than 400 million miles from the sun, Rosetta's flight computer responded to a
countdown timer that signaled the end of hibernation, triggering a complex
sequence of events to slow the spacecraft's spin and warm its star trackers so
it could determine its position and orientation in space.
six hours after the initial wakeup, Rosetta was programmed to re-orient itself
to aim its high-gain antenna back at Earth for the long-awaited call home.
signal was expected anytime between 12:30 p.m. EST (GMT-5) and 1:30 p.m. For 45 minutes, there
wasn't a peep. Then, at 1:18 p.m., huge antennas in NASA's Deep Space Network
picked up Rosetta's broadcast, prompting wild applause and raucous cheers at
the Rosetta control center in Darmstadt, Germany.
made it! Yes, yes! We can definitely see the signal from Rosetta,"
exclaimed Andrea Accomazzo, Rosetta spacecraft operations manager. "This
is a big success for everybody."
$1.7 billion mission, launched by an Ariane rocket on March 2, 2004, spent the
past decade following a convoluted trajectory to reach Comet
67P/Churyumov-Gerasimenko, discovered in 1969. The comet's 6.5-year orbit
carries it beyond Jupiter and then in between the orbits of Earth and Mars
before it returns to deep space.
Assuming the spacecraft endured its long hibernation with no ill effects, Rosetta will carry out a series of carefully choreographed maneuvers in the months ahead, slipping into orbit around the nucleus of 67P, flying lower and lower until it reaches an altitude of just six miles or so in September.
After carefully studying the comet's surface, mission managers will select a landing site and if all goes well, a small lander named Philae will be released to land on the nucleus in November.
Comets like 67P are "time capsules, they are remnants of the birth of the solar system and they go back to the beginning of the solar system more than 4.6 billion years ago," said Mark McCaughrean, senior scientific advisor with ESA's Directorate of Science and Robotic Exploration.
"When the solar system was forming out of gas and dust, it formed the planets, the one we live on today, it formed asteroids and it formed the comets. And the comets are a remnant, therefore, something we can investigate about the very earliest phases of the evolution and the birth of our own solar system."
Of particular interest is the ice found in comets, which can "give us great clues to the origin not only of our own solar system, but potentially even life," McCaughrean said. "Because we know that comets also contain organic molecules, the building blocks of even DNA and RNA. We know that there are amino acids in comets, for example. So comets play a key role in our understanding of the cycle of star formation, planet formation, perhaps life formation."
To rendezvous with Comet 67P/Churyumov-Gerasimenko, Rosetta flew past Earth a year after launch and then past Mars in February 2007, using the gravity of both planets to increase its velocity and adjust its trajectory.
After a second Earth flyby in November 2007, Rosetta flew past an asteroid and returned to the vicinity of Earth in November 2009 for a third gravity-assist flyby. The spacecraft flew past a second asteroid in July 2010 and then went into extended hibernation on June 8, 2011.
"We came to such a distance from the sun that even our large solar arrays, even our high technology solar cells, were not enough to keep the full spacecraft active," Paolo Ferri, head of mission operations, told reporters late last year. "What we had to do in June 2011, we had to switch off most of the systems, spin up the spacecraft and leave it alone.
"Since the 8th of June 2011, we have no signal form the spacecraft. This was planned. It's not something we liked doing, but this is really what the last two-and-a-half years were about."
67P will generate streams of icy debris as it responds to solar heating, it
"is never going to be bright, it's not going to be visible to the naked
eye," said McCaughrean. Even so, "it's a superb comet to go visit and
do science. But we won't be able to see it with the naked eye."
do not yet know enough about 67P to plan Rosetta's close approach or pick out
any potential landing sites. But as the spacecraft closes in, its cameras will
capture sharper and sharper views, unveiling the comet's surface in
have cameras in the visible, the infrared, the ultraviolet and at millimeter
wavelengths to investigate the surface structure and the temperature and the
materials the comet's made of by looking from a distance," McCaughrean
said. "We're going to measure the particles in the coma, the material
flowing away from the comet, we're going to be able to measure the masses, the
materials that the gas and dust are made out of that's flowing away."
also will analyze the dust that hits the spacecraft and "we're going to be
able to take microscopic images of the dust in the coma," he said.
"We're also going to conduct a lot of experiments on the plasma, the
ionized gas flowing away from the comet."
the Philae lander descends to the nucleus in November, it will use a variety of techniques to anchor itself to a body with just 20 millionths the gravity of Earth. On-board cameras will
document the journey, followed by a panorama from the surface "all the way
around, 360 degrees, in stereo of the surface and then looking downward, doing
microscopy, looking in high resolution at the surface of the comet,"
then going to have a number of little laboratory experiments that will measure
the gas and the dust, the organic material and the plasma coming away," he
said. "And then we're actually going to drill beneath the surface to look
at material just under the surface and melt some of that material, we'll dig
(it) up and bring into the spacecraft."
The lander and Rosetta mothership will work
together in another investigation, beaming radio signals back and forth that
will "go through the comet and measure it's inside, we'll actually be able
to measure the internal structure of the comet through a form of tomography."
also plan to precisely measure the time delay of signals sent from Rosetta to
Earth to map out the comet's gravity.
mission's been going on for more than 10 years, but the exciting phase takes
place now," McCaughrean said. "This time capsule has been locked away
for 4.6 billion years. It's time to unlock the treasure chest."