This is realized by a two-step setup consisting of a thermodynamic and a mechanical separation unit. Thermodynamic separation is realized by an heat exchanger HX1 to condense water out of the product stream and further reduce its vapor pressure without solidification . The subsequent mechanical separation of liquid and gas streams takes place in the water separators WS1 and WS2. Unreacted educts, CO2 and H2, are separated in the purification step P1 via pressure-swing adsorption. In SPO the separated reactants are not utilized and emitted to the Martian atmosphere. In RO the recycled gas stream ( ) is combined with the inlet stream (in) in the mixer MIX1 prior to entering the reactor. The produced methane is liquified (stream 13') and stored in a thermally isolated tank S1 including liquid traces of CO2, CO and H2. The gaseous part of the stream into the storage after HX3 is vented prior entering the tank (stream 13'').