|LAUNCHER/LOCATION||Soyuz-STB Fregat/Kourou, French Guiana|
|LAUNCH MASS||2030 kg|
|ORBIT||Second Lagrange point L2 - 1.5 mn km from the Earth|
|NOMINAL MISSION||Five years|
|++ Will generate the most precise-ever 3D map of our Galaxy by surveying over 1 thousand million stars and potentially discovering hundreds of thousands of new objects, such as extrasolar planets ++|
The Gaia Mission will conduct a census of one thousand million stars in our Galaxy, monitoring each target star about 70 times over a five-year period and precisely charting their positions, distances, movements and changes in brightness. Gaia may also discover hundreds of thousands of new celestial objects, such as extra-solar planets and failed 'brown dwarf' stars.
Within our own solar system, Gaia should also identify tens of thousands of asteroids, and provide stringent new tests of Albert Einstein's general relativity theory.
Gaia will orbit the Sun-Earth system from the second Lagrange point L2, and the mission is designed to last for a nominal five-year period.
Gaia will carry a single integrated instrument that comprises three major functions: astrometry, photometry and spectrometry. The three functions use two common telescopes and a shared focal plane, with each function having a dedicated area on the large 0.5 m x 1 m CCD (charge-coupled device) detector array.
The Gaia spacecraft is now being built, with EADS Astrium SAS as prime contractor. The Gaia Mission Operations Centre (MOC) will be located at ESOC, Darmstadt, Germany. The Gaia Science Operations Centre (SOC) will be established by ESA at the European Space Astronomy Centre (ESAC), in Villafranca, Spain.
The Flight Control Team
The Flight Control Team will operate from a Dedicated Control Room located at ESOC.
The team is led by Spacecraft Operations Manager (SOM) David Milligan, from the UK; he moved over to Gaia from ERS-2 and after working as a systems engineer on Envisat and a propulsion and power specialist on SMART-1, which ended with a spectacular impact on the Moon on 3 September 2006. He joined Gaia as SOM in 2008 and is now responsible for preparation of the ground segment, the selection and training of the flight control team, and Gaia operations preparations.
Like all missions controlled from ESOC, the Gaia team will rely on experts from other ESOC teams to ensure operations success, including Flight Dynamics, Ground Facilities, Navigation and Mission Data Systems.
Mission operations overview
Gaia will travel into orbit in 2013 on a Soyuz-ST rocket from Kourou, Europe's Spaceport in French Guiana.
Soyuz-ST, the commercial version of the Soyuz-2, is the last version of the renowned family of Russian launchers that placed the world's first satellite, Sputnik, and the first astronaut, Yuri Gagarin, into orbit.
The critical Launch and Early Orbit Phase (LEOP) will last approximately two days. Gaia will be injected into its transfer trajectory toward the L2 Lagrange point. This phase also covers the initial configuration and the deployment of the spacecraft.
LEOP will be followed by the transfer and in-orbit commissioning phase, during which all operations to prepare for the routine operational phase are performed. In particular, all scientific instruments will be thoroughly tested and calibrated.
Gaia will operate in a Lissajous-type orbit, around the L2 point of the Sun-Earth system, which is located 1.5 million km from the Earth in the anti-Sun direction. The orbit is not affected by Earth eclipses. The typical revolution period is about 180 days and the size of the orbit is typically 340 000 x 90 000 km.
This location in space offers a very stable thermal environment, very high observing efficiency (since the Sun, Earth and Moon are behind the instrument field of view) and a low radiation environment.
However, orbits about the L2 point are dynamically unstable; small departures from equilibrium grow exponentially overtime. Like ESA's Herschel and Planck missions, which also orbit about L2, Gaia will use its propulsion system to perform periodic orbit maintenance manoeuvres.
