Wednesday, August 6, 2014

Probe's 'final burn' for comet orbit

The European Space Agency's Rosetta probe has started the final engine burn that will take it into an historic orbit around a comet.

The spacecraft will fire its thrusters for six and a half minutes to achieve a triangular orbit around Comet 67P/Churyumov-Gerasimenko.

If successful, it will be the first craft to attain this goal.

Rosetta has been chasing the 4km-wide comet for over 10 years.

Launched on board an Ariane rocket in March 2004, Rosetta has taken a long route round our Solar System to catch up with comet 67P.

In a series of fly-pasts, the probe used the gravity of the Earth and Mars to increase its speed during the 6 billion km chase.

To save energy, controllers at the European Space Agency's centre in Darmstadt, Germany put Rosetta into hibernation for 31 months.

In January they successfully woke the craft from its slumber as it began the final leg of the daring encounter.

For the past two months Rosetta has been carrying out a series of manoeuvres to slow the probe down.

The comet is travelling at 55,000km per hour (34,175 mph), so the spacecraft's speed has been adjusted so that in relative terms it will be flying beside the comet at a slow walking pace of 1m/sec (2.2mph, 3.6kph).

At around 550m km distance from the Earth, messages are taking over 22 minutes to get to Rosetta.

The distances involved are so great that the complex final command sequence for the latest thruster burn had to be issued on Monday night.

Project scientist, Dr Matt Taylor, said: 'We have to make baby steps as we approach it, because we don't know exactly how the comet is behaving and how the spacecraft will behave around it.

Rosetta key facts

  • Total cost of the mission is said to be 1.3bn euros

  • The probe weighed in at 3,000kg at liftoff back in 2004, with over half of that made up of propellant

  • It has two 14m long solar panels to provide electrical power

  • The orbiter carries 11 experiments

  • The lander, Philae, carries nine experiments including a drill to sample beneath the surface

'We have a rough idea but we have to take a gradual approach to really get a handle on how to fly around a comet.

'For me this is the sexiest, most fantastic mission there's ever been. It's ticking a number of boxes in terms of fascination, exploration, technology and science - predominantly science.'

The gravity of 67P is thought to be weak so Rosetta will have to continue to fire its thrusters every few days to maintain a triangular orbit at 100km above the rotating rock.

The craft will then travel alongside the comet for the next 15 months, studying it with a range of instruments.

Rosetta has been taking increasingly detailed photographs of 67P as it gets closer. The mysterious comet has been dubbed the 'rubber duck', as some images seem to show the familiar shape as it twirls in space.

Harpooning a comet

As it moves towards the Sun, 67P will warm up and its trailing halo of gas and dust - known as the coma - will increase, offering the orbiter the chance to do some detailed scientific work.

The mission gets even more ambitious in November when, after moving Rosetta closer to 67P, mission controllers will attempt to put the Philae lander on the surface.

The lander will use harpoons to anchor itself and will carry out a series of experiments, including drilling into the material that makes up the comet.

The mission will aim to add significantly to our knowledge of comets and their role in ferrying the building blocks of life around the early Solar System.

Already Rosetta has learned some intriguing details about 67P.

Using the visible, infrared and thermal imaging spectrometer, VIRTIS, Rosetta recorded temperatures on the icy object around -70C, about 20 degrees warmer than expected.

'This result is very interesting, since it gives us the first clues on the composition and physical properties of the comet's surface,' says principal investigator of the VIRTIS instrument, Dr Fabrizio Capaccioni from INAF-IAPS, Rome, Italy.

Some experts have speculated that the surface is very dusty, except at the neck where the two parts of the comet connect.

Scientists will be eagerly looking forward to seeing the first high resolution images from Rosetta as it closes in on 67P.