Orbital Maintenance of a Constellation of CubeSats for Internal Gravity Wave Tomography

The advent of radio occultation (RO) instruments aboard CubeSats leads to the possibility of a mission to sound atmospheric internal gravity waves if such satellites are deployed in close-flying constellation. The satellites in the constellation must have slightly perturbed orbital inclinations in order to spread the RO soundings within clusters in two horizontal dimensions, and consequently the satellites will disperse because they will experience different rates of regression of nodes. This dispersion must be countered by propulsive maneuvering in order to maintain the close formation of the constellation. Here, a theoretical approach to the necessary propulsive maneuvering is presented and simulations using comprehensive orbit propagators are performed to analyze four propulsive systems: two cold gas propulsion systems and two electrospray propulsion systems. Cold gas propulsion permits greater separations in inclination between satellites in a constellation by virtue of the greater thrust they can exert on a spacecraft: cold gas propulsion can permit inclination separations of 1 to 10 $^\circ$ while electrospray limits separations to less than 0.2 $^\circ$ . On the other hand, electrospray propulsion provides much longer mission lifetime by virtue of the greater total thrust it offers: cold gas propulsion expends all of its fuel in maintaining the constellation formation in less than approximately 100 days while electrospray propulsion can maintain formation for greater than 1000 days before expending all of its fuel. Mission lifetime is the most critical consideration for a mission, thus electrospray propulsion is recommended for the constellation-flying of CubeSats, but the accelerations that they offer must be greatly increased to enable spacecraft separations useful for tomography of internal gravity waves. Note that any close-flying constellation involving satellites with slightly perturbed inclinations will experience the same dispersing effect as the constellations described herein and, thus, require the same propulsive maneuvering to maintain formation.