Performance analysis of IMU-augmented GNSS tracking systems for space launch vehicles

European space launch operators consider the potential of GNSS (global navigation satellite system) as a promising novel means of localization for the purpose of range safety of launch vehicles like Ariane and Vega, since it is expected that recurring costs are lower and accuracy is higher than currently existing systems like radar tracking. Range safety requires continuous information about the position and velocity of the launch vehicle to quickly detect the occurrence of catastrophic events. However, GNSS outages due, for example, to high jerks at fairing and stage jettisons or other external interferences like (un-)intentional jamming cannot be precluded. The OCAM-G experiment on Ariane 5 flight VA219 has provided evidence that GNSS is capable of providing a highly accurate position and velocity solution during most of the flight, but that outages of several seconds do occur. To increase the continuity of a GNSS-based localization system, it is proposed that the GNSS receiver is augmented by an inertial measurement unit (IMU), which is able to output a position and velocity solution even during GNSS outages. Since these outages are expected to be short, a tactical- or even consumer-grade IMU is expected to be sufficient. In this paper, the minimum IMU performance that is required to bridge outages of up to 10 s, and thereby meeting the accuracy requirements of range safety, is determined by means of a thorough simulation study. The focus of the analysis is on current generation microelectromechanical system (MEMS)-based IMU, which is lightweight, low-cost, available commercially and has reached acceptable maturity in the last decade.