An advanced ECLSS for long duration manned space missions - such as planetary flight missions or planetary bases - requires an almost complete closure of all relevant material loops. The current state of ESA development in the oxygen reclamation system does, however, not correspond to this requirement, because of considerable losses of hydrogen due to the production of methane in the Sabatier reactor. Concerning the recovery of hydrogen from methane, experimental and theoretical work on methane pyrolysis has been performed meanwhile. Different pyrolysis reactor concepts have been investigated. This paper will present the results of the experimental and theoretical investigations in addition to a preliminary design of a breadboard model for a methane pyrolysis system to close the hydrogen loop on the basis of a three-persons crewed space vehicle.