Original URL: http://www.theregister.co.uk/2010/10/25/altb_test_fluff/

US raygun jumbo fluffs another test missile-blast attempt

Blaster-biggun in Nork shot splash cockup

By Lewis Page

Posted in Science, 25th October 2010 14:10 GMT

The United States' enormous jumbo-jet-mounted raygun, the Airborne Laser Testbed (ALTB), has suffered another embarrassing test failure. During an attempt to beam down a target missile off the Californian coast last week, a technical hitch saw the 747's blaster cannon fail to fire up.

Warfare of the future as foreseen by the Missile Defence Agency. Credit: Boeing

It was all going to be so cool ...

According to an MDA statement (pathetically headlined "Airborne Laser Test Bed Exercise Conducted"):

The objective of this mission was for the ALTB to destroy a solid-fuel, short-range ballistic missile while its rocket motors were still thrusting.

The Terrier Black Brant target missile was launched successfully. Preliminary indications are that the system acquired and tracked the plume (rocket exhaust) of the target, but never transitioned to active tracking. Therefore, the high energy lasing did not occur.

Program officials will conduct an investigation to determine the cause of the transition failure. The intermittent performance of a valve within the laser system is being examined.

Originally the ALTB, then known as the Airborne Laser (ABL), was expected to attack long-range intercontinental ballistic missiles (ICBMs) able to deliver nuclear weapons to the continental USA from far afield.

The idea was that a fleet of ABL laser-jumbos could patrol within raying distance of enemy missile fields in North Korea and burn down ICBM rocket stacks as they soared upward. This is a good time to blast an ICBM, as once it is out of the atmosphere the warhead(s) will separate from the upper stage. Identifying the actual warheads among a "threat cluster" (also including bits of upper stage and possible purpose built decoys) is difficult and striking at them is more so. Shooting them down as they re-enter at hypersonic speed is also very challenging.

Thus it could make sense to deal with the nukes in job lots while they are still moving slowly and while they are attached to a big, easily identified rocket stack spewing fire from the bottom.

But this means striking from hundreds of kilometres away very quickly indeed - the reason the lightspeed laser was given the job.

Inconveniently, however, North Korea has failed to develop a working ICBM - and though the rogue state is thought to have conducted nuclear explosions, it remains a long way from having warheads that could be mounted on an ICBM even if it had one. Other countries of concern would be difficult for ABLs to tackle, as putting the laser-jumbos within range of the launch sites would mean incursions into national airspace - perhaps triggering the very attack the rayguns were intended to prevent.

Then the incoming Obama administration cut funding to the Missile Defence Agency - in particular for the ABL, cancelling plans for the rest of the fleet and downgrading the single prototype craft to an experiment. Hence the name change to ALTB.

Thus it is that recent ALTB tests have seen the raygunship engage targets simulating shorter-ranging missiles of the sort actually possessed by rogue states, in an attempt to demonstrate real-world relevance for energy weapons - and to save cash compared to pricey ICBM-type targets.

The ALTB did manage to blast a missile in February: but the next test, repeatedly postponed by technical glitches, was a failure. The second test was at much longer range than the first, and was thought to have failed due to difficulties in holding the multi-megawatt hellray on the soaring rocket. This is one of the most difficult engineering challenges implicit in the building of the raygun - holding a narrow beam precisely on the target through scores or hundreds of kilometres of variable, beam-warping atmosphere.

The ALTB achieves this in part by use of a low-power tracking laser, which is used to sweep the sky near the heat signature of the boosting target. Once the aiming laser is locked onto the missile (the plane knows this by looking for its light reflected back off the rocket's hull) the full-bore megawatt beam knows where to point and can be fired up. (The full-fat ray can only be kept lit for a sharply limited amount of time, so it can't be used to get a lock on itself.)

This time, it seems that the ALTB didn't even manage to get the aiming laser locked on, so the main beam couldn't light up. The test programme would appear to be making progress backwards, rather than forwards.

The USA may deploy energy weapons in the foreseeable future - but all the indications are that they will use different technology to the ALTB's, and be carried by different platforms. The dying struggles of the raygun jumbo are probably of only limited relevance to the future. ®