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Philae spacecraft lands on comet
Quote:The signal broke a seven-hour wait of agonising intensity and sparked scenes of jubilation at the European Space Agency’s mission control in Darmstadt. The team in charge of the Rosetta mission achieved what at times seemed an impossible task by landing a robotic spacecraft on a comet for the first time in history.

The moment the tension broke came shortly after 1600 GMT when the Philae called home. “We are there. We are sitting on the surface. Philae is talking to us,” said a jubilant Stephan Ulamec, Philae lander manager at the DLR German space centre. “We are on the comet.”

Andrea Accomazzo, the Rosetta flight operations director, added: “We cannot be happier than we are now.”

But celebrations were tempered by the later discovery that the probe’s two harpoons had not fired to fasten the craft down in the ultra-low gravity. Scientists now think the probe may have bounced after first coming into contact with the surface. Ulamec said: “Maybe today we didn’t just land once, we landed twice.”

The safe, if precarious, touchdown of the lander gives scientists a unique chance to ride onboard a comet and study from the surface what happens as its activity ramps up as it gets closer to the sun. The first images beamed back from the lander’s descent revealed a dramatic landscape of pits and precipices, craters and boulders. However, there have been gaps in its radio link with the orbiting Rosetta mothership.
The harpoons and thruster that should have secured it to the comet both failed, so it is relying on its weight to hold it down; this is about 15 grams, if my calculations are correct ( on the 'head' of the 'duck' it might be even less).

It will be really tricky to take any samples if it isn't anchored, and it may be upside-down or at any angle. Communications are really poor.
Magnetic field analysis revealed 3 landings at 15:33, 17:26 and 17:33 UTC

It bounced twice in two hours. Ouch! This environment is nothing like anything we are familiar with. Can you even imagine a spaceship a metre across that weighs fifteen grams, and bounces that take two hours to complete?
Some insider info from someone working on the harpoon experiment;
Quote:After long discussions the current status is that we had in fact three landings on a comet. At first touch down both the AOCS thruster and the anchors were not activated for reasons yet not fully understood. Philae bounced two more times. The first bounce took two hours and was possibly up to one kilometre. The second bounce was then only 20m. Since then the Lander appears to be stable and upright on the the surface. FSS is commencing nominal and next radio link is expected for about 7:30 CET. If radio contact is established we are back on the mission track. No deployment though until situation is clear. All instruments are working and we received data until end of radio link. All active instruments concur with the bouncing and a rotation of the lander during the first bounce in fact spin stabilising the Lander.
One thing I noticed in all articles is that they don't mention any further attempts to fire the harpoons.

It is disturbing to imagine the possibility of probe like this failing to do anything else than take pictures, especially so close to its goal.
The harpoons would probably flip the lander over if they were fired now; they need to be counterbalanced by a thruster, and that seems to have stopped working.
Does anyone know, whether it would have been advantageous to build the lander in the form of a Roly-poly toy? At least this way it would have returned to an upright position on its own. Although it wouldn't have solved the problem of it landing in a shady place, it would have at least solved the problem of it falling over.
"Hydrogen is a light, odorless gas, which, given enough time, turns into people." -- Edward Robert Harrison

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