Planck's Orbit

 


Image credit: ESA

Planck was launched in 2009 from French Guiana on an Ariane 5 rocket. It has a sister-experiment, Herschel, which was launched on the same rocket. Following launch, Planck will travel to a point called "L2", short for "Lagrange Point 2", and orbit around it. L2 is a particularly useful place to be, at around 1.5 million km (around 1 million miles) from Earth in the opposite direction to the Sun. The combined gravity of the Earth and the Sun means that anything near this location orbits the Sun in exactly 1 year, and so stays in the same place relative to the Earth.

Planck doesn't sit exactly on the L2 point, but orbits around it at an average distance of around 400,000 km (around 250,000 miles). This is important because it means that it's never in the Earth's shadow, so its solar panels (which provide all of the power to the satellite) will always see the Sun. Besides, it's going to get a bit crowded up at L2 - the WMAP satellite is already there, and Planck and Herschel will also be joined in a few years by the Gaia probe and later the James Webb Space Telescope.  Click on the image above to see an animation of Planck's cruise to L2.  The animation below shows the position of the satellite over the first year from a range of angles.  The cross marks are plotted every 7 days.  Click so see a bigger version.


Planck's position relative to the Earth and L2 over the first year of the mission.  Image credit: Chris North, Cardiff University
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A Spinning satellite


Image credit: ESA

Planck will continually spin around an axis pointing away from the Sun, at a rate of one revolution per minute, and look nearly at right angles to that axis. Every minute it will look at a ring around the sky, and as it orbits the Sun the rings will gradually move round the sky. Click on the image on the right to see animation of Planck mapping the sky (.mov format).  After a little over 6 months it will have made a map of the whole sky, and will continue to observe to make its maps even better. Eventually, all the Helium coolant used to cool the detectors will run out, at which time Planck will stop observing.

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