Optical intersatellite links for navigation constellations

Abstract

Satellite constellations are used for navigation purposes since long. Connecting the satellites in a constellation by intersatellite links (ISLs) offers a full range of new possibilities. Ranging and time synchronization information can be exchanged between the satellites to improve the in orbit SC positioning knowledge. Besides ranging and time synchronization, ISLs can be used for service channel purposes or to distribute SW updates for the spacecrafts in a short period of time. ISLs improve the navigation constellations autonomy properties being less vulnerable to ground station unavailabilities. For ISLs, radio frequency (RF) and optical technologies have been investigated. Due to the shorter wavelength, a better ranging resolution can be achieved with optical than with RF ISL solutions. Optical ISLs (OISLs) offer a very attractive solution for intersatellite links in terms of size, weight and power while providing multi gigabit per second data rate capabilities. In addition, optical communication links offer high operational security and immunity to interference sources while benefitting from a non-regulated optical frequency spectrum. For those reasons, optical intersatellite links for navigation constellations have been investigated in several studies supported by DLR and ESA. TESAT with partners have investigated the benefit of OISLs for navigation systems and on the Galileo OISL Terminal design. In this paper, the results of these studies will be presented. Various OISL connection schemes in a navigation constellation are compared. The key design parameters of a Laser Communication Terminal for navigation systems will be given. Furthermore, the results of a lab demonstration showing the parallel distribution of ranging and communication data will be summarized. The focus of the investigation is on the Galileo navigation constellation.