The March 1 launch of Cargo Resupply Service mission 2 [CRS2] to the International Space Station was flawless. Space X’s Falcon 9 brought the Dragon capsule into orbit. But at 9 minutes into the flight, the Dragon capsule’s Draco thruster system did not activate as planned.
The capsule is equipped with 18 of SpaceX’s Draco thrusters, which use nitrogen tetroxide and monomethylhydrazine fuel to maneuver the spacecraft in orbit.
“Issue with Dragon thruster pods,” SpaceX founder Elon Musk wrote on Twitter. “System inhibiting three of four from initializing. About to command inhibit override.” Given the thruster issue, SpaceX engineers initially held off on commanding Dragon to deploy its solar arrays, which gather energy from the sun to power the vehicle.
“One thruster pod is running. Two are preferred to take the next step, which is to deploy the solar arrays,” SpaceX officials said in a statement. “We are working to bring up the other two in order to plan the next series of burns to get to station.” By about 11:50 a.m., EST, about two hours after launch, SpaceX engineers had made enough progress to deploy the Dragon capsule’s solar arrays.
“Solar array deployment successful,” Musk wrote in a Twitter post, after noting that “Thruster pod 3 tank pressure trending positive.” A few hours later, all four pods were operational.
Musk said the SpaceX team was still examining what caused the thruster pod problem, but a “preliminary guess” is that there was a blockage in oxidizer pressurization. After cycling and pressure hammering the stubborn valve, SpaceX was able to free up the blockage, Musk said. “All of the oxidizer tanks are now holding the target pressure on all four pods.”
Musk, meanwhile, acknowledged that this morning’s trouble was “a little frightening.” But the good news is that there does not appear to be any leaks or debris. “All systems appear to be intact and functioning quite well at this point, so hopefully things go in that direction.”
Bill Gerstenmaier, associate administrator for Human Exploration and Operations at NASA, praised SpaceX’s efforts. “They did everything right with the vehicle,” he said, and “showed the patience it takes to operate in space.”
Dragon docked at the space station March 3; installed onto the Earth-facing port of the Harmony module. Five hours later, astronauts on board the station opened Dragon’s hatch and begin unloading cargo. Dragon arrived with more than 2,300 pounds of pressurized and unpressurized cargo and packaging to ensure safe travel. During the next 22 days, astronauts will unload and then load cargo, including materials to support critical science experiments. Dragon will return to Earth with more than 3,000 pounds of cargo, and has a targeted splashdown in the Pacific Ocean off the coast of Baja, Calif., March 25. Dragon is the only spacecraft in the world today capable of returning significant amounts of cargo to Earth.