LEO Satellites as Sensors for Thermospheric Mass Density and Drag Research

The charge to the space science community is to improve specification and forecast of the low Earth orbit (LEO) space environment to provide reliable collision avoidance and risk assessment analyses for space traffic management and reduce the number of false conjunction warnings. The challenge is that the prediction of LEO object trajectories is severely limited. This is due primarily to poorly captured variability in neutral density estimates during space weather events, resulting in large and variable position errors of all resident space objects across LEO. To improve operations in LEO, the specification and forecast of the thermosphere neutral mass density must improve.

Most recently launched LEO satellites are equipped with global navigation satellite system (GNSS) devices, making them excellent sources of continuous orbit ephemeris to enable precision orbit determination (POD). Many are also equipped with attitude and vehicle knowledge to allow for the construction of an accurate force model. Combining these “data of opportunity” from LEO satellites with POD processing tools offers the possibility of extracting thermospheric mass density information regularly and globally from the multitude of GNSS-equipped LEO satellites in operation today.

This talk explores this possible trove of LEO space environment data by investigating methods and providing specificity to the level of data information required to provide useful mass density outcomes. The ICESAT-2 spacecraft is used as a test vehicle for this type of analysis. The NASA GSFC GEODYN POD software is employed to produce precise science orbits for the ICESAT-2 spacecraft. These precise science orbits are then used to extract mass density estimates along specified orbital arcs. Simulation is also employed to address the potential errors of system requirements and how they can influence the thermospheric mass density estimate from LEO spacecraft. The future GDC mission will also be highlighted as a much-needed LEO space environment resource for direct multi-point measurements of the thermospheric gas and ionospheric plasma. These direct neutral measurements will enable a careful validation of POD-extracted densities. By fully characterizing all free-stream parameters, GDC is also a well-equipped constellation for studying the gas-surface interactions critical for drag research.