Star Crossed
FROM ORBITING LASERS TO MICROSATELLITE MINES TO HEAVY METAL
RODS THAT STRIKE FROM THE HEAVENS, THE POTENTIAL TO WAGE WAR
FROM SPACE RAISES STARTLING POSSIBILITIES—AND SERIOUS PROBLEMS
BY BRUCE M. DEBLOIS, RICHARD L . GARWIN, R . SCOT T KEMP & JEREMY C. MARWELL
March 2005 | IEEE Spectrum | INT 3
Today, such a scenario is pure science fiction, but it—or something like it—could become reality within the next decade or two.
The irony is that the economic and political price the United States
would have to pay to bring about such a system, even if it could
be done, might well outweigh its obvious strategic advantage.
No country today is known to have weapons deployed in space,
and many countries oppose their development. However, at least
some U.S. Pentagon officials have been arguing that the United
States must now, after decades of debate, develop and deploy offensive space weapons. In fact, over the past 10 years, the U.S. government has spent billions of dollars researching and testing such
weapons. If deployment became official U.S. policy, such a step
would have profound—and, we feel, profoundly negative—implications for the balance of global power.
The United States itself, our analysis suggests, would discover
that the military advantages that might be gained from space-based
weapons are outweighed by their political and economic costs. It
would also create new, asymmetric vulnerabilities to U.S. armed
forces, as we will describe in this article. In addition, such systems
would be a significant political and strategic departure from 50 years
of international law and diplomatic relations.
The U.S. and North Atlantic Treaty Organization (NATO) militaries already make extensive use of space-based systems. Satellites
revolutionized conflicts such as Operation Iraqi Freedom, letting U.S.
aircraft fly one-third the number of sorties and use one-tenth the
number of munitions than they had expended just 10 years earlier in
the Persian Gulf War. That economy was largely due to the great
increase in accuracy offered by space systems.
Satellites are now routinely used to detect, identify, locate, and
track targets. They also provide mobile, secure communication links
between military control centers and theaters of operation, nearreal-time imaging, signals intelligence, and meteorological data.
And, of course, the constellation of Global Positioning System (GPS)
satellites ensures that military personnel need never be lost amid
a war’s chaos.
With capability, however, has come reliance. In the words of one
U.S. Air Force space official, space systems are now “woven inextricably” throughout the military capabilities of the United States
and its allies. And the pace of space operations is accelerating: by
2010, the U.S. military expects it will need twice the capacity of
its existing space-based infrastructure—in everything from the
number of images per day acquired from spy satellites to the bandwidth carried by communications satellites.
Without a doubt, the exploitation of space has helped the U.S.
military become the most technologically advanced fighting force
4 IEEE Spectrum | March 2005 | INT
in the world. At the same time, though, it has made that force deeply
vulnerable to an attack on its satellites and other space-based systems. What’s more, the means to disable or disrupt this valuable
and complex machinery are well within the reach of even technologically unsophisticated adversaries.
Indeed, with some U.S. military planners advocating the development of what would be the first-ever space-based systems for
offensive operations—what the military refers to as force projection—the country finds itself fast approaching a crossroads. Space,
these planners assert, will usher in a revolution in global warfare,
with U.S. space-based weapons delivering destructive force to any
point on the globe within minutes, and without the risk or cost
of sending soldiers.
Realizing the growing strategic value of space, in January 2001
a congressionally mandated space commission headed by incoming Secretary of Defense Donald H. Rumsfeld urged the United
States to maintain the option of weaponizing space, identifying
three potential missions for space weapons:
• Protecting existing U.S. systems in space.
• Denying the use of space and space assets to adversaries.
• Attacking from space a target anywhere on Earth, at sea, or
in the air.
In the four years since the Rumsfeld commission released its
conclusions, the report has continued to guide U.S. policymaking
in this arena. For instance, the U.S. Air Force last year outlined a
series of potential space weapons initiatives as part of its 176-page
Transformation Flight Plan. Among the weapons described were
space- and ground-based lasers, antisatellite missiles, and a futuristic constellation of orbiting high-power radio frequency transmitters capable of disrupting or disabling electronics. A press statement that accompanied the report’s release in February 2004
described it as “a road map to the future.”
THE IDEA OF PUTTING WEAPONS IN SPACE is not new.
Beginning in the 1960s, at a time when satellites were still quite
rare, the former Soviet Union and the United States both tested
antisatellite weapons. Despite several decades of development,
however, neither country managed to deploy any such weapons.
Then, during the Reagan administration, supporters of the Strategic
Defense Initiative advanced proposals ranging from space-based
lasers to “Brilliant Pebbles,” numerous small orbiting projectiles
to be fired at ballistic missiles in hopes of destroying them.
Again, considerable research netted no system worth deploying
[see box, “Missile Defense from Space”]. Though such systems
were positioned as defensive in nature, the line between offensive
and defensive space weaponry is more philosophical than technological: the same laser that could be trained on a rogue missile could
easily target a commercial satellite instead. Likewise, the technological problems that plagued defensive space weapons will also
apply to new offensive designs.
