Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_3/V16NO331.TXT

Internet Message Format | 1993-07-13 | 42KB

Date: Thu, 18 Mar 93 05:22:39
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #331
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu, 18 Mar 93       Volume 16 : Issue 331

Today's Topics:
                                 DC-X
                Just a little tap (was Re: Galileo HGA
                          Retraining at NASA
                    Semi-technical aspects of SSTO
                 SSTO: A Spaceship for the rest of us

    Welcome to the Space Digest!!  Please send your messages to
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Date: Wed, 17 Mar 1993 21:43:07 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: DC-X
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Matthew R. Feulner) writes:

>I haven't been keeping up to date, so could someone give me a reference
>where I can read about DC-X?

I'll re-post a couple of papers I have. The first was written by me and
is the draft NSS position paper on SSTO. The second was written by Henry
Spencer for the Freshmen Orientation project.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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

Date: 17 Mar 93 21:01:47 GMT
From: "Don M. Gibson" <[e-mail]>
Subject: Just a little tap (was Re: Galileo HGA
Newsgroups: sci.space

In article [e-mail], [e-mail] (Jeff Bytof) writes:
>This is really off the wall, but would there be any way to calculate
>the effect of forces due to induced magnetic fields on the spacecraft
>structure and antenna as it passes through the intense Jovian magnetic
>and particle fields?  Perhaps a way could be found by proper orientation
>of the spacecraft to apply differential pressure to some critical area
>of the structure.

it seems calculatable, but i have no idea how.  the S/C orientation is
determined by the need for the orbit insertion burn.
--DonG

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

Date: 17 Mar 93 14:19:42
From: Steinn Sigurdsson <[e-mail]>
Subject: Retraining at NASA
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Nick Szabo) writes:

   Get off this stupid forum and get back to work, you lazy,
   good-for-nothing exemplar of why socialism sucks.  If you

Cut it out Nick.

|  Steinn Sigurdsson    |I saw two shooting stars last night        |
|  Lick Observatory    |I wished on them but they were only satellites    |
| [e-mail] |Is it wrong to wish on space hardware?        |
| "standard disclaimer"    |I wish, I wish, I wish you'd care - B.B. 1983    |

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

Date: 17 Mar 93 21:48:19 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Semi-technical aspects of SSTO
Newsgroups: sci.space

[This paper was written for the Freshmen Orientation Project by Henry
  Spencer]


(Semi-)Technical Aspects of SSTO by Henry Spencer

This paper will try to give you some idea of why SSTO makes technical
sense and is a reasonable idea.  We'll concentrate on the overall issues,
trying to give you the right general idea without getting bogged down
in obscure detail.  Be warned that we will oversimplify a bit at times.

Why Is SSTO Challenging?

Getting a one-stage reusable rocket into orbit doesn't look impossible,
but it does look challenging.  Here's why.

The hard part of getting into orbit is not reaching orbital altitude,
but reaching orbital velocity.  Orbital velocity is about 18,000mph.
To this, you have to add something for reaching orbital altitude and for
fighting air resistance along the way, but these complications don't
actually add very much.  The total fuel requirement
is what would be needed to accelerate to 20-21,000mph.

So how much is that?  (If you don't want to know the math, skip to the
next paragraph for the results.)  The "rocket equation" is
desired_velocity = exhaust_velocity * ln(launch_weight / dry_weight),
where "ln" is the natural logarithm.  The exhaust velocity is determined
by choice of fuels and design of engines, but 7,000mph is about right
if you don't use liquid hydrogen, and 10,000mph if you do.

The bottom line is that the launch weight has to be about 20 times the
dry weight (the weight including everything except fuels) if you don't
use liquid hydrogen, and about 8 times the dry weight if you do.  This
sounds like hydrogen would be the obvious choice of fuel, but in practice,
hydrogen has two serious problems.  First, it is extremely bulky,
meaning that hydrogen tanks have to be very big; the Shuttle External
Tank is mostly hydrogen tank, with only the nose containing oxygen.
Second, some of the same properties that make hydrogen do well on the
weight ratio make it difficult to build hydrogen engines with high thrust,
and a rocket *does* need enough thrust to lift off!  Both of these
problems tend to drive up the dry weight, by requiring bigger and heavier
tanks and engines.

