One of the tools desired by even the earliest space visionaries, dating back to 1930s Nazi Germany, has been an orbital spaceplane capable of rapid launch preparation, good orbital and landing crossrange performance, and quick turnaround for the next launch. Such craft have been envisioned as strategic bombers, reconnaissance aircraft, and mini-shuttles to deliver personnel and equipment to space stations and perform on-orbit service for satellites. Both the U.S. and USSR had active spaceplane programs during the Cold War, in the form of the Boeing X-20 Dyna-Soar and MiG-105, though both were ultimately canceled. Nevertheless, the spaceplane requirement still remains on top of most military space professionals “get” list almost eight decades after Eugene Sänger and Irene Bredt conceived the concept.
Enter the Boeing X-37B Orbital Test Vehicle (OTV).
The X-37B OTV is an evolved version of small lifting body designs going back to the X-20 of the early 1960s. What makes the X-37B OTV different from earlier spaceplane programs is the absence of one vital feature: a manned crew. By eliminating the requirement for a human pilot, using state-of-the-art lightweight materials and aerostructures, and a clear dose of “Keep It Simple, Stupid” design philosophy, Boeing’s “Phantom Works” in Palmdale, Calif., seems to have produced the Low Earth Orbit (LEO) equivalent of the General Atomics MQ-1 Predator Unmanned Aerial Vehicle (UAV). The X-37 family of vehicles has evolved from the 85 percent scale test-bed NASA X-40 proof-of-concept model to a nearly operational U.S. Air Force (USAF) unmanned spaceplane in just a few years.
The X-37B OTV is, in itself, something of a marvel, even in an era of advanced UAVs like the RQ-4 Global Hawk and MQ-9 Reaper. Thanks to use of state-of the-art materials and structures, the X-37B OTV weighs in at only about 11,000 pounds. For propulsion, de-orbit burns, and on-orbit maneuvering, the X-37B OTV is powered by a Rocketdyne AR2-3 engine burning hydrazine monopropellant fuel. For thermal protection during reentry, the X-37B uses an advanced derivative of the improved silica ceramic tiles used on the space shuttle. Trim and clean looking, the OTV is just 29 feet, 3 inches long, with a wingspan of just 14 feet, 11 inches, and a normal set of landing gear allowing it to return to virtually any 10,000 foot runway.
Getting the X-37B into LEO is surprisingly cheap (about $200 million a launch), using the most basic version of the Atlas V family of boosters, the 501. Covered by a standard 5-meter diameter shroud, the OTV/501 stack is fired from Launch Complex 41 at Cape Canaveral, Fla., into LEO. On its first mission it operated at an altitude of about 250 miles.
The OTV then deploys its Gallium arsenide solar cells feeding an array of lithium-ion batteries to power the spacecraft systems. This allows the X-37B to conduct up to 270 days of on-orbit operations, which can include operating, deploying, and presumably recovering payloads weighing perhaps 500 to 660 pounds from its 7 foot by 4 foot cargo bay. Once the OTV has completed its mission and is ready to return to Earth, the X-37B fires its main engine and conducts a fully automatic reentry. Using a Honeywell 12-channel Space Integrated GPS/INS system with a flight profile similar to that of the space shuttle, the OTV lands conventionally on the main runway at Vandenberg AFB, with Rogers Dry Lake at Edwards AFB as a backup.
The success of OTV-1 on its first orbital flight, USA-212, was nothing short of spectacular, accomplishing every mission objective with a precision that stunned the aerospace world. Despite blowing out a tire on landing, which caused some minor damage to the underside of OTV-1, the spacecraft is in excellent shape and being refurbished for a second flight sometime in late 2011. The second X-37B, OTV-2, is presently being prepared for flight, with an announced liftoff scheduled for March 4, 2011, again onboard an Atlas V 501 booster. Plan on seeing a regular stream of these launches, especially if the USAF pursues the program further. One of the major objectives of the X-37 program was to create a basic scalable spaceplane design with common systems, much like the various versions of the Joint Strike Fighter. This makes it very likely that somewhere out at the Phantom Works in Palmdale, Boeing workers are cutting composites and readying new versions of this exciting and versatile spacecraft for flight in the near future.