Purpose of military space shuttle is closely-guarded secret

Tuesday, May 12, 2015, 8:16 PM - NASA's Space Shuttles are museum pieces now, but a miniature, robotic space shuttle - the US military's X-37B space plane - has been flying since 2010. With another launch set for May 20, what's this secretive space plane up to?

The US Air Force's Boeing X-37B space plane isn't exactly a closely-guarded secret. We have images of it. We know when it launches and lands. We even know the details of (at least some of) the science experiments it carries into orbit.

Where this special military spacecraft does get mysterious, though, is in this fact: while every Space Shuttle mission was highly publicized, with crowds gathering for the launch, news and footage from space during the entire mission, and up-to-the-minute details for the landing, the X-37B launches and lands with little fanfare, and it spends its entire time in space (sometimes up to two years at a stretch) doing who-knows-what.

The basics

The X-37B is less than a quarter the size of NASA's Space Shuttles. This allows it to launch into space atop an Atlas V rocket, rather than having to use the huge external boosters the shuttles had, and it lands just like the Space Shuttles did, coming in like an airplane to touch down on a runway.

Boeing X-37B, with comparison to Space Shuttle. Credit: Giuseppe De Chiara/Kelvin Case/Wikipedia, edited by author.

It's a robotic, uncrewed spacecraft. So, there are no pilots or astronauts to report on when it's in space, which is one reason it can stay up in space for so long. It runs on solar energy, so it has an inexhaustible power supply while it's up there. Thus, it technically doesn't need to come down to Earth to refuel, and only really returns to deliver its payload back to Earth for study, and for any maintenance it might need.

So far, the two Orbital Test Vehicles the Air Force has have made three orbital flights - the first for over 7 months in 2010, the second for a total of 469 days between March 2011 and June 2012, and the third launched in December 2012 and landed in mid-October 2014, having spent 675 days in orbit.

The space plane even earned its team the Space Foundation's 2015 Space Achievement Award, which was awarded at the 31st Space Symposium, in Boulder, CO, in March.

Why this "secret" Military shuttle?

So, why does the US Military need its own space shuttle? If the experiments it's performing are innocent, why aren't they just ferried up to the International Space Station by SpaceX or Orbital Sciences?

When the International Space Station was first established, a rule was put into place that designated the station not only a multinational installation, but a strictly civilian one as well. No military involvement.

Therefore, if the US Air Force is interested in testing new propulsion systems and materials for future spacecraft, even though those experiments could be done on the ISS, this rule prevents them from conducting them there. A case could be made for the military to wait for similar civilian experiments to be performed and then benefit from those, however when a military wants, or needs, to stay on the forefront of technological developments, waiting likely does not work with their timetable.

As for NASA's use of the space plane, that seems like an issue of convenience. With the number of experiments being performed on the ISS, it has to come down to prioritizing their work. Also, the X-37B can and does fly at different altitudes than the International Space Station (between 177-805 km compared to 330-435 km for the ISS), which means that the materials they're testing can be exposed to different space environments for better comparison and contrast with their previous results.

What's the X-37B up to now?

Slated for a May 20 launch date, two different science objectives have been announced for this X-37B mission.

On board will be a new ion propulsion system, similar to the one currently in use by NASA's Dawn spacecraft (which is now orbiting the dwarf planet, Ceres). This "Hall thruster" is an electric propulsion system, which drives a spacecraft by ionizing Xenon - the heaviest non-radioactive noble gas - and accelerating it away from the spacecraft. The thrust at any one time is very light, but the thruster takes a very small amount of fuel and can run for very long periods of time, allowing the spacecraft to build up some impressive speeds. At the same time, unlike rocket propulsion, course adjustments with ion engines are very gradual and smooth, which allowed Dawn to become the first spacecraft to orbit two different objects in our solar system (Vesta and Ceres).

According to a press release from Wright-Patterson Air Force Base, this ion propulsion system is undergoing testing to be included in the US Military's Advanced Extremely High Frequency communications satellite system.

In addition to this test, NASA is sending up an experiment called METIS - Materials Exposure and Technology Innovation in Space - which will expose nearly 100 material samples to space for the duration of the mission. The results of this will be compared to the over 4,000 results gathered during the MISSE (Materials on International Space Station Experiment) from 2001 to 2013, to guide engineers in the best use of materials for future space mission.

"When we flew newly developed static-dissipative coatings on MISSE-2, we did not know they would be used for both the Curiosity rover and the SpaceX Dragon," Miria Finckenor, who was co-investigator for MISSE and is now the principal investigator for METIS, said in a NASA press release. "Some program we don't know about now will be successful because engineers found the data they needed."

What else the space plane may be up to in space during its 200+ day mission, well that's anyone's guess.

Sources: SpaceFlightNow | NASA | Wright-Patterson Air Force Base | Space Foundation

RELATED VIDEO: CNN's Rachel Crane discusses the X-37B's secretive missions, just prior to the space plane's last return to Earth, in October 2014.