SPACE TECHNOLOGY: MYTH AND PROMISE
_____ ___________ ____ ___ _______
by
Richard L. Garwin
IBM Research Division
Thomas J. Watson Research Center
P.O. Box 218
Yorktown Heights, NY 10598
(914) 945-2555
(also
Adjunct Professor of Physics,
Columbia University;
Adjunct Research Fellow,
CENTER FOR SCIENCE AND INTERNATIONAL AFFAIRS
Kennedy School of Government
Harvard University)
December 3, 1988
for
WAYS OUT OF THE ARMS RACE
Second International Scientists Conference
"From the Nuclear Threat to Mutual Security"
London, ENGLAND
ABSTRACT. Widespread myths distort our understanding and in-
hibit valuable programs to apply space to civil and to non-
weapon military purposes. Six so-called "&Delta.V myths"
are discussed in this paper, three of the dealing with SDI
and space weapons, and three relevant to reusable launchers,
space stations, and laser-powered satellite launch. Two
non-&Delta.V myths (survivability of defensive satellites,
and the utility of manned space flight) complete the se-
lection. Scientists have a special role to play to educate
the public and decision makers if we are to make safer and
more rewarding public choices in our use of space.
326>STMP 112188STMP DRAFT 11 12/15/88
Views of the author, not of his organizations
INTRODUCTION
A perceptive American saying goes, "It isn't so much what
you don't know that can hurt you; it's the things you think
you know that are not so." One modern example is the set of
myths and taboos that have arisen in recent decades in re-
gard to the use of space for civil and military purposes.
These rise above simple misconceptions, and spread through
political and journalistic channels, often with resulting
benefit to some special interest but with detriment to both
efficiency and economy. Some of these myths drive the arms
race by, for instance, exaggerating the threat that would be
posed by nuclear weapons in orbit, or the capability of
space-based defenses. But if we are able to find our way
out of the arms race it will be good also to be clear headed
about non-weapon and civil uses of space.
While the Strategic Defense Initiative (SDI)(1) is associ-
ated with some of these myths, others impede our civil and
military non-weapon use of space. That myths are not benign
can be seen in the case of the SDI. According to Paul H.
Nitze, President Reagan's chief arms control advisor, and
President Reagan himself,(2) to be considered for deployment
SDI must be (1) militarily effective, (2) adequately surviv-
able, and (3) cost-effective at the margin. If not, then
____
SDI can compel an offensive arms race rather than quench it;
it can provoke nuclear war rather than prevent it. There-
fore, even the attractive myth (if such it were) of effec-
tiveness, survivability, and low cost for SDI would be
downright dangerous.
__________
On the civil side, NASA has focused on the space shuttle as
the most efficient launcher to low earth orbit (LEO), and on
a space station for performing science and other space
missions of the early 21'st century. At $10 billion and $30
billion respectively, a wrong guess could be disastrous. In
fact, the erroneous claims about the cost and efficiency of
the space shuttle as launcher have already had a disastrous
effect on the US civil and military space programs, punctu-
ated and slightly only slightly worsened by the Challenger
catastrophe of January, 1986. Indeed, had it not been for
the destruction of the space shuttle Challenger, the US
might still be saddled with the sacred cow of the high-cost
space-shuttle-only access to space.
What can we say, with generality and simplicity, about SDI
and shuttles and space stations? I will discuss in some
quantitative detail two general kinds of myths-- &Delta.V
myths and non-&Delta.V myths (that is, myths that do or do
not involve centrally the "delta-V" or change of velocity of
a payload or satellite). I leave for the final section of
this paper the discussion of the origin of such myths and an
attempt to evaluate their cost. The list follows:
1. &Delta.V myths.
a. Offensive-defensive mass ratio in SDI.
b. Railguns vs. rockets for space-based intercept.
c. The pop-up anything for boost-phase intercept.
d. The problem of reusability of satellite launchers.
e. The myth of the equatorial space station.
f. Laser-launch of rockets and satellites.
2. Non-&Delta.V myths.
a. Survivability of satellites for defense against
ballistic missiles.
b. Man in space.
3. Lessons learned.
DELTA-V MYTHS.
All existing or planned satellite launchers or rockets oper-
ating in space are propelled by the continued expulsion of
mass from the vehicle at high speed, communicating an equal
and opposite impulse to the vehicle.(3) Essentially all
rockets thus far function by creating hot gas in a com-
bustion chamber, and expanding the gas through a nozzle into
_________
the vacuum of space, to form a directed jet, thereby con-
verting with almost 100% efficiency the thermal energy of
the gas to kinetic energy of the gas along the axis of the
___
nozzle. What is the efficiency of conversion to kinetic en-
ergy of the payload in orbit? Asssume a small amount of
mass &Delta.M is ejected to the left from the vehicle, at
exhaust velocity Ve. Eq. 1
dP/dt = 0 = +Ve&Delta.M + M&Delta.V (1)
states that the overall momentum P of the universe remains
constant, in that the sum of the momentum of the ejected
mass and the increased momentum of the spaceship of mass M
(due to its increased velocity as a result of the expulsion
of the gas) remains zero in the reference frame moving with
the spacecraft before the mass was ejected. Eqs. 2
dV/dM = -Ve/M, dV/Ve = -dM/M, (2)
&Delta.V/Ve = -&Delta.ln M; Mo/Mf = e&Delta.V/Ve
relate the increase of spacecraft speed with the mass
ejected, and the initial mass of the rocket Mo to the final
mass Mf, with the velocity gain &Delta.V and the exhaust ve-
locity Ve. Apparent from this equation, as is well known,
is that velocities very much greater than Ve can't be ob-
tained in a single-stage rocket because of the mass of the
"tanks" and of the rocket nozzle, which must be sized for
the rocket launch mass and initially massive propellant flow
rate. Accordingly, long-range missiles and rockets for
launching satellites to low earth orbit (LEO) are staged, so
_______
that large tanks and engines are discarded early in flight
rather than being carried to the final high speed. By the
use of this "rocket equation" one can follow in detail the
staging process, including the use of fuels with different
"specific impulse" on successive stages, nozzles with dif-
ferent expansion ratio, and different tankage mass fraction.
