Technical issues related to missile defenses are often discussed in isolation, but the technology's performance relative to the "actual" threat is what really determines whether missile defenses are feasible. In fact, the threat is the most demanding and relevant criterion. After all, in war, the "enemy gets a vote," and ignoring the enemy's intentions and capabilities is a fatal mistake. Therefore, the best way to understand technical feasibility is to examine the six major earlier missile defense systems, the technical problems posed by adversaries, and the measures used to offset them.
The Nike and Safeguard missile systems of the 1950s and 1960s had to prove that "a bullet can hit a bullet" (i.e., an interceptor can hit an incoming reentry vehicle or warhead). Even with their low-accuracy radars, that was not a problem. The missiles carried nuclear warheads to shoot down enemy missiles, and the high-altitude nuclear explosion covered a large area. However, Nike's unhardened radars were vulnerable and not expected to survive long during a nuclear war. Safeguard's hardened radars were more survivable but could not discriminate between real incoming missiles and decoys.
For the Nike and Safeguard systems, missiles and warheads were not the problem. The problem was sensors-the ability to find and track the target. Even interceptors armed with nuclear warheads could not kill what their vulnerable and inaccurate radars could not find. Thus, from a technical standpoint, Nike and Safeguard were not very feasible.
The challenge of the 1970s was to develop non-nuclear kineticenergy interceptors and show that these interceptors could also "hit" a bullet (an incoming enemy missile). That required roughly a millionfold improvement in accuracy. This goal was achieved in less than a decade by the Homing Overlay Experiment and other weapons analysis and tests. These developments made it possible to discriminate more effectively between warheads and decoys.
In the 1980s, the goal was to show that a new technology-non-nuclear kinetic space-based interceptors, often called Brilliant Pebbles-could defeat an armada of Soviet missiles, decoys, and other enemy countermeasures. Brilliant Pebbles showed great promise. On June 10, 1984, in a flight test that was part of the Homing Overlay Experiment, a kinetic kill vehicle successfully intercepted a reentry vehicle (warhead) from an intercontinental ballistic missile (ICBM). Because Brilliant Pebbles would intercept missiles in boost phase, they were relatively insensitive to decoys. However, Brilliant Pebbles was not developed. The fundamental opposition to the technology was philosophical and political, not based on technical feasibility. The challenge of the 1990s, after the Iraqi short-range Scud missile attacks during Operation Desert Storm, was to show that interceptors on trucks and ships could defend troops in the field. This was demonstrated by the successful development of land-based and seabased interceptors. In addition, the Aegis Standard Missile intercept of a decaying surveillance satellite in 2008 showed that interceptors are not sensitive to target altitude or speed, so it is valid to combine theater and strategic missile intercepts in determining the overall effectiveness of missile defense systems. Interceptors have been tested successfully more than 30 times.
In the mid-1990s, National Missile Defense (NMD) was stimulated by North Korea's launch of an intercontinental range missile. NMD was based on deployments of the ground-based interceptors, in compliance with the 1972 U.S.-Soviet Anti-Ballistic Missile Treaty, that had been designed to complement Brilliant Pebbles. National Missile Defense, however, could not meet projected threats, so it was not deployed.
The challenge of this decade has been to show that these systems can negate rogue intercontinental missiles. This led to the groundbased missile defense program. The ground-based system has been successful in six of seven tests, not including two non-launches and a target missile failure. The test in September 2007 used largely operational components in other systems that would actually be used to shoot down real missile threats. Indeed, the current deployment of 30 interceptors in Alaska could effectively engage a few missiles out of North Korea. With more interceptors, it could address larger numbers of missiles from that area. With extensions of its sensors, it could protect troops and allies in other regions as well.
There are questions about whether ground-based defenses can deal with the threat of multiple decoys. There are effective defenses against current decoys, but these threats are unlikely to remain static. However, potential defensive developments in advanced concepts for discrimination offer more robust means of sorting real reentry vehicles from the decoys. Such defensive concepts have not been a priority in this decade's programs, so they are still immature, but they could mature by the time enemies try to field more sophisticated decoys.
Each of these systems has proved to be technically feasible, but only about half were successful relative to their threats. Nike and Safeguard could not handle the large threats for which they were designed. Next-generation interceptors demonstrated the ability to hit but not the desired ability to discriminate between warheads and decoys. Brilliant Pebbles appeared to be the one system with the ability to address large attacks, but it lacked political support. Theater missile defense systems ultimately achieved good performance against the limited threats.
If there is a lesson in these developments, it appears to be that feasible missile defense requires a careful balance between available technology and threat and a focused development toward realistic ends, putting politics aside.
While progress has been slow and expensive, it has been real. The lessons learned at each step have been built upon rather than repeated. If there is a concern, it is that this progression has only left the U.S. in a position of rough parity with respect to current missile threats.
Technical progress has been important in advancing missile defenses, but the Missile Defense Agency's flexibility has also been important. The agency created a flexible implementation with the ability to shift people and resources and to reallocate priorities as developments dictated. Such flexibility will likely be required to remain ahead of evolving threats in the future.
Find out more about the U.S. missile defense systems in place and whether or not they are sufficient to protect against a ballistic nuclear missile at the site, 33 Minutes - Missile Defense. The new documentary film about missile defense will be released in February, 2009. Find out all the details at the site, 33 Minutes. You can view the film trailer at the site and also find out more detailed information about missile defense in the U.S.