So how bad is this?  Well, it's not good.  Even with hydrogen, an SSTO
launcher which weighs (say) 800,000lbs at launch has to be 7/8ths fuel.
We've got 100,000lbs for tanks to hold 700,000lbs of fuel, engines to
lift an 800,000lb vehicle, a heatshield to protect the whole thing on
return, structure to hold it all together at high acceleration... and
quite incidentally, for some payload to make it all worthwhile.  Most
of the dry weight has to go for the vehicle itself; only a small part
of it can be payload.  (That is, the "payload fraction" is quite small.)
To get any payload at all, we need to work hard at making the vehicle
very lightweight.

The big problem here is:  what happens if the vehicle isn't quite as
light as the designer thought it would be?  All rockets, and most aircraft
for that matter, gain weight during development, as optimistic estimates
are replaced by real numbers.  An SSTO vehicle doesn't have much room for
such weight growth, because every extra pound of vehicle means one less
pound for that small payload fraction.  Particularly if we're trying to
build an SSTO vehicle for the first time, there's a high risk that the
actual payload will be smaller than planned.

That is the ultimate reason why nobody has yet built an SSTO space
launcher:  its performance is hard to predict.  Megaprojects like the
Shuttle can't afford unpredictability -- they are so expensive that
they must succeed.  SSTO is better suited to an experimental vehicle,
like the historic "X-planes", to establish that the concept works and
get a good look at how well it performs... but there is no X-launcher
program.

Why Does SSTO Look Feasible Now?

The closest thing to SSTO so far is the Atlas expendable launcher.  The
Atlas, without the Centaur upper stage that is now a standard part of
it, has "1.5" stages:  it drops two of its three engines (but nothing
else) midway up.  Without an upper stage, Atlas can put modest payloads
into orbit:  John Glenn rode into orbit on an Atlas.  The first Atlas
orbital mission was flown late in 1958.  But the step from 1.5 stages
to 1 stage has eluded us since.

Actually, people have been proposing SSTO launchers for many years.
The idea has always looked like it *just might* work.  For example,
the Shuttle program looked at SSTO designs briefly.  Mostly, nobody has
tried an SSTO launcher because everybody was waiting for somebody else
to try it first.

There are a few things that are crucial to success of an SSTO
launcher.  It needs very lightweight structural materials.  It needs
very efficient engines.  It needs a very light heatshield.  And it
needs a way of landing gently that doesn't add much weight.

Materials for structure and heatshield have been improving steadily
over the years.  The NASP program in particular has helped with this.
It now looks fairly certain that an SSTO can be light enough.

Existing engines do look efficient enough for SSTO, provided they can
somehow adapt automatically to the outside air pressure.  The nozzle
of a rocket engine designed to be fired in sea-level air is subtly
different from that of an engine designed for use in space, and an
SSTO engine has to work well in both conditions.  (The technical
buzzword for what's wanted is an "altitude-compensating" nozzle.)
Solutions to this problem actually are not lacking, but nobody has
yet flown one of them.  Probably the simplest one, which has been
tentatively selected for DC-Y, is just a nozzle which telescopes,
so its length can be varied to match outside conditions.  Making
nozzles that telescope is not hard -- many existing rocket nozzles,
like those of the Trident missile, telescope for compact storage --
but nobody has yet flown one that changes length *while firing*.
However, it doesn't look difficult, and there are other approaches
if this one turns out to have problems.

We'll talk about landing methods in more detail later, but this is one
issue that will be resolved pretty soon.  The primary goal of the DC-X
experimental craft is to fly DC-Y's landing maneuvers and prove that
they will work.

So... with materials under control, engines looking feasible, and
landing about to be test-flown, we should be able to build an SSTO
prototype:  DC-Y.  The prototype's performance may not quite match
predictions, but if it works *at all*, it will make all other launchers
obsolete.

Why A Rocket?

As witness the NASP (X-30) program, air-breathing engines do look like
an attractive alternative to rockets.  Much of the weight of fuel in
a rocket is oxygen, and an air-breathing engine gets its oxygen from
the air rather than having to carry it along.  However, on a closer
look, the choice is not so clear-cut.

