Space Weapons: Not Yet
by Richard L. Garwin (USA)*
In this paper I attempt
to sketch the utility of space weaponry, primarily from the point
of view of the United States.
In this I draw upon the excellent RAND book 1,
“Space Weapons, Earth Wars.” That study was commissioned
by LGen Roger DeKok, DCS Plans and Programs, HQ USAF. I am guided
also by the views expressed in presentations and discussions of which
I am aware over the past year. But these are my own judgments, which
will be refined by the interactions at this Pugwash session.
I come to this study from a background of 40 years as scientist and
manager with the IBM Research Division, and more than 50 years of
involvement with the US Government’s national security programs,
beginning with the development and testing of nuclear weapons, and
extending to missiles and space.
The US Space Commission Report2 cited
several needs for space-weapon capability:
- Defensive Counter-space:
To reduce US military space vulnerability.
- Offensive Counter-space:
To deny the use of space and space assets to adversaries
- Rapid and global power
projection to earth.
To address these needs, the RAND Report assesses distinct classes
of weapons:
- Directed-energy weapons
such as space-based lasers.
- Kinetic-energy weapons
against missile targets.
- Kinetic-energy weapons
against surface targets.
- Conventional warheads
delivered by space-based, or space-traversing, vehicles.
In addition, any assessment
must consider the potential for non-space weapons to perform any of
these tasks. This introduces the competing capabilities of:
- Surface-based anti-satellite
(ASAT) weapons such as high-power lasers, or missiles with pellet
warheads, or hit-to-kill vehicles.
- Rapid-response delivery
of conventional munitions by forward-deployed cruise or ballistic
missiles, or non-nuclear payloads on ICBMs.
And one must consider
also countermeasures to space weapons and to these competing systems.
A final element of assessment is the vulnerability of space weapons
or of competing systems.
In this preliminary assessment, I take into account the experience
of my civilian and military colleagues and their judgments of existing
and future threats to US military space, as well as their views of
the potential utility of various space and non-space weapons.
We turn to the first application in our list, defensive counter-space.
Here we discover that space weapons have little capability for meeting
the felt needs identified above.
Satellite vulnerability is and probably will continue to arise in
considerable part from jamming or other electronic countermeasures,
sensor blinding from high-powered lasers on earth, and pellet payloads
on short-range pop-up missiles. Perhaps most proliferated is the threat
of Denial and Deception, camouflage that undermines the effectiveness
of our reconnaissance satellites, or operations scheduled under cloud
or when satellites are not in position to observe. Here is a tabulation
of threats, with the most likely ones listed first:
- denial & deception
- electronic warfare
- attack on ground stations
- sensor blinding
- microsatellites
- direct-ascent interceptors
- nuclear detonation
in space
But for most of these
threats, space weapons do not help to reduce vulnerability. They are
limited to intercepting objects that approach satellites in a noticeably
offensive way, such as hit-to-kill kinetic energy weapons; and that
capability remains to be assessed.
One of the most effective threats is a microsatellite in the form
of a "space mine." Surrey Satellite Technology Ltd., a Surrey
University company, is a leader in developing microsatellite technology,
and has numerous collaborative programs with other countries and with
non-state groups. Although microsatellites have peaceful and military
non-weapon uses--observation, communication, and the like--they make
particularly good antisatellite weapons. In this role, a microsatellite
space mine equipped with maneuver capability exceeding that of the
quarry satellite would sit always within lethal range (even a few
tens of meters) ready to explode at a moment's notice.
A microsatellite as inspection device might have been useful in conjunction
with Columbia’s final flight, but a long-endurance microsatellite
is a more difficult task. Nevertheless, a cautionary tale is this
account of a January 29, 2003, US microsatellite exercise; the XSS-10
repeatedly maneuvered to within 115 ft of its final-stage rocket,
taking pictures. A shotgun shell could have destroyed a satellite
from such a range.
China carried out similar maneuvers with Surrey technology several
years ago.
Since in the vacuum of space (as was known to Galileo) a feather and
lead shot fall at the same speed without significant drag, a microsatellite
with little payload necessary to devote to other tasks can be equipped
to outmaneuver and outlast a major satellite, the primary job of which
is surveillance, high-bandwidth communication, and the like.
It is difficult to counter space mines once they are in place. It
might be done with defensive microsatellites, but the asymmetric nature
of the threat (i.e., tiny expenditures for the microsatellite vs.
$200 million-plus for a major US LEO satellite, makes it desirable
to prevent the emergence of such threats.
Two general tools for resolving the microsatellite dilemma are rules
of conduct in peacetime, and deterrence by holding non-space assets
at risk.
In summary, space weapons are generally not good at protecting satellites.
