Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v13_6/v13_640.txt

Internet Message Format | 1991-06-13 | 17KB

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/UcK6nrq00WBw83Ok5G>;
          Fri, 14 Jun 91 03:15:03 -0400 (EDT)
Message-ID: <[e-mail]>
Precedence: junk
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Fri, 14 Jun 91 03:14:59 -0400 (EDT)
Subject: SPACE Digest V13 #640

SPACE Digest                                     Volume 13 : Issue 640

Today's Topics:
               Re: The Un-Plan
                Re: lifeboats
            Re: lifeboats....ACRV
         Re: Self-sustaining infrastructures
           Re: Rational next station design process
                  Re: SR-71

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: 25 May 91 21:20:41 GMT
From: sequent!muncher.sequent.com![e-mail]
Subject: Re: The Un-Plan

In article <[e-mail]> [e-mail] (Jim Bowery) writes:

>....the actual numbers for
>U.S. vs Japanese, public vs private technology R&D funding is:
>
>                R&D Funding Sources
>                Public          Private
>Unite States    67%             33%
>Japan           22%             78%
>
>Examples of successesful, low cost, R&D efforts that "meet international
>challenges" with the financial risk taken by the private sector:
>
>Wright Bros., the automobile, the telephone, Spirit of St. Louis, lasers,
>the transistor, Seymour Cray/supercomputer (1604 - Cray-3), railroads,
>microcomputers, the light bulb, radio, television, electrical generators,
>communications satellites,
>...
>The government has served technology advance best when it:
>
>...
>2) Supported education and scientific (unpatentable) research.
>...

This is an important point: distinguishing between patentable research,
which should be done primarily by private industry, and basic and
applied (but unpatentable) scientific research for which the government
should provide ample funding.  The DoC should have more say in this
research than DOE, DoD, or NASA during this era where international
competitiveness is more important than defense or raw energy to the
existence, growth and well-being of our society.  You provide a good
legal and scientific definition for distinguishing what should be done
by government labs and what should be done by industry.


>> * Our sample size of earth-crossing and Jupiter-crossing asteroids and
>>   comets is increased 1,000-fold, so that we find several small objects
>>   that can be captured into earth orbit for less than 500 m/s impulse
>>   delta-V.
>
>
>1)... Even "small" objects that hit the earth from space are exceedingly
destructive....

This is an important point that needs to be discussed.  Specifically,
we need to determine:

* What is the maximum size and composition that can be safely fast-aerobraked
  in Earth's atmosphere.  Currently, the Shuttle (c. 100 tons?) does
  this regularly, over Los Angeles to boot, with little safety concern.
  Skylab (c. 200 tons?) did this in an uncontrolled manner, and
  cause some furor but the danger was not overwhelming.  Using nuclear
  power adds another dimension, but fortuneately nuclear power is not
  needed for capturing material.

* What is the maximum size and composition that can be safely
  gravity-assisted by the Earth.  Some major factors:
  --  What is the ability to correct errors on the incoming spacecraft
      full of materials
  --  What is the maximum worst-case destructiveness and its probability
      that can be tolerated.
  --  What are the effects of volatile (eg ice) and hard (eg nickel-iron)
      materials.

* What is the maximum size and composition that can safely be
  slow aerobraked (< 1/100 g) in Earth's upper atmosphere.

The rule of thumb I am working with is that up to 1,000 tons of easily
crushed volatile materials can be safely fast-aerobraked, and that up
to 10,000 tons of such material can be gravity-assisted or slow aerobraked.
The figure for hard material such as steel, nickel-iron, or the typical
earth-launched spacecraft would be 1,000 tons for well-controlled flyby
and 100 tons for well-controlled aerobraking.  These are just rules of
thumb; the actual figures for reasonable safety should be worked out.

Note that _not_ using Earth for gravity assist and/or aerobraking imposes a
very large energy cost, typical one or two orders of magnitude, on the
cost of returning asteroid materials to LEO.  Not using Earth aerobraking
also adds to the energy cost of returning lunar materials to LEO.
Determining and agreeing to margins that both protect Earth and enhance
our ability to develop space is a very important issue.

If our ability to detect small and distant comets and asteroids greatly
increases, we will be able to detect small Jupiter-crossing asteroids
and comet fragments.  Using Jupiter and the Moon for gravity assist is a
very powerful and safe technique for capturing materials into high Earth
orbit.