The biggest problem of using air-breathing engines for spaceflight is
that they simply don't work very well at really high speeds.  An
air-breathing engine tries to accelerate air by heating it.  This works
well at low speed.  Unfortunately, accelerating air that is already
moving at hypersonic speed is difficult, all the more so when it has
to be done by heating air that is already extremely hot.  The problem
only gets worse if the engine has to work over an enormous range of
speeds:  NASP's scramjet engines would start to function at perhaps
Mach 4, but orbital speeds are roughly Mach 25.  Nobody has ever built
an air-breathing engine that can do this... but rockets do it every week.

Air-breathing engines have other problems too.  For one thing, to use
them, one obviously has to fly within the atmosphere.  At truly high
speeds, this means major heating problems due to air friction.  It
also means a lot of drag due to air resistance, adding to the burden
that an air-breathing engine has to overcome.  Rocket-based launchers,
including SSTO, do most of their accelerating in vacuum, away from
these problems.

Perhaps the biggest problem of air-breathing engines for spaceflight
is that they are *heavy*.  The best military jet engines have thrust:weight
ratios of about 8:1.  (This is at low speed; hypersonic scramjets are not
nearly that good.)  The Space Shuttle Main Engine's thrust:weight ratio,
by comparison, is 70:1 (at any speed).  The oxygen in a rocket's tanks
is burned off on the way to orbit, but the engines have to be carried
all the way, and air-breathing engines weigh a lot more.

And what's the payoff?  The X-30, if it is built, and if it works
perfectly, will just be able to get into orbit with a small payload.
This is about the same as SSTO, at ten times the cost.  Where is the
gain from air-breathing engines?

The fact is, rockets are perfectly good engines for a space launcher.
Rockets are light, powerful, well understood, and work fine at any
speed without needing air.  Oxygen may be heavy, but it is cheap (about
five cents a pound) and compact.  Finally, rocket engines are available
off the shelf, while hypersonic air-breathing engines are still research
projects.  Practical space launchers should use rockets, so SSTO does.

Why No Wings?

With light, powerful engines like rockets, there is no need to land
or take off horizontally on a runway, and no particular reason to.
Runway takeoffs and landing are touchy procedures with little room
for error, which is why a student pilot spends much of his time on
them.  Given adequate power, vertical takeoffs and landings are easier.
In particular, a vertical landing is much more tolerant of error than
a horizontal one, because the pilot can always stop, straighten out
a mistake, and then continue.  Harrier pilots confirm this:  their
comment is "it's easier to stop and then land, than to land and then
try to stop".

What if you don't have adequate power?  Then you are in deep trouble
even if your craft takes off and lands horizontally.  As witness the
El Al crash in Amsterdam recently, even airliners often don't survive
major loss of power at low altitude.  To make a safe horizontal landing,
especially in less-than-ideal weather conditions, you *must* have enough
power to abandon a bad landing approach and try again.  Shuttle-style
gliding landings are dangerous, and airline crews go to great lengths
to avoid them; the Shuttle program, with the nation's best test pilots
doing the flying and no effort spared to help them, has already had
one near-crash in its first fifty flights.  Routine access to space
requires powered landings.

If we are going to rely on powered landings, we must make sure that power
will be available.  Airliners do this by having more than one engine,
and being able to fly with one engine out.  SSTO is designed to survive
a single engine failure at the moment of liftoff, and a second failure
later.  Since (at least) 7/8ths of the takeoff weight of SSTO is fuel,
it will be much lighter at landing than at takeoff.  Given good design,
it will have enough power for landing even if several engines fail.
If SSTO has an engine failure soon after liftoff, it will follow much
the same procedure as an airliner:  it will hover to burn off most of
its fuel (this is about as quick as an airliner's fuel dumping), and
then land, with tanks nearly empty to minimize weight and fire hazard.

Note that in an emergency, vertical landing has one major advantage
over horizontal landing:  horizontal landing requires a runway, preferably
a long one with a favorable wind, while a vertical landing just requires
a small flat spot with no combustible materials nearby.  A few years ago,
a Royal Navy Harrier pilot had a major electronics failure and was unable
to return to his carrier.  He made an emergency landing on the deck of a
Spanish container ship.  The Harrier suffered minor damage; any other
aircraft would have been lost, and the pilot would have had to risk
ejection and recovery from the sea.

Given vertical landing and takeoff, is there any other use for wings?
One:  crossrange capability, the ability to steer to one side during
reentry, so as to land at a point that is not below the orbit track.

