# Gaia

> European Space Agency astrometric mission

**Wikidata**: [Q767805](https://www.wikidata.org/wiki/Q767805)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Gaia_(spacecraft))  
**Source**: https://4ort.xyz/entity/gaia

## Summary
Gaia is a European Space Agency (ESA) space telescope and astrometric mission designed to chart a three-dimensional map of the Milky Way. Launched on December 19, 2013, it operates from the Sun-Earth Lagrange point L2, serving as the successor to the Hipparcos mission to measure stellar positions, distances, and motions with high precision.

## Key Facts
- **Classification:** Space telescope and artificial satellite of the Earth.
- **Operator:** European Space Agency (ESA).
- **Launch Date:** December 19, 2013.
- **Launch Vehicle:** Soyuz-2.1b.
- **Launch Site:** Ensemble de Lancement Soyouz.
- **Launch Contractor:** Arianespace.
- **Mass:** 2,029 kilograms.
- **Orbit:** Lissajous orbit around the Sun-Earth Lagrange point L2.
- **Orbital Period:** Approximately 180 days.
- **Predecessor:** Hipparcos (ESA space telescope devoted to measuring stellar positions, operated 1989–1993).
- **Power Consumption:** 1,910 Watts.
- **COSPAR ID:** 2013-074A.

## FAQs
### Q: What is the primary purpose of the Gaia mission?
A: Gaia is an astrometric mission designed to measure the positions, distances, and motions of stars with high precision. It aims to create the most precise 3D map of the Milky Way to date.

### Q: Where is the Gaia spacecraft located?
A: Gaia operates in a Lissajous orbit around the Sun-Earth Lagrange point L2, a gravitationally stable point approximately 1.5 million kilometers from Earth.

### Q: What does the name "Gaia" stand for?
A: The name was originally an acronym for "Global Astrometric Interferometer for Astrophysics." Although the mission no longer uses interferometry, the name "Gaia" was retained for continuity.

### Q: What instruments does Gaia carry?
A: The spacecraft carries three main scientific instruments: the Astrometric instrument (Astro), the Photometric system (BP/RP), and the Radial-Velocity Spectrometer (RVS).

## Why It Matters
Gaia represents a critical advancement in the field of astrometry, serving as the European Space Agency's successor to the Hipparcos mission. By positioning a high-precision observatory at the Lagrange point L2, Gaia avoids the atmospheric distortions that limit ground-based telescopes, allowing for measurements of stellar positions and velocities that are orders of magnitude more accurate than its predecessors.

The mission's data is fundamental to understanding the formation, composition, and evolution of the Milky Way galaxy. Through its "billion-star surveyor" capabilities, Gaia provides astronomers with the data necessary to test theories about the gravitational potential of the galaxy and the distribution of dark matter. Its three instruments work in unison to provide a comprehensive physical and chemical profile of the stars it observes, making it one of the most prolific space observatories in operation.

## Notable For
- **Successor to Hipparcos:** Building on the legacy of ESA's first space astrometry mission to provide twenty-first-century measurements.
- **Orbital Position:** Operating at the L2 Earth-Sun Lagrangian point, which offers a stable thermal environment and uninterrupted celestial viewing.
- **Billion-Star Survey:** Described at launch as ESA's "billion-star surveyor," tasked with mapping the Galaxy in three dimensions.
- **Naming Origin:** Retaining the acronym "Gaia" (Global Astrometric Interferometer for Astrophysics) even after the optical technique changed from interferometry.
- **Comprehensive Instrumentation:** Integrating astrometry, photometry, and spectroscopy into a single platform to measure positions, brightness, and radial velocities simultaneously.

## Body

### Mission Overview
Gaia is an artificial satellite and space telescope operated by the European Space Agency. It was launched on December 19, 2013, using a Soyuz-2.1b rocket from the Ensemble de Lancement Soyouz. The launch was managed by contractor Arianespace, with a Fregat-MT upper stage delivering the satellite into its transfer orbit. The mission follows the Hipparcos space astrometry mission, which operated from 1989 to 1993.

### Orbital Characteristics
Gaia operates in a Lissajous orbit around the L2 Earth-Sun Lagrangian point. This orbit allows the spacecraft to maintain a stable position relative to the Earth and Sun, which is essential for precise thermal control and long-duration observations. The orbit has a period of approximately 180 days and a periapsis (closest approach in the orbital path relative to the central body) of 370,000 kilometers.

### Spacecraft Specifications
The spacecraft has a total mass of 2,029 kilograms and consumes 1,910 Watts of power. It was manufactured by Astrium (now Airbus Defence and Space) and Teledyne e2v.
*   **Communications:** Gaia transmits signals in the S band and receives signals in the X band.
*   **Identifiers:** The satellite is tracked under COSPAR ID 2013-074A and NSSDCA ID 2013-074A. Its Satellite Catalog Number (SCN) is 39479.

### Scientific Instrumentation
Gaia carries three primary scientific instruments to achieve its mission objectives:
1.  **Astrometric Instrument (Astro):** The main instrument responsible for obtaining accurate measurements of the relative positions of all objects that cross the fields of view of Gaia's two telescopes.
2.  **Photometric Instrument (BP/RP):** This system uses low dispersion optics to measure the brightness of objects. It consists of a Blue Photometer (BP) for short wavelengths and a Red Photometer (RP) for long wavelengths.
3.  **Radial-Velocity Spectrometer (RVS):** An instrument designed to acquire radial velocities by observing the Doppler shift of spectral lines.

### Naming and Nomenclature
The name "Gaia" was originally derived from the acronym **Global Astrometric Interferometer for Astrophysics**. This name reflected early designs that utilized interferometry. While the working method changed prior to launch, the name "Gaia" was retained to provide project continuity. The mission is also known by various aliases internationally, including *Gaia mission*, *GAIA*, and *Gaia-Weltraumteleskop*.

## References

1. [Gaia](https://www.esa.int/Science_Exploration/Space_Science/Gaia/)
2. [Gaia overview](https://www.esa.int/Our_Activities/Space_Science/Gaia_overview/)
3. [A history of astrometry - Part IIIAstrometry moves to space: the mapmakers guide to the Galaxy - Gaia - Science Portal](https://sci.esa.int/gaia/53198-astrometry-in-space/)
4. [ftl/data/wikimap at master · JohnMarkOckerbloom/ftl](https://github.com/JohnMarkOckerbloom/ftl/blob/master/data/wikimap/)
5. Jonathan's Space Report
6. Freebase Data Dumps. 2013
7. [Liftoff for ESA’s billion-star surveyor](https://www.esa.int/Our_Activities/Space_Science/Gaia/Liftoff_for_ESA_s_billion-star_surveyor/)
8. [Source](http://sci.esa.int/gaia/40129-payload-module/?fbodylongid=1917)
9. [Source](http://sci.esa.int/gaia/40129-payload-module/?fbodylongid=1915)
10. [Source](http://sci.esa.int/gaia/40129-payload-module/?fbodylongid=1916)
11. [Fact Sheet - Gaia - Science Portal](https://sci.esa.int/gaia/47354-fact-sheet/)
12. [Gaia enters its operational orbit](https://www.esa.int/Our_Activities/Space_Science/Gaia/Gaia_enters_its_operational_orbit/)