LOS ANGELES — Boeing is studying scaled-up variants of the reusable X-37B orbital test vehicle (OTV) for potential delivery of cargo and crew to the International Space Station (ISS) and other low-Earth-orbit destinations.
The development plan is believed to be aimed at providing a larger cargo adjunct to the company’s CST-100 crew vehicle as well as a possible longer-term, crew-carrying successor. The plan builds on the ongoing OTV demonstration with the U.S. Air Force, the first phase of which ended when the classified, unmanned OTV-1 demonstration flight concluded in December 2010 with an autonomous landing at Vandenberg AFB, Calif., following 244 days in orbit. A second mission, OTV-2, is under way.
OTV-2 has been in space since March 5, and assuming it has not already been covertly recovered, is expected to remain in space until at least mid-October. A landing around Oct. 15 will equal the OTV-1’s mission length. Given the 270-day mission endurance limit of the X-37B, as earlier described by the Air Force, the early March launch means the landing at Vandenberg can be expected on or before Nov. 30.
The X-37B evolution study, which harks back to the pre-military NASA origins of the OTV, envisages a three-phase buildup. The first would see the current 29-ft.-long vehicle used for demonstration flights to the ISS. In its current configuration, the X-37B launched inside the 5-meter (16.5-ft.) fairing of the Atlas V could already take bulky items such as the station’s control moment gyros, battery discharge and pump module, Boeing says.
The second phase would see the development of a 165% scaled-up version, roughly 47 ft. long and large enough to transport larger line replaceable units (LRUs) to the station. The larger version would demonstrate operations to and from the ISS, paving the way for a human-carrying derivative in the third phase. This would see a human-rated version transport “five to seven astronauts,” says Art Grantz, Boeing’s X-37B project chief.
Speaking at the American Institute of Aeronautics and Astronautics Space 2011 conference in Long Beach, Calif., Grantz says “the next step is a larger cargo vehicle that can deliver and return large ISS LRUs while retiring the risks associated with autonomous transportation of astronauts to and from LEO.”
Although many details of the OTV-1 flight remain unknown and with OTV-2 shrouded in even more mystery than the first flight, Grantz says the initial launch was aimed at “making it operate like an airborne test platform.” From a vehicle viewpoint, however, it also demonstrated autonomous de-orbit using “shuttle-style” trajectory and aero-braking manuevers as well as a “soft landing” on a runway. The test also validated the X-37B’s autonomous guidance, navigation and control system, electro-mechanical flight control system and thermal protection. During the X-37B’s eight months in space, Air Force controllers also demonstrated deployment of the solar wing, its subsequent stowage and return for reuse.
Photo: USAF
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