This evening (20/01/14) saw a fairy-tale ending to a tense chapter in the story of Europe’s Rosetta space mission when the spacecraft sent its first signal after 31 months of hibernation.
Operating on solar energy alone, the Rosetta comet chaser was placed into a deep space slumber in June 2011 as it cruised out to a distance of nearly 800 million km from the warmth of the Sun, beyond to the orbit of Jupiter.
Now, as Rosetta’s orbit has brought it back to within ‘only’ 673 million km from the Sun, there is enough solar energy to power the spacecraft fully again.
Still about 9 million km from the comet it is chasing, Rosetta was awoken by its pre-programmed internal ‘alarm clock’. After warming up its key navigation instruments, coming out of a stabilising spin, and aiming its main radio antenna at Earth, Rosetta sent a signal to let mission operators know it had survived the most distant part of its journey.
Dr Chris Castelli, Acting Director of Technology, Science and Exploration at the UK Space Agency, said, “Rosetta is a big mission for the UK, with much of the spacecraft built and designed in the country and UK scientists involved in 10 of the mission’s instruments. We’re all relieved that Rosetta didn’t miss its alarm call and will soon be ready to begin its primary mission of unlocking the secrets of a comet.”
Christopher Carr, Imperial College London, added “Rosetta is an extremely exciting mission which will give us the first ever chance to operate a satellite within the evolving plasma environment of a comet. We’re really looking forward to seeing how the solar wind interacts with the gas expelled by the comet, and we’ll be able to test our predictions about the formation and composition of the comet’s ionosphere.”
Rosetta is chasing down Comet 67P/Churyumov-Gerasimenko, where it will become the first space mission to rendezvous with a comet, the first to attempt a landing on a comet’s surface, and the first to follow a comet as it swings around the Sun.
Since its launch in 2004, Rosetta has made three flybys of Earth and one of Mars to help it on course to its rendezvous with 67P/Churyumov-Gerasimenko, encountering asteroids Steins and Lutetia along the way.
The signal was received by both NASA’s Goldstone and Canberra ground stations at 6:18pm GMT/ 7:18pm CET, during the first window of opportunity the spacecraft had to communicate with Earth. It was immediately confirmed in ESA’s space operations centre in Darmstadt and the successful wake-up announced via the @ESA_Rosetta twitter account, which tweeted: “Hello, World!”
“We have our comet-chaser back,” says Alvaro Giménez, ESA’s Director of Science and Robotic Exploration. “With Rosetta, we will take comet exploration to a new level. This incredible mission continues our history of ‘firsts’ at comets, building on the technological and scientific achievements of our first deep space mission Giotto, which returned the first close-up images of a comet nucleus as it flew past Halley in 1986.”
Comets are considered the primitive building blocks of the Solar System and likely helped to ‘seed’ Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through its comprehensive, in situ study of Comet 67P/Churyumov-Gerasimenko, Rosetta aims to unlock the secrets contained within.
“All other comet missions have been flybys, capturing fleeting moments in the life of these icy treasure chests,” says Matt Taylor, ESA’s Rosetta project scientist. “With Rosetta, we will track the evolution of a comet on a daily basis and for over a year, giving us a unique insight into a comet’s behaviour and ultimately helping us to decipher their role in the formation of the Solar System.”
But first, essential health checks on the spacecraft must be completed. Then the 11 instruments on the orbiter and 10 on the lander will be turned on and prepared for studying Comet 67P/Churyumov-Gerasimenko.
Rosetta’s first images of 67P/Churyumov-Gerasimenko are expected in May, when the spacecraft is still 2 million km from its target. Towards the end of May, the spacecraft will execute a major manoeuvre to line up for its critical rendezvous with the comet in August.
After rendezvous, Rosetta will start with 2 months of extensive mapping of the comet’s surface, and will also make important measurements of the comet’s gravity, mass and shape, and assess its gaseous, dust-laden atmosphere, or coma. The orbiter will also probe the plasma environment and analyse how it interacts with the Sun’s outer atmosphere, the solar wind. Using these data, scientists will choose a landing site for the mission’s 100 kg Philae probe. The landing currently scheduled for 11 November and will be the first time that a landing on a comet has ever been attempted.
In fact, given the almost negligible gravity of the comet’s 4 km-wide nucleus, Philae will have to use ice screws and harpoons to stop it from rebounding back into space after touchdown.
Among its wide range of scientific measurements, Philae will send back a panorama of its surroundings, as well as very high-resolution pictures of the surface. It will also perform an on-the-spot analysis of the composition of the ices and organic material, including drilling down to 23 cm below the surface and feeding samples to Philae’s on-board laboratory for analysis.
The focus of the mission will then move to the ‘escort’ phase, during which Rosetta will stay alongside the comet as it moves closer to the Sun, monitoring the ever-changing conditions on the surface as the comet warms up and its ices sublimate.
Speaking about the Philae lander’s UK-led Ptolemy instrument – a laboratory the size of a small shoebox - Ian Wright, Professor of Planetary Sciences at The Open University, said, “Once the Philae lander touches down on the comet, we will be looking for evidence recorded in remnants of debris that survived the processes of planet formation. This is not merely a period of pre-history, but one that pre-dates the origin of life itself. Our quest is to gain insights into this transitional era, which took place more than 4.5 billion years ago.”
The comet will reach its closest distance to the Sun on 13 August 2015 at about 185 million km, roughly between the orbits of Earth and Mars. Rosetta will follow the comet throughout the remainder of 2015, as it heads away from the Sun and activity begins to subside.
“We will face many challenges this year as we explore the unknown territory of comet 67P/Churyumov-Gerasimenko and I’m sure there will be plenty of surprises, but today we are just extremely happy to be back on speaking terms with our spacecraft,” adds Matt Taylor.
Rosetta and the UK
With funding from the UK Space Agency, Rosetta is a mission with significant UK involvement. UK scientists are involved in ten of the 21 experiments that Rosetta will carry out during its mission:
- the Open University is leading the team for the Ptolemy instrument on the lander
- Armagh Observatory will be helping to analyse the results from the OSIRIS instrument
- Imperial College London and University College London’s Mullard Space Science Laboratory (MSSL) supply the team studying the comet’s plasma
- scientists at Oxford University are part of the science team for VIRTIS
- Queen Mary College at the University of London will be investigating the results of the CONSERT instrument
Industry involvement includes:
- Astrium Limited, based in Stevenage, was the major subcontractor for the Rosetta platform
- the Science & Technology Facilities Council (STFC) Rutherford Appleton Laboratory managed to reduce a lab full of chemistry equipment to enable it to fit into a space the size of a shoebox
- SciSys UK Ltd is responsible for the spacecraft Mission Control System development and maintenance; in recognition of this work on the Rosetta and the Beagle 2 missions, SciSys were awarded the title of “Innovator of the Year” by the UK Computing Awards for Excellence 2004
- VEGA Group plc was involved in many aspects of the Rosetta mission, from the overall design of the spacecraft to the on board software
- technology created by Logica (now CGI) helped to explore some of the issues involved in such a long mission, the company was also involved in the development of the Rosetta on board software.
- AEA Battery Systems Limited provided innovative batteries for the spacecraft and lander. These are smaller, lighter and much more reliable than the traditional nickel-cadmium batteries
- AEA Technology, European Space Tribology Laboratory (ESTL) developed the Micro-Imaging Dust Analysis System (MIDAS)
- Polyflex Space Ltd provided tanks to store the helium used by the lander
- Surrey Satellite Technology Limited (SSTL) designed a wheel that will stabilise the probe as it descends and lands on the comet