Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_6/V13_627.TXT

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Subject: SPACE Digest V13 #627

SPACE Digest                                     Volume 13 : Issue 627

Today's Topics:
           Re: Rational next station design process
           Re: Rational next station design process
           Re: Keck (was Re: Privatization)
          Re: Tethers (was Re: Gas Guns and Tethers
       Re: Request For Discussion: sci.space.moderated
          Re: space news from March 18 AW&ST
        Some statistics on the Keck Telescope
            Re: Launch technology

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

Date: 23 May 91 04:31:44 GMT
From: agate!tornado.Berkeley.EDU![e-mail]  (George William Herbert)
Subject: Re: Rational next station design process

In article <[e-mail]> [e-mail] writes:
>It is precisely the approach that is wrong.  I could point out
>thousands of needs _not_ met by a space station, and demonstrate
                  ^^^^^^^^ Nick, there are millions of needs that aren't
          solved by a space program in any way shape of form. The
          point is to pick needs and missions you want to fulfil
          and figure out how to do so.
>the opportunity costs.  I could show how the needs you are trying
>to meet can be better met by other methods.  But if we
>don't consider alternative concepts, our only recourse would be to
>redefine the needs, as space planners have redefined the space
>station customers from defense (1960's) to earth observation
>(1970's) to microgravity research (1980's) to "life sciences"
>(the study of a too small sample size of unrepresentative humans in
>an unrepresentative space environment).  We could argue about these
>until we were blue in the face.  But until we consider the
>alternatives to a station, and all the major needs of space
>users and their relative importance, the notion that a space station
>is a desirable or useful part of a space infrastructure is a
>non-sequitur.  It is merely the classic Solution in Search of a
>Problem.
>
>The whole approach -- and any infrastructure that may result from
>it -- is, like Fred itself, bankrupt.

All right, Nick, put your brain where your mouth is.

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
    * some Microgravity (not all)
    * most Biological science
    * Spacecraft Refurbishment

Assume, as I do, that these are worthwhile things to do.  (Not more or less
worthwhile than any other mission).  If you disagree, then we stop here.  If
not, proceed to step 2:
    How else can we do these missions?

-george william herbert
[e-mail]

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

Date: 22 May 91 18:41:15 GMT
From: van-bc!rsoft!mindlink![e-mail]  (Nick Janow)
Subject: Re: Rational next station design process

[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
>         * some Microgravity (not all)
>         * most Biological science
>         * Spacecraft Refurbishment
>
> Assume, as I do, that these are worthwhile things to do.  (Not more or less
> worthwhile than any other mission).  If you disagree, then we stop here.  If
> not, proceed to step 2:
>
>         How else can we do these missions?

        * Long-term Human studies
There is likely still quite a bit of preparatory research that can be done with
test animals in zero-g, biochemical reactions in zero-g, short-term human
experiments (monitoring shuttle crew, etc) and computer simulations based on
all those results.  That won't cover everything, but until we are really ready
to build a proper space station, it is a (comparatively) inexpensive way to do
some of the groundwork.

I'm sure there will be many surprises when we do finally get a proper long-term
human studies facility in orbit.  However, there is still a lot to be learned
without it.  Let's not confuse flashy science with real science which often
consists of tedious, repetitive experiments.  Those scientist who labour in
small laboratories, making precise measurement after precise measurement; the
ones who sit in leaky tents in tropical rainforests, counting frog croaks; the
ones who pore over the masses of data, trying to figure out what that slight
bias in the readings means: they are the "unsung heros" of science.

        * some Microgravity (not all)
        * most Biological science
        * Spacecraft Refurbishment

A fair amount of this can be done with unmanned facilities.  That will require
a fair bit of R&D in robotics, teleoperation and AI, but we should be doing
that anyways.  Think of the spin-offs!

Sure, the astronauts fixed Solar Max when it was obvious that machines weren't
flexible enough.  However, can we always afford to send humans?  What if Solar
Max was in close solar orbit?  We will have to develop flexible teleoperation
ability eventually, so why not spend the time, money and effort now?

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

Date: 22 May 91 12:19:45 GMT
From: agate!spool.mu.edu!think.com!zaphod.mps.ohio-state.edu!wuarchive!emory!wa4mei!ke4zv![e-mail]  (Gary Coffman)
Subject: Re: Keck (was Re: Privatization)

In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>In article <[e-mail]> [e-mail] (Jonathan Leech) writes:
>
>>pain.  Further, no planetary mission will return as much science in
>>its brief lifetime as the Keck will over decades, and the risk factor
>>is very high.
>
>One wonders, then, why we should spend multiple billions on planetary
>science when the scientific return on the dollar is so much greater
>from ground-based telescopes (and, last I heard, telescope time
>worldwide is oversubscribed by at least 4 to 1).  Sure, there are
>questions that can only be answered on-site, but the questions the
>telescopes are trying to address (the fate and nature of the universe
>as a whole) seem more fundamental.
>
>The question "why spend money on planetary probes" is at least as
>problematic as "why spend money on manned spaceflight".
>
>    Paul F. Dietz
>    [e-mail]

A fundamental hidden assumption is that all scientific return is equally
valuable. While it can be said that all knowledge is valuable in the
abstract, specific knowledge is often of great value to a specific
application. The lobbying comes in deciding whose application is more
valuable. To the man in space folks, zero G life science is much more
valuable than any telescopic study of the big bang. The planetary
science folks have about reached the limits of Earth based telescopes.
Their application requires space based sensors, or better, planetary probes.
So spending on Earth bound telescopes is a waste of money for their
application. And so on.

