September 10, 2012
Shortly after Japan’s Kounotori cargo ship undocks from the space station on Wednesday, ground controllers will fire its rockets to steer the schoolbus-size craft into the atmosphere so that it burns up over the ocean. Normally, the end would come discreetly off camera. This time, we’ll get to watch the fireworks.
In the 55-year history of satellites re-entering the atmosphere, nobody (or at least nobody in the unclassified world) has ever gotten pictures from the satellite’s point of view. For Kounotori’s demise, Japanese investigators have placed a camera-equipped device called i-Ball inside the spacecraft. The spherical i-Ball has two cameras. One will return 10 images from inside Kounotori as it’s breaking up. The second camera will take 40 pictures after the breakup, and the i-Ball will continue on to a splashdown in the ocean.
This Japanese space agency video shows how it’s all supposed to go:
Japan’s i-Ball won’t be the only instrument recording the spacecraft’s breakup. Another experiment package, called REBR (Re-Entry Breakup Recorder), will collect information on temperature and accelerations as Kounotori is torn to pieces during re-entry.
“Getting data off a satellite that’s coming in and breaking apart is a bit of a trick,” says William Ailor of The Aerospace Corporation, principal investigator for REBR, whose team worked on the technology for more than a decade before flying it for the first time on another Kounotori last year. REBR is contained in a copper shell held together by plastic bolts. Once the spacecraft starts to break up, the bolts melt and the instrument package is set free. “The whole vehicle that we’re riding in has to come apart for us to get out at all,” says Ailor. REBR has no cameras, but its data — transmitted to the ground during a five-minute fall to the ocean — will tell scientists about the timing and conditions of the breakup.
Why do they care? Currently, spacecraft operators err on the side of caution when it comes to de-orbiting a satellite at the end of its lifetime. Rather than risk an uncontrolled entry over a populated area, they command the satellite to re-enter slightly early. “If your casualty expectation exceeds 1 in 10,000, you have to put it in the ocean,” says Ailor. The risk of casualties is based on estimates of when a given satellite would break up as its orbit decays. “What we’re trying to do [with REBR] is calibrate the models that make these estimates.” If satellite owners could be less conservative in their estimates, they could leave valuable satellites — say, the Hubble Space Telescope — operating longer in space.
Information on satellite breakup is considered important enough that a commercial venture called Terminal Velocity Aerospace has licensed the technology from The Aerospace Corp. to do routine data collection on future spacecraft. Meanwhile, Ailor is looking forward to i-Ball’s first-time photos. “I hope they succeed,” he says. “That will be really significant in itself.”
Below: In 1984, cameras in Hawaii captured the space shuttle’s external tank breaking up over the ocean. The STS-41C astronauts narrated video of the re-entry during a postflight press conference:
In 2008, the European ATV cargo vehicle was filmed during re-entry: