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Everything You Need to Know About Rosetta, The Comet-Harpooning Robot

We’re about two months away from an awesome little bit of space science: the European Space Agency’s Rosetta spacecraft is going to release a lander that will harpoon and land on a comet. It’s the first ever in situ science mission on a comet’s surface, and here’s everything you need to know about the mission before it all goes down.

Rosetta launched on March 2, 2004 from Europe’s Spaceport in Kourou, French Guiana. After a brief stay in Earth’s orbit, it set out on the scenic route to its target, Comet 67P (properly Comet 67P/Churyumov-Gerasimenko in honor of its discoverers). The spacecraft entered into an orbit around the Sun that had it fly by Mars (once in 2007), back past the Earth (three times: in 2005, 2007, and 2009), and through the asteroid belt twice.

After four orbits around the Sun in ten years, Rosetta sidled up to its target comet. After a breaking maneuver that lasted hours, the spacecraft had lost enough velocity to match the comet’s speed to within a few miles per hour, an impressive feat when you think that these objects are flying through space at about 10 miles per second.

Rosetta spent the earlier part of this year drifting about 125 miles (about 200 kilometers) from the comet’s nucleus, mapping and characterizing its surface, and taking pictures to help the science team understand just what kind of rock they were dealing with. The spacecraft’s speed was also gradually reduced during this period; by the end of August, it was orbiting about 15 miles (25 kilometers) above the comet’s surface, matching its speed within a few inches per second.

Rosetta 1

With its cameras trained on the comet’s surface, Rosetta started photographing potential landing sites for its payload, a 220-pound (100 kg) lander called Philae that is currently hitching a ride aboard Rosetta. In November — the date is currently set as November 11 — Philae is going to attempt to land on the comet.

The landing site has already been selected. Called site J, it’s on the comet’s head in an area largely free of large rocks and boulders and where nearby slopes are relatively gentle. Site J also gets a fair amount of sunlight that Philae will need to power its batteries.

The landing attempt will begin when Philae self-ejects from its stored position on Rosetta’s side. On its way to the surface it will unfold its three legs, legs that have been specially designed to absorb the shock of landing and stop the little lander from bouncing around as it settles on the surface. The legs are already ready to lift, rotate, and tilt to keep Philae upright once it touches down.

The instant Philae touches down, it will release a harpoon into the comet, effectively anchoring it into the rock. Then it’ll get to the science.

The little lander has ten instruments on board. Philae has a series of cameras that will give us panoramic and stereo views. A spectrometer will tell us about the elemental composition of the comet’s surface. A neat experiment called the Comet Nucleus Sounding Experiment by Radiowave Transmission will send radio waves from Rosetta to Philae through a probe, the latter will lodge into the comet’s nucleus.

There are two gas analyzers on the lander as well, one that will look for organic molecules and another that will measure ratios of elements. Another experiment will use sensors to measure the thermal and mechanical properties of the comet’s surface, as well as the density. Magnometers and plasma sensors will study the comet’s magnetic field and its interaction with the solar wind. A drill on board will collect samples from about 8 inches (20 cm) beneath the surface and deliver them to on-board ovens and microscopes for analysis. And finally, a suite of instruments will study the comet’s outer layers: how sound travels through the surface, its electrical characteristics, and the way dust behaves as it falls.

Rosetta 2Rosetta snaps a selfie with Comet 67P looming large in the background.

Rosetta, meanwhile, will stay in orbit around the comet, serving as a relay between Philae and Earth while also continuing its own science mission. It will observe what happens as the icy comet first approaches and then moves away from the Sun.

The next phase of Rosetta’s mission is pending a comprehensive readiness review on October 14. Should the spacecraft pass, which seems likely at this point, Philae will get a green light to attempt its landing in November. From that point, the primary mission will last a little more than a year; the mission is scheduled to end in December of 2015.

IMAGES: ESA/Rosetta/NAVCAM; ESA/Rosetta/Philae/CIVA

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