Next X-37B Mission Set Begin Soon: The fourth flight of the X-37B robot spaceplane will soon begin. This mission is groundbreaking! It's hardly the first launch, but it's the first time that we have been openly told about the payloads carried inside the spaceplane. This caught the spaceflight community by surprise, given the tight secrecy that has surrounded the previous three missions.
X-37B is roughly the size of a car, and carries a small payload bay with clamshell doors that open in orbit. It deploys a small solar panel from this bay after the doors open. There is no cockpit. The spaceplane is launched atop an Atlas V rocket, covered by a large payload fairing. It stays in orbit for months or even more than a year before gliding to a runway landing.
Let's recap what we know about this flight. We were first told by the US Air Force that the X-37B is carrying a Hall Effect thruster in its payload bay, along with the associated parts to run the thruster. Hall Effect thrusters are different from normal chemical fuel rockets. They use a single propellant (such as xenon gas) and ionize it with the use of electricity. The electrically charged propellant is thus expelled from the engine at a high velocity, making this thruster very fuel-efficient. Hall thrusters are great for making minor orbital corrections over long periods of time, but they are useless for launching objects from the ground.
The thruster is a modified version of a Hall Effect thruster used on some USAF satellites. The new, upgraded version will find its way on board future satellites if it proves its worth on this flight.
Soon afterwards, NASA explained that the mission will also carry a materials test experiment provided by the space agency itself! This will expose "more than 100 different materials" to space. Like the Hall thruster, these material samples are intended for use in future spacecraft.
