A boost phase intercept is a method for destroying enemy ballistic missiles in flight (rant on: and a much more fscking practical method than the fscking BMDO seems wedded to! Rant off). The basics of it are simple. I'll use the U.S. for an example, since that's the nation most likely to first deploy something that does this.

The first condition required for this to work is that you have a fairly good idea of where these enemy ballistic missiles will be launched from. By fairly good idea, I mean a radius of perhaps 1000 nautical miles or so per defense system. The second is that you need to have access to land bases or airspace within that range of suspected enemy launch facilities.

The basics are this: When a launch is detected, your system goes into action and engages the ballistic missile during its boost phase, when it is extremely vulnerable. It is vulnerable for many reasons:

  • It is still moving relatively slowly
  • It is highly visible (a high power rocket motor makes a lot of light and heat)
  • It is in a very fragile state (a fueled rocket booster makes a big bang if you mistreat it)
  • It is easily disrupted (tilt it enough and it'll fall, or at least miss widely)
  • It is not yet over your territory, so any successful intercept will ensure that it doesn't fall on you.
  • As an added bonus, it might fall on the launcher's territory!

Detection is not terribly difficult; the U.S. and Soviet Union spent enormous sums to develop means of swiftly detecting missile launches in inconvenient parts of the globe from space. Even during the Gulf War, before being modified to perform this particular task, the U.S. missile warning systems were able to inform Coalition forces of SCUD launches within minutes, allowing attack warnings to sound at their intended targets. Infrared sensors watch the earth for any sudden, large and accelerating plume. A missile powerful enough to leave the atmosphere vents an enormous amount of energy (that's how it works) which cannot be hidden.

Engaging the target may be done in a variety of ways. One would be to have small, extremely fast interceptor missiles within a few hundred miles; these missiles could, in fact, be quite similar to long-range air defense missiles in existence today. Relatively cheap to make, these types of missiles could probably have a several-minute window where they would be able to catch up to and intercept the outbound missile. They need not actually hit the missile, unlike terminal defense interceptors; high powered fragmentation warheads would be more than sufficient to disrupt a boosting target. One possible system is the NTW, a TLA for Navy Theater-Wide. The U.S. Navy, eager to have its fingers in every budget pie, offers us a VLS-launched version that can be situated just off the opponent's coastline.

Another, more exotic method is to use directed energy weapons to engage the missile. Lasers, masers and the like might be used. These have several advantages. One, they might be made small enough to fit in an aircraft (the U.S. Air Force is already building a version that fits inside a Boeing 747 fuselage for use against theater ballistic missiles). Thus you might not need land-based facilities which are politically and logistically difficult to deploy. Two, they might be fired multiple times, or even (with a sustained beam) track the target. Three, they are zero-time-of-flight weapons; no computation for intercepting the target is required, you don't need to guide them to intercept, and you know immediately whether or not you were successful. On the other hand, they are fragile and at the bleeding edge of technology; only in recent years have lasing methods been developed that have a chance of producing adequate energy for this task. Also, they are subject to atmospheric dispersion and transference (energy diminishing proportionally to the square of the distance travelled, especially through atmosphere,as quanta transfer energy to particles of the medium).

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