Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_0/V16NO067.TXT

Text File | 1993-07-13 | 33KB | 768 lines

Date: Thu, 21 Jan 93 05:05:44
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #067
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu, 21 Jan 93       Volume 16 : Issue 067

Today's Topics:
                       *** BUSSARD RAMSCOOP ***
                     ** MORE BUSSARD RAMSCOOP **
                              Clementine
           Clinton's Promises (space) in Charlotte Observer
                      ESA internal PR info 01/93
                          ESA press release
                           Freedom's orbit
                      Galileo Update - 01/20/93
                       Goldin's future (2 msgs)
                      I want to be a space cadet
                        JPL Anonymous FTP Site
                           Oak heat shields
                 Planets around nearby sun-like stars
                      RTG's on the Lunar Module
                             Solar sails
                           Soyuz as an ACRV

    Welcome to the Space Digest!!  Please send your messages to
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----------------------------------------------------------------------

Date: 20 Jan 93 17:30:08 GMT
From: Jack Coyote <[e-mail]>
Subject: *** BUSSARD RAMSCOOP ***
Newsgroups: sci.space

In sci.space, [e-mail] (Henry Spencer) writes:
>
>Incidentally, to avoid running into the fabled ramscoop speed limit,
>you must *not* use an engine design that converts all the kinetic energy
>of the incoming gas into heat.  Otherwise your thrust will drop to zero
>when the incoming gas temperature reaches the exhaust temperature of
>your fusion reaction.  As with chemical jet engines, kinetic heating
>of the gas stream is your *enemy*, not your friend, because the reaction
>you're using for power produces a fixed final temperature, not a fixed
>temperature rise.  The simplest way around this is the Bussard equivalent
>of the scramjet:  don't slow the gas down much, just heat it as it goes
>past.  Alas, this has the same sort of problem that scramjets do:  to
>make a relativistic-combustion ramjet work, whatever heating reaction you
>use must be fast FAST *FAST*, because it must happen within microseconds
>at the very most.

  As I recall, this still will not solve the ~.1c speed limit.  You still get
big-time energy losses from bremsstrahlung (free-free) interactions and from
cyclotron radiation.

  bremsstrahlung: Fancy term for collisions between unbound electrons in a
                  plasma.  You WILL get this kind of radiation if you have a
                  hot fusion reaction.  Any radiation means energy loss.

  cyclotron:      You have charged particles in a magnetic field, ergo cyclotron
                  radiation.  Again, the energy has to come from somewhere, and
                  that somewhere is your accelleration.

  More hazards/limits:

  magnetic drag:  The large magnetic field will have a (admittedly smaller)
                  interaction with the (unmapped) interstellar magnetic field.

  dust:           Non-magnetic & relativistic (ouch)

  Bok globules:   Blobs of cold dark gas. Rich in hydrogen, but the rapid rise
                  in density is problematic to a ramscoop.

  etc.


  Sorry, few solutions, just more problems.


  Note to flamers: I LIKE the idea, it just needs work.  The best way to solve
                   the above requires that people know about them.  They haven't
                   been mentioned (that I have seen), so I did.
--
"Pound for pound, lame puns are your best entertainment value." -- Gogo Dodo

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

Date: Tue, 19 Jan 93 20:27:45 PST
From: Jason Cooper <[e-mail]>
Subject: ** MORE BUSSARD RAMSCOOP **
Newsgroups: sci.space

Just a few questions for those interested or able to reply...

1.  I have been advised by somebody that creating antimatter out of the
incoming protons, storing them, then dropping them into the stream, is
really rather inefficient, since it requires HUGE amounts of input.
Getting antimatter made beforehand seems equally impractical.  He DID
suggest that I might heat up (or otherwise energize) that reaction by
other means.  Any ideas?  A couple of things have become evident (to me
at least, though some may disagree).  Though they sound great in the
beginning, both the antimatter idea and the idea of using a solar sail is
seeming less and less practical, since one takes in too much energy, and
one firstly is bulky for such a ship and secondly won't accelerate it
much anyways.

