Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v11_0/v11_067.txt

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Date: Tue, 20 Feb 90 01:35:47 -0500 (EST)
Subject: SPACE Digest V11 #67

SPACE Digest                                      Volume 11 : Issue 67

Today's Topics:
                SSX vs Phoenix
                  Planets...
        Hydrocarbons vs. Hydrogen for Boosters (long)
             Soviet Shuttle News
       Re: Did SEASAT See More Than It Was Supposed To?
----------------------------------------------------------------------

Date: Mon, 19 Feb 90 13:08:27 CST
From: [e-mail] (Edward V. Wright)
Subject: SSX vs Phoenix


Following a conversation I had with Max Hunter last
week, I would like to correct and clarify some of the
information that I posted previously.

SSX appears to differ from Pacific American's Phoenix
in several important respects.  These include:

1) Propellents:  Phoenix uses densified liquid hydrogen
   (hydrogen slush) and LOX.  For SSX, Hunter prefers
   to use liquid methane, although hydrogen has not
   been completely ruled out.

2) Propulsion:  Phoenix uses an aerospike engine
   concept to increase the performance (specific impulse)
   of its engines.  SSX, contrary to my previous
   statements does not. Hunter prefers not to use
   an aerospike because the loss of a single combustor
   causes flow problems, which result in the loss of
   specific impulse as well as thrust.  This makes
   the vehicle harder to save in the engine-out case.

3) Structure:  The Phoenix airframe is primarily
   aluminum, with some composite materials used to
   save weight.  Hunter envisions an all-composite
   airframe and fuel tank.  (LOX tank would still
   be aluminum, due to the inability of most composites
   to withstand exposure to LOX.)

4) Thermal Protection and Reentry: Phoenix reenters
   base-first using a water-cooled heat shield.  SSX
   reenters at a high angle-of-attack using an improved
   version of the quartz-blanket heat shield found on
   the upper surfaces of the Shuttle.

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

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Date: 19 Feb 90 11:02:19+0100
From: Joseph C. Pistritto <[e-mail]>
Subject: Planets...
To: <[e-mail]>

>Mailer: Elm [revision: 64.9]


If planets are an inefficient way to use mass, we have an alternative:
asteroids...  Theres at least one Mars-sized planet out there,
conveniently disassmbled for us already.  All we need is to go and get
it.  We get our first look  in 1991 I believe, when Galileo will make
a close approach of an asteroid in between its first and second earth
passes, but I believe the presence of carbon and oxygen, as well as
various metals have already been confirmed on the larger asteroids from
spectral analysis.

I suspect it will be *A LOT* easier to make an asteroid a place to live
than your typical planet.  And it's always a lot easier to leave if
things go wrong.

Do the available surface area alone, I would expect the vast majority
of the human race will exist on asteroid like objects in say 1000 years
(or 2000...) from now.  In fact, the most efficient use of the remaining
planets in the solar system may be to turn them into asteroids first, then
live on them...

For instance, an earth sized planet (radius 4000km), would produce
1E9 bodies of radius 4km, with 1E6 times the surface area of the earth.
Assuming you took the entire population of the earth now, and transferred
them, only 5 people would inhabit each object on average.  (roughly
50sq. km. per object).  Now that sounds like serious elbow room...

I'll even make it easier for you.  I can think of, say 10 people I'll take
with me to my asteroid.  More room for the rest of 'ya.
The only 'Limit to Growth' is a stunted imagination...

                                        -jcp-

======================================================================
Joseph C. Pistritto  HB9NBB N3CKF
                    'Think of it as Evolution in Action' (J.Pournelle)
  Ciba Geigy AG, R1241.1.01, Postfach CH4002 Basel, Switzerland
  Internet: [e-mail]                  Phone: [phone]
  Bitnet:   [e-mail]   Fax:   [phone]
  From US:  cgch![e-mail]

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

Date: 17 Feb 90 18:42:31 GMT
From: van-bc!rsoft!mindlink![e-mail]  (Bruce Dunn)
Subject: Hydrocarbons vs. Hydrogen for Boosters (long)


     A number of recent postings have discussed the relative merits of hydrogen
and hydrocarbons (RP-1, propane, methane) as fuels for boosters.  For those
interested in literature references, the following are worth reading.  I have
summarized relevant results for those who do not have access to the papers, and
calculated some figures from other information given in the papers.  Paper 1
was published in American units, which I have mostly converted to SI - all
other papers were in SI to start with.

1) Kelly, W.D. 1983  Integrating Engine Performance and Trajectory Analysis in
Designing Future Shuttle Systems.  Paper AIAA-83-1189, given at the
AIAA/SAE/ASME 19th Joint Propulsion Conference June 27-29, 1983 in Seattle.

