Although launch of a spacecraft gets much of the attention from the public, every space traveler respects the dangers on entry.
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| | | Jay Apt is executive director of the Carnegie Mellon Electricity Industry Center at Carnegie Mellon's Graduate School of Industrial Administration and the Department of Engineering and Public Policy, where he is a Distinguished Service Professor. Dr. Apt joined NASA's astronaut program in 1985 and has spent more than 35 days in space on four Shuttle missions. | |
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Around an airless moon, Mike Collins in Columbia was apprehensive when he pulled away from the landing ship Eagle on July 20, 1969, during the Apollo 11 moon landing. He wrote later that as he radioed "See you later," he thought, "I hope so." Eagle's descent engine had to do all the work, rather than rely on air to slow the spacecraft. But there was much that could go badly. Fortunately, it did not and Armstrong and Aldrin landed Eagle successfully.
A spacecraft entering our planet doesn't need a big engine forcing it to slow down from 17,500 mph. A mere 500 mph reduction is enough for the craft to dip into the thin air at the top of the atmosphere and let it do the work. The forces make themselves known up around 300,000 feet, where there's often a bit of windshear causing mild turbulence.
Then it's smooth and quiet. But around 220,000 feet and at 19 times the speed of sound, the molecules smashed by the ship's passage signal their presence in a rippling plasma fire seen out the overhead windows, lasting until about Mach 12. There is no doubt you are racing through the fires of heaven. The entry flight deck is a very busy place, with the crew checking the computers for any sign that the flight path is wandering or the systems are acting up.
Entry is also one of the most beautiful times of a spaceflight. The cockpit of Columbia was bathed in the glow of her meteor tail. Commander Rick Husband had a great view of the ground rushing by in a 57-degree left bank. This crew clearly loved flight.
As President Bush said, "These astronauts knew the dangers, and they faced them willingly, knowing they had a high and noble purpose in life. Because of their courage and daring and idealism, we will miss them all the more."
Venturing back into the Earth's atmosphere has always been a challenge. The first entry accident happened on April 23, 1967, when Russian cosmonaut Vladimir Komarov was killed during the first test flight of the Russian Soyuz spacecraft when the parachutes fouled after electrical malfunctions had made attitude control impossible.
Redesign and one unpiloted test took 18 months, when the launch of Soyuz 3 recovered their program. Three years later in Soyuz 11, cosmonauts Dovrovolsky, Volkov and Patsayev docked with the Salyut 1 space station and stayed three weeks. When they entered the atmosphere on June 30, 1971, they were found dead after an automatic landing. A pipe connecting the jettisoned orbital module to the entry module had failed to seal upon separation, and the manual hand crank was too slow to avoid depressurization (they wore no pressure suits). The next Soyuz launch was 26 months later.
The U.S. space program has encountered similar delays due to ground and launch accidents: 19 months after the Apollo 1 pad fire in 1967 and 26 months after the Challenger breakup in 1986.
All four of these incidents -- Russian and American -- involved extensive redesign due to fundamental flaws in the spacecraft that had been overlooked in the initial design. Where does the Columbia accident fit by comparison? It is possible that the thermal protection system may be subject to a similar redesign, but my intuition is that this is closer to the Apollo 13 case.
In that accident, an oxygen tank exploded on April 13, 1970, as the spacecraft was outbound toward the moon. The subsequent investigation revealed component failures in a tank heater made worse by a worker dropping the tank, not a fundamental flaw in design. Apollo 14 was launched on Jan. 31, 1971, only nine months later, leading to a very successful landing and exploration mission.
Columbia was a very different ship than her sisters. She was the testbed for the tiles, blankets and composites that form the thermal protection system on all of the Shuttles. She had large numbers of tiles, their underlying felt pads and their carrier plates removed and reapplied several times.
One round involved replacing original tiles with ones of higher density; another replacement was required when it was discovered that a waterproofing agent weakened the bonding agent. What was learned was applied to the newer ships as they were built.
The investigation board named Sunday is filled with experienced accident investigators, and NASA management is the finest I've seen in decades. The leadership team set a frank and open tone immediately after Columbia was lost. A front-page story in The New York Times Tuesday ("NASA Offers Access and Instant Answers") led with, "When the news media showed up at its gates this time, NASA let them in. Not only is the investigation of this shuttle disaster more open than the inquiry into the destruction of the Challenger 17 years ago, the agency itself has presented a different, less-veiled face."
Agency officials have been open with their critical self-assessment that "we missed something." NASA commissioned rigorous studies in the early 1990s that showed the coupling of risk between external tank debris and tile damage. Many of the inspection, work force and management techniques recommended by these studies were implemented.
It is possible that Columbia had one heavily reworked area where the thermal protection system was more vulnerable to damage. It is also possible that the thermal protection failure was caused by something else entirely, since accident investigations often lead to causes not imagined in the first days after the ship is lost.
With any luck, the failure mode will be determined from recovered debris and the program can make appropriate changes and move forward quickly.
President Bush said of Columbia's crew, "The cause in which they died will continue. Mankind is led into the darkness beyond our world by the inspiration of discovery and the longing to understand. Our journey into space will go on."
At their memorial service in Houston Tuesday, he spoke for many of us who have partaken of this first century of flight when he said, "This cause of exploration and discovery is not an option we choose; it is a desire written in the human heart."
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