2.  How dense is interstellar hydrogen?  I've heard estimates anywhere
from one atom per cubic centimeter to one atom every ten cubic
centimeters.  Anybody have a DEFINITE figure on this?  What I'm trying
for specifically is an estimate of how big the field's going to have to
be to collect REASONABLE amounts of matter.

3.  Although unnecessary at the moment, it may be wise to build in a
system for storing some of the incoming protons "for a rainy day".
Anybody have any concepts for how such a feat can be done?  I'm no ASCII
artist, so I won't try to draw it, but the internal shape of the engine
will be very much like an elipse (medium eccentricity) just overlapping a
parabolic form of the same base diameter (ah yes, that's HALF of an
elipse, long dimention along the engine's radial center).  That is the
cavity shape.  I'm looking for some sort of device to pull protons out
from inside that cavity into a container on the external of the ship.

4.  Any ideas for how to SLOW DOWN on the other end?  I'm not sure of any
myself, but nothing really comes to mind...  Figured somebody else might
have an idea.

5.  What sort of devices could the ship (which I figure will basically be
built around one engine, since that engine will be huge) be equipped with
to prepare it for conditions at the other end?

Just a few questions.  If anybody out there wants to play devil's advocate,
I'd be glad to take any _mail_ (please, it's easier to carry on a
discussion there since I may be missing half of the messages here) from
people who'd like to do so.  This project, I have just been informed, has
been chosen to participate in the INTERNATIONAL science fair in Taiwan,
so I'm welcoming ALL input.

                                                Jason Cooper

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

Date: 20 Jan 93 18:08:52 GMT
From: "Edward V. Wright" <[e-mail]>
Subject: Clementine
Newsgroups: sci.space

In <[e-mail]> [e-mail] writes:

>What is the status of Clementine at this time (post-Clinton election)?

Clementine is on track for launch earlier next year (February?).  It
will orbit and map the Moon for two months, then procedure onward for
a roundezvous with the asteroid Geographos.



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

Date: 20 Jan 93 18:15:12 GMT
From: "Edward V. Wright" <[e-mail]>
Subject: Clinton's Promises (space) in Charlotte Observer
Newsgroups: sci.space

In <[e-mail]> [e-mail] (rabjab) writes:

>>        B. Support completion of the space station Freedom.

>Looks like Clinton is going to make some rather severe cuts in space
>projects.  And "supporting completion" doesn't mean actual completion.

You don't understand.  NASA doesn't *want* Space Station Freedom
completed.  Completing a project means you no longer have job
security, which is why these things go on forever.  This is also
why no one comes right out and opposes a project anymore.  Instead,
they "support it as a research program" (as in Les Aspin's "I support
SDI as a research program" or Gary Coffman's "I support SSTO...").
That way, you not only ensure that nothing useful will ever get built,
you also establish a permanent aerospace jobs program, and ultimately
discredit anyone who supported the original project as anything more
than a jobs program.

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

Date: Wednesday, 20 Jan 1993 14:59:58 CET
From: [e-mail]
Subject: ESA internal PR info 01/93
Newsgroups: sci.space

                    ******** Ariane V 56  **********
          The first Ariane launch of 1993, flight V56, has now been
          rescheduled for the night from Tuesday 2 to Wednesday 3
          February.
          An Ariane 42P launcher, equipped with two solid strap-on
          boosters, will place into geostationary transfer orbit the
          American telecommunications satellite Galaxy IV.
          The lift-off will take place from the Ariane launch complex
          nr. 2 (ELA 2) in Kourou, French Guiana, as soon as possible
          within the following launch window:
          Kourou time: 21:50 hrs- 22:45 hrs on 2 February
          GMT/UT     : 00:50 hrs- 01:45 hrs on 3 February
          Paris time : 01:50 hrs- 02:45 hrs on 3 February





