APOD mission status and preliminary results

On September 20th, 2015, twenty satellites were successfully deployed into a near-polar circular orbit at 520 km altitude by the Chinese CZ-6 test rocket, which was launched from the TaiYuan Satellite Launch Center. Among these satellites, a set of 4 CubeSats conform the atmospheric density detection and precise orbit determination (APOD) mission, which is projected for atmospheric density estimation from in-situ detection and precise orbit products. The APOD satellites are manufactured by China Spacesat Co. Ltd. and the payload instruments include an atmospheric density detector (ADD), a dual-frequency dual-mode global navigation satellite system (GNSS) receiver (GPS and Beidou), a satellite laser ranging (SLR) reflector, and an S/X-band very long baseline interferometry (VLBI) beacon. In this paper, we compare the GNSS precise orbit products with co-located SLR observations, and the 3D orbit accuracy shows better than 10 cm RMS. These results reveal the great potential of the onboard micro-electro-mechanical system (MEMS) GNSS receiver. After calibrating ADD density estimates with precise orbit products, the accuracy of our density products can reach about 10% with respect to the background density. Density estimates from APOD are of a great importance for scientific studies on upper atmosphere variations and useful for model data assimilation.