Critics of space weapons have long insisted that developing and
deploying space weapon systems—if feasible at all—would be prohibitively expensive and technologically difficult. The majority of
the international space-faring community call instead for a perpetuation of the status quo: use space to support terrestrial military activities through communications, reconnaissance, navigation, and even weapon guidance, but not for direct application of
force. In other words, the militarization of space is acceptable;
the weaponization is not.
Now, as the U.S. national security community nears a decision
point, policymakers are split on several fundamental questions:
• Can space weapons effectively mitigate the existing vulnerabilities of U.S. and other satellites and space systems?
ILLUSTRATIONS: JOHN MACNEILL
The world awakens to an international
crisis: officials at the Tokyo airport have
detained a foreign airliner suspected of carrying illegal arms. The aggressive and threatening response from the plane’s country of origin, a “rogue”
Asian state believed to possess both nuclear and biological weapons,
adds credibility to the suspicion. Hamstrung by its rogue status, the
aggressor country’s economy has been in free fall for decades, and
with this latest incident, it’s widely feared that the country will launch a
nuclear attack against Japan. U.S. satellites report escalating activity
at the country’s rocket-launch facility; other U.S. intelligence indicates
that three intermediate-range missiles are being fueled and are within
a 15-minute launch window. No air-, sea-, or land-based military system is available to respond. The U.S. president demands that the country cease and desist immediately, but receives no response. Five minutes later, the U.S. Strategic Command activates a heretofore undisclosed
space-based laser; within minutes, it incinerates the launch facility’s
command and control center, thus narrowly averting a catastrophe.
12 June 2018
• Will space weapons be better than terrestrial alternatives at projecting force and denying adversaries the use
of space?
• Will expected gains from space weapons outweigh
financial, strategic, and political costs?
• Assuming for the moment that space weapons would
further U.S. interests, but taking into account that several
other countries also have the ability to deploy them, should
the United States be the first to do so?
WHAT IS A SPACE WEAPON? As commonly defined, it is
SPACE ARROWS: Rods of tungsten, stored on an orbiting platform,
would be released to strike buried targets on Earth. However, each rod
would take several minutes to reach its
target and would be difficult to steer,
limiting the weapon to attacking fixed
positions. There is also an upper bound
on the rods’ velocity, which means
their destructive force would be similar to cheaper conventional explosives.
a system designed to project destructive force between Earth
and outer space or within space itself. Antisatellite weapons,
space-based lasers, space-based platforms that fire projectiles, and ground-based lasers that rely on orbiting mirrors
to reflect beams to space or back down to Earth—all fit the
definition. On the other hand, intercontinental ballistic missiles, ground-based electromagnetic jammers aimed at satellite signals, and explosives used to attack satellite ground stations are not considered space weapons.
For the most part, space weapons can be classified into
four categories: directed-energy weapons, kinetic-energy
weapons, conventional warheads delivered to or from space,
and microsatellites.
A directed-energy weapon uses a beam of electromagnetic energy, whether laser light or high-powered radio waves,
to destroy a target. In the case of a laser, the beam heats a
target until it melts or catches fire. For radio waves, the
weapon stimulates the target’s electronic circuits until they
are inoperable [see “The Dawn of the E-Bomb,” IEEE
Spectrum, November 2003].
The most widely discussed directed-energy weapon is
the space-based laser (SBL), an orbiting system that would
use powerful lasers with large mirrors to focus energy on a
selected target on Earth, producing damaging or destructive levels of heat. Over the past decade, the Pentagon has
spent roughly US $750 million on SBL research, funded primarily by the Air Force and the Ballistic Missile Defense
Organization (now the Missile Defense Agency).
Various components have been tested on the ground and
in the lab, including a megawatt-class chemical laser and the
apparatus for pointing and controlling the beam, but the full
system has yet to be tested in orbit. Although the U.S.
Congress suspended funding in 2003 and called for a review
of the program, the concept remains very much alive.
Directed-energy weapons propagate their energy at the
speed of light, so their effects begin with no appreciable
delay beyond the time necessary to acquire a target and
point the laser. However, to have the desired effect, the
beam must remain on target for some time. For example, to
attack a ballistic missile, a space-based 3-MW laser with
a 3-meter diameter mirror stationed 1000 kilometers above
Earth’s surface, in low-Earth orbit (LEO), requires an
impractical 2 hours and 13 minutes to burn through the
rocket casing at a range of 3000 km; a 30-MW laser with a
10-meter diameter mirror in the same orbit and at the same
range would take a more reasonable 80 seconds [see illustration, “Light Saber”]. For comparison, the entire flight of
an intercontinental ballistic missile, from launch to impact,
would last only about 45 minutes.
“Burn” time aside, directed-energy weapons’ speed-oflight propagation cannot be matched by any other weapon.
This feature suits them well for targets in remote locations
March 2005 | IEEE Spectrum | INT 5
MISSILE DEFENSE
FROM SPACE
The partial deployment of the U.S. ground-based
missile defense system in recent months—and more
specifically, its technical failures—naturally raises
the question of basing a ballistic missile defense system in space. Would such a system work?