Uninterrupted mapping of the sky takes place during the operational mission phase, planned to last for five years.<<hr style="height:0px; border-top:1px solid #03729F; border-bottom:0px; border-right:0px; border-left:0px">
The ground stations
New Norcia, Cebreros
ESA's most powerful ground stations, the 35 m deep-space stations in New Norcia, Australia (DSA 1), and Cebreros, Spain (DSA 2), will be used to send commands to Gaia and receive its science data during routine operations.
DSA 1 and DSA 2 entered service in 2002 and 2005, respectively, and provide state-of-the-art facilities for communications, radio range and location finding and radio science.
Gaia's transmitter, with much less power than a standard 100-Watt light bulb, approximatively 4 Watts, will nonetheless be able to transmit at an extremely high data rate, about 5 Mbps, from its orbit location some 1.5 million km away from Earth.
During the critical LEOP phase, additional ground station support will be provided by the Kourou, Maspalomas and Perth stations.
Ground segment & mission control system
Mission operations will be conducted by the Flight Control Team at ESOC, comprising spacecraft operations (mission planning, spacecraft monitoring and control, and all orbit and attitude determination and control) as well as scientific instrument operations (quality control and collection of the science telemetry). The ground segment at ESOC will comprise all facilities, hardware, software and documentation required to conduct mission operations.
The ground operations facilities will consist of:
- Ground stations and the communications network
- Mission control centre
- Flight control system
- Software-based spacecraft simulator
The science data will be distributed to ESAC directly via high-speed communication lines.
The science data processing requirements for Gaia are among the most challenging of any scientific endeavour to date. Due to the immense volume of data that will be collected, for 1 billion stars, it will be a major challenge, even by the standards of computational power in the next decade, to process, manage and extract the scientific results necessary to build a 3-dimensional view of our Galaxy, the Milky Way.
A total of some 100 Terabytes of science data will be collected during Gaia's lifetime. The estimated total data archive will surpass 1 Petabyte, roughly equivalent to 4000 250-gigabyte hard drives from a top-end home PC.
The platform and payload
Gaia contains two optical telescopes that can precisely pinpoint the location of stars and split their light into a spectrum for analysis. The spacecraft itself can be divided into two sections: the payload module and the service module.
The service module contains the propulsion system and the communications units, essential components that allow the spacecraft to function and return data to Earth. Beneath the service module and the payload module is the sun-shield and solar array assembly.
The payload module is housed inside a geometrical, dome-like structure called the thermal cover, and the payload consists of a single integrated instrument including the dual telescopes, with a common structure and a common focal plane. Both telescopes are based on a three-mirror anastigmat (TMA) design.
There are also three instrument functions:
- Astrometry: Accurate measurements, even in densely populated sky regions of up to 3 million stars/deg². The astrometric instrument is dedicated to the accurate measurement of stellar positions and brightnesses.
- Photometry: Continuous spectra in the band 320-1000 nm for astrophysics and chromaticity calibration of the astrometry. Photometric measurements will record the colours and brightness of all stars; this is valuable information which astronomers will use to determine the physical parameters of celestial objects.
- Spectrometry: High resolution, grating, narrow band, at 847-874 nm. The spectroscopic instrument will detect whether celestial objects are moving toward or away from us. This information can then be combined with that from the astrometric instruments, to give a full picture of how the celestial object is moving through space.
Gaia will always point away from the Sun. After launch, it will unfold a 'skirt' that performs two functions. The first is as a sunshade. This will permanently shade the telescopes in the payload module and allows their temperature to drop to -100°C. In this way, the stability of the telescope and its optical system will be maintained at precise levels.
The other function of the sun-shield is to generate power for the spacecraft. As the underside of the shield will always be facing the Sun, its surface will be partially covered with solar panels that generate electricity from sunlight. The sun-shield 'skirt' is the only deployable structure on Gaia. It consists of twelve separate panels that will be folded for launch. Once in space, the spacecraft will unfold these panels into a roughly circular disc, just over 10 metres in diameter.
Last update: 24 October 2011