That would carry us too far afield here, and I summarize a
very useful reference(4) by asserting that Eq. 2 represents
the required mass ratio well enough if Ve is reduced from
the 3 km/s typical of good solid-fuel rockets to an effec-
tive Ve' of 2.5 km/s, to compensate for the lack of explicit
consideration of penalties due to tankage and engine mass.
The specific impulse of a propellant, Isp, is defined as a
time-- the reciprocal of the mass expulsion rate of
______
propellant supporting unit mass against gravity at the
Earth's surface, in the rocket arrangement provided. The
rate of expulsion E of mass required to support a constant
mass M is dP/dt = Mg = EVe, from which it is clear that
Isp == M/E = Ve/g.
Furthermore, a rocket can do no better than to expand the
hot gas from its combustion chamber "fully" so that it is
essentially a cold stream moving at speed Ve along the axis
of the rocket nozzle. To do this requires a relatively long
nozzle, with a large area ratio, so that the pressure and
____ ______
hence the internal energy of the gas is reduced and almost
all of the initial thermal energy is converted into directed
kinetic energy. Thus the performance of a rocket is bounded
by the conversion of all of the chemical energy of the
propellant per gram, Ec,
into kinetic energy of the uni-directional cold-gas stream
as determined by 1/2 Ve2 = Ec.
Taking a nominal 1000 cal/g energy content(5) for high ex-
plosive (which has properties not necessary for a rocket
fuel), one can compute the Ve for high explosive as
2.893 km/s.
We are now ready to explore the &Delta.V myths.
Offensive-defensive Mass Ratio.
Since before there were ICBMs, thought has been given to
antiballistic missile systems (ABM) involving orbiting kill
vehicles. Clearly, an orbiting vehicle striking an ICBM
booster or warhead in space would do so with collision speed
comparable with orbital speed of 8 km/s. We have just seen
that high-explosive energy per gram corresponds to a speed
of 2.9 km/s, so that an orbiting mass without warhead strik-
ing a stationary object of larger size would deliver to it
(8/2.9)ý, or about 7.6 times the energy of an equal mass of
stationary high explosive. Thus, space-based interceptors
can kill effectively with their kinetic energy alone-- hence
the name Kinetic Kill Vehicles or KKV.
The SDI Organization (SDIO) as recently as November 1988(6)
emphasizes that the destruction of ICBMs and SLBMs in boost
phase is critical and can be carried out only by orbiting
KKVs (space-based interceptors or SBI), until directed-
energy weapons (DEW) are available at some later date. The
SDIO program goal, however, has been to provide KKVs with a
homing "head" of 5 or 10 kg mass. Even if the SDIO were to
achieve its goal, such a system would not satisfy the Nitze
criteria of cost-effectiveness at the margin, and hence it
would not be a desirable system to deploy, as indicated by
the following analysis:(7) The rocket equation is important
in determining the mass of the defensive system required to
counter a current offense. For instance, discussion of
'near-term deployment' of SDI would achieve the essential
boost-phase intercept within the boost-time T of the ICBMs
by basing the SBI on space garages. Those garages in their
________
90-minute orbits of the Earth which are in the vicinity of
the Soviet Union could contribute an SBI out to a distance
from the garage of T multiplied by &Delta.V, and although by
appropriate choice of orbit the density of garages over the
Soviet Union could be increased about a factor 3 from that
of uniform coverage of the Earth's surface, that is about
the best that could be done. Since the area which can be
____
reached by an SBI from a garage is proportional to the
square of this outreach distance, the minimum number of ga-
______
rages goes inversely as the square of the SBI velocity-gain.
If there is a homing warhead mass Mf required (at present
15 kg for the small homing warhead of the US aircraft-based
ASAT, after the two-stage rocket falls away which brings it
to orbital altitude), the initial mass of the SBI housed in
____
the garage is given again by Equation 2, in terms of the
homing warhead mass and the required velocity gain from the
garage. One can reduce the mass of a given SBI by having
only a small velocity gain, but then a lot of SBI will have
to be placed on orbit in many garages in order to ensure
that the required areal density of SBI will be available to
_______
handle the boosters. Because the boosters in flight are not
spread uniformly, one must provide an SBI areal density
which at every point can equal this maximum required. The
number of SBI on orbit thus increases as the reciprocal of
the area to which an SBI can be dispatched from its space
____
garage, so that the total mass of SBI on orbit has an expo-
nential factor from Equation 2, and an inverse square factor
in velocity gain as just indicated.
SBI area coverage: If Ao = &pi.n(T&Delta.V)ý, and
n &approx. (1/&Delta.V)ý,
mass on orbit = Mf n e&Delta.V/Vc, proportional to (e&De(3)
Equation 3 shows that the mass on orbit is minimized at a
velocity gain equal to twice the escape velocity or some
6 km/s. Actually, since the SBI must descend from their or-
_______
bital altitude to intercept the boosters, far more SBI are
required than indicated.
Calculations(8) show that only 13% of the orbiting SBI can
in any way attack either the SS-18 booster or its post-boost
__
vehicle, (2.5% in boost phase, 10% against the MIRV bus)
while only 2.3% could attack the Soviet SS-25. Furthermore,
if the Soviets continue with the 10-warhead SS-24 but use
instead a 6-warhead 'minibus' only 1.9% of the KKVs could
attack the SS-24, compared with 9.5% against the current
version SS-24.
In summary, a 15-kg homing kill vehicle would require about
300 kg SBI housed on the garage, with a garage mass total-
ling some 500 kg per SBI (including the SBI itself). This
is more than the weight of a nuclear warhead (some 300 kg,
____
including reentry vehicle), and if 10 percent of the SBI in
flight can reach a booster or RV, this is the minimum re-
quired against a 10-MIRVed missile to be effective in de-
stroying boosters carrying 10 MIRVs instead of warheads.
With only 2% of the SBI capable of boost-phase intercept,
even a 10-warhead booster cannot be destroyed cost-
effectively in this way, and a single-warhead offensive mis-
sile certainly cannot be.