>2) Delta-V isn't the overriding consideration -- round-trip mission
>time is.  As with airlines, costs are dominated by amortization rates
>on the flight equipment.

I disagree. "Money-time" is easily computed by the cash flow equation.
This can be found in a good business calculator, or start up your
nearest spreadsheet.

Here is a cash flow analysis for a mission that takes 4 years of
round-trip time.  For this analysis the $numbers are made up and not
important; the relationship between $$ and time is.  Let's say it costs
$1.5e9 to develop, launch, and set up the equipment.  Since this is
high-risk, time cost of money is 18%/year.  Assume that we must replace
$6e8 of machinery every year after the operation is going.

Assuming $1.2e9 revenue per year, and an R&D period of 4 years (fairly
short for the aerospace industry) the annual cash flow for the mining
project will look something like this:

-.1                      ($1e8)
-.2
-.4
-.8                     (launch: total development costs $1.5e9)
0; 4 years              (round-trip travel & setup time)
.6; indefinitely        ($12e8 revenue - $6e8 costs: 100% gross margins)

Net present value (NPV) of this cash flow at 18% is >$0, which
means that if the numbers I pulled out of the air were realistic,
it would be a good investment.

The annual market/development costs ratio is 12/15.  In other words,
due to the round-trip travel time and the time cost of money, we need
an annual market equal to 80% of the development costs, sustainable at
100% gross margins.  If the Fed dropped rates just 3%, we could get by
with a market equal to 58% of development costs [n.b. for those who think
big budget deficits are OK].  For a two year round trip time we only need
a market equal to 46% of development costs to provide an 18% return.  The
Moon (0 years) needs a 34% market, giving us a money-time ratio of
2.35 between a four-year round trip to an asteroid vs. the Moon at
the junk-bond rate of 18%.

While the time advantage of the Moon is significant, it is not overwhelming.
Using aerobraking, we can get material from asteroid 1982DB, and probably
several thousand other as yet undiscovered asteroids, with 9,000 times less
fuel than from the Lunar surface.  With gravity assist, the ratio is about
100:1.   Launch, fuel, tankage, and payload-design constraint costs related
to energy constraints dominate for deep-space missions (about 60%).  This
gives 1982DB a cost advantage of between a factor of 60 and a factor of
5400.  These both dwarf the time cost of money ratio of 2.35.

Furthermore, asteroids contain a wide variety of materials (refined
nickel-iron, water, nitrogen, carbon, etc.) which are much more difficult
or impossible to obtain on the Moon.  Mining equipment on the Moon will
greatly "outweigh", in both mass and  development cost, mining equipment
on asteroids.  There will be an even larger difference between the rock
or metal asteroids and comet fragments, since ice mining is much easier
than rock or metal mining.  That is why the "Un-Plan" shows Encke
earth-crossing comet fragments being mined first, although the existence
vs. nonexistence of such earth-crossing ice is speculative due to the
inadequate state of our exploration of these bodies.


>Due to the probability of our achieving economical fusion in the near
>future, I seriously doubt SPS will ever be important.

We certainly should not _count_ on it, just as we should not count
on any other single speculative space industry [microgravity and
vacuum manufacturing, platinum-group metals, diamonds, He-3, pharmaceuticals,
etc. etc.]. It is important that primary industries -- exports from space to
Earth -- be developed, but we can't get ourselves stuck on preconceived
notions of which ones will dominate.  We need to be ready for another
Amgen to come along and spoil our plans.   Keep our options open, and
keep looking for new options.  That's why I called this the "Un-Plan".


--
Nick Szabo                [e-mail]
"If you understand something the first time you see it, you probably
knew it already.  The more bewildered you are, the more successful
the mission was." -- Ed Stone, Voyager space explorer

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

Date: 25 May 91 14:39:03 GMT
From: spool.mu.edu!rex!rouge![e-mail]  (Fraering Philip)
Subject: Re: lifeboats

Please ignore article <[e-mail]>. Accident
with the posting mechanism, I believe.

- Phil

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

Date: 25 May 91 18:12:54 GMT
From: agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: lifeboats....ACRV

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>The other side of this, of course, is that either one is more reliable after
>storage for years in orbit than a set of maneuvering engines.  If David
>can postulate a violently-out-of-control station, I can postulate undetected
>equipment failure in the lifeboat.

I personally like the solution used by the Soviets: Their "lifeboat" is one
of their crew transports, which is keep docked to the station. This way,
every time there is a crew rotation, the old "lifeboat" is replaced along
with the old crew. As a result, they never have the lifeboat in storage
on orbit for "years." Usually it is up there for only 6 months, though I
seem to remember that one was up for as long as 9 months.

