Rosetta reaches comet
August 5, 2014
On March 2, 2004 - ten years and five months ago - the Rosetta spacecraft and its lander robot Philae were attached to an Ariane 5 rocket and launched into space with the goal of eventually studying comet 67P/Churyumov-Gerasimenko. It is considered to be the most ambitious mission ever undertaken by the European Space Agency (ESA).
On Wednesday (06.08.2014) the spacecraft will enter the comet's orbit. During its journey it has so far covered over six billion kilometers (3.75 billion miles) and gone through 30 months of hibernation, during which it had no contact with Earth.
Rosetta reestablished contact to ground control at the ESA Satellite Control in Darmstadt on January 20, 2014, and Philae "woke up" on March 28.
Entering the comet's orbit is an essential phase of a gradual process, which ideally should result in the first landing ever on the surface of a comet. If all goes well, on November 11 Philae will attach itself to the comet, drilling holes, taking samples and studying the comet's material composition.
A search for the origins of life
Comets act like time capsules for the solar system: they can preserve organic matter for billions of years by keeping it frozen solid. Substances researchers hope to find in the comet, such as amino acids, could provide clues to the origin of life on Earth some 4.6 billion years ago.
"The comets are very old components of our solar system. By studying them, we try to understand how our solar system came to be," said Johann-Dietrich Wörner, chair of the executive board at the German Aerospace Center (DLR), which worked together with ESA and various national space institutes to develop Philae.
Over the course of Philae's time on the comet, researchers hope to find out whether the water on Earth could have been brought here by comets. "It really is a journey into the unknown," Wörner said.
Rosetta, which will navigate around the comet before dropping Philae to its surface, is equipped with cameras capable of mapping the comet to a decimeter degree of accuracy.
Making contact without gravity
History's few instances of space landings makes Philae's mission to the comet's surface worthy of attention, but to call Philae's rendezvous with the comet a "landing" isn't entirely accurate. Given the comet has a diameter of only five kilometers at its widest point, its mass is not large enough to generate a gravitational pull strong enough to support a landing. A more accurate description of the event is a docking.
The docking process is no small feat. Rosetta will bring the Philae lander within three kilometers of the comet, which travels through space at speeds up to 135,000 kilometers per hour. Philae will then fire a harpoon into the comet's outer layer of ice and reel itself in.
"It is a difficult mission," said Wörner. "But I trust my technicians and scientists. They've had success harpooning various materials."
The harpooning is the first of a number of tricky maneuvers. If the harpoon holds fast and Philae can reel itself onto the comet's surface, screws will then extend from the feet of the lander into the ice. Measurement instruments on the lander will then analyze the comet's make-up.
"We only have a rough idea about the comet's density based on its mass and trajectory," Wöner said, adding that a spectrometer will identify what the lander finds. "We don't really know what it is made of. That's what we want to find out."