_________
The Myth of the Rail-gun Advantage Over the Rocket.
A "rail gun" is simple in concept-- an electromagnetic
launcher in which the projectile slides between two metallic
rails and conducts a large current between them as it
slides; the accelerating force is provided by the inter-
action of the current with the magnetic field provided by
that same current in the rails. The SDIO has funded rail
gun development and power supplies for space-based intercept
as an alternative to rocket propulsion, and in a speech in
October, 1984, Gen James A. Abrahamson stated that "chemical
propulsion" (rockets) would prevail up to speeds of about
5 km/s, but that the region above 5 km/s belonged to the
rail gun. What must the rail gun accelerate in order to
help do the SDI job? If it is to operate at a range of
2000 km (call it 2 megameters or 2 Mm), and if the
projectile flies at 10 km/s, it will take 200 seconds to
reach its target. During that time, an ICBM moving at
7 km/s would have moved 1400 km, so that it is very clearly
necessary to project a homing head and not an inert "bul-
______
let." In comparison with the rocket-propelled head, no as-
pect of the rail gun propulsion would allow the head to be
made smaller and lighter than the rocket head. In fact, if
rail-gun acceleration is to be limited to 10¹ g (so that the
force on a 10-kg homing head would be "only" 1000 tons dur-
ing acceleration), the rail gun would be 50 m long. A typi-
cal rocket-propelled SBI would have an acceleration of 20 g,
so that the force on the homing head would be less by a fac-
tor 5000. Clearly, the high acceleration forces of a rail
gun pose serious design constraints on the homing technol-
ogy. Furthermore, multiple SBIs can be launched simultane-
ously from an orbiting garage, whereas the substantial
investment of a rail gun and power supply would be amortized
over sequential launch of multiple homing projectiles, with
the necessity to re-aim the rail gun between shots. Fur-
thermore, the rail gun must supply the 500 MJ kinetic energy
of the homing head (10 kg; 10 km/s) in about 10 millisec-
onds, or at a delivery rate of 50 GW. If the rail gun were
30% efficient, the power supply to the rail gun would have
__
to supply 170 GW in pulsed power.
SDIO has been looking at homopolar generators or other
mechanical-electrical devices to provide such high-power
pulses-- a subject on which I worked long ago.(9) In fact,
SDIO has reported approvingly to have reached 1 km/s
circumferential speed in flywheels for storing energy, to be
delivered in this way.
How significant an achievement is kinetic energy storage in
steel (for example) at 1 km/s? To propel a 10 kg homing
head at 10 km/s would require (at 100% conversion and accel-
eration efficiency) all of the kinetic energy in a flywheel
___
of mass 1 ton, (assuming that all of the flywheel is moving
___
at the 1 km/s). Assuming a 30% efficiency between kinetic
energy loss of flywheel and kinetic energy gain of homing
head, and assuming that only 30% of the total kinetic energy
of the flywheel is available (15% reduction in speed), a
flywheel of 11 tons would be needed to propel a single hom-
ing head of mass 10 kg. Furthermore, to shoot at a rate of
1 per second, would mean an average power during the engage-
ment of some 170 MW from the prime source of electrical
power and into and out of the staging flywheel. In a sense,
however, these are details; these are all problems incurred
________
by the rail gun-- none of them problems for the mature tech-
nology of rocket propulsion. What persuaded SDIO leaders
that the range above 5 km/s "belongs to the rail gun"? Per-
haps Eq. 2 provides a hint, since rocket payloads become
small at speeds high compared with the rocket exhaust veloc-
ity of 2.5-3 km/s. How small is shown in the following Ta-
ble 1, in which the first row is the final velocity Vf; the
second &alpha. is the ratio of final velocity to rocket ex-
haust velocity Ve. The third row is the mass ratio m from
the rocket equation,
+----------------------------------------------------------+
| TABLE 1: For final velocity Vf achieved by rocket pro- |
| pulsion |
| |
| with exhaust velocity Ve = 3 km/s, the payload |
| fraction |
| |
| is &mu. and the fraction of fuel total energy |
| present |
| in the payload kinetic energy is &epsilon.. |
+----------------------------------------------------------+
| |
| Vf 3 6 9 12 15 18 km/s |
| |
| &alpha. 1 2 3 4 5 6 |
| |
| &mu. 37% 13.5% 5.0% 1.83% 0.67% 0.248% |
| |
| &epsilon. 59% 62% 47% 30% 17% 9.1 |
| % |
| |
+----------------------------------------------------------+
while the fourth row is the energy efficiency in converting
to kinetic energy of payload the internal energy of a mass
of propellant equal to the initial mass of the rocket less
the final payload. Eq. 4 shows the relevant formula,
&epsilon. == (K.E.)/(P.E.) = ¤1/2 MfVf2‡/¤1/2 Ve2
(Mo-Mf)‡ (4)
with numerical values tabulated in the fourth row of the Ta-
ble.
It is doubtful that the rail gun can convert electrical en-
ergy into kinetic energy of the homing head with an effi-
ciency greater than 30%, and it is likewise doubtful that
the thermal energy of fuel (or rocket propellant powering a
space-based turbine) can be converted into electrical energy
with an efficiency much above 30%. Taking the composite
conversion efficiency (9%) from satellite-based fuel to the
kinetic energy of the homing head, we see that ordinary
chemical rockets have far better conversion efficiency at
homing head speeds up to 18 km/s, where the rocket converts
9% of the energy of all its propellant to kinetic energy of
a homing head that has a mass only 0.25% that of the initial
rocket mass.
Even if homopolar generators and rail guns weighed and cost
nothing, the rocket would win the competition below 18 km/s.
The more one works on rail guns (even successfully), the
less effective one's space-based defense.
The Pop-up Anything.
