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Twinkle twinkle little stars!

-December 17, 2013

Earlier this year, I had the good fortune of making my first visit to the beautiful Canarian island of Tenerife. During the trip, my wife and I signed-up for the Teide by Night excursion. Mount Teide is an active volcano, which last erupted in 1909, with a summit of 3,718 metres making it the highest point in Spain and the third overall globally. Initially, I was very surprised to discover that Teide is the second most visited national park in the world after Yellowstone.

The view of Mount Teide with its hardened lava flows is simply breathtaking and reminds me a lot of the Martian pictures sent back by NASA's Pathfinder lander in 1997. I now understand why so many tourists flock to Teide each year and highly recommend this trip to anyone visiting Tenerife.

Mount Teide

Sunset was equally spectacular with the islands of El Hierro, La Gomera and La Palma in the opposite direction. After a short detour at El Parador Del Teide, Spain's highest hotel, we returned to Mount Teide for several hours of stargazing. The skies above Tenerife are protected by UNESCO preventing airlines flying directly overhead. The view was clear, dazzling, with the Milky Way Galaxy visible, and hearing the stories of the various constellations brought back happy memories of Carl Sagan's Cosmos series.

Many satellites are now fitted with star trackers to control the attitude of the spacecraft. Essentially, a star tracker is an electronic camera - typically charge coupled/injected devices or active pixel sensors - connected to an on-board digital processor. The sensed image of the sky is analysed to identify stars and then determine the 3D orientation of the spacecraft. An autonomous tracker performs pattern recognition of the star pattern in the field of view and calculates position with respect to the celestial sphere.

Conceptual Illustration of a Star Tracker

The following video illustrates Jena-Optronik's star tracker mounted on the Alphasat telecommunication satellite and the photograph below shows an on-board processor.

The Operation of a Star Tracker


On-Board Processing Unit used on SSTL's Altair HB+ Star Tracker

ESA's GAIA spacecraft is scheduled to launch on the 19th of December at 09:12 UTC with a five-year mission to precisely chart the positions, distances, movements and changes in brightness of a billion stars within our Milky Way galaxy. The astrometry information that will be gathered will significantly advance astronomy, and GAIA is expected to discover new planets, black holes, quasars, dwarfs and asteroids within our solar system.

This huge stellar census will provide the data needed to tackle a huge range of important problems related to the origin, structure and evolutionary history of our Galaxy. The vast catalogue of celestial objects expected from GAIA will not only benefit studies of our own solar system and galaxy, but also the fundamental physics that underpins our entire universe.

The GAIA spacecraft is illustrated below and comprises the payload and service (platform) modules. The payload is housed under a protective dome and contains two identical telescopes, an astrometer to determine the positions of the stars in the sky, a photometer which measures spectral energy and a spectrometer to provide velocity information. Beneath the service module, a large sunshield keeps the spacecraft in shadow maintaining the exterior of the payload around -110°C to help the instruments take precise measurements.

The GAIA Spacecraft

The Payload Data Handling Unit (PDHU) is the 'hard-disk' of GAIA, storing the data received from both telescopes before transmission back to Earth. The PDHU contains seven Video Processing Units, one for each detector row of the focal plane, feeding 960 GB of solid-state mass memory each with a processing power of more than 1000 MIPS.

Detailed information about the GAIA mission, instruments, payload and platform can be viewed at: https://directory.eoportal.org/web/eoportal/satellite-missions/g/gaia

Last week GAIA was fueled with the propellants it will need to travel to the 'L2' destination, a gravitationally stable location 1.5 million km away from Earth, from where it will survey our Milky Way galaxy. This morning the spacecraft was secured inside the fairing and added to the Fregat upper stage of a Soyuz launcher as shown below:

The GAIA spacecraft being placed inside the fairing and added to the upper stage

GAIA will fly the largest focal plane ever to be used in space containing a mosaic of custom CCDs developed by e2v Technologies. A panel of flight CCDs is shown below, and similar sensors are being used within the upgraded, wide-field camera on-board NASA's Hubble Space Telescope providing images from ultraviolet to near infrared.

Integration of CCDs onto panel and Astrium Ltd.'s Video Processing Unit

I'd love to hear about your star gazing experiences and wish all readers of Out-of-this-World Design a very Merry Christmas. Don't forget the launch of GAIA this week! A little Christmas present - hope you enjoy this beautiful time-lapse video of stargazing in Tenerife created by the very talented Terge Sorgjerd - turn-up the volume on your computer!

Stargazing in Tenerife

p.s. I will have a short tutorial entitled, Hardware Design Considerations when using FPGAs for Spacecraft Avionics, published in this quarter's edition of Microsemi's SpaceBrief. It would be very informative for all readers of this blog to hear what features you would like the next generation of space-grade FPGAs to offer to support your future missions and applications.

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