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By Andy Pasztor 

NASA's next-generation manned spacecraft, initially envisioned to be roughly 10 times safer than the retired space shuttle fleet, will fall significantly short of that goal, according to industry and former agency officials.

Two fleets of commercially developed crew taxis separately being built by Boeing Co. and Elon Musk's SpaceX, as well as the Orion deep-space capsule under development by a Lockheed Martin Corp.-led team, still are expected to meet minimum government risk standards, according to a National Aeronautics and Space Administration spokeswoman. But questions about relative safety, costs and engineering trade-offs -- which have roiled the space community for more than a decade -- are coming to the fore as the agency moves toward certifying the new vehicles and locking in launch schedules.

After the space shuttle Columbia exploded during re-entry in 2003, killing all seven crew members, the head of NASA's astronaut office urged management to adopt a safety standard for future human spacecraft of no more than one projected fatal accident per 1,000 flights. But that quickly proved technically unachievable. So when the space shuttles were retired in 2011 after a total of 135 flights, including two catastrophes, the hope was that future spacecraft would meet a standard of one fatal accident per roughly 700 flights -- roughly 10 times safer than the shuttles.

Yet that benchmark also was adjusted downward over the years, as detailed rocket and capsule designs were altered and entire programs were scrapped or overhauled. "There is no way they can achieve those numbers in the real world," according to Don Nelson, a retired NASA engineer who raised safety concerns before the Columbia tragedy.

Now, NASA says Boeing and Mr. Musk's Space Exploration Technologies Corp. will be mandated to meet a standard of no more than one potential catastrophic event in 270 flights, more than twice as risky as the proposed post-shuttle benchmark. NASA said it hasn't yet calculated even general safety standard covering the entire first Orion flight intended to carry astronauts to the vicinity of the moon, anticipated to last about three weeks. Industry officials, however, said NASA has issued "design guidance" covering capsule safety on that mission, for which a trajectory already has been decided. The number is no more than one fatal accident in 240 flights.

The commercial capsules are expected to conduct routine flights by mid-2019, which means they probably have to be well on the way to being certified before the end of next year.

An agency spokeswoman said "our safety requirements remain consistent" across commercial and traditional acquisition programs intended to transport astronauts, adding that specific calculations are based on factors ranging from duration of the flight to proximity to tiny meteorites to likely radiation exposure. NASA said the guidance number for Orion doesn't reflect launch hazards and certain other risks associated with the projected overall mission.

Underlying the numbers, NASA is struggling with a host of technical issues amid wide-ranging industry discussions over the variability of agency safety assessments. Experts inside and outside the government describe existing risk calculations as often imprecise. Such statistical measures, officially called "loss of crew" numbers, are based on various engineering assumptions and can shift markedly depending on design changes and revised mission profiles. They also can be wildly optimistic. Just before the space shuttles stopped flying, NASA determined that based on their actual flight history and documented safety incidents, the statistical chance of having a catastrophic failure fatal to the crew was roughly one in nine.

Against this confusing backdrop, William Gerstenmaier, a career NASA official with three decades of high-level experience who is in charge of human exploration, told an industry-government conference earlier this year in Washington that lawmakers, agency officials and the public have failed to explicitly acknowledge the full extent of the risks.

Based on physics and the nature of space flight, he said, in the end "we're going to be flying with some risk, no matter how hard we try to remove that risk."

NASA and its supporters "should figure out a better way to talk about these risks," Mr. Gerstenmaier told the conference, "not to scare people" but "just to recognize what they are."

Write to Andy Pasztor at andy.pasztor@wsj.com

(END) Dow Jones Newswires

May 26, 2017 16:50 ET (20:50 GMT)

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