A ballistic missile is most vulnerable during its
boost phase, when it is not maneuvering and the stillburning rocket presents a strong infrared signature.
Boost phase for a liquid-fueled intercontinental ballistic missile (ICBM) lasts some 250 seconds, while a
solid-fuel ICBM may burn out in 170 seconds.
The U.S. military has understandably shown a
great deal of interest in boost-phase missile defense.
A recent study by the American Physical Society, in
College Park, Md., analyzed two types of space
weapons that have been proposed for intercepting
incoming missiles during boost phase: space-based
interceptors (SBIs) that would propel a kinetic “kill
vehicle” into a collision with the missile (much like
the ground-based interceptors currently being
deployed) and space-based lasers.
As the study noted, the size of the constellation of
SBIs or lasers that would be needed grows in proportion to the number of simultaneous launches that
might occur. For example, if a missile-defense constellation can handle at most three simultaneous
missiles from a small region, an adversary could
surely defeat this defense by launching four.
For use against missiles launched from, say, the
small state of North Korea, boost-phase interceptors
on nearby ships, or on Russian territory south of
Vladivostok, would likely be considerably more capable, not to mention cheaper, than space-based interceptors. What’s more, these fragile battleships of
space would need to be protected from preemptive
attack; we describe in the main text how low-Earth
orbit satellites are relatively easy to destroy.
Another proposal for space-based missile defense
involves intercepting ICBMs in the 20 minutes of
their midcourse fall through space. Though this has
been a mainstay of missile-defense advocates since
the Star Wars days of the mid-1980s, it is not part of
the current administration’s program for national
missile defense. In large part, this is because midcourse SBIs have no technical advantage over
ground-based interceptors and are more expensive.
Although the purpose of this article is not to analyze in depth the prospects for intercepting ICBMs, it
is worth mentioning that systems limited to destroying missiles in the vacuum of space (that is, midcourse systems) will be useless unless they can deal
with the countermeasure of cheap and easily
deployed balloon decoys.
—B.M.D., R.L.G., R.S.K., J.C.M.
6 IEEE Spectrum | March 2005 | INT
or beyond the reach of conventional forces, such as the launch facility described in the opening scenario. But even if the target’s location is known precisely, the laser is useless if clouds or smoke intervene; it has other shortcomings, too, which will be described later.
Kinetic-energy weapons destroy targets by smashing into them
at high speed (they are not explosive). According to basic Newtonian
physics, the impact energy increases linearly with the projectile’s
mass, but as the square of its impact velocity. Because collision speed
is comparable to orbital or missile speed, lightweight projectiles
would be sufficiently destructive—assuming they find their target.
Such velocities would also help the projectile elude countermeasures and defenses, penetrate armor, and reach buried targets.
Hypervelocity Rod Bundles are a leading candidate. More colloquially known as Rods from God, they are long, slim, dense metal
rods, typically of tungsten or uranium, each weighing perhaps 100
kilograms and deployed from an orbiting platform. Once a rod is
released by the platform, a large two-stage rocket would bring it to
a stop, after which orbital dynamics determine the projectile’s
trajectory to a terrestrial target [see illustration, “Space Arrows”].
The slender rods would eventually reach a speed of 3 kilometers
per second if dropped from LEO, their length facilitating the penetration of hard or buried targets.
Because the rods’ trajectory paths from LEO would be many
hundreds of kilometers long, they would require about 5 minutes
to reach their targets, and so it would be difficult to use them against
moving objects. Since no target is likely to be directly under the
platform’s orbital path, each rod would have to be equipped with
a rocket or some other means to position it in orbit. Also, the
rods would need shielding to keep them from burning up during
reentry. The shielding and rocket both add weight and thus increase
the cost to put these weapons into orbit in the first place. Once the
rod has reentered Earth’s atmosphere, it could be maneuvered by
shifting an internal mass or by ejecting gas.
How destructive could such a weapon be? A 100-kg rod of,
say, tungsten falling from an altitude of 460 km and reaching an
impact velocity of roughly 3 km/s would have the destructive force
of a similar amount of conventional high explosives delivered by
bomb or missile. The rod would be more effective than conventional high explosives at penetrating to a buried target, because
the rod’s force would be concentrated and directed in the line of
motion. Higher orbits would deliver greater energies but would
take even longer to strike a target—about 6 hours, for instance,
from geosynchronous orbit.
Conventional warheads delivered from space are yet another
candidate for the space weapons arsenal. (A conventional intercontinental ballistic missile, or ICBM, which also delivers bombs
from above, spends a relatively brief time in space during its trajectory, and is not a space weapon.) One proposal for delivering
large quantities of conventional explosives is the Common Aero
Vehicle (CAV), a robotic hypersonic aircraft much like a miniature
space shuttle. Championed by the U.S. Air Force and the Defense
Advanced Research Projects Agency, the Pentagon’s entrepreneurial R&D wing based in Arlington, Va., the CAV would be launched
into orbit by a land-based missile, aircraft, or some as-yet undeveloped military space plane [see illustration, “Orbital Bomber”].