In the case of microsatellites, one might plagiarize Jonathan Swift
and commit to deploy “smaller still to bite ‘em.” This
is an arms race in which United States resources far outweigh those
of any other state, but this advantage is outweighed by the vulnerability
inherent in the cost of existing and future high-capability satellites
in low Earth orbit.
We turn now to the remaining two uses for space weapons, power projection
and offensive counter-space. Different space weapons have varying
degrees of utility in these areas, so we will now look at the utility
of specific weapons.
We have already seen how useful space mines may be AGAINST those who
have valuable satellites and useless against those who have none.
Another weapon much discussed is long-rod penetrators. The
idea is that these long tungsten or uranium rods would be orbited,
and (according to the RAND Report) de-orbited by canceling their orbital
velocity, so that they would fall essentially vertically through the
atmosphere, striking their target with enormous energy. Two problems
that will not be alleviated by the progress of technology: the energy
is larger the higher the orbit, but the fall time is greater as well.
The energy of high explosive corresponds to a material speed of 3
km/s, and one does not arrive at a similar energy per gram from a
projectile dropped from altitude until one reaches 460 km, with a
corresponding fall time of 12 minutes; a fall from GEO takes almost
6 hours and provides about ten times the energy density of high explosive.
A rod would need to be guided accurately to strike its target within
some meters in order to destroy a surface target by the explosion.
Long rods might be used to penetrate through earth to hard or deeply
buried targets. However, the physics of high-velocity impact limits
penetration depth as shown by high-speed photography of a bullet impacting
steel at just above 1 kilometer per second. A copper-jacketed lead
bullet fragments against the hardened steel, but in the process produces
a pressure sufficient to leave a small crater. Very strong projectiles
impacting earth or rock at similar speed can penetrate to depths several
times their length.
Tests done by Sandia laboratory confirm predictions that, even for
the hardest rod materials, penetration is maximum around 1 km/s. Above
that speed, the rod tip simply liquefies, and penetration depth falls
off, becoming effectively independent of impact speed. Therefore,
for maximum penetration, such rods would need to be orbited at very
low altitudes, and could only deliver one ninth the destructive energy
per gram as a conventional bomb. The effort is entirely mismatched
to the results.
Dominating the cost is the need to put the rod into orbit in the first
place and later cancel its orbital velocity so that it drops back
to earth. The propellant required to place the entire weapon in orbit
must suffice to lift both the rod and its attendant deorbiting propellant.
For low earth orbit, the total velocity change of about 15 km/s typically
requires several thousand times the orbiting mass in propellant. Taking
the typical $10,000 per kg launch cost to LEO, and assuming a 0.1
ton rod with the 3 tons of propellant to stop its orbital motion,
the launch cost to orbit would be some $30 million. And for timely
delivery against a single target at temperate latitude, several rods
in each orbit would be required and a good many orbits—say 10.
Clearly, the more conventional deorbit maneuver would be preferable,
with a small energy change and the use of atmospheric drag (combined
with wings or a lifting-body approach) to preserve much of the orbital
velocity as the rod approaches the vertical.
Whatever the effect actually achieved against a target, it is far
better to propel the rod directly from launch to target and avoid
orbits altogether-- by placing the rods on ballistic missiles. Specifically,
a one-km/s penetrator could be provided flexibly by a nominal solid
rocket motor giving an acceleration 30 times that of gravity—so
300 m/sec2. The desired 1 km/s would be obtained in 3.3 s, over a
distance of 1.65 km. A speed of 3 km/s would take 10 s and a distance
of 15 km. The cost would be some $100,000 or less, plus whatever cost
for the terminal guidance system--which is surely no greater for the
ballistic missile than for the orbiting projectile.
Looking now at the common aero vehicle (CAV) carrying conventional
ordnance or intelligence payloads, one finds again that this capability
is dominated by CAV delivery by ballistic or cruise missiles-- perhaps
guided by observation from space. Indeed, the role of the CAV itself
is largely supplanted by the familiar “bus” technology for
delivering multiple payloads from a ballistic missile launch.
We turn now to space weapons (and their competition) for missile defense.
For boost-phase intercept—BPI-- space-based kinetic-energy (hit-to-kill)
interceptors are in competition with surface-based interceptors (on
land or sea, or even on aircraft). The non-space options excel against
a small state such as North Korea, largely surrounded by water. For
BPI, space-based interceptors must be given acceleration and divert
capabilities very similar to those required for surface-based interceptors,
if they are not to pass harmlessly by the quarry missiles. For missile
launches from a small area, space-based interceptors have their required
number multiplied by the number of simultaneous launches, and also
by the "absentee ratio" because most of the SBI will be
on the other side of the Earth and unable to join the fray for a clustered
launch.
