After 9 years of space journey, DAWN space probe finished its primary mission successfully!
Three days ago on June 30, DAWN probe finished its main mission. It sent to Earth 69000 images and 132 GB of data, among others with results of research performed on composition of surface of both celestial bodies. For example thanks to DAWN we know that Vesta is completely dry, but Ceres surface contains almost 25% of ice. DAWN also created maps of Vesta and Ceres not to mention about adding experience in deep space exploration. Spacecraft will remain and continue its flight on Ceres orbit at least until 2017. Advanced construction of probe, incorporated many innovative solutions like utilizing electrical propulsion which was able to provide 3100 seconds of 90 mN of thrust; high efficient solar panels (able to provide 11 kW for payload and propulsion) and whole avionics and payload designed to resist high radiation and degradation caused by long duration of the mission. Payload equipment consisted cameras, mapping spectrometers, gamma ray and neutron spectrometers. Probe was utilizing attitude control system based on reaction wheels and additional thrusters.
Whole DAWN program was largely disputed due its cost which reached in 2007 $446 million. Luckily, in spite of stretched budget, probe was launched on September 27, 2007, from Launch Pad 17B at Cape Canaveral AFS on atop of Delta II rocket. After in orbit propulsion tests, probe started its first phase of mission - flight to Mars to use its gravity for increasing speed for further flight. Mars was reached on February 17, 2009 flying only 549 km from Red Planet. Gravity assist was also first moment when first serious problems appeared-DAWN switched into safe mode and started to operate correctly 48 hours later (it was caused due the error in DAWN software). Next two years DAWN continued its flight in elongated spiral trajectory. After two years on July 16, 2011, DAWN reached Vesta and was captured by its gravitation after insertion maneuver performed earlier with utilization of electric propulsion of the probe. During orbiting around Vesta, JPL spotted problems with reaction wheels in attitude control system of DAWN. Probe spent additional nine days on orbit of Vesta and left its orbit on September 5, 2012, but since then, it was using reaction wheels and thrusters for attitude control. After two years another technical problem appeared. Ion thruster stopped to operate and probe switched to safe mode on September 11, 2014. After exiting from safe mode which was performed successfully on September 15, 2014, ion thruster started to operate correctly and DAWN was able to continue mission. It reached Ceres Polar orbit on March 6, 2015. Since then probe change its orbit to Rotation Characterization 3 between April and May 2015 and started measurements and imaging process of Ceres. On May 9, 2015, started to move to Survey orbit reducing altitude from 13500 km to distance of 4300 km. On August 17, 2015 orbit was changed and DAWN reached altitude of 1450 km and HAMO (High Altitude Mapping Orbit) orbit. This was necessary to start mapping process of Ceres, which was finished on October 2015 when DAWN moved into LAMO orbit with altitude of 375 km. Low Altitude Mapping Orbit was reached on December 8, 2015. Since then DAWN started research on Ceres chemical composition of surface with utilization of gamma-ray and neutron detector (GRaND).