HEADLINE: THE SHUTTLE INQUIRY: NASA DISCUSSES EVIDENCE; INVESTIGATORS EXAMINE DATA FOR POSSIBLE BOOSTER FLAMES
BYLINE: By WILLIAM J. BROAD, Special to the New York Times
DATELINE: CAPE CANAVERAL, Fla., Feb. 2
Faulty seams, flawed casings and poorly packed fuel are among the flaws that could explain a rupture in a solid-fuel booster rocket on the space shuttle Challenger, which is viewed by many as the cause of the explosion Tuesday that destroyed the Challenger.
On Saturday night the National Aeronautics and Space Administration made public a videotape of the flight showing what it called an ''unusual plume'' on the right-hand rocket. NASA spokesmen have refused to speculate about the significance of the plume or whether it indicated that the wall of the booster rocket was ruptured. On the videotape the plume appeared to be a spreading, feathery orange light.
But sources close to NASA's investigation of the accident and many independent aerospace experts say they believe that a rupture of the rocket's wall emitted flames that ignited the adjacent external fuel tank of the shuttle, causing the explosion that destroyed the external tank and the Challenger.
Today Dr. William R. Graham, head of the National Aeronautics and Space Administration, said a great many possible flaws were being considered by investigators looking for the cause of the plume. He also acknowledged that it was conceivable that two or more unusual factors may have combined to produce the plume.
For many years rockets employing solid fuel, though simple and efficient, were considered too dangerous to be used for manned space flight because of their construction. They are like big firecrackers: Once started, they cannot be stopped. In contrast, rocket engines that run on liquid fuels can be throttled back and even stopped.
Near-Disaster in '83
In the quarter of a century since man first ventured into space, only the American shuttle program has used solid-fuel boosters to propel humans. In October 1983 a shuttle flight almost encountered disaster when the nozzle on one of its boosters came within one-fifth of an inch of burning through. If it had, the shuttle would have begun spinning catastrophically, like a pinwheel. The problem was found after the shuttle returned to earth.
But no serious malfunctions in the solid-fuel booster rockets occurred until their 25th use, on the Challenger's last flight.
A shuttle's two solid-fuel booster rockets, each 149 feet long and 12 feet in diameter, provide the main power to lift a shuttle and its external liquid-fuel tank to a height of 27 miles. The shuttle boosters are the largest solid-fuel rockets ever flown and are the first designed to be re-useable.
Each booster rocket carries 1.1 million pounds of propellant. The battleship-gray fuel has the consistency of a hard rubber eraser. The rocket's body is built in four separate segments, which are put together after they arrive at the Kennedy Space Center. Through the center of the fuel packed in the finished booster runs a hollow channel. At ignition, a flame at the top of the booster ignites the fuel surrounding the channel, and the thrust out the rear of the rocket helps push the shuttle skyward.
Boosters Were Blown Up
There is a severe shortage of information about what happened in the booster rockets Tuesday. The boosters had few sensors, from which information could have been gathered for automatic transmission to the ground. Further, range safety officers blew the rockets up by remote control when, having separated from the shuttle in the explosion, they threatened to hit populated areas.
According to Sam T. Beddingfield, who retired in November as deputy director of shuttle management projects at the Kennedy Space Center, the solid-fuel rocket boosters have three sensors to measure pressure in the combustion chamber. He said that in early shuttles there was a fourth presssure sensor. There are no temperature sensors inside the rockets or on their skins.
The dearth of information is reportedly making it difficult for investigators to pin down unambiguously the cause of the problem in the rocket, but the three main possibilities are bad fuel, faulty casings and poor seams.
At the top of the booster rocket the fuel is arranged around the central channel, which is in an 11-point star pattern to give it more surface area so the fuel will burn faster and produce greater thrust. According to some aerospace experts, the fuel in one of the rockets used Tuesday might have been contaminted or improperly distributed, creating uneven burning and great stresses on the rocket's shell.
