Space based QKD from proof of concept to operational commercial systems

Satellite based Quantum Key Distribution (QKD) systems appear as a potential solution to cover long distance links that cannot be satisfied through fiber links. In this frame, different alternatives are being evaluated involving both geostationary and low earth orbit. Most existing or planned space based QKD missions focus on the build, analysis and performance optimization of the physical quantum channel. This represents only a tiny part of the complexities that imply the design and operation of a commercial oriented full operational end to end QKD system. Based on the state of the art development of the future Spanish GEO QKD system, this paper covers a systemic approach to space based QKD systems, focusing on some limiting factors that need to be taken into account in order to achieve continuous operation of a QKD system from space. Systems parameters such as the on-board memory or the different system delays and their impact on continuous operation are studied. Finally, the paper presents how these different interactions have been arbitrated in the current design of the Spanish GEO QKD system that shall be built, launched and operated before 2030 with the support of the Spanish government and under EC funding.