Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v08/v8_287.txt

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Date: Thu, 21 Jul 88 19:06:14 PDT
From: Ted Anderson <[e-mail]>
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Subject: SPACE Digest V8 #287

SPACE Digest                                      Volume 8 : Issue 287

Today's Topics:
               Re: OZONE cont.
             Re: Ramscoop engine
            Interstellar Ramscoops
 NASA calls Hubble Space Telescope ground test a success (Forwarded)
              Re: Rocket engine
                Re: New Ideas
             Re: Ramscoop engine
   re:Radiation in Near-Earth Space (was re: Mir and Solar Flares)
              Re: Rocket engine
              Re: Rocket engine
----------------------------------------------------------------------

Date: 6 Jul 88 00:33:22 GMT
From: tektronix!tekcae!vice![e-mail]  (Keith Lofstrom)
Subject: Re: OZONE cont.

I'm sure to get flamed for this:

---------------------
Abstract:  Science, February 12, 1988, vol. 239, pp. 762-4.

Biologically Effective Ultraviolet Radiation:
Surface Measurements in the United States, 1974 to 1985
J. Scotto et. al.

"Recent reports of stratospheric ozone depletion have prompted concerns about
the levels of solar ultraviolet radiation that reach the earth's surface.
Since 1974 a network of ground monitoring stations in the United States has
tracked measurements of biologically effective ultraviolet radiation (UVB,
290 to 330 nanometers).  The fact that no increases of UVB have been detected
at ground levels from 1974 to 1985 suggests that meteorological, climatic,
and environmental factors in the troposphere may play a greater role in
attenuating UVB radiation than was previously suspected."
---------------------

The data in the paper actually show a 0.7% DECREASE per year.  Perhaps,
before we panic and replace clorinated fluorocarbons with something that
could be MORE dangerous, we should calm down and look at ALL the data.

Meanwhile, remember to put the cover back on the board cleaning tank.

--
Keith Lofstrom   ...!tektronix!vice!keithl   [e-mail]
MS 59-316, Tektronix, PO 500, Beaverton OR 97077  (503)-627-4052

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

Date: 6 Jul 88 11:13:51 GMT
From: [e-mail]  (Paul F. Dietz)
Subject: Re: Ramscoop engine

In article <[e-mail]> [e-mail] writes:
>
>   I've read in various places (Carl Sagan's COSMOS, among others) that a
>ramscoop engine is possible.

Wonderful source.  He's wrong, as far as I know.  There are numerous
apparently insurmountable problems with the concept.  The most obvious
is that fusing ordinary hydrogen is damn near impossible (luckily,
otherwise all stars would burn out quickly). The losses in collecting
and fusing the hydrogen would also likely overcome any thrust produced.
The magnetic fields required are too high.  And so on.

Perhaps a better idea is a variant of an idea by Hans Alfven.  I call
it a "bootstrap rocket".  It uses the interstellar medium as a momentum
sink, not a fuel source.  Basically, the relative motion of the spacecraft
and the ISM is used to drive a generator (type unspecified).  This
exerts a drag force on the spacecraft.  The energy from the generator
is used to power some kind of rocket (using an onboard supply of
reaction mass).  If the exhaust velocity of the rocket is low enough
and the mass flow rate high enough, thrust will exceed drag, and the
spacecraft accelerates. (Exercise: why does this not violate conservation
of energy?)

The ISM, at least in the vicinity of he sun, is pretty sparse, although
some evidence suggests it is substantially ionized, perhaps by a
nearby (100 pc) supernova explosion in the last 10^5 to 10^6 years.
Let's hope the Pioneer and Voyager spacecraft encounter the
heliopause before they expire.

    Paul F. Dietz
    [e-mail]

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

Date: 6 Jul 88 23:25:38 GMT
From: aramis.rutgers.edu!klaatu.rutgers.edu![e-mail]  (J Storrs Hall)
Subject: Interstellar Ramscoops


Recent messages to this group indicate that the ramscoop
idea as originally posed may be unworkable because of the
difficulty/worthlessness of fusion in the collected hydrogen.

Now suppose we carry a small tank of antimatter and use it as an
energy source, merely using the interstellar medium as reaction
mass?  Are the magnetic fields required still too strong?
We don't have to squeeze nearly so hard, and if the i.m.
*is* ionized already...

--JoSH

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

Date: 7 Jul 88 01:23:36 GMT
From: [e-mail]  (Peter E. Yee)
Subject: NASA calls Hubble Space Telescope ground test a success (Forwarded)

Charles Redmond
Headquarters, Washington, D.C.                       July 6, 1988

Michael Braukus
Goddard Space Flight Center, Greenbelt, Md.


