# Small Satellite Constellations for Earth Geodesy and Aeronomy

## Session

Pre-Conference: CubeSat Developers' Workshop

## Abstract

Drag-free nano-satellite constellations can improve the sensitivity and spatial and temporal resolution of Earth aeronomy and geodesy measurements relative to a single satellite or a satellite pair. It is clear that multi-satellite systems improve the frequency with which data can be collected for a given location over the Earth. Nonetheless, a broad quantitative assessment has not been performed for the particular applications of Earth geodesy and aeronomy. This research is necessary to produce a meaningful cost/benefit analysis for this class of nano-satellite constellations. The enabling technology is a precision small-scale drag-free system, called the Drag-free CubeSat, currently under development at the University of Florida and Stanford University. Drag-free satellites provide autonomous precision orbit determination, accurately map the static and time varying components of Earth's mass distribution, aid in our understanding of the fundamental force of gravity, and will ultimately open up a new window to our universe through the detection and observation of gravitational waves. At the heart of this technology is a gravitational reference sensor, which (a) contains and shields a free-floating test mass from all non-gravitational forces, and (b) precisely measures the position of the test mass inside the sensor. A feedback control system commands thrusters to fly the “tender” spacecraft with respect to the test mass. Thus, both test mass and spacecraft follow a pure geodesic in spacetime. By tracking the position of a low Earth orbiting drag-free satellite we can directly determine the detailed shape of geodesics and, through analysis, the higher order harmonics of the Earth’s geopotential. The commanded thrust, test mass position and GPS tracking data can also be analyzed to produce the most precise maps of upper atmospheric drag forces and, with additional information, detailed models that describe the dynamics of the upper atmosphere and its impact on all satellites that orbit the Earth. This paper will focus on the performance of drag-free CubeSat constellations for measuring Earth’s geoid and upper atmospheric winds and density. Advances in the development of the Drag-free CubeSat hardware and control software will also be described.

*Presentation Slides*

Small Satellite Constellations for Earth Geodesy and Aeronomy

Drag-free nano-satellite constellations can improve the sensitivity and spatial and temporal resolution of Earth aeronomy and geodesy measurements relative to a single satellite or a satellite pair. It is clear that multi-satellite systems improve the frequency with which data can be collected for a given location over the Earth. Nonetheless, a broad quantitative assessment has not been performed for the particular applications of Earth geodesy and aeronomy. This research is necessary to produce a meaningful cost/benefit analysis for this class of nano-satellite constellations. The enabling technology is a precision small-scale drag-free system, called the Drag-free CubeSat, currently under development at the University of Florida and Stanford University. Drag-free satellites provide autonomous precision orbit determination, accurately map the static and time varying components of Earth's mass distribution, aid in our understanding of the fundamental force of gravity, and will ultimately open up a new window to our universe through the detection and observation of gravitational waves. At the heart of this technology is a gravitational reference sensor, which (a) contains and shields a free-floating test mass from all non-gravitational forces, and (b) precisely measures the position of the test mass inside the sensor. A feedback control system commands thrusters to fly the “tender” spacecraft with respect to the test mass. Thus, both test mass and spacecraft follow a pure geodesic in spacetime. By tracking the position of a low Earth orbiting drag-free satellite we can directly determine the detailed shape of geodesics and, through analysis, the higher order harmonics of the Earth’s geopotential. The commanded thrust, test mass position and GPS tracking data can also be analyzed to produce the most precise maps of upper atmospheric drag forces and, with additional information, detailed models that describe the dynamics of the upper atmosphere and its impact on all satellites that orbit the Earth. This paper will focus on the performance of drag-free CubeSat constellations for measuring Earth’s geoid and upper atmospheric winds and density. Advances in the development of the Drag-free CubeSat hardware and control software will also be described.