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Historic Cosmic Catch

The first capture of a free-floating spacecraft by Canadarm2

The Canadian Space Agency’s (CSA) Canadarm2 successfully captured an unpiloted, free-flying Japanese vehicle —a first Canadian cosmic catch for the robotic arm on the International Space Station (ISS).
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Canada's technological prowess in space robotics was put to the test on September 17, 2009, when the International Space Station's (ISS) Canadarm2 made conduct its first-ever capture of a free-flying space vehicle. Nearly twelve years in the making, the nerve-wracking maneuver involved the debut flight of the Japanese unmanned HII Transfer Vehicle (known as HTV), which delivered 4.5 metric tons of cargo to the orbiting laboratory.

Part of the Canadian-built Mobile Servicing System on the Space Station, the heavy-lifting Canadarm2 has played a critical role in the assembly of the ISS. With the orbiting outpost nearing completion in 2010, the future role of the robotic arm will change significantly: it will shift gears from building the ISS to supporting its maintenance. This includes helping to catch free-flying, cargo spaceships carrying everything from science payloads to necessities for the 6-person crew living aboard the ISS.

The September flight of the HTV was the first demonstration of a new generation of automated spaceships that can carry unpressurized and pressured cargo, and tested Canadarm2's ability to conduct a tricky capture of a free-flying spacecraft. Once the Space Shuttle retires in 2010, unmanned resupply vehicles (like the HTV, the European Space Agency's Jules Verne Automated Transfer Vehicle (ATV), and the U.S. Commercial Orbital Transportation Services vehicles, Dragon and Cygnus) are scheduled to play a vital part in resupplying the Station. Currently, Russia's Progress are the only automated spacecraft that dock with the ISS on a regular basis (other than a demonstration flight for ATV in March 2008). Whereas the Progress and ATV vehicles are programmed to dock automatically to the ISS, all other spaceships will be captured and docked by Canadarm2.

A high-flying rendezvous with the ISS

The 10-metre HTV launched from Japan's Tanegashima Space Center at 1:01 p.m. Eastern on September 10, 2009. The autonomous spacecraft then slowly increased its orbital height and caught up to the ISS and its crew, including Canadian Space Agency Astronaut Bob Thirsk.

(Credit: Canadian Space Agency)

The final approach and subsequent grapple of the HTV called for both precision flying and deft work from the Station's 17-metre robot arm. Using GPS technology and laser navigation, the HTV slowly closed in on the ISS. Once it moved into position about 500 metres below the ISS, the crew began to monitor its progress to ensure a safe approach.

The HTV then gently pulsed its steering thrusters to pull itself up from beneath the Station. When it reached a predetermined area about 10 metres from the ISS's Kibo lab module, the HTV's guidance and control system synchronized the spacecraft's motion with respect to the Station. At this point, the two spacecraft were flying in formation at 7.7 km per second at more than 350 km above Europe. Canadarm2's operator, NASA Astronaut Nicole Stott, had just 99 seconds to safely grapple the HTV before its flight parameters were considered too risky. While working at the controls of the robotic work station inside the ISS, Stott used Canadarm2 to seize the Japanese cargo vehicle at 3:47 p.m. Eastern while the Station was over Romania.

Once the HTV has been captured, the ISS crew will attach it to the Station's Node 2. They will later open the hatches between the ISS and the HTV to unload supplies (such as food, clothes and a variety of equipment for science experiments), and restock it with waste cargo. Once its mission is complete, the HTV will be released and will follow a controlled path to reentry into the Earth's atmosphere.

Canadian Space Agency Astronaut Bob Thirsk's Key Role

Canadian Space Agency Astronaut and ISS crewmember Bob Thirsk played a major role in the success of the mission. Once Nicole Stott completed the capture maneuver, Bob used Canadarm2 to pick up the HTV from its parked position, moved it to ISS Node 2, and then docked it to the ISS.

With the HTV safely docked, the ISS crew will unload supplies (such as food, clothes and a variety of equipment for science experiments), and restock it with waste cargo. When its mission is complete, the HTV will be released and will follow a controlled path to reentry into the Earth's atmosphere.

Around September 23, , Bob will command Canadarm2 to extract part of the HTV called the Exposed Pallet (which carries a science experiment led by NASA and the Japanese Aerospace Exploration Agency). He will then hand over the Exposed Pallet to the Japanese robotic arm on the Station, which will then attach it to the JEM Exposed Facility (recently installed on the ISS by Canadian Space Agency Astronaut Julie Payette).

Diagram of Kibo (Credit: NASA)

Once Exposed Pallet has done its work, Bob will be back at the controls of Canadarm2 to receive pallet from the Japanese robotic arm, and place it back inside the HTV like sliding a drawer on wheels back inside its track. This operation will mark the first time one of Canadarm2's special features, called Force Moment Accommodation, is used. Akin to fine motor control in the human arm, Force Moment Accommodation gives Canadarm2 a delicate touch to prevent jamming the pallet's wheels should excessive force be applied.

At the end of the HTV mission, Bob will use Canadarm2 again to undock the HTV and maneuver it to a parking position.

The HTV will complete its mission by being released from the ISS on October 30.

The International Space Station, July 28, 2009 (Credit: NASA)