Videogrammetry Measurements Successfully Completed
15 August 2006
The Planck space telescope was removed last week from the Large Space Simulator (LSS) at ESTEC, ESA's research and technology centre in Noordwijk, the Netherlands, after a thorough two-week test down to -178 °C. The telescope has performed well under the cold-vacuum conditions. The test is an important milestone in the build-up to launch in 2008.Once in space, Planck will investigate the cosmic background radiation: the remnants of the Big Bang over 1400 million years ago. The telescope will make observations in the far-infrared; this can only be achieved using super-cooled instruments. It is essential to test the telescope at very low temperatures.
Cold Vacuum
Video: Hoisting of Planck Telescope out of the LSS
"Central to this test is exposure of the mirrors and their structural frame to a very cold vacuum", explains ESA scientist Philippe Kletzkine. "The telescope is built at room temperature and then cooled to way below the freezing point. Even though the materials were chosen carefully, this makes each individual component of the telescope shrink to some small but not negligible extent. We need to know whether the resulting changes in shape match our predictions. We have to be spot on, so the mirrors are lined up properly."
Videogrammetry is used to get a clear picture of the telescope's changes in shape. Thousands of photographs, taken from many different angles, are used to build up a three-dimensional image of the mirrors, their structural frame and the place where the telescope's cameras will be mounted. This process is repeated at several temperatures.
Test Results
The telescope has been returned to a cleanroom at ESTEC. This completes the hands-on part of the measurement - now it is time for the arithmetics. Kletzkine: "Over the next few weeks we will be busy interpreting the test results. According to our first impressions the telescope has behaved well."
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Hoisting Planck out of the LSS |
Planck resting on support stand |
Earlier this year, Planck's mirrors were tested individually without the telescope structural frame at Alcatel, in Cannes, France. The results of their videogrammetry tests met expectations. Alcatel Alenia Space France is Prime Contractor to ESA for the Planck spacecraft.
Preparations for the mission continue at ESTEC. All the components needed to complete the spacecraft will be delivered and tested together in the coming months. Eventually the flight model will undergo a vibration test, acoustic test, high and low temperature test, as well as various tests of the computers and communications equipment on board.
Balance Testing
When the satellite is nearly completed, it will once again be placed in the Large Space Simulator. Planck is a spin stabilised spacecraft, that will rotate around its axis to obtain a stable platform for performing observations. New test runs in the LSS, again under vacuum but this time at normal room temperature, will check that the complete spacecraft is well balanced.
If everything goes to plan, at the end of 2007 Planck will pass its Flight Readiness Review: a last step before proceeding with launch activities in 2008. Planck will be launched together with the Herschel spacecraft on an Ariane 5 ECA heavy-lift launch vehicle.