It's not just return for the buck, it's specific return for specific bucks
that's the real hidden issue.

Gary

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

Date: 23 May 91 02:16:23 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!wuarchive!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:
>In article <[e-mail]>, ke4zv!gary (Gary Coffman) writes:
>>In article <[e-mail]> [e-mail] (Ron Carter) writes:
>[tidal/centrifugal acceleration is 4e-6 m/sec^2/m vertical sep]
>>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?
>
>I think not.
>
>Simplifying assumption:  tether tension is set so that there is a
>net 10 N downward acceleration on the Shuttle.  Initial separation
>is 50 meters, initial tension is 10 N.  Shuttle mass is 1e5 kg.
>
>d = .5 * a * t^2  implies  t = sqrt( 2 * d / a )
>
>d = 5e4 m (minus a bit)
>a = 1e-4 m/sec^2
>
>t = sqrt(2 * 5e4m/1e-4 m/sec^2) = sqrt(1e9 sec^2) = 3.16e4 sec = 8.78 hours.
>
>If tether tension was not increased to maintain a constant acceleration,
>but was kept to a constant proportion of the tidal/centrifugal force,
>then the Shuttle's speed would increase exponentially and this time
>would be MUCH shorter.  I haven't worked the diffeq yet, but the
>acceleration rises roughly linearly with increasing distance, so...
>
>Would you mind posting your analysis if it's so different?

I screwed up again. I implicitly set the mass of the shuttle to
1. This gave me a bogus force and a bogus acceleration. Your numbers
look correct. However, see below.

>Perhaps you caught some glitch that I ignored.  The requirement
>of rotating the relative velocity vector at omega might make a
>big difference, and my above simple analysis would have missed it.
>I also didn't take into account the requirement for tidal force
>to spin up the tether; as the two masses separate, their angular
>inertia increases, and angular momentum must be input to keep its
>rate of spin at omega (1/orbit).  This must come from tidal torque;
>the lower mass moves forward as spin slows, and the upper moves
>backward, yielding a tidal torque increasing the spin.

A 1e5 kg mass with a 50 meter vertical separation has a net force
of 20 newtons between it and the station. At 5e4 meters vertical
separation the force is 2e4 newtons for an average force of 1e4
newtons. That's 5e8 joules and an equivalent average acceleration
of 0.1 meter/sec^2. Plugging in to t=sqrt(2*d/a) we get 16.66 minutes.
Total power 500 kilowatts. Average relative speed 180 kph. Of course
the reel is freewheeling and there is 0 tether tension so this answer
is somewhat bogus. Still it sets a maximum on the power available.
Subtracting a constant 10 newtons to keep the tether tensioned will
cause only a 500 watt reduction in power.

A 1e5 kg mass travelling in a 5e4 m circle with a period of 5.4e3
seconds has an equivalent power of 1.3e4 watts. 13 kilowatts. This
is the parasitic power required to create the 1/orbit (90 min) spin.

Holding drop time to 8.78 hours will only generate 15.82 kilowatts.
This leaves about 470 kw to play with.

There! I hope I didn't pull another boner.

Gary

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

Date: 22 May 91 00:55:16 GMT
From: amdcad!brahms![e-mail]  (Phil Ngai)
Subject: Re: Request For Discussion: sci.space.moderated

[e-mail] (Mary Shafer) writes:
>I must say that it was in sci.space that I discovered the need for and
>learned how to use local kill files.  I'm currently debating about a
>global kill file, since I have discovered that the people whose
>posting are most objectionable in sci.space are objectionable
>everywhere.  (It's also true that the people whose postings are most
>interesting in sci.space, like Henry, are interesting everywhere.)

Ain't that the truth. I've gone beyond kill files to select files,
mainly keyed on poster, not subject.  I only read the people I know
will be interesting. nn is very useful in this regard.

What would be neat is to see the select files of the people in my
select files...

--
For the Welfare system to flourish, its clients must not.
Conflict of interest?

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

Date: 22 May 91 07:42:55 GMT
From: stanford.edu!agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: space news from March 18 AW&ST

In article <[e-mail]> [e-mail] (Alan M. Carroll) writes:
>I'm missing this. The fast orbit takes a total of 34 months, or
>roughly 1020 days. That's too long, but a 1000 day mission isn't?

