If U.S. airlines had the same failure rate as the now-retired space shuttles, there’d be 272 fatal crashes a day.
As the investigation begins into the unmanned Orbital Sciences Corp. rocket that blew up seconds after liftoff this week, the history of space travel suggests such failures are neither rare nor unexpected.
“You have so much energy required to get out of the earth’s gravity field, you’re always essentially sitting on a bomb,” John Hansman, a professor of aeronautics and astronautics at the Massachusetts Institute of Technology, said in an interview. “You’re basically trying to have the bomb go off in a controlled way.”
Not only are rockets packed with explosive fuel, they are also complex machines made up of thousands of moving parts that can fail spectacularly over even a modest hiccup. It takes years to understand how systems may fail and where vulnerabilities lie, making it even more difficult to reduce risks as private companies get into the business.
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Companies such as Virgin Galactic LLC will have to address such risks before selling tickets to space travelers, Paul Ceruzzi, chairman of the Smithsonian’s National Air and Space Museum’s space history division, said in an interview.
“They have to address the safety issue very carefully,” Ceruzzi said.
The $200 million Antares rocket and spacecraft exploded in an orange plume over the Wallops Flight Facility on Virginia’s eastern shore on Oct. 28.
Out of 284 launches in more than 30 years, the company has succeeded 95 percent of the time, said Orbital Chief Executive Officer Dave Thompson earlier this week. id. The record improved to 96 percent in its 106 launches in the last 10 years, he said.
The overall unmanned rocket success rate is about the same, Ceruzzi said.
By comparison, U.S. airlines reported one fatal crash in the past five years, a success rate of 99.999998 percent.
The space shuttle Columbia was destroyed in 2003 as it burned up while re-entering earth’s atmosphere. Days earlier during its liftoff, a piece of foam had struck the shuttle’s heat shield with such force that it allowed hot gases to enter the orbiter’s left wing. The two accidents killed 14 crew members.
Engineers at NASA initially thought they had designed the shuttle to have a risk of failure of one in a thousand or better. Only after the accidents and a more thorough review of potential failures did the space agency’s engineers understand how risky it had actually been.
A NASA study concluded the chance of a failure on the shuttle’s first launch was one in 12, or 8.3 percent. Some of the other early launches were deemed even riskier, about 10 percent, according to the study.
“It is not uncommon for a final system design to present significantly more risk than its original designers expected due to what are known as ‘unknown unknowns,’ ” NASA’s Aerospace Safety Advisory Panel wrote in a report on Jan. 15. The group makes safety recommendations to the U.S. space agency.
At the end of the shuttle’s life, risks had been reduced to about one in 90 per flight. At that rate, 272 U.S. airliners would crash out of the average 24,000 flights a day.
By comparison, there has been one fatal accident on a U.S. passenger carrier since 2009 out of more than 50 million flights, according to the U.S. National Transportation Safety Board.