- Kelly is from Martin Marietta

- Part of this paper is an analysis of replacing the solid rocket boosters on
the Shuttle with liquid rocket boosters fueled with RP-1, methane, propane
(normal boiling point) or hydrogen (all with LOX as the oxidizer).  All
boosters were designed to give a nominal 45,000 kg payload (up from original
nominal payload of 29,500 kg with solids).

- Reading off a graph, for booster engines with 3500 psi chamber pressure and
50:1 expansion ratio, Isp at specified MR (mixture ratio = oxidizer mass/fuel
mass) is approximately:

     hydrogen: 390 sea level, 450 in vacuum at 6.0 to 1 MR (SSME)
     methane : 320 sea level, 360 in vacuum at 3.2 to 1 MR (optimum)
     propane : 315 sea level, 350 in vacuum at 3.1 to 1 MR (optimum)
     RP-1    : 310 sea level, 340 in vacuum at 2.7 to 1 MR (optimum)

- Note that the MR of 6.0 for hydrogen is far from that giving the optimum
specific impulse.  Lowering the MR (adding more hydrogen to the mix) raises the
Isp at least down to a MR of 4, but the added tankage for the hydrogen kills
off the advantage of the Isp.  The Space Shuttle Main Engine MR of 6 is a
compromise between tankage mass and Isp.

- The engine installation mass per booster was assumed to be identical for all
engines at 9500 kg, for a predetermined vacuum thrust of 2.5 million pounds.
This looks awful low to me, but I will accept it as written for the purposes of
calculating total booster dry mass.

- Kelly assumes a 4.6 m diameter booster for hydrocarbons and a 6.1 m diameter
booster for hydrogen.  For volumes of propellant around 600 cubic meters,
tankage dry mass from his figures can be calculated to be approximately 74
kg/cubic meter for hydrogen/oxygen and 81 kg/cubic meter for
hydrocarbon/oxygen.

- The following information is given or can be calculated about the various
boosters (at optimum MR for hydrocarbons, or at 6.0 for hydrogen).  Tank volume
is from a graph, tank dry mass is from the volume times either 74 or 81 (see
above), total dry mass is tank dry mass plus engine mass, and total booster
mass is from a graph.

hydrogen: tank volume 1020 cubic meters, tank dry mass 75,500 kg
          total dry mass 85,000 kg, total booster mass 441,000 kg

methane:  tank volume 540 cubic meters, tank dry mass 43,500 kg
          total dry mass 53,000 kg, total booster mass 510,000 kg

propane:  tank volume 510 cubic meters, tank dry mass 41,500 kg
          total dry mass 51,000 kg, total booster mass 514,000 kg

RP-1:     tank volume 450 cubic meters, tank dry mass 36,500 kg
          total dry mass 46,000 kg, total booster mass 516,000 kg

- If the dry masses seem high relative to the mass of an ET, remember that the
liquid boosters, unlike the ET:
   1) are meant to withstand the strains of recovery
   2) must transmit very large thrust forces throughout their length
   3) must support the vehicle on the launch pad

- Clearly, when designing with a clean sheet of paper (assuming for instance
that you can have any engine you want) hydrogen gives the lowest booster gross
mass but the largest booster dry mass.  Roughly speaking, dry mass is
proportional to cost.  The main reason that hydrogen is still being given
serious consideration for liquid fueled boosters is that hydrogen fueled SSMEs
are available but hydrocarbon engines would have to be developed (unless NASA
were to get smart and build a slightly updated F-1).  Note that in this
analysis, RP-1 gives the lowest dry mass.  However, if subcooled propane rather
than normal boiling point propane had been considered, it probably would beat
RP-1.



2) Martin,J.A. 1983 Hydrocarbon Rocket Engines for Earth to Orbit Vehicles.
Journal of Spacecraft and Rockets, Vol. 20, pp 249-256.

- Martin is with NASA Langley.

- I have not read this, but some of its data are quoted in Martin 1984 (see
below).

- Modeling is done of a single-stage-to-orbit vehicle, varying the vehicle
parameters to give a constant 13,600 kg payload to low earth orbit. [note that
the paper is all in SI, as is journal policy, although since 13,600 kg equals
30,000 lbs, it looks like the original modeling was done in American units and
the editor required the conversion - another good reason to start with SI !]

- A hydrocarbon engine comparison shows that for gas-generator engines, in
terms of minimizing ultimate vehicle dry mass, subcooled propane easily beats
RP-1 which in turn easily beats methane. Staged-combustion engines beat
gas-generator engines with the same propellant, and for staged-combustion
engines subcooled propane marginally beats RP-1, and both are markedly superior
to methane.

- For detailed analysis a staged-combustion subcooled propane engine is
assumed, coupled with an SSME with a two-position nozzle.

- Both hydrogen and propane are burned during the early part of the flight,
then the vehicle stops burning propane at a point which can be optimized by the
model.