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

Date: 20 Jan 93 17:54:55 GMT
From: Hermann Schneider <[e-mail]>
Subject: ESA press release
Newsgroups: sci.space

     Press Release No. 03-93
     Paris, 19 January 1993

     The Euro/Russian BION 10 mission completed

          On 10 January 1993, at 04.16 UT, eight experiments jointly
     developed by scientists in five ESA member states, Russia and
     Ukraine, landed in a forest near the city of Karaganda
     (Kazakhstan), after a space journey of eleven and a half days.
     The experiments, covering research areas in biology, medicine
     and cosmic radiation, were carried by the retrievable "Bion-10"
     satellite, which had been launched from Plesetsk in Northern
     Russia on 29 December 1992. Due to thermal control problems the
     satellite had to be landed two days earlier than planned. On the
     whole the payload does not seem to have been adversely affected
     by these problems.

          The flight of these experiments was the result of a
     cooperation agreement between the European Space Agency (ESA)
     and the Institute of Bio-Medical Problems (IBMP) in Moscow.

          A major part of the payload on "Bion-10" was ESA's
     "Biobox" facility, a fully automatic and programmable incubator
     for research in gravitational biology, which housed three of the
     eight experiments jointly prepared by ESA and IBMP. The
     experiments in "Biobox", dealing with studies in bone tissue and
     cells under conditions of microgravity, were successfully executed
     during the first nine days of the mission. The first analyses
     carried out on some of the samples immediately after their retrieval
     from Space indicate a reduced mineralization in microgravity,
     confirming earlier flight results.

          Three joint experiments were also flown to study the effects
     of microgravity on the development and ageing of fruit flies, and
     on the cell structure development of unicellular algae. The fruit
     fly experiments produced a wealth of high quality data. The algae
     experiment, which, for scientific reasons had to be executed
     during the final days of the originally planned thirteen and a half
     days spaceflight, was unfortunately truncated because of the
     early return of the spacecraft, and will yield only partial results.

          The remaining two experiments, parts of which were
     directly exposed to the space environment, investigated the
     effects of cosmic radiation on plants and plant seeds, and



     performed dosimetric studies of the radiation in the "Bion-10"
     orbit. The results of these experiments will not be known until a
     few months after their retrieval.

          As was the case on the four previous "Bion" missions
     carried out since 1983, the payload provided by IBMP consisted of
     two Rhesus monkeys, which were subjected to numerous
     physiological, neurological, behaviourial and other investigations
     during their stay in Space. According to the first post-flight
     reports, both animals were in a reasonably good shape after their
     mission, though one of them had experienced problems with the
     food supply system after some days in orbit.

          Pre-launch and post-landing work on most of the
     experiments, as well as all engineering activities on "Biobox",
     were done in MOSLAB, the ESA facility built on the IBMP premises
     in Moscow.

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

Date: 20 Jan 93 13:48:35 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Freedom's orbit
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Brian Stuart Thorn) writes:

>>>And Alan thinks you'll see a Soyuz sitting on top of a U.S. booster launched
>>>from a U.S. facility....

>>Oh, that's a given. The booster may be the Shuttle...

>    Why do you say that's a given?

Because NASA won't crew Freedom without a lifeboat and Soyuz is the only
one they will get.

>    Isn't it cheaper to let the
>    Russians deliver the Soyuz ACRVs to Freedom?

I don't know if they can deliver Soyuz to the Freedom orbit. I would prefer
Atlas since it could result in significant cost reductions for other US
payloads. Building NASA's ACRV or using Russian transport will not achieve
those goals.

