Space probe signals it’s awake
GERMANY
THE comet-chasing Rosetta spacecraft sent its first signal back to Earth after a 31-month hibernation on its decade-long mission into deep space.
Scientists at the European Space Agency’s mission control in Darmstadt, Germany, jumped up and cheered when the signal registered about 7.20pm local time. It came during the agency’s predicted one-hour window and more than eight hours after the craft’s alarm clock woke it up from a hibernation period far in space.
‘‘We made it!’’ Rosetta spacecraft operations manager Andrea Accomazzo said. ‘‘The signal from Rosetta is up there, you can see it on the screen. It’s a big success for everybody.’’
The Rosetta mission is the first attempt to orbit and land a probe on a comet, and researchers hope to glean more about the role of comets in the evolution of the solar system. Made from dirty ice, dust and gas, they are considered building blocks that likely helped seed Earth with water and possibly even life. Its target is the Churyumov-Gerasimenko comet, which it is due to reach in August.
After receiving the alarm call, the craft began a six-hour wakeup procedure that included switching on some heaters to warm the units that controlled the direction it pointed, ESA’s head of mission operations, Paolo Ferri, said.
Then the instruments had to halt the craft’s rotation, point an antenna to Earth and send a signal. The National Aeronautics and Space Administration monitoring station in Goldstone, California, was used to pick up the signal.
Rosetta’s scientists will now test all of its subsystems and activate each of the craft’s scientific instruments in turn between now and April, according to Ferri. In May, they would begin to slow the craft down to a pace of a few metres a second from one kilometre a second, he said.
‘‘Then we will be starting the final approach, and in August we can basically say we are in orbit around the comet,’’ Ferri said. ‘‘That’s when we start our phase of detailed characterisation of the comet and we take pictures and we measure the gravity potential.’’
Astrium, now part of Airbus Defence and Space, was the main contractor for the spacecraft launched on March 2, 2004. After reaching the ChuryumovGerasimenko comet, Rosetta is then scheduled to orbit until the end of 2015, placing its lander, called Philae, on the icy mass, this November after identifying a suitable site. Rosetta has 11 packages of scientific instruments, and Philae 10.
‘‘The mission is staying around the comet, studying it and seeing its evolution as it gets closer to the Sun,’’ Ferri said.
When the lander is in place, it will shoot two harpoons into the comet to anchor it. The main craft will be ‘‘flying over the landing site, collecting signals, storing them on board and periodically pointing the antenna to Earth to send them back,’’ he said.
While Philae would be the first probe to touch down on a comet and beam data back, ESA’s first deep-space mission, Giotto, was sent to investigate Halley’s comet in 1986. Nasa has also launched two missions to study comets in the past 20 years.
In 2005, Nasa fired a projectile from its Deep Impact spacecraft into the comet Tempel 1. It monitored the ejected material using two instruments on the main craft, and the projectile beamed data back until nearly the point of impact.
Rosetta is about 670 million kilometres from the Sun and more than 800m km from the Earth, according to ESA. Its planned hibernation began in June 2011 because it was too far from the Sun for its solar panels to generate sufficient energy. Since then, only the computer and some heaters had been active so the craft didn’t freeze.
‘‘For mission control, not having the signal of the spacecraft is the worst thing that you can have,’’ Ferri said. ‘‘When we have a signal, we know what is the status. Even if there are problems with the spacecraft we can intervene. Even though it was planned, 21⁄ years without contact is very bad.’’
The Churyumov-Gerasimenko comet orbits the Sun every 6.6 years at a distance that ranges from 186m km to 857m km. Discovered in 1969, the comet has a nucleus estimated to be 4km in diameter.