Escape System May Be Added to Next Shuttle

When the space shuttle Discovery is ready for launch, perhaps as early as Feb. 18, 1988, it will have better brakes, more efficient engines and perhaps a crude escape system for the crew--in addition to redesigned solid rocket boosters, Adm. Richard H. Truly, NASA’s associate administrator for space flight, announced Tuesday.

These are part of more than 400 separate modifications that will make “a true enhancement to safety,” Truly said at a press conference in Washington.

His announcement came just a week shy of the anniversary of the Challenger explosion, which killed all seven crew members 73 seconds after liftoff on Jan. 28.

Escape System Not Certain

Truly said he is not sure if there is enough time to add the escape system to Discovery in time for its scheduled launch, adding that the launch will not be delayed if the system is not ready.

In the post-Challenger reanalysis, NASA ruled out ejection seats and escape pods because either would require major structural changes in the orbiter without assuring crew safety, according to William A. Chandler, NASA’s manager of crew escape systems.

Instead, Truly said Tuesday, a side hatch will be fitted with explosive bolts and the astronauts issued parachutes and survival gear so they can bail out.

This escape route might be used if a launch had to be aborted after the solid rocket boosters have stopped firing, just over two minutes into the flight, and before the shuttle reaches orbital velocity seven minutes later. The crew would bail out only if the orbiter were unable to make it to an emergency landing site.

A major drawback is that astronauts could not escape during the first two minutes, when the booster rockets are firing, or if the orbiter were out of control, because they would be pinned to their seats by the acceleration.

Such an escape system would not have saved the Challenger crew.

Before the Challenger accident, NASA planned for astronauts to ditch the shuttle in the ocean if it were unable to reach an emergency landing site. But the accident showed that “ditching is not survivable” because the orbiter would be destroyed on impact, Truly said.

He said he is still considering a supplementary system in which small rockets would pull the astronauts clear of the orbiter. But he said he is concerned that such “extraction rockets” might create more hazards than benefits.

Safety Lanyard

To use such rockets, each astronaut would lie on a launch ramp at the hatch, and one designated crew member would attach a small emergency rocket to a 10-foot lanyard strapped to each astronaut’s safety harness.

The rocket would be launched with pressurized gas. When it reached the end of the lanyard, it would ignite and jerk the astronaut clear of the shuttle in less than half a second.

Tests in a simulator at Rockwell International Corp. have shown that eight astronauts could escape from the orbiter in about 115 seconds--well below the 200 seconds that might be available, according to Chandler.

Another significant change Truly announced has to do with the orbiter’s three main rocket engines.

The durability of the engines had been a major source of concern even before the Challenger accident.

Turbo-Pumps Critical

The critical components of the engines are the high-speed turbo-pumps that force hydrogen fuel and liquid oxygen from the giant external tank into the rocket chamber. The turbo-pumps were designed to last for about 7.5 hours of operation, the equivalent of 55 flights.

But NASA has had to replace them after every four or five flights because of excessive wear.

Extensive ground tests also have revealed cracked turbine blades, unexplained vibrations and valve failures. A broken turbine blade during launch could cause a catastrophic explosion, while the failure of other pump parts would lead to engine shutdown and necessitate an emergency landing.

The Rocketdyne Division of Rockwell will make about 20 different modifications in the engines before the next shuttle flight, David Winterhalter, NASA’s director of propulsions, said in an interview.

Among the changes: beefing up all the bearings in the turbo-pumps; gold-plating the turbine blades in the fuel pump to prevent embrittlement by hydrogen, and installing dampers on the blades of the oxygen pump to minimize vibrations.

‘Added Margin of Safety’

“These changes aren’t really a safety factor because we know we can use any engine for at least one flight,” Winterhalter said. “They’re simply to give an added margin of safety and to extend (the pumps’) life.”

Last month, NASA awarded Pratt & Whitney a $198-million contract to design new turbo-pumps. But those pumps are not expected to be ready for use before 1991, he said.

NASA also intends to modify the disconnect valve on the 17-inch fuel line that connects the external fuel tank to the orbiter, Truly said.

The valve is designed to close just before the tank separates from the orbiter about nine minutes after launch. But astronauts have long feared that it could close prematurely, shutting off the flow of fuel and necessitating an emergency landing or ditching at sea.

NASA engineers will put a latch on the valve to keep it from closing prematurely.

Brakes Improved

The orbiter’s brakes also are being improved.

Some experts and astronauts long have been concerned that the orbiter’s brakes are not capable of stopping the craft in a short enough distance, according to aerospace expert John Pike of the Federation of American Scientists. The shuttle requires at least 10,000 feet to stop, he said, and most emergency runways are only 10,000 feet long, at best.

Furthermore, the lightweight beryllium brake pads that rub together to provide braking have cracked during some previous landings. Such cracks could lead to complete failure of the braking system.

Pike also noted that the nose gear is designed so that a failure during landing would cause the wheel to turn to one side, which could force the orbiter to veer or spin out of control. Some astronauts reportedly have been so afraid of such failure that they avoided using it during landings. Instead, they steered by applying differing pressure on the brakes.

NASA is replacing the beryllium brake pads with heavier carbon pads, similar to those found on commercial jets, to increase braking efficiency.

Nose Wheel Redesign

The nose wheel assembly also is being redesigned so that a failure would leave the wheel pointed straight ahead, according to NASA’s Wayne Miller, who is in charge of orbiter modifications. But the redesigned assembly is not expected to be available for several years, he said.

Finally, the most significant change in the shuttle system will be in the solid rocket boosters.

It was the rupture of a field joint--the site at which individual segments of the solid fuel rockets are joined--that allowed hot exhaust gases to escape, which ignited the external fuel tank, causing the Challenger explosion.

To overcome this problem, engineers at Morton Thiokol Inc. are adding a metal flange, called a capture feature, and a third O-ring to each field joint.

Now, when the field joint expands on ignition, the capture feature is supposed to compress the third O-ring so that the joint seals more tightly, preventing damage to the other O-rings, Winterhalter said.

Lost Flexibility

At Challenger’s launch, the O-rings lost flexibility because of the cold temperature and did not seal properly. Thiokol had hoped to use a more resilient material for the O-ring, but its engineers recently discovered that the new material deteriorates badly after prolonged exposure to a rust-inhibiting grease that is also used on the field joints, Winterhalter said.

It now appears most likely that the original O-rings will be used after all, he said.

Winterhalter also said that heating tapes will be used in the future to keep keep the O-rings warm and flexible.

Most experts think the redesign of the solid rocket boosters will solve its problems, but a National Research Council committee monitoring the shuttle’s propulsion systems cautioned last week that NASA should be considering alternatives.

“We want them to have something to fall back on if (the redesign) doesn’t work,” said the panel’s chairman, H. Guyford Stever, a top official of the National Academy of Sciences.