The Space Plane Returns to Earth

October 15, 2014 | 4:31 pm
Laura Grego
Research Director, Senior Scientist

The third X-37B space plane flight is coming to an end this week, after a record 22 month long mission. We have written pretty extensively on the “space plane” here on ATN, and have a factsheet where we condensed that thinking.

The X-37B Orbital Test Vehicle (OTV) returning to Vandenberg AFB from orbit on a previous mission. (Source: Boeing)

The X-37B Orbital Test Vehicle (OTV) returning to Vandenberg AFB from orbit on a previous mission. (Source: Boeing)

The space plane program inspires speculation in part because its purpose, its budget and most of its details are kept secret. And in part because while the technology is intriguing, few missions are especially suited to a long-duration, elegantly-returning spacecraft with low on-orbit maneuverability and small payload—most space missions can be done cheaper or better using existing technology. Its history of being kicked between NASA, DARPA and the Air Force, and then getting funded in the classified realm inspires skepticism whether the program would survive if it had to compete for funding in the light of day.

Space Plane Missions?

One mission that seems to be frequently suggested is a maneuvering sensor to look at “hot spots” on earth. The space plane may be able to do that. But the problem is that the ability to maneuver and the ability to return to earth work at cross purposes. Returning to earth requires massive landing gear and heat shielding, which is like putting rocks in your backpack when you’re trying to be agile. It’s not well-suited—this mission could be done much better and cheaper using other platforms.

And there is nothing stealthy about this craft. It is easily observed from the ground and because of all the extra mass must be launched on a large rocket (Atlas V). So while the space plane may be carrying advanced sensors to orbit so that they can be tested and returned, roving or stealthy sensors are not good missions for it.

Much is being made of the X37B’s long tenure on-orbit. Is there something magic about combining the ability to stay on orbit for a long time and then come back to earth? For a normal satellite, of course, two years on-orbit is brief (take a look at the UCS Satellite Database to see expected lifetimes and time-on-orbit for active satellites) and I’d venture that few customers would pay for an Atlas V launch for a satellite with only a two-year lifetime.

But is two years a long time for a craft that is meant to come back down from orbit? That’s harder to say since staying up in orbit for years and then coming back down is not a high-demand mission and there’s not much to compare it to.  Almost all satellites remain on-orbit after they no longer function, or are de-orbited destructively, mostly burning up as they travel through the earth’s atmosphere. Those that do have returning capsules, such as the Space Shuttle, do not have particularly long missions. The Soyuz TMA-9 capsule reportedly has a 210 day warranty (though it’s been on orbit a few more days than that), but it is designed to carry humans, which requires significantly more mass and higher standards than nonliving cargo does. Russian satellites still send back film from satellite-borne cameras, but these also tend to come back relatively quickly because the photographs are time-sensitive.

And there are the occasional orbiting capsules doing experiments that come back to earth, but those also generally have durations of weeks or months.  I don’t know about any other craft whose mission requires that it stay on-orbit for long periods of time before it returns, and would be interested in reader comments.

So the X-37B program does seem to be exploring a bit of parameter space that is uncharted-— long-ish duration orbiting then returning to earth, and is developing cutting edge materials and technologies for return and autonomous landing. These are interesting technologies, but returning to earth using valet parking, as David Wright notes, isn’t a mission, it’s a technology. Why classified, though?

Which is really the interesting point. It’s a well-resourced classified military program, so will generate plenty of raised eyebrows and interest in similar technologies in other countries. Is it worth it?

We have yet to hear anything approaching a convincing argument.