The -led International Space Station (ISS) Mission Management Team has approved plans for the scheduled unberthing of the first U.S. commercial resupply mission spacecraft later this week, as the astronauts aboard the orbiting science laboratory wrapped up a fast-paced, 2,400-lb. cargo exchange.
TheDragon’s unberthing is scheduled for May 31 at 4:05 a.m. EDT. Astronaut Don Pettit, who will carry out the operation using the station’s Canadarm2, will release the freighter below the orbital outpost at 6:10 a.m. After three orbits of the Earth, Dragon will fire its braking rockets at 10:51 a.m. for re-entry into the Earth’s atmosphere, ending the nine-day Commercial Orbital Transportation Services test flight with a parachute descent into the Pacific Ocean. A splashdown several hundred miles off Southern California is expected at 11:44 a.m.
The Dragon hatch was opened by the six-man ISS crew early May 26, a day after Pettit and European Space Agency astronaut Andre Kuipers grappled the freighter with the 58-ft.-long Canadarm2 and berthed it to the U.S. segment Harmony module.
Slightly more than 1,000 lb. of cargo, food, clothing, computer equipment and a NanoRacks experiment module were off-loaded. The capsule was refilled with nearly 1,400 lb. of station hardware, crew personal items, science equipment and unneeded spacesuit gear. The return items will be extracted from Dragon and turned over to NASA for distribution to scientists or vendors for refurbishment. The exchange of non-essential cargo unfolded over 18 hr. versus the scheduled 25 hr.
“The first time you fly a new vehicle, it’s always challenging. You never know what to expect,” said Paul Brower, NASA’s lead integrated systems engineer for the flight, on May 29. Bower occupies the NASA Mission Control position responsible for the interplay of communications, power and propulsion systems on the two spacecraft.
He praised SpaceX for its operational prowess, as the company flight control team in Hawthorne, Calif., joined with NASA in working through an assortment of computer and propulsion issues, guidance sensor adjustments during the rendezvous, and a prelaunch GPS issue on the station.
“It was definitely an interesting and challenging mission,” Brower says. “But in the end, we won against all the demons.”
Pettit and Joe Acaba, the two NASA astronauts aboard the station, offered a thumbs-up as well at the prospect that a human-rated version of Dragon could one day transport astronauts to and from orbit.
“I spent quite a bit of time in here this morning, just looking at the engineering and the layout,” Pettit reported soon after the hatch opening. “It looks like it carries about as much cargo as I can put in my pickup truck, and it’s roomier than a Soyuz. So, flying up in a human-rated Dragon is not going to be an issue.”
“It was phenomenal to watch the Dragon approach the space station, and see these guys do their job in grappling it and attaching to the space station,” added Acaba, who assisted Pettit with the Canadarm2 capture activities. “I have a lot of confidence in our future. This was a great first step to move us forward. I think we would feel very comfortable in a human-rated vehicle just like this one.”
NASA is currently funding the development of commercial crew transport services through Blue Origin,, Sierra Nevada and SpaceX. The agency is assessing proposals from funded and unfunded prospective commercial partners for a third round of crew transport development.