  Allen

--
+---------------------------------------------------------------------------+

| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------146 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 20 Jan 1993 18:01 UT
From: Ron Baalke <[e-mail]>
Subject: Galileo Update - 01/20/93
Newsgroups: sci.space,sci.astro,alt.sci.planetary

Forwarded from:
PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109.  TELEPHONE [phone]

                     GALILEO MISSION STATUS
                        January 20, 1993

     The Galileo spacecraft is almost 31 million kilometers, or
about 19.2 million miles, from the Earth, receding at more than a
quarter of a million miles each day.  It is 1.12 astronomical
units (104.3 million miles) from the Sun, and has traveled almost
2.6 billion kilometers (1.6 billion miles) since launch, or two-
thirds of its total path to Jupiter.

     The spacecraft is in the dual-spin mode, spinning at just
over 3 rpm with the lower part fixed in orientation.  It is
transmitting coded telemetry at 1200 bits per second over the
low-gain antenna.  Except for the fact that the high-gain antenna
remains undeployed, Galileo's health and performance are
excellent.

     Yesterday the flight team sent commands to pulse the antenna
deploy motors 1800 times, concluding ten days of motor hammering
this year.  Counting the hammering session of December 29-30,
1992, a total of 13,320 pulses have been executed in the latest
attempt to free the three stuck antenna ribs.  Although there has
been some motion in the deployment system and in the antenna, the
ribs have not yet been freed.  The last remaining action in the
plan for the stuck antenna is to spin up the spacecraft to 10 rpm
in March; there is little expectation that this will help.  Very
shortly the Project plans to focus on doing the Galileo mission
with the low-gain antenna.

                              #####
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Every once in a while,
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | try pushing your luck.
|_____|/  |_|/       |_____|/                     |

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

Date: 20 Jan 93 17:19:50 GMT
From: Pat <[e-mail]>
Subject: Goldin's future
Newsgroups: sci.space,talk.politics.space

>In article <[e-mail]> [e-mail] (Jeffrey David Hagen) writes:
>>Besides, catch a clue about JPL. It is widely considered to be the single most
>>bloated, pig-headed, and inefficient part of NASA among industry folks I have


I am here in Washington DC, and mostly deal with NASA HQ and GOddard people.
The senior Scientist I met who was heavily involved in funding Planetary
Science programs (Name withheld due to confidence) Blamed JPL for the
cancellation of Magellans Cycle 4-5 imaging.  His comments were that
JPL can't do mission support for under 50 million/year.

In fact,  the big push on now is to design probes that bypass
NASA infrastructure.  NO TDRSS, No SHuttle, NO JPL.  direct comms
back to the PI's.

pat

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

Date: 20 Jan 93 18:07:11 GMT
From: Ron Baalke <[e-mail]>
Subject: Goldin's future
Newsgroups: sci.space,talk.politics.space

In article <[e-mail]>, [e-mail] (Pat) writes...
>I am here in Washington DC, and mostly deal with NASA HQ and GOddard people.
>The senior Scientist I met who was heavily involved in funding Planetary
>Science programs (Name withheld due to confidence) Blamed JPL for the
>cancellation of Magellans Cycle 4-5 imaging.  His comments were that
>JPL can't do mission support for under 50 million/year.

Hmmm... sounds like you have your facts garbled.  Cycle 4 has never
been cancelled.  In fact, Magellan has been doing the Cycle 4 gravity
mapping since last September, and will complete it this May.  Cycles 5
through 7 may be cancelled, but it requires only 30 million *total* to
support these last three cycles through 1995.  Also from what I hear, Cycle 5
(which consists of the aerobraking maneuvers and improved gravity mapping)
may not get cancelled.  The Magellan team is being downsized to lower the
costs and keep the mission alive.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Every once in a while,
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | try pushing your luck.
|_____|/  |_|/       |_____|/                     |

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

Date: Thu, 21 Jan 93 04:54 GMT
From: Karl Dishaw <[e-mail]>
Subject: I want to be a space cadet

Fuzzy writes:
>Most new guys
>(military) who enter AFSPACECOM go to Undergraduate Space Training for a few
>months to learn all about rockets and satellites and astrodynamics.

