Philae lander’s lead scientist reflects on achievements and hopes for reactivation

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The European Space Agency (ESA) is desperately waiting for Philae to wake up and is attempting to establish a communication link with its lander through Rosetta by sending out wake up signals from March 12 through to March 20.

In a post on ESA’s blog, Lead lander scientist Jean-Pierre Bibring reflects on Philae’s achievements and ESA’s hopes that the lander will reactive once again to provide us with more vital and critical data that will enable the research community as a whole to broaden their horizons about the universe and solar system in specific.

Bibring mentions how the first of many challenges was to get the Philae to land on the comet. ESA had pre-fed all the scientific operations planned for the descent up to 10 hours after touchdown ready to be run in an automated fashion and Philae performed them as planned.

The scientist reveals that some of the add-on sequences of measurements that Philae took during its two hour bounce around on the comet’s surface greatly contributed towards revealing the physical properties of the nucleus surface.

Bibring goes on to add that Philae went onto perform quite a few operations it was meant to during the subsequent ~50 hours of duration. Due to the awkward position of the Philae, the lander team had to quickly execute a major reshuffling and adaptation of the overall sequence, balancing the risks and the desired goals to acquire as many scientific results as possible.

“The initial [first science sequence] FSS plan was to start with drilling (with SD2) and analysing subsurface samples (with COSAC and PTOLEMY); imaging the surface below Philae (ROLIS); deploying other mechanisms to measure temperature profile (MUPUS) and surface composition (APXS), and monitoring physical properties (SESAME). This sequence required Philae to be rigidly anchored to the surface, which did not happen”, Bibring notes.

In a bid to characterize the orientation and location of Philae, the team commanded the lander to snap a new set of CIVA panorama images. The lead scientist added that Philae did send out the images early on 13 November and that proved that Philae had indeed landed

“We were face-to-face with pristine cometary constituents –the dream had become reality!” Bibring notes.

“But, at the same time, the images demonstrated that Philae had rested in a hole with an odd attitude, one foot up, and in a site largely shadowed by surrounding boulders/cliffs: greatly unfavourable for energy, as well as for surface access of deployable systems.”

Owing to the awkward angle of Philae’s landing, the team designed and uploaded a new sequence of operations that the lander was required to now perform. The team enabled most of the investigations to be run, from the least to the more risky. The new design saw reduced duration of investigations and some were not enabled because of potential lack of energy. The FSS lasted 63 hours.

Bibing notes that “Long Term Science” (LTS), though considered a major contribution of overall Philae’s science mission, will only run if the lander has enough energy to resume operations.

The scientist notes that two factors may contribute to an increase in energy with respect to the situation in mid-November – the first being comet’s heliocentric distance, which decreases substantially with time, and second the seasonal evolution, which may bring the solar elevation over the surrounding boulders/cliffs.

The heliocentric distance indicates that there could be favourable slots around June/July when the lander should have enough power at hand, but the second factor is largely unknown at this point.

“It has thus been decided to stay on the optimistic side, betting on a favourable seasonal effect”, Bibring notes.

“Preparing for Philae’s resuming activity and continuing scientific operations is presently the focus of all Philae teams. Wake-up tries are now being executed; a new chapter of the Philae thriller should start soon!” Bibring concludes.