October 26, 2007, Mainz, Germany--Shortly after 1:00 p.m PDT on October 18th, the protective lid that covers the camera eye of the space probe Dawn opened for the first time and set its sights on the asteroid belt beyond the orbit of Mars. Its onboard camera included optics made from SCHOTT's synthetic "Lithosil" quartz glass, "BK7G18" boron crown glass, and "SFL6" heavy flint glass to prevent radiation darkening.
"In space, normal optical glass would become as brown as a latte' in a few days," explains Thorsten Döhring, who is in charge of optical applications in astronomy at SCHOTT in Mainz. "Compared to the specialty glass types SCHOTT provided for this unique application, radiation stability is particularly high, thus ensuring a permanent high transmission so that we can still get photos from Ceres in the year 2015."
The German components onboard the probe follow a long tradition of European/American collaboration in space exploration. "This participation is a great demonstration of trust for us," explains Holger Sierks of the Max Planck Institute of Solar System Research (MPS) located in Katlenburg-Lindau, Lower Saxony, Germany. "Our two cameras on board are the eyes of the space probe. They are not only for the scientific exploration of Vesta and Ceres, but also for the optical navigation of the probe with the help of star fields."
The cameras, operating one at a time, will take approximately 50,000 photos of the asteroid Vesta and the dwarf planet Ceres. The cameras' construction is extremely stable, which allowed it to withstand the multiple g-force acceleration it experienced when the rocket containing the probe lifted off from Cape Canaveral, FL on September 27, 2007. In order to ensure the success of the Dawn mission, two identical units are being deployed in the probe, should one camera system fail.
"Every lens of the 5.5-kg camera could only weigh, at most, 750 grams," according to Herbert Mosebach of Kayser-Threde in Munich, the company commissioned by the Max Planck Institute to develop the camera lenses. "For this reason, we had to limit ourselves to four lenses for the optics. Each lens therefore had to have optimal transmission, thermal stability and resistance values with respect to cosmic radiation in order to keep sending perfect photos from space, even after nine years. Another challenge was the actual suppression of scattered light that allowed the effective measurement of asteroid surfaces in spite of their low brightness."
For more information, visit www.us.schott.com/advanced_optics.