An Astronauts Perspective On The Return To Earth
Dr. Jay Apt joined NASAís astronaut program in 1985 and has spent more than 35 days in space on four Shuttle missions. His experience includes a visit to the former Russian space station, Mir, and two space walks, one the emergency rescue of a satellite. Dr. Apt is currently Executive Director of the Carnegie Mellon Electricity Industry Center and holds the position of Distinguished Service Professor in Engineering and Public Policy at Carnegie Mellon University. After leaving NASA, Apt authored a stunning book, "Orbit: NASA Astronauts Photograph the Earth," which features his photography from space. The book has sold more than 600,000 copies in 11 languages. (See some of his photos at his Web site.)
Dr. Apt is an active pilot with more than 4500 hours of flight time. He currently owns and regularly flies a Beech Model 18. Over the weekend, he graciously provided AVweb with his perspective on the Columbia accident.
Although launch of a spacecraft gets much of the attention from the public, every space traveler respects the dangers on entry. Around an airless moon, Mike Collins in Columbia had his heart in his throat when he pulled away from Eagle on July 20, 1969, during the Apollo 11 moon landing. 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 Eagle landed successfully.
On our planet, we don't have to take a big engine into orbit to slow from 17,500 mph -- a mere 500 mph reduction is enough to dip into the thin air at the top of the atmosphere and let it do the work. The forces first make themselves known to you up around 300,000 feet, where thereís often a bit of windshear causing mild chop.
Then itís smooth and quiet, but around 220,000 feet and at Mach 19 or so, the molecules smashed by your passage signal their presence in a rippling plasma fire you see out the overhead windows, lasting until about Mach 12. There is no doubt you are racing through the fires of heaven.
Entry is also one of the most beautiful times of a spaceflight. The cockpit of Columbia was bathed in the glow of the meteor tail, and my former office mate Rick Husband had a great view of the ground rushing by in a 57-degree left bank. This crew clearly loved flight, and as the President said, ďThese 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 earthís atmosphere has always been a challenge. The first entry accident on this planet happened on April 23, 1967, when Russian cosmonaut Vladimir Komarov was killed during the first Soyuz test flight when the parachutes fouled after electrical malfunctions had made attitude control impossible.
Redesign and one unpiloted test took until October 26, 1968, when the launch of Soyuz 3 recovered the Soyuz program 18 months after Komarov's death. Three years later in Soyuz 11, cosmonauts Dovrovolsky, Volkov and Patsayev docked with the Salyut 1 station and stayed three weeks. When they entered on June 30, 1971, they were found dead after an automatic landing. A line 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. The next Soyuz launch was 26 months later.
Students of the U.S. space program know that it has encountered similar delays due to accidents. The Russian stand-downs were similar to the 19-month and 26-month recovery times after the Apollo 1 pad fire in 1967 and 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, not a fundamental flaw in design. Apollo 14 was launched on January 31, 1971, only nine months later.
Columbia was a very different ship than her sisters. Uncertainties in the aerodynamic parameters before her first four test flights led to beefy structure; even after half a ton of developmental flight instrumentation was removed, she weighed 6800 pounds more than the newest ship, Endeavour.
She was the testbed for the tiles, blankets and composites which 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.
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.
Columbia lost two full tiles on two 1980s missions, but only 15 percent of the 25,000 tiles are in critical areas and tiles in these areas are subject to more frequent inspections. 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, workforce and management techniques recommended by these studies were implemented.
The investigation board named Sunday is filled with experienced folks and NASA management is the finest Iíve seen in decades. The Administrator has excellent rapport with the White House; the Deputy Administrator is a Shuttle commander who was Capcom during the last Challenger launch and who ran the NASA safety program for years after. The present safety chief is a former Shuttle pilot and veteran aviation safety investigator and the head of the Shuttle and Station programs is one of the best human beings ever to have landed a Shuttle. He is a great leader.
President Bush said Saturday of Columbia, "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."
With any luck, the failure mode will be determined from recovered debris and the program can make appropriate changes and move forward quickly.