[meteorite-list] European Space Probe Makes First Landing On A Comet (Rosetta/Philae)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 12 Nov 2014 16:42:16 -0800 (PST)
Message-ID: <201411130042.sAD0gG1d009835_at_zagami.jpl.nasa.gov>

http://spaceflightnow.com/2014/11/12/european-space-probe-makes-first-landing-on-a-comet/

European space probe makes first landing on a comet
by Stephen Clark
Spaceflight Now
November 12, 2014

DARMSTADT, Germany - After making history Wednesday as the first spacecraft
to touch down on a comet, Europe's Philae lander collected data on the
rugged alien world's environment and may have rebounded into space before
settling back on the surface, scientists said Wednesday.

The small landing craft deployed from the European Space Agency's Rosetta
spacecraft Wednesday to begin a seven-hour descent to the comet. Tension
grew inside ESA's operations center here as the expected time of touchdown
approached, and views inside the Rosetta mission control room showed engineers
with strained faces waiting for radio signals confirming the lander had
reached the comet.

The dramatic space gymnastics all occurred at comet 67P/Churyumov-Gerasimenko,
a bizarre object orbiting the sun more than 300 million miles from Earth.
The comet's tenuous gravity field is one hundred thousand times weaker
than Earth's, and officials worried the lander could bounce off the comet
with little pull to hold it on the surface.

Philae flew with a top-mounted cold gas thruster to fire and keep the
probe on the surface while it engaged harpoons and ice screws to anchor
it to the comet.

But at least two of the landing assist devices did not work.

The thruster system failed to pressurize during lander preparations Tuesday
night, and officials said Philae's two harpoon anchors did not fire when
the craft reached the comet Wednesday.

Officials could also not definitively confirm whether the ice screws bored
into the comet to keep the lander on the surface.

Ground controllers received the initial notification of Philae's landing
at 1603 GMT (11:03 a.m. EST), triggering an immense emotional release
and a wave of cheers and applause.

The status of the lander was put in doubt a few minutes later after a
manager from Philae's control center in Cologne, Germany, reported the
craft apparently did not fire the harpoon anchors as planned.

"What we know is that we touched down, so we landed at the comet at the
time when you all saw us cheering, when it was announced we had a very
clear signal," said Stephan Ulamec, manager of the Philae mission for
DLR, the German Aerospace Center.

Ulamec said Philae transmitted information on its status, and at least
some of the lander's 10 science instruments collected data and delivered
the results to Earth.

"The not so good news is that the anchoring harpoons apparently did not
fire, so the lander is not anchored to the surface," Ulamec said. "We
started to think about what could be the situation. Did we just land in
a soft sand box and everything is fine...or is there something else happening."

Engineers say they saw fluctuations in the radio signals from Philae being
relayed by the Rosetta orbiter, which carries a more powerful communications
system.

Cautioning his statement as speculation, Ulamec said information received
from Philae is consistent with the lander moving across the surface after
its initial contact with the comet.

"Some of these data indicated that the lander may have lifted off again,'
Ulamec said.

The lander may have "touched down and we were re-bouncing very slowly
because the landing gear worked perfectly well," Ulamec said. "It was
designed to dampen the majority of the impact energy."

Data signatures from the lander also showed changes in power being generated
by solar cells covering the craft's outer skin, "which could be interpreted
that the lander lifted off and started to turn itself because flywheel
(stabilization system) was switched off at touchdown," Ulamec said.

After about two hours, the fluctuations in Philae's electrical system
ceased but the radio signals continued, meaning the lander may have come
to a rest.

"Maybe today we didn't just land once, we even landed twice," Ulamec said.

Mission control lost contact with Philae soon after - a little earlier
than expected, said Paolo Ferri, head of mission operations at ESA.

"We lost the radio link earlier than planned, which is something that
we never like, but this is not at the moment concerning," Ferri said.

Rough terrain may have blocked the line-of-sight radio link between Philae
and Rosetta sooner than expected, according to Ferri.

Officials said the next chance to contact Philae will be around 0600 GMT
(1 a.m. EST) when Rosetta again flies in range of the lander.
Received on Wed 12 Nov 2014 07:42:16 PM PST