Philae’s Comm Problem has Lander’s Operators Concerned

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PARIS — Europe’s Philae lander, riding Comet 67P as it heats up and spews off increasing amounts of gas and dust as it approaches the sun, has likely changed position or suffered transmitter failure, raising concern over whether it will be able to communicate again, the lander’s control center said July 20.

Philae last reported in July 9 and since then has been unable to maintain stable, predictable communications lines. As it closes in on its Aug. 13 perihelion — its closest approach to the sun – the comet’s outgassing turns its surface into a more dangerous spot for a fragile lander whose purchase on the surface was never secure in the first place.

Just as important, the Rosetta orbiter that relays Philae data to the Earth cannot maintain its close orbit to scan for Philae signals because that puts Rosetta at risk of being blinded by the same outgassing.

The Philae Lander Control Center, located in Cologne, Germany, at the German Aerospace Center, DLR, said Rosetta’s star trackers, which have been troubled before by cometary dust, were compromised again July 12.

Rosetta has since moved to a safer distance of between 170 and 190 kilometers from Comet 67P.

While the plucky Philae has captured much of the attention, Rosetta has its own suite of 11 comet-studying instruments. Some of the Rosetta work is best done from orbits that are not the most favorable from a Philae-looking point of view.

The center said that Rosetta’s attention will remain focused on Philae until July 24, when its orbit will be changed to focus on Comet 67P’s southern hemisphere, which is increasingly illuminated by the sun.

Philae last communicated July 9. Philae project leader Stephan Ulamec said in a July 20 statement that the most recent telemetry from Philae suggests that it could have moved, changing the orientation of its antennas and making communications more difficult.

Philae landed at the rim of a crater, with images suggesting it was in a precarious position and could be easily jostled, even slightly, by an perturbation on the nearby terrain.

The control team has sent Philae commands that order it to communicate only with the transmitter that appears to be functioning. Other commands were sent that permit Philae to activate five of its instruments without further instructions from Earth.

“The lander is obviously still functional, because it sends us data, albeit at irregular intervals and at surprising times,” Ulamec said. “There have been several times when we feared the lander would not switch back on, but it has repeatedly taught us otherwise.”