Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/spacedig/V16_0/V16NO048.ZIP/V16NO048

Internet Message Format | 1993-07-13 | 32KB

Date: Fri, 15 Jan 93 05:00:07
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #048
To: Space Digest Readers
Precedence: bulk


Space Digest                Fri, 15 Jan 93       Volume 16 : Issue 048

Today's Topics:
                        ** BUSSARD RAMSCOOP **
                        averting doom (2 msgs)
                         best food for space?
                        Defuse Xray Experiment
                          ESA press release
          Galileo Stuck Ribs / Remote Manipulator? (3 msgs)
                           Helium (2 msgs)
                  How much? (was Re: Moon Dust Sold)
      Let's be more specific (was: Stupid Shut Cost arguements)
                    Saving an overweight SSTO....
                     Shuttle timetable wanted....
                            SNC meteorites
                             TPS Systems

    Welcome to the Space Digest!!  Please send your messages to
    "[e-mail]", and (un)subscription requests of the form
    "Subscribe Space <your name>" to one of these addresses: listserv@uga
    (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle
    (THENET), or [e-mail] (Internet).
----------------------------------------------------------------------

Date: 13 Jan 93 14:27:50 GMT
From: Jason Cooper <[e-mail]>
Subject: ** BUSSARD RAMSCOOP **
Newsgroups: sci.space

Just been talking to Lynn Wahl over in my mailbox, and came up with an
idea for using a light sail to bring the thing into orbit.  The plan is
this:

1. Laser-assist out of earth orbit
2. Close approach to sun with sail edge-on to sun (for minimum drag)
3. Sail up to orbit sequence out of the solar system

It was broken into a lot more categories in my mail, but I _believe_ that
was the gist of it, though Lynn could correct me on here if I'm fatally
at fault.  The sail could _also_ act as a solar panel.  You could
probably generate HUGE amounts of energy to store for the long trip on
your close approach to the sun.  Ah, yes, and the sail can be used as a
BRAKE at the destination.

Second thing that I've been thinking about...  What's the average
temperature of space (just "empty" space, not including planets, etc)?
I've been reading up about superconductors and found one that apparently
can THEORETICALLY reach superconductivity even at 160 degrees kelvin (or
was that the real measurement?).  Just wondering if the temperature of
deep space would help much in the way of cooling the magnetic coils and
other components of HUGE concern.  Also, does anybody know if a
superconducting electromagnet still works?  Would that work for the
collection magnets?

                                                Jason Cooper

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

Date: Thu, 14 Jan 93 03:37:45 GMT
From: Tino <[e-mail]>
Subject: averting doom
Newsgroups: sci.astro,sci.space,sci.physics,sci.environment

In article <[e-mail]> [e-mail] (Patricia C. Vener-Saavedra) writes:
>Hi there. As I recall, in about a billion years the sun will have
>about twice the luminosity it presently has. The average surface of
>Earth will be about 100 degrees C. Some lakes and rivers will have
>begun to boil. It will not be pleasant for homo sapiens.:-)

Don't Panic.

Tino
--
     "Here are the young men, the weight on their shoulders..." - J.D.
----------------------------------------------------------------------------
             Purdue University School of Nuclear Engineering
----------------------------------------------------------------------------

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

Date: Thu, 14 Jan 1993 05:24:45 GMT
From: Marvin Minsky <[e-mail]>
Subject: averting doom
Newsgroups: sci.astro,sci.space,sci.physics,sci.environment

In article <[e-mail]> [e-mail] (Tino) writes:
>In article <[e-mail]> [e-mail] (Patricia C. Vener-Saavedra) writes:
>>Hi there. As I recall, in about a billion years the sun will have
>>about twice the luminosity it presently has. The average surface of
>>Earth will be about 100 degrees C. Some lakes and rivers will have
>>begun to boil. It will not be pleasant for homo sapiens.:-)

Sure it will, because by that time we'll be composed of complex
polymers of zirconium phosphide or something adequately thermophilic.
That is, unless the Rifkins succeed in outlawing evolutionary
engineering.