Rocket Seams Not Welded
The casings of the booster rockets used Tuesday were two tons lighter than those used in the earliest shuttle missions. According to engineers at Rockwell International, which builds the shuttles, the thickness of the steel casings has been reduced by two to four hundredths of an inch.
The third theory, which is receiving some of the closest attention, concerns the seams between the booster's four main segments. Because the fuel is in the segments when they arrive at the space center, they cannot be welded together. Instead they are connected by more than 170 steel pins at each joint, with high-pressure seals where the segments are joined.
According to aerospace experts, the segments could have been incorrectly connected or the seals flawed. Technicians working on used boosters have reportedly sometimes found soot from inside the rocket that had got though the primary seal.
Any of these possible causes could have been compounded by enviromental factors, such as air temperature, which was in the 20's the morning the shuttle was launched.
In addition, the rupture in the booster appeared in the Challenger's ascent just as the shuttle was going though its point of ''maximum dynamic pressure,'' the point when its great speed and vibrations from its rockets and engines combine to put the greatest stress on the shuttle structure.
Report Criticized Technicians
Another factor could be problems with technicians working on the boosters. A report in Florida Today, a newspaper published in Cocoa, Fla., said today that the Challenger's left solid-fuel booster suffered an accident in November, and that a subsequent NASA investigation was critical of workers and equipment. The report, according to the paper, said, ''The failure to follow the approved procedure was the principal cause of this incident.'' A booster segment was damaged in the accident at the rocket assembly facility at the Kennedy Space Center. NASA officials said that the segment had been replaced before Tuesday.
Other factors are undoubedly being considered as NASA's interim investigation panel examines the available evidence.
''There is a very large structure of what we call 'fault trees,' things that can affect other things, things that can go wrong,'' Dr. Graham said today on the ABC News program ''This Week.''
''There are so many different possibilities,'' he added. ''There are many issues that have to be taken into account.''
Inside a Rocket Booster
Two reusable solid-fuel rocket boosters, attached to the external fuel tank, provide 80 percent of the thrust required to lift the shuttle off the pad. The remaining 20 percent comes from the orbiter's three main engines. The four fuel sections of each booster arrive unassembled at Kennedy Space Center, where they are joined with one-inch steel pins placed two inches apart around the circumference of the rocket. The entire joint is then covered by a steel band. External fuel tank Boosters Ignition Sequence xhrrAbout 4 seconds before liftoff, the liquid-fueled engines on the orbiter are ignited. When they reach 90 percent of power, a computer command ignites the solid boosters, which cannot be shut off. The shuttle lifts off. It is extremely difficult to abort the mission successfully in the first two minutes of flight while the boosters are attached to the external fuel tank. The burning of fuel begins at the top, where the igniter is located. Each booster has a hollow core surrounded by solid fuel; this core allows fuel to burn from the inside out. The top fuel segment is cut in a star-shaped pattern. This pattern burns more fuel, which creates more thrust in the first seconds of flight. The fiery blast from this section ignites the other three fuel cylinders, which burn simultaneously. When the fuel is exhausted, the boosters are jettisoned into the Atlantic Ocean, where they are recovered by the Navy, then reused up to 20 times. Height: 149 feet Diameter: 12.2 feet Weight: 1.3 million pounds Solid fuel components: Aluminum perchlorate, powdered aluminum, iron oxide and a plastic binder. They are mixed, poured into a mold with a hollow core and allowed to harden. Maximum tempurature: 3,000 degrees Fahrenheit Maximum thrust: 3 million pounds 20 seconds after liftoff Rocket burnout: About 2 minutes after liftoff at an altitude of 27 miles Nose cone Parachutes Recovery beacon Antenna Instrumentation Igniter within star-shaped fuel segment SOLID FUEL Hollow core Forward fuel segment Midsegments Aft fuel segment Ring attachment to fuel tank Ring attachment Nozzle Skirt Possible site of rupture
JOINTS ATTACHED AT LAUNCHING SITE
GRAPHIC: photo of rocket