- An all-hydrogen vehicle has a dry mass of 119,000 kg to deliver 13,600 kg to
orbit, while adding propane engines reduces the dry mass to approximately
94,000 kg (reading from a graph) for the same payload.



3) Martin, J.A. 1984 Two-Stage Earth-to-Orbit Vehicles with Dual-Fuel Orbiter
Propulsion. Journal of Spacecraft and Rockets, Vol. 21 pp. 65-69

- Similar analysis to that in Martin 1983, but for two stage systems burning
hydrogen and subcooled propane in both the lower stage and the orbiter.  Both
stages are winged, and are oriented belly to belly with all engines in one
plane.  Both stages burn in parallel during takeoff. The lower stage crossfeeds
propellant to the upper stage while attached, and is recovered aerodynamically
after staging.

- Adding propane to hydrogen is useful not only for the lower stage, but also
for the upper stage.

- The total dry weight of an optimized vehicle is 82,000 kg for a 13,600 kg
payload (vs. approximately 94,000 kg for the best single-stage-to-orbit vehicle
in Martin 1983)



4) Martin, J.A. 1986  Comparison of Methane and Propane Rockets. Journal of
Spacecraft and Rockets, Vol. 23. p. 658

- A more detailed comparison of subcooled propane and normal boiling point
methane coupled with hydrogen in the same single-stage-to-orbit vehicle
analyzed in Martin 1983.

- Subcooled propane, with a dry vehicle mass of 94,000 kg beats methane with a
dry vehicle mass of 107,000 kg.

- Reading from a graph, gross mass for the vehicle is approximately 1,100,000
kg for an all-hydrogen vehicle, compared with 1,115,000 for a methane-hydrogen
vehicle and 1,050,000 for a subcooled propane-hydrogen vehicle.



Conclusions:  Hydrocarbon boosters have a lower dry mass than hydrogen boosters
(and a lower propellant cost, considering the cost of liquid hydrogen vs.
hydrocarbons).  Gross vehicle mass however is generally higher, and vehicles
using both hydrocarbons and hydrogen need two types of engines instead of one,
and three propellant tanks instead of two.

- Bruce Dunn

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

Date: 18 Feb 90 21:11:13 GMT
From: cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!mips!prls!philabs!briar.philips.com![e-mail]  (Robert Casey)
Subject: Soviet Shuttle News

copied from amateur radio packet:

From: [e-mail] (John)

The following is excerpted (without permission, but hopefully
they won't mind too much) from Via Satellite magazine, 2/90 issue,
page 15:

Soviet Shuttle--No Flights until 1991

The reusable Soviet space shuttle Buran, lying idle since its maiden flight
a year ago, is to undertake its next mission in 1991, the Soviet Union's
chief rocket designer, said yesterday.

Yuri Semyonov told Soviet television that Buran would make an unmanned
flight in the first half of 1991, with a manned mission to follow a year
later.  Long-range plans call for Buran to dock with the orbiting station
Mir with the possibility of astronauts moving between the two to simulate
a rescue operation.


M. Baker
AT&T-BL, Holmdel, NJ

(Via Satellite is published monthly by Phillips Publishing, Inc. at 7811
Montrose Road, Rockville, Maryland 20850, [phone].  Circulation is
free to qualified recipients.)

0626z, 1279 msgs, #18716 last @KD6TH-4 MailBox>

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

Date: 20 Feb 90 01:31:20 GMT
From: tahoe!chaos![e-mail]  (J.A. MacDonald)
Subject: Re: Did SEASAT See More Than It Was Supposed To?

In article <[e-mail]> [e-mail] (John A. Weeks III) writes:
>
>    "JPL's study of options for its radar orbiter
>    took as its base NASA's ocean-scanning SEASAT
>    spacecraft, which in 1978 used synthetic aperture
>    radar from a circular orbit so successfully
>    that it showed things in the world's oceans
>    that the Navy neither expected nor wanted to
>    have shown."
>
>Does anyone know exactly what is being alluded to here?


  From what I know about radar it has the ability to detect very subtle
features on ocean surfaces. I've seen Seasat images of ocean scenes that
contained a peculiar "wake" shaped (i.e. V shaped) pattern with no
surface vessel at the point of the V. One possible explanation of these
patterns that has been put forth is that they are the wake of a
submarine in motion. When one considers the mysterious nature of the
shutdown of the Seasat system (I know there was some "official" excuse
released, but do you believe everything your government tells you) as
well as the general power of the military in this country, this does not
seem to be too far fetched an idea. Who's to say, eh? 8-)

JaM

Real BMWs have two wheels
==================================================================
[e-mail]    |  I lit out from Reno
[e-mail]    |  I was trailed by twenty hounds...
==================================================================

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End of SPACE Digest V11 #67
*******************