CAPE CANAVERAL, Fla. -- The space shuttle's landing gear system is being modified to reduce the tremendous stress of touchdown and to minimize the generally minor but costly brake damage that has marred 16 of 17 landings.
Top NASA officials recently decided to activate a dormant system aboard the shuttle to let pilots steer the ship with its nose wheel, taking pressure off the four main landing gear brakes and lowering the potential for damage.
Because of brake damage suffered by the shuttle Discovery April 19 during its landing at the Kennedy Space Center in a stiff crosswind, engineers are debating whether to divert upcoming shuttle flights to Edwards Air Force Base, Calif., until nose-wheel steering can be implemented later this year.
Concern about the damage to Discovery and about crosswinds prompted NASA to land Challenger at Edwards on May 6 where the broad, smooth lakebed runways offer plenty of margin for error.
But engineers say the shuttle's brakes have earned an undeserved reputation for poor reliability. Tom Moser, a top NASA engineer in Houston, said the lightweight brakes are tough enough to handle the job and that the shuttle has stopped safely every time.
'We've got a system that's got the capability, but we've got some problems we need to sort out, those mechanical and temperature problems,' he said.
B.F. Goodrich of Troy, Ohio, began designing the shuttle brakes in the early 1970s -- long before engineers knew precisely what forces the system would experience during an actual landing.
Technology existing at the time was used, including carbon pads and beryllium discs to absord the hellish heat generated as the 100-ton shuttle rolls to a stop after landing at more then 200 mph.
NASA engineer Raymond Bradley said of 68 brakes used on 17 missions to date, 27 suffered no damage, 27 others suffered very minor damage and 14 suffered 'significant' damage with cracked rotors or stators -- the discs that absorb the braking energy.
A set of shuttle brakes costs about $800,000 and NASA spends an average of $50,000 after each flight to tear down the brakes, inspect them to determine which are damaged and to make repairs.
The trouble is, technicians do not know what is causing the damage. It could be a problem with the brakes, the hydraulic systems that power them, control systems or a combination of those and other factors.
'We have at this point conducted four years of almost continuous testing on the brakes,' said David McClure, a spokesman for Goodrich. 'We've done virtually every test that we ... can dream up to test the brakes and we have not been able to duplicate the damage.'
Special instruments were mounted aboard Challenger last October to provide detailed information about the brake system during landing and similar instruments will be mounted aboard Discovery.
Goodrich engineers also expect approval next month of a program to simulate forces experienced by the entire landing gear system in a bid to pinpoint the problem.
The two brakes on the shuttle Discovery's right landing gear locked up and a tire blew out after commander Karol Bobko used varying brake power during the crosswind April 19 to bring the spaceship back to the Florida runway's centerline.
With the wind blowing from the right, Bobko applied about 40 million foot pounds of energy to the shuttle's right-side brakes -- twice as much as on the left side -- to steer the big space freighter down the runway.
Nose-wheel steering should alleviate some of the landing stress, but the plan cannot be implemented for several months because the steering system already in place aboard the shuttle must be modified to allow backup hydraulic power and computer control. The steering system has never been used.
'With nose-wheel steering, it allows the pilot to be more relaxed and to use the brakes only when he needs them and we would expect less damage,' Bradley said. 'It'll reduce the requirements for differential energy left to right. The lower the speed you put on the brakes the better off you are.'
Bradley said brake damage classified as 'minor' generally is so slight it would defy detection by anyone other than an expert.
'The type of damage that we're getting is not that great to get us all the bad publicity that we've been getting,' Bradley said. 'We define failures differently than everybody else.'
He said brake lockups cannot happen at speeds greater than about 60 mph because the shuttle's momentum would simply shear away any broken parts that might otherwise hamper a wheel's rotation.
Only in two instances -- Discovery's April landing and the shuttle Columbia's fifth touchdown in November 1982 -- did the damage result in locked brakes and then only when the shuttle was creeping to a stop.
Other options to reduce brake damage being assessed include smoothing out the relatively rough runway at the Kennedy Space Center and increasing hydraulic pressure in the front wheel strut to raise the shuttle's nose slightly. That would reduce the weight on the main landing gear by increasing the ship's lift.
