Special Sensor Aboard HTV Records Tug’s Fiery Re-entry

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The Japanese H-2 Transfer Vehicle (HTV) dubbed Kounotori 2 intentionally re-entered the Earth’s atmosphere and burned up March 29, one day after the unmanned cargo tug departed the international space station carrying a load of trash.

A high-tech sensor onboard the HTV successfully monitored the spacecraft’s plunge into the southern Pacific Ocean, relaying its data via satellite to researchers for later analysis. The spacecraft, the second HTV that Japan has sent to the station, also carried three paper cranes folded by the space station’s three-person crew as a symbol of hope for the victims of the massive earthquake and tsunami that struck Japan March 11. The sensor on Kounotori 2 — a small and autonomous device called the Re-entry Breakup Recorder, or REBR for short — recorded temperature, acceleration, rotational rate and other data during the spacecraft’s high dive into Earth’s atmosphere.

“REBR collected data during the breakup of the Kounotori 2 vehicle and successfully ‘phoned home’ that data prior to final impact,” said William Ailor, director of the Center for Orbital and Reentry Debris Studies at the Aerospace Corp. in El Segundo, Calif. “In fact, it is still transmitting while floating in the ocean.”

Recovery of the device is not planned.

REBR’s designers at the Aerospace Corp. combined tiny sensors with cellphone technology to create what was essentially a satellite phone with a heat shield. Ailor said that analysis of the data will take six to eight weeks. The Aerospace Corp. designed REBR to collect data during atmospheric re-entries of space hardware in order to help understand breakup and increase the safety of such re-entries.

The REBR project was supported by the U.S. Air Force, NASA and the Boeing Co. The first flight test of the small, autonomous device was coordinated by the Defense Department’s Space Test Program. A second test will be REBR’s re-entry aboard the European Autonomous Transfer Vehicle 2, called Johannes Kepler, in early June.

Kounotori 2 was the second disposable H-2 Transfer Vehicle built by the Japan Aerospace Exploration Agency (JAXA) to ferry tons of cargo to the international space station. The first HTV spacecraft, HTV-1, visited the station in 2009.

“The HTV-2 carried various important cargo, including spare units of the external [space station] system and potable water for the crew, which has been mostly transported by the space shuttle up to now,” JAXA President Keiji Tachikawa said in a statement. “I believe that this success proves that the HTVs are reliable transportation vehicles essential for maintaining the [international space station], and that Japan, as an international partner of the [space station], is eligible to play an important role for [space station] operations.”

The spacecraft are about 10 meters long and 4.4 meters wide. They can carry cargo inside a pressurized compartment — which astronauts can retrieve after docking — as well as haul spare station parts on an unpressurized pallet to be retrieved by a robotic arm.

The Kounotori 2 spacecraft launched in January and arrived at the station Jan. 27. The next HTV spacecraft is expected to fly in January 2012.