Gaia commissioning was successfully finished – and routine observations have started

Yes, finally we can spread the news: The In-Orbit Commissioning Review (IOCR) for Gaia was successfully concluded on July 18. The ESA Gaia project team handed over the responsibility for the satellite to the Gaia mission team under the leadership of Wil O’Mullane, the new Gaia Mission Manager.

Handover of the Gaia flag to the Gaia mission manager

Handover of the Gaia flag to the Gaia mission manager

Now, 11 days later this news has been published by ESA. That was not very fast – we agree on that. But notice that ESA is very busy with the Rosetta mission going into the most interesting phase now, the final ATV will be launched soon and many things more. And we have an astronaut on-board the ISS. And do not forget that we have the holiday season already. To organize this publication was really complicated. 😉

Gaia has  started the normal operations already last Friday and will now observe the sky for 28 days in the so-called Ecliptic Pole Scanning Law (EPSL). This scanning law allows to observe a high number of stars near the Ecliptic poles very often to allow an initial photometric calibration of the instrument.

For more details please see this release of ESA:

http://www.esa.int/Our_Activities/Space_Science/Gaia/Gaia_Go_for_science .

Even more details are available here:

http://www.cosmos.esa.int/web/gaia/news_20140729 .

 

Personal note:

In the operational phase the news about the Gaia mission will be rare. Thus, please do not expect many publications here until the release of the first catalogue with Gaia data expected for the summer of 2016.

In the meantime ESA will publish all news about the progress of the mission via their Twitter accounts:

https://twitter.com/ESAGaia & https://twitter.com/esascience .

News will also be posted on Facebook at: https://www.facebook.com/ESAGaiaMission .

The team I am part of will also update you on Twitter as @GaiaUB and on Facebook: http://www.facebook.com/GaiaUB .

And not to forget there are such old school things like this website from ESA http://www.cosmos.esa.int/web/gaia  and from our GaiaUB team: http://gaia.am.ub.edu/ .  😉

In this blog I will continue to post more about my non-Gaia activities . You see the topics listed at the left side of this page. Feel free to open one or the other topic and you will be surprised. 😉

 

 

 

 

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Gaia – before starting the normal scientific observations

GaiaScanning

Final preparations are underway to start the normal routine scientific observations of Gaia. Part of the final preparations to start the normal operations was a mild heating of some of the mirrors of Gaia to remove a very thin layer of ice particles on June 30. Now the mirrors have to cool down again until thermal equilibrium is reached. An update of the on-board software was successfully performed. The focus for both telescopes over the entire focal plane will be checked again. Some parameters for detection of sources on-board will be optimized, too. This includes parameters for activating shorter observations for the stars brighter than magnitude 13 to avoid that the corresponding images will saturate. We call this “observations with “activated gates”. How does this work?

There are different “gates” with different effective exposure times available ranging from 0.01 seconds to 4.3 seconds to cover a huge magnitude (brightness) range that can be observed. These “gates” will be activated depending on the magnitude of the stars determined on-board the satellite by the star mapper (SM) CCDs which will “see” the stars first. A few seconds after these observations with the SM CCDs the same detected source will be observed by 11 more CCDs in the same row of the SM CCD that has detected this source. If the star is detected as bright then the “gates” will be activated to avoid the saturation of the images. Saturation depends on many factors such as the colour of the star, the scan motion of the satellite, the point spread function (how the image of a stars looks like) and even how the image centre is located in intra-pixel space.

Parameters for the activation of the short gate 4 computed in a test for all AF CCDs.

Parameters for the activation of the short gate 4 computed in a test for all AF CCDs.

We have updated our knowledge about these characteristics of the observations based on data collected during the commissioning phase and in this moment new parameters for the activation of the gates are computed. Almost 1 billion of 2D images are simulated for this purpose at this moment to be able to find the perfect parameters. Parameters are computed for all 55 AF (astrometric white light) CCDs, all BP (blue photometer) CCDs and all RP (red photometer) CCDs. More than 7000 parameters are determined and need to be uploaded to the satellite before Gaia will start the normal scientific observatons. By the way, the corresponding LUT (Look Up Table) is  the biggest parameter table used on-board Gaia.

More details about this topic can be found in an earlier entry in the ESA Gaia blog following this link.

And now, after this very work intensive commissioning phase we are really looking forward to start the normal operational phase of our very interesting Gaia satellite mission to create the world biggest, multi-dimensional map of about one billion stars and other light sources in our galaxy and beyond.