In his (favorable) comments on defense against nuclear war-
heads carried on strategic ballistic missiles, Dr. Edward
Teller has often remarked that "one can't base a defense in
space, because satellites are costly to put up and can be
shot down in advance of an attack."(10) In fact, the
Lawrence Livermore National Laboratory (Dr. Teller's home
base) has long been working on x-ray lasers to be pumped by
powerful nuclear explosions, with the purpose of destroying
missiles in boost or post-boost phase; if these nuclear-
pumped x-ray lasers are not to be based in space, they are
to be "popped up" from their safe havens on earth or under
the oceans. In April, 1983(11) I showed that because the
earth is round, very severe requirements are put on the
rocket that carries the x-ray laser warhead to its firing
position. The actual transparency shown 04/13/83 will be
presented to the conference. In brief, if the booster must
be attacked by the time it reaches its burnout height A, and
the interceptor is based at range R measured on a great cir-
cle along the earth's surface, and if we assume that there
is no atmosphere and the interceptor instantly achieves its
final velocity, the mass ratio (ratio of required launch
mass to x-ray laser mass) for the interceptor is still
impressively large. Other critical assumptions in the Table
are that the booster reaches 7 km/s in a total of 200 s (av-
erage acceleration 3.5 g), of which 120 s
+----------------------------------------------------------+
| TABLE 2: For a ground-based directed-energy defensive |
| weapon to climb high enough to attack Soviet ICBMs in |
| their boost phase requires large boosters for the defen- |
| sive payload and would subject the payload to large |
| forces. |
+----------------------------------------------------------+
| RANGE from ICBM launchpo|
| nt |
| to defensive launcher|
| |
| 6000 5000 4000 30|
| 0 nmi |
+----------------------------------------------------------+
+----------------------------------------------------------+
| |
| Altitude defensive weapon* 2960 2050 1260 6|
| 0 nmi |
| must reach in 120 sec |
| |
| Mass of defensive missile 2.1 MT 19,000 330 |
| 4 tons |
| assuming instant burn** |
| |
| Mass of defensive missile ..... ..... 270 KT 4|
| 0 tons |
| assuming constant acceleration** |
| |
| Acceleration required 78 54 33 |
| 7 g's |
| assuming constant acceleration |
| |
| *Assumes 100-nmi clearance of the line-of-sight from |
| earth's surface, and that offensive booster has reached |
| 200 nmi height. |
| **Payload mass = 500 kg; specific impulse = 300 sec. |
| |
| Source: Author; from Ballistic Missile Defense, Edited |
_________ _______ ________
| by A.B. Carter and D. Schwartz (1984). |
+----------------------------------------------------------+
is available for the flight time of the interceptor. Under
those circumstances, for a booster burnout height of 300
miles (pardon the units), the mass ratio of the interceptor
is 150,000, so that for an x-ray laser weighing 1 ton, the
interceptor would weigh 150,000 tons at launch. This large
mass ratio is determined by the necessity for the
interceptor to fly out a distance P in order to reach the
horizon plane of the booster at the time of booster burnout;
by simple geometry, the interceptor would have to fly 2630
miles in 120 s, if the interceptor were initially based 6000
miles from the ICBM launch.
If one abandoned basing the interceptor on US soil and moved
it to a submarine at 3000 mile range from the silo launch
site, the interceptor would have to fly only 650 miles to
see the booster at 200-mile altitude burnout, and the re-
quired mass ratio (for instant-burn interceptors) would be
only 20-- 20 tons for a 1 ton x-ray laser payload.
Interceptors of infinite acceleration are not very practi-
cal, and they would in any case burn up in going through the
dense atmosphere even at the 5 mi/s speed of the last exam-
ple. If one assumes constant acceleration for the
________
interceptor, then the mass ratio is the square of that shown
______
in Table 2, since the final speed of the interceptor is dou-
ble the speed required for instant burn, if the two
interceptors are to arrive at their firing point with the
same delay. Furthermore, x-ray laser weapons don't exist,
and one must ask about available countermeasures to the of-
fense if x-ray lasers and their high-performance
interceptors were produced and deployed. From the begin-
ning, it has been obvious that reducing the duration of
boost phase would be a highly effective counter to pop-up
anything. For instance, if instead of 120 s to reach its
firing point, the pop-up had only 60 s (perhaps from a 90 s
ICBM boost time, less a 30 s delay for observation, communi-
cation, and interceptor launch), the mass ratios in the Ta-
ble would once again be squared.
_____
These considerations are summarized in the statement by Cory
Coll, director SDI systems analysis, Livermore National Lab-
oratory, (quoted by R.J. Smith, SCIENCE, 11/08/85) "In the
end, the pop-up x-ray laser is simply not feasible against a
fast-burn booster. Fast-burn boosters rule out pop-up any-
thing."
The Problem of Reusable Launchers (Not Necessarily For
SDI).
The goal of the US space shuttle program was a capability to
____
launch a payload East out of Cape Canaveral, Florida, of
65,000 lb maximum, of approximately 300,000 lb put into or-
bit as shuttle structure, engines, maneuvering fuel, crew
and crew support systems, and the like. Thus only about 20%
of the orbital mass is payload, and to begin with, the sys-
tem must be five times cheaper per unit mass into LEO just
____
to break even with expendable boosters launching the same
payload.
If one considers scaling the propulsion system of the shut-
_______
tle for an expendable launcher, the "large external tank"
containing liquid hydrogen and liquid oxygen would be five
times smaller (and use five times less hydrogen and oxygen),
and the expendable boosters would be five times smaller (and
use five times less solid fuel). No matter how many times
the solid-rocket boosters (SRB) are to be reused in the ac-
tual shuttle, each use expends five times the fuel required
to launch the same payload on an expendable. And each use
incurs costs of returning the rockets to the factory, in-
specting and refurbishing, and the like.
But the deficiencies of the shuttle have not yet been fully
enumerated. Another aspect is the much more severe payload
loss due to "earth rotation" in the case of the shuttle. A
near-equatorial launch site allows a greater payload into
LEO than would be the case from a stationary earth, because
the eastward velocity of the earth's surface,
VE(&lambda.) = (40,000/86,400) cos&lambda. km/s
need not be supplied by rocket propulsion. This amounts to
some 0.4 km/s at Cape Canaveral, Florida.
