WASHINGTON — The National Aeronautics and Space Administration announced Wednesday that it has set Aug. 4 as the new target date to launch a U.S. space shuttle on the first mission since the Challenger tragedy.
The announcement came on the eve of the second anniversary of the worst accident of the space age and shortly after plans were unveiled for a memorial honoring the seven crew members who died as a fireball destroyed the shuttle and an additional seven astronauts who have died in training and aircraft accidents.
As the space agency disclosed its new launch plan for the shuttle Discovery, program officials told Congress that they have completed their investigation of last month's test failure of a redesigned shuttle booster rocket and have satisfied themselves that two other potential problems discovered in recent days are under control.
"We did have a hiccup," Richard H. Truly, NASA's associate administrator for space flight, told a House subcommittee as officials reported on the December test mishap. "We got bit on that design, and it cost us a couple of months."
Says Program Is 'Stable'
But he said the troubled shuttle program is now "stable" and once again progressing "extremely well" toward a return to flight.
"We are going to take time to look back," he said, referring to today's second anniversary of the Challenger accident. "We, collectively, will take time to remember that date, but the flags are back at full staff. . . . That is what our friends would expect of us."
Initially, NASA had planned to launch the shuttle again in June.
But after a full-scale test firing of the shuttle system's redesigned booster in December, engineers discovered that a carbon "boot ring" in the rocket's nozzle assembly had failed.
Officials said their investigation has confirmed that the failure actually occurred about two seconds after the huge motor stopped firing, meaning that the failure would have had no effect had the rocket actually been in flight.
Two Designs Produced
In qualifying the booster for flight once again, engineers for NASA and Morton Thiokol Inc., the booster rocket contractor, produced two new nozzle assembly designs with a boot ring to better protect an area that had shown some "distress" in eight of the 25 shuttle flights before the accident.
Experts thought that the design used in the December test would be a further improvement.
But in view of the failure, they said they will now use the first new design, which was successfully tested last August.
Under plans announced Wednesday, the booster will be test fired three more times before Discovery is launched on a four-day mission to be highlighted by deployment of a new tracking and data relay satellite.
Truly said that the test firings at the Morton Thiokol plant outside Brigham City, Utah, are scheduled for April 7, June 9, and July 6. The April exercise will use flaws purposely introduced in redesigned seals to test backup systems and the June firing will test the booster's safety margins.
The final test will use a full-scale production motor rather than a rocket designed specifically for ground testing.
New Inspection Techniques
Announcement of the target date for launch was delayed two days while officials reviewed two new potential problems turned up by sophisticated new inspection techniques.
Ultrasonic scanning of the skirt surrounding the booster rocket nozzle turned up two flawed welds and required a further inspection of all of the 30 skirts produced so far.
Tuesday, a small flaw was detected in a skirt to be used on one of the boosters for the Discovery launch.
Marshall Space Flight Center Director J. R. Thompson said Wednesday that analysis of the small "void" in the latter weld had determined that "we've got plenty of margin in that part" and that the weld poses "no problem." Officials said that any flaws found in the other skirt welds will be repaired.
Still under study is a faulty weld in a turbo pump, discovered when engineers disassembled a test version of the space shuttle's main engine. Truly said that evaluation of "high use parts" in test engines is continuing but that the assessment has no "schedule implications."
Coincides With Unveiling
The space agency's outline of its latest plan to get the civilian space program moving again came shortly after the design for the $4-million astronaut memorial at the entrance to Kennedy Space Center was unveiled.
San Francisco architect Paul Holt said that it will feature a "space mirror" composed of granite slabs in a framework designed to track the sun. Sunlight will be reflected by mirrors through "stencils" so that visitors will see the names of the fallen astronauts projected in the sky above it.
At NASA's field centers across the country, flags will be lowered to half staff today, and at the moment of Challenger's ill-fated flight, there will be 73 seconds of silence, corresponding with the time after launch that the explosion occurred.