XMM in safe hands
10 December 1999During the first hours after XMM's acquisition by the Perth groundstation, the spacecraft control teams at ESOC nursed their babythrough its initial in-orbit sequences. Triggered by the onboardtimer, the two wings of the solar array opened faultlessly, thetelescope sunshield equally well. The star trackers were switched onand the spacecraft's reaction wheels were spun up.
On a large screen in the Main Control Room, an animation showed XMM's position in space, moving away from Earth on its first orbit. Dietmar Heger, spacecraft operations manager commented : "It's going very, very nicely. Almost better than the simulations we have been through before launch".
To reach its definitive orbit, commands will be sent to the satellite to fire its onboard motors several times. On the first orbit, in two burns some 22 and 24 hours after liftoff, the velocity of the spacecraft will be increased so as to start raising the perigee. A second perigee raising manoeuvre will take place at + 69 hours and a third at + 117 hours. At the start of orbit 4 another manoeuvre will fine-tune the apogee, before XMM is configured for its definitive operational orbit (114 000 x 7000km)
During the early orbit phase, part of XMM science payload (notably the three EPIC cameras) are to be switched on, in order to vent the instruments of any residual air. On orbit 5, the radiation monitor will be switched on (to start collecting data on the passages through the Earth's radiation belts) and on the sixth orbit, the door to the Optical Monitor will be opened.
XMM will be placed in a "sleep mode", pointing at a bright star that will not be occulted during this period over the Xmas and New Year holidays. Operations will resume on 4 January. A long phase of commissioning the spacecraft in orbit and calibration of the instruments will precede the start of the first science observations, scheduled next spring.