The Shuttle has quite a large crossrange capability, 1500 miles.
However, if we examine the history of the Shuttle, we find
that this was a requirement imposed by the
military, to make the Shuttle capable of flying some demanding USAF missions.
A civilian space launcher needs a crossrange capability of, at most, a
few hundred miles, to let it make precision landings at convenient times.
This is easily achieved with a wingless craft:  the Apollo spacecraft
could do it.

Finally, wings are a liability in several important ways.  They are heavy.
They are difficult to protect against reentry heat.  And they make the
vehicle much more susceptible to wind gusts during landing and takeoff
(this is a significant limitation on shuttle launches).

SSTO does not need wings, would suffer by carrying them, and hence does
not have them.

Why Will It Be Cheap And Reliable?

This is a good question.  The Shuttle was supposed to be cheap and
reliable, and is neither.  However, there is reason for hope for SSTO.

The Shuttle's costs come mainly from the tremendous army of people
needed to inspect and refurbish it after each flight.  SSTO should get
by with many fewer.

The basic SSTO concept opens major possibilities for simple, quick
refurbishment.  With no discarded parts, nothing needs to be replaced.
With no separating parts, there is no need to re-assemble anything.
In principle, an SSTO vehicle should be able to "turn around" like
an airliner, with little more than refuelling.

Of course, this is easier said than done.  But there is no real reason
why SSTO should need much more.  Its electronics experience stresses
not much worse than those of an airliner -- certainly no worse than
those of a jet fighter.  Its structure and heatshield, designed to fly
many times, will have sufficient margins that they will not need
inspection and repair after every flight.  Most space-vehicle components
don't inherently need any more attention than airliner components.

The one obvious exception is the engines, which do indeed run at much
higher power levels than airliner engines.  But even here, airliner
principles can be applied:  the way to make engines last a long time
is to run them at less than 100% power.  SSTO engines have it easy in
one respect:  they only have to run for about ten minutes at the start
of the flight and two or three minutes at the end.

Still, the Shuttle engines certainly are not a shining example of low
maintenance and durability.  However, it's important to realize that
the Shuttle engines are not the only reusable rocket engines.  Most
liquid-fuel engines could be re-used, were it not that the launchers
carrying them are thrown away after every flight.  And the durability
record of these other engines -- although limited to test stands -- is
*much* better.  The RL-10 engine, which will be used in DC-X, is rated
to fire for over an hour, in one continuous burn or with up to ten
restarts, with *no* maintenance.  Several other engines have comparable
records.  Conservatively-designed engines are nowhere near as flakey
and troublesome as the Shuttle engines.

Here again, DC-X should soon supply some solid evidence.  Although its
engines and other systems are not the same ones that DC-Y would use,
they should be representative enough to demonstrate rapid, low-effort
refurbishment, and the DC-X program will try to do so.

Airliners typically operate at about three times fuel costs.  The fuel
cost for an SSTO vehicle would be a few dollars per pound of payload.
It may be a bit optimistic to try to apply airline experience to the
first version of a radically new vehicle.  However, even advanced
aircraft typically cost no more than ten times fuel cost.  Even if
SSTO comes nowhere near these predictions, it should still have no
trouble beating existing launchers, which cost several thousand dollars
per pound of payload.

We can look at this another way:  head counts.  Airlines typically have
about 150 people per aircraft, and most of those sell tickets or look
after passengers' needs.  Perhaps a better example is the SR-71, which
is like SSTO in that it was an advanced craft, pushing the frontiers
of technology, operated in quite small numbers.  Although it is hard
to get exact numbers because of secrecy, it appears that USAF SR-71
operations averaged perhaps one flight per day, using perhaps eight
flight-ready aircraft, with a total staff of about 400 people.  That's
50 per aircraft.  If SSTO can operate at such levels -- and there is
every reason to think it can -- it should have no trouble beating
existing launchers, which typically have several thousand people
involved in preparations for each and every launch.  (NASA's Shuttle
ground crew is variously estimated at 6,000-10,000 for a fleet of
four orbiters flying about eight flights a year.)

