Others have filled in the void created by the U.S. Government's lack of initiative.  For some, including the governments of Russia and China, the centerpiece of a new diplomatic initiative should be a ban on weapons in outer space.

After the Bush administration discarded the Anti-Ballistic Missile Treaty, Moscow and Beijing dipped into the old Soviet playbook to propose a draft "Treaty on the Prevention of the Deployment of Weapons in Outer Space."  In this draft treaty, space weapons are defined as "any device placed in outer space, based on any physical principle, which has been specially produced or converted to destroy, damage or disrupt the normal functioning of objects in outer space, on the Earth or in the Earth's atmosphere."  This draft treaty goes on to state that, "A weapon shall be considered to have been ‘placed' in outer space if it orbits the Earth at least once, or follows a section of such an orbit before leaving this orbit, or is permanently located somewhere in outer space."

There are many problems with making a ban on space weapons the centerpiece of a new diplomatic initiative. To begin with, the most pressing threat to satellites and space flight at present is space debris, and the worst debris-causing event in low earth orbit has been caused by a Chinese anti-satellite (ASAT) test.  The draft Russian and Chinese text does not define ground-based ASATs as "space weapons" - a gaping omission.

The Russian and Chinese draft treaty is problematic in many other respects, as well.  For example, unless there are common understandings on whether a multi-purpose device has been "specially produced or converted" so as to qualify as a space weapon, the ban proposed by Moscow and Beijing has no practical effect.

How might observers conclude that an object has been "specially produced or converted" to serve as a space weapon?  One way would be to inspect satellite payloads, an idea first proposed by President Dwight D. Eisenhower.  But space-faring nations are unenthusiastic about permitting prying eyes to inspect sensitive payloads before they are launched.  A few space-faring nations do, however, have the ability to observe closely some space objects.  They can also infer the purpose of space objects from their form, placement, and behavior in orbit.  But it would nevertheless be a stretch to assume that common understandings could be reached on the purpose of non-inspected space-spaced objects.

The same problem applies to ground-, sea-, or air-based capabilities that could be used to attack objects in space but which have other military applications.  For example, ground-based interceptor missiles could be used for ballistic missile defense as well as for ASAT purposes. It is unclear whether externally observable differences could help distinguish satisfactorily between these uses, or whether such differences would have any credible meaning.

Another problem arises in limiting an agreed definition of space weapons to those with destructive effects.  Many close observers of military space programs now assume that the most destructive and irresponsible means of destroying satellites - by means of kinetic energy ASATs or nuclear detonations - are also the least likely to be carried out in crises or warfare, precisely because they are so escalatory, indiscriminate and long-lasting in their effects. ASAT weapons using nondestructive effects, such as cyber and jamming attacks, are far more likely. It will be very hard to include these capabilities in any workable definition of a space weapon. 

A treaty banning Cold War-era "space strike weapons" tackles only a small subset of the problem - one which is not likely to materialize and yet which retains fervent supporters on Capitol Hill.  Trying to come up with a broader treaty definition of space weapons is likely to be an unrewarding exercise.  An inclusive definition would foreclose essential military capabilities, while a limiting definition would allow many kinds of latent ASAT systems to run free.

How nations act in space matters far more than how they define space weapons. There are other, far more realizable ways to strengthen norms for responsible space-faring nations - including the norm of not using satellites for target practice.

Over the past two decades, Iraq, Iran and Libya have tried to interfere with satellites.  Is this a practice that responsible space-faring nations wish to emulate?  The European Union has endorsed the Stimson Center's proposed norm of "no harmful interference" against space objects. Yes, this invites a debate over the definition of "no harmful interference. But reaching a reasonable conclusion on this subject is far easier than trying to define a space weapon.

Michael Krepon is the co-founder of the Stimson Center and the author of "Better Safe than Sorry: The Ironies of Living with the Bomb" (Stanford University Press, 2009).

A version of this article first appeared in the March 29 issue of Space News.