RELEASE: 88-91

NASA CALLS HUBBLE SPACE TELESCOPE GROUND TEST A SUCCESS


     The most comprehensive ground test ever conducted with
NASA's Hubble Space Telescope (HST) has been called a success by
NASA despite the challenge of an unplanned anomaly which provided
an unexpected bonus.

     The fourth in a series of ground system tests (GST-4) began
Monday, June 20, 1988 at NASA's Goddard Space Flight Center
(GSFC), Greenbelt, Md.  It was scheduled to end early Sunday,
June 26.  This "full-up test" was designed to simulate almost a
week of space flight operations and involved direct communication
with the HST located in a clean room at the Lockheed Missiles and
Space Company, Sunnyvale, Calif.

     "Overall, the test was very successful," said Ron Felice,
GSFC's deputy project manager of flight operations for HST.  "Up
until the anomaly, the test had exceeded our expectations in
terms of science instrument operations, spacecraft operations and
control room personnel."

     The problem developed without warning on Thursday at 5 p.m.,
when the HST's science computer and the instruments were placed
in a safe mode by the on-board computer system.  The system,
which is in a pre-planned state, sensed unsafe conditions and
activated itself for safe mode.  The spacecraft's remaining sub-
systems continued to operate according to the GST-4 time line.

     "Normally that would have been the end of the test," said
Felice. "Instead, we convened systems and instrument specialists
and on a real-time basis developed processes to trouble-shoot the
problem.  Sixteen hours later, we established plans to work
around the problem and recover safely into the GST-4 time line."

     Felice reported that although NASA technicians are still
studying the problem, a timing incompatibility between the
science instruments and their computer appears to have caused the
problem.  If this proves correct, the problem can be avoided in
the future by software adjustments.

     On Friday at approximately 12:15 p.m., the problem appeared
again as expected.  "Once again the on-board science computer and
the instruments went into a safe mode.  This time, because our
technical people were exhausted from working 30-hours straight,
we decided not to work the problem and to terminate the science
portion of the test.  The other elements of GST-4, which did not
involve the science computer and its instruments, continued until
late Friday evening when the test was ended."

     "Actually the HST's problem was an unexpected bonus for us,"
Felice explained.  "It proved that we have established a team
that is able to resolve problems involving an extremely complex
and sophisticated spacecraft."

     The HST is scheduled to be carried into space on board the
Space Shuttle Discovery in 1989.  When placed in orbit, the HST
will allow astronomers to see farther into the Universe with
greater clarity than ever before.

     The six scientific instruments the HST will carry are: wide
field and planetary camera, faint object spectrograph, high speed
photometer, high resolution spectrograph, faint object camera and
fine-guidance astrometer.  The faint object camera was provided
by the European Space Agency.

     The HST is managed by NASA's Marshall Space Flight Center,
Huntsville, Ala.  The GSFC manages the HST's operations and
observations.  It also manages the Space Telescope Science
Institute, Baltimore, Md.  Additionally, GSFC manages five of
HST's six instruments.  HST is a cooperative project with the
European Space Agency.

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

Date: 7 Jul 88 03:10:25 GMT
From: thumper![e-mail]  (Phil R. Karn)
Subject: Re: Rocket engine

> Designing and constructing rocket engines is largely an art.

I'm not a rocket designer, but I think I can agree with this. When the
second Ariane (L-02) went into the ocean back in 1980, taking AMSAT
Phase 3-A with it, I followed the AW&ST articles that described ESA's
failure analysis and design correction process.

For those of you who don't remember, this launch failed because of
severe combustion instabilities in one of the four hypergolic first
stage Viking engines. The first oscillation occurred barely off the pad;
on the tape you can see a bright flash in the plume before the rocket
even cleared the tower. Later oscillations resulted in the destruction
of the engine. The instabilities were in the 2-3 KHz region.

According to AW&ST, the problem was corrected by enlarging the holes in
the engine fuel/oxidizer injectors and conducting hundreds of test
firings.  I could be wrong, but I got the *very* strong impression that
the process was one of "diddle with it until it works".

Before castigating the "rocket scientists" for their computational
backwardness, however, consider what it would take to model a large
rocket engine like Ariane's Viking on a computer. Pressures in the order
of 50-60 atmospheres. Hypersonic hot gas flows, with extreme variations
in temperature and pressure over very short distances and times. Mass
flows on the order of tons/second.  I don't know how much computational
modeling of rocket engines is going on now, but it has got to be one of
the most demanding CAD jobs around.

Phil

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

Date: 5 Jul 88 15:39:30 GMT
From: att!whuts!homxb!homxc![e-mail]  (J.CONANT)
Subject: Re: New Ideas

In article <[e-mail]>, [e-mail] (Dani Eder) writes:
[in reference to deorbiting the shuttle with tethers]
> There has been observed by myself and others a 'signal delay' of about five
> years within NASA for new ideas.