As for reliability, the crucial reason for thinking that SSTO will do
a lot better than existing launchers is simple:  testing.  It should
be feasible and affordable to test an SSTO launcher as thoroughly as
an aircraft.  This is *vastly* more thorough than any launcher.  The
F-15 fighter flew over 1,500 test flights before it was released for
military service.  No space launcher on Earth has flown that many
times, and the only one that even comes close is an old Soviet design.
It is no wonder that the Shuttle is somewhat unreliable, when it was
declared "operational" after a grand total of four test flights.
By aircraft standards, the Shuttle is still in early testing.  Some
expendable launchers have been declared operational after *two* tests.

Each and every SSTO vehicle can be tested many times before it carries
real payloads.  Moreover, since SSTO can survive most single failures,
it can be tested under extremes of flight conditions, like an aircraft.
For example, unlike Challenger, an SSTO vehicle would launch with
passengers and cargo in freezing temperatures only after multiple
test flights in such conditions.  There will always be surprises when a new
craft is flown in new conditions, but SSTO should encounter -- and
survive -- most of them in test flights.

Conclusion

Although there is reason for some uncertainty about the exact performance
of the first SSTO spacecraft, the basic approach being taken is sensible
and reasonable.  It should work.  The imminent test flights of the DC-X
test craft should resolve most remaining technical concerns.  Nobody can
be sure about costs and reliability until DC-Y is flying, but there is
reason to believe that SSTO should be much better than current launchers.
If the program is carried through to a flying DC-Y prototype in a timely
way, it really could revolutionize spaceflight.
From [e-mail] Thu Jan 28 08:55:06 1993
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Date: Thu, 28 Jan 93 08:51:52 -0500
From: Ken Sheppardson <[e-mail]>
To: [e-mail]
Subject: Resume (text)
Status: R

                            Kenneth C. Sheppardson

                            125 Signature Way #216
                              Hampton, VA 23666
                                [phone]

OBJECTIVE    To use my expertise in system modeling and analysis to support
             the design, development, operation and management of complex
             dynamic systems.

EDUCATION  * Stanford University, Stanford, California
             M.S. Engineering-Economic Systems                    June 1992

             - Courses included Decision Analysis, Economic Analysis,
               Optimization, Probabilistic Analysis, Strategy and Planning
               Models, Accounting, and Investment Science
             - Projects included the application of decision analysis and
               optimization methods to develop a facility operations and
               maintenance plan for a division of Sandia National
               Laboratories

           * The University of Michigan, Ann Arbor, Michigan
             M.S.E. Aerospace Engineering                        April 1990
             B.S.E. Aerospace Engineering                       August 1988

             - Courses included Dynamics, Simulation, System Theory and
               Computer Aided Design
             - President of the Epeians Engineering Leadership Honor
               Society, Engineering Council Executive Secretary, College of
               Engineering Curriculum Committee Rep., University Research
               Policy Committee Rep., and a member of Tau Beta Pi and Sigma
               Gamma Tau

EMPLOYMENT * NASA / Langley Research Center
             Space Station Freedom Advanced Programs Office

             Aerospace Engineer                                  since 1990
             Graduate Student Researchers Program Participant   1989 - 1990
             Langley Aerospace Research Summer Scholar          Summer 1989

             - Managed and took part in space station systems engineering
               and analysis studies
             - Developed software to perform static and dynamic analysis of
               spacecraft and to facilitate the exchange of data between
               analysis packages

           * The University of Michigan
             Computer Aided Engineering Network

             RA - Control System Software Support Coordinator   1989 - 1990
             RA - Instructional Innovation Program              1988 - 1989
             Counselor / Lab Monitor                            1988 - 1989

             - Developed instructional material and provided group and
               individual instruction on the use of system modeling and
               analysis software

           * McDonnell Douglas Helicopter Company
             Engineering and Training Simulation

             Engin. Assoc.- Flight Dynamics Group               Summer 1987
             Engin. Assoc.- Visual Database Development Group     Fall 1986

             - Developed computational models of helicopters and missiles
               for flight simulation
             - Developed software to expedite the generation of flight
               simulator terrain databases and to allow real-time
               communication between simulation system workstations and
               mainframes

           * Houk and Soles, Inc. - Food Service Computing Consultants 1984
             - Worked with food service industry clients to design and
               develop planning, inventory control, and purchasing systems
               for restaurants and institutions

