ESA’s Rosetta spacecraft stirred from its long hibernation
ESA’s Rosetta spacecraft has awoken from its 957 days in slumber on Monday, ahead of its mission to rendezvous with the Churyumov–Gerasimenko comet in August. The spacecraft awakening was confirmed by controllers at ESA’s Space Operations Centre (ESOC) in Darmstadt, Germany.
The spacecraft was launched from Europe’s Spaceport in Kourou on March 2, 2004 on an Ariane 5G rocket.
Its journey has seen it travel to a distance of 800 million kilometres (500 million miles) from the Sun. It has made an orbit of Jupiter during its journey, which has also involved passing by Earth three times and Mars once, while also flying past two asteroids.
It is now closing in on its destination, Comet 67P/Churyumov–Gerasimenko, as it moves farther into the inner Solar System.
Rosetta is the first mission designed to orbit and land on a comet. It consists of an orbiter, carrying 11 science experiments, and a lander, called ‘Philae’, carrying 10 additional instruments, for the most detailed study of a comet ever attempted.
The mission had to be refined even before it had even launched, with a delay caused by the failure of the Ariane 5 ECA’s debut launch in December, 2002.
As a result, Rosetta switched targets, from an encounter with Comet 46P/Wirtanen – that had been planned for 2011 – to the 67P/Churyumov-Gerasimenko comet.
Rosetta greeted two asteroids during the first part of its mission, the first in August 2008, when the spacecraft passed by (2867) Steins, a rare E-type asteroid. The second occurred two years later, this time with (21) Lutetia, a large asteroid, about 10 times bigger than Steins.
In June of 2011, Rosetta was switched to its hibernation mode, protecting its vital payloads from the coldness of deep space.
Monday’s key event was initiated by a pre-set timer tasked with waking up the spacecraft. ESA enjoyed some fun on social media for this event, calling on people to participate in waking up Rosetta, as much as it was the responsibility of the spacecraft’s “alarm clock” timer to provide the actual awakening.
The spacecraft’s internal alarm clock buzzed at 10:00 GMT on Monday, although confirmation all had gone to plan came via the first signal from the spacecraft reaching Earth at around 18:17 GMT.
Deep space tracking dishes were tasked with listening out for the signal, starting with NASA’s ‘big ears’ – the 70 m-diameter station at Goldstone, California, followed by, as the Earth rotates, the Canberra station in eastern Australia.
ESA’s New Norcia 35 m antenna, in Western Australia, is next in line to await the signal’s arrival.
Immediately after the spacecraft has been awoken, its startrackers began to warm up, a task that is expected to be complete within six hours.
Once the spacecraft had “rubbed its eyes” after its long sleep, its thrusters will have fire to stop the slow rotation. This involves a slight adjustment to Rosetta’s orientation to ensure that the solar arrays are still facing directly towards the Sun, before the startrackers are switched on to determine the spacecraft’s attitude.
Once that has been established, Rosetta made a turn directly towards Earth, before switching on its transmitter and pointing its high-gain antenna to send the signal to announce that it is awake.
With confirmation Rosetta is awake and well, the focus now switches to the upcoming rendezvous that will mark several space firsts.
Once at its target, Rosetta will be the first to orbit the comet and to land the Philae probe on the nucleus – to a site in the southern hemisphere of comet 67P/Churyumov-Gerasimenko – making it one of the most complex and ambitious missions ever undertaken.
“Churyumov-Gerasimenko is a time capsule holding material from the birth of the Solar System,” said ESA’s Jeremie Lasue. “The nucleus’s southern hemisphere has been heavily eroded, so Philae will not have to drill down far to find those pristine samples.
“At the time of Rosetta’s rendezvous, gas will be escaping mainly from the northern hemisphere, so it will be safer for Philae to touch down in the south. In addition due to the orientation of the comet, the southern hemisphere will be protected from extreme temperature variations at the time of delivery.”
The south also offers the most stable landing conditions, not least because Philae is powered by solar cells. The probe will experience higher levels of illumination as the comet approaches the Sun, aiding its health.
“When Philae lands, temperatures at the equator may rise above freezing and could fluctuate by around 150 degrees Celsius. However, the regions close to the south pole will keep more stable temperatures,” added ESA’s Maria Cristina De Sanctis.
“From our present results, we’ve concluded that the southern hemisphere promises the best landing sites. As more data on Churyumov-Gerasimenko becomes available to better quantify our results, we will be able to add to the picture and help prepare for a safe landing for Philae.”
Should Philae successfully land, it will obtain the first images ever taken on the surface of a comet and it will make the first in-situ analysis of the composition by drilling into the surface.
Philae will be only the second human-made object to land on a cosmic body far from Earth. It will follow the Huygens probe that landed on Saturn’s moon Titan, 1.3 billion kilometers from Earth, in January 2005.
However, Rosetta will be the first spacecraft to witness, at close proximity, how a comet changes as it is subjected to the increasing intensity of the Sun’s radiation.
(Images via ESA).