Think of the X-37B as the Space Shuttle’s smaller, younger brother and you wouldn’t be wrong.
With its bullet-like shape, stubby wings, and two tone black and white appearance, the X-37B Orbital Test Vehicle looks like a smaller, cuter version of the manned orbiter that served NASA for decades. That’s where the comparison ends though: property of the U.S. Air Force, the secretive, unmanned X-37B is built to spend months in orbit, carrying out classified missions on behalf of America’s military space program.
The story of the X-37B starts in the 1990s, when NASA was studying cheaper alternatives to the Space Shuttle orbiter. The Shuttle, designed to be flown frequently and with recoverable, reusable booster engines, was supposed to dramatically lower the cost of transporting people and hardware to low-Earth orbit. Unfortunately, the Space Shuttle ended up being a far more maintenance-intensive shuttle than original envisioned and failed to lower payload-to-orbit costs. Worse, the Shuttle took months to refurbish between flights, making it nowhere near as responsive a platform as originally planned.
One option to boost spaceplane readiness and lower costs was to dispense with human crews entirely, which meant getting rid of their crew living spaces and life support systems. An unmanned spaceplane can be far smaller than a manned one, requiring less thrust and a smaller rocket to put it into space. Without a human crew, an unmanned spaceplane could spend weeks, months, or even years in low earth orbit—as long as the mission requires—before returning to Earth.
NASA began development of a small, unmanned spaceplane concept in the mid-1990s while simultaneously, the U.S. Air Force was planning a similar craft, the Space Maneuver Vehicle, and Boeing built a single X-40A test aircraft for the Air Force. An 85 percent scale version of a notional spaceplane, the X-40A flew one mission for the Air Force before being loaned to NASA for its program concept.
The unmanned, unpowered X-40A was built to test autonomous guidance and navigation systems. The spaceplane was carried aloft by a U.S. Army CH-47D Chinook helicopter to an altitude of 15,000 feet and released to glide to a landing at a nearby landing strip. NASA carried out seven X-40A flight tests before the test program ended.
Following the X-40A, NASA planned to build two vehicles: the Approach and Landing Test Vehicle, or ALTV, and an Orbital Vehicle. Unfortunately in 2004, the civilian space agency decided an unmanned spaceplane “did not directly support NASA’s goals” for exploration. Rather than shelve the program, control shifted to the Pentagon’s Defense Advanced Research Projects Agency, or DARPA.
DARPA built the ALTV, which it called the X-37. The X-37 was a full scale craft designed not to go into space but to further test unmanned, autonomous landing hardware and software. The X-37 was carried by Scaled Composites White Knight launch aircraft with five captive flights and three free fall flights recorded.
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The next step was to build a full-scale, fully capable vehicle. Unlike previous craft, the new vehicle would include heat-resistant tiles and a propulsion system. The Air Force’s Rapid Capabilities Office awarded Boeing a contract to build the new craft, designated X-37B, which would finally fulfill the full mission profile of an unmanned spaceplane.
Placed on top of a rocket, the Air Force would shoot it into space, where it would stay for weeks and even months at a time. Once the mission was complete, the X-37B would de-orbit and glide to a landing at an Air Force runway.
Ready for Launch
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The X-37B was launched into space for the first time on April 22, 2010, strapped to the top of an Atlas V rocket. The two X-37B spacecraft have carried out a total of four missions racking up 2,086 days in orbit. The fifth mission, OTV-5 is currently underway and at 689 days in orbit, it is one of the longest X-37B missions to date.
The X-37B is 29 feet, 3 inches long with height of just 9 feet, six inches, and its wingspan stretches 14 feet, 11 inches. It has a launch weight of 11,000 pounds though that excludes the booster rocket.
The fourth mission, involved tests of “an Air Force ion thruster and a NASA materials experiment”— not exactly James Bond stuff.
The spacecraft is powered by Gallium Arsenide Solar cells with lithium-ion batteries, and it has thrusters for orbit maneuvering and de-orbiting but has no engines to travel long distances in space or for powered flight through the atmosphere. The spacecraft are controlled by the 3rd Space Experimentation Squadron at Schriever Air Force Base, Colorado.
The X-37B has been described as pickup truck with a payload bay measuring 7-feet-by-4-feet wide—or about the size of a truck bed. What makes the X-37B unique among current spacecraft, however, is its ability to take cargo into space and then return them. The result is a space platform that can act as the test vehicle for a variety of new technologies that can go into space and then return to the scientists and engineers that built them.
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The Air Force’s secrecy about the program has led to all kinds of speculation. As an Air Force platform, especially one that resembles an aircraft, it’s natural to think of it as some kind of exotic weapon system. There are even suggestions it could be used to snatch enemy satellites, bringing them home to study.
The public statements by the Air Force and an analysis of the spacecraft’s technical capabilities tells a different story: Air & Space Magazine revealed in 2015 that OTV-4, the fourth mission, involved tests of “an Air Force ion thruster and a NASA materials experiment”— not exactly James Bond stuff.
The Secure World Foundation, a space policy nonprofit organization, ranked the likelihood of all suggested X-37B mission scenarios. The most likely mission for the spaceplane is as an “on-orbit sensor platform and technology test bed.” The X-37B could allow the Air Force to test technologies bound for the next generation of spy satellites, before building a billion dollar satellite around them, and returning them to study after long missions in space. The X-37B could also allow such technologies to be used early, in case of a crisis or emergency on the ground.
While less probable, other scenarios exist pertaining to the spaceplane’s true purpose. The X-37B could be used as a quick response satellite launcher capable of filling gaps in coverage left by anti-satellite weapon attacks. But the cost to do so would be very expensive, and the spaceplane has a very small payload bay. It would be more feasible to simply boost a badly needed satellite into orbit on an existing rocket.
Also less feasible is using the X-37B as a satellite inspection vehicle, anti-satellite weapon carrier, and platform for grabbing malfunctioning satellites and bringing them home. In each case a smaller, cheaper satellite would probably be a better choice, or a platform with a larger payload bay.
The least likely use of the X-37B is as a weapon or weapons carrier. Some have suggested the X-37B itself could track target across the globe within minutes of the decision to attack, perhaps carrying a thermonuclear bomb. But, as the Secure World Foundation points out, the X-37B is a glide vehicle in its last moments, “easy prey for any air defense system along its path to the target.”
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Another concept is the spacecraft as a carrier and launch vehicle for so-called “Rods from God”.
“Rods from God” is a theoretical weapon system that consists of a tungsten bar with a guidance system. On command, the rods de-orbit and slam into targets at hypersonic speeds, using kinetic energy to do tremendous damage. But such weapons would require a large de-orbit thruster to kick off their descent, likely too big for the X-37B’s payload bay.
The X-37B is, above all, a test aircraft and in that respect is exactly what the Air Force says it is. It is far more likely that the secrecy behind the OTV missions is not because the service is testing weapons but technologies that go into equally—if not more secret—spy satellites.
Although larger, more capable spaceplanes that will dwarf the X-37B are almost certainly in the works, the reality is such craft are unnecessary for deploying most space-based weapon concepts.
The X-37B is indeed a spacecraft that carries out secret missions—just not the kind written about in spy novels.
Writer on Defense and Security issues, lives in San Francisco.
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