However capable the surface-based interceptors would be against North
Korea, Iraq, or even against launches from Iran, unless based within
the target country they are ineffective against ICBMs launched from
China or Russia, because the interior of those countries is so far
from the borders.
Yet China and Russia are highly capable powers, and it would be much
easier for them to destroy space-based interceptors as the constellation
is gradually built than it would be for the US to use the SBIs to
counter ballistic missile launch. Some observers are skeptical that
Russia or China (or France, for that matter) would destroy SBIs in
peacetime, but when the question is posed what the US would do if
another state deployed a vast number of SBIs, the response of many
of my colleagues is that we would destroy them—“shoot them
down”.
The airborne laser (ABL) under development and in early flight test
(in contrast to the SBL for which no US program currently exists)
might serve as a BPI capability against ICBMs launched from North
Korea. In the spirit of a “capabilities based” system, it
would to some extent complicate NK’s ICBM program: North Korea
would need to deploy from the beginning countermeasures to mid-course
and would have to consider countermeasures to an ABL BPI defense.
Unlike the mid-course interceptors which once deployed would always
be ready for use, the ABL would incur large operating costs to maintain
a constant presence.
Another weapon of considerable interest is the Space Based Laser.
These weapons could attack over long distances at the speed of light,
although space mines and the ABL could be equally prompt. A SBL could
also attack terrestrial targets, but only with suitable laser wavelengths
to penetrate the atmosphere. The current candidate SBL lasers cannot
attack ground or airborne targets.
A single SBL, costing billions of dollars, could typically have a
range of at most 3000 km, unless the SBL constellation were conceived
to have a large number of redirecting ("fighting") mirrors3.
Under those circumstances, a competitive system could use a ground-based
laser, redirected by such mirrors3.
Cloud at the GBL site would cancel the capability of a GBL, so several
would be needed to have high probability that the system would be
operable at any time. In any case, the fighting mirrors might be classed
by the potential victims as weapons in space as well.
An SBL would be a very expensive means of attacking a satellite, but
might be more useful for missile defense purposes. With relatively
few SBL in orbit, one might need to be used at 3000 km range. At that
distance, with no loss through the atmosphere, a perfect mirror of
3 m diameter, and laser power output of 3 MW in the 3.8-micron DF
band, a target protected with 3 cm of cork could withstand about 200
MJm-2 before exposing the target surface to laser heat.
(Some Minuteman ICBMs have had a 0.6-centimeter layer of cork to protect
the booster from skin friction heating during launch. Such a layer
would be vaporized with about 50 MJm-2 (5 kJcm-2)
from a SBL.) The laser consumes fuel at a rate of some 3kg/MWs, or
9 kg/s, and it would need to fire for 1700 s at the assumed 3000-km
range, thus using 15 tons of fuel, at a launch cost for fuel of $150
million per target attacked. At a range of 1000 km, the launch cost
would be some $16 M per target.
Other countermeasures are feasible and could be multiplicative—such
as the slow rotation of the booster during launch.
A substantial constellation of SBLs covering the strategically important
region of the Earth could consist of 20-50 such satellites, which
could provide rapid illumination of most important points, providing
that the target can be destroyed by the laser, and that it is not
covered by cloud. Cloud coverage is typically 30-40%, but can range
to 70% or more in parts of Germany or North Korea.
But, as analyzed in detail in the RAND publication, many targets are
not vulnerable to destruction by SBL, and many that are can be protected
by smoke, by water shields, or in other ways. Aircraft yes, and combustible
targets or thin-skinned storage tanks. But not bunkers, armored vehicles,
or many buildings.
We have already seen that the use of an SBL can easily cost in the
range of $100 million per target and is contingent on the target being
thin-skinned and not obscured by a cloud. For comparison, a Tomahawk
missile costs some $600,000 and will attack heavily armored and non-flammable
targets, and is not affected by cloud.
Even enthusiasts consider SBLs a weapon to attack very special targets,
while most military capability against similar targets is to be provided
by more conventional means. In contrast almost all portions of the
earth are reachable by existing cruise missiles (Tomahawk Block 3)
launched from outside the 12 nmi limit. The flight time can be several
hours.
For the space-based laser, "rapid response" is a sometime
thing, since it is necessary to have clear air to allow the laser
beam to strike the target—no cloud in the way.
With these competitive means of striking the target, observation could
still be provided by non-weapon space assets, so that in addition
to attack by navigation (using GPS) one could use a laser-target designator
from space with observation and designation provided at the time when
a destructive payload arrives in the vicinity of the target—an
example of non-weapon military space capabilities contributing to
US military capability.
In summary, the one target which can surely be held at risk at modest
cost is important and costly satellites, of which the US possesses
by far the greatest number and value.
