For a global quantum communication network, we need to have long distance links over which we can distribute entangled photon pairs. Due to exponential losses, using optical fibres alone is unfeasible. Quantum repeaters extend the range of quantum networks, but intercontinental links are still unfeasible. Because of this, research has gone towards exploring space based segments, where a satellite can be used to make long-distance links by making use of the lower losses of free space transmission compared to fibre transmission. Here, we develop a general analytical model to compute the rate and fidelity of setups consisting of two ground stations connected by a satellite in orbit. We consider three different schemes: a direct downlink and two memory assisted schemes where the satellite is used as a quantum repeater, in an uplink and a downlink. Combining orbital mechanics for the satellite with a detailed model for transmission probability, allows us to track what happens to the rate and fidelity at any point in time. The generality of the model allows for a broad applicability, fitting to many different setups. We apply our model to different setups by tuning the different parameters and identify that the rate of the protocol will benefit most from increasing the multimode capacity of our assisting quantum memory and that the fidelity is most benefited by a good entanglement swap in the memory assisted schemes. If we have small links, bad memories or a bad entanglement swap, the direct downlink protocol will be the best choice, but for an intercontinental link we will need our memory assisted schemes.

There has been a lot of research focused on the next generation of the internet, the so-called quantum networks. This analysis has been so far limited to mostly symmetrical architectures, but any near-term realisations of quantum networks using existing fibre topologies will contain asymmetry. In this thesis, we investigate how midpoint asymmetry affects quantum repeater protocols implemented with atomic ensembles. We extend the existing simulation framework to allow for midpoint asymmetry. By simulating asymmetry in elementary links, we show that the performance of an elementary link executing quantum key distribution decreases with an increasing degree of asymmetry. This effect can be mitigated by individual optimisation of photon sources at both ends of the elementary link. We present a way how to reduce the search space of such optimisations by developing a heuristic. The contributions of this thesis provide a crucial starting point for investigations of asymmetry in quantum repeater chains.