Planning to operate a taxi service for NASA astronauts? Here’s what’s required.
- By Andrew Chaikin
- AirSpaceMag.com, November 16, 2011
Sierra Nevada Corp.
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Chaikin: What about abort? People have said to me that’s the hardest part of commercial crew. Do you agree?
Mango: No, I don't. It is hard, but it's just as hard as guidance and navigation to dock with the station. It's just as hard as mass properties within a capsule or within a winged vehicle, to make sure your center of gravity on your vehicle is right not only for the mission but also for the landing—and when you have a winged vehicle, to make sure that you have the right sink rate and the right control of your spacecraft as it’s entering and landing. Those are just as hard, in fact sometimes harder, because you have less variables you can play with.
But I would say that the abort system, from a systems design standpoint, could be very complex. And I believe that most of our partners in [commercial crew] are very much seeing that the abort system is driving some of their key components and key drivers of their overall design. So it is definitely a driver, a huge driver. But I cannot necessarily say it's the most complex. That depends on the actual system itself.
Chaikin: Let me just broaden the question then. For a vehicle that has not flown crew before, what do you need to see? Is it a question of saying, you've done X number of tests and the results are within X percentage of reliability? For these brand-new vehicles, how will you know when it's okay to put NASA astronauts on them?
Mango: Very good question. There are a number of things we are going to require in order for us to certify the vehicle. For an abort system, we are going to have a reliability number that says that when you push the ‘big red button,’ the system will actually work, and you get the crew back to the surface safely. Whatever that abort system is, whether it’s parachutes, or you’re going to a landing strip, or whatever. We are going to declare we've got to have 95 percent reliability, which is pretty high for an abort system that you’re hopefully never going to use in the life of your program. But it’s got to be there.
Now, how do you get there? What we will request during the next phase of our program is a proposal from the bidders [describing] what they plan to do to verify that their system can meet our certification requirements. I always get this question: “How many abort tests do companies gotta go do?” And there isn't a right answer. Because it depends a lot on all the other variables. How many component tests are you doing? How much are you making sure the reliability of those components are up to speed and ready to meet the requirement? …. I believe at some point we will have to have some level of demonstration that says you have met the capability of your abort system.
Chaikin: What you're saying is there's no prescribed test sequence or flight test plus ground test sequence. It could be a whole matrix of tests that would then give you an acceptable result.