Adsorbed xenon propellant storage: are nanoporous materials worth the weight?
Xenon is used as a propellant for spacecraft. The conventional method to store xenon onboard the spacecraft is compression to high pressures (75-300 bar). In this work, we develop a simple mathematical model of an adsorbed xenon pressure vessel by coupling together a mechanical model for the pressure vessel and a thermodynamic model for the density of adsorbed
xenon in the adsorbent. The model allows us to 1nd the optimal storage pressure, tailored to each adsorbent, with the objective of minimizing the mass of the storage media (walls of the pressure vessel + adsorbent) required to store xenon propellant onboard spacecraft. This enables us to rank adsorbents for xenon propellant storage and compare their performance to the baseline of compressed xenon storage. Using experimental xenon adsorption data as input
to our model, we evaluate several nanoporous materials, mostly metal-organic frameworks (MOFs), for adsorbed xenon propellant storage. We 1nd that Ni-MOF-74 and MOF-505 outperform the conventional adsorbent, activated carbon. Compared to bulk storage, however, the reduction in the mass of metal composing the walls of the pressure vessel, as a result of reduced storage pressures provided by the adsorbent, does not compensate for the additional
mass of the adsorbent. Our model suggests that, for an adsorbent to provide weight savings compared to bulk xenon storage, the saturation loading of xenon in the adsorbent must exceed ca. 94 mmol Xe/g adsorbent.