Emergency command path for Space Traffic Management

Abstract

The availability of command time slots is a key factor in determining orbital spacecraft manoeuvre execution. Command paths are typically provided via existing ground infrastructure and set at pre-determined times with limited ability to react quickly. Collision avoidance manoeuvre commands may need to be sent many hours in advance, thus increasing decision uncertainty, and leading to higher overall risk in the space environment. With significantly more satellites expected in the next few years, the strain on ground infrastructure will only grow. In particular, the deployment of mega-constellations will radically increase conjunctions involving at least one active object, as well as conjunctions involving two active objects. Fortunately, Europe has infrastructure in place to provide an alternate or emergency command path for Space Traffic Management and collision avoidance on a global scale.The Galileo Navigation System has embedded in the Galileo Signal in Space (SiS) various data channels that are near real time, very reliable, and highly available anywhere in Earth orbit. Satellites equipped with a Galileo GNSS receiver are therefore not only provided with accurate positioning data, but also with the means to continuously receive commands, even in the event that nominal TT&C ability is impaired or lost. These channels would be limited to emergency commands (e.g. manoeuvres or loss of contact situations) and would not be intended for nominal commanding. The use of the Galileo SiS will allow operators to significantly extend the time taken to make manoeuvre decisions, wherever the satellite is located. As such, it would act as a backstop command path, thereby significantly enhancing global orbit protection. This paper provides information on current and planned collision avoidance programs, details about the SiS data channel, its possible implementation on-board the user spacecraft, potential ground interfaces, and operational considerations along with a request for industry feedback on its possible adoption.