Navigating a Dual-Spacecraft Bistatic Radar Around an Asteroid

DROID, a low-cost mission concept being proposed by NASA JPL and CNES, is a multispacecraft mission to the potentially hazardous asteroid 99942 Apophis. The goal is to make in-situ observations of the asteroid before, during and after its 2029 close approach, when it will pass between the Earth and the Moon. The mission system consists of a Mothership and two 6U CubeSats, where the pair of CubeSats form a multistatic radar system designed to measure the internal structure of Apophis. To facilitate these measurements, the two CubeSats must be navigated with sufficient accuracy to maintain a near-antipodal orbital configuration at a low altitude. Indeed, navigation capability is a key driving factor in the overall mission design due to the extremely sensitive dynamical environment. In this paper we present the navigation analysis, comprised of both linearized covariance analysis and non-linear Monte Carlo, that is being used to drive mission requirements.