COMPUTER     - Developed software in Ada, BASIC, C, FORTRAN, Pascal, and
SKILLS         assembly languages
             - Developed and supported software on platforms including UNIX
               workstations, Apple Macintosh systems, DEC VMS systems,
               Gould TSM systems, and IBM PCs
             - Extensive use and support of software including I-DEAS,
               MatrixX, ADAMS, MatLab, Easy5, MSC/NASTRAN, word processors,
               graphics packages, and spreadsheets


--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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

Date: Wed, 17 Mar 1993 21:45:22 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: SSTO: A Spaceship for the rest of us
Newsgroups: sci.space

[First of two papers on SSTO. This is also the draft NSS position
  paper on SSTO]


                            SSTO
               A Spaceship for the Rest of US

Introduction
Space is an important and growing segment of the U.S.
economy.  The U.S.   space market is currently over $5
billion per year, and growing.  U.S. satellites, and to a
lesser degree U.S. launch services, are used throughout the
world and are one of the bright stars in the U.S. balance of
trade.

The future is even brighter.  The space environment promises
new developments in materials, drugs, energy, and resources,
which will open up whole new industries for the United
States.  This will translate into new jobs and higher
standards of living not only for Americans but for the rest
of the world's people.

Standing between us  and these new industries is the
obstacle presented by the high cost of putting people and
payloads into space.  This paper addresses the reasons why
access to space is so expensive and how those costs might be
reduced by looking at the problem in a different way.

Finally, this paper will describe a radical new spacecraft
currently under development.  Called Single Stage to Orbit
(SSTO), it promises to greatly reduce costs and increase
flexibility.

Access to Space: Expensive and Dangerous
Access to space today is very expensive, complex, and
dangerous  With U.S.  expendable launchers like Atlas,
Delta, and Titan, it generally costs about $3,000  to $8,000
to put a pound of payload into low Earth orbit (LEO).  In
addition, U.S.  expendables require extensive ground
infrastructure to do final assembly and payload integration
and complex launch facilities to actually launch the rocket.
Finally, despite all the extra care and effort, they don't
work very well and even the best launchers fail about 3% of
the time (would you go to work tomorrow if there was a 3%
chance of your car exploding?).

Even the U.S. Space Shuttle, which was supposed to give the
U.S. routine low cost access to space, has failed.  A
Shuttle flight costs about $500 million (roughly $10,000 per
pound to LEO).  Even going full out, NASA can only launch
each  Shuttle about twice a year (for a total of eight
flights).

The effects of these high costs go deeper than the price tag
for the launches themselves.  Space equipment is much more
expensive than comparable equipment meant for use on Earth,
even when tasks are similar and the Earthly environments are
harsh.  The difference is that space equipment must be as
lightweight as humanly possible and must be as close as
humanly possible to 100% reliability.  Both of these extra
requirements are ultimately problems of access to space: if
every extra pound costs thousands of dollars, and replacing
or repairing a failed satellite is impossibly expensive,
then efforts to reduce weight and improve reliability make
sense.  Unfortunately, they also greatly increase price.

With equipment so expensive, obviously building extra copies
is costly, and launching them is even worse.  This
encourages space projects to try to get by with as few
satellites as possible.  Alas, this can backfire: when
something does go wrong, there isn't any safety margin...as
witness the U.S.'s shortage of weather satellites at this
time.  Expensive access to space not only produces costly
projects, it produces fragile projects that assume no
failures, because safety margins are too expensive.
Lamentably, failures do happen.

Finally, although research in space holds great promise for
new scientific discoveries and new industries, it is
progressing at a snail's pace, and companies and researchers
often lose interest early.  Why?  Because effective research
requires better access to space.  Scientific discoveries
seldom come as the result of single experiments: even when a
single experiment is crucial, typically there is a long
series of experiments leading up to it and following through
on it.  And getting the "bugs" out of a new industrial
process almost always requires a lot of testing.  But how
can such work be done if you only get to fly one experiment
every five years?  Good researchers and innovative companies
often decide that it's better to avoid space research,
because it costs too much and takes too long.   The ones who
haven't abandoned space research are looking hard at buying
flights on Russian or Chinese spacecraft: despite technical
and political obstacles, they can fly their experiments more
often that way.

People excuse this because it has always been this way and
so probably always will be (after all, this is rocket
science).  But there are a lot of reasons to think that it
needn't be so complex and expensive.

