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 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.

First image of a single star taken by Gaia published

Image

This is Sadalmelik. a bright star (V magnitude 3) in the constellation Aquarius. It is also known as Alpha Aquarii. The image was taken by Gaia recently. The star was observed when the satellite was spinning – the normal mode of observations. And I can tell you, that more stars are out there, many more. 😉 Unfortunately, I am not allowed to show.

Update: Earlier today I was thinking that maybe Astrium could provide some more info about this image as they are leading the commissioning of Gaia at the moment. Seems to be somebody is reading my thoughts! Here it is: http://www.astrium.eads.net/en/news2/gaia-on-its-way-to-the-stars.html. Merci!

Gaia news flash #15

Thruster as used for the CPS of Gaia. (Source: Astrium)

Thruster as used for the CPS of Gaia. The diametre of the nozzle is 3.7 cm (Source: Astrium).

1.) Gaia has successfully finished the second insertion manoeuvre into the L2 orbit. This final insertion burn was executed this afternoon and could be followed based on tweets of @esaoperations, @ESAGaia and @danielscuka. The latter is a very active ESA employee working at the control centre ESOC in Darmstadt ;). For the manoeuvre the spinning of Gaia was stopped. Then the satellite was oriented for the manoeuvre in a way that during the manoeuvre the instrument will never see the sun. Observing the sun with an instrument build to observe stars of magnitude 20 or even fainter would yield heavy damage to the instruments and had to avoided at any time.

For the burn today 5 of the total 8 10N thrusters of the Chemical Propulsion System of Gaia were used. The burn took about 30 minutes and 25 kg of propellant were used. With this burn Gaia has reached its operational orbit around the L2 point. One orbit will take about 180 days. About every 45 days a small manoeuvre will be necessary to avoid that Gaia will drift away into interstellar space. Note, that orbits around L2 are not completely stable, from time to time small adjustment manoeuvres are necessary to keep the desired orbit.

Update 15/01/2014: ESA has published an article with more interesting facts about this manoeuvre at this location: http://www.esa.int/Our_Activities/Operations/The_experts_behind_Gaia_s_arrival_at_nothingness.

2.) ESA has published a very neat time-lapse video showing launch preparations for the Gaia mission in Kourou starting with the impressive test of the sunshield deployment and ending with several views from the launch. Very impressive. Enjoy the video here: http://www.esa.int/spaceinvideos/Videos/2014/01/Time-lapse_film_Soyuz_flight_VS06_with_Gaia.

3.) A colleague of me working at ESAC near Madrid, Emmanuel Joliet, has a nice blog, and now he is also writing about Gaia. There is a very interesting article posted about his involvement in the mission during recent years and his impressions from the launch. A very nice read – and here it is:  http://ejoliet.wordpress.com/2014/01/14/gaia-a-chronicle-of-a-launch-foretold/.

Gaia news flash #14

The orbit of Gaia around the L2 point of the Sun-Earth system. Note that with this orbit it is avoided that Gaia will pass the shadow of the Earth.

The orbit of Gaia around the L2 point of the Sun-Earth system. Note that with this orbit it is avoided that Gaia will pass the shadow of the Earth (Source: ESA).

1.) Very good news! Based on information on Twitter by @esaoperations Gaia has just finished to brake successfully into an orbit around the second Lagrange point of the Sun-Earth system, shortly called L2. This orbit will be the place where the real observations by the instruments of Gaia will take place during the 5-year nominal mission and hopefully 1-2 years of extended mission. You can learn all about this critical manoeuvre in the latest post of the ESA Gaia blog: http://blogs.esa.int/gaia/2014/01/07/the-flight-dynamics-expertise-behind-gaias-critical-manoeuvre/. This manoeuvre is/was much more complicated than you may think!

2.) Over the weekend the focal plane of Gaia including all the 106 CCDs was activated for the first time in space. Some first images were taken for test purposes only in some unusual modes. Please have a look here at this ESA website: http://www.cosmos.esa.int/web/gaia/news_20140106.

This article was written by William O’Mullane, the Gaia Science Operations Manager. This leads to the following news.

3.) William O. Mullane has uploaded nice photos, among other things from the Gaia launch campaign in Kourou, at his Flickr site http://www.flickr.com/photos/womullan/page1/. Many known faces there! Feel free to take a look behind the curtain! Some images from the commissioning phase work for the Gaia mission can be seen there, too. Thank you, Will!