To attack, a CAV would come down from orbit, reenter Earth’s
atmosphere, and maneuver to its target at speeds as high as Mach
25. The CAV would have one political edge over conventional aircraft: because the vehicle would reenter sovereign airspace only
over the target country, the attacker would need no permission to
fly over other countries.
CAVs could strike hard and deeply buried targets, naval bases,
surface combatants, massed forces, mobile targets, airbases, and
military and civilian infrastructure, to name a few examples. To
strike a target on the other side of the globe would take about 90
minutes. Other advantages of such rapid strikes include having
global reach from the continental United States, the ability to bypass
enemy air defenses, and the absence of risk to pilots or support
staff. However, in comparison with existing airborne alternatives
and missile payloads, the CAV would be costly, and development
would take many years.
Microsatellites, of all the space weaponry now being developed,
are the closest to operational use. Microsatellite “mines” that would
blow up or collide with other satellites could be ready to deploy
within a few years of a decision to do so. That decision might already
have been made, so that deployment could occur within days of a
triggering event.
These small, maneuverable satellites would be launched into
space on rockets or from larger satellites. Once in orbit, they would
be self-powered and -guided. Microsatellites are being developed
today for surveillance, inspection, and other nonoffensive tasks, but
they could also be used as weapons—for example, to attack a far
larger and more valuable satellite by blowing up or simply colliding
with it at high speed. With compact communications, guidance,
control, sensing, and propulsion systems, a microsatellite might
weigh only tens or at most hundreds of kilograms, compared to its full-sized cousins
weighing thousands of kilograms or more [see
illustration, “Mobile Mine”].
Drawing a line between peaceful and hostile microsatellites may be impossible. In
January 2003, the U.S. Air Force demonstrated
its XSS-10 microsatellite, which repeatedly
maneuvered to within 35 meters of a target to
take photographs. Had it been equipped with
a gun instead of a camera, it could have
destroyed the target.
Within a few months, the Air Force is due
to launch the follow-up XSS-11, designed for
“rendezvous and proximity operations”—that
is, meeting up with other satellites to perform
inspections, maintenance, and the like. However, as an unnamed U.S. defense official candidly acknowledged
in an interview with Inside The Pentagon in December 2003, the
XSS-11 could also be used as an antisatellite weapon.
The United States is not unique in its microsatellite capability.
Over the last decade, for instance, researchers at the University of
Surrey, in Guildford, England, have successfully launched a range of
nonmilitary microsatellites, often in partnership with teams from
other countries, and have orbited and tested a “nanosatellite” weighing less than 10 kg.
In a sense, microsatellites are as old as space exploration itself.
Sputnik-I, weighing in at 84 kg, was technically a microsat, and
many of the spacecraft that followed in those early years were similarly small. In the five decades since then, researchers worldwide
have steadily refined microsat components, helped tremendously
by the general shrinking in sensors and circuitry for computers and
communications. At present, a microsat’s guidance and control systems can be miniaturized to considerably less than 1 kg, and can
derive both propulsion and power from solar cells, thus reducing
weight and launch costs.
Although microsatellites are perceived primarily as a threat to
satellites in LEO, they could be adapted to attack assets in geosynchronous orbit as well. A space mine would be effective only if it
were orbiting very close to its quarry, in almost identical orbit.
The space mine would not need to be deployed covertly; there would
be no means of destroying or disabling the mine without also risking the destruction of its much more valuable target, so the mine
poses a similar threat whether its presence is known or unknown.
SHOULD THE UNITED STATES, or any nation for that matter,
weaponize space? The answer depends not simply on the capabilities and limitations of proposed space weapons, but also on the
military objectives. The Rumsfeld commission laid out three objectives in which space weapons might play a role: to defend existing military capabilities in space; to deny adversaries the military benefit of space; and to attack adversaries from or within space.
The last objective is perhaps the most alluring: the prompt and
deadly projection of force anywhere on the globe. The psychological impact of such a blow might rival that of such devastating attacks
as Hiroshima. But just as the unleashing of nuclear weapons had
unforeseen consequences, so, too, would the weaponization of space.
Each of the leading proposed space weapons systems has significant physical limitations that make alternatives more effective and
affordable by comparison.
All orbital systems, including space weapons, share the problem
of moving relative to Earth. Space weapons to be used in a localized
theater of conflict—say, over a battlefield several hundred kilometers across—continuously move with respect to
targets on the ground; a satellite in LEO, for
example, circumnavigates the globe roughly
every 90 minutes. Traveling at high speed relative to the ground, each satellite has a limited
window during which to strike a ground location—typically, 1 or 2 minutes from LEO.
A reasonable response time, then, means
having an overlapping constellation of many
satellites. Straightforward calculations show that
17 identical laser-weapon satellites would be
needed to ensure continuous coverage over a
single location; this number would suffice for
satellites capable of destroying a target up to
3000 km away from the satellites’ ground track.