Spacecraft are complex, expensive, and built to aerospace
tolerances but they are not the only products of that nature
we use.  A typical airliner costs about the same as a
typical launcher.  It has a similar number of parts and is
built to similar tolerances.  The amount of fuel a launcher
burns to reach orbit is about the same as an airliner burns
to go from North America to Ausralia.  Looked at this way,
it would seem that the cost of getting into orbit should be
much closer to the $1500 it takes to get to Australia than
to the $500 million dollars plus it takes to put an
astronaut up.

Why the differences in cost?  Largely they are due to
different solutions to the same problems.  Some of these
differences are:

1.  Throw away hardware.  A typical expendable launch
vehicle costs anywhere from $50 to $200 million to build
(about the cost of a typical airliner) yet it is used  one
time and then thrown away.  Even the 'reusable' Space
Shuttle throws away most of its weight in the form of an
expendable external tank and salvageable solid rocket
motors.  This is the single biggest factor in making access
to space   expensive.

Airlines use reusable hardware and fly their aircraft
several times every day.  This allows them to amortize the
cost of the aircraft over literally thousands of passenger
flights.  The entire Shuttle fleet flies only eight times a
year, while many airliners fly more than eight times per
day.

2.  Redundant Hardware and Checks.  Since expendable
launchers are used one time and then thrown away, they
cannot be test-flown; huge amounts of effort therefore go
into making sure they will work correctly.  Since the
payloads they launch are typically far more expensive than
the launcher (a typical communication satellite can cost
three times the cost of the launcher) millions can be and
are spent on every launch to obtain very small increases in
reliability.  This is well beyond the point of diminishing
returns and sometimes results in greater harm.  For example,
a couple of years ago a Shuttle Orbiter was almost damaged
when it was rotated from horizontal to vertical with a loose
work-platform support still in its engine compartment.  The
support should have been removed beforehand...and three
signatures said it had been.

Airliners, since they are reusable and can also be tested
before use, thus are able to be built to more relaxed
standards without sacrificing safety.  The exact same
aircraft flew to get to your airport and it is likely that
any failure would already have been noticed.  In addition,
aircraft are built with redundancy so they can survive
malfunctions; launchers usually are not.  Most in-flight
failures of airliners result, at most, in delays and
inconvenience for the passengers; most in-flight failures of
launchers result in complete loss of launcher and payload.

3.  Pushing the Envelope on Hardware.  Current launchers
tend to use hardware that is run all the time at the outside
limit of its capability.  This may be fine for expendable
launchers which are used one time and don't need to be
repaired for reuse.  But this has also tended to carry over
to the Shuttle which, for example, operates its main engines
at around 100% of its rated thrust (this is like driving
your car 55 MPH in first gear all the time).  Because the
hardware is used to its limit every time, it needs extensive
checkout after every flight and frequent repair.

Airliners tend to be much more conservative in their use of
hardware.  Engines are used at far less than their full
rated thrust and airframes are stressed for greater loads
then they ever see.  This results in less wear and tear
which means they work with greater reliability and fewer
repairs.

4.  Labor Requirements.  For all of the reasons given above,
existing launchers require vast amounts of human labor to
fly.  The efforts of about 6,000 people are needed to keep
the Shuttle flying.  This represents a huge expense and is
amortized only over eight or so Shuttle flights every year.

Airliners are far more streamlined and, for the reasons
given above, don't need nearly as many people.  A typical
airliner only has 150 people supporting it, including
baggage handlers, flight crews, ticketing people, and
administration.  Since the cost of those 150 people are
amortized over thousands of flights per year, the cost per
flight is very low.

Our current  launchers are expensive and complex vehicles.
Yet the fact that we routinely use vehicles with similar
cost and complexity for far less cost indicate that the
causes of high launch costs lie elsewhere.  If we looked at
the problem in a different way, we could try to build
launchers the same way Boeing builds airliners.  The next
section will describe just such a launcher and how it is
being built.

A Spaceship that Runs Like an Airliner: SSTO
For a long time, some launcher designers have realized that
designing launchers the way airliners are designed would
result in lower costs.  Several designs have been proposed
over the years and they are generally referred to as Single
Stage to Orbit (SSTO) launchers.