I should have been more exact. The stay on the surface is too long. Either
transfer orbit will result in long stay on the surface. In the case of a
minimum energy transfer, 400 days or so. The "fast" orbit could give you
a stay of 700 - 800 days. However, the "fast" orbit requires MUCH more
fuel. A "fast" mission could only land a limited amount of equipment. Not
enough for 26 months of surface exploration. Spending only 400 days, with
the equipment needed to do a good, detailed job of exploring is much more
effective. In general, "fast" missions are suggested to shorten the trip:
The fuel costs are almost prohibitive, but if you HAVE to return in less
than one year, this is the only way. A "fast" mission that waits on the
surface for the next launch window (26 months) does not do this, but still
has to pay the price in fuel.

                       Frank Crary
                       UC Berkeley

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

Date: 22 May 91 14:45:28 GMT
From: agate!spool.mu.edu!rex!rouge!pc.usl.edu![e-mail]  (Fraering Philip)
Subject: Some statistics on the Keck Telescope

Here are some interesting figures on the original Keck
scope from the July 1990 {\em Sky and Telescope}. There
is no mention about the possibility of an interferometer
being built. I suppose that those ideas are more recent.

From the article "The Keck Telescope's Giant Eye":

"Principal funding came in the form of a $ 70 million grant
from the W. M. Keck Foundation, hence the telescope's name."

From the sidebar interview with Jerry Nelson:

S&T: Now who was funding this work in the early days?

Nelson: Prior to 1980 the funding was approximately equal
        between UC and Lawrence Berkeley Laboratory. I was
        a staff member at LBL and managed to convince the
        director of the lab to provide funding -- $ 200,000,
        something like that.

[...]

S&T: But you folks didn't really get funded until 1984, when the
     [Keck Foundation's] check came in?

Nelson: We had several million dollars that was spent on what we
        call technical demonstration -- this money came from UC in
        about 1981 through '84. By then we had tackled many exotic
        engineering tasks and even had a design for the telescope
        as a whole. Then formally in January, 1985, the project
        got this wonderful grant from the W. M. Keck Foundation.

[...]

Nelson: ...The Keck grant went to Caltech, and Caltech has agreed to
        provide additional capital expenditures to build the observatory,
        while UC will provide monies to operate it for roughly 25 years.

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

End of quoted figures;

"There are lies, damn lies, and statistics." - Theodore Roosevelt

It seems to me that these figures could be used to support both
sides of the current argument.

Phil Fraering || Usenet (?):[e-mail] || YellNet: 318/365-5418
''It hardly mattered now; it was, in fact, a fine and enviable
madness, this delusion that all questions have answers, and nothing is
beyond the reach of a strong left arm.`` - Larry Niven and Jerry
Pournelle, _The Mote in God's Eye_

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

Date: 22 May 91 14:49:48 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!watserv1!watdragon!watyew![e-mail]  (James Davis Nicoll)
Subject: Re: Launch technology

In article <[e-mail]> [e-mail] (Mark William Hopkins) writes:
>
>   So here's my question: what are the propellant velocities of the currently
>used fuel sources?  Is there any non-nuclear process currently existing that
>can achieve propellant velocities on the order of 1000 km/sec?!?!

    Why non-nuclear? The sources I've seen seem to show an ISP of
450 is about the best you can get from chemical.

    Isn't the Isp of Orion-style propulsion about 50,000? That's
half way to your goal.

    Why an Isp of 100,000, btw?

>   What can electromagnetic or nuclear process do in the way of propellant
>speed under a controlled environment?
>
>   Exercise: calculate the distance you can travel in a period equal to one
>time constant with 1000 km/sec fuel under constant 1 G thrust.  Discuss the
>implications.  Tell NASA about them. :)

    Hmmm.   MV=mv
        MV/v=m    Let M = 1kg, V = 10m/s and v = 10**6 m/s
        (1kg)(10m/s)x /10**6 m/s = 10**-5 kg

    To change your velocity by 10m/s, you need to throw out 10**-5 kg.

        Ek=.5 MV**2
          =(.5)(10**-5)(10**6)**2
          = 5x10**6 J

    Assuming I haven't srewed up, you are going to have to generate
5x10**6 Joules per second to accelerate your 1kg object at 1 G. That's an
impressive power output for a 1 kg object. Perhaps you might want to consider
smaller accelerations or a smaller Isp?

    In any case, I think the question is better phrased 'what can you
do with delta vees of about 1400 km/s?'

    Right now, I think the biggest cost involved in putting things in
space is the hardware cost, not the fuel cost (although obviously the Isp
of the launcher determines the biggest delta vee you can reasonably expect
to be able to cause. Even if chemical fuels were a penny a tonne, you won't
see delta vees of ,say, 1000 km/s out of a chemical rocket).

    You also may want to consider possible side effects of using a
high Isp propulsion system to launch from the Earth's surface. If you
were launching a 100 tonne object with the mythical Isp 100,000 at
2 G, you would be generating about 10**12 watts, and I can't help but
wonder if a terawatt jet wouldn't have some minor effect on whatever
happens to be in the way of the jet. I suspect that Earth surface to orbit
launches will be constrained by the need not to do gross property damage
to propulsion systems that have relatively low Isps (or which skirt
the issue, like tethers). I realise that you didn't specify launching
from Earth's surface, but right now, that's our primary problem.

                                James Nicoll

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

End of SPACE Digest V13 #627
*******************