Dragon's flight to space station put on hold
BY STEPHEN CLARK
Posted: March 1, 2013
SpaceX's robotic Dragon resupply freighter appeared to overcome a "frightening" propulsion glitch shortly after successfully launching from Cape Canaveral on Friday, giving managers hope the $133 million mission can keep its charge of delivering more than a ton of cargo to the International Space Station.
The trouble sparked a scramble to respond, diagnose and recover from the setback, which threatened to end the mission the same day it began.
Only a fraction of the spacecraft's thrusters were operational, keeping engineers from controlling the capsule's orientation or sending it toward the space station.
"We noticed after separation that only one of the four thruster pods engaged or was ready to engage," said Elon Musk, SpaceX's founder, CEO and chief designer. "And then we saw that the oxidizer pressure in three of the four tanks was low."
The Dragon spacecraft has 18 Draco thrusters, tiny rocket engines designed to change the capsule's orbit and adjust its orientation. The Draco engines are divided into four pods, each with four or five thrusters.
Controllers had trouble aligning Dragon's antenna with communications satellites, so SpaceX turned to an Air Force network of ground stations to contact the spacecraft.
SpaceX extended the Dragon's solar panels shortly before 12 p.m. EST (1700 GMT) and brought the spacecraft's other thrusters back online through the next several hours.
Musk said the situation was a "little frightening" while engineers struggled to salvage the mission.
Musk said engineers commanded valves in Dragon's propulsion system to repeatedly open and close, hoping to dislodge potential blockage in helium pressurization lines leading to oxidizer tanks supplying three of the craft's four thruster pods.
"We think there may have been a blockage of some kind or stuck check valves going from the helium pressurant tank to the oxidizer tank," Musk said, cautioning that conclusion was just one possibility based on a preliminary investigation. "Whatever that blockage is seems to have alleviated."
The 15-story rocket rose from the launch pad and pointed northeast from the Florida spaceport, dispatching a window-rattling thunder for miles around as it was swallowed in a thin cloud deck hanging overhead.
Cameras mounted on the launcher showed it smoothly rocketing into the upper atmosphere before jettisoning its nine-engine first stage three minutes after liftoff.
The Falcon 9's second stage fired its single Merlin engine for six minutes, racing northeast up the U.S. East Coast as the engine's niobium alloy nozzle glowed red hot.
The rocket's flight computer commanded the second stage engine to turn off once it reached its target orbit, and the Falcon 9 released the Dragon spacecraft moments later. A camera on the Falcon 9 rocket showed live footage of the cargo craft drifting away.
That is when Dragon's propulsion trouble began.
"They did everything exactly right with the vehicle," said Bill Gerstenmaier, NASA's associate administrator for space operations. "The team in Hawthorne was awesome. They prioritized immediately what things they needed to do."
Gerstenmaier, a former space shuttle flight controller, said SpaceX engineers faced a "tough" and "demanding" job overcoming the problem.
"They did a phenomenal job of pulling that all together," Gerstenmaier said. "They showed the patience it takes to operate in space, to not give up and keep their options open."
But the ship's arrival at the massive 450-ton complex will not occur on schedule.
It was supposed to climb into the space station's orbit and approach the outpost early Saturday, less than 21 hours after liftoff. NASA and SpaceX said Friday that Sunday is the earliest the resupply craft will reach the complex, depending on analysis of the Dragon's thruster system and a safety review to ensure the capsule will not pose a threat to the station or its six-man crew.
SpaceX developed the Falcon 9 launcher and Dragon spacecraft in a public-private partnership with NASA, which partially funded the design and testing of the vehicles with the intention of using the system to replace part of the space shuttle's cargo-carrying capacity after its retirement.
NASA and SpaceX have a $1.6 billion contract for 12 cargo delivery missions through 2016. The current mission is the second flight under the contract.