On 19 December 2013, The European Space Agency (ESA) launched the Gaia spacecraft. This spacecraft will maps the Milky Way in 3D, while collecting data on the composition of stars and the presence of planets. The result of Gaia's five-year mission will be an exceptionally accurate three-dimensional map of more than a billion stars throughout our galaxy. Thanks to TNO, Gaia will have an extremely detailed view of the universe.
TNO supplied three separate components for Gaia. The WFS OMA (WaveFront Sensor Opto Mechanical Assembly) is used to help align the telescope. The FSS (Fine Sun Sensor) determines the position of the spacecraft relative to the sun. This information is used for various purposes, such as aligning the solar panels. The BAM OMA (Basic Angle Monitoring Opto Mechanical Assembly) is critical to the success of the mission. It is also one of Gaia's most complex components. BAM enables Gaia to make measurements at a staggering resolution, comparable to pinpointing a single strand of hair at a distance of one thousand kilometres. With this exceptional degree of precision, Gaia is expected to discover about 100 new asteroids a day in our solar system. The daily tally elsewhere is projected at 10 new stars with planets, 50 new exploding stars in other galaxies, and 300 new distant quasars.
Exo-planets will be detected by measuring the tiny movement of the star, caused by the small gravitation pull of the planet. It is also estimated that Gaia will discover about 15,000 new exoplanets during its operational lifetime.
In order to achieve this revolutionary measurement accuracy, the spacecraft must remain absolutely stable while it is operating. Wim Gielesen, the Project Manager, explains that "Gaia's measuring instrument measures the angles between stars using two telescopes set at a fixed "basic angle" of 106.5 degrees. In order to map space reliably, you need to be very sure that it is the stars that are moving, not the measuring instrument itself. For this reason, the Basic Angle Monitoring system (BAM) monitors the basic angle between the mirrors every five minutes." Mr Gielesen explains: "The BAM fires two pairs of parallel laser beams at the telescope mirrors. These are reflected into a detector, creating two interference patterns. Any shift in these patterns is measured with an accuracy of 0.5 micro-arcseconds. Next, the data arriving from the mirrors is corrected for any changes in the basic angle."
The spacecraft is made almost entirely of silicon carbide, an extremely rigid material that can withstand temperatures as low as minus 170 degrees Celsius. Wim Gielesen points out that "Silicon carbide is a ceramic, so it is brittle and very hard. No-one has ever produced mirrors like this before, so TNO had to develop them itself. These are highly-curved mirrors. We ground the mirror using a polishing robot, while a team from Leipzig removed any local irregularities. That was extremely challenging work, as these irregularities were right at the detection limit of our equipment. The result is a mirror that surpasses ESA's performance requirements by a factor of two. "The new knowledge we have developed will have many other applications, in fields such as laser technology." BAM OMA's components were developed in close collaboration with Eindhoven University of Technology and with the support of the Netherlands Space Office (NSO). The silicon carbide components were manufactured by Airbus DS/Mersen-Boostec.