This approximation is shown as the curve in Fig. , along which the data approximately lie. So, the performance of an adsorbent for adsorbed xenon propellant storage tends to be determined by, to first order, its saturation loading, M. This result is intuitive because (i) the optimal storage pressure tends to be near saturation conditions (KP opt >> 1), (ii) we wish to minimize the mass of storage materials, dominated by the adsorbent, and (iii) M is the amount of Xe stored per mass of adsorbent at saturation conditions.