Fewer satellites would mean less latitudinal
coverage on Earth. One could settle for as few
as seven satellites, for example, if one were willing to limit coverage to a global swath that measures 3000 km on either side of the
equator; this configuration gives coverage, but not without the risk
of a delay (not exceeding 13 minutes) for targets near the far edges
of the swath.
For satellites with a reach shorter than 3000 km, such as kineticenergy weapons, the number of satellites escalates. For a 500-km
range, one would need 600 satellites for global coverage. The main
point is that many weapons need to be orbiting to ensure that just
one weapon is available to strike any possible target at any given time.
A particular challenge for space-based lasers is their vulnerability to countermeasures. As mentioned before, even the highest
power lasers do not penetrate clouds or smoke. Some wavelengths
cannot penetrate Earth’s atmosphere, including those used by the
hydrogen-fluorine chemical laser currently proposed for the spacebased laser for missile defense. For ground targets, smoke pots could
disrupt an attack already in progress.
Vulnerability is increased by the need to keep the laser on target for, typically, tens of seconds at least. The target could move in
an unpredictable path or simply be covered with reflective coating
or paint, which could increase the time required for a successful kill
by a factor of 10 or more. A layer of titanium oxide powder, for
instance, could reflect 99.9 percent of the incident laser energy. Even
a shallow pool of dyed water would offer serious protection. Since
Detonating
a nuclear
warhead in
space would
disable hundreds
of satellites
March 2005 | IEEE Spectrum | INT 7
a 20-MW laser boils water at a rate of 10 kg/s, a pool of water about
3 centimeters deep on the flat roof of a two-car garage would protect
against 100 seconds of illumination by a space-based laser. This all
adds up to abundant opportunity to thwart laser weapons.
Meanwhile, the laser would be burning its supply of hydrogen
and fluorine at a rate of 500 kg/s. Over the course of 100 seconds,
it would consume 50 tons of fuel, for which the launch costs alone
are about half a billion dollars.
The issue of energy requirements warrants a closer look. Today,
the most efficient high-power lasers typically consume 2 to 3 kg of
chemical fuel per megawatt-second. So a pulse of 20 seconds from
a 10-MW laser corresponds to about 400 to 600 kg of fuel per target in the absence of any countermeasures. At current launch costs
of some $22 000/kg into low-Earth orbit, each 20-second laser shot
would cost approximately $11 million.
For a constellation of 17 lasers, each loaded with a 12-shot capacity, the launch cost to maintain on-orbit fuel alone would exceed
$2 billion. Weigh that against a stock of highly effective $6 smoke
grenades, a stray cloud, or a 3-cm-deep pool of water, and this
multibillion dollar weapon system starts to look like a bad deal.
If lasers are prohibitively expensive, might long tungsten rods
used as high-speed penetrators be a relative bargain? Not really. To
guarantee that a single target (located near the equator, to take
the easiest case) could be attacked at will, and not only when a single orbiting rod happened to pass overhead, a distributed constellation of some 40 rods would be necessary, with launch costs totaling some $8 billion.
The additional problems of targeting at supersonic speeds and
coping with the intense heat of reentry demand extremely advanced,
and therefore costly, technologies. Although one can steer the rod
by shifting its center of mass, one would still need to obtain the
error signals to guide the penetrator to the target. Communicating
with the penetrator is complicated by the fact that the surroundORBITAL BOMBER: A robotic hypersonic aircraft
could carry large amounts of conventional explosives to
terrestrial targets. However, basing such a system in space
would be prohibitively expensive.
8 IEEE Spectrum | March 2005 | INT
ing air is heated into a radio-opaque plasma, obstructing even the
reception of GPS navigation signals. Although none of these problems is insoluble, they defy inexpensive solutions.
For attacking hardened or deeply buried targets, the long rods
would not outperform existing missiles equipped with conventional penetrating warheads. That’s because the physics of highvelocity impact limits the penetration depth; basically, too much
energy at impact causes the projectile to distribute its energy laterally rather than vertically. Tests done since the 1960s by Sandia
National Laboratories, in Albuquerque, N.M., confirm that for even
the hardest rod materials, maximum penetration is achieved at a
velocity of about 1 to 1.5 km/s.
Above that speed, the rod tip liquefies, and penetration depth
becomes essentially independent of impact speed. Therefore, for
maximum penetration, the long rods would need to be slowed to
about 1 km/s, thereby delivering only one-ninth the destructive
energy per gram as a conventional explosive—or about 1.5 percent
of the energy the rod had in LEO. The wasted energy would be
immense, and the effort, cost, and complexity of an orbital system would be entirely out of proportion to the results.
For soft targets on the surface, such as aircraft, ships, or even
tanks, the United States already has many quicker, simpler alternatives to space-based kinetic energy systems such as long rods.
Explosives delivered by long-range cruise missile, ICBM, or submarine-launched ballistic missile are all more attractive options.
