One year after its launch, the purpose of a secret U.S. space plane remains a mystery



Nearly a year after a mysterious unmanned U.S. Air Force plane made its fourth trip into orbit, the purpose of the mission remains a secret.

The X-37B Orbital Test Vehicle began as part of a NASA project to test unmanned spacecraft but in 2004 was taken over by Defense Advanced Research Projects Agency, a branch of the Department of Defense that tests emerging technologies for use by the U.S. military.

According to the U.S. Air Force, “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.”

The most recent spacecraft was originally supposed to stay in orbit for about 200 days but has yet to return one year later, and speculation has been rife. The Pentagon has repeatedly refused to release details about the purpose of the space craft since it first launched in 2010, adding to the theories about why the program exists. The costs of the program are still unknown to the public.

In 2012, Dr. David Baker, the editor of

Spaceflight, a magazine published by the British Interplanetary Society, suggested that the craft might used for space surveillance.

AFP / Getty Images

He drew attention to the similarity between the orbital path of the shuttle and the Chinese space lab Tiangong-1: “With a period differential of about 19 seconds, the two vehicles will migrate toward or against each other, converging or diverging, roughly every 170 orbits.”

But if that’s true, it may not necessarily be bad.

Baker told the BBC that “if this is what the X-37B is doing, I think it really is no bad thing…as with the Cold War, the proliferation of space surveillance systems enabled us to get arms agreements that would not have been possible without each side knowing fully what the other side was doing.”

According to one conspiracy theory, the X-37B is a space bomber, able to rain down fire anywhere on Earth within 2 hours. Popular Mechanics put this idea to bed shortly after it emerged, however, showing how the space craft would quickly burn up too much fuel to be feasible as a bomber.


Another possibility is that the Air Force’s stated research explanations are true, and that the vehicle is indeed being used to test, among other things, advanced propulsion systems. This is consistent with the structure of the craft itself, which includes a set of Hall thrusters that use xenon gas and electrical currents instead of traditional rocket fuel to propel the ship.

The Pentagon also refuses to reveal the costs of the program, which adds to the uncertainty about how money is being spent.

Whatever the reasons may be secret military programs are a lightning rod for speculation, and after a year in orbit, people still prefer some explanation to no explanation at all.

This Week's Flyers

