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Lost Russian Mars Probe Phones Home
astroengine writes "The lost Russian Mars mission Phobos-Grunt has made a surprise announcement: she's alive. According to the European Space Agency (ESA) in the early hours of Wednesday morning, a tracking station in Perth, Australia, picked up a signal from the ailing spacecraft."
The location/position of the probe has been known almost from the beginning. It was never that they couldn't find it, the problem was that the booster pack that was supposed to send the probe on to Mars never fired and the probe wasn't responding to the Russian's radio commands. What has changed in the last day is that receivers here on Earth are finally picking up radio signals from the probe itself, indicating that it is still alive and at least theoretically operational. Telemetry hasn't yet been received, but now there is a possibility we can communicate with it and try to diagnose the failures it suffered. As for if it can be recovered, I've not heard a definitive answer on this. One source will say the window has already closed, another says it's open until sometime in December. The window can probably be extended if they have enough fuel to try some exotic gravity assist with the Earth or Moon, but if it hasn't already passed it will soon.
It's not really the position, it's the signal strength. In low Earth orbit the orbit can be (and routinely is) determined from radar and optical observations without any cooperation from the spacecraft at all. The dish at Perth is 15 meters. At 10 cm wavelength, it has a beamwidth of order 7 milliradian, so at 300 km range they need about 2 km orbital accuracy for pointing, which should be easily achievable.
Note, from the same ESA press release :
In the past few days, ESA's 15 m-diameter Perth dish was modified by the addition of a 'feedhorn' antenna at the side of the main dish so as to transmit very low-power signals over a wide angle in the hopes of triggering a response from the satellite.
This wasn't about pointing the antenna, it was about lowering the signal power. The omni-directional antenna on the spacecraft is intended for use in deep space and was probably being saturated by full power blasts from regular tracking stations. It needed to be "tickled" by something weaker.
Kudos to ESA for doing this. You can bet this was a major effort at the ground station. The feedhorn receiver was probably jury-rigged from spare parts, and probably took days of round the clock work to install and get operational.