Laser Reaches Rocket in Space, Pentagon Says

Defense scientists last week sent a concentrated laser beam from the ground to a rocket in space, demonstrating for the first time that the United States can fire such a beam through the atmosphere and prevent air molecules from distorting and weakening it, Defense Secretary Caspar W. Weinberger announced Thursday.

The demonstration, using a research rocket 350 to 400 miles over Hawaii as a target, appeared to be a significant technical achievement because distortion, or “blooming,” of a laser as it passes through air can totally block the beam.

Potential Weapon

Many weapon applications envisaged for lasers--particularly in the Administration’s Strategic Defense Initiative project, commonly known as “Star Wars”--would place such directed energy devices in space rather than on the ground. From positions in orbit, they would shoot at enemy missiles as they rose through the upper atmosphere and traveled through space.

This was the second successful weapon test of a laser during September. Earlier in the month, a high-energy laser destroyed a large, stationary missile on the ground at White Sands, N.M., demonstrating that the beam had enough power to blast apart the missile section.

Weinberger announced the latest test during a speech at a Philadelphia World Affairs Council luncheon in what appeared to be the start of an Administration campaign to justify continuing its $26-billion “Star Wars” research effort in the face of intensified Soviet attacks.

The Pentagon chief charged that the Kremlin--despite its complaints about U.S. research on missile defense--has long rejected the idea of nuclear deterrence through mutual vulnerability of both sides to offensive weapons. He said that the Soviets’ extensive buildup of offensive weapons, together with large expenditures on strategic defense, requires an American “research program into all forms of strategic defense.”

Weinberger broke no new ground in repeating the Administration’s rationale for “Star Wars.” But the timing of his address and the scheduling of a high-level press briefing on it today indicates that the Administration is mounting a counterattack to prevent Moscow’s arms control offers from creating public pressure to cancel the controversial project.

Soviet leader Mikhail S. Gorbachev confirmed in Paris on Thursday that the Kremlin has offered to trade a 50% cut in offensive nuclear weapons on both sides for a total ban on “space strike arms,” meaning anti-satellite and anti-missile space weapons.

Today’s briefing will provide details on Soviet efforts to devise space defenses. The briefers will be Paul H. Nitze, the Administration’s chief arms control adviser, and Richard N. Perle, assistant defense secretary, who is one of the most skeptical officials in the Administration on arms control.

The latest laser success, which Weinberger interpolated into his speech, came from a test Sept. 27 in which a Carrier-Malemute research rocket, 24 feet long with a maximum span of 5 feet, was illuminated with a low-power, visible laser.

Mirror Adjusted Beam

In that experiment, he said, “we succeeded for the first time in demonstrating our ability to track a sounding rocket in space with a low-power visible laser after adjusting the beam for atmospheric distortion.”

In a similar test in July, the instruments on the target rocket failed to send back information on the laser beam.

To correct distortion of the beam, engineers have developed a flexible mirror that, taking orders from computers, distorts the beam at the start of its journey to compensate, or correct, in advance the dispersing effects of the air molecules.

This achievement was considerably more important than tracking the target rocket. In a test involving the shuttle last summer, the same laser in Hawaii showed that the beam could point and track a moving space vehicle.