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

Date: 13 Jan 1993 21:58:48 GMT
From: steve hix <[e-mail]>
Subject: best food for space?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (rabjab) writes:
>I watched Robinson Crusoe on Mars the other day and got the idea to
>put my food in toothpaste tubes.  I squezed out all the paste into
>jars and used the blender to turn various foods into paste.  I'm
>having some problems getting the paste in the tubes, however.  Does
>anyone have suggestions?

Are you having fun?  :-/

If you're even marginally serious, you could go down to a backpacking
store like REI and look for the tubes they sell for bringing honey,
peanut butter and the like on trips.  They're polyethylene, open at
one end with a clip to seal them shut after filling.  Reusable, too.

RCoM was a pretty bad movie, no?

--
-------------------------------------------------------
| Some things are too important not to give away      |
| to everybody else and have none left for yourself.  |
|------------------------ Dieter the car salesman-----|

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

Date: Wed, 13 Jan 93 19:31:58 EST
From: Tom Schruefer <[e-mail]>
Subject: Defuse Xray Experiment

>With the successful deploy of TDRS-F, STS-54's other primary payload bean
>operations. During orbital night, the Diffuse X-Ray Spectrometer will tke
>measurements of the x-ray background of the solar system's interstellar
>medium. This information will be used to answer questions about a nearb
>super nova that scientists believe occurred about 300,000 years ago.

   Does anyone know which star they are talking about ???

-
*====================================================================*
|          Howard County Public School System, Maryland              |
|--------------------------------------------------------------------|
|                    From the Collected Works of:                    |
|---------------------------------|----------------------------------|
| Tom Schruefer                   |              Bitnet : TCS1@DCC   |       :::
| Applications Programmer         |          CompuServe : 76446,1667 |  MUSIC
*====================================================================*

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

Date: Thu, 14 Jan 93 16:57:05 CET
From: [e-mail]
Subject: ESA press release

     Press Release Nr. 01-93
     Paris, 13 Janaury 1993

     ESA at the starting blocks of 1993

     The calendar of space activities for 1993 is, like every year,
     full of events and activities taking place all over the world.
     ESA will again play a chief role in or will be present at the
     following events at European and at international level.

     February
     1st half    Ariane V56: Launch of the American telecommunications
                 satellite Galaxi IV.
     22/02       Meteosat 3: Inauguration of the Wallops Island
                 ground station.
     2nd half    Ariane 5 B1 : First firing test of the Ariane 5
                 solid rocket booster in Kourou.
     end         STS 55/Spacelab D2 : Second German Spacelab
                 mission with heavy ESA involvement.
     March
     12-21       MUBA, Basel -Switzerland: International trade
                 fair and exhibition.
     2nd half    STS 56/Atlas 2 : Follow-up of Atlas-1 mission
                 for atmospheric applications and science.
     April
     t.b.c.      Ariane V57 : Launch of Astra 1C
                 telecommunications satellite with Arsene as
                 seconday passenger.
     end         STS 57/Eureca: Retrieval mission of ESA's
                 Eureca platform.
     May
     t.b.c.      Ariane V58 : Launch of Hispasat 1B and Insat
                 2B telecommunications satellites.
     05-08       Geotechnica, Cologne- Germany:
                 International geotechnology and Earth sciences
                 trade show and congress.
     11-13       Neo-Com 93, Kiev- Ukraine:
                 Telecommunications and information industry
                 fair and conference.
     10-13       SPOT and ERS-1 symposium and exhibition,
                 Paris: The results and applications of these two
                 satellites. Co-organized by ESA and CNES.
     June
     11-20       Le Bourget, Paris- France: Space and Air
                 show. ESA will have a large Pavilion open to the

