ESA's Gaia mission is generating an enormous amount of data as it works to plot the position of a billion stars in three dimensions. But during pre-flight testing one of Gaia's memory modules – part of the spacecraft's onboard 'hard disk' – failed. ESA's Materials and Electrical Components Laboratory was called in to assess the failure, to see if it was a one-off or else caused by a general manufacturing issue. The team made use of their 3D X-ray Tomography Machine to perform non-destructive internal scanning of the module and pin down the source of the fault.
Date: 24 June 2016
Time-lapse film Soyuz flight VS06, with Gaia
Soyuz VS06, with Gaia space observatory, lifted off from Europe's Spaceport, French Guiana, on 19 December 2013.
This time-lapse movie shows Gaia sunshield deployment test, the transfer of the Soyuz from the assembly building to the launch pad and the lift off
Watch the full replay of the launch coverage of ESA's billion-star surveyor Gaia. Liftoff occurred at 09:12UT/10:12CET on 19 December and the successful deployment of Gaia's sunshield was confirmed approximately 90 minutes later.
This highlight video provides background scenes from Kourou, showing final integration of the launcher, installation of the aerodynamic fairing, mating of the upper composite to the launcher and roll out to the launch pad. It also includes statements by Giuseppe Sarri, ESA's Gaia Project Manager, and Timo Prusti, ESA's Gaia Project Scientist.
ESA's Gaia mission will produce an unprecedented 3D map of our Galaxy by mapping, with exquisite precision, the position and motion of a billion stars. The key to this is the billion-pixel camera at the heart of its dual telescope. This animation illustrates how the camera works.
Our Galaxy the Milky Way is made up of a hundred billion stars. To truly understand its evolution we need to know exactly where we stand in this mass of constantly moving and changing celestial objects. To do this, Astrometry, the science of measuring the position, distance and movement of stars around us, is just about to take a giant leap forward with the launch of ESA's new space telescope, Gaia. Gaia will make it possible to measure a billion stars of our Milky way.
Time-lapse sequences from the deployment test of the Gaia Deployable Sunshield Assembly (DSA) on 10 October 2013 in the cleanroom at Europe's spaceport in French Guiana.
Since the DSA will operate in microgravity, it is not designed to support its own weight in the one-g environment at Earth's surface. Therefore, during deployment testing on the ground, the DSA panels are attached to a system of support cables and counterweights that bears their weight, preventing damage and providing a realistic test environment.
Once in space, the sunshield has two purposes: to shade Gaia's sensitive telescopes and cameras, and to provide power to operate the spacecraft. Gaia will always point away from the Sun, so the underside of the skirt is partially covered with solar panels to generate electricity.
This is a video of a test of the separation mechanism that will free Gaia from its launcher's upper stage being conducted at Astrium Toulouse. The Gaia Service Module (SVM) is suspended from an overhead crane with the Launch Vehicle Adapter (LVA) attached using a clamp band. Compressed gas is fed to the clamp band locking mechanism via a quick-opening valve. Gravity is used to effect the separation, with the springs that will be used during launch in place but locked so that they just touched the spacecraft's interface ring. As the LVA falls away from the SVM, it lands on a cushioned protector.
At the start of the close-up video, the threaded fasteners holding the clamp band closed can be seen near the top centre of the screen. Between them are the flywheel and its locking mechanism, with the hose that supplies the compressed gas.
After separation, the clamp band is retained on the LVA by a set of brackets. The now disengaged fasteners can be seen in the clamp band end plates.
This movie shows the number of field transits (for both fields of view).
The coordinates are in ICRS, longitude increasing to the left.
The ecliptic plane in this system is given by the blue warped line.
The sun is represented by a yellow dot.
The spin axis of Gaia is represented with a black dot
The movie has three intervals, interesting features to note are:
1) From 0 to 2 days:
The two fields of view scan great circles.
Due to slow precession of the spin axis, different great circles are scanned.
The 'holes' between the great circles are real, since the across scan rate is too high there to overlap everywhere with the previous great circle. You will see that these holes are observed at later times.
2) From 2 to 183 days:
The 63 day precession period of the spin axis can clearly be seen, and the spin axis is obviously in the middle of the great circles that are being scanned.
The spin axis is always at an angle of 45 degrees with the sun.
It shows that after half a year we have covered the whole sky at least once.
3) From 183 days to 5 years:
It shows how the particular NSL scan pattern is being built up.
It shows that the overabundant regions at +/- 45 deg latitude in ecliptic co-ordinates are caused by the 45 deg angle between the spin axis and the sun (remember that the ecliptic plane is indicated by the blue line).
The movie was made by scanning the central positions of each pixel of a healpix map of depth 8 (3.1 million pixels) with the scanner in AGISLab and taking the number of SM-observations (of which there is just 1 per field transit). Then the map was projected into a Hammer-Aitoff plot using the graphics library in GaiaTools.
The picture, in particular, shows the number of field transits in ICRS after 5 years.
