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Subject: SPACE Digest V13 #013

SPACE Digest                                      Volume 13 : Issue 13

Today's Topics:
               Re: Interstellar travel
               Re: Interstellar travel
               Re: Interstellar travel
        Space News from Flight Int. for Dec90
        pure oxygen and spacecraft fire safety

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Date: 29 Dec 90 00:18:41 GMT
From: unixhub!shelby!neon!Neon![e-mail]  (John McCarthy)
Organization: /u/jmc/.organization
Subject: Re: Interstellar travel
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Here's a method of interstellar travel based entirely on present science
and technology.  It could be developed in time to start an interstellar
journey in the next 25 to 50 years.  However, the time to get to nearby
stars is in the low thousands of years, so mult-generation voyages would
be required at the present level of bio-technology.  It seems likely
that waiting longer to start, even a few hundred years, would result
in an earlier arrival time.  The only reason why anyone would want to
start sooner would be to escape political events.  Thus either side
in World War II, faced with the certainty of defeat, would probably
have launched such an interstellar voyage.

The idea is to use an ordinary fission reactor to generate electricity,
and use the electricity to expel a working fluid at an appropriate
velocity.  The appropriate velocity is a compromise between wanting
a high specific impulse to get a large delta-v and getting a high
enough thrust to build up velocity in a reasonable time.  It turns
out that the exhaust velocity should be low at first and increase
during the journey and should depend on the distance to the star
to which the voyage is made.

The time  t  required to go a distance  s  is given by a formula that
looks like

    t = 2.1 p**(- 1/3) s**(2/3).

The constant 2.1 is approximate.  Here  p  is a figure of merit
of the power generator and rocket system, namely the power handled
per unit mass of equipment, e.g. watt/kg if mks units are used.
The calculation is non-relativistic, and the formula is over-optimistic
if relativistic velocities are to be obtained.  It also is correct
only when the optimal mass flow is much larger than the rate at which
the reactor generates fission products.  If this is not the case,
then the correct strategy is to just use the fission products, somewhow
separated, as reaction mass.

The formula leads to the following conclusions.

1. It provides an existence theorem for the feasibility of human
 occupation of the galaxy in less than a million years.  This conclusion
requires no new science and not much new technology.

2. The factor  p**(- 1/3)  means that improving the technology is
not going to avoid multi-generation voyages even to nearby stars.
You need a factor of 1000 improvement to reduce the time by a factor
of 10.

3. The factor  s**(2/3)  means that all the nearby stars are accessible
in qualitatively similar times.  If I remember correctly, the
formula is approximately correct to distances of 600 light years.

Here are two social opinions.

1. Multi-generation voyages are feasible socially.  The existence theorem
is provided by the existence of reasonably stable tribes of the
population level that can be supported.

2. It is a mistake to suppose that whether to undertake the colonization
of the galaxy is necessarily a decision to be taken by humanity as a
whole.  The corrrect question is whether any group with the necessary
resources will undertake the journey, and whether the rest of humanity
will refrain from suppressing the effort.

I don't believe this is the most likely variant to be chosen.  Probably,
Robert Forward's ideas about using solar system based lasers to transmit
power to spacecraft that it will use to expel working fluid will work
and will have higher performance.  This idea was advanced only to
argue that interstellar colonization is feasible in times small compared
to the normal life of a species.

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Date: 29 Dec 90 11:14:29 GMT
From: prometheus![e-mail]  (Paul M. Koloc)
Organization: Prometheus II, Ltd.
Subject: Re: Interstellar travel
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
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In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Mark Gellis) writes:
>>... [fusion drives] It may be that the technology is simply too far in
>>the future, but people seem to drool over matter-antimatter, or
>>solar sails, but never talk about the possibilities of fusion
>>for interplanetary travel.  Any comments?

>Antimatter is probably easier than fusion, unless some seriously oddball
>approach to fusion gives us a practical way to use the high-order reactions
>with minimum neutron emission, or we find some way to reflect fast neutrons
>efficiently.  Even the D-He3 reaction produces enough neutrons to be
>troublesome, and He3 is almost impossible to find or make in the quantities
>needed for large-scale high-performance rocketry.  (Terrestrial power needs
>negligible amounts by comparison.)

We may have just such a spheroidal approach to fusion.

Initially, the moon has a sufficient supply of (3^)He to run trawlers to
seine it from the exosphere of Jupiter.  The likely neutron output from a
refined D-3^He reactor would be about two percent.  Further, the neutron
energy per reaction is not nearly as ripping as that from the D-T reaction.

For our aneutronic generator approach, this reaction is far more tolerable
since it would be trapped in an extremely dense liquid density gas blanket.
It is certainly, a better situation than the current solid vacuum wall mag
approaches of the DoE ...   ah,   approach of ..

Until we find out otherwise, "p-11^B" looks like the ideal aneutronic
(neutronless) burning fuel.