                 general public.
     28/6-3/7    COSY: Columbus Symposium in Ischia
                 (Naples), Italy.
     t.b.c.      Ariane 5 M1: First firing test of solid rocket
                 booster with flight structure in Kourou.
     August
     31/8-5/9    MosAeroshow 93, Moscow- Russia : second
                 Russian aviation and aerospace exhibition.
                 Open to the general public.
     t.b.c.      Ariane: 20 years of the Ariane Programme,
                 decided in Brussels in August 1973.
     September
     11-14       2nd ERS-1 Symposium, Hamburg- Germany.
     t.b.c.      Ariane V59 : Launch of Spot 3 and Stella for
                 France.
     October
     t.b.c.      Ariane V60 : Launch of Intelsat VII-F1
                 telecommunications satellite.
     16-22       IAF, Graz- Austria: Congress and exhibition.
                 The worldwide yearly gathering of space
                 specialists.
     19-23       SITEF, Toulouse- France: International market
                 for advanced technologies.

     t.b.c.      ESA Washington Office : 20 years of ESA
                 presence in Washington for close cooperation
                 with NASA.
     t.b.c.      Ariane 5 M2: Second firing test of the Ariane 5 solid
                 rocket booster with flight structure in Kourou.
     t.b.c.      Spacelab: 10th anniversary of ESA's manned
                 space laboratory first launch.
     November
     t.b.c.      Ariane V61/ MOP-3 : Launch of ESA's
                 meteorological satellite Meteosat MOP-3 and the
                 Mexican telecommunications satellite
                 Solidaridad 1.
     t.b.c.      Maser 6 and Texus 31 sounding rocket launch
                 with major ESA payload participation.
     December
     1st half    STS-61/HST servicing : Repair mission of
                 Hubble Space Telescope with ESA astronaut
                 Claude Nicollier on his second shuttle flight.
     t.b.c.      ARIANE V62: launch of DirecTV1 and Thaicom
                 telecommunication satellites.

     Dates related to launches are very much dependent on
     different  factors (readiness of spacecraft and/or space
     transportation system/launcher, etc.) and thus remain

     t.b.c. (to be confirmed) for quite some time. We will timely
     keep you informed of all these events - and of many more -
     with a constant flow of information.

Regards Hermann Schneider
        Network Coordinator
        ESOC (European Space Agency's Operations Centre)

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

Date: 14 Jan 93 05:34:07 GMT
From: justin sullivan <[e-mail]>
Subject: Galileo Stuck Ribs / Remote Manipulator?
Newsgroups: sci.space,sci.astro,alt.sci.planetary

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

>Bear in mind that the Galileo malfunction is of a fairly unusual type.
>Most failures are subtle things ailing in the innards of the boxes.

Well, I'm not one to dig up old ghosts, and I don't mean to sound negative,
BUT.. It was 'a fairly unusual type' of problem that took the lives of
seven astronauts (seven years ago this month).

One could always argue that it wasn't an unusual problem that caused
Galileo to have a crippled antenna, but an oversight of hoardes of fine
engineers. Nobody's perfect, but when you get so many superbrains together
and give them piles of money, they're expected to deliver a perfectly
functioning piece of hardware. If they're so damn smart (I believe they are..)
things like this shouldn't happen. Either way, 40bps means that my great
grandchildren will have to analyze the data.

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

Date: 14 Jan 93 07:48:50 GMT
From: Robert Glock <[e-mail]>
Subject: Galileo Stuck Ribs / Remote Manipulator?
Newsgroups: sci.space,sci.astro,alt.sci.planetary

[e-mail] (David Hinz ([e-mail])) writes:
:
:                                                   .....  How feasable
: would it be to incorporate a robotic arm manipulator into these designs,
: articulated so that it could reach everything on the probe/satellite?
:

As several readers already have pointed out, a device of that complexity
would be *very* likely to break down.

