10 January 2007
Since COROT was powered up on 2 January, work has begun to calibrate its light sensors. The sensor calibration process, which paradoxically takes place in total darkness, is designed to check the detector arrays pixel by pixel. Three different-colour light-emitting diodes generate a series of flashes to measure the response of each pixel to the type and amount of light it receives.
Each individual pixel responds differently: “For a given amount of light, a pixel doesn’t generate exactly the same amount of current as its neighbours,” explains Laurent Boisnard, COROT System Manager. “We therefore have to factor in these individual responses when applying corrections to the data.” Checks also serve to detect any pixels showing an abnormally high or low response.
Il s’agit également de déceler d’éventuels pixels au comportement anormal, présentant un rendement trop faible ou au contraire trop élevé.
Waiting for 1st light
On the evening of Monday 8 January, engineers at the mission control centre pivoted the satellite 6° about its roll axis to test its 4 thruster nozzles, which all worked perfectly.
The next major step for COROT will be “1st light”, always a crucial phase for any ground- or space-based telescope. “We’re waiting expectantly for the 1st image of the sky,” says Laurent Boisnard.
“That will be the 1st true test of the telescope’s overall performance, particularly the quality of its optical settings.” The moment of truth will come on 17 January when the cap on the sunshield designed to protect the satellite from stray terrestrial light is opened.
Like a jack-in-the-box
On that day, the engineers at the control centre will uplink a command from Toulouse to heat a shape-memory metal alloy. When the metal returns to its original shape, it will cut through a bolt to release a spring mechanism that will open the lid within seconds.
Crédits : CNES.
The much-awaited 1st image of the sky will then be received some time later, after which the telescope will be pointed at the 1st star field selected for the science mission. The telescope will then switch to fine-pointing mode, the last critical step in the project since specifications call for a boresight stability of 0.5 arc seconds—equivalent to viewing a 10-centime coin 3 km away.
Once these final checks are completed, COROT should be all set to begin its 1st science observations in early February, less than 6 weeks after launch and exactly to the schedule initially announced.