Early on Sunday morning, for parts of Florida along the Atlantic Coast, the tranquil calm was broken by a sonic boom. Residents didn't know it at the time, but the US Air Force's secretive X-37B uncrewed space plane had just returned to Earth after 718 days—the longest of its four missions into orbit.
"This mission once again set an on-orbit endurance record and marks the vehicle's first landing in the state of Florida," said Lt. Col. Ron Fehlen, X-37B program manager. "We are incredibly pleased with the performance of the space vehicle and are excited about the data gathered to support the scientific and space communities. We are extremely proud of the dedication and hard work by the entire team."
Not much is known about the secretive X-37B program. Prior to Sunday's landing, two identical space planes had completed three missions of increasing lengths: 224 days, 469 days, and 674 days. The spacecraft were built by Boeing for the Air Force as part of the military's effort to develop a rapid launch and reuse spacecraft capability.
Although the X-37B resembles the space shuttle, at 8.9 meters in length and a height of 2.9 meters, it is much smaller. The vehicle has a cargo bay that could hold something about the size of a standard refrigerator, and it seems to fly in a relatively low orbit below the International Space Station.
What is going on up there?
The military isn't saying what the X-37B is doing up there for so long, beyond furthering "operations development for reusable space vehicle technologies." About a year ago, however, Air & Space spoke with a number of space plane experts to get a sense of what the Air Force might be up to. According to the magazine, the vehicle is likely testing autonomous systems for navigation and other functions, including landing.
Additionally, most of the experts believe the Air Force is interested in using the vehicle as an on-orbit test bed for developing advanced surveillance sensors, as the military looks to transition from massive, expensive, and vulnerable observation satellites to smaller, cheaper, but just-as-capable reconnaissance satellites. The experts also speculated that the Air Force might be testing technologies that could be incorporated into a human-rated version of the vehicle that could carry a flight crew. Among the applications contemplated for the X-37B would be the recovery of satellites for repair on Earth.
During the last several years, private industry has begun to develop similar capabilities in terms of rapid reuse and launch. Recently the Air Force's Air University conducted a study that found that developments by SpaceX, Blue Origin, and other companies, such as Vulcan Aerospace and Virgin Galactic, had given the United States a definitive edge over global competitors in this new area of reusable rocket technology. However, the report warns, other countries such as China could copy these ideas and surpass the United States if strategic government investments are not made.
The study recommends the Air Force create a new organization, the “NewSpace Development Office,” to develop innovative acquisition strategies. The overall aim would be to move away from the existing model of launches, which are rare and expensive, to a model where they are common and inexpensive. It is not entirely clear how much overlap there is between these capabilities and those sought by the X-37B vehicle, which presently launches on an expendable Atlas V rocket.