+---------------------------------------------------------+**********+
|                                                         +Commercial*
| Paul M. Koloc, President          [phone]        ***FUSION***
| Prometheus II, Ltd.; College Park, MD 20740-0222        ***in the***
| mimsy!prometheus!pmk; [e-mail]               **Nineties**
+---------------------------------------------------------************

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Date: 29 Dec 90 15:34:12 GMT
From: rochester![e-mail]  (Paul Dietz)
Organization: University of Rochester Computer Science Dept
Subject: Re: Interstellar travel
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
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In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>
>Antimatter is probably easier than fusion, unless some seriously oddball
>approach to fusion gives us a practical way to use the high-order reactions
>with minimum neutron emission, or we find some way to reflect fast neutrons
>efficiently.  Even the D-He3 reaction produces enough neutrons to be
>troublesome [...]

But antimatter reactions also produce considerable neutral radiation.
Reaction of hydrogen and antihydrogen produces neutral pions (which
decay immediately to very energetic photons).  The electrons and
positrons present also react to make gammas.  More importantly, if the
antiprotons are annihilated in higher nuclei, the reaction will
produce energetic nuclear fragments, including neutrons.  Finally, if
the charged pions are used to directly heat ordinary matter, they will
cause other nuclear reactions, including the production of nuclear
fragments and the direct reaction with protons to make neutrons.

That aside, the very low efficiency of antimatter production (.1%,
maybe, if we're real good) is a real constraint.  A low performance
inertial fusion rocket might have a power output in the gigawatts.
You'd need terawatts of input power (expensive power, in the form of
electricity) to make enough antimatter to achieve the same performance
for extended periods.  For really low performance, why not just
use fission-thermal rockets?

    Paul F. Dietz
    [e-mail]

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Date: 30 Dec 90 01:13:46 GMT
From: mcsun!ukc!axion!phoebe![e-mail]  (swaraj jeyasingh)
Organization: British Telecom Research Labs
Subject: Space News from Flight Int. for Dec90
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Many thanks to those who replied to my  posting and  confirmed that  they
were  receiving  me loud  and clear.   Obviously I  neednt have  doubted.
Anyway,  here  is  a summary  of space  related news  culled from  Flight
International during  December.  I  am only  posting news  which I  think
would not have been covered by other reports (e.g Henry Spencer on AWST).

ESA denies that it will quit the ISS effort, despite a delay of at  least
*5* years for the  launch of  its Columbus  attached pressurised  module.
(Delay due to redesign of Fred).  According to Roget Elaerts of ESA, they
are  "closely  participating with  NASA on  the restructuring  exercise".
Should Fred be cancelled, Europe would stil be free to  concentrate on  a
Columbus  Free  Flyer to  be  launched  on  Ariane  5  in  late 1990s.   An
independant, man tended European space base may also be considered by ESA
as a precursor to a space station.Such a move would boost the chances  of
the Hermes space shuttle winning the ESA's approval.

Also  mention  of  first  flight  of the  Ariane 42P  model in  November,
launching 2 US comms  sats. 42P  has two  strap on  solids.  Next  Ariane
launch due in Jan.

Report on  RAE (Royal  Aerospace Establishment,  UK) plans  to develop  a
Space  technology Research  Vehicle (STRV)  to investigate  the in  orbit
performance of several new space  technologies.  Weighing  50kg, it  will
carry eight experiments researching technologies aimed  at improving  the
performance, life and cost-effectiveness of future spacecraft.  The  STRV
mission will address three major hazards: radiation damage to solar cells
and  microelectronics,  electronic anomalies  and other  damage to  comms
satellites caused by electrostatic charges and arcing at high  altitudes;
and surface corrosion of Earth observation spacecraft by atomic oxygen at
low altitudes.  STRV will be carried as an auxiliary payload on an Ariane
4 commercial comms launch.  It will traverse the  earths radiation  belts
at GTO 4 times a day, enabling accelerated radiation tests to be  carried
out.

Soviet Ministry of Defence has undertaken its first commercial spacecraft
launch.  The Gorizont geostationary comms sat launched  from Baikonur  on
Proton  booster  on  Nov23  was  undertaken  for  the Russian  Federation
(RSFSR).   The  RSFSR's  Ministry  of   Communications  and   Information
Technology will pay R100 million  ($176) for  what will  eventually be  a
three sat system.

Nasa doctors at JSC develop drug to cure space sickness.  Am injection of
promethezine administered after the onset of symptoms has  shown a  mrked
decrease in the severity of the problem.  It has  been used  14 times  on
shuttle  flights  since  Sep  1988.  Previously  they had  oral doses  of
scopolamine  (!) and  dextroamphetamine but  the absorption  of these  in
weightless conditions is unpredictable.

The Soviet Union is to resume Zenit booster launches early in 1991  after
maintenance work on the second launch pad at Baikonur  is complete.   The
Oct 4 Zenit launch failure destroyed Launch pad one.  That explosion  has
been attributed to Zenits RD-170 first stage engine.  It  is regarded  as
random  and  not  a  sufficient  reason to  stop launches  for a  lengthy
investigation.

