'Major step' on the stairway to orbit.

"Major step' on the stairway to orbit

Less than three months after the Jan.28, 1986, explosion of the space shuttle Challeger, there began a bizarre, six-week period that included the launch failures of three different major types of conventional, unmanned rockets, due to as many different malfunctions. First came an Air Force Titan 34D, most powerful member of the U.S. military space fleet, followed by a NASA Delta rocket and finally by European Ariane. Of the lot, only the Delta is so far back on track.

Last week, however, another memberof the grounded group took a partial step toward recovery.

The Titan 34D consists of a two-stage,liquid-fueled main booster with a pair of solid-propellant "strap-ons,' similar to those that have been linked with the Challenger disaster. On Aug. 28, 1985, a 34D failed due to problems with the liquid-fuel portion, destroying its classified payload. The next attempt was made last April 18, with the difficulties presumably under control, but that time it was the strap-ons that failed, only seconds after liftoff, with the same costly result. The 34D's liquid-fueled "heart,' in other words, had yet to be re-proven.

On Feb. 11, the Air Force did just that,launching a classified payload this time with a less powerful rocket called a Titan 3B--essentially the core of a 34D but without the strap-ons. Secretary of the Air Force Edward C. Aldridge Jr. called the event "the first major step in the recovery of the space program,' no doubt joining the Pentagon's collective sigh of relief at being able to continue launching a variety of photographic and electronic-monitoring reconnaissance satellites.

The solid-fuel strap-ons, meanwhile,are undergoing an extensive testing program to confirm that the cause of last year's mishap--the peeling of insulation inside the rockets, different from the leaky seals (still being redesigned) cited in the shuttle's case--is under control before the 34D goes back into service.