Another point: How would one control such an arm? Consider the time the
control signals will need to reach a probe near the sun (several minutes)
or near the outer planets (several hours!) - no chance to do remote control
from earth. But it is equally impossible to send a movement program which
will be executed by the vessel's computer, because one cannot foresee what
the arm will have to do (e. g. when the stuck antenna ribs will come free).

--
Robert Glock                           Dept. of VLSI Design
[e-mail]            University of Technology, Vienna
                                       Austria / OLD EUROPE

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

Date: 14 Jan 93 15:10:07 GMT
From: "John F. Woods" <[e-mail]>
Subject: Galileo Stuck Ribs / Remote Manipulator?
Newsgroups: sci.space,sci.astro,alt.sci.planetary

[e-mail] (justin sullivan) writes:
>In <[e-mail]> [e-mail] (Henry Spencer) writes:
>>Bear in mind that the Galileo malfunction is of a fairly unusual type.
>>Most failures are subtle things ailing in the innards of the boxes.
>One could always argue that it wasn't an unusual problem that caused
>Galileo to have a crippled antenna, but an oversight of hoardes of fine
>engineers.

It is an unusual problem in that most failures of spacecraft are subtle things
ailing in the innards of the boxes.  This is an assertion about STATISTICS,
not some kind of value judgement -- of the total failures of spacecraft
components, big mechanical things outside where they can be reached are a
small fraction of the list.  Now, as to what went wrong with Galileo's antenna,
it wasn't an oversight of even one engineer, really -- it was the mechanical
damage caused by trucking Galileo across country several times due to missed
launch opportunities and the shutdown of the space program after Challenger.
The engineers didn't design the joints to withstand that much of that kind of
vibration because Galileo shouldn't have been subjected to it -- I'll bet they
didn't design the antenna to survive having someone whack it several times
with a 15 pound sledgehammer, either.

> Nobody's perfect, but when you get so many superbrains together
> and give them piles of money, they're expected to deliver a perfectly
> functioning piece of hardware.

Yeah, and my daughter expected a fat man in a red suit to come down the
chimney a couple of weeks ago.  The engineers do the best that they can.

> Either way, 40bps means that my great
> grandchildren will have to analyze the data.

No, 40bps means your great grandchildren will have to launch another probe
if they want pretty pictures.  Most of the science work of Galileo isn't
images, and doesn't need the incredibly high bandwidth.

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

Date: Thu, 14 Jan 1993 05:30:20 GMT
From: Christopher Neufeld <[e-mail]>
Subject: Helium
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:
>
>-From: [e-mail] ("Phil G. Fraering")
>
>-\Having a limited education in cryogenics is hampering my understanding
>-/of this phenomenon. I understood that helium cannot exist in liquid
>-\state at 6 Atm.
>
>-In general gas laws work the other way: increace the pressure, and the
>-"boiling" point of the liquid will increace.
>
>In general that's true, but don't take any bets on helium - it's extremely
>weird stuff.
>
   It's true for helium, too. Unless I'm mistaken, that's a stability
condition, and can be proven true for any liquid whose density is greater
than the density of the vapour phase. Increasing the pressure of vapour
over the liquid would increase the energy required to cross from the
liquid to the vapour phase, implying a higher temperature would be
required.
   One way we generate temperatures below 4.2 degrees is to fill a vessel
with liquid helium and then pump out the space above the liquid with a
very high capacity pump (ours is about the size of a volkswagen, a huge
Kinney pump which is far too noisy for my tastes). It is possible to
lower the temperature of the liquid to below the lambda point (so that it
undergoes a superfluid transition) at 2.174 degrees. We routinely go
down to about 0.8 degrees simply by pumping on a liquid helium pool.

>Helium can't exist as a *solid* at atmospheric pressure -
>its melting point is -272.2 C at 26 atmospheres pressure. The part about
>liquid at 6 Atm doesn't sound right.
>
   I just checked my CRC and, technically, you're right. The critical
point for He-4 is at 0.227 MPa (2.24 atmospheres) and 5.19 degrees
kelvin. Above that pressure the element forms a supercritical fluid, not
a liquid.