Update 08/01/2014: Here you can find the statements from ESA:

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

http://blogs.esa.int/gaia/2014/01/08/and-we-got-there/?utm_source=rss&utm_medium=rss&utm_campaign=and-we-got-there

 

Gaia: After the launch, on the way to L2

As you know the Gaia satellite was launched already on December 19, and now is still on the way to its final destination: an orbit around the Lagrange point L2.

The Lagrange points of the     Sun-Earth system with a satellite orbiting the L2 point as Gaia will do.

The Lagrange points of the Sun-Earth system with a satellite orbiting the L2 point as Gaia will do.

So what has happened after the launch? After the separation from the Fregat upperstage an automated sequence started to activate the primary systems of the satellite:

  • Switch on of the transponders to enable communication with the ground stations.
  • Switching on the gyroscopes for the stabilization of the satellite.
  • Releasing the bipod ramps that were supporting the glass-fibre reinforced polymer bipods during the dynamic launch event. The latter will allow a thermal insulation of the payload module from the service module, but were not strong enough to withstand the loads during the launch.
  • Pressurizing the Chemical Propulsion System (CPS).
  • Activating the thermal control system of the spacecraft to avoid damage to the electronic components.
  • Orienting the spacecraft in relation to the Sun to allow the solar panels to be directed towards the Sun.
  • Start of the deployment sequence of  the sunshield of Gaia by activating the explosive charges in the 12 bolts that were connecting the sunshield elements to the thermal tent (main satellite bus). The successful deployment was confirmed by 14 micro switches.

Everything went smoothly as we could follow at the control center of the Gaia satellite at ESOC, Darmstadt (more information about the launch event at ESOC you can find at https://hvossgaia.wordpress.com/2013/12/21/the-launch-of-gaia-as-followed-from-esoc/).

The control room of Gaia at ESOC, Darmstadt, Germany.

The control room of Gaia at ESOC, Darmstadt, Germany.

The commissioning phase for Gaia had begun. Teams from Astrium, ESA and DPAC will prepare the satellite for its nominal mission. This commissioning phase will take more than four months. The following steps were already successfully taken:

  • Decontamination of the payload by activating heaters on the optical elements four hours after launch for about 7 days. This should release all gas molecules sticking on the mirrors.
  • Activation of the star trackers to allow a more precise pointing of the spacecraft.
  • “Day 2” manoeuvre with the CPS to give Gaia a final push towards the targeted L2 orbit.
  • Inclining the vertical axis of the satellite 45 degrees away from the Sun. This is the orientation of the satellite that will be used during its observations. This manoeuvre happened on December 20.
  • Switch on of the atomic clock and the main memory (PDHU) of the spacecraft (Dec 21).
  • Test of the engines of the propulsion system (Dec 21).
  • Gaia passes the orbit of the Moon in 388400 km distance from the Earth (Dec 21).

moon-distance

  • Testing the Phased Array Antenna (PAA) of Gaia. Note, that this is an antenna that can direct its transmission without using any moving parts. Any movement would disturb the observations of Gaia (Dec 22).
PAA

The Phased Array Antenna (PAA) can be seen in the center of the service module of Gaia.

  • Test of the Micro Propulsion System (Dec. 22).
  • End of the contamination heating. Now the satellite starts to cool down to its operational temperature (Dec. 26).
  • On December 30 Gaia has reached a distance of 730000 km from Earth – about half of its way to the L2 orbit. A calibration burn of the thrusters of the CPS is conducted in preparation of the first big insertion manoeuvre into the L2 orbit planned for January 7.
The Lagrange point L2 in the Sun-Earth system - also called SEL 2.

The Lagrange point L2 in the Sun-Earth system – also called SEL 2.

All operations went very smoothly this year. Let us hope it will continue this way next year! All the best for 2014!

Note: The original version of this article you can find in the blog of Isabelle D., the QA engineer of the Gaia spacecraft of EADS Astrium,  at: http://reves-d-espace.com/2013/12/31/gaia-apres-le-lancement-en-route-vers-l2/ . Many thanks for allowing me to reblog this in English. Merci beaucoup!

Please follow also @ESAGaia and @esascience on twitter for the latest information about the mission.