X-37B�s Fourth Mission Launch on 20 May 15

The United States Air Force's (USAF) mysterious unmanned reusable space plane, the X-37B, will lift off for the fourth time on 20 May 2015 from Cape Canaveral Air Force Station in Florida. The USAF’s official website defines X-37B Orbital Test Vehicle (OTV) as “an experimental test program to demonstrate technologies for a reliable, reusable, unmanned space test platform with twofold primary objectives: reusable spacecraft technologies for America's future in space and operating experiments which can be returned to, and examined, on Earth.” During its first three missions in the Low Earth Orbit since April 2010, no further details had been forthcoming from any official sources about their mission profiles or the payloads carried, leading to speculations about the mission goals beyond the official declarations. Prior to its fourth launch, however, the USAF has declared some details regarding the mission objective and the payload being carried.

X-37 began as an experimental project of (NASA) in the late 1990’s and involved two vehicles, X-40 an Approach and Landing Test Vehicle (ALTV) and X-37A, a slightly larger Orbital Vehicle. The programme was eventually transferred to Defense Advanced Research Projects Agency (DARPA) in 2004 and converted into a classified project. Boeing has been involved with the project since its beginning and its Phantom Works division, has built two OTVs. Measuring 8.9 meters long and 2.9 m tall, with a wingspan of 4.5 m and with a launch weight of 4,990 kilograms, the X-37B while resembling the NASA's now-retired space shuttle orbiter, is much smaller in size.It has a small payload bay with clamshell doors measuring 2.1 by 1.2 m, about the size of a pickup truck bed. According to Boeing, it is designed to operate in LEO at altitudes ranging from 110 to 500 miles (177 to 805 km) and depends on solar energy – obtained through a small solar panel deployed after the doors open - to power its long duration missions.

Since its maiden launch in April 2010, the X-37B has undertaken three clandestine missions, all launched vertically atop a United Launch Alliance’s Atlas V (501) rocket from Cape Canaveral Air Force Base in Florida and cruising back to Earth for an autonomous runway landing at California's Vandenberg Air Force Base. While it has been designed for an on orbit endurance of 270 days, the three mission durations have varied depending on the objectives and operational imperatives:

• OTV-1 - 22 April 2010 – 3 December 2010 - 225 days
• OTV-2 - 5 March 2011 – 16 June 2012 - 469 days
• OTV-3 - 11 December 2012 – 17 October 2014 - 674 days. (The same spacecraft that flew the OTV-1).

Despite all the mystery surrounding the mission profile, the space craft has been tracked by amateurs and governments alike. It is the secrecy surrounding the payload that has raised doubts and inciteda number of conspiracy theories. The fact that the program is being run by the Air Force's Rapid Capabilities Office (AFRCO), a unit that some believe to have links to the US intelligence community,[1] has further fuelled these concerns. With hundreds of satellites already in space, discussions focus on the options that the attributes of recovery and reusability provide. The most popular theory is that the X-37B is a test bed for secret sensors or a versatile surveillance platform that can clandestinely bring back data that is too sensitive to be transmitted electronically. What has rattled most other nations is the potential of such a platform of being a space weapon – capable of launching multiple missions or being available in orbit to fire weapons from space, targeting terrestrial or space based targets. The US has repeatedly refuted these charges and analysts have cited varied reasons involving its size, design and vulnerability among others to disprove this theory.

Probably in an effort to address these global concerns, the USAF has gone ahead and declared the objectives of the fourth X-37B mission.  The (US) Air Force Research Laboratory (AFRL) has confirmed that it will be testing a Hall thruster in the space environment.  Hall thruster is a type of electric propulsion device that uses an electric field to ionise and accelerate a noble gas like xenon, propelling it outwards to produce thrust for the vehicle.[2] These generate lower thrust when compared to that of conventional rocket engines and have to operate for longer periods of time to achieve the desired result. They are however more efficient for small velocity changes and also provide better fuel economy. As Xenon weighs much lesser than the conventional fuel, hydrazine, it allows more payload carrying capacity and also enhances the space craft’s operational flexibility, survivability and longevity. Hall thrusters were first used in the 1960s and are now commonly used on satellites and deep-space probes. The Hall thruster being tested is a modified version of the one being used onboard the US’s Advanced Extremely High Frequency (AEHF) military communications satellites.[3] The test would allow extrapolation of ground test results to actual on-orbit performance and the resulting data would be used to improve upon the performance of the existing thrusters to be used on these and other satellites.[4]

NASA is also undertaking Materials Exposure and Technology Innovation in Space (METIS) investigation as part of the mission for which the space craft will be carrying almost 100 different samples of advance materials, including polymers, composites, and coatings. Exposing these samples, some of which have flown earlier on the International Space Station (ISS), to the space environment for such long duration and testing them on their return would provide valuable inputs about their performance in the environment in which they have to operate.[5] Similar tests have already been conducted aboard the ISS as part of the Materials on International Space Station Experiment (MISSE)[6] and information gleaned from these has allowed gains for the aerospace industry through development and selection of optimum materials for specific applications. METIS is expected to build upon the existing data.

There is also a secondary payload being flown aboard this mission - the Planetary Society sponsored Light Sail 2.  It is a 3U CubeSat that is flying under the NASA’s Educational Launch of Nanosatellites program. It is a design test for LightSail’s systems ahead of a full-fledged demonstration to be launched in 2016.[7] It has not been made clear which of the two spacecraft will fly the upcoming mission. Experts opine that sending the first vehicle on a third trip would enable testing the reusability factor further as single reusability has already been proved by OTV-3.[8] There has also been no communication regarding the mission duration.

The USAF press release stated, "With the demonstrated success of the first three missions, we’re able to shift our focus from initial checkouts of the vehicle to testing of experimental payloads." What is being implied is that the first three missions were mainly to check the various structural and functional aspects of the space craft, a theory not many analysts are ready to accept. US has a record of having undertaken a number of secret or misleading tests in the past including some aboard the space shuttle. Sceptics are even claiming that only a small part of the full mission objectives has been declared for the fourth mission. Considering the small size of the cargo bay, this seems highly unlikely but it cannot be ruled out altogether. Notwithstanding, the space plane would contribute positively to future space missions and in technology development. After the very first successful mission, Boeing had announced plans for a scaled up variant, designated X-37C that would be able to carry six astronauts inside a pressurized compartment housed in the cargo bay.It could be used to deliver cargo or astronauts to the International Space Station (ISS) and could also be employed for space tourism. With Boeing now developing the CST-100 commercial space capsule as part of the NASA funded Commercial Crew Development Programme (CCDEV), the future of X-37C is uncertain. What is certain is that the outcomes from the X-37B programme would contribute greatly to the development of CST-100.

The author is Senior Fellow at CLAWS. Views expressed are personal.