Philae communicates again after two weeks of silence

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Credit: ESA/Rosetta/Philae/CIVA

The European Space Agency (ESA) has revealed that its Philae comet lander has communicated with the Rosetta orbiter again yesterday and transmitted measurement data from its COmet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) instrument.

Though the communication lasted for only 12 minutes and subsequent attempts to establish a communication link failed, ESA said that during those 12 minutes the connectivity was stable and mission control was able to receive data, which is being currently analysed.

The communication from Philae proves that at least one of the lander’s communication units remains operational and is receiving mission control’s commands, said Koen Geurts, a member of the lander control team at DLR Cologne.

Philae last communicated on June 24 and since then there was a radio silence from Philae’s end. Despite this the DLR Lander Control Center (LCC) didn’t lose hope and remained optimistic, Geurts added.

The mission control team had sent out commands to turn on the power to CONSERT on 5 July 2015, but there was no response from Philae post that attempt, raising concerns about the survival of the lander on Comet 67P/Churyumov-Gerasimenko.

A transmission from Philae on July 9 instead of the days following the relay of the commands on July 5 has surprised the team because conditions of communications like the trajectory of the Rosetta orbiter have not changed over the last three weeks.

There was great excitement when Philae ‘reported in’ on 13 June 2015 after seven months of hibernation and sent data about its health. The lander was ready to perform its tasks, 300 million kilometres away from Earth.

However, Philae has to communicate with the ground stations through Rosetta, which acts as a radio relay. Restrictions on the orbiter’s approach to and orbit around the comet have not permitted regular communication with the lander. The data sent on 24 June did not suggest that the lander had experienced technical difficulties.

Now, Philae’s internal temperature of zero degrees Celsius gives the team hope that the lander can charge its batteries; this would make scientific work possible regardless of the ‘time of day’ on the comet.

The received data is currently being evaluated. “We can already see that the CONSERT instrument was successfully activated by the command we sent on 9 July,” explained Geurts. Even now, Philae is causing the team some puzzlement: “We do not yet have an explanation for why the lander has communicated now, but not over the past few days.”

However, one thing is certain; Philae has survived the harsh conditions on the comet and is responding to commands from the LCC team. “This is extremely good news for us,” said Geurts.