Undergraduate Space Training is a 14-week combination of freshman
physics and memorizing statistics on AFSPACECOM's assets, one of the
worst wastes of $taxes I've seen.  I had wonderful time partying in
Denver but the only time I learned stuff was talking to instructors
outside class (the only time they're allowed to mention stuff that can't
fit into a multiple-choice test).  TDY pay was nice too--you KNOW a
lieutenant's overpaid when he sends money to his parents.  :-)


Karl
sold my soul to Uncle Sam . . . now marked down for resale.

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

Date: 20 Jan 1993 16:15 UT
From: Ron Baalke <[e-mail]>
Subject: JPL Anonymous FTP Site
Newsgroups: sci.space,sci.astro,alt.sci.planetary

Forwarded from:
PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE [phone]

                           JPL Pubinfo
                         January 20, 1993

A public access computer site containing information on and
images from missions conducted by NASA's Jet Propulsion
Laboratory has been opened by the JPL Public Information
Office.

The site may be reached by modem over phone lines, or by file
transfer protocol (ftp) over Internet.

Contents of the site include:

     -- JPL news releases, status reports, fact sheets and
        other data on JPL missions.

     -- Images from JPL missions as GIF computer files.
        These may be displayed on various makes of computers;
        viewing software may also be downloaded.

     -- Back issues of JPL's in-house newspaper, Universe.

In addition, teacher materials provided by the JPL Public
Education Office are planned to be added shortly.

Public users of the site currently may connect to it by the
following methods:

     -- By modem over commercial telephone lines to
        [phone].  Set parameters to no parity, 8 data
        bits, 1 stop bit.  This line supports speeds up to 9600
        bps with the v32/v42bis/MNP5 error correction and
        compression protocols, and supports up to two callers
        simultaneously.

     -- Users with Internet access can use anonymous ftp to
        pubinfo.jpl.nasa.gov (128.149.6.2).  Log on as user
        ANONYMOUS, then send your city and state (city and
        country if other than USA) as the password (commas
        and spaces are ok, up to a total of 15 characters).

For more information on this site, please call
[phone].

[Note to Internet users:  Although this site is not intended
to support interactive communication, your comments or
questions are welcome via email to [e-mail].]

                              #####
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Every once in a while,
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | try pushing your luck.
|_____|/  |_|/       |_____|/                     |

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

Date: Wed, 20 Jan 1993 21:28:50 -0600
From: [e-mail] (Phil G. Fraering)
Subject: Oak heat shields

\I believe that what the Chinese are reported to be using is oak, not
/bamboo.  they are also reported to produce a lot of their space
\hardware in a refrigerator factory, or soemthing like that.  So much
/for Western requirements for Level 100 cleanrooms.

Back before the big cleanup I could have gotten you a good deal on
enough oak to have retrieved a couple Skylabs intact; but we weren't
able to sell it, the lumberyards don't take "windfalls" from people's
yards, because they might have old nails and stuff in them...  as if
we don't know where all the nails are...

It basically got hauled away with all the other fallen trees.

\"Insisting on perfect safety is for people who don't have the balls to live
/ in the real world."   -- Mary Shafer, NASA Ames Dryden

Yup. An industry too chicken(explicitave deleted) to learn about
post-stone-age devices such as metal detectors turned our potential
resource back into trash. I wonder how much they'd be paying for it
if it were from virgin forest that species were driven extinct for
instead of from our backyard.

Needless to say, I think I now support efforts to save the Northern
Spotted Owl. If the lumber mills don't want to live in the real world,
and throw away (possible total for the area) tens of millions of dollars
worth of good oak and pine in a time when everyone could have used
financial help in the cleanup, then I don't want to either.

God, I think you *could* have heat-shielded several Skylabs with that
wood...

\------------------------------------------------------------------------------
/[e-mail] - I don't speak for others and they don't speak for me.

