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After 675 days in space, the Air Force’s reusable X-37B mini-shuttle successfully returned to Earth today, completing its second flight in space.
There has been a lot of speculation about the secret payloads that the two X-37B’s have carried into space. The Air Force has been very tight-lipped about this, though they have said this:
“The primary objectives of the X-37B are twofold: reusable spacecraft technologies for America’s future in space, and operating experiments which can be returned to, and examined, on Earth,” Air Force officials wrote in on online X-37B fact sheet. “Technologies being tested in the program include advanced guidance, navigation and control; thermal protection systems; avionics; high-temperature structures and seals; conformal reusable insulation, lightweight electromechanical flight systems; and autonomous orbital flight, re-entry and landing,” they added.
The obvious advantage of the X-37B is that it allows the Air Force to test these new technologies in space, then bring them back to Earth for detailed analysis.
However, I think the most important engineering knowledge gained from this flight will not be from the payload, but from the X-37B itself.
The X-37B that landed on Earth today now holds the record for the longest flight in space by a spacecraft that has then been safely returned to Earth. No other reusable spacecraft has ever been in space that long and gotten back to Earth. In fact, no manned spacecraft, even the disposable kind, has ever been in space that long and returned to Earth. The longest an Apollo capsule ever flew was six months on the last Skylab mission, while the longest the Russians have kept a Soyuz capsule in space before return was I think eight months. Previous space stations burned up in the ocean, so we were unable to study them after their sojourn in orbit. And shuttles could never stay in space more than 30 days at the very most.
The twenty-two month mission of this X-37B was long enough to get to Mars and back. Thus, in many ways this spaceship simulated a Mars mission, and its post-flight condition will tell us a great deal about what works and what doesn’t work on future vessels intended for such long missions, information invaluable for building interplanetary spaceships.
The Air Force and Boeing engineers that are now inspecting the X-37B are certainly aware of this and are likely drooling with glee at what they are learning. I just hope the knowledge eventually percolates out into the civilian aerospace community.