Specifically, the satellite speed is given by Eq. 5,
(VLEO)2/RE = g, VLEO = 7.94 km/s. (5)
As a function of latitude &lambda. and orbital inclination
&alpha. the required velocity gain from the moving launch
site is given by
&Delta.VLEO(&lambda.,&alpha.) = VLEO - VE(&lambda.) cos((6)
Most satellites in LEO are in polar or near-polar orbit, so
that they can observe the entire surface of the earth as the
earth turns under the circular orbital track. For polar or-
bit, we have &Delta.V = VLEO &approx. 7.94 km/s,
compared with the &Delta.V required of 7.54 km/s needed for
least-energy launch eastward from Cape Canaveral.
For an expendable booster, this difference of 0.4 km/s means
__________
an off-load &Delta.M from the payload Mp, so that
(Mp-&Delta.M)/Mp = e-&Delta.V/Ve. With &Delta.V = 0.4 km/s
and Ve = 3 km/s,
this amounts to &Delta.M/Mp = 0.4/3 = 13% for polar orbit
with an expendable booster.
For the shuttle, however, this same fraction of reduction of
________
mass to orbit applies now not to the payload but to the
gross or total mass into orbit, and the payload reduction is
_____
not 13% of 65,000 lb (8400 lb) but 13% of 300,000 lb, or
39,000 lb. A 13% loss of payload for an expendable booster
becomes a 60% loss of payload for the shuttle into polar or-
bit.
Indeed, the shuttle normally launches into orbits of very
low altitude above the surface of the earth. The shuttle
suffers severe penalties if it is to carry a payload into a
higher orbit (hence longer life against atmospheric drag).
Now that the Soviet Union has followed the United States
down the mind-altering path of space shuttles, I quote my
own words broadcast(12) during the first flight of the
space-shuttle Columbia:
"I feel that there is nothing to be done with the
shuttle that couldn't be done better with expenda-
ble boosters... The shuttle, like the Concorde
aircraft, is a technical marvel and an economic
disaster... a real detriment to our military ca-
pability..."'
In the current era of glasnost, we have also the comments of
R.Z. Sagdeev on the Soviet shuttle approach:(13)
"...an outstanding technological achievement...
but it had absolutely no scientific value. It
went up; it came down. My personal view is that
American experience with the shuttle indicates
that from the point of view of cost efficiency,
the shuttle is in deep trouble. It is much sim-
pler and cheaper to fly a payload with any kind of
expendable vehicle."
The Myth of the Equatorial Space Station.
In the United States during the decade of the 1960s, as the
Apollo program to put an American on the moon within that
decade and to bring him back safely was drawing to a close,
NASA was looking to its next major and popular project.
NASA wanted a space station, but the costs were apparently
too high, and it accepted the shuttle program instead. The
arguments advanced in support of the space station in the
1960s were much the same as they are now, although with ex-
perience, we now have a substantially better understanding
that, in my opinion, should reduce even further our desire
for such an investment.
A space station would be a near-earth base from which one
could refuel, refurbish, and occasionally provide staff for
satellites. Furthermore, one could conduct scientific ex-
periments, carry out militarily significant activities, and
the like. Never mind that even in the 1960s, these things
could be better done with the remote involvement of men and
______
women. In the 1990s, performance of the very best individ-
uals has improved marginally, but the performance of commu-
nication and automated systems has improved enormously,
thereby further tipping the choice toward keeping people on
the ground. The role of people in space is left for a later
section; we now address a &Delta.V myth regarding the space
station.
More recently, Lennard A. Fisk, Associate Administrator for
Space Science and Applications, NASA, has explained that in
the era of the space station, "... a polar-orbiting platform
associated with the station would be ideal for a proposed
major mission to study the Earth and its resources."(14)
For reasons indicated in the previous section about the
shuttle, the space station elements are expected to be
launched eastward from Cape Canaveral into an orbit the in-
clination of which is thus equal to the latitude of Cape
Canaveral (about 28 degrees). Into polar orbit, the same
number of shuttle launches could carry less than half the
payload. What, then, is the nature of the "association" of
the polar orbiter with the space station? If the two are at
similar altitude, then it might be practical to phase the
satellites in their orbits so that they came close together
twice each revolution. But is it practical to go from an
equatorial platform to a polar platform for servicing, refu-
eling, or modifications? Of course, it is always possible
to supply a person into orbit via an expendable booster.
The United States did that in the Mercury, Gemini, and
Apollo programs. In this paper, we have paid a lot of at-
tention to the crucial question of velocity gain and the
minimum mass ratio thereby imposed by rocket propulsion.
For visiting a polar-orbiting platform directly from Earth,
one would need 8 km/s velocity gain to go up to the plat-
form, and about 0.2 km/s to come down, since return from or-
bit to the Earth can readily be accomplished by firing a
small retro-rocket in order to have the orbit graze the at-
mosphere about half a revolution ("rev") later. The Soviet
Union's unmanned first shuttle test has now shown what we
have always known-- that automated and accurate return from
orbit is possible. Thus ground-based servicing for the po-
lar orbiter is possible with a total velocity gain of some
8.2 km/s. How about servicing from the space station?
Avoiding irrelevant conceptual complications, we consider a
space station in pure equatorial orbit, and assess transfer
from that orbit to a polar orbiting satellite. To go from
the 8 km/s eastward velocity of the space station to an
8 km/s northward velocity of the polar orbiter can be done
in various ways, three of which are now considered. Concep-
tually, the simplest is to brake the orbital speed with a
rocket, and then to increase it in the northward direction
(Path A). This would mean a rocket-induced velocity change
of 16 km/s, and is obviously far from optimum. Path B (a
quarter circle in velocity space) corresponds to maintaining
the magnitude of the speed at all times, while adding veloc-
ity perpendicular to the existing instantaneous velocity.
The transfer vehicle remains in orbit, but the velocity
change required is &pi./2 times orbit velocity, or some
12.57 km/s. Path C (a straight line in velocity space) ob-
viously involves a velocity change &sqrt.2 times orbital ve-
locity or about 11.3 km/s.
