affected by microgravity is usuful basic research that
could provide spinoffs.

>>    * Spacecraft Refurbishment
>this is the best point - but wasn't the capability to serve other s/c the FIRST
>thing they threw away when they had be begin to descope Fred? Here (in the light
>of GRO's successful and HST's upcoming orbital repair) I would argue for
>developing a fleet of flexible shuttles, manned (for LEO) and unmanned (for GSO)
>and highly maneuverable (for GTO, like for catching defective HIPPARCOSses).
>Imagine what could have been done in this respect with the billions already
>wasted on Fred...
    Not much; apparently only $5G has been spent of Fred so far.
That buys two current shuttles, whose development cost has already
been paid for; or starting devlopment of the nifty shuttles you want,
spending $5G, and getting the project axed because the budget was cut.
Not much different than Fred.  (Fred costs *so far* are certainly much
less than 10 years * $2G/year (which was to be spent this year) =
$20G, so my $5G isn't far off even if I'm misremembering it).
    The amount spent so far is not be confused the the $120G
figure floating around which is a *projected* figure on how much it
would cost to build, lauch *and operate* Fred for 30 years.  I hope no
one has got the impression that that $120G has been redirected to
other things; it was never appropriated to start with.  (The actual
loss to the NASA budget was $817 million.  Aside from small items and
"general reductions", the gainers were: space transport, +$375
million; space fight R&D, +$215 million;  space science, +177 million;
and aeronautics and space tech., +$162 million).

^.-.^ Mark Purtill         [e-mail]         [phone] (O)
((")) DIMACS, P.O. Box 1179, Rutgers U., Piscataway, NJ 08855 [phone] (H)
****** I'm moving on or about August 24th; watch this space for details. ******

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

End of SPACE Digest V13 #664
*******************