SpaceX's first attempt to send its Dragon cargo capsule to the International Space Station ended abruptly Saturday morning when computers aboard the company's Falcon 9 rocket shut off the craft's engines just after ignition.
The control system for the rocket, which uses a cluster of nine of the company's Merlin engines in its first stage, checks to ensure all the engines are running properly before the craft is released to begin its climb to space.
After a flawless countdown, the engines ignited at 4:55 a.m. as scheduled. But the flight-control computer detected too much pressure in the combustion chamber of one of the engines and aborted the pre-dawn launch. The next launch opportunity comes at 3:44 a.m. Monday.
This mission combines into one attempt the objectives of two demonstration flights the company must perform for NASA before it begins regular cargo runs to and from the International Space Station under a $1.6 billion, 12-mission space-station resupply contract.
SpaceX must show that the automated Dragon spacecraft is capable of the precision flying needed to operate safely in the station's vicinity before docking – including a rendezvous-abort maneuver – as well as perform the maneuvers needed to bring it within reach of the space station's robotic arm.
Once station crew members have Dragon in their grasp, they use the arm to dock the craft with the station.
This mission represents only the third for the Falcon 9. The rocket's initial test launch in June 2010 was successful. SpaceX's hardware cleared another key milestone the following December, when the company lofted, orbited, and recovered its Dragon capsule – becoming the first commercial venture to pull off such a feat.
Although the previous successes have fed high expectations for this mission, SpaceX founder and chief designer Elon Musk cautioned during a press briefing in April previewing the mission that the rocket “is still relatively new.”
At a post-scrub briefing Saturday morning, SpaceX president Gwynne Shotwell said all nine engines ignited normally, but the flight-control computer detected too much pressure in engine five's combustion chamber, triggering the abort a half second later.
Although the rocket can still reach orbit if up to two engines fail, it needs all nine to lift off.
Asked if today's aborted launch represented a failure, she replied that it would have been a failure if the rocket had launched with the glitch.
After engines ignite, “we hold the vehicle down for this purpose, to watch for this exact issue,” she said. “ Just like a pilot at the end of a runway revs the engines and looks at the gauges, we were revving the engines, looking at the gauges, and we decided not to fly,” she said.
Although problems like this can crop up if a pressure sensor or software is faulty, neither seems to be the case here. “We can't blame the software guys for this one,” Shotwell said.
SpaceX saw a similar event during the Falcon 9's first launch in 2010, she said. But since that mission involved no on-orbit rendezvous, SpaceX was able to troubleshoot the problem and launch later the same day. Today, the launch window for the mission was only a few seconds long to ensure Dragon reaches the station with enough propellant for its thrusters to repeat test maneuvers if necessary.
A quick early look at the data on the engines indicated that the pressure was too high in engine five because it was running hot – a sign it wasn't getting enough fuel, Ms. Shotwell said. Technicians will inspect the engine today to determine the cause and begin any repairs. If the engine needs to be replaced, SpaceX has another Falcon 9 in the hanger at the Kennedy Space Center technicians can tap for a replacement.
Ms. Shotwell noted that if the engine needs to be swapped, workers can perform the change-out and still have the rocket ready for another launch Monday. The next launch opportunity after that comes Tuesday morning at 3:22 a.m.
SpaceX is one of two companies that have contracts with NASA to provide resupply flights to the space station. The second is Orbital Science Corporation, which inked a deal worth $1.9 billion for eight resupply missions between 2012 and 2015. The company is slated to launch its Antares rocket and Cygnus cargo craft on their first demonstration flight later this year.
But the Falcon 9/Dragon package represents a unique capability for NASA and the space-station program, NASA officials say. Unlike all the other automated cargo craft supplying the station, Dragon is designed to bring cargo back to Earth as well – ranging from samples used in on-orbit science experiments to space-station components that can be repaired or refurbished.
In a process started in 2006, NASA has turned to commercial launch providers to resupply the space station in order to focus its efforts on sending human explorers beyond low-Earth orbit. In addition to using commercial carriers for cargo, the agency is working with six companies on systems that would carry humans to low-Earth orbit as well.