Just so y'all don't think Mary wrote that...
--
Phil Fraering         |"...Who in the valley shed the poison tear
318/365-5418          |no one knows...
[e-mail]|An old legend of a mythical hero..."

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

Date: 20 Jan 93 18:04:31 GMT
From: Steve Willner <[e-mail]>
Subject: Planets around nearby sun-like stars
Newsgroups: sci.space,sci.astro

In article <[e-mail]>, [e-mail]
(Francisco da Fonseca Rodrigues) writes:
>     Does someone know where can I get information about the formation
> or the possibility planet formation around the nearby stars?

You will probably get better answers in sci.astro.  I've cross-posted
and directed followups there.

As I understand it, the current situation is:

1) Everybody believes that planet formation ought to be a natural
part of star formation, at least for single stars and maybe for some
multiple star systems too.

2) There is lots of indirect evidence supporting 1) - but no proof.

3) There is not (yet) any single observation that is unambiguously a
planet circling another star.  But see below.

> after that in Astronomy Magazine, about the evidences of planets around the
> stars Epsilon Eridani and Gamma Cephei. This research was made by Bruce Camp-
> bell, from The Dominion Astrophysycal Observatory, and the article said he
> and his team would continue to reaserch others stars, and that they had 5
> more candidates, in a total of 16 stars.

The observation is that the radial velocity of the star varies
periodically by a very small amount.  This variation is interpreted
as the "reflex motion" of the star due to one or more orbiting
planets.

The main problem is that the mass inferred for the orbiting body
depends on the angle with which we view the system.  If we are
viewing from a direction near the pole of the orbit, we see only a
small portion of the true velocity variation, and we infer a mass
that is too small.  Thus it could be that the companions are really
faint stars, not planets.

If enough systems show variations, it may be possible to rule out the
"pole-on" interpretation on statistical grounds.  Or for some
individual systems, it may be possible to rule out a pole-on
orientation.  If this has actually been done, I'd like to hear about
it.
--
Steve Willner            Phone [phone]         Bitnet:   willner@cfa
Cambridge, MA 02138 USA                 Internet: [e-mail]
  member, League for Programming Freedom; contact [e-mail]

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

Date: 20 Jan 93 21:29:22 GMT
From: [e-mail]
Subject: RTG's on the Lunar Module
Newsgroups: sci.space

The RtG supposedly was warm enough to be felt through the astronauts gloves.
However the same astronaut (name eludes me) that shared that with me, did not
believe that there was significant danger (especially as compared to all the
other dangers inherent to the environment they were in when near the RTG).

I am not sure how this will post because I am not sure how to post a reply to
the group about an individuals post ("Re:...").  I fsomeone would like to share
the basic command (ANSWER? REPLY? POST?  etc???) I would appreciate it.  Moot
point if this posts the way I wanted it to (Re: RTG Lunar blah Blah blah).

Thanks,

Paul Shanley

[e-mail]
or
[e-mail]

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

Date: Wed, 20 Jan 93 17:46:35 EST
From: Tom <[e-mail]>
Subject: Solar sails

Josh Hopkins: >
Jason Cooper: >>

>>Hmm, can anybody here think of a way to retract a HUGE sail that's giong
>>to be external of all tanks, etc, down close to the hull?

>The next question though is _why_ you want to combine a solar sail with a
ramjet.  Solar sails are fairly slow and ramjets have to be moving very quickly
>to work.  Solar sails have to be near the sun for efficiency whereas I suspect
>bussard ramjets benefit from being outside the solar system (someone want to
back me up or shoot me down on this one?).  Get a first stage with more thrust.
>Or better yet, build a big laser in the solar system and just use the sail for
propulsion.  It may well be easier than trying to build an interstellar ramjet.

