Philae Falls Silent : Was a Landing Success or Failure?

Estimate of Philae’s approximate orientation imposed over image taken shortly after landing. Image Credit : ESA

Mission Update ESA’s Rosetta Blog, Comments follow:

“With its batteries depleted and not enough sunlight available to recharge, Philae has fallen into ‘idle mode’ for a potentially long silence. In this mode, all instruments and most systems on board are shut down.

“Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence,” says DLR’s Stephan Ulamec, Lander Manager, who was in the Main Control Room at ESOC tonight.

“This machine performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered.”

Contact was lost at 00:36 UTC / 01:36 CET, not long before the scheduled communication loss that would have happened anyway as Rosetta orbited below the horizon.

From now on, no contact would be possible unless sufficient sunlight falls on the solar panels to generate enough power to wake it up.

The possibility that this may happen was boosted this evening when mission controllers sent commands to rotate the lander’s main body, to which the solar panels are fixed. This may have exposed more panel area to sunlight.

The next possible communication slot begins on 15 November at about 10:00 UTC / 11:00 CET. The orbiter will listen for a signal, and will continue doing so when its orbit enables communication visibility in the future.

However, given the low recharge current available from the solar cells, it is considered unlikely that contact with Philae will be established in the coming days.

The hugely successful Rosetta mission will continue, as the spacecraft tracks comet 67P/C-G on its journey to the Sun. Rosetta is the first spacecraft to rendezvous with and orbit a comet and has already returned incredible scientific data.”

Some thoughts: Described as a stunning success in the moments following confirmation that the Philae lander made initial contact with Comet 67/C-G, one wonders if that will be the historical perspective. While the Rosetta mission has succeeded marvelously on other accounts, Philae’s descent to the surface was marked by the failure of both of the systems designed to keep in there.

Had events unfolded differently, with the cold gas thruster working, the harpoons firing, but the lander bouncing off or overturning because an unknowable surface environment proved uncooperative, the verdict would be more clear, a valiant effort and experience gained in pioneering what truly is a new frontier.

But that is not what happened. Instead, the thruster system failed to initialize before Philae ever separated from Rosetta. Two redundant mechanical pins, charged with penetrating a wax seal and thereby charging the system, simply failed to fire despite two attempts each. Despite the time and distance, activating a nitrogen gas system should have been one of the simpler elements of a very complicated mission. There is of course no guarantee that Philae would have “stuck the landing” even if the thruster had worked. Furthermore, the apparent failure (the record is less clear here) of the twin harpoons to fire as well, might have led to a similarly unhappy result anyway.

If the brief data returned from the surface before the battery depleted really is the “treasure trove” mission scientists have declared it to be, the failed landing, and that’s beginning to look like the only accurate way to describe it, will likely become little more than a historical footnote in what will be described as brilliant success.  At least that is, up until the point another lander settles safely on the surface of another comet, prompting whoever launched it to claim that they, and not ESA, have recorded history’s first truly successful comet landing.

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2 Comments on "Philae Falls Silent : Was a Landing Success or Failure?"

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  1. The decision to use solar panels and batteries for powering a spacecraft this far from the Sun is now looking like a colossal mistake. And RTG would have saved weight and would have been much more reliable.

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