The space-based common aero vehicle also comes out a loser
in comparison with weapons delivered by ICBM or shorter-range
missile. Although the CAV may take only 90 minutes from launch
to detonation, that would be preceded by as much as 12 hours for
the target to come into range. Recall that an ICBM can get almost
anywhere on Earth in well under an hour. Of course, populating
many orbits with CAVs would reduce the response time, but would
also run up the cost. Aircraft carriers, submarines, and even CAVs
launched on demand by missile would all provide better performance than a space-based CAV.
ANOTHER OBJECTIVE laid out by the Rumsfeld commission was to defend existing military capabilities in space.
While everyone agrees on the desirability of this goal, opinions vary over whether and how space weapons might help.
In framing the debate, it helps to consider the kinds of
threats that existing satellites face. In roughly decreasing
likelihood, these threats include: denial and deception (where
an adversary conceals or camouflages his activities, hiding
a chemical weapons lab within a mundane-looking agricultural fertilizer plant, for example, or using an underground
bunker); electronic warfare (such as the jamming of satellite
signals); physical attacks on satellite ground stations; blinding of satellite sensors with lasers; attacks in space by
microsatellites; hit-to-kill antisatellite weapons; and highaltitude nuclear detonation.
Each threat would affect satellites differently. For instance,
denial and deception thwarts only satellites performing intelligence-gathering missions. And satellites in geosynchronous orbit are less vulnerable to hit-to-kill weapons or a
high-altitude nuclear burst. Other threats, such as electronic
warfare and attacks on ground stations, could degrade the
performance of all kinds of satellites.
Nor would space weapons be equally effective against these
threats. Denial and deception, electronic warfare, attacks on
ground stations, and satellite blinding—the four most likely
threats—would be mounted predominantly from the ground,
and space weapons would offer little or no defense against
them. Moreover, they are low-tech and inexpensive
compared with space weapons.
Space weapons might prove useful against microsatellites, antisatellite weapons, and nuclear explosions—attacks occurring in space and therefore more
difficult to fend off from the ground. For example, a
nuclear warhead detonated in space, even one 100
times less powerful than the 1.4-megaton hydrogen
bomb that the United States tested at an altitude of
400 km in July 1962, would destroy or disable many
of the hundreds of satellites in LEO [see illustration, “Easy Prey”].
The blast wave from such an explosion would be
insignificant, and even the powerful pulse of X-rays
would affect only those satellites near the blast site.
But many of the high-energy electrons from the products of nuclear fission would be trapped in the Van
Allen radiation belts, degrading almost all satellites
in LEO over the course of several months.
By initiating a high-altitude nuclear burst, a country must be willing to forgo its own space assets (or
be one with few such assets to begin with). But the
attack could do significant damage to valuable LEO
satellites, including most military reconnaissance,
surveillance, and intelligence satellites, as well as
MOBILE MINE: Cheap, maneuverable,
commercial and research satellites used for imaging
and stealthy, a microsatellite could creep up
and communication.
on an enemy satellite and explode or collide
The means for such an attack already exist, in the
with it. But if the United States deployed
form of thousands of Soviet-designed Scud missiles.
such weapons, it would open the floodgates
to similar threats to U.S. military and
The Scud-C, for example, sold by North Korea to Syria
commercial satellites.
and other states, has a horizontal range of 600 km with
a 700-kg payload; fired vertically, a Scud-C could reach
300 km. The positions of most large satellites are tracked by amaMicrosatellites could also launch an explosive or projectile. For
teur astronomers and others and readily available on the Internet. instance, a quarry would be unable to elude a space mine hoverAccordingly, even a country with modest resources would be able ing just tens of meters away and equipped with an explosively
to launch a Scud or some other short-range missile on a nearly ver- driven pellet weapon or shaped-charge projectile. The microsat
tical trajectory, arranged so that the apogee is in the path of an could also be programmed to fire if blinded or disturbed.
approaching satellite.
Various defenses to microsats can be imagined. A quarry satelA single satellite in LEO can be destroyed without a nuclear war- lite could be outfitted with sensors capable of detecting small, lowhead: if, for instance, a Scud used a mild explosive or a gas puff to speed satellites, or it might be equipped with specialized defensive
disperse a few hundred kilograms of sand or gravel in LEO. The vehicles (perhaps even a fleet of bodyguard microsatellites of its
cloud of debris, falling only 1 km in the initial 15 seconds, would own) to repel approaching space mines without harming the quarry.
gravely threaten any satellite passing through it at orbital speeds
How easy would it be to detect and track such space mines, and
of about 27 000 km/hr.
thereby thwart their attack? The U.S. Air Force Space Command,
The threat that microsatellites could pose to existing space sys- headquartered at Peterson Air Force Base in Colorado, indicates that
tems is probably greater than their potential benefit to the United it “is responsible for tracking objects larger than 10 centimeters
States as weapons. An adversary microsatellite could use two quite orbiting Earth,” and currently tracks some 9000 such objects.
