Soyuz ST-B successfully launches Gaia space observatory

by Chris Bergin and William Graham

An Arianespace Soyuz ST-B rocket successfully launched the impressive Gaia space observatory from the Kourou Spaceport in French Guiana on Thursday. The launch – occurring on schedule at 9:12 am UTC – marks the beginning of an ambitious project to map a billion stars in our Milky Way galaxy.

The Spacecraft:

The Gaia spacecraft is a successor to the Hipparcos satellite that was launched by Arianespace in 1989.  Gaia will be placed into deep space in an orbit that will be of a Lissajous-type around the second Lagrange point (L2).

Gaia’s main goal is to create a highly accurate 3D map of our Milky Way Galaxy by repeatedly observing a billion stars to determine their precise positions in space and their motions through it.

The resulting census will allow astronomers to determine the origin and the evolution of our Galaxy.

Gaia will also uncover tens of thousands of previously unseen objects, including asteroids in our Solar System, planets around nearby stars, and exploding stars – supernovas – in other galaxies.

To achieve these results, Gaia will carry two identical telescopes, each fitted with four mirrors (M1 to 4). A further two mirrors (M5 and 6) will send the light from these dual instruments into the same focal plane.

Z9The mirrors also have an unusual curved shape, which is calculated using a very precise mathematical formula so that there will be no distortion of the incoming light across the telescopes’ field of view and at all wavelengths from blue to red.

“The M1 mirrors have a collecting area about 11 times bigger than the primary mirror of its predecessor, ESA’s Hipparcos astrometry spacecraft, enabling them to collect many more photons,” said Jos de Bruijne, Deputy Project Scientist for Gaia.

“The combination of size, smoothness and special shape is required to provide a wide angle of view – about 0.7 degrees – and a small wave front error that will give extremely sharp images of a billion stars in our Galaxy.”

Z7Once into its mission phase, Gaia will monitor each of its target stars approximately 70 times over a five-year period and precisely chart their positions, distances, movements and changes in brightness.

Built by Astrium, the 2,120 kg – of which 743 kg is payload – spacecraft is expected to enjoy a five-year mission, with its full archive to exceed 1 petabyte in size – providing enough information to tackle many important problems related to the origin, structure and evolutionary history of the galaxy.

“Gaia is a grand challenge to understanding our galaxy, to find out what it is made of and, thus, where we have come from,” added David Southwood, Director of Science and Robotic Exploration at ESA.

“Europe alone has taken up the challenge. We therefore are very pleased to be launched by Arianespace.”

Launch Vehicle:

The Soyuz-2-1 rocket family is a descendent of the R-7 Semyorka, the world’s first intercontinental ballistic missile. The R-7 was designed by Sergei Korolev, and first flew in 1957. A modified version was used to launch the first satellite, Sputnik 1, on 4 October of that year.

The R7The R-7 formed the basis for the Luna, Vostok, Voskhod, Molniya and Soyuz families of rockets, and to date all Soviet and Russian manned spaceflights have been launched using rockets derived from the R-7.

The Soyuz, which first flew in 1966, was a modification of the Voskhod rocket featuring an upgraded and lighter telemetry system, and more fuel efficient engines. It was initially used to launch only Soyuz spacecraft; however with the introduction of the Soyuz-U in 1973 it began to launch other satellites as well.

The Soyuz-U, which remains in service, is the most-flown orbital launch system ever developed, having made around 750 flights to date, plus around 90 more in the Soyuz-U2 configuration optimised to use synthetic propellant.

The Soyuz-2 was developed from the older Soyuz models, and features digital flight control systems and modernised engines. It first flew in 2004, and this is its twelfth launch.

Two variants are currently in service; the Soyuz-2-1a, and the Soyuz-2-1b which features an RD-0124 third stage engine which provides additional thrust.

A third configuration, the Soyuz-2-1v, is currently under development and is expected to make its maiden flight later this month. It features an NK-33 engine in place of the RD-108A used on the core stages of the other configurations, and does not include the strapon boosters used by other configurations. Exclusive documentation on this vehicle was acquired by L2 (LINK).

The Soyuz-2 forms the basis for the Soyuz-ST rocket, which made its maiden flight from Kourou in French Guiana. The Soyuz-ST is optimised to fly from Kourou, and also incorporates a flight termination system and a modified telemetry system.

Soyuz’ Fregat upper stage – as was used on this mission- is an autonomous, highly flexible orbital vehicle built by the Lavochkin Research and Production Association. It can be restarted up to 20 times in flight – enabling the system to carry out complex mission profiles.

The launch phase lasted for near 42 minutes, ahead of spacecraft separation, involving two burns of the upper stage.

The Launch Site:

The Spaceport’s Soyuz launch site combines the proven design elements from the long-existing site at Baikonur Cosmodrome with satellite integration procedures that are in concert with the spacecraft processing used for Ariane missions.

New Soyuz PadLocated 12 kilometers northwest from the existing Ariane 5 launch complex, the Soyuz facility extends the Spaceport’s operational zone further up the French Guiana coastline.

The launch vehicle’s assembly building is 92 meters long, 41 meters wide, and 22 meters tall, allowing the vehicle to be assembles horizontally, prior to rolling out to the launch site, which is configured after the Russian Baikonur and Plesetsk Cosmodromes, albeit with a new mobile launch service tower.

The Soyuz’ transfer to the Spaceport’s launch zone is performed with the launcher riding horizontally atop a transporter/erector rail car.  Soyuz is then raised into position on the pad, and in contrast with the Baikonur Cosmodrome processing flow, is protected by a gantry that moves into place for payload integration.

Soyuz launching out of KourouArianespace had already conducted five Soyuz launches from French Guiana, beginning with the workhorse medium-lift vehicle’s historic inaugural Flight VS01 at the Spaceport in October 2011 – which orbited two Galileo IOV (In-Orbit Validation) navigation satellites for Europe.

It was followed by Flight VS02 inDecember 2011, carrying a mixed payload of France’s Pléiades 1A dual-use imaging platform, the Chilean SSOT observation satellite and four French ELISA micro-satellite demonstrators.

Flight VS03 was performed in October 2012 with two more Galileo IOV spacecraft, and Flight VS04 occurred in December 2012 to deploy the Pléiades 1B payload.

The fifth mission involved the launch of four O3B satellites this summer.

Images via ESA, Arianespace and L2.

Related Articles