 

Summary of Gaia news during recent days

Sorry for not posting more about the Gaia mission during recent weeks. I just did not find the time for it as there was and is still is a lot  of work to be done during the process of commissioning and performance verification for all persons involved. To give a more or less complete overview about things related to the Gaia mission here on this site I would like to summarize the latest news here and now. Here we go:

1.) A sky map/movie was released showing all the regions in the sky already scanned by Gaia during the recent five months. This movie was produced by the @GaiaUB team (with a small involvement from me ;)) and published jointly by ESA, DPAC and Airbus DS – as all publications made during the joint commissioning phase. If you have not seen it yet here it is:

2.) First spectroscopic observations of Gaia were published. The @GaiaUB team contributed also to this publication. You can find it here at the ESA Gaia blog:

http://blogs.esa.int/gaia/2014/06/05/gaia-takes-science-measurements/.

3.) And finally, there is a new blog entry in the ESA Gaia blog giving an official, very up-to-date status update, discussing issue like stray light, contamination and variations of the basic angle (the angle between both telescopes of Gaia) and their influences on the scientific measurements. Please read the blog entry here:

http://blogs.esa.int/gaia/2014/06/16/preliminary-analysis-of-stray-light-impact-and-strategies/ .

Thanks.

Gaia news flash #17: How stars are detected and some additional information about the commissioning status

SMdetectionsAnot

ESA has published today some very interesting information how stars are actually detected by Gaia. This is done with the help of 14 Sky Mapper (SM) CCDs. A real SM CCD image (please see above) was published showing the image with and without detection markers. Feel free to find some undetected stars, but please do not mix them with hits by cosmic rays.  😉

Much more details about this topic can be found in the ESA blog entry:  http://blogs.esa.int/gaia/2014/04/03/detecting-sources/.

There is also some additional information given about the current commissioning activities. We are still working on the issue of unexpected stray light levels. Several manoeuvres of Gaia with different orientations towards the Sun were performed to identify the source(s) of the stray light observed. Significantly progress was made in understanding the situation. The analysis of the data collected by Gaia and from the ground is still ongoing by the teams of ESA, Airbus DS and our DPAC.

Another issue mentioned is that there are indications of some contamination of the payload, presumably by water ice. The water may have entered the payload module during the final launch preparations in Kourou as it was raining at the spaceport at this time – despite the fact that Gaia was under air-condition almost all the time. Several parts of the payload were heated to get rid of the remaining water. Now the payload has to cool down again to operational temperatures. Nevertheless, data is already taken to start to analyse if still some water ice is present within the thermal tent enclosing the payload. The entire process will take a few more weeks to be finished.

Complex space missions are not easy – otherwise someone else would have done a mission like this already. We are doing our best and are working hard to bring Gaia in the best condition possible for the normal operations. We are on a good way I think. 😉

 

Gaia news flash #16

1.) New images taken by the Gaia SM (Sky Mapper) CCDs were just published by ESA. There are images of the cluster NGC 2516, the spiral galaxy Messier 94 and Cat’s Eye Nebula available. Enjoy the new images here:

http://www.cosmos.esa.int/web/gaia/iow_20140214 .

Image

The spiral galaxy M94 as seen by two SM CCDs. You can clearly recognize the gap between the two CCD chips. Most likely this is the last time that images of these kind of extended objects are downloaded, as Gaia will observe only point sources during nominal observations.

2.) There are some more news about the status of Gaia available now in an article by my colleague Stefan Jordan in the German journal ‘Sterne und Weltraum’. The commissioning is ongoing quite well and will continue until May at least.

Two issues are mentioned for the first time (I think) in this article:

http://www.sterne-und-weltraum.de/news/den-himmelsvermesser-gaia-plagen-kleine-pannen/1224160 .

  • There was a problem with one thruster of the MPS, the Micro Propulsion System. It was delivering much more thrust than desired. But the issue was solved very quickly by a recalibration of the nitrogen supply mechanism.
  • A contamination issue was detected for one of the mirrors reducing the throughput of the affected telescope by more than the half. The contaminant has still to be determined, but the contamination was already successfully cleaned by heating this particular mirror. Investigations are ongoing to identify the contaminant to make sure that a similar scenario cannot happen again. It is not ruled out that there is a correlation to the stray light issue (more information about this here https://hvossgaia.wordpress.com/2014/02/12/gaia-status-update-after-one-month-of-commissioning/). Parts of the thermal tent are most likely heated by the stray light and an increased outgassing of the paint used for the thermal tent could be an explanation for the contamination seen. But other scenarios are still under investigation. Most likely we will learn more about the issue after next Monday, when the sun aspect angle of Gaia is changed by three degrees to reduce the stray light effect. Let us keep the fingers crossed that this manoeuvre will yield the desired results. 😉

All these are small issues normal for the initial phase of a space mission. In Germany we call it ‘Kinderkrankheiten’ – these kind of not so serious illnesses that small children are suffering from. Solutions were found and in most cases already applied. Overall, the mission progress is quite impressive.

