A previous version of this article contained erroneous information on several accounts. The corrections, which are significant, are illustrative of the unique approach SpaceX is taking in its Falcon / Dragon system.
Innerspace.net originally reported that during a meeting of the NASA Advisory Council’s Human Exploration and Operations Committee, ISS Station Manager Mike Suffredini discussed a number of issues related to the recent SpaceX CRS-1 mission to ISS, once the Dragon was successfully berthed to the station.
Speaking to the committee, ISS Station Manager Mike Suffredini relayed that one of Dragon’s three redundant flight computers, Computer “B” desynched from the other two, presumably due to a radiation hit. Although the computer was successfully rebooted, SpaceX , after discussion with, and at the suggestion of NASA, did not attempt to re-synch the computer because that was actually the easiest course of action. Furthermore it was completely within the logical parameters of the Dragon’s triple string redundant voting architecture which requires two of three computer units, each of which consists of two computers, to agree on each course of action. Reports carried elsewhere that SpaceX was “un-able” to resynch were simply incorrect.
What was originally described as an undisclosed problem with a set of Draco thrusters was in fact merely a problem with sensors. Specifically, two pressure transducer sensors and one injection resistance temperature detector. The Dragon’s onboard fault detection, isolation and recovery system handled the sensor issues without difficulty.
It is worth noting that for almost any system, whether it was the Space Shuttle or the old family sedan, there is a world of difference between a failed sensor, which is altogether common, and one that is correctly reporting a failing component, and this was definitely a case of the former.
Finally, the original version incorrectly associated a rise in the GLACIER freezer temperature, which contained biological samples taken aboard ISS over the previous year in space, from -95 degrees Centigrade, to the -65 threshold with a failure of on-board cooling pumps. The issue was actually caused by temporary loss of electrical power due to suspected water immersion of a power management unit after splashdown.
Multiple points here:
The cooling pumps are for use while the Dragon is in orbit. After splashdown, the cabin is cooled by a combination of the surrounding sea, which incidentally has a current temperature of approximately 77 degrees in the recovery zone, and re-circulation fans, which provided uninterrupted service throughout the recovery process. As a result, the cabin temperature remained within its intended range at all times.
The GLACIER freezer was re-started immediately upon recovery. This took place very quickly due to the Dragon’s remarkably precise re-entry and landing within view of awaiting recovery vessels. By contrast, the Soyuz capsule containing three ISS Expedition 33 crew members, including U.S. astronaut Sunny Williams who directed the Dragon’s capture and release, landed nearly 20 miles off target.
As for the water immersion, the Dragon capsule, like everything else SpaceX is undertaking is an evolutionary project. Some changes are small, some are large, but the goal is a constantly improving system. Its a fairly safe bet that by the time of the next launch, improvements will already be incorporated to prevent a recurrence.
The radiation issue is another matter, and once again the original comments by Mike Suffredini about SpaceX looking to incorporate radiation hardened chips are somewhat misconstrued. Rather than incorporate rad-hardened chips as a sort of Maginot line in space, SpaceX is taking a far more flexible and evolutionary layered system approach which is covered in-depth in this interview with SpaceX director of vehicle certification, John Muratore, in Aviation Week. The very informative article is a must read for anyone following SpaceX’s long-term ambitions, and is indicative of the sea change the company is taking in its approach.
As for the engine shutdown issue, data analysis has yet to result in any definitive conclusions. Although the analysis will continue, the observation that this particular engine had undergone a comparatively high degree of pre-flight testing, may ultimately lead to the conclusion that the shut down was related to the accumulating fatigue of an engine firing more than its nominal mission requirements. If this turns out to be the case; it would prove to be both somewhat ironic, as well as easily addressed by limiting cumulative firings for flight engines. Ongoing analysis has likely pushed the likely date of the next Dragon flight to ISS into the early March time frame.
While certainly both NASA and SpaceX would have preferred the mission to have come off flawlessly, there is a clear upside to having some issues to address. SpaceX is still only at the beginning of a long learning curve in its quest to develop a routine, affordable space transportation system based on this first generation Falcon and Dragon. The critical difference which distinguishes the SpaceX effort from prior developments, is that the company is configured to incorporate necessary changes quickly, and with little fuss, all while maintaining a vital focus on long-term affordability. It is an environment made possible by the unique structure of NASA’s COTS and CRS programs and the foresight of the people who championed them.
SpaceX’s remarkable success to date sometimes makes it easy to overlook the fact that we are only just now attempting to access space in an economically rationale manner. And while it is true that the U.S. as well as Russia, have both been launching rockets and recovering space capsules for 50 years, the current Falcon / Dragon system is the first to attempt to do so affordably, and in an architecture which can be steadily evolved to substantially reduce costs and improve performance, a necessary path if we are to ever break out of the cycle of high costs which have kept us in LEO for 40 years. Along the way there will almost certainly be bad days and failed missions, but this one wasn’t even close.