Illustration showing Philae attacked to the underside of the Rosetta spacecraft

Comet 67P/Churyumov–Gerasimenko (or 67P/C-G)It may sound like science fiction but alas, this is really about to happen. On November 11, 2014, the European Space Agency (ESA) will land a small robotic spaceship, known as Philae, on a comet. It will be the first comet landing in the history of mankind.

Rosetta’s (and Philae’s) mission

The mission to land on a comet began on March 2, 2004 when the solar-powered robotic space probe, Rosetta, was launched by the European Space Agency attached to an Ariane 5 rocket engine. Rosetta’s objective was simple – to study the comet 67P/C-G. To do so, Rosetta carried on board a small robotic lander, Philae (pronounced Fie-Lee), named after the Philae Island where an obelisk was found that was used along with the Rosetta Stone to decipher Egyptian hieroglyphics.

The Rosetta spacecraft looks like a 10-foot-tall large, black box.  Several scientific instruments are mounted on its top (including cameras and probes to measure gases, radio waves, and comet dust grains) with large satellite communication dishes mounted on one side and the Philae lander mounted on the other side.  On both sides are two huge, rotating solar wings (each about 46-feet long) used to collect solar energy to charge Rosetta’s batteries.

What is Comet 67P/C-G?

The target of the mission, Comet 67P/C-G (officially known as 67P/Churyumov–Gerasimenko), orbits the Sun every 6.45 years. Its next close approach to the Sun will happen on August 13, 2015, just a few months after Philae lands on the comet’s surface. Comet 67P/C-G was discovered in 1969 after a scientist noticed a small smudge on a photographic plate was not mayo from his sandwich but rather, was a new comet that had never been noticed before.

A scientific mistake turns into a new opportunity

Closeup picture of the surface of Comet 67P/Churyumov–Gerasimenko (or 67P/C-G)Surprisingly, 67P was not ESA’s first choice for a comet landing. Originally the plan was to land Philae on the surface of comet 46P/Wirtanen but a failure in a rocket engine caused them to miss the launch window. Like good scientists, rather than giving up altogether, they simply blamed the mistake on the janitor and changed their target to comet 67P/C-G.

To make it to the new target, the scientists had to make several adjustments. Rosetta carries a very low power supply (it is partially powered by solar power) and thus, has to use carefully-timed gravity assist maneuvers to slingshot the craft through the gravity field of planets. Unfortunately, since the original target changed, the gravity assist maneuvers had to change too. On February 25, 2007, one risky maneuver involved flying very close to Mars, through the planet’s shadow, where Rosetta would not receive any solar light for 15 minutes. Since Rosetta requires solar energy to power its radios and engines, this period of darkness caused a dangerous shortage of power for the craft. To compensate, scientists put Rosetta in a hibernation mode, flying only on batteries that were not designed for this task. The maneuver was called “The Billion Euro Gamble” and fortunately for the janitor, it worked.

The Rosetta spaceship becomes a planet

A few months later, another group of scientists spotted the craft flying through the sky (it was approaching Earth for a fly-by) and misidentified it as an asteroid. Thus, for a brief period, Rosetta was designated as minor planet 2007. The embarrassed scientists blushed and explained, “Sorry, the janitor told us it was a planet.”

The landing on comet 67P/C-G

Finally, on August 6, 2014, after 10 long years hurtling through space, Rosetta reduced its speed to prepare to orbit around the comet. Today Rosetta is making several triangular orbits around 67P/C-G. On November 11, 2014, Rosetta will deploy Philae which will slowly fall towards the comet’s surface at a speed of 1 meter per second (the comet’s gravity is 1/10,000th of that on Earth so it will fall very slowly). Using special legs designed to keep it from bouncing, the spacecraft will carefully land and a harpoon will be deployed to anchored Philae to the comet’s surface. Once it lands, Philae will stay for at least a week (possibly longer if the janitor makes no more mistakes) studying the comet.

Here is where Philae will land:

Philae's landing site on the surface of Comet 67P/Churyumov–Gerasimenko (or 67P/C-G)

And here’s what it will look like on its descent to the surface of 67P/C-G:

Philae's flying towards the surface of Comet 67P/Churyumov–Gerasimenko (or 67P/C-G)

 

After Philae lands, it will be a stunning 317 million miles away from Earth.  Its radio signal, travelling at the speed of light, will take 28 minutes to reach planet earth.  You can check out the latest Philae pictures here.

Sources: European Space Agency
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