If a person is assigned to go from the space station to the
polar orbiter and back again via path C, he or she would
need provision for a velocity change of 22.6 km/s. Includ-
ing the launch to the space station to begin with (some
__
8 km/s), the velocity gain associated with this caper would
be some 30.6 km/s or a mass ratio of some 27,000, assuming
an effective exhaust velocity of 3 km/s for the rocket en-
gines involved. Considering that the same job could have
been done from the ground to the polar orbiter and back with
a velocity gain of 8.2 km/s (and a mass ratio of 15.4), it
is, to say the least, not at all clear how the space station
would be involved with the associated polar orbiter.
Laser-powered Launch of Satellites.
Ground-based lasers might be used to launch satellites or
deep-space probes. Powerful lasers on the ground would heat
inert propellant material in the rocket as it rises through
the atmosphere and into space. The propellant might be con-
tained in a heating chamber and expelled through a standard
rocket nozzle, or repeated intense laser pulses could ablate
______
(evaporate) it from a flat plate at the base of the rocket.
To minimize the absorption of laser light as it traversed
the atmosphere, such a system might involve a relay satel-
lite in geosynchronous orbit and a number of focusing mir-
rors in low earth orbit, in order to provide most
flexibility for delivering energy to the rocket powered by
the ground-based laser. It is not the pressure of the light
itself, but the driving of material off the rocket at high
speed, that would provide recoil momentum to the body just
as in normal rocket propulsion.
Consider the approach involving an ordinary "combustion
chamber" into which laser light is fed, to heat an effluent
material. Hydrogen gas, provided with an additive for ab-
sorbing light, would be an efficient propulsion medium, but
such a system has no element of advantage over ordinary
rocket propulsion. For launch of satellites to low earth
orbit, there can be no energy saving over the normal rocket,
which achieves near-maximum efficiency of energy utilization
(some 30% of the propellant energy) in providing kinetic en-
ergy of payload. Providing the energy from the ground does
little to reduce the mass or cost of the rocket, compared
with providing both expulsion mass and chemical energy in
the fuel, so there is no possibility of recovering the cost
of the laser system.
An approach with more promise is to illuminate a flat plate
of specially designed ablative material with carefully timed
pulses of intense laser light. Successive pulses might dif-
fer in wavelength so as to continue to deposit energy in the
blown-off material so that it can achieve blowoff speeds
perpendicular to the ablating plate-- kinetic energy per
gram blown off-- large compared with the thermal energy at
any containable temperature. This approach, however, would
be useful only for speeds far in excess of satellite and
ICBM needs.
In the velocity regime that might be used for space defense
against ballistic missiles, there is no potential benefit
associated with laser propulsion. Nevertheless, supporters
of such an approach have called for funding related work
within the SDIO budget.
The deployment of laser-powered launch systems would result
in a significant (but vulnerable) ABM capability, not from
the propulsion of interceptors but from the potential for
direct destruction of missile boosters by the intense laser
light. For instance, to launch 10 tons into low-earth orbit
(8 km/sec velocity gain) in 320 seconds (during which time
the vehicle would have moved under constant acceleration
some 1,300 kilometers) would require the transfer to the
payload of some 320 gigajoules of kinetic energy; that is,
the payload would have to gain kinetic energy at the rate of
1 gigawatt (GW). This is the power output of a large civil
nuclear power station.
The lasers proposed directly for space defense would have
power outputs on the order of 0.1 GW, and not 1.0 GW. Fur-
thermore, one can hardly conceive of a laser-rocket effi-
ciency much better than 50 percent, and even that would
require a 2 GW laser source if all the laser light traversed
the atmosphere without scattering or loss. If one assumes a
tenfold loss of laser light in traversing the atmosphere and
spilling over at the relay mirrors, a laser of 20 GW would
be required as a source. In fact, it would be remarkable to
obtain a laser efficiency (conversion of electrical power to
laser light) of 30 percent, which would require a prime
electrical power input of some 70 GW during launch, and
hence a laser enormously overpowered even for the space de-
fense role.
Such an enormous program would offer no possibility of bene-
fit for satellite launch, since ordinary rocket fuel energy
is converted to satellite kinetic energy at 31 percent effi-
ciency.
NON-&DELTA.V MYTHS.
Of the two remaining myths to be discussed, neither involves
the rocket equation for velocity gain &Delta.V. The first
has hardly achieved myth status, since it was debunked be-
fore it was offered, but I discuss it here because it may
arise again before naive audiences. The second myth is the
very serious one elevating beyond reality the contributions
of people in space.
The Myth of Survivability of Defensive Satellites in "Non-
Keplerian" Orbits.
In an exchange between Congressman Les AuCoin and General
Abrahamson on pages 612 and 642 of "HAC, DOD Appropriations
for 1987, Part 5" regarding space mines, General Abrahamson
suggests a "very interesting kind of concept is a tethered
satellite ... so long ... that it exceeds the range of ef-
fectiveness of a nuclear burst." Since a nuclear burst is
likely to kill satellites at a distance of 100 km,(15) this
is quite a long tether, indeed. But this proposal is nei-
ther new nor effective.(16)
"... For instance, in principle a satellite could de-
part continuously by 100 km from an elliptical orbit by
attachment via a 200-km-long tether to a similar satel-
lite-- the two rotating about the center of the tether.
Two space mines could do the same.
"Ultimately, as the feared effectiveness of defensive
systems increased, the space mines would be semi-
autonomous, so that any attempt by the quarry to disa-
ble the space mines or to evade them would result in
the destruction of the quarry. This certainly in-
creases the volatility of space and of the nuclear con-
frontation in general, but would surely be regarded as
preferable by either superpower to allowing the other
side to disarm it by effective space defenses."
The idea, however, that a powerful nation is going to lie
down and play dead while the other side "protects" its sat-
ellites by increasing their mass and deploying each one on a
200-km tether is just not persuasive. Does SDIO understand
the critical vulnerabilities that they introduce for them-
selves with these tethers? For instance, if we imagine a
pair of satellites each weighing 1000 kg, separated by a
200-km tether and rotating once every 16 minutes (1000 sec-
onds), each satellite is tugged by 0.36 g, and the force on
the tether is about 360 kg. Assuming that the tether can
operate at a stress equal to that in high-strength steel,
but is only as dense as plastic (100,000 psi, and density
1.0), it would need a cross-sectional area of 0.05 sq cm,
and the tether itself would weigh one ton.
