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A heartbreaking, out-of-the-gate failure of Russia’s sample return mission early this year created a wide circle of disappointment. For Russia, it was supposed to be a "cavalry charge" toward a hyperambitious goal that would have redeemed a quarter-century of interplanetary impotence but instead became a cosmic humiliation when the craft died shortly after liftoff. For planetary science, it meant that the composition of the Martian moon Phobos remains speculative and its origins still undetermined. For future human space strategies, the possibility of obtaining valuable supplies of oxygen en route to Mars, as the Phobos-Grunt mission was intended to determine, remains uncertain.
Within weeks of the probe's fiery burnup on January 15 over the far southeastern Pacific (where despite official Moscow assurances, it probably dropped some unobserved fragments onto dry land in Chile and Argentina), Roscomos, the Russian space agency, posted a summary of the accident investigation results on its Web site.
The report, posted in Russian earlier this year, raised more questions than it answered. And those issues may have an impact on plans for future Russian participation in European and U.S. planetary missions.
Even though top Russian officials previously offered well-publicized speculations about interference from American radar, that hypothesis was rejected. Instead the investigation suggested that cosmic rays had knocked out two non-radiation-hardened microchips at exactly the wrong moment. This event led the probe's computer to default to "safe mode" and await remedial commands from Earth. Although American experts in radiation hardening found the conclusion unlikely, they admitted it was not impossible.
Now that finding is in serious doubt because it is so statistically unlikely and because reports of more likely fatal flaws have appeared.
Before the report’s release (and, in fact, in some cases prior to the Phobos-Grunt launch), experts quoted anonymously in the Russian press were alleging that the flight software for the probe was badly designed and implemented and that last-minute modifications to the probe were numerous and not well controlled. But the official report discounted any such suspicions about the software or the hardware.
It did obliquely admit that two fundamental design flaws were ultimately responsible for the probe's inability to tolerate the cosmic-ray environment. First, most of the overwhelmingly foreign-built microchips—more than 90,000 in all—were never screened for radiation hardness and were purchased in full knowledge that they were not "space qualified." Second, the vehicle was designed so that emergency radio commands from Earth (the kind of signals required to coax it out of safe mode) were practically impossible to get onboard until after it had left its low parking orbit and headed out toward Mars. At that point, it would become much easier to track for long periods.
According to the report’s timeline, because of the initial failure to ignite the engines to head for Mars, the probe remained in its low parking orbit under full autopilot control. Sun-pointing orientation was maintained through thruster firings. Yet because ground sites could not accurately point their signals at the rapidly moving and only briefly visible probe, it took almost two weeks before any two-way communication could be established.
During that period, ground tracking revealed a bizarre behavior pattern. The low elliptical orbit actually began rising, mainly at its perigee (low point). The rise was steady until, after 10 days, it abruptly stopped and began a natural decay. These unexpected changes made precise predictions of its future flight path more complicated, perhaps contributing to the inability of ground sites to point their signals with sufficient accuracy.