While space may be ideal for some services, like GPS navigation (above), it’s not the best location for basing weapons intended for use against targets on Earth. (credit: Boeing)

The problems of orbital strike constellations

by Laura Grego and David Wright
Monday, June 12, 2006

Christopher Stone, in his recent essay (“Orbital strike constellations: the future of space supremacy and national defense”, The Space Review, Tuesday, May 30), illustrates the importance of understanding the technical issues related to space weapons. Stone states emphatically that the United States should pursue a space-based global strike system, and early in his article asks, “Why do we seem to have such a negative attitude toward the deployment of orbital bombardment groups?” He suggests that such systems have not been pursued because of political concerns and an inability to envision an aggressive role for space. While there may be some truth to this, even more compelling are the technical problems, as we show in some detail in our report “The Physics of Space Security”.

Briefly, for a space-based weapon to be able to reach a ground target rapidly, it must be positioned close to the ground, in low Earth orbit (LEO) at an altitude of several hundred kilometers. However, satellites in LEO move quickly with respect to the ground, and to ensure that one is in the right place at the right time, a constellation of many satellites would be necessary. Timeliness and number of satellites required play off of each other, but to be competitive with ground-based systems and have a response time of about 30 minutes, one would need some 100 satellites in orbit. Those 100 would provide for a single satellite to cover a target; to have two-on-one targeting or allow two nearly simultaneous attacks on nearby targets would require doubling the size of the constellation, and so on.

While Mr. Stone correctly notes that three satellites in geostationary orbits (GEO) can view the entire equatorial regions of the earth, GEO satellites are 100 times farther from the earth than LEO satellites—much too far to be able to strike the ground rapidly.

Moreover, the intuitive appeal that bombing from space has for many people—that weapons can be “dropped” from above a target—is simply wrong. Objects in orbit stay in orbit unless there is a force to push them back toward the ground. Not only do orbiting ground-attack weapons require a large rocket to get them into space in the first place, they must carry large amounts of fuel (essentially another rocket) to accelerate them back out of their orbit and down to earth. Since launching mass into orbit costs roughly $10,000 per pound, such a constellation becomes very expensive. Moreover, since the weapons and their rockets are orbiting in space for years, reliability becomes a concern.

In reality, space is already used for those tasks it is best suited to, and not those it isn’t. Basic physics dictates this. The long distances and high orbital velocities characteristic of satellites make space-basing a poor choice for missions which require transferring mass back and forth to Earth, especially if it needs to be done rapidly. When it is electromagnetic signals that need to be transferred back and forth—such as for communication, navigation, and observation missions—space-basing is a natural choice.

Mr. Stone pairs his call for space-based global strike weapons with the idea that the United States’ enormous investment in space needs to be protected. While this concern is legitimate, such global strike weapons have at most a superficial relationship to satellite safeguarding. Space-based weapons can do very little to protect satellite systems from being attacked. Satellites systems are visible and easily tracked from the ground, and are vulnerable to many kinds of attack, few of them addressable with space-based weapons. Nations will not be able to reliably protect individual satellites from interference by a determined adversary. As we discuss in our report, the best solution to the issue of satellite system vulnerability is to make satellites less attractive targets and to protect the functioning of the systems they are part of by hardening the satellite systems, distributing the tasks of large satellites to suites of smaller ones, developing the capability to rapidly replace lost satellites, and providing air- and ground-based backup systems for critical capabilities. In addition, the United States should be doing everything it can to strengthen the current taboo against the testing and deployment of destructive anti-satellite weapons by all countries.

Although there may be a desire for space-based ground-attack weapons, there is very little to recommend it.

Laura Grego and David Wright are physicists in the Global Security Program at the Union of Concerned Scientists.

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