RendezVous sensor for automatic guidance of transfer vehicles to the International Space Station

Abstract

Based on a Predevelopment Program ' initiated by the European Space Agency (ESA), an automatically operating RendezVous Sensor (RVS) is currently developed. This sensor -a Scanning Tele-Goniometer -will guide docking and retreat of the European Automated Transfer Vehicle (ATV) as well as berthing and retreat of the Japanese H-IT Transfer Vehicle (HTV) to the International Space Station (155). The RVS is able to measure directly the Range and Line-of-Sight angles between the chaser spacecraft (ATVIHTV) and the target spacecraft (155). The entire measurement chain consists of the sensor itself mounted onboard ATV/HTV and retroreflector(s) (corner cube type) mounted onboard 155. Range and Line-of-Sight are measured by a LaserRangefinder and optical encoder means. Subsequent data processing allows to calculate relative attitude angles (roll, pitch, yaw). The sensor itself consists of an Optical Head covering scanning as well as passive optical functions, and an Electronics Box containing the LaserRangefinder, data processing, communication interface and power supply functions. The laser pulses are generated inside the LaserRangefinder and are routed via an optical fiber to the transmitter optic of the Optical Head. The Optical Head directs the laser beam to the retroreflectors by two scanning mirrors arranged subsequently and perpendicular one to the other. The retroreflected laser pulses pass the two mirrors and are then coupled into a second optical fiber through a corresponding receiver optic. The LaserRangefinder measures the time-of-flight of the pulses thus giving the needed range data. Optical encoder mounted on the mirror shafts measure the corresponding Line-of-Sight angles. RVS software is not limited to measurement data processing and evaluation tasks but also serves for sensor health supervision, sensor communication with Guidance and Navigation subsystem and automatic target acquisition and tracking. This paper describes in more detail the RVS concept emphasizing the electro-optical elements of the sensor.