SpaceX Dragon heads to space; Station astronauts prep for Wednesday spacewalk

Friday's launch of the third SpaceX commercial resupply services mission sent the Dragon space freighter on a course to rendezvous with the station Sunday morning. Commander Koichi Wakata and Flight Engineer Rick Mastracchio will capture Dragon using the Canadarm2 robotic arm at 7:14 a.m. to set it up for its berthing to the Earth-facing port of the Harmony module. Live NASA Television coverage of Sunday's Dragon activities begins at 5:45 a.m. and returns at 9:30 a.m. for coverage of the berthing of Dragon to the Earth-facing port of the Harmony node.

The scientific payloads on Dragon include investigations that focus on efficient ways to grow plants in space, demonstrating laser optics to communicate with Earth, human immune system function in microgravity and Earth observation. Also being delivered is a set of high-tech legs for Robonaut 2, which can provide the humanoid robot torso already aboard the orbiting laboratory with the mobility it needs to help with regular and repetitive tasks inside the space station.

Dragon also will deliver the second set of investigations sponsored by the Center for the Advancement of Science in Space (CASIS), which manages the portion of the space station designated a U.S. National Laboratory. CASIS investigations on Dragon are part of the organization's initial suite of supported payloads linked to Advancing Research Knowledge 1, or ARK 1. The investigations include research on protein crystal growth, which may lead to drug development through protein mapping, and plant biology.

Meanwhile aboard the International Space Station, the Expedition 39 crew is in the homestretch of preparations for a spacewalk to replace a failed backup computer relay box in the S0 truss. That 2 ½-hour spacewalk by Mastracchio and Flight Engineer Steve Swanson is slated to begin at 9:20 a.m. Wednesday.

The spacewalk will be the 179th in support of space station assembly and maintenance, the ninth in Mastracchio's career and the fifth for Swanson. Mastracchio will carry the designation of EV 1, wearing the spacesuit bearing red stripes. Swanson will be EV 2, wearing the spacesuit without stripes.

Mastracchio and Flight Engineer Steve Swanson installed a new circuit board inside a spare multiplexer-demultiplexer (MDM) that they will carry with them outside the station to replace the backup MDM that failed during routine testing April 11. The failed unit is one of the station's two external MDMs that provide commands to some of the space station's systems, including the external cooling system, solar alpha rotary joints and mobile transporter rail car.

After the two NASA astronauts installed the new card in the spare MDM, Wakata worked with the ground team at Mission Control in Houston to perform a functional checkout of the spare.

Afterward, Mastracchio trimmed a spare thermal insulator sheet to properly fit the MDM.

Wakata also found time for station science with another session of the Hybrid Training experiment. This Japan Aerospace Exploration Agency study takes a look the health benefits of applying electric stimulation to a muscle opposing the voluntary contraction of an active muscle. In addition to providing a backup to the traditional exercise devices aboard the station, Hybrid Training may be useful in keeping astronauts fit as they travel beyond low Earth orbit aboard smaller spacecraft.

Mastracchio took a brief break from his work to talk with students at his three alma maters -- the University of Connecticut, the Rensselaer Polytechnic Institute in Troy, New York, and the University of Houston-Clear Lake near the Johnson Space Center.

Flight Engineer Mikhail Tyurin spent much of his day working in the Zvezda service module as he cleaned ventilation screens and performed routine maintenance on the Russian life-support system.

Flight Engineer Alexander Skvortsov performed another session of the Kulonovskiy Kristall experiment, gathering information about charged particles in a weightless environment.

Skvortsov also teamed up with Flight Engineer Oleg Artemyev to unload items from the ISS Progress 53 cargo craft docked at the aft port of Zvezda. Progress 53 is set to undock from the station on Wednesday, April 23, at 4:54 a.m. to test its Kurs automated rendezvous equipment. The vehicle will redock with Zvezda on April 25 at 8:16 a.m. Progress 53 delivered 2.9 tons of food, fuel and supplies to the station on Nov. 29 following a four-day journey that included a "flyby" of the station to test a new lighter, revamped Kurs system .

And after 11 days of free flight for engineering tests, the Russian ISS Progress 54 cargo ship, now loaded with trash from the station, was commanded to deorbit for its fiery entry into the Earth's atmosphere for disposal. The deorbit burn at 10:52 a.m. sent the cargo craft on a course for atmospheric entry over the Pacific Ocean at 11:32 a.m.