Indonesia is considering using China's Long March booster  to launch  its
Palapa satellites.  This was announced during  the Indonesian  presidents
trip to China.  Also raised the possibility of cooperation in  developing
rocket technology for use  in Indonesia's  own space  program.  The  Long
March launch is expected to be about $17m cheaper than a shuttle launch.

AEA Technology, the commercial  arm of  the UK  Atomic Energy  Authority,
plans to  develop an  upper stage  for small  low cost  satellites to  be
propelled by an ion-thruster.   Called Argos,  the upper  stage is  being
designed for launch on Hercules/Orbital Sciences Pegasus, to place  300kg
spacecraft into a 400-2000km high orbits.  Propulsion  would be  provided
by the UK10 ion thruster system.  Argos uses xenon propellent and  offers
exhaust velocities,  10 times  higher than  convetional chemical  rockets
(that  is VELOCITY not THRUST).  After delivery by Pegasus into iniial orbit,
the  thruster  will  manoeuvere  the payload  into its  final orbit  over
several months.A UK10 thruster is scheduled to fly on  the ESA's  Artemis
technolgy demonstrator satellite in 1993/94, to provide station keeping.

Lockheed is bidding to supply heatshields to the  Italian Space  Agency's
CARINA recoverable capsule.  This 530kg spacecraft is being developed  by
Aeritalia to carry microgravity payloads into LEO.  It  will be  launched
into 300-400km high orbit by a version of the LTV Scout from the  Italian
run San Marco platform off the coast of Kenya.  Lockheed is proposing  to
use the same insulatiom material used on some parts of the Shuttle.

Israel Aircrfat  Industries says  that it  will continue  its efforts  to
enter the civil space launch market with versions of the Shavit  booster.
It  has  dropped  out  of  NASA's  commercial  experimental   transporter
competition, aimed at selecting a medium class civil booster.  Shavit  is
variant of the Israeli ballistic missile, Jericho.

A Briton may yet make it into space in  May 1991.   The Mir-Juno  project
which was threatened with cancellation due to lack of  finance, will  now
take  place  it  seems  -  on  a  fly  now  pay  later  deal. (All  other
international  guest  cosomonauts  have had  to pay  first.) The  British
astronaut  chosen  will be  announced on  Jan 15th.   Two, a  male and  a
female, are currently in tarining in Star City.

Fianlly, here are the space questions from the annual Christmas Quiz:

1> Which Ferdinand went to Venus
2) Which Edwin needs some specs
3) Who are the two "Gennadis"
4) What suffered from unofficial leaks
5) Which Chinese booster flew for the first time in 1990 and which Soviet rocket did not reach its zenith.
6) Name the oldest man in space and the newest
7) What made an unexpected arrival at Kennedy
8) Which satellite operating organisations now operate their own satellites

Answers next time

Thats all folks for 1990. Have a Happy New Year !



Swaraj Jeyasingh                [e-mail]
British Telecom Research Labs
England.

The above is in no way connected with my employer.  I am not employed  by
Flight International either

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Date: 29 Dec 90 07:48:20 GMT
From: news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: pure oxygen and spacecraft fire safety
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In article <[e-mail]> [e-mail] (Steve Nuchia) writes:
>There was a deeper error behind the failure to recognize 1 atm of O2
>as a hazard.  Prior to the fire the official fire prevention philosophy
>was to have no ignition sources.  Since it was official policy that
>there be no ignition sources on board, there was not very much thought
>given to what might happen if there was a fire.

Actually, not true.  Fire *in flight* was considered at great length
(source: Frank Borman's testimony to Congress as a member of the fire
investigation board), and avoidance of flammable and smoke-producing
materials when practical was definitely policy.  (There is a complaint
on record just a few weeks before the fire that eliminating hazardous
materials from the cabin was proving more difficult than it had been
on Mercury and Gemini.)  And the KSC safety people had given quite a
bit of attention to pad fires and escape from same.

However, Steve is correct that the basic approach was to avoid ignition
sources, and containing a fire was second priority.  (This is, after all,
the normal and quite successful approach elsewhere.)  There were still
a lot of flammables in the cabin, since tradeoffs tended to weight other
issues more heavily.  And many things that would pass a 3psi oxygen test
would flunk a 15psi oxygen test; in fact, NASA eventually abandoned
making the cabin proof against a 15psi-oxygen fire -- it was virtually
impossible -- and settled for a mixed-gas atmosphere until mid-ascent.
In 3psi oxygen, the fire probably would not have been serious, and the
limited precautions that had been taken might well have proved adequate.
At the very least, it would probably have spread slowly enough to be
coped with -- what took the KSC safety people by surprise was not the
possibility of a spacecraft fire (always non-zero with experimental
hardware) but the ferocious intensity and near-instantaneous spread.
(JSC basically assumed that fires were impossible, but KSC did not.)

As Steve describes, the revised approach assumes the presence of an
ignition source -- probably overly paranoid if spaceflight ever becomes
routine, but realistic for semi-experimental vehicles that are constantly
changing -- and insists that a fire must go out by itself when started.
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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End of SPACE Digest V13 #013
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