Date: Sun, 12 Aug 90 15:55:01 -0700 From: sklein@cdp.uucp Subject: Space Shuttle O-Rings NOT the real problem [Selections from SKlein] There is much more to the article excerpted below, which appeared in Washington CityPaper, a weekly muckraking free newspaper distributed in and around the Washington, DC area. The article was written by Greg Kitsock, August 10th issue (Volume 10, No 32?). Washington City Paper at 724 9th Street NW, 5th floor, Washington, DC 20001. Phone (202) 628-6528. They can also be reached at MCI Mail 384-9327. Bent Out of Shape: Four years and millions of dollars after Challenger, NASA thinks it's got the shuttle's glitches all straightened out. But engineer Ali AbuTaha insists there are a fatal few that NASA missed. Ali AbuTaha, an engineer with 20-years of aerospace experience traces the Challenger disaster--and future disasters if his warnings aren't heeded--to a radical change in launch procedures that was mandated by NASA officials just prior to the shuttle's maiden voyage in 1981. That change in launch procedures, says AbuTaha, has subjected every mission to liftoff forces far exceeding the hardware's safety margins. excerpting from the article: "The shuttle can't reach orbit velocity unless [the main engines] perform properly, so NASA tests them by revving them up to full throttle during the 6.5 seconds before liftoff. (It takes about 1 second for the engines to reach 100 percent thrust.) The shuttle stays put on the launch pad because it's fastened to the pad by restraining bolts attached to the skirts of the solid fuel boosters. If NASA's diagnostic computers detect anything amiss in this 6.5-second interval, the orbiter's main engines are shut down and the liftoff aborted. "The shuttle broke decades of design precedent by mounting the airplane like orbiter on the side of the solid fuel boosters and fuel tank--a highly asymetrical arrangement thaty puts enormous stress on the whole assembly at liftoff. When the orbiter's main engines fire, they do so about 30 feet from the vehicle's geometric center of the attachment of booster to pad. This off-center thrust produces torque--a tendency to bend or rotate--that is so enormous it would rest the shuttle to the ground if the vehicle were not securely fastened to the pad. "The 185-foot-tall shuttle is designed to bend forward several feet under the brunt of the launch force before snapping back. It vibrates for several seconds after liftoff to dissipate the energies. This motion is called 'twang,' since it's essentially what happens to a guitar string when you pluck it. "Shuttle hardware was designed to match the stress and strain of very specific launch procedures. The launch procesures laid out in the late 70's as the first shuttle was being designed and constructed called for the restraining bolts to be blown at 3.8 seconds after ignition of the orbital thrusters. Just prior to this moment, the load on the base of the shuttle (also called the 'bending moment') is 350 million inch-pounds, well within the hardware's capacity to absorb. "But before the maiden voyage of the shuttle, NASA engineers got worried. Their engineering studies showed that if it were released 3.8 seconds after ignition, the vehicle would snap back far enough that it would scrape the launch pad rigging. This could damage the orbiter and the force of snapback alone could harm delicate payloads. "NASA considered several launch options to evade this dilemma. One option was to ignite only two of the orbiters' three engines at liftoff; the other was to offset the bending by tilting the vehicle in the opposite direction on the launch pad. NASA found these cures worse than the disease. Instead, the agency settled on an apparently simple solution: Delay launching to 6.5 seconds after ignition of the orbiter's main engines. At this point, the bending moment is reduced to about 190 million inch-pounds--once again, well within hardware limits. The shuttle snaps back a smaller distance and clears the launch pad with ease. "But AbuTaha says it's not that simple. According to his calculations, the bending moment doesn't decrease steadily between 4 and 7 seconds after the orbiter's main engine ignition. On the contrary: It reaches a peak of nearly 590 million inch-pounds at 5 seconds after ignition before declining. Although he worked out the curve independently, AbuTaha's figures agree with the results of a February 1981 ground test of the shuttle Columbia engine, as cited in aeronautics expert R.E. Gatto's article 'Effects of System Interactions on Space Shuttle Loads and Dynamics,' which was presnted to the International Council of Aeronautical Sciences Congress in 1982. "The Rogers Commission was not oblivious to shuttle "twang." But it rejected the idea that twang had anything to do with the Challenger disaster. Page 54 of the first volume of the commission's report states, 'The resultant total bending moment experienced by [the Challenger] was 291 x 10^6 inch-pounds, which is within the design's allowable limit of 347 x 10^6 inch-pounds.' However, on Page 1,351 of Volume 5 of the report, the commission cites the same figure, written as '291,000,000,' as the bending moment for the _right_ solid booster only. The effect on the entire assembly, argues AbuTaha, should be the combined bending moments of both boosters. Multiply by two, and you arrive at the maximum force that AbuTaha calculated. "This figure is 70 percent greater than the design's allowable limit, as cited in the Rogers report. And every shuttle mission up to the Challenger explosion (and possibly afterward) has experienced this force. 'This is the kind of error that catches up with you,' warns AbuTaha. "Not only does this miscalculation explain the shuttle disaster that killed seven astronauts and set our space program back nearly three years, as AbuTaha suggests, it also reveals the source of the mysterious malfunctions that have plagued the shuttle program since its first launch in 1981, from tiles knocked off and booster segments warped to satellites that inexplicably failed to work. ------------------------------