I wanted to revisit my earlier story on the failed Russian Phobos-Grunt probe, since I left the origin of the problems as a mystery. In February, the results of an inter-agency committee tasked to study the failure reported an on-board computer reboot "influenced" by heavy charged particles was the main cause:
...the
emergency situation onboard had been caused by a restart of two
semi-sets (processors) of the TsVM22 computer in the onboard calculation
complex, BVK, Roskosmos said. As a result of such "dual restart," the
nominal pre-programmed flight sequence was interrupted and the
spacecraft entered solar orientation, simultaneously waiting for ground
commands in X-band frequencies. However the spacecraft was designed to
communicate in X-band only during the cruise stage of the flight
(between the Earth and Mars, following the escape from the Earth orbit),
Roskosmos admitted.
The
most likely factor which caused a "double restart" was a local
influence of heavy charged particles from space, Roskosmos concluded.
This influence led to errors in the random-access memory modules, OZU,
in the TsVM22 computer during the second orbit of the mission. Errors in
RAM modules could be caused by intermittent interference caused by
heavy space particles on particular cells in computer modules, which
contain two chips of the same type -- WS512K32V20G24M. The influence of
heavy particles caused a distortion of the computer code and activated a
"guard" timer, which in turn triggered a reboot. Existing certification
documents do not regulate the particular model of heavy particle
influence, Roskosmos said. The investigation commission recommended to
develop and implement new certification guidelines which would contain
updated models of ionized radiation in space.
What is also interesting is how the Russians are willing to give it another try. According to Science magazine,
Lev Zelenyi, director of the Russian Academy of Science's Space Research
Institute (IKI), said at a 1 February press conference that the team
behind
the mission was keen to try again. A repeat would only cost half
as much as the first time round, he noted, because the infrastructure
for the mission
is already in place. Zelenyi told Science that this is still just an IKI proposal and is not yet funded. Phobos-Grunt-2 would be "improved and
simplified," he says, and would use a Soyuz Fregat booster rather than the Zenit booster of the original craft.
I am glad the Russians are no longer blaming outside parties and they are willing to give Phobos another try. Whether China and the Planetary Society are up for another mission remains to be seen, but this is a hopeful restart.