Gaia status update after one month of commissioning

The Gaia payload in all its complexity. Reflection of light can be seen in many places in this well-illuminated scenario.

The Gaia payload in all its complexity. Reflection of light can be seen in many places in this well-illuminated scenario.

Earlier today ESA has published an update about the Gaia commissioning after one month of operations in the orbit around the Lagrange point L2. Please read the blog post here:  http://blogs.esa.int/gaia/2014/02/12/one-month-at-l2/.

Several important systems and subsystems of the satellite were already tested – among them the Micro Propulsion System (MPS), the Phased Array Antenna (PAA) for the downlink of the data and all of the 106 CCDs in the focal plane. All these systems are working now as expected.

One unexpected feature seen in the test observations are temporary high background signals due to stray light. This stray light is entering the telescope openings in the thermal tent around the payload and reaches unfortunately the focal plane with the CCDs. This is obviously an unwanted issue as it influences the error budget of some measurements.

Gaia model at ESOC. Currently it is assumed that diffraction of light from the Sun (which is below the sunshield in 45 deg inclination from the spin axis of the satellite) is diffracted on the edge of  the sunshield - sometimes towards the telescope openings.

Gaia model at ESOC. Currently it is assumed that light from the Sun (which is below the sunshield in 45 deg inclination from the spin axis of the satellite) is diffracted on the edge of the sunshield – sometimes towards the two telescope openings on the top of the satellite.

How is it possible that stray light can enter the telescope openings? Several theories were discussed, the leading theory is that light from the Sun is the origin of the stray light as this light shows a periodic behaviour in agreement with the 6 hour spin period of the satellite. Gaia has a sunshield supposed to protect the payload from the Sun light all the time. Is something wrong with the sunshield? The favoured explanation of the experts is that light from the Sun is diffracted at the edges of the sunshield – sometimes unfortunately towards the telescope openings. There it enters the payload module, is reflected on the wall of the thermal tent and reaches somehow the focal plane. 10 mirrors, some more optical elements and other reflective components are installed inside the thermal tent. The very complex analysis of the situation is still ongoing.

Gaia in launch configuration. The sunshield is folded and is forming the outer limitation of Gaia towards the inner payload fairing.

Gaia in launch configuration. The sunshield is folded and is forming the outer limitation of Gaia towards the inner payload fairing.

Nevertheless, there is already a solution for this issue under preparation. The orientation of Gaia towards the Sun will be changed a little bit. The inclination of the spin axis in relation to the Sun will be moved from 45 deg to 42 deg to reduce the chances of diffraction of Sun light on the edges of the sunshield. This manoeuvre is planned for early next week after some intensive planning. The experts of ESA, Astrium and our DPAC payload experts group are waiting eagerly to analyse the data collected after this manoeuvre is executed – hopefully with the expected positive result of lower background levels in the images.

The commissioning (testing) of Gaia will be ongoing for a few more months. Many things still have to be optimized and calibrated to allow the high-precision measurements of the nominal observations during the next 5 years or more.

Note: If you have comments or questions please let me know. I may be able to give some replies in the comment section! 😉

Short update about the Gaia commissioning

Image of cluster NGC 1818 taken by the Gaia satellite. (Source: ESA)

Image of cluster NGC1818 taken by the Gaia satellite. (Source: ESA)

ESA has published an update about the status of the commissioning phase for the Gaia satellite. The iterative process of the optimization of the spin rate, the alignment of the telescope mirrors and the focusing is ongoing. The calibration of the different instruments will also continue for a few more months. As part of the early calibration an (for Gaia) unusual operation mode was conducted by taking full images with the SM (Sky Mapper) CCDs. One of these images was published with the ESA article. It shows the star cluster NGC1818 in the Large Magellanic Cloud. Enjoy the article and the image at

http://www.esa.int/Our_Activities/Space_Science/Gaia/Gaia_comes_into_focus.

A personal note: Sorry for not posting more often. This has two reasons: 1.) We are very busy with the commissioning work and its challenges, and 2.) We have to follow some rules for publishing info set by the Gaia Data Processing and Analysis Consortium (DPAC) and ESA.

Expect more news next week.

A recommendation: Follow @ESAGaia and @ESAScience on Twitter – there are almost daily updates available.