In-situ measurement of atmospheric density in very low Earth orbits

Very low Earth orbit (VLEO) has unique advantages in Earth observation and scientific research due to their low orbital altitude; however, the knowledge of the atmospheric density variation in these orbits is insufficient. A preliminary analysis and discussion of the in-situ results of atmospheric density in VLEOs in China is carried out, based on the description of the history and current status of in-situ exploration of VLEO atmospheric density, and on the summary of the existing in-situ detection techniques of atmospheric density. The results show one order of magnitude difference in atmospheric density between 250 km and 350 km altitudes during the quiet period of the space environment in October 2020. During the orbit ascent and descent, the atmospheric density of VLEOs decreases by 0.025 × 10-12 kg/m3 and 0.041 × 10-12 kg/m3 per kilometer, respectively, each 0.5 times less than that of the NRLMSISE00 model. At 40°N, the atmospheric density in the ascending section at midnight (~ 250 km) is 11.2 times higher than that in the descending section at noon (~ 420 km), and the effect of altitude is greater than that at local time. At different latitudes, the daily mean ratio of the observed values to the model values decreases from 0.49 at high latitudes to 0.39 at low latitudes, with the NRLMSISE00 model values being larger. At the VLEO, the observed values are generally smaller than the NRLMSISE00 model values, which can provide basic data for atmospheric physical studies and applied research. © 2022 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.