    Actually, the Niven & Barnes novel an earlier poster referred to
didn't originate the idea. An ESA scientist - G.Colombo, I believe -
developed the tether concept in lots of neat ways long before their book.
NASA was considering a joint missions with the Italian space agency to
lower an instrument package into the upper atmosphere on a tether,
though the concept seem to have langusihed.

    Jon Leech
    AT&T Pixel Machines
    __@/

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

Date: 6 Jul 88 17:22:00 GMT
From: a.cs.uiuc.edu!p.cs.uiuc.edu![e-mail]
Subject: Re: Ramscoop engine


The ramscoop engine idea is used in larry Niven's books.  I don't know if
he "invented" it.

It is also used in S. Lem's new book "Fiasco."

The advantage (especially plot-device-wise), is that with constant
acceleration, no need for fuel-storage, fusion-propulsion of some kind,
you could eventually build up speeds close to the speed of light,
and thus travel long distances in a short period of time (by the reference
of the ship) because of the relativistic effects of near-light speed.

The questions you ask are rarely bothered with in any stories I have
read that have used this.

One more question I can think of off the top of my head -- what happens
to heat dissipation as time slows down?  As the fusion reactor approaches
light-speed, would its heat dissipation also slow down, thus causing
a meltdown?

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

Date: 6 Jul 88 22:52:17 GMT
From: att!mtuxo![e-mail]  (54317-T.EBERSOLE)
Subject: re:Radiation in Near-Earth Space (was re: Mir and Solar Flares)

In article <[e-mail]~, [e-mail] (Glenn Chapman) writes:
~A rather interesting point concerning Mir was made by Bill Higgins of Fermi
~Lab in a mail message to me. He said:
~>I encountered a brief headline about a "magnetic storm" that's supposed
~>to hit this planet this week and stopped to wonder-- what do the Mir & Salyut
~>cosmonauts do when there's a solar flare?  Obviously they don't pack up
~>and go home. Is there a storm cellar arrangement aboard Mir?  Can you explain
~>the details?
~
~...I would suspect that would give them substantially higher
~radiation levels than normal. It is interesting that they went ahead with
~the space walk under these conditions.
~

Sorry I have no answers, but to continue the questions, what levels of
radiation have current *-nauts been exposed to? Any data on what has
happened to older astro-cosmo-nauts, which could be attributed to
radiation exposure? Or is LEO fairly benign to the humans who have been
there? Any data on the radiation levels Apollo crews were exposed to?

--
Tim Ebersole ...!{allegra,ulysses,ihnp4,mtune,...}!mtuxo!tee

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

Date: 7 Jul 88 10:16:32 GMT
From: jplpub1![e-mail]  (Jordan Brown)
Subject: Re: Rocket engine

In article <[e-mail]> [e-mail] (Phil R. Karn) writes:
>... consider what it would take to model a large rocket engine like
>Ariane's Viking on a computer. Pressures in the order of 50-60
>atmospheres. Hypersonic hot gas flows, with extreme variations in
>temperature and pressure over very short distances and times. Mass flows
>on the order of tons/second.

Los Alamos simulates nuclear explosions using their Crays; I suspect that
the pressures and speeds are somewhat larger than in rocket engines.

(they like to make color 16mm films of the explosion in various axes -
temperature, pressure, etc.)

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

Date: Thu,  7 Jul 88 14:06:48 -0400 (EDT)
From: Ted Anderson <[e-mail]>
X-Andrew-Message-Size: 1026+0
Subject: Re: Rocket engine
Date: 6 Jul 88 20:51:19 GMT

Designing and constructing rocket engines is largely an art.  There is
some empirical study involved, but if your think the Shuttle or SV
engines were fully simulated by computer, you are a decade too early.
There have only recently been programs to simulate engine circulation
and these programs are not yet for release outside the US.

Engines are by and large a hack job.  I think you might be able to write
Rocketdyne Division of Rockwell Intl. and get some litearture.  You will
also obviously check the aeronautics section of your library thoroughly.
Sorry, I can't help you much more than that.  We have not yet begun to
make a perfect engine.

Another gross generalization from

--eugene miya, NASA Ames Research Center, [e-mail]
  resident cynic at the Rock of Ages Home for Retired Hackers:
  "Mailers?! HA!", "If my mail does not reach you, please accept my apology."
  {uunet,hplabs,ncar,decwrl,allegra,tektronix}!ames!aurora!eugene
  "Send mail, avoid follow-ups.  If enough, I'll summarize."

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

End of SPACE Digest V8 #287
*******************