Hardware-in-the-Loop Simulations of a Navigation Camera in a Cometary Dust Environment

Abstract

This paper presents a novel hardware-in-the loop (HIL) simulation tool with the capability to accurately and realistically test the response of optical systems during a fly-by of a comet through the central coma region i.e. in a heavy dust environment. The HIL simulations are performed using the Dynamic Optical Ground Support Equipment (DOGSE) developed at DTU Space which can expose representative optical sensors to high fidelity, dynamic, optical stimulations on a small, high-resolution screen, thus enabling flexible, yet complex HIL simulation tests. The simulations are part of a predevelopment activity within the Comet Interceptor AOCS/GNC preliminary design with OHB Sweden leading the effort. The Comet Interceptor mission aims to intercept a Dynamically New Comet or an interstellar body with the closest encounter at a distance of less than 1000 km from the comet nucleus and a relative velocity between 10 and 70 km/s. The spacecraft will be launched towards the Sun-Earth L2 (SEL2) Lagrange point where it will wait up to three years until an interesting target object is identified. The spacecraft will then initiate a transfer phase which will last between 0.5 and 4 years. The final approach starts approximately 60 days before the encounter and mission success depend on the navigation system ensuring that the spacecraft can track the comet nucleus throughout the encounter. The navigation solution is realized with navigation cameras in combination with star trackers, and with an on-board navigation filter which processes and fuses the measurement data. Due to the inherent uncertainties associated with intercepting an a priori unknown, fast-moving comet with an unknown and likely dynamic dust environment it is essential that new, effective, and flexible methods for testing fly-by scenarios are developed and refined. The DOGSE tool is partially automated to test mission scenarios with a fast turn-around and it can realistically display the translucent coma against an accurate projection of the starry sky (i.e. stars can be observed through the dust). The tool takes as its input a trajectory file and generate synthetic images of the comet based on a detailed cometary dust distribution model in the vicinity of the comet nucleus, including distributions of different particle sizes, their phase angle dependent albedo and Sun-distance dependence. This paper presents current results from the HIL simulations based on the navigation architecture of the Comet-I mission and describes how the dynamic optical stimulator is calibrated and handled. Results include the operation of the navigation camera and the performance of star tracker functionality from afar to the closets encounter in the coma dust environment.