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Atlas 5 rocket blasts off with military's experimental space plane

Irene Klotz, Spaceflight Correspondent
May 21, 2015, 1:41 UTC

Sen—One of the U.S. Air Force’s two X-37B robotic space planes blasted off aboard an Atlas 5 rocket Wednesday for the program’s fourth foray in orbit.

The 20-story tall United Launch Alliance rocket lifted off as planned at 11:05 a.m. EDT (1505 UTC) from Cape Canaveral Air Force Station in Florida. Perched on the booster’s nose was a diminutive robotic space plane that resembles NASA’s now-retired space shuttles.

The Orbital Test Vehicles (OTV) are about one-quarter the size of the shuttles and designed to remain in orbit for at least 270 days. Details of the program are classified, but the Air Force says the vehicles are used to demonstrate technologies for reliable and reusable unmanned spacecraft and to operate experiments that can be returned and analyzed on Earth.

The program has its roots in an NASA technology development effort that ran from 1999 to 2004 before it was picked up by the Air Force's advanced research agency, DARPA, and later transferred to the Air Force Rapid Capabilities Office.

The first X-37B vehicle made its orbital debut in 2010, circling the planet for 224 days before landing itself at Vandenberg Air Force Base in California, blowing a tire in the process.

The second vehicle launched the following March and ended up staying in orbit more than twice as long as its sister ship, touching down in California after 469 days aloft.

OTV-3, launched on Dec. 11, 2012, marked the first reflight of an X-37B. The mission lasted nearly 675 days.

For OTV-4, the military isn’t saying whether it is making a third flight on its fleet leader, or flying its second ship a second time.

“That information is not releasable due to the program's operational objectives. For each launch, the program selects the orbital test vehicle (OTV) for each activity based upon the experiment objectives,” the Air Force wrote in an email to Sen.

The intended mission duration, as well as its landing site, likewise was not disclosed.

The X-37B program is relocating to NASA’s Kennedy Space Center in Florida, taking over two of the space shuttle’s processing hangars. The third hangar is leased to Boeing for its CST-100 human spaceship, which is being developed in partnership with NASA. Boeing also built and is the Air Force’s prime contractor for the X-37B program.

The Air Force said the shuttle’s runway may be ready to support an X-37B landing by late next year.

“The future landing location will be determined by a variety of factors. Work is still ongoing to stand up Florida as a landing site for the X-37B, and Vandenberg AFB is still being maintained as a landing location … At this time it would be premature to specify where OTV-4 will land,” Air Force spokesman Chris Hoyler wrote in an email.

For the first time though, a few of the experiments to be conducted during the OTV-4 mission were released. They include an Air Force-backed demonstration of an ion propulsion system known as a Hall thruster.

“While producing comparatively low thrust relative to conventional rocket engines, Hall thrusters provide significantly greater specific impulse, or fuel economy. This results in increased payload carrying capacity and a greater number of on-orbit maneuvers for a spacecraft using Hall thrusters rather than traditional rocket engines,” the Air Force said in a statement.

“The experiment will include collection of telemetry from the Hall thruster operating in the space environment as well as measurement of the thrust imparted on the vehicle. The resulting data will be used to validate and improve Hall thruster and environmental modeling capabilities, which enhance the ability to extrapolate ground test results to actual on-orbit performance,” the Air Force said.

A second X-37B experiment is a NASA materials science investigation known as Materials Exposure and Technology Innovation in Space, or METIS. As its name implies, the experiment is designed to expose various advanced materials to the harsh environment of space so engineers can assess if and how they chance.

“By exposing materials to space and returning the samples to Earth, we gain valuable data about how the materials hold up in the environment in which they will have to operate,” lead researcher Miria Finckenor, with NASA's Marshall Space Flight Center in Huntsville, Alabama, said in a statement.

“Spacecraft designers can use this information to choose the best material for specific applications, such as thermal protection or antennas or any other space hardware.”

Hitching rides on the Atlas launcher were 10 CubeSats, including one developed by the non-profit Planetary Society to test a deployment mechanism for a solar sail.