Objective: The objective of the activity is to develop and demonstrate a GSO satellite communication system that integrates an intermediate layer of High Altitude Pseudo-Satellites (HAPS) to provide command and control links, broadband payload data communicationsand inter-vehicle links to swarms of unmanned vehicles. The activity will develop the physical, data link and network layers of theend-to-end satellite communication system and will implement them in a software demonstrator to validate the concept. Targeted Improvements:Enabling communication between GSO satellites and Remote Piloted Aircraft Systems (RPAS) using High Altitude Pseudo-Satellites (HAPS) as a relay. Description: Remotely Piloted Aerial Systems (RPAS) are unmanned aircraft that play a key role in a variety ofapplications such as fire fighting, environmental protection, surveillance, law enforcement, search and rescue or disaster reliefamong others. To fulfil their mission, they fully depend on communication links that allow their command and control and sending back the data generated by their payload(s). Depending on the operational scenario, these links may be Line-of-Sight (LoS) or Beyond-Line-of-Sight (BLOS). Several satellite solutions exist to provide beyond-line-of-sight communications to aircraft. However, most RPAS cannot use these solutions because their size, weight and power constraints preclude them from embarking a satellite terminal. Some RPAS can only embark smaller L-band terminals that provide minimum connectivity (a few hundred kbps), which is not sufficient to support broadband applications. Only a minority of larger RPAS can embark high throughput satellite terminals in Ku or Ka band. High Altitude Pseudo-Satellites (HAPS) are solar powered platforms that can fly in the stratosphere uninterruptedly for months. This allows them to act as a permanent relay node between RPAS and the satellite. The link budget gains rising from the short distance between RPAS and HAPS allow for smaller user terminals and higher data rates. In this way, HAPS enable communication between GSO satellites and RPAS that cannot embark a satellite terminal. Hence, this activity will develop a satellite system for RPAS communication using HAPS as a relay node. Flight dynamics of RPAS and HAPS, and their constraints in terms of mass and power will be taken into account. The development will include the end-to-end link as well as physical, data link and network layers. The activity will focus on the elements that drive the satcom system design taking the aeronautical link as an input. A system demonstrator will be developed to validate the concept and assess its performance in representative conditions. The demonstrator will consist of a test bed capable ofassessing the end-to-end throughput, availability and latency of the links. Footnote: On Delegation Request (formerly called Priority 2) activities will only be initiated on the explicit request of at least one National Delegation.