WASHINGTON — The chief of the U.S. space shuttle program said Monday that the National Aeronautics and Space Administration is taking a considered risk of a far longer hiatus in shuttle flights by shipping newly modified booster rockets to the Florida launching site before completion of their scheduled test firings.
But, added Richard H. Truly, NASA's associate administrator for space flight: "We are in the real world on a real schedule." To wait until the final test is completed on a backup design now set for use on shuttle boosters, he said, "would delay the launch of the space shuttle to sometime in 1989 or later."
The new booster rockets are manufactured by Morton Thiokol in Utah. Truly was addressing concerns that their shipment before they are fully tested may cause more delays in the long run because the manufacturer would not be able to send further-modified rocket segments to Florida until June or later.
'Doing the Right Thing'
"The only risk here is schedule. I believe we are certainly doing the right thing," Truly said. He made his comments as NASA officially announced that, in the wake of a December booster test problem, it will adopt a design previously tested and press ahead.
With the next test firing scheduled for late March, officials said that they will go ahead and ship solid rocket boosters for the shuttle Discovery to Florida as soon as they can be modified to remove a "boot ring" that failed in a Utah test firing last month.
Truly said this means that the Discovery's launching on the first manned space flight since the Challenger disaster could occur no earlier than July 15 and more likely would be in August. An official date is expected to be set in about two weeks.
The latest delay in the beleaguered shuttle program occurred when engineers discovered that a "boot ring" protecting the bearings that swivel the booster rocket's engine nozzle had failed in the December test.
Removing 'Boot Ring'
An earlier design, test-fired last August, performed perfectly and will be adopted. The aft segments of boosters already manufactured to launch the Discovery mission are to be modified, eliminating the suspect "boot ring" that deteriorated in the December test.
Marshall Space Flight Center Director J. R. Thompson told reporters Monday that the cause of the failure has not been pinned down. He said he suspects that it was caused by a flaw in the manufacturing of the 8-foot carbon fiber ring that apparently failed about a second after the two-minute test.
During the firing, the ring is subjected to temperatures of about 4,000 degrees, and Thompson said he believes that it was the thermal effects and not the purposely vigorous swiveling of the engine nozzle that led to the failure. During the test, the engine nozzle was swiveled to create stresses far exceeding anything expected in a shuttle flight.
In the wake of the "boot ring" failure, there had been speculation that the first post-Challenger flight might be delayed for months, suggesting that the space agency would not launch in the period before the presidential election.
Political Concerns Denied
But NASA Administrator James C. Fletcher said Monday that political considerations in no way will enter into the decision of when to launch the shuttle on its much-anticipated return to service.
"The next launch of the space shuttle will be determined by one consideration, and one consideration alone," he said. "We will fly when we are ready. I say that because there has been some talk in Washington that political considerations--the national conventions and the presidential elections, for example--could affect the timing of the next shuttle flight.
"I can tell you that, as long as I'm in this job, politics will continue to take a back seat to readiness, and readiness means that the shuttle will fly only when it's as safe as we can make it," Fletcher added.
The additional delay raised a possible complication for launching of the Magellan spacecraft to map the planet Venus. Until the most recent delay, Magellan had been scheduled to be aboard the fourth shuttle flight, in April, 1989. To make its encounter with the planet, the spacecraft must be launched within a 21-day period beginning April 27.