Without having done the experiment, it is difficult to say
exactly, but it is highly likely that a tether under tension
would be severed by collision with a tether of 1/10th the
diameter, striking it at orbital speeds. In the predomi-
nantly polar orbits which would be used for space-based
ballistic missile defense, satellites are as often going
south over a given point on Earth as they are going north,
and a reasonable collision speed would be up to twice the
orbital speed of 8 km/s-- for instance 11 km/s.
One might imagine that the satellites are deployed over an
orbital altitude band of 500 km. Imagine that the other
side deploys some inert smaller satellites (weighing only 1%
as much, and connected by a tether only 1/10th the diameter)
but spinning at the same rate. (This is only an example.
It will be even easier to defeat this system than indicated
here.) If the tethers were always arranged for maximum vul-
nerability (for instance, as the satellite moves forward in
its path, the tether of one satellite might be vertical
while the tether of the satellite coming the other way might
be horizontal), then the pass would be sure to sever the
tethers if the center of the second tether were anywhere
within a 200-km square (40,000 sq km). If one imagined low-
altitude equatorial tether cutters, the defensive satellites
would cross the Equator every 45 minutes-- so 36 times per
day. The 40,000 km circumference of the Equator, times the
500-km altitude band assumed for these satellites has a
total of 20 million sq km, and a single 200-km-long anti-
tether tether would (with most vulnerable orientation) sweep
out 36 times 40,000 or about 1.44 million sq km per day. A
single anti-tether tether would thus destroy a single defen-
sive satellite pair in about 14 days, on the average.
In fact, at times the satellite tethers are oriented along
_____
the line of flight, and the anti-tether tether is oriented
in the wrong direction as well, so the collision rate proba-
bly has to be reduced by about a factor 10 to obtain a
proper average. Nevertheless, for the 100 anti-tether sat-
ellites ("ATS") which could be launched with the same launch
capability as a single defensive pair, any defensive satel-
______
lite would last only a day or so. But the ATS need have no
smarts at all-- they are a lot cheaper than real defensive
satellites which must be equipped with sensors, rockets,
communications, and the like.
In reality, each "anti-tether tether" could simply be 10
kilograms of wire-- 10,000 one-gram bits each 0.25 mm diam-
eter and 20 m long, with no satellites attached.
__
No doubt many throughout the world would accept General
Abrahamson's claim that space mines are no problem because
SDI defensive satellites can (and will?) be deployed in
pairs at the ends of tethers so long that they exceed twice
the lethal range of a space-mine nuclear warhead.
The Mystique of Man in Space.
The dreams of an individual childhood, the dreams of our
species-- of soaring in the air like the birds or roaming in
space free of the ever-felt bonds of the earth's pull-- ac-
count in part for the large US and Soviet manned space pro-
grams. But there are less innocent causes as well, among
them the recognition that careers and money are to be made
by providing people something that appears inherently good,
without bothering them about the true cost, the cost of dis-
carded alternatives ("opportunity cost"), and the degrada-
tion of the national ability to make decisions.
It was indeed interesting and a major accomplishment in the
1960s to confirm that the human species can survive in the
zero-g environment of space (properly supplied with atmos-
phere and temperature) and to extend that finding to un-
interrupted stay of a year or more, as has now been done.
But not one person thus far has paid his or her way into
space; nor has the overall manned program repaid its cost in
any way but entertainment value on television. It is easy
enough to point to moments in which an astronaut has done
something useful or valuable, such as the recovery and re-
pair of a satellite that has failed to boost itself into
GEO, but there is no possibility of eliminating all fail-
___
ures, and it is much cheaper to provide appropriate backup
elements on satellites (or redundant satellites and
launchers) than to maintain a manned satellite program as
thus far defined.
Certainly in near-earth orbit the resupply, repair, and re-
covery of satellites can be achieved more cheaply and more
reliably by unmanned vehicles and remote-manned activities.
Satellites to be returned to earth in the payload bay of the
shuttle must be designed specifically for that portion of
their life cycle, including the re-folding and secure stor-
age of solar panels. They could more readily be equipped
with an ablative heat shield for unmanned reentry to the at-
mosphere, with remote guidance to a soft landing on a track-
mounted sled or to a parachute landing further softened by
the vertical retro rockets in use for the past two decades
for air-delivered military equipment. Furthermore, recovery
from LEO after normal life of 5-10 years will, one hopes,
bring back of a satellite of old technology, and there is a
very real question whether the progress of technology is not
such to make it uneconomic to re-use such an old satellite.
If one were presented with a free 10-year-old video re-
corder, would one really want to upgrade it to modern stand-
ards, or would it be cheaper to start fresh?
Of course, people in space would be a necessity for space
colonies, but space colonies will be a great economic drain
on earth-based life, without any possibility of moving a
significant fraction (even 1%) of people from Earth to
space. Arguments that space colonies can prosper and sup-
port themselves involve an unsupported assumption of 17% an-
nual growth in productivity, without any consideration of
political organization and without comparison with putting a
similar isolated colony into even the most inhospitable re-
gions on Earth, such as the oceans or the deserts.
Another argument for a vigorous manned space program is the
necessity to "maintain the momentum" of the manned space
program itself. Why? The first eight years of manned space
flight led to the Apollo landing on the moon and the safe
return of the astronauts to Earth. No matter how long a hi-
atus without manned space flight, how is it possible (with
ever advancing general progress of technology) that we would
not be ready to fly again, and more effectively? In fact,
constant practice within budget constraints largely results
in preserving old and diminished capabilities rather than
___
the modern, effective space-flight capability that would
emerge if we restarted the program when we had a use for it.
LESSONS TO BE LEARNED.
I say "lessons to be learned," because they have not already
been learned. The first lesson is that we pay a very high
price to maintain these myths, far beyond the cost of the
particular program.
