Japan's HTV cargo freighter proves useful to the end
BY STEPHEN CLARK
Posted: March 29, 2011
Japan's HTV cargo craft plunged back to Earth overnight Tuesday with a unique sensor designed to record the heated death throes of the throwaway garbage-filled spaceship.
Designed and built by the Aerospace Corp., the REBR was programmed to autonomously measure, record and transmit temperature, acceleration, rotation rate and other variables during the HTV's return.
It will yield unprecedented insight into the dynamics of the destructive re-entry of a satellite. Only the shuttle Columbia accident in 2003 gave scientists any useful data on how a spacecraft breaks up in the atmosphere.
Bill Ailor, the leader of the REBR development team, said it is critical to learn more about how spacecraft behave during re-entry to better predict hazards to the public and discern which satellite components will impact the surface.
"Hardware fragments can hit the ground anywhere along a footprint that is hundreds of miles long," Ailor said. "Except for the Columbia accident, when the shuttle disintegrated over Texas during re-entry into Earth's atmosphere, fewer than 250 fragments are known to have been recovered over the past 40 years, and only a very few of these fragments have been examined in detail."
The REBR is designed to fill in some of the knowledge gaps.
"Excluding the Columbia accident, virtually no useful telemetry has ever been received," Ailor said. "Since nearly 75 percent of Earth's surface is water, much of the re-entered debris falls in water and is never seen."
The robotic H-2 Transfer Vehicle was finishing a resupply mission to the International Space Station, during which the craft delivered 8,500 pounds of cargo and disposed of the outpost's trash.
A series of engine firings since the HTV's release from the space station Monday gradually put the craft in position for the fiery plummet back to Earth. A final de-orbit burn ended at about 0244 GMT Wednesday (10:44 p.m. EDT Tuesday) to set the HTV's course toward the southern Pacific Ocean, according to the Japan Aerospace Exploration Agency.
Re-entry was expected around 0309 GMT (11:09 p.m. EDT), wrapping up nearly 67 days in orbit for the barrel-shaped spaceship. Most of the 33-foot-long spacecraft is designed to burn up during the scorching high-speed return to Earth, and any debris that survived the re-entry was supposed to fall into the remote South Pacific.
Nicknamed Kounotori 2, the HTV spent 60 days berthed at the space station before departing the complex Monday. It left behind spare components for the lab's electrical circuitry and cooling system outside the space station and provisions, experiments and computers for the crew inside.
It was the second HTV mission launched to the space station by Japan. The next Japanese cargo craft is being prepared for liftoff in January 2012.
The REBR will separate from the HTV as the ship heats up, breaks apart and tumbles, sending a stream of data through an Iridium communications satellite back to scientists in El Segundo, according to Lindsay Chaney, a spokesperson for Aerospace.
"It will make a phone call to Earth and have about five minutes to send its data before it lands in the Pacific Ocean," Ailor said.
Developed with internal Aerospace funding and investments from the Air Force and NASA, the REBR is not outfitted with a parachute and will not be recovered, officials said.
"No images will be collected on either of the first two missions this year," Chaney said. "However, images and other types of data collection are under discussion for the future, depending on how these first two go."
The second REBR unit launched aboard the HTV was moved to the European Automated Transfer Vehicle, which is slated to leave the station and dive back to Earth to a similar fate in June.
The rides aboard the HTV and ATV were provided for free by Japan and Europe because both space agencies are also interested in data obtained by the REBR.
"There was in-kind assistance from Boeing on building the heat shield, as well as from NASA Ames," Chaney said. "(Ames) provided wind tunnel time and some preliminary heat shield design work."
The REBR missions were integrated and flown under the direction of the Department of Defense Space Test Program.