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The ESA Planck spacecraft heads off to its final destination after successful launch

15 July 2009

Planck, ESA’s new spacecraft to map the cosmic microwave background, successfully took its first steps into space on 14 May when it was launched together with the far-infrared space telescope Herschel from Europe’s Spaceport in French Guiana. The two spacecraft were on board an Ariane 5 launcher that took off from Kourou at 13.12 UTC.

Planck is designed to map tiny irregularities in fossil radiation left over from the very first light in the Universe, emitted shortly after the Big Bang (CERN Courier April 2009 p26). Herschel, equipped with the largest mirror ever launched into space, will observe a mostly uncharted part of the electromagnetic spectrum to study the birth of stars and galaxies as well as dust clouds and planet-forming discs around stars (XMM-Newton observes emission from matter around a black hole).

Almost 26 minutes after launch, Herschel and then Planck were released separately on an escape trajectory towards the second Lagrangian point (L2) of the Sun–Earth system, some 1.5 million km from Earth in the opposite direction to the Sun. This triggered the execution of automatic sequences on board, including switch-on of the high-frequency radio transmitters. Nine minutes later, the first signals from both spacecraft were acquired by ESA’s New Norcia and Perth stations. Shortly afterwards, telemetry confirmed that both spacecraft were in good health.

On 5 June, Planck carried out the critical mid-course manoeuvre to place the spacecraft on its final trajectory for arrival at L2 early in July. The manoeuvre, in which Planck’s main thrusters make repeated “pulse burns”, lasted about 46 hours. This pulse-burn technique is necessary because Planck is slowly spinning as it travels through space, rotating at 1 rpm. The thrusters, which are fixed to the spacecraft and are not steerable, can only burn when they are oriented in the correct direction, which occurs for 6 seconds during each 60 second rotation. The successful manoeuvre provided an overall change in speed of 155 m/s in an initial speed of 105,840 km/h with respect to the Sun. A “touch-up” manoeuvre was scheduled for 17 June to provide a final 5–10 m/s correction.

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