Gaia (spacecraft)

Gaia is a launched on December 19, 2013 astronomical spacecraft of the European Space Agency ( ESA) is to carry out a high-precision optical survey of the entire sky. Here, approximately one percent of the stars in our Milky Way is ( consisting of estimated more than 100 billion stars ) are recorded cartographically with previously unattainable precision astrometric, photometric and spectroscopic. Gaia is the successor of Hipparcos ESA mission (1989-1993).

The name Gaia was an acronym for " Global Astrometric Interferometer for Astrophysics ". It features the originally planned for this telescope technique of optical interferometry. The name was later maintained in spite of the changed in the course of planning the measuring principle, he also referred to the Erdmuttergöttin Gaia in Greek mythology.

Scientific Objectives

The main scientific goal of the Gaia mission is with the help of their star measurements to elucidate the origin and evolution of our home galaxy, the Milky Way. The data collected by Gaia measurement data should in particular provide information on where, when and how the stars are created and how they enrich their surroundings with matter when they die. To this end Gaia will determine with hitherto unattained accuracy the positions, distances ( parallaxes ) and motions ( proper motions, radial velocities ) of about one billion stars. In compliance with the planned flight time of 5 years, there would probably capture Gaia regarding parameters mentioned more than 6 stars per second.

The position and Parallaxengenauigkeit is for bright stars (up to 15 mag) to be better than 25 μas (1 μas = 10-6 seconds of arc ) and the weakest stars ( 20 mag) μas drop to around 300, the latter value is still better than the previously most accurate measurements of very bright stars (500-2000 μas, carried out as part of the Hipparcos mission). In addition, to be measured with high accuracy for a billion stars brightness and colors. For the brightest 100-200 million stars Gaia will also provide well-resolved spectra from which radial velocity, temperature, surface gravity, and chemical composition of stars can be determined.

In addition to information about the structure and evolution of the Milky Way, astronomers hope to gain from this data, new insights into the internal structure, the formation and evolution of stars.

A possible time variation of the gravitational constant G (or more precisely ) to be detected with an accuracy of better than 10-13/Jahr. The relativistic light deflection by the gravitational force of the sun shall be measured with a relative accuracy of about one millionth of the light deflection and be the first direct by the gravity of the planets.

In addition, the astronomers hope to gain from the Gaia measurements, the discovery of a number of previously unknown objects in the sky, in the following orders of magnitude, according to estimates:

Gaia is a five-year original: designed future / In 4 years mission duration. A created from the data obtained by Gaia star catalog with over a billion stars to be published in 2022.

Costs and industry participation

The cost of the ESA for the mission, including seed, ground control and payload amounts to approximately 577 million euros. The cost of scientific data reduction (which must be applied by the Member countries of the ESA) are estimated at approximately 120 million euros. Several industry studies, which cost about 15 million euros, were brought to a conclusion in 2005. In February 2006, ESA commissioned the company EADS Astrium with the construction of Gaia. On 11 May 2006, including the construction contract of Gaia between ESA and Astrium signed.

Start

The launch took place on December 19, 2013 at 9:12 UTC clock with a Russian Soyuz -Fregat rocket from the Guiana Space Centre in French Guiana.

Orbit

On January 8, 2014 Gaia reached its orbit around the Lagrange point L2. The L2 point is from the Sun about 1.5 million kilometers behind the earth. That's about four times the lunar distance. This gravitational equilibrium point runs at a fixed distance with the Earth around the sun and allows ungestörteren view of the universe than would be possible from a low Earth orbit. Gaia has taken a Lissajous path at a distance of 263,000 x 707,000 x 370,000 km around L2, so as to ensure that they do not occur at least six years in the penumbra of the earth. This would interrupt the power supply and affect by the thermal expansion of the optical components during temperature changes, the image quality temporarily.

Spacecraft

Construction

The nearly circular array of solar cells and " parasol " dominating the appearance of Gaia. The sun shield is composed of twelve broad pursuit, between which span 48 triangular faces during the deployment of the shield. There is a dome that houses the payload to the sun shield. Below the payload is a cylindrical supply unit, which contains as essential components such as drive unit, data transmission system and power supply. The satellite is three -axis stabilized and will use its slow rotation to continuously sense the current through the field of sky. Payload and power supply unit are during the academic always operating in the cooling shade of the " umbrella ". In the above sketch of the Gaia satellite, the sun is shining at an angle of 45 degree angle from the bottom of the spacecraft.

Dimensions

When the solar cells have developed, Gaia will have a diameter of eleven meters. The payload dome has a diameter of about three meters and a height of two meters. The supply unit also has three meters in diameter and one meter height.

Engines

For fine control during the measurement operation Gaia has 12 cold gas nozzles with very small variable thrust from 10 to 150 micro- Newton on board. These use nitrogen as the pressurizing gas. In addition, Gaia has 8 engines with 10 per Newton thrust, in order to enter the Lissajousbahn to L2 can. The stronger engines use a chemical fuel.

Mass and power consumption

When you start Gaia had a mass of approximately 2030 kg, the payload contributes 690 kg. Gaia has a total power consumption of 1720 W, the payload of which about 830 W required.

Main instruments

Gaia carries three main scientific instruments that are commonly supplied by a reflecting telescope with two widely separated fields of view in the sky. The telescope has not circular, but a rectangular primary mirror the size of 145 cm × 50 cm. All the instruments look the same to 106.5 ° separate sky sections. The two visual fields are about 1.4 ° × 0.7 ° in size, thus covering the sky about four times the area of the sun or the full moon disk. They are collected from a field of 106 CCD detectors with a pixel count of 4500 × 1966 pixels. Together, the cameras of the satellite have thus approximately one billion pixels.

Astrometry

A field of 62 of the CCD detectors in a 7 × 9 grid will register the objects in the sky. The detector array will capture during the Gaia mission, the star positions in the sky with a precision of partially better than 30 micro arc seconds. The accuracy was improved compared to the previous mission Hipparcos by a factor of 20 to 50. The multiple measurements of stars during the life of the satellite velocity from star movements are derived therefrom.

Photometry

14 CCD detectors in two rows will measure brightness and colors in a wide wavelength range.

Spectroscopy

The radial velocity spectrometer uses the same field of view as the combined astrometric and photometric instrument. It works with twelve CCD detectors record the line spectra of the stars, from which can be derived the motion of the stars along the line of sight. Together with the photometer will be possible a precise classification of many of the observed objects.

Operation

The ground control and all scientific operations are performed by the European Space Operations Centre (ESOC ) in Darmstadt using the Spanish ground station in Cebreros.