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Moment that mattered: Philae lands on comet 67P

On the afternoon of 12th November I was sitting in the main control room at the European Space Operations Centre [ESOC] in Darmstadt, Germany, next to the flight directors Andrea Accomazzo and Elsa Montagnon. As the time edged closer to 5.03pm, when we were expecting to hear from the Philae lander, it fell completely silent. Usually you can hear people using their headsets and talking over voice loops, checking parameters and comparing information. But you couldn’t hear anything. The concentration levels remained extremely high because each person had to focus on particular bits of information.

Then I began hearing Andrea and Stephan [Ulamec, lander manager] saying that Philae had touched down on comet 67P. They were shouting various indications that we were on the comet’s surface but I was concentrating entirely on whether the lander was still alive. On my display I was getting regular messages saying that a new packet of information had been received; there was a 10 or 20-second wait between each packet and each wait seemed eternal. Between every update I wondered if we had lost the link to the lander. In those first few minutes we were all comparing our information, and when the conclusion was finally reached that the lander was definitely on the surface, that it had survived, there was a huge release of tension. People were crying and hugging each other. We were very emotional.

But it turned out to be a tense evening after all. The people at the Philae Lander Control Centre in Cologne began telling us they thought Philae might be bouncing around on the comet. This was hard to believe because it seemed to us that the lander was sitting there quietly doing its job. But Cologne confirmed by analysing Philae’s engineering telemetry – it was not anchored and was flying. We were concerned. We thought we might lose the signal at any moment, which would mean losing the mission completely. At around 7pm the oscillation in the power produced by Philae’s solar cells stopped, the signal and power were there, and it was not modulated any more. Philae had settled somewhere. Then, 20 minutes later, we lost the signal completely.

We were confident the signal would return but it was a long night. The next morning Philae started sending signals again – it was working wonderfully. When we saw the images it sent it was another emotional moment for us. By the end of the second day Philae had been on the comet for 24 hours and had completed two rotations of it, because the comet day lasts 12.4 hours. It became clear that [because it had landed in the shadow of a cliff] there wasn’t enough sun to recharge its battery, which runs on solar power. We had concentrated on the primary mission, which was maximising the 60 hours of battery we knew we had, but now we knew we couldn’t recharge the secondary battery.

“We thought we might lose the signal at any moment, which would mean losing the mission completely”

My colleagues in Cologne are optimistic that Philae will wake up later in the year. They believe that as the comet moves towards the sun the battery-charging electronics will start working and the lander will wake up. For the lander community it’s important that this happens, but for the overall Rosetta mission I can’t say it’s critical. The primary mission was a success and in any case it was only covering ten or 20 percent of Rosetta’s overall mission, which is to help understand the origin and evolution of the solar system. [An analysis of the comet should help explain how comets helped form oceans and atmospheres, and how their complex organic molecules may have been involved in the origin of life on Earth.]

There’s been a change in Rosetta’s operations since 12th November. Until then we were learning how to fly around this comet and finding a strategy for the landing. Now we have entered a new phase, the full science phase, which is about implementing the requests and objectives of the scientists with instruments onboard the Rosetta. [There are plans to analyse the composition and structure of the comet’s surface material, and measure how the comet changes as it approaches the sun].

Having worked on Rosetta for 18 years it’s difficult to think ahead but from an ESA perspective the next steps in space exploration are Mercury, Mars and Jupiter. Another field which is very important is dealing with extrasolar planets. They are our long-term future. That’s the next frontier.

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