According to NASA, human-rating requires not just that a system is designed to be tolerant of failure and to protect the crew even if unrecoverable failure occurs, but also that astronauts aboard a human-rated spacecraft must have some control over it. This set of technical requirements and the associated certification process for crewed space systems is required in addition to the standards and requirements that are mandatory for all of NASA's space flight programs.
NASA Commercial Crew Program
In November 2011, Ed Mango, the agency head of the NASA Commercial Crew Program (CCP), gave an extended interview on the new NASA requirements for human rating of spacecraft that will fly to the International Space Station (ISS).
The NASA CCP human-rating standards require that the probability of a loss on ascent is no more than 1 in 500, and that the probability of a loss on descent is no more than 1 in 500. The overall mission loss risk, which includes vehicle risk from micrometeorites and orbital debris while in orbit for up to 210 days, is required to be no more than 1 in 270. Maximum sustained G-loads are limited to three Earth-standard g's.
The development of the Space Shuttle and the International Space Station pre-dates the NASA Human-Rating requirements. After the Challenger and Columbia accidents, the criteria used by NASA for human-rating spacecraft have been made more stringent.
The United Launch Alliance (ULA) published[when?] a paper submitted to AIAA detailing the modifications to its Delta IV and Atlas V launch vehicles that would be needed to conform to NASA Standard 8705.2B. ULA has since been awarded $6.7 million under NASA's Commercial Crew Development (CCDev) program for development of an Emergency Detection System, one of the final pieces that would be needed to make these launchers suitable for human spaceflight.
- "Human Rating Requirements for Space Systems". NASA. 10 July 2017.
Chaikin, Andrew (2011-11-16). "Certified Safe: Planning to operate a taxi service for NASA astronauts? Here's what's required". Air & Space Smithsonian. Retrieved 2011-11-27.
we've separated [the “loss of crew” criteria] into what you need for ascent and what you need for entry. For ascent it’s 1 in 500, and independently for entry it’s 1 in 500. ... The probability for the mission itself is 1 in 270. That is an overall number. That’s loss of crew for the entire mission profile, including ascent, on-orbit, and entry. The thing that drives the 1 in 270 is really micrometeorites and orbital debris ... whatever things that are in space that you can collide with. So that’s what drops that number down, because you’ve got to look at the 210 days, the fact that your heat shield or something might be exposed to whatever that debris is for that period of time. NASA looks at Loss of Vehicle the same as Loss of Crew. If the vehicle is damaged and it may not be detected prior to de-orbit, then you have loss of crew.'
- "Atlas and Delta Capabilities to Launch Crew to Low Earth Orbit" (PDF). United Launch Alliance. n.d. Retrieved 2011-11-27.
- "NASA and ULA confirm Atlas V baseline for human rated launches". NASASpaceflight.com. Retrieved July 24, 2014.