>(Heard recently - helium 3 does form a superfluid, but at a substantially
>lower temperature than helium 4. I'm pretty sure I got that right.)
>
   I've heard that too, in the range of a millikelvin, I believe.


--
 Christopher Neufeld....Just a graduate student  | Everyone talks about
 [e-mail]    Ad astra  | apathy, but no one does
 utzoo.utoronto.ca!generic!cneufeld              | anything about it.
 "Don't edit reality for the sake of simplicity" |

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

Date: Thu, 14 Jan 93 17:24:10 MET
From: [e-mail]
Subject: Helium

>In general that's true, but don't take any bets on helium - it's
>extremely weird stuff. Helium can't exist as a *solid* at atmospheric
>pressure - its melting point is -272.2 C at 26 atmospheres pressure.
>The part about liquid at 6 Atm doesn't sound right. (J. Roberts, Wed,
>13 Jan 93 22:30:31 EST)

According to the "Gas encyclopaedia/Encyclopedie des gaz", Elsevier/
L'Air Liquide, liquid helium does exist at 6 Atm. Of course, it is
very cold !
BTW, reading again more carefully the article in the CERN courrier,
I noticed that the reported experiments were in fact different:
1) the Japanese (KEK) used liquid helium, but pressure and temperature
were not specified in the article;
2) the Europeans (CERN) used gaseous helium at 6 Atm, but the temperature
was not specified in the article. They intended to use helium-3 and
helium-4, solid, liquid and gaseous.

J. Pharabod

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

Date: Thu, 14 Jan 1993 15:54:13 GMT
From: Hartmut Frommert <[e-mail]>
Subject: How much? (was Re: Moon Dust Sold)
Newsgroups: sci.space

[e-mail] (Bill Higgins-- Beam Jockey) writes:

[discussion on dust price deleted]

>I can't find the article with results of the

>(cost of Apollo)/(mass of rocks returned)

It was on sci.space.shuttle if I remem right.
BTW, as I posted there when somebody requested for "any questions":
  Was the rocks all gain obtained from Apollo ? :)

>calculation. How does this compare?  I would guess it gives somewhere
>around $80M/lb.
-
 Hartmut Frommert                 <[e-mail]>
 Dept of Physics, Univ of Constance, P.O.Box 55 60, D-W-7750 Konstanz, Germany
                                           -- Eat whale killers, not whales --

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

Date: Thu, 14 Jan 1993 08:25:35 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Let's be more specific (was: Stupid Shut Cost arguements)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>Even the SR71 uses fuel to help cool it's titanium skin, and it travels
>>more than four times slower than a re-entry vehicle...
>
>However, it does it for a much longer period.  I don't claim to be a
>hypersonics guru, but my understanding is that you get *very* different
>design solutions for a "hypersonic accelerator" and a "hypersonic cruiser"
>(where the former is at hypersonic speeds only briefly, accelerating
>towards orbit, and the latter spends much of its operating life there).

That's true, but the heat loads go up roughly as the square of the
velocity. So a re-entry vehicle is going to experience at least 16
times the heat load of the SR71 during the re-entry period. So a 2
minute re-entry is equivalent in total heat load to a 32 minute SR71
high speed dash. That's not exactly true, the plasma sheath does offer
some heat shielding, but it's in the rough ballpark. The design
considerations for handling very high heat loads for relatively short
periods are, of course, different than those for lower heat loads for
longer periods, so it's not strictly comparable. But the point remains
that a titanium skin by itself isn't good enough.

>The X-20 Dyna-Soar's heat protection was mostly refractory metals, as
>I recall.

Honeycomb composites.

>>The only practical
>>metal more refractory than titanium is tungsten...
>
>A curious claim.  The X-15 used titanium only for its *low temperature*
>structure, and did not use tungsten at all.  Most of its hot structure
>was stainless steels of various types.  They are heavy, but not impossibly
>so.  The B-70's wing and main body was stainless-steel honeycomb.

