Wednesday, November 14, 2012

More SpaceX Anomalies Documented

The SpaceX Dragon arrives at the Port of Los Angeles on October 30, 2012 after returning from the International Space Station. Image source: SpaceX.

Marcia Smith of reports that the first SpaceX cargo service flight in October to the International Space Station suffered several anomalies not yet reported by the media.

The overall success of SpaceX's first operational cargo mission to the International Space Station (ISS) last month overshadowed the fact that the mission also encountered several problems, including the failure of one of the nine Falcon 9 engines.

Speaking to the NASA Advisory Council's Human Exploration and Operations Committee today, ISS program manager Mike Suffredini said that Space X is still trying to determine what happened to the engine. NASA is participating in the investigation, he said, and a fault tree analysis is underway.

Several other problems also arose during the mission. While berthed to the ISS, one of the three computers on the Dragon spacecraft failed. Dragon can operate with only two computers, and SpaceX chose to proceed with the two functioning units rather than trying to fix the faulty unit while on orbit. According to Suffredini's charts, Flight Computer-B "de-synched" from the other two "due to a suspected radiation hit" and although it was rebooted successfully, it was "not resynched." Dragon experienced other anomalies because of radiation as well. One of three GPS units, the Propulsion and Trunk computers and Ethernet switch all experienced "suspected radiation hits," but all were recovered after a power cycle. Suffredini said that SpaceX is considering whether it needs to use radiation-hardened parts instead, but noted that "rad-hardened" computers, for example, not only are more expensive, but slower. He speculated that the company would ultimately decide to use rad-hardened components in the future unless it is cost-prohibitive.

Problems with one of the Draco thrusters and a loss of all three coolant pumps after splashdown also marred the mission. The Glacier freezer onboard Dragon used to return scientific samples from the ISS was at -65 degrees Centigrade (C) instead of the required -95 degrees C when it was accessed three hours after splashdown. Suffredini said that some of the samples "exceeded limits" (presumably temperature limits), but that the limits were conservative. How much of a problem the warmer temperature could cause apparently is not yet clear.

Smith quotes Suffredini, "If NASA is not sufficiently confident that the system works, it will not put its cargo aboard and 'they don't get paid if I don't fly.'"

The meeting's agenda is online but the meeting minutes are not.

UPDATE November 19, 2012A blog entry on the Aviation Week web site offers much more detailed insight into the radiation tolerance issue.

AWST: So, NASA does not require SpaceX to use radiation-hardened computer systems on the Dragon?

John Muratore: No, as a matter of fact NASA doesn't require it on their own systems, either. I spent 30 years at NASA and in the Air Force doing this kind of work. My last job was chief engineer of the shuttle program at NASA, and before that as shuttle flight director. I managed flight programs and built the mission control center that we use there today.

On the space station, some areas are using rad-hardened parts and other parts use COTS parts. Most of the control of the space station occurs through laptop computers which are not radiation hardened.

The radiation environment is something people have known about for a long time. It's part of the natural environment, and it varies. It matters what kind of mission you're doing. With Dragon we're doing low-Earth orbit, short-duration missions and that drives a lot of the architecture.

So NASA didn't require radiation-hardened parts. It did, however, require us to do a hard analysis of the radiation environment, the effect of the environment on the Dragon systems and how we'd respond to that. We not only produced that analysis, but it was reviewed by an independent panel of experts. So NASA had very strong requirements for us to understand the environment and have planned out our responses to the environment, and we've done that.

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