ESA’s Gaia space observatory takes to the sky
A spacecraft that promises to revolutionize our understanding of the galaxy in which we live has been successfully launched. The European Space Agency’s Gaia mission blasted off from the Guiana Space Center at 09:12:19 GMT (4:12:19 a.m. EST) atop a Soyuz/Fregat rocket and booster. The $1.2-billion, 4,475-pound observatory, which is designed to catalog the positions, movements, and properties of around a billion objects in the Milky Way Galaxy with unprecedented accuracy, rose into the sky above French Guiana on schedule, powered by a 151-foot-tall Soyuz ST-B/Fregat-MT launch stack. Stage separations and burns were nominal. Two minutes into the flight, the four strap-on boosters of the Soyuz rocket separated at an altitude of 37 miles, leaving just the core stage firing. At T+plus 3 min 50 sec, with the launcher clear of the atmosphere, the 13.5-foot-tall nose fairing was jettisoned.
Just under five and half minutes after launch, the Soyuz second stage shut down and the third stage RD-0124 engine ignited. At T+plus 9 min, the Soyuz third stage separated from the Fregat upper stage which subsequently completed the first of two burns — the first to place the vehicle in Earth orbit, the second and much longer one, lasting about 15 minutes, to set Gaia on course for its final destination – the L2 Lagrangian point, 930,000 miles from Earth. A little under 42 minutes after liftoff, the Fregat upper stage separated and Gaia began its three-week journey to where it will begin its billion-star observation program.
Crucial to Gaia’s success was a 13-minute automatic sequence of deployment events that commenced 88 minutes after launch.
This sequence included activating the spacecraft’s transmitters, setting its attitude with respect to the Sun, and unfurling a 34-foot-wide, circular sunshield. With the sunshield opened up, Gaia now has the shape of a broad-brimmed hat, the reflective brim providing shade for the observatory’s sensitive, billion-pixel camera so that it can work optimally at a bone-chilling minus 148°F.
For the first four days of its mission – the so-called Launch and Early Orbit Phase (LEOP) – Gaia will be monitored 24 hours a day by engineers and controllers at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany. During this critical period, teams at ESOC will switch on and check out various onboard systems, including star-trackers, navigation gyroscopes, and data systems.
About 27 hours after launch, a thruster burn lasting for about 30 minutes will put Gaia on course for L2 – the exact timing and duration of the burn is dependent on the earlier performance of the Soyuz/Fregat launcher.
The end of LEOP will mark the start of Gaia’s four-and-a-half month commissioning phase. This is the lengthy time during which all the observatory’s instruments will be turned on, validated, and calibrated ready for the beginning of the first star survey. Also at the end of LEOP, the mission teams will move to a more relaxed, daytime monitoring routine until the next critical milestone which should take place on or around January 7, when Gaia is scheduled to enter orbit around L2. This will involve a delicate maneuver with little margin for error – a firing of the spacecraft’s thrusters in vectoring mode so as to give a push in the right direction while keeping the sensitive instrument away from the Sun.
A second, smaller, burn may be need about a week later. Once L2 orbit has been achieved, the commissioning phase will resume prior to the start of the science mission, the chief highlight of which will be to create the most precise 3D map ever of our home galaxy.
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Dr. David Darling is an astronomer and author of numerous books, including We Are Not Alone, Megacatastrophes, The Complete Book of Spaceflight, and his latest, The Rocket Man. His website, The Worlds of David Darling, is one of the largest and most visited science resources on the Internet. Darling is a renaissance man, he is a musician, noted author and journalist and serves as our science writer. Darling provides The Spaceflight Group with articles detailing what he knows best - space exploration.