After Stumble, SpaceX’s Dragon Reaches the ISS

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WASHINGTON — Overcoming a propulsion glitch that delayed its arrival by a day, a Dragon cargo capsule operated by Space Exploration Technologies Corp. (SpaceX) arrived at the international space station (ISS) March 3. 

After several hours of maneuvering that began when Dragon got within 10 kilometers of ISS, astronauts used the station’s robotic arm to grapple the capsule at 5:31 a.m. EST,  an hour earlier than SpaceX had announced the evening before. At 8:56 a.m., NASA Mission Control and the ISS crew confirmed that Dragon was succesfully berthed with the station.

Dragon was installed on the Earth-facing port of the station’s Harmony module. Ground controllers at the Johnson Space Center in Houston controlled the arm during berthing.

When Dragon reached orbit the morning of March 1, three of the capsule’s four thruster pods failed to activate as expected, delaying solar array deployment and severely limiting Dragon’s maneuverability. Later that day, SpaceX brought all four thruster pods back on line, but not in time to make its scheduled rendezvous with ISS the morning of March 2. 

The culprit may have been blockage or a stuck check valve somewhere in the system that pressurizes the oxidizer tanks that feed Dragon’s thrusters, Elon Musk, founder and chief executive officer of SpaceX, said in a post-launch press briefing March 2.

After launch, “only one of the oxidizer tanks was at the right pressure,” Musk said. “We think there may have been a blockage of some kind, or stuck check valves going from the helium pressure tank to the oxidizer pressure tank. Whatever that blockage is seems to be alleviated.”

Dragon will deliver more than 1,000 kilograms of pressurized and unpressurized cargo to ISS and return 1,210 kilograms of cargo to Earth. The capsule is scheduled to splash down March 25 in the Pacific Ocean off the coast of Baja California, Mexico.

This is the second contracted cargo delivery mission SpaceX is flying for NASA under a 12-flight, $1.6 billion Commercial Resupply Services contract it got from the agency in 2008. NASA also awarded an eight-flight, $1.9 billion contract to Orbital Sciences Corp. The Dulles, Va.-based company is expected to send send its first Cygnus cargo freighter to ISS later this year aboard an Antares rocket launched from Wallops Island, Va.

SpaceX’s latest cargo mission launched March 1 aboard the company’s Falcon 9 rocket, which lifted off from Launch Complex 40 at the Cape Canaveral Air Force Station in Florida. The launch, Falcon 9’s fifth to orbit, went exactly according to plan, SpaceX said March 1 on its website. 

That marks an improvement over Falcon 9’s Oct. 7 launch — SpaceX’s first Commercial Resupply Services launch for NASA — in which the rocket lost one of its nine engines 79 seconds after liftoff, forcing SpaceX to drop off a piggyback commercial payload into a lower-than-intended orbit. That satellite fell out of the sky four days later, prompting owner Orbcomm, a Fort Lee, N.J.-based provider of machine-to-machine communications services, to file an insurance claim.

Despite Falcon 9 engine failure on SpaceX’s first contracted cargo delivery, the mission was considered a success from a NASA point of view, as Dragon delivered its cargo to ISS on schedule.