different modes to destroy a quarry satellite. The first means is
But even perfect tracking would reveal only after the fact which
direct impact: placed in an orbit that nearly intersects with its satellite or launch was responsible for destroying the quarry. A real
quarry’s, the microsatellite could leisurely fire its rocket to convert defense would require additional measures, such as those described
a normal and nonthreatening 100-km miss into a direct collision.
above. And it is unclear, at least to us, how proposed U.S. space
Accelerating just 0.1 km/s (an expenditure of 3 percent of the weapons would protect themselves against such threats.
satellite mass as rocket fuel) will net a 100-km displacement in 1000
seconds—about one-fifth of an orbit period in LEO, and far too lit- IF SPACE WEAPONS ARE NOT OUR BEST HOPE for protecting
tle time for the quarry satellite’s operators to take effective coun- valuable communications, imaging, and other satellites, what are
termeasures. As the microsat approached the quarry, it might deploy the alternatives? One attractive solution that avoids the political,
a “lethality enhancement device,” such as a weighted net, to improve economic, and technical difficulties of space weapons would be
its chances of success. No short-range defense seems possible to reduce our dependence on space assets.
Satellite communication, for instance, typically relies on large
against such a high-speed intercept, unless the quarry satellite were
capable of rapidly maneuvering out of harm’s way, or unless it and expensive satellites, and the loss of even one of these would
deployed confusion devices, such as balloon reflectors, to prevent have a crippling effect. Although some defense satellites do have
the microsatellite from homing in on it. Current satellite systems backups, the majority of U.S. commercial communications and imaging systems have little redundancy. But if communications instead
do not have these protective capabilities.
March 2005 | IEEE Spectrum | INT 9
EASY PREY: Hundreds of commercial,
military, and research satellites now orbit
relatively close by, in low Earth orbit.
Others lie in relatively safer geosynchronous
orbit, visible here as the ring of dots
circling furthest from the Earth.
NETWORKING ON THE FLY: High-altitude
COMSAT
UAVs can supplement satellites during conflicts, relaying
radio signals and intelligence imagery between
headquarters and the battlefield.
Aircraft carrier
Global Hawk UAV
DarkStar UAV
Unmanned aerial
vehicle (UAV)
E-8 aircraft
Front line
Deep-strike
aircraft
Highly defended area
Predator UAV
Headquarters
Troops
were configured in a distributed, load-balancing network of smaller
satellites, an attack on one node, or even several, would do little
harm. Such a strategy would also protect against system failures,
accidents, and other disruptions to satellite communications.
As an alternative to redundancy and distribution, existing communications and intelligence-gathering satellites could be enhanced
temporarily with terrestrial and airborne measures using unmanned
aerial vehicles (UAVs), piloted aircraft, high-altitude balloons, or
even rockets [see illustration, “Networking on the Fly”]. These strategies would also arouse far less international opposition than would
the deployment of space weapons. Such backup systems would also
be more effective in many settings than the satellite system at risk.
10 IEEE Spectrum | March 2005 | INT
Take the Global Positioning System, which currently consists of
28 satellites in medium-Earth orbit. An adversary might have an
interest in denying GPS capability in a particular locale—such as the
battlefield—but rarely in denying the service worldwide. Also, it is
far easier to jam the weak GPS signal across a few hundred kilometers than to destroy several of the GPS satellites in their high orbits.
In effect, a handful of jammers would do as much damage to local
U.S. capability as the destruction of the satellites themselves.
Space weapons would be useless in countering such a scenario.
Instead, within the expected area of jamming, the United States
could deploy a network of short-range GPS transmitters carried by
high-altitude UAVs, balloons, or, if necessary, rockets. Such
“pseudolites,” flying at altitudes of 20 to 30 km, would use an
antenna to distribute a powerful GPS-like signal.
Pseudolites aboard sounding rockets, on the other hand, would
have to be launched a few times a day to maintain a strong signal
and would need a large antenna to focus the energy on a small area.
Either way, the pseudolites would effectively protect the real GPS
network, because the enemy would not achieve its goal by destroying the satellites. In similar fashion, battlefield communications
satellites could be replaced by radio relay transmitters aboard UAVs.
For imaging, UAVs could not only replace satellites, but in many
cases outperform their high-flying counterparts, as recent experiences in Iraq and Afghanistan have demonstrated. To begin with,
UAVs can almost always get at least 10 times closer to an area of
interest; a 20-cm mirror or lens on a UAV at 20 km above Earth
would be equivalent to a 300-cm mirror aboard a satellite orbiting
at 300 km. Furthermore, UAVs can linger over a site of interest,
unlike satellites, and can carry a wider variety of imaging equipment, including optical, infrared, and advanced synthetic aperture radars, which can image through darkness and cloud cover.
Beyond imaging, UAVs can readily track moving targets on the
ground across an area of hundreds of kilometers.
On the other hand, satellites can and do provide global coverage that UAVs can never match. But most military operations are
local. The real threats come from regional disruption, and those
threats can be countered by regional alternatives.
