Rosetta and Philae: Searching for a good signal

After seven months in hibernation on the surface of Comet 67P/Churyumov-Gerasimenko, Rosetta’s lander Philae communicated with Earth via the orbiter on 13 June. Since then, seven periods of connection have been confirmed between the orbiter and lander, but all have been intermittent. One of the key issues being worked on is to adjust Rosetta’s trajectory to see whether a more reliable communications link can be established with Philae. This report describes the status of those efforts as of 26 June, and has been prepared with inputs from ESA’s Rosetta Science Ground Segment team at ESAC and the flight control team at ESOC, along with the Lander Control Centre at DLR. When have contacts been made? Confirmed contacts between Rosetta and Philae have been made on 13, 14, 19, 20, 21, 23, and 24 June, but were intermittent during those contact periods. For example, the contact on 19 June was stable but split into two short periods of two minutes each. Conversely, the contact on 24 June started at 17:20 UT (on board Rosetta) and ran for 20 minutes, but the quality of the link was very patchy and only about 80 packets of telemetry were received. Prior to this, on Tuesday, 23 June, there was a 20-second contact, but no stable link was established and consequently no telemetry data were received. How frequently do Rosetta and Philae try to make contact? Comet 67P/C-G rotates with a 12.4 hour period and thus Philae’s location is not always visible to Rosetta. Roughly speaking, there are two opportunities for contact between the two spacecraft each Earth day, but their duration depends on the orientation of the transmitting antenna on Philae and the location of Rosetta along its trajectory around the comet. Similarly, as the comet rotates, Philae is not always in sunlight and […]

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