About the ramjet:  Inside the solar system, you have all those tasty ionized
protons from the sun, which is exactly what you need, presumably in a
smooth and predictable distribution, mening you could control the engine
quite well.  On the other hand, the solar wind may be relatively thin
compared to outside the solar system.  Time will tell.  Also, inside the
solar system there is probably a lot more floating junk that will interfere
with the operation (by killing everyone, for example, when it hits at
huge velocities :-).  We'll see about that someday, too (I hope!)

You are right about the speed differences, but with a laser, you could
get a sail up to ramjet speeds, within the solar system, perhaps, before
the laser loses it's effectiveness due to distance (scattering, extinction,
collimnation, etc.)

>>  Okay, anyways,
>>(no more parentheses anymore) does anybody know of a way to retract this
>>solar sail (which must be rigid (but possibly foldable), as it will
>>contain solar panels VERY useful for the initial approach

>I'd be very impressed if you could combine the function of pv cells with solar
>sail material.  The sail material must be very thin and strong (as well as a
>few other requirements) and should be reflective to a very high degree.  Solar
>cells must absorb light, and tend to be to thick and heavy to be very useful.

True.  But, there is a potential advantage.  If you could catch the photons,
rather than reflect them, you could store half their energy, while still
getting the other half as actual momentum.  The mass required will have to
decrease for this to be realizable, no doubt.

>Besides, even if you could make a solar sail the generated power you'd have a
>hard time figuring out what to do with it all.  A sail big enough to boost an
>interstellar probe up to the speeds you require would be intercepting enough
>light to power a good sized planet.

OK, how about, as long as we are imagining solar sails and ramjets (both
ideas, not objects) we also imagine solar cells covered in lcds, which
take up very little mass.  A stretch, sure, but what the hell.

Now, at first, open the lcds, so the sail absorbs.  Store this energy, till
your battery is full.  Now close the lcds so the sail reflects.   Once
near the heliopause, 86 the sail, run the ship on stored energy, using
ion thrust.  When up to speed, fire up the ram, away you go!

Small glitch:  The energy used by the ion thruster is the same energy that
could have propelled the sail in the first place.  If the difference
in mass due to dumping the sail can't increase efficiency after the
disadvantages of the mass required for other system, as well as the
complexity involved, it's all a waste.

Has anyone given any thought to sailing on something besides optical/IR
waves?  How about a giant radio antenna?  X-ray reflectors?

-Tommy Mac
------------------------------===========================================
Tom McWilliams               |Is Faith a short '  `      '   *.;     +%
[e-mail]       |cut for attaining    +    .      '
[phone] -or- 353-2986 |  . knowledge? ;"'       ,'    .   '     .
a scrub Astronomy undergrad  |      *     ,    or is it just  .       .
at Michigan State University |   ';   '        * a short-circuit?   ,
------------------------------===========================================

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

Date: 20 Jan 93 13:55:22 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Soyuz as an ACRV
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:

>AW>Oh, that's a given. The booster may be the Shuttle but we will see Soy
>AW>being launched for (at the very least) ACRV on US launchers.

>Under the terms of the Launch Services Purchase Act, NASA is prohibited
>from orbiting non-shuttle-specific payloads. Therefore,
>using the shuttle to orbit Soyuz spacecraft contravenes the LSPA.

In a perfect world you would be correct. However, it is currently too
easy for NASA to declare a payload Shuttle specific.

>However, several U.S. commercial vendors can supply launchers that
>can easily orbit a Soyuz for a more reasonable price than the shuttle.

As you well know, I have long supported exactly this. It is obvious that
using non-shuttle based logistics systems are both cheaper and more
reliable. The problems are political and not technical.

>AW>+----------------------990 DAYS TO FIRST FLIGHT OF DCX----------------

>Does this mean that you are now a Delta Clipper pessimist?

Not as long as they seem to be on track. Rest assured that if they ever
get off track I will loudly proclaim it.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------146 DAYS TO FIRST FLIGHT OF DCX----------------------+

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End of Space Digest Volume 16 : Issue 067
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