From European Space Agency: “Gaia’s biggest operation since launch and commissioning”

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From European Space Agency

15 July 2019

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Gaia mapping the stars of the Milky Way

On Tuesday 16 July, teams at ESA’s mission control will perform an ‘orbit change manoeuvre’ on the Gaia space observatory – the biggest operation since the spacecraft was launched in 2013.

Gaia is on a mission to survey more than a billion stars, charting the largest three-dimensional map of our galaxy, the Milky Way. In so doing, the spacecraft is revealing the composition, formation and evolution of our galaxy, and a whole lot more.

For the last five and a half years, the spacecraft has travelled in an orbit designed to keep it out of Earth’s shadow, the second Lagrange point.

At 1.5 million km from Earth – four times further than the Moon – the ‘L2’ is a fabulous place from which to do science. As the Sun, Earth and Moon are all in one direction relative to the spacecraft, the rest of the sky is free to observe.

LaGrange Points map. NASA

Placing Gaia in L2 has also ensured the star-catcher’s stability, because to this day it has never passed into Earth’s shadow. This has kept the spacecraft undisturbed by any change in temperature or varying infra-red radiation that would result from an Earth eclipse.

Although at the end of its planned lifetime, Gaia still has fuel in the tank and a lot more science to do, and so its mission continues. However, its eclipse-dodging path will not. In August and November of this year, without measures to change its orbit, the billion-star hunter will become partially shrouded by Earth’s shadow.

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Avoiding Earth’s shadow

These two eclipses would prevent enough of the Sun’s light reaching Gaia’s solar panels that the observatory would shut down. As well as affecting its stability and power, such shade would cause a thermal disturbance, impacting the spacecraft’s scientific data acquisition for weeks.

Eclipse Avoidance

To keep Gaia safe from these shady possibilities, operators at ESA’s mission control are planning the ‘Whitehead eclipse avoidance manoeuvre’.

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On 16 July, Gaia will use a combination of its onboard thrusters to push it in a diagonal direction, away from the shadow, in a special technique known as ‘thrust vectoring’.

“We’ve named this operation after a great colleague of ours, Gary Whitehead, who sadly passed away last month after serving on the Flight Control Team for more than 11 years,” says David Milligan, Spacecraft Operations Manager for the mission.

“The manoeuvre will allow us to change Gaia’s orbit without having to turn the spacecraft body, keeping sunlight safely away from its extremely sensitive telescope.”

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Four years of Gaia
20/12/2017

Four years ago, on 19 December 2013, Gaia was launched from Europe’s Spaceport in Kourou, French Guiana. The mission’s operations teams led by Spacecraft Operations Manager David Milligan (pictured), followed the event from the control room in Darmstadt, Germany.

Gaia is charting a 3D map of the Milky Way, accurately measuring and cataloguing the positions, distances and motions of more than a billion stars.

This ambitious mission aims to reveal the composition, formation and evolution of the Galaxy. Gaia instruments are collecting over 10 000 times the data of its Hipparcos predecessor, launched in the late 1980s.

Measuring stellar positions and motions to the required accuracy is not easy, requiring extreme precision in the stability of the spacecraft, detailed knowledge of its position and unprecedented accuracy in timing.

This marvel of technology has executed over 1.6 million commands, completed 29 manoeuvres, performed some 1108 billion total measurements, made more than 3100 ground-station contacts and accumulated 47.5 TB of science data.

Once the data are acquired and downlinked, the work is just starting, as they have to be processed by a large consortium of scientists and engineers across Europe. Astronomers will delve into the data to investigate the present and past history of our Galaxy – a process that will continue for years after the spacecraft has competed its task.

ESA’s Hipparcos yielded a primary catalogue with positions, distances and motions of about 118 000 stars, and a secondary catalogue with less precise measurements for over two million stars.

ESA/Hipparcos satellite

Gaia’s instruments not only collect more data but also provide extremely more accurate information. The data produced during the first five years of Gaia could fill 70 000 CDs.

In September 2016, Gaia published its first data release, a ‘taster’ catalogue containing more than a billion positions of stars on the sky and, for a subset of two million, also the parallax and proper motion. Next April, a new catalogue will be published containing positions, parallaxes and proper motions for more than a billion stars. This ground-breaking release will also include the brightness and colours of almost all stars, and other astrophysical parameters, such as radial velocity or temperature, for a subset of them.
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The world’s most stable space observatory

Gaia is an incredibly stable spacecraft. In fact, it is many, many times more stable – and therefore precise – than any other spacecraft in operation today.

“In space, stability takes time to establish,” explains David.

“Because any temperature change or unusual movement could take weeks to diminish or dampen, we always limit the time where special activities are performed that disturb scientific observations.”

“As well as the Whitehead manoeuvre, we will perform some maintenance and calibration activities on the spacecraft’s complex subsystems, which would otherwise have disturbed Gaia’s science.”

Because of its position and unparalleled precision, Gaia is one of the most productive spacecraft out there. Last year alone, more than 800 scientific papers were published based on its observations.

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Gaia’s sky in colour

Follow Live

Follow the manoeuvre in real time via @esaoperations on Twitter, from 08.30UTC (10.30CEST) on 16 July. We’ll be coming direct from ESA’s Main Control Room, sharing the moment that Gaia starts its new life in orbit.

See the full article here .


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The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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