In his speech on defense and foreign policy at South Carolina’s Citadel Military Academy on October 7, former Massachusetts governor Mitt Romney said: “I will begin reversing the Obama-era missile defense cuts and prioritize the full deployment of a multilayered national ballistic-missile defense system.” If conservatives hold him to this promise, it will be a significant step towards fulfilling the goal of making nuclear weapons “impotent and obsolete” that Ronald Reagan laid out in his famous March 1983 “Star Wars” speech.

The key word that Romney pronounced, which heartened missile-defense advocates and almost certainly disturbs the opponents of such defensive systems, is “multilayered.”

Once launched, a long-range missile such as an ICBM creates three basic opportunities for a missile-defense system to knock it out. The first and most important is the “boost phase,” just after launch, when the missile is firing its rocket engines and giving off a large amount of easily detected heat. The second targeting opportunity is the “mid-course phase,” when the missile has deployed its warheads and its decoys. This is the most difficult targeting problem that a defense system must solve. It is also the phase during which our currently deployed interceptors, the ones in Alaska and California, are designed to work. The third and final phase is called the “terminal phase,” when the warhead enters the atmosphere and dives toward its target. This is the second-hardest missile-defense problem to solve, because the warhead may maneuver as it approaches its destination.

A multilayered missile defense will use a variety of different systems to try and kill the missile and its warhead during each of these phases. Obviously, if a missile is caught and destroyed during the first phase of its flight, the result is better for all concerned. During the Reagan and George H. W. Bush administrations, this goal led to the so-called Brilliant Pebbles program of space-based heat-seeking interceptors, designed to hit missiles in the boost phase. The program was canceled by Bill Clinton and Les Aspin in 1993. At the time, Aspin reportedly said that he was going to “take the stars out of Star Wars.”

Since then, there have been several efforts to develop a non-space-based boost-phase interceptor system. None of them have been satisfactory, since they all require the interceptor to get as close as possible to the target missile and then chase it after it has been launched. As they used to say in the days of sailing navies, “a stern chase is a long chase.”

From orbit, however, an interceptor does not have to follow its target; instead, it dives onto it. Brilliant Pebbles relied for its effectiveness on the law of gravity, not on having a bigger rocket engine.

George W. Bush never revived Brilliant Pebbles, as the arms-control establishment, liberals in Congress, and the forces of inertia inside the Defense Department successfully blocked any attempt to restart the program. Bush was content to fund the Clinton-designed, ABM Treaty–compliant National Missile Defense mid-course intercept system, which is what we have now. If Romney is elected, and if he is serious about defending the homeland from missile attack, he will have to be ready to spend considerable political capital, as well as time and money, to make it happen.

One promising program, the Miniature Kill Vehicle (MKV), which was intended to be launched in large numbers from the ground, was killed by the Obama administration. But a space-based version of MKVs, which are about the size of a loaf of bread, could make space-based missile defense a reality within the first term of a Romney presidency.

Earlier this year, Rep. Trent Franks (R., Ariz.) persuaded the House Armed Services Committee to allocate $8 million for the Defense Department “to conduct a study examining the technical and operational considerations associated with developing and operating a limited space-based interceptor capability.” It is doubtful that this will survive the legislative process, and even if it did, the forces inside the Pentagon that have long opposed space-based missile defense will fight hard to ensure that the results of the study will be negative. Still, the mere fact that a few gutsy members of Congress have not given up on effective missile defense shows that if Romney wants to fight this fight, he will not be without allies.

Make no mistake: If Mitt Romney is serious about a multilayered national missile defense, he is going to have a major struggle ahead of him. He will have to be prepared to junk Obama’s National Space Policy on January 21, 2013, and will have to fight hard against the arms-control establishment, the liberals, the Russians, the Chinese, and probably also the Europeans. (Officially, the EU is terrified of a so-called and much-hyped “Arms Race in Space.”)

Even before the election, Romney will come under serious pressure to promise not to deploy weapons in space, which means conservatives will have a chance to see how he stands up under liberal assault. This should be interesting.

— Taylor Dinerman is a senior editor at Hudson New York.