                       Frank Crary

PS: I do agree that a fail-safe emergency mode for undocking is also a very
good idea.

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

Date: 26 May 91 01:13:22 GMT
From: news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Self-sustaining infrastructures

In article <[e-mail]> [e-mail] (Frank Crary) writes:
>On this note, I would like to mention that the lifetime of a satellite in
>Low Earth orbit is limited by its fuel supply...

Well, for those that *have* a fuel supply.  A good many, e.g. Hubble, don't.
A better way of putting it is that the life of a low-orbit satellite is
usually limited by air drag.

>... Geostationary satellites (if they can be used
>to measure lifetimes NOT limited by fuel consumption) ...

Kind of dubious, since their useful lifetime usually *is* limited by fuel.
They need it for precision station-keeping.

>... As such, being able to refuel a satellite in Low Earth orbit could
>as much as triple its lifetime...

Being able to reboost it would, in many cases, be just as good as refuelling,
and less hassle.  Unless it's using fuel for something else, like attitude
control, there's little difference between giving it a push and refuelling
it so it can give itself a push, except that the latter is more complicated
and puts more constraints on the satellite design.

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.

>... 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.  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.

>Could a unfueled and deactivated satellite be claimed as
>salvage, re-fueled, re-activated and sold as salvage?

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.
--
"We're thinking about upgrading from    | Henry Spencer @ U of Toronto Zoology
SunOS 4.1.1 to SunOS 3.5."              |  [e-mail]  utzoo!henry

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

Date: 23 May 91 20:24:42 GMT
From: van-bc!rsoft!mindlink![e-mail]  (Nick Janow)
Subject: Re: Rational next station design process

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

> Again, looking at the needs of long-term human bio research, I can't see any
> solution other than doing research on a manned station. I'm open to having my
> mind changed, but all the research into bioscience needs that I've done says
> 'Station!' all over it 8-)

I don't think anyone is denying that some research can't be done without a
long-term manned facility.  However, there's also a question of time.  The
research is valuable, but does it have to be done this year?  Next year?  the
year 2000?  Could it possibly wait until space engineering can provide better
facilities for less cost?

Furthermore, are biologists properly prepared for that manned space research.
Have they done all the preparatory work and have absolutely nothing more to do
until the orbiting facility is ready?  I'm not a biologist, but I assume that
research into the effects of spin on humans, cell growth in zero-g, bone growth
at 1-g, etc is not complete.  That detailed research here can eliminate many
side-issues and provide useful techniques and knowledge that can be applied to
an orbiting facility.  Why waste (expensive) days of research in space studying
an effect that can be studied here or using unmanned experiments?  At some
point the cost of further research here will be greater than that of an
orbiting facility, but until then, there's work to be done on Earth.

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

Date: 24 May 91 12:55:00 GMT
From: dev8g.mdcbbs.com![e-mail]
Subject: Re: SR-71

In article <[e-mail]!n5abi>, lobster.hou.tx.us!n5abi!gak (Gene A. Kennedy) writes:
>  The June issue of Popular Mechanics includes an article on the SR-71 and
> mentions that NASA is putting three back in service for research. Does
> anyone know where they will operate from? I would guess Edwards but the
> article never says.
>
> -----------------------------------------------------------------------
> Gene Kennedy - Ham Radio Operator, N5ABI - lobster.hou.tx.us!n5abi!gak
> -----------------------------------------------------------------------
>
--
At least one is at Edwards, and was operational when I saw it, even though
the plane had been officially "retired". A second SR-71 is supposedly
going to be used to help monitor the ozone hole over antartica. In both
cases, the aircrafts value lies in its extreme altitude.

Guess you can't keep a good airframe down!



==========================================================================
\\\\    Michael Rivero      | "I drank WHAT!" |"Why bother with marriage?|
  (.    [e-mail] | Socrates  -------------------Just find a   |
   )>   DISCLAIMER:::       |-----------| "Life is CHEAP! |woman you hate
  ==    "Hey man, I wasn't  |Looking4luv| But toilet paper|and buy her a |
---/    even here then!"    |Settle4sex!| is EXPENSIVE!"  |  house!"     |
++++++++++++++++++++++++++++++++++++++++-------------------+++++++++++++++

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

End of SPACE Digest V13 #640
*******************