In this vodcast Rebecca Barnes discovers the motions of the stars, learns how astronomers measure their distances and looks at the new European mission that will really get to grips with our place in the Universe: Gaia.
Gaia Payload Module: X-axis vibration at qualification level
In late June 2011, mechanical testing of the Gaia Payload Module was performed at the facilities of Intespace in Toulouse, France, under the direction of the Prime Contractor, Astrium. The results have been analysed and the testing was declared successfully completed.
This a picture of the Structural Model of the Gaia Payload Module undergoing X-axis swept-sine vibration testing at qualification level. The frequency is sweeping from high to low; at the higher frequencies, the movement of the test item is very small.
Gaia Payload Module: Z-axis vibration at qualification level
In late June 2011, mechanical testing of the Gaia Payload Module was performed at the facilities of Intespace in Toulouse, France, under the direction of the Prime Contractor, Astrium. The results have been analysed and the testing declared successfully completed.
This a picture of the Structural Model of the Gaia Payload Module undergoing Z-axis vibration testing at qualification level.
Conjugate-gradients method for the global astrometric solution
AGIS, the software system to produce the global astrometric solution for Gaia, uses a block-iterative scheme to perform the global astrometric parameter adjustment. In the framework of ELSA (the Marie Curie Research and Training Network associated with Gaia) it was investigated whether the usage of the conjugate-gradients method instead of a block iteration might give more pleasant convergence properties.
For this purpose, the conjugate-gradients method was implemented in AGISLab, a simplified simulation environment to mimick the Gaia global adjustment problem. From the experiments done so far Alex Bombrun concludes that the conjugate gradients are an efficient algorithm to compute the global astrometric solution. The convergence rate is higher than that of the (un-accelerated) block iterations.
The pictures and the video display show - for one particular experiment - the successive error maps during the iterations. The quantity shown are the differences between the computed right ascensions (of the simulated stars) and their true values, averaged over small bins on the sky. The map itself is a full-sky projection in equatorial coordinates.
The sky used in this simulation is composed of 60000 single stars, isotropically distributed, which have been observed according to the Gaia scanning law. The simulated measurements were of homogeneous precision except in a a small sky area, dubbed the P region, having the size of one field of view and containing 252 stars.
In that region the precision was simulated to be five times higher, and a large systematic error was added to the initial position and parallax values used to start the iterative process. On the rest of the sky, onlya white normal noise has been added to the true values (the P region was introduced to investigate whether special adjustment methods are needed for big, bright open star clusters in the sky).
The conjugate gradient scheme is seen to quickly converge to the correct solution, and in just a few iterations it removes the systematic errors. As expected, the solution has a higher precision in the P region than in the rest of the sky. Note that we can also observe the effect of the scanning law on the solution: The precision is better near the ecliptic poles (top right and bottom left) than along the ecliptic plane (wavy band through the center).
Three animations illustrating the scanning law envisioned for Gaia have been created. Each animation shows the celestial sphere as viewed from the "outside". Gaia is at the centre of the box, which just encloses the celestial sphere. (The image above shows extracts from the animations - the original animations (in mpg format) can be viewed by following the links below.)
The first animation shows, in red, the path of the Sun in one year. The blue line is the vector from Gaia towards the Sun.
The second animation shows the motion of the Sun as before, but also (in purple) the path of the spin axis of Gaia. The spin axis is always 50 degrees away from the Sun and moves in a circle about the Sun. If the Sun had remained fixed on the sky, the spin axis would have traced a cone around the solar direction. But because of the Sun's motion, the resulting path of the spin axis is a series of loops on the sky. Each loop takes about 70 days.
The third animation shows, in addition to the Sun and the spin axis, the path of one of the Astro fields (in green). Only the first two months of the scanning is shown, and the spin of the satellite is shown with only one revolution per day (instead of four rev/day, as will be used for Gaia). Already after two months a large fraction of the sky is covered with scans that cross each other in different directions. After six months, the whole sky gets at least a three-fold coverage. Gaia is designed to scan the sky in this manner for at least five years, after which every point has been thoroughly criss-crossed, which allows to measure the positions, motions and parallaxes of the stars.
At microarcsecond accuracy levels, such as those measured by Gaia, relativistic effects begin to play a considerable role. In particular, general-relativistic gravitational light deflection due to Solar System bodies will have profound effects on Gaia measurements over the planned 5 year lifetime of the mission. This is vividly illustrated in an animation, created by Jos de Bruijne, from which the image above has been extracted.
This animation depicts an all-sky map of the sky as seen from L2 - Gaia will perform its observations from here. Ecliptic coordinates (increasing from left to right, with 0 degrees in the center) are used in a Hammer projection. The integrated amount of light bending due to all planets in the Solar System, plus Ceres and our Moon, is shown with a colour scale (see object names and time scale on image). Contributions from the Sun are excluded. Further details on the contributions from Solar System bodies, and on how the animation was created, can be found in the technical note (Gravitational light deflection; GAIA-JdB-001) prepared by de Bruijne (available on request from the author).
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