Array of Neutral Density Relative Observations MEasuring Divergence in the Atmosphere (ANDROMEDA), A Constellation Concept for Studying Thermospheric Dynamics

Abstract:

In addition to being critical to the prediction of satellite orbits, total mass density is a fundamental property of the thermosphere. Density measurements from accelerometers on the CHAMP satellite have revealed quasi-steady state distributions of density structures around the globe, density responses to changing solar and geomagnetic activity, and spatial structures of wave-like phenomena along the orbit. However, a basic limitation on the time scale of any observable phenomenon is the ~90-minute orbital period. Thus, single-satellite missions like CHAMP are unable to measure the time derivative of density or the mass flux divergence (MFD) at a single point in the atmosphere. While the two accelerometer-carrying GRACE satellites could theoretically measure the density time derivative, in practice this measurement is hampered by the very low-signal levels in the tenuous atmosphere at the ~500-km GRACE orbits, as well as inter-satellite biases and drifts.

The Array of Neutral Density Relative Observations Measuring Divergence in the Atmosphere (ANDROMEDA) is a constellation of CubeSats aimed at improving our understanding of atmospheric dynamics by measuring and interpreting the characteristics of traveling atmospheric disturbances as well as the distribution of MFD in the thermosphere. The ANDROMEDA constellation consists of two to three identical CubeSats spaced approximately 300 km apart and making multi-point measurements of total mass density with an accuracy of <2%. The mass density measurements will be made using a novel torque balance technique enabled by an extremely accurate attitude determination and control system (ADCS) that actively compensates for atmospheric disturbance torques. The benefit of the torque-balance technique is the high level of inter-satellite accuracy. The constellation will be deployed from the ISS and will make observations between 400 km and 250 km altitude as the satellite orbits decay. Distance between the spacecraft will be controlled by modifying the relative ballistic coefficients through small changes in the angle of attack.

In this poster, we present the ANDROMEDA science objectives and requirement flow-down. We then describe the constellation design and present a series of measurement simulations showing the feasibility of this approach.