I used tungsten as an example of a refractory metal because it's possible
to build large structures from it and it's heat resistance is higher than
titanium. I know of no other industrially available metal with a higher
heat tolerance that can be used for large structures. As was pointed out
by someone more knowledgeable, tungsten is highly reactive in a hot oxygen
atmosphere, so it's an unsuitable material in practice, though it makes
great lamp filaments. Stainless steels are less reactive to oxygen, but
lose their strength at much lower temperatures than titanium or tungsten.
They aren't completely inert to oxygen at high temperatures either. Honeycomb
structures make fine insulators because of the air, or vacuum, gap between
layers. They work much the same way as double pane windows in that regard
to limit conduction of heat from layer to layer. If the heat load is high,
however, the outer layer will ablate away since it can't effectively conduct
the heat away due to the fine insulating property of the structure. Ceramic
sandwiches like the Shuttle tiles are even more effective insulators while
also having high direct resistance to heat and oxidation. NASP reportedly
uses carbon-carbon composite honeycombs for strength and heat resistance.
Apparently they've found some way to passivate them against oxidation at
high temperatures.  Diamond films ordinarily burn at relatively low
temperatures.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     | emory!ke4zv![e-mail]

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

Date: Thu, 14 Jan 1993 05:09:22 GMT
From: Bruce Dunn <[e-mail]>
Subject: Saving an overweight SSTO....
Newsgroups: sci.space

> Allen W. Sherzer writes:
>
> Note that the 15% margin allows for lots of mistakes. However, if
> it turns out that overruns are too great, the program is still
> a success. We will know EXACTLY what systems must be weight reduced
> to make it work. After a few years of research in those areas, we
> will have a working vehicle.


        We will know not only what systems must be weight reduced, but will
get information on how they can be reduced.  Doubters may wish to investigate
the history of the weight of the shuttle external tank, which was lightened
considerably after a few instrumented flights gave detailed information on
exactly what stresses it was subject to.
--
Bruce Dunn    Vancouver, Canada   [e-mail]

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

Date: 14 Jan 93 05:57:34 GMT
From: [e-mail]
Subject: Shuttle timetable wanted....
Newsgroups: sci.space

  Could someone please post the shuttle launch timetable for June, July and
August 1993 ?  Also how do I find out about viewing facilities at a launch
(do they exist, etc.).
                                                Many Thanks,
                                                 Daryl OWEN.

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

Date: 14 Jan 93 11:37:00 GMT
From: [e-mail]
Subject: SNC meteorites
Newsgroups: sci.space,sci.astro,alt.sci.planetary

Just another update to my update:
There are NOT seven, but five Shergottites known.
For those who are interested, here is a list of all known SNCs:

Shergottites:
  Shergotty, India             Single stone of 5kg fell on August 25, 1865
  Zagami, Nigeria              Single stone of 18kg fell on October 3, 1962
  Allan Hills ALHA77005        Single stone of 482g found in Antarctica 1977
  Elephant Moraine EETA79001   Single stone of 7942g found in Antarctica 1979
  Lewis Cliff LEW88516         Single stone of 13g found in Antarctica 1988

Nakhlites:
  Nakhla, Egypt                40 Stones (total 40kg) fell on June 25, 1911
  La Fayette, Indiana, USA     Single stone of 800g known prior to 1931
  Governador Valadares, Brazil Single stone of 158g found 1958

Chassignite:
  Chassigny, France            One or more stones of 4kg fell on Oct.3, 1815

Two interesting facts:
* Three Shergottites were recovered in Antarctica, but not a single Nakhlite
  or Chassignite was found there.

* Zagami and Chassigny both fell on October 3. This may be a simple co-
  incidence, but possibly the meteorid stream released by an impact on
  the surface of Mars is still "alive".

