ESA: Philae Landed THREE Times, not Two, But is OK

The European Space Agency’s (ESA’s) Philae lander bounced twice — landing three times — when it reached the surface of Comet 67P yesterday, but is working fine and returning images and other scientific data.   Philae separated from its Rosetta mother spacecraft yesterday and reached the comet’s surface at 10:34 am EST (November 12), the first spacecraft to land on a comet.

Philae (pronounced fee-LAY) communicates with Earth through Rosetta, which is orbiting Comet 67P/Churyumov-Gerasimenko.  Radio communications with Philae initially were intermittent yesterday and then ended as Rosetta moved below the horizon.   Scientists waited many hours until Rosetta was once again in position to serve as a relay.  Right on schedule, communications were reestablished at 06:01 UTC (01:01 am EST) today.  That communications session lasted until 09:58 UTC.

ESA released photographs of the surface of the comet from the ÇIVA (pronounced SHE-va) instrument on Philae.  ÇIVA is a set of six identical micro-cameras that can take panoramic pictures of the surface.  One of the six images (below) shows Philae’s foot on the surface of the comet.

Comet 67P imaged by Philae lander (lander’s foot clearly visible).
Released by ESA November 13, 2014  Credits: ESA/Rosetta/Phiae/ÇIVA 

Comets have almost no gravity, so Philae was equipped with harpoons that were supposed to fire down into the surface of the comet to hold the lander in place.  The harpoons did not fire, however, so Philae bounced.  Yesterday, Philae project manager Stephan Ulamec said “maybe today we didn’t just land once, we even landed twice.”

Now they know there were two bounces, with three landings.  

As Ulamec explained today, the first contact with the surface was at 15:34 UTC (10:34 am EST) precisely where Philae was intended to land.  However, it bounced off the surface and remained aloft for almost two hours.  Ulamec said they think it bounced about 1 kilometer high and moved 1 kilometer in distance, touching down a second time at 17:25 UTC (12:25 EST).  It then bounced again and was aloft for 7 minutes, landing for the third time at 17:32 UTC (12:32 EST).   They do not know exactly where the lander is now.    ESA is using the OSIRIS camera on Rosetta to search the surface for Philae.   The cameras on Philae shows that it is very close to a cliff, which may complicate finding it.  

The lander is in good shape.  The only wrinkle concerns how long it can function.   Philae has primary and secondary batteries.  It is operating off of the primary battery now, but it will soon run out of power unless it and the secondary battery can be recharged from its solar cells.    Because it landed near a cliff, however, the solar cells are receiving much less sunlight than expected — only 1.5 hours of 6-7 hours — during this first period of time.   The Philae team is looking at options, such as trying to reposition it so the solar cells get more sunlight, but is moving cautiously lest the lander’s position be further disturbed.  

Philae  is designed to be able to survive long periods in hibernation and the lighting conditions will change as the comet moves through the solar system.  Ulamec said it is possible that even if the lander loses power, it could reawaken months from now if more sunlight is available, but he was not willing to even guess at the possibility that would happen.  Rosetta will continue to orbit the comet until August-September 2016 when it will run out of fuel.