Conveniently, the optimal storage pressure and tankage fraction do not depend on the amount of xenon required for the mission, n Xe , for both bulk and adsorbed storage systems (see eqn. 5 and eqns. 10 and 11, respectively). However, the choice of the safety factor β does affect our results. First, the ranking of adsorbents according to their optimal tankage fractions could conceivably change with β (see eqn. 11). Second, the ratio of the optimal tankage fractions for bulk and adsorbed storage systems depends on β (divide eqn. 5 by eqn. 11).