The US Space Commission Report is generally considered as support
for the proposition that the US should proceed to develop and deploy
space weapons in order to counter the evolution of space weapons by
others, and to effect the needed reduction in vulnerability of US
satellites. In fact the commission does not specifically advocate
the development of offensive weaponry for deployment in space. In
particular, it reads,
“The government…should:
- Invest in technologies
to permit the US Government to field systems one generation ahead
of what is available commercially to meet unique national security
requirements.
- Encourage the US commercial
space industry to field systems one generation ahead of international
competitors.”
Also,
“Fourth, we know
from history that every medium—air, land and sea—has seen
conflict. Reality indicates that space will be no different. Given
this virtual certainty, the US must develop the means both to deter
and to defend against hostile acts in and from space.”
And
“The US must participate
actively in shaping the space legal and regulatory environment.”
My own analysis indicates
that US deployment of space weapons will encourage and demand the
development and deployment of space weapons by others. Others can
and will respond to space weapons in asymmetric ways--including the
deployment of space mines in their vicinity and the use of short range
missiles to lift ton-class pellet payloads against LEO weapons. Furthermore,
such responses would inevitably threaten and legitimize counters to
US non-weapon LEO satellites essential to our entire military capability.
It is therefore essential to judge the utility and necessity of space
weapons. Of course, any proposed augmentation of US military capability
must compete with other means for accomplishing the task. Capabilities
unique to space weapons use resources, which must be taken into account.
Net judgments on space weapons utility:
– For offensive counterspace—deny military space to others
- Jam uplinks or downlinks
(from ground or space)
- Attack ground stations
essential to satellite capability
- Obscure line of sight
by screens in space
– For defensive counterspace—preserve
US military space capability
- Attack ground systems
which might be disabling satellites
- Interdict ASAT in powered
flight
- Deter by promise of
retaliation—not against satellites but against military and
political assets
– For destructive
antisatellite (ASAT)
- The most prompt means
is probably microsatellite as space mine, orbiting Earth within
10-100m of its quarry
- Short-range missiles
lobbing ton payloads of coarse sand to orbital altitude at the right
time
- Homing kill vehicles
as direct-ascent ASAT
The United States can
do it best, but others will soon do it well enough.
– Global and prompt force projection
- Kinetic-energy (KE)
weapons on ICBMs or shorter-range missiles
- Advanced conventional
weapons on ICBMs (CAV?) with observation or designation from space,
ground, or UAV
– Non-space weapons
will provide more capability and sooner than space weapons
– Destructive ASAT
and space-ASAT weapons are a serious threat to overall US military
capability and its dependence on space.
Countering satellite vulnerability: A general approach to reducing
satellite vulnerability is to reduce our dependence on satellites
while maintaining the benefits of satellites at reasonable cost. This
can be achieved by supplementing satellite capabilities in wartime
by theater resources:
- High-power pseudolites
(on the ground and on UAVs) in the theater of operations so that
the adversary would obtain no benefit in theater conflict by destroying
GPS satellites.
- UAV and rocket capabilities
for imagery. At altitudes of 20-30 km, a 20-cm aperture would have
the same resolution as a 2-m diameter mirror at a range of 300 km.
Such platforms can provide near-constant presence, as well.
A primary means of reducing
vulnerability is to reduce the threat—by agreements not to damage
or destroy non-weapon satellites. This should be backed up by US developments
to intercept or counter such weapons or ASAT used in violation of
such an agreement.
We have found general acceptance of this (conditional) conclusion:
If space weapons
and destructive ASAT could be avoided by the United States giving
up such capability, it would be in our national security interest
to do so.
Asserting a "might
makes right" rule in space and elsewhere leads, again, to the
asymmetric use of force, and this might be the destruction of valuable
satellites in peacetime rather than holding them at risk for future
destruction.
Nothing is forever--perhaps not even the regime we favor--so an aggressive
campaign to prevent the deployment of weapons by others might best
be implemented as a US commitment:
not to be the first
to test or deploy space weapons or to further test destructive antisatellite
weapons.
This should be supported
by a US initiative to codify such a rule—first by parallel unilateral
declarations and then by a treaty. Such a campaign would legitimize
the use of force against actions which would imperil satellites of
any state.
*
rgarwin@cfr.org. Work done with
Bruce M. DeBlois, Jeremy C. Marwell, and Scott H. Kemp, of the Council
on Foreign Relations.
Notes:
- "Space
Weapons, Earth Wars," by Robert Preston, et al, RAND MR1209,
June 2002.
- Rumsfeld,
D.H. et al. “Report of the Commission to Assess United States
National Security Space Management and Organization,” January
11, 2001.
- Bethe,
H.A., and Garwin, R.L., “Space-based Ballistic-Missile Defense,”
Scientific American, Volume 252, No. 4, October 1984. (Figure on
p. 44).
* *
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