RETURN NOW TO THE THREE POTENTIAL ROLES for space
weapons: protecting existing satellites, denying the hostile use of
space, and projecting force worldwide. It is difficult to identify a
space weapon that is more attractive than its competing terrestrial
alternatives. Offensive space weapons face inherent limitations,
including long distances to targets and high energy requirements,
which suggest in many circumstances a non-space-based alternative, such as forward-deployed missiles and conventional ICBMs.
In nearly every case, space weapons are more complex, more costly,
and less effective than Earth-based weapons.
Moreover, we have seen that there are a number of ways to render military space systems inoperable without destroying the satellites themselves, such as attacks on their ground stations. In such
cases, space weapons would be rendered useless. We have also
argued that satellites could be better defended with redundant systems that would mitigate attacks, or with stand-in capabilities provided by UAVs or balloons above the battlefield.
As for denying adversaries the use of space, this may likewise
be more readily achieved by less-expensive terrestrial alternatives,
such as electromagnetic jamming and the temporary blinding of
adversaries’ reconnaissance systems.
The United States would prefer a world in which it alone had
military space systems, weapons in space, and antisatellite capability. However, such a world never existed and never will. Already,
several states and consortia have autonomous space-launch capabilities, notably Russia, China, Ukraine, Japan, India, and the
European Union. Such groups would likely respond if the United
States took a first step toward weaponizing space.
Consider, instead, a U.S. declaration that it would not be the
first to deploy space weapons or to test destructive antisatellite
systems, issued in parallel with an urgent challenge to negotiate an
international treaty to this effect. From such a position, the United
States could credibly declare that deploying space weapons would
be regarded as a threat to U.S. security and that destruction of a
U.S. satellite would be regarded as an attack on U.S. territory.
Even without space weapons, the United States could respond
to an attack on its satellites with its unmatched terrestrial military
capabilities. Adversaries would expect that a heavy toll would be
exacted as a result of any attack on U.S. satellites; that expectation alone would almost certainly suffice to deter any such attack.
In an all-out shooting war on Earth, we cannot expect that space
would be a sanctuary for military systems supporting the weapons
of that war. But the scenario sketched here, with the United States
leading an urgent effort to ban space weapons and antisatellite tests
or use, would help ensure that a shooting war on Earth would not
be provoked by weapons in space.
This article opened with a fictional incident illustrating the
appeal of space weapons. We will close by describing a possible
outcome of such an incident, to offer a cautionary note about the
risks and possible consequences of deploying space weapons.
On the one-year anniversary of the
destruction of the command and control
center of the rogue nation, a U.S. congressional review commission
releases its findings. The center suffered minimal damage, returning to
75 percent capacity within 30 days, suggesting that the rogue country’s
leadership had been expecting such an assault. Additionally, no illegal
weapons of any kind were found on the airliner in question. Several months
after the incident, one of the six orbiting U.S. space-based laser satellites
inexplicably exploded—causing an international space-debris incident
of its own. This satellite happened to be the same one used against the
launch facility, having thus revealed its location. Suspicions include an
adversarial space mine, but the orbiting clouds of debris tell no tales.
The final conclusion of the congressional commission: the rogue country’s leadership instigated the incident by feeding the U.S. intelligence
machine disinformation. The United States came away having disclosed
its deployment of space-based weapons, to international outcry. Also, the
incident was widely portrayed as U.S. bullying of a Third World nation.
While it is surmised that the smaller country had a hand in destroying a
$20 billion U.S. satellite, its officials rigorously denied any role in the
episode. In the end, the incident was recorded not as a measure of U.S.
superiority in space, but as a U.S. space debacle.
■
12 June 2019
ABOUT THE AUTHORS
Bruce M. DeBlois is director of systems integration for BAE Systems in
Reston, Va. Richard L. Garwin (F) is IBM Fellow Emeritus at the
Thomas J. Watson Research Center, Yorktown Heights, N.Y.
(Correspondence should be addressed to him at [email protected].)
R. Scott Kemp is a member of the research staff of the Program on
Science and Global Security at Princeton University, in New Jersey.
Jeremy C. Marwell is a Furman Scholar at the New York University
School of Law, in New York City. This article is based on work the
authors did while at the Council on Foreign Relations.
TO PROBE FURTHER
For a similar classification of space weapons, see a report by Bob
Preston et al., “Space Weapons, Earth Wars,” published by RAND
Corp., MR-1209-AF (2002) and available online at http://www.rand.
org/publications/MR/MR1209/.
“Report of the Commission to Assess United States National
Security Space Management and Organization,” by Donald H.
Rumsfeld et al., was published 11 January 2001. It is available online at
http://www.fas.org/spp/military/commission/report.htm.
See also “Space Operations: Through The Looking Glass (Global
Area Strike System)”, by Jamie G. G. Varni et al., published by the Air
War College, Maxwell Air Force Base, August 1996.
The feasibility of space-based missile defense was assessed in
“Report of the APS Study Group on Boost-Phase Intercept Systems
for National Missile Defense,” published 15 July 2003. It is available
online at http://www.aps.org/public_affairs/popa/reports/nmd03.cfm.
March 2005 | IEEE Spectrum | INT 11