Friday, January 28, 2011

Annual time of Mourning at NASA

There have been three fatal accidents involving NASA astronauts and their spacecraft. They all happened at this time of year. On January 27, 1967 astronauts Gus Grissom, Ed White and Roger Chaffee were running a "plugs out" test in their Apollo spacecraft atop the AS-204 Saturn IB rocket with the hatch sealed shut and the cabin pressurized to about 16.7 psi with pure oxygen. Hindsight is 20/20 and everyone was as shocked and surprised that no one foresaw the incredible hazard of such a configuration - pure oxygen at such pressures makes almost everything a fire hazard and it was pure luck over the previous 6 years that such an accident had not happened to a Mercury or Gemini spacecraft. Apollo was very much more complex and it had fallen behind schedule. Mistakes were made and the best estimate for what occurred is that a spark from some frayed wiring ignited a fire that rapidly spread through the cabin, asphyxiating the crew with smoke and fumes from the explosive fire. The crew was dead by the time the ground support personnel could get the inward opening hatch opened. The ensuing investigation uncovered flaws in design and workmanship as well as higher level decisions. Improvements in the Apollo spacecraft and in operations almost certainly saved the program from later disaster that could have ended the program.

25 years ago, on January 28, 1986, NASA launched its 25th Space Shuttle flight into a chilly Florida sky. The previous 24 flights were a model of success, at least from a casual perspective. The 24 flights included the first re-use of a manned spacecraft when Columbia launched on STS-2. It included the launch of a variety of spacecraft as well as the retrieval of a pair of malfunctioning spacecraft. It included the first spacewalks of the shuttle program as well as the first untethered spacewalk when Bruce McCandless flew a jet backpack called an MMU (Manned Maneuvering Unit) which was later used for the retrieval of the Solar Max satellite. But beneath the facade of success was a disaster waiting to happen. On many flights, hot gases caused damage to O-rings in the solid rocket boosters (SRBs). Rather than delay the program by stopping flight, disrupting a crowded flight schedule, NASA management chose to continue flight while working the problem in the background. On this cold January morning, the crew of STS-51L made its way to the launch pad like the 24 space shuttle crews before it. The crew consisted of 4 veteran shuttle astronauts including the 2nd woman and 2nd African American astronauts to fly as well as the first Asian American astronaut all making their 2nd spaceflights. The commander, also making his 2nd spaceflight was Francis R. "Dick" Scobee. The three rookies on this flight included teacher in space Christa McAuliffe. As space shuttle Challenger left Launch Complex 39B, the odds caught up with manned spaceflight as hot gases burned past the O-ring near the base of the right hand SRB releasing puffs of black smoke for a moment as the shuttle rose off the pad. For another 50 seconds or so, the leak sealed but as it flew through maximum dynamic pressure, the seal failed and the SRB began burning through, releasing hot gas that rapidly started damaging first the SRB, then the base of the giant orange external tank (ET) including the mount points of the SRB to the tank. 73 seconds into the flight the damage to the SRB and external tank reached catastrophic levels. In the preceeding moments, the flames from the SRB burned through the base of the Hydrogen tank at the bottom of the ET. The rear attachments of the SRB to the ET burned through allowing the SRB to hinge on the forward attachpoint. The nose of the SRB punctured the forward part of the tank where the Oxygen tank is located. The net thrust from leaking Hydrogen at the base of the ET pushed forward into the oxygen tank causing rapid disintegration of the ET. Without the ET to hold the vehicle together, the SRBs flew off into their "Y" shaped paths. There was no explosion - the hydrogen and oxygen cloud expanded with only minimal burning giving the distinctive shape to the expanding debris and vapor. Without the ET, the shuttle could only respond to all the forces acting on it. There was the thrust from the still burning 3 main engines. There were the aerodynamic forces of the airflow over the wings and aero surfaces. The net result was for the orbiter to pitch itself belly into the wind and the aerodynamic stress on Challenger caused it to shatter into pieces. The structurally strongest parts of the orbiter remained somewhat intact including the crew compartment and each flew out of the expanding debris cloud. There was evidence that the crew survived the initial breakup of the vehicle and possibly were alive (but likely unconscious) for the remainder of the fall to the ocean as the cabin flew upward another 3 miles before descending to the water below. The investigation revealed the cause of the disaster to be O-rings chilled to more than 30 degrees below the previous record cold launch temperature which in itself was almost 20 degrees below the rated temperature of the O-rings. Without a proper seal, the hot gas eroded through the O-rings and then into the case of the SRB before burning through and continuing to damage the vehicle. The orbiter was responding to the slightly varying thrust of the two SRBs and continued to try to fly even after the start of the breakup, adjusting the gimbal of the main engines to compensate. The root cause of the accident showed many similarities to the events of 19 years and a day earlier, though management not listening to the concerns of their staff combined with the need to meet demanding launch schedules kept the problem from being dealt with before the disaster happened.

8 years ago on February 1st the crew of space shuttle Columbia were returning home from a demanding 16 day mission of science. They did not make it home. Just 16 minutes from the runway at the Kennedy Space Center the shuttle broke up into debris similar to what had occured 17 years earlier, though moving at mach 18 over the skies of Texas. In the days and weeks that followed we learned that the shuttle and crew of 7 were doomed from nearly the start of their mission when a piece of ET foam broke away from the tank at about 82 seconds into the launch of mission STS-107 and slammed into the leading edge of the left wing of the orbiter at about 500 miles per hour. A piece of the light grey Reinforced Carbon Carbon leading wing surface broke free of the orbiter near the base of the left wing shortly after arriving in orbit. The hole in the wing would allow the hot gases of atmospheric entry inside the wing 16 days later during re-entry of the orbiter. The hot gases ate up the inside of the wing until it finally reached a critical point where the shuttle flew out of control and broke up due to aerodynamic forces. Once again, the crew cabin remained intact for some time after the breakup of the orbiter but was destroyed later as it fell into the thicker atmosphere. Pieces of Columbia were spread over parts of two states as they fell out of the sky. Many of the symptoms from the Challenger accident resurfaced in the face of the Columbia Accident Investigation Board analysis including signs and portents of disaster going all the way back to the earliest shuttle flights as debris strikes on the orbiter from launch were a problem on every flight. Most were harmless but required repair of the tiles between every flight. The 2nd flight after Challenger nearly caused the loss of orbiter Atlantis on STS-27 when a foam strike on the belly of the shuttle which caused over 700 "dings" to the belly and the loss of one tile and near burn through during re-entry. During the STS-107 mission, analysis of the debris strike underestimated the potential for damage to the orbiter and since the strike area was out of sight of the crew and believed to have been a glancing blow on the belly of the orbiter, the debris analysis suggested it would not produce significant damage. Only in hindsight when impact tests using a large gun that could shoot foam at speeds similar to those estimated during Columbia's flight into wing leading edge material did the potential for disaster become fully apparent.

These three accidents along with two fatal accidents in the Russian space program are reminders of the dangers of exploring new frontiers. The danger should never be forgotten but also should never prevent us from pursuing exploration. We learn from our mistakes and move on keeping the memory of lost pioneers in our minds to help motivate us to continue the work in their names while improving hardware and procedures to help minimize the chances for future accidents. Imagine if we stopped sailing the high seas the first time we lost a ship at sea! Here is to those who gave their all in the pursuit of space.

In the words of Gus Grissom: "If we die, we want people to accept it. We are in a risky business and we hope that if anything happens to us it will not delay the program. The conquest of space is worth the risk of life."

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