[image-51]As work continues at the Cape Canaveral Air Force Station in Florida for Friday’s 3:25 p.m. EDT launch of the SpaceX Falcon 9 rocket and the Dragon cargo craft, the International Space Station’s Expedition 39 crew geared up Thursday for a contingency spacewalk to replace a failed backup computer relay box on the station’s truss. The 2 ½-hour spacewalk is set for Wednesday, April 23, unless SpaceX scrubs its launch attempt Friday, in which case the excursion will move up earlier to Sunday, April 20.
NASA Television coverage of the Dragon launch will begin at 2:15 p.m.
A launch on Friday for the Dragon cargo craft loaded with nearly 5,000 pounds of supplies and experiment hardware would send the commercial space freighter on a course to rendezvous with the station Sunday morning. Commander Koichi Wakata and Flight Engineer Rick Mastracchio will capture the space freighter 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 U.S. Air Force 45th Weather Squadron predicts a 40 percent chance of favorable conditions for the launch of SpaceX-3 on Friday, April 18. For a backup launch opportunity on Saturday at 3:02 p.m., the weather is 60 percent “go” with a possibility of violating the Thick Cloud, Liftoff Winds and Flight Through Precipitation rules.
[image-67]Aboard the station Thursday, Mastracchio and Flight Engineer Steve Swanson donned their U.S. spacesuits for a fit check as they prepare to venture outside the space station next week to replace a backup multiplexer-demultiplexer (MDM) that failed during routine testing April 11. The box 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.
NASA TV coverage of the April 23 spacewalk will begin at 8:30 a.m. The spacewalk is scheduled to begin at 9:20 a.m. If Friday's SpaceX cargo launch is postponed, the two NASA astronauts will conduct the spacewalk Sunday, April 20. NASA TV coverage would begin at 8 a.m. with the spacewalk scheduled to begin at 8:55 a.m.
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.
Swanson also spent time Thursday configuring the tools that he and Mastracchio will use during the excursion.
In addition to the spacewalk preparations, the station’s astronauts participated in scientific research into the effects of long-duration spaceflight on the human body.
Wakata began his workday with the Body Measures experiment, which collects anthropometric data to help researchers understand the magnitude and variability of the changes to body measurements during spaceflight. Predicting these changes will maximize crew performance, prevent injury and reduce time spent altering or adjusting spacesuits and workstations. The investigation also could help scientists understand the effects of prolonged bed rest, which produces physiological changes similar to those experienced in microgravity. Mastracchio assisted Wakata throughout the experiment session, setting up the calibration tape, collecting data and taking photographs.
Afterward, Mastracchio participated in a periodic fitness evaluation while he worked out on the station’s exercise cycle. Swanson assisted Mastracchio with the session as he initiated blood pressure measurements. Flight surgeons use these measurements as well as electro-cardiogram data recorded during these exercise sessions to keep track of the long-term health of the astronauts.
On the Russian side of the complex, Flight Engineer Alexander Skvortsov worked with the Kulonovskiy Kristall experiment, gathering information about charged particles in a weightless environment.
Afterward, he joined up with his fellow cosmonauts aboard the station -- Flight Engineers Oleg Artemyev and Mikhail Tyurin -- to talk with students gathered at the Russian Mission Control Center in Korolev, outside Moscow.
Skvortsov rounded out his day unloading more cargo from the ISS Progress 55 cargo ship, which delivered nearly three tons of supplies to the orbital laboratory when it launched and docked with the station’s Pirs docking compartment on April 9.
Artemyev meanwhile continued his checkout of Vizir photography equipment, which is designed to automatically detect sites for Earth photography using ultrasonic angle measurement. He also downloaded data from the Matryoshka experiment. Named after the traditional Russian nesting dolls, Matryoshka analyzes the radiation environment onboard the station.
Tyurin focused his efforts on repacking Russian spacewalk equipment, conducting an inventory of cargo stowed in the Russian segment and performing routine maintenance on the life-support system in the Zvezda service module.