What properties of an adsorbent are desirable for xenon propellant storage? Addressing this question could lead to improved adsorbents that yield an adsorbed xenon storage system with a lower tankage fraction than bulk storage. While eqn. 11 provides insights into how K, M, and ρ ads influence the optimal tankage fraction, these parameters are in practice not independent, but correlated. For example, denser materials tend to offer a stronger interaction with xenon but a lower saturation loading (see Fig. ).