1.  Single Stage to Orbit (SSTO).  Unlike an existing
launcher which has multiple stages, a SSTO launcher has only
one stage.  This results in far lower operational costs and
are key to reusability.  Conventional launchers need
expensive assembly buildings to stack the stages together
before going to the launch pad.  An SSTO only has one stage,
so these facilities are not needed.  This means that the
only infrastructure needed to launch a SSTO is a concrete
pad and a fuel truck.

2.  Built for Ease of Use.  SSTO vehicles are built to be
operated like airliners.  They can fly multiple times with
no other maintenance needed other than refueling.  If a
problem is discovered, all components can be accessed with
ease (by design).  The defective Line Replaceable Unit (LRU)
is replaced and launch can occur with only a short delay.
If the problem is more complex or other maintenance is
needed, the SSTO is towed to a hanger where the easy
accessibility of parts insures rapid turnaround.

3.  Standard Payload Interface.  Payloads need access to
services like power, cooling, life support, etc., while
waiting for launch.  The interfaces which provide these
services are not standardized, adding cost and complexity to
existing launchers.  In effect, part of the launcher must be
redesigned for each and every launch.  SSTOs, however, would
be designed with standard payload interfaces.  This allows
payload integration to occur hours before launch instead of
weeks before launch.  (Although in all fairness, the makers
of expendable launchers are also slowly moving in this
direction).

4.  Built to be tested.  Unlike expendables, SSTO vehicles
do not have to be perfect the first time.  Like airliners,
they can survive most failures.  Like airliners, they can be
tested again and again to find and fix problems before real
payloads and passengers are entrusted to them.  Even when a
failure does occur with a real payload aboard, usually
neither the vehicle nor the payload will be lost.  The
reliability of SSTO vehicles should be close to that of
airliners -- a loss rate of essentially zero -- and far
better than the 3% loss rate of existing launchers.


SDIO Single Stage Rocket Technology Program
Recent advances in engine technology and materials have made
most critics believe that the technology is now available to
build a SSTO.  In 1989, SDIO recognized the potential of
this approach and commissioned a study to assess its risk.
The study concluded that a SSTO vehicle is possible today.
As a result of this study, SDIO initiated the Single Stage
Rocket Technology Program  (SSRT).  The goal of the three
phase SSRT program is to build a SSTO, thus providing
routine cheap access to space.

Phase I consisted of four study contracts to develop a
baseline design for a SSTO.  General Dynamics and McDonnell
Douglas proposed vehicles which both take off and land
vertically (like a helicopter).  Rockwell proposed a vehicle
which takes off vertically but lands horizontally (like the
Space Shuttle does today).  Finally, Boeing proposed a
vehicle which both takes off and lands horizontally (like a
conventional aircraft).

In August 1991, SDIO selected the McDonnell Douglas vehicle
(dubbed Delta Clipper) for Phase II development, and
contracted for the construction of a 1/3 scale prototype
vehicle called DC-X.  This prototype is currently under
development and should begin flying in April, 1993.

DC-X will provide little science data but a wealth of
engineering data.  It will validate the basic concepts of
SSTO vehicles and demonstrate the ground and maintenance
procedures critical to any successful orbital vehicle.

Phase III of the program will develop a full scale prototype
vehicle called DC-Y.  DC-Y will reach orbit with a
substantial payload, hoped to be close to 20,000 lbs,  and
demonstrate total reusability.  In addition, McDonnell
Douglas will begin working with the government to develop
procedures to certify Delta Clipper like an airliner so it
can be operated in a similar manner.

Phase III was scheduled to begin in September of 1993 but
SDIO will not be able to fund the Phase III vehicle.  There
is some interest in parts of the Air Force and it is hoped
that they will fund DC-Y development.  It will be a great
loss for America if they do not.

After Phase III, it will be time to develop an operational
Delta Clipper launcher based on the DC-Y.  At this point
government funding shouldn't be needed any longer and the
free market can be expected to fund final development.

Conclusion
If a functional Delta Clipper is ever produced it will have
a profound impact on all activities conducted in space.  It
will render all other launch vehicles in the world obsolete
and regain for the United States 100% of the western launch
market (half of which has been lost to competition from
Europe and China).  It will allow the United States to open
up a new era for mankind, and regain our once commanding
lead in space technology.

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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End of Space Digest Volume 16 : Issue 331
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