The Buzz

Why Russia and China Should Fear the X-37B Space Plane

A transformation in military space capabilities is occurring hundreds of kilometers above the Earth’s surface as the US Air Force X-37B Space Plane logs over 500 days in orbit in its latest mission.

The unmanned X-37B Space Plane is designed for long-endurance missions that are highly classified. It’s officially referred to as the ‘Orbital Test Vehicle’, and is described as a platform for testing “reusable spacecraft technologies for America’s future in space and operating experiments which can be returned to, and examined, on Earth.” A total of four missions have been flown since April 2010, with the fourth in progress since 20th May 2015. It’s designed to be launched on an expendable Atlas V booster, and there are currently two operational X-37Bs in the USAF’s inventory.

The current mission is testing a new type of ion-engine called a ‘Hall-effect thruster’. It was the Hall thrusters on the first USAF Advanced Extremely High Frequency (AEHF) satellite that saved the satellite when a rocket motor failed to raise it to the correct orbit. Hall thrusters provide higher thrust than traditional ion propulsion, with sustained thrust allowing a spacecraft to reach about 50km per second—much faster than even NASA’s Voyager 1 space probe now travelling out of the solar system at mere 17km per second. For satellites they provide a much more cost effective way of remaining in the right location within an orbit.

The laws of orbital dynamics and the fact that rockets use fuel at an alarming rate means satellites and spacecraft are not maneuverable like fighter aircraft within Earth’s atmosphere. Minimizing fuel use also demands the use of Hohmann transfer trajectories to move between orbits, reducing their orbital agility even further. Rocket engines and the need to carry large amounts of fuel adds mass and complexity to spacecraft design, blowing out cost and extending development time. Once the rocket fuel is used up, the spacecraft or satellite is useless.

The X-37B potentially changes this situation, as not only can the spacecraft be recovered and reused, but it uses a small amount of Xenon gas that is far lighter than traditional rocket fuel like hydrazine, though it has a high storage density to allow greater useful fuel. Maneuvering with Hall thrusters is slow compared to rockets (even though prolonged acceleration over time produces much higher velocities), but far more cost effective in terms of fuel. So the X-37B can stay up longer, maneuver at far lower cost in terms of fuel than a similar vehicle with traditional rockets, and enjoy a greater ability to maneuver within and between orbits. This flexibility would allow it to do more in space, including close surveillance of an adversary’s satellites in orbit, both in terms of optical imaging, and electronic intelligence and signals intelligence gathering. It can also fill a gap if satellites are badly positioned to respond to short notice events like a nuclear test in North Korea. The X-37B suggests a new generation of space capabilities beyond traditional satellites.

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