To catch a comet – the Rosetta Mission

The European Space Agency (ESA) launched the Rosetta spacecraft from Earth in March 2004. It then took Rosetta 10 years to catch Comet 67P.

On 12 November 2014, history was made when the Philae probe, carried by Rosetta, was successfully dropped onto Comet 67P. This was the result of decades of research, production and testing involving thousands of people from around the world.

Every single one of you is made of cometary dust from the elements of a supernova explosion more than 4.5 billion years ago. How did we all get here? How can we make a spacecraft to go back and land on a comet?

Avionics systems engineer, Warwick Holmes

Rosetta and Philae

The Rosetta spacecraft is also referred to as an orbiter. Now Philae has landed on Comet 67P, Rosetta continues to orbit the comet, transmitting data from Philae and from its own scientific instruments back to Earth. Three purpose-built satellite dishes on Earth receive the data.

Rosetta is comprised of:

• 11 different scientific instruments
• 64 square metres of solar panels that can be rotated 180° to catch the maximum amount of sunlight (the Sun is a long, long, long way away!)
• a port where the Philae lander was attached
• a satellite dish and antennae
• 24 thrusters for trajectory and altitude control
• a propulsion system with two large propellant tanks for fuel and the oxidiser.

Philae – the smaller landing module – is about the size of a home washing machine. It carries scientific instruments for nine different experiments and a drilling system to collect samples from the comet.

Rosetta and Philae were built to withstand huge variations in the environments they’d encounter over the 12 years of the mission. They required years of testing prior to launch, and testing continued on the long journey to Comet 67P.

Getting to Comet 67P

After launching from French Guiana in 2004, it took Rosetta over 10 years to reach Comet 67P, which is on the outer edge of our Solar System

Scientists used a technique called gravity assist so Rosetta could hitch a ride with other planets. Gravity assist occurs when the spacecraft enters the orbit of other planets and uses their gravity to propel or kick itself forward.

Rosetta also had a lengthy 2 and half years of hibernation to limit its use of power while waiting for certain alignments. During hibernation, the spacecraft spun once per minute while it faced the Sun so that its solar panels could receive as much sunlight as possible, and almost all of the electrical systems were switched off.

To enter hibernation, scientists set four timers on board to 80 million seconds. Each was counting backwards to 0, with two required to reach 0 in order to wake the spacecraft up. As there was only enough electrical power to keep the timers running, they had to switch off the receivers. This meant that, even in an emergency, they could not wake Rosetta up. This is the first time a hibernation like this has been done in a deep space project, and the scientists were understandably very nervous about whether Rosetta would wake up.

Landing on the comet

In January 2014, Rosetta came out of hibernation, and everyone was very excited. By August, it had caught up to Comet 67P and was able to undertake the first orbit of the comet. Rosetta then began the intensive science phase of the mission – collecting data on the comet.

The initial data collected from the comet helped the scientists and engineers work out the best place to land the Philae probe. It had to be landed so that its solar panels would receive enough sunlight to power the different experiments.

On 12 November 2014, Philae separated from Rosetta and began to descend from 22 kilometres above Comet 67P to its surface. For 3 days, Philae was able to send the first images and data back to Earth via Rosetta, before going into hibernation again.

On-going mission

On 13 June 2015, Philae woke up again, this time from its new home on the comet. Communications between Philae and the orbiting Rosetta have been intermittent partly due to issues with the position of aerials. Scientists are now working out how to get a more stable connection between the spacecraft. They also need to make sure the craft are safe, as the comet is getting closer to the Sun and becoming more active. Rosetta’s planned lifetime is about 12 years. After the comet reaches its closest point to the Sun in August 2015 and starts heading back towards the outer Solar System, the plan is for Rosetta to land on the comet in December 2015 to complete some final experiments. It is expected to run out of fuel and die some time in 2016.

Update – the end of Rosetta

A carefully controlled crash landing into the comet occurred on 30 September 2016, bringing an end to the Rosetta mission. Additional science data was collected in this final phase as Rosetta descended into the comet. See the European Space Agency website for further information.

Scientists now have years of work ahead of them analysing the mountains of data collected during this mission.

Find out more about Comets.