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Japan's robotic cargo craft nears space station
BY STEPHEN CLARK
SPACEFLIGHT NOW

Posted: January 26, 2011


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Five days after launching from southern Japan, an automated cargo freighter will arrive at the International Space Station Thursday with 8,500 pounds of fresh supplies, spare parts and science experiments.


Footage of the launch of the H-2B rocket with Japan's second robotic cargo spacecraft. Liftoff occurred at 0537 GMT (12:37 a.m. EST; 2:37 p.m. JST) Saturday. Credit: JAXA
 
The spacecraft has performed a series of engine burns since blasting off early Saturday from the Tanegashima Space Center, an island launching base in southern Japan. The thruster firings raised the ship's altitude and tweaked its approach to the complex, which flies 220 miles above Earth.

Nicknamed Kounotori 2, meaning white stork, the mission follows the HTV's successful first flight in late 2009. The Japan Aerospace Exploration Agency, or JAXA, designed and built the HTV as part of its contribution to the space station program.

More maneuvers are planned in the final phase of the rendezvous, guiding the HTV through a series of hold points on the way to the space station.

Integrated operations between NASA's Mission Control Center in Houston and the HTV control room in Japan will begin around 0430 GMT Thursday (11:30 p.m. EST Wednesday).

The rendezvous is designed to include several holds, points where engineers can evaluate the ship's health and readiness before continuing further.

The barrel-shaped spacecraft should reach an approach initiation point 5 kilometers, or 3.1 miles, directly behind the space station early Thursday morning, U.S. time. When the HTV stops at the initiation point, flight controllers in Houston and Japan will review the spacecraft's status before committing to the next phase of the rendezvous.

The HTV will already be in two-way communications range of the space station, permitting GPS navigation and commanding from the lab's crew. A control panel aboard the station gives astronauts the ability to order aborts, holds and retreats should the HTV encounter problems as it closes in on the complex.

The ship will next move to a rendezvous insertion point 500 meters, or 1,640 feet, below the station using its relative GPS navigation system. Once it halts at the insertion point, the HTV will switch to a futuristic laser rendezvous sensor, which shoots beams of light toward reflectors mounted on the bottom of the station's Kibo laboratory module.

The laser beams will bounce off the reflectors and back to receivers on the front end of the HTV, allowing the ship to determine its exact position relative to the station.

The navigation data will be fed into the HTV's flight computers to send commands to the freighter's propulsion system to fine-tune the approach.

After passing through the rendezvous insertion point, the HTV will halt 250 meters, or 820 feet, below the space station at about 0949 GMT (4:49 a.m. EST). The plan calls for the spacecraft to perform a 180-degree yaw flip maneuver to line up its grapple fixture with the position of the station arm.


Artist's concept of the HTV approaching the International Space Station. Credit: JAXA
 
The ship will stop again 30 meters, or 98 feet, under the space station for 20 minutes beginning at about 1048 GMT (5:48 a.m. EST).

If controllers give final approval, engineers will order the HTV to move even closer to the outpost. The craft will stop once more, hovering about 30 feet beneath the Kibo lab module.

Astronauts aboard the space station will extend the lab's robot arm to catch the HTV at about 1144 GMT (6:44 a.m. EST), when the unmanned space tug reaches an imaginary capture box about 30 feet below the complex. The capture is supposed to occur in daylight.

NASA astronaut Cady Coleman will be at the controls of the lab's robot arm inside the cupola, a seven-windowed module giving crews unrivaled views of incoming and outgoing traffic outside the space station.

"[The cupola] is really important to our crew because we will have the Japanese supply vehicle, the HTV, and that will approach right below that cupola window, and from the cupola window we can actually see the entire robotic arm, the part of the robotic arm that we will use to capture the HTV, which is huge, and also the HTV itself," Coleman said. "And it's one thing to see those views on a camera, on a video monitor in front of you, and it is really another one to have part of yourself just understand the physical size of everything and how close everything is to everything else."

Italian astronaut Paolo Nespoli and space station commander Scott Kelly will assist Coleman with the grapple and berthing procedures.

"It actually gets to the station and doesn't dock to the station," Nespoli said in a preflight interview. "It stops at about 10 meters, 30 feet, below the station, and stops there and the control mechanism [makes it] stay in a little box there, and then we are supposed to take the robotic arm, go and grab the vehicle and bring it up to [the] station."

Firm berthing of the HTV to the space station's Harmony module should begin around 1415 GMT (9:15 a.m. EST).

The HTV is the only operating vehicle designed to be grabbed by the robot arm, but other spacecraft will soon use a similar technique. SpaceX and Orbital Sciences Corp. are developing U.S. cargo capsules to start flying to the station later this year, and both vehicles will be manually berthed to the outpost.

"The last few meters are very, very delicate and if we do it with the robotic arm, then we can be really precise and we take away the fact there are two vehicles flying independently because not only the [HTV] moves, but the station moves," Nespoli said. "So you can have all sort of problems. Obviously we are not stopped. It looks like we are stopped but you are flying in space at seven kilometers a second, so things need to be controlled carefully and the fact that you go and grab it with the arm takes away a lot of these problems."


The first HTV mission reached the station in September 2009. Credit: NASA
 
The European Space Agency's ATV cargo ship docks automatically with the station's Russian segment. Space shuttles and Russian vehicles also dock directly with the complex.

The HTV's arrival starts a hectic schedule for the space station, which is set to receive three more visiting vehicles by the end of February. Russia will launch a Progress resupply mission early Friday, Russian time, and Europe's Automated Transfer Vehicle will start its journey toward the outpost Feb. 15. The shuttle Discovery will launch Feb. 24 with a stowage module and more supplies for the station.

The spacecraft's pressurized cabin is packed with food, water, clothing and toiletries for the lab's crew, two refrigerator-sized Japanese science racks, computers, cameras and other supplies. The HTV's external cargo module carries two massive spare parts units to be mounted on the station's truss backbone. The unpressurized cargo amounts to 2,043 pounds.

Astronauts will use the robot arm to pull the external cargo pallet from the HTV Feb. 1. A smaller Japanese arm will place the pallet on the porch of Japan's Kibo module.

Between Feb. 2 and 4, robotics systems will transfer a cargo container and spare flex hose rotary coupler to a logistics platform on the station's truss. A human-like robot called the Special Purpose Dextrous Manipulator, or Dextre, will be used during the moves.

Once the external cargo is removed, the robot arm will place the empty exposed pallet back inside the HTV.

The HTV's visit was supposed to occur between space shuttle flights, but Discovery's mission was delayed from November by cracks in the shuttle's external fuel tank.

Fearing damage from the shuttle's powerful steering jets, managers decided to move the HTV from Harmony's Earth-facing, or nadir, port to the top of the module for Discovery's mission. That maneuver is expected around Feb. 18, and the spacecraft will be returned around March 8 to the lower position on Harmony.

Station residents will unload 6,455 pounds of supplies from the pressurized section of the 33-foot-long craft over the next two months. The astronauts will cram trash and other unneeded items into the HTV before releasing the ship in late March. The freighter is designed to burn up as it plunges back into the atmosphere, disposing of the lab's garbage over the Pacific Ocean.

The departure and re-entry are scheduled for March 28 and 29.