Sure enough, there ARE more SNCs on earth.
So keep your eyes open...
  Herbert

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

Date: 14 Jan 93 03:19:36 GMT
From: [e-mail]
Subject: TPS Systems
Newsgroups: sci.space

Gary Coffman writes:
>A lander presents a blunt surface to the atmosphere and tries to
>shed as much velocity as possible by atmospheric braking. The dwell
>time is very much longer, and the heat loading much higher. Shuttle
>designers originally considered a titanium skin for the Orbiter,
>but even a metal as refractory as titanium wasn't up to the job
>(besides driving up fabrication costs dramatically), so they chose
>to use refractory silicates in the form of tiles. These are very
>poor conductors of heat, you can place your bare hand against one
>side of the tile while playing an oxy-acetylene torch on the other
>and not notice a temperature rise. There has been much progress in
>artificial ceramic refractory materials since Shuttle was designed,
>and better choices are likely available now. Indeed, special
>refractory blankets have replaced tiles in certain non-critical
>areas on Shuttle. But copper, or any other metal won't do for a
>lander as opposed to a hypersonic plunger like a warhead.

 I put this data together a while ago, and thought it might be
useful to share with the net on this related subject.
   There are 7 basic types of thermal protection materials - here is
a summary of them
TYPE           EXAMPLES     MAXTEMP(F)  ADVANTAGES    DISADVANTAGES
Metallic       Columbium      2500        Durable       Very Costly
Refractories   Tungsten                   Reusable      Very Heavy
                                                        Hard to manuf

Superalloys    Inconel 617    2000        Durable       Limited Temp
               Haynes 188     1850        Reusable        capability
               Rene 41        1600                      Expensive

Non-metal      Carbon/Carbon  3000        Reusable      Very Costly
Refractories   Silcon Carbide 2700                      Heavy
                                                        Brittle

Ceramic Tiles   FRCI          2400        Light Wt      Durability
                                          Reusable
                                          Easy to Make

High-density   Phenolic silica  4000      Heat capacity  No reuse
Ablators       Phenolic Carbon                           Heavy
                                                         Insulation
                                                           required
Med/Low        Phenolic Cork    4000      Limited heat   No reuse
Density        Filled Silicone            capacity       Moderately
Ablators       Filled Expoxy                               heavy

High temp      Nextel/Nomex     2000      Reusable       Durable
Fabrics                                   Non-Rigid      Easy to
                                                          manufacture

  It is also important to note that the tiles are very light (about
8-9 lbs per cubic foot), whereas some of the metals (tungsten for
example) are heavier than lead.... Ablators are also usually pretty
heavy, and have definite problems in turn-around since they require
replacement each flight.

   To calculate the maximum temperature seem, it typically scales
inversely with the radius of curvature of the leading edge going
through reentry -- that is, higher temperatures are seen at sharper
points.  Thus, on the shuttle, RCC (Reinforced Carbon Carbon) is
used on the leading edges along the wings and the nose, whereas
ceramic tile is used over the broad flat areas of the wings.

   For DC-whatever, based upon my back of the envelope calculations,
the nose and flaps will probably have to be RCC or a similar
material.  For the broad areas of the vehicle considering the angles
of attack needed for their cross range requirement, they'll need TPS
capable of over 2000 F ; using a refractory metal is probably too
heavy -- which leaves either tiles, ablators, or superalloys.
Ablators are immediately eliminated for turnaround time impacts, and
tiles follow somewhat behind.  That leaves some of the new
superalloys, which are not as light weight as tiles, but hopefully
more durable (most are pretty brittle, though, based upon the NASP
materials I've worked with ... virtually no ductility, have a
tendency to catastrophically fail rather than yield, and are real
expensive bitches to make, install, or maintain.)
  --------------------------------------------------------------
 Wales Larrison                        Space Technology Investor


--- Maximus 2.01wb

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

End of Space Digest Volume 16 : Issue 048
------------------------------