The second lesson is that there is a continued, important
role for scientists. Neither the Challenger disaster of
January 1986, nor the Chernobyl disaster of April 1986 re-
quired deep scientific insight to observe that something had
gone wrong. But in both cases, the hazards existed before
______
the disaster, and was reasonably accessible to scientific
inquiry. In both cases, in my opinion, the entrenched bu-
reaucracy prevented the voices of scientists and other know-
ledgeable critics from being heard, although the problem of
cost-ineffectiveness of the space shuttle program, and the
hazard of suppressing the evolution and continued procure-
ment of expendable boosters was far simpler to state than
was the task of analyzing the hazard of the combined phys-
ical and management deficiencies in the case of the
Chernobyl-type power reactors in the Soviet Union. Scien-
tists should vigorously report the truth, and this should be
welcomed by their colleagues and by society. Even a program
that is "merely wasteful" is denying wealth to people and is
damaging the ability to make proper decisions.
Returning to the arms race, we note that in many cases it
takes participation of both sides to become a real hazard,
____
as can be seen in interpersonal relations. As small a mat-
ter as inadequate calibration or judgment of the effort on
the other side (or "worst-case analysis") can over the years
and successive budget cycles result in a threatening arms
race. This might be avoided if one side is vastly richer
than the other and can afford much "greater" security, but
if both sides are comparable and look to compensate "capa-
bilities" and not intentions on the other side, one will
eventually see, on both sides, vast military machines for
which there is no rational reason, which will therefore in-
spire fear and instability on the other side.
We have in these myths the danger of jargon and of rhetoric.
Many honest, loyal people are involved in the continuation
of these programs. In the modern world of persuasion and
advertising, they are asked to turn their talents to the
support of the program of their organizations, and they do
this very well-- with public relations and lawyerly skills
that must be admired, but with results that can be disas-
trous. In the SDI program, we now see that the promise of
President Reagan to "share the technology" of strategic de-
fense with the Soviet Union has officially become a commit-
ment "to share the fruits of technology." As I have
commented,(17) "sharing the fruits of technology" can be un-
derstood as the mutual occupation of a peaceful world in
which one side has nothing to fear from the nuclear weapons
of the other side, because of an impenetrable shield, while
the other side (with useless nuclear weapons) has nothing to
fear because the protected side has no "reason to attack."
More simply, in feudal days, both lord and serf "shared the
fruits of the wealth" of the lord. The lord did this di-
rectly, and the serf lived whatever kind of life was optimum
as directed by the leadership of society. Human beings owe
their society honesty and candor, and they should be very
cautious before using their talents to deceive or mislead,
especially in the service of a program of their government
or society.
The code of honor of the United States Military Academy for-
bids not only lying but also "quibbling," which is the use
of words in such a way that they give a misleading im-
pression of assurance, threat, etc. If we all perceive the
reality, then we can all turn our attention to improving
this world. At present, the myths of space technology in-
hibit our putting an end to the extension of the arms race
into space, and they deny modern societies the full produc-
tive civil and military (non-weapon) uses of space.
----------------
1 Created to pursue President Reagan's goal of a techno-
logical program to render nuclear weapons impotent and
obsolete, as stated in his speech of March 23, 1983.
The SDI was officially formed one year later, and Lt.
Gen. James A. Abrahamson selected to head it.
2 As stated in National Security Decision Directive 172,
discussed in The Strategic Defense Initiative, US De-
___ _________ _______ ___________
partment of State Special Report No. 129, June 1985,
p. 4.
3 Thus far untested in space is propulsion within the in-
ner solar system by the momentum of sunlight itself, re-
flected from vast "solar sails". See R.L. Garwin,
"Solar Sailing-- A Practical Method of Propulsion Within
the Solar System," Jet Propulsion, March 1958, 28,
___ ___________
No. 3, pp. 188-190. Also, L. Friedman, Starsailing: So-
____________ ___
lar Sails and Interstellar Travel, John Wiley & Sons,
___ _____ ___ ____________ _______
Inc, (1988).
4 Spacecraft Propulsion Systems-- What They Are and How
They Work," by Robert H. Frisbee, Foundation
__________
Astronautics Notebook-6, World Space Foundation, Jan-
____________ ___________
July 1983.
5 One cal = 4.186 joule.
6 Speech of Lt. Gen. James A. Abrahamson to the National
Press Club, November 15, 1988.
7 From R.L. Garwin, "Defensive and Offensive Weapons in
Space, and Civilian Space Technologies," Presented at
the Third International Conference of the USPID on
"Technology, the Arms Race, and Arms Control," at
Castiglioncello, September 26, 1987 (to be published).
8 Chris Cunningham, Tom Morgan, and Phil Duffy, 'Near-Term
Ballistic Missile Defenses' Strategic Defensive Systems
Studies Group of the Lawrence Livermore National Labora-
tory, (1987).
9 "The Production of Axially Symmetric Magnetic Fields,
and New Power Sources for Large Betatrons and
Synchrotons," R.L.Garwin, (Thesis for the B.S. in Phys-
ics at Case Institute of Technology.) May 15, 1947.
10 Quoted, for example, in National Geographic, March 1984,
________ ___________
page 363.
11 Arms Control Symposium panelists: H.A. Bethe, D. Kerr,
R.L. Garwin, E. Teller, April 13, 1983, Los Alamos Na-
tional Laboratory (40th Anniversary commemoration)
12 MacNeil-Lehrer Report, "The Space Shuttle and Defense,"
April 13, 1981.
13 Quoted by J.N. Wilford in The New York Times of November
___ ___ ____ _____
22, 1988.
14 Quoted in The New York Times of May 3, 1988.
___ ___ ____ _____
15 The SDI goal (paper supplied by Major Simon P. Worden,
Special Assistant to the Director SDIO, re Near-term SDI
Architecture Study, 1986) is to harden satellites to re-
sist a 1 megaton nuclear burst at 100 km.
16 For instance, H.A. Bethe and I wrote the above inset
section for our chapter (draft of 11/19/84) for the
"Weapons in Space" book of the American Academy of Arts
and Sciences, published 1985.
17 Symposium on "New Defense Technologies and the Strategic
Balance," Southern Methodist University, Dallas, Texas,
September 1986.
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