The Commercial Passenger Transport: Precursor to Routine Travel between the Earth and the Moon

Abstract

Listen

Translate article

In September 2021, SpaceX flew four private citizens to low Earth orbit (LEO) on the Inspiration4 “space tourist” mission lasting ~3 days. In April 2022, SpaceX flew an extended ~15-day private mission to the International Space Station (ISS), arranged by Axiom Space. NASA is also working with Axiom Space and three other companies, Blue Origin, Nanoracks, and Northrop Grumman, to develop their plans for a commercial LEO space station to replace the ISS when its operational lifetime concludes at the end of the decade. With these activities underway, how long will it be before a future tourist vacationing at a commercial LEO station points to the Moon and says, “I'd like to go there, can you take me?” In this paper we examine some of the key systems (e.g., next generation RL10 cryogenic engines, lunar propellant plants, solar and fission power systems) and supporting infrastructure (e.g., commercial space stations, propellant depots) that could be developed over the next several decades to enable routine travel between the Earth and Moon to become a reality. A reusable, space-based Commercial Passenger Transport (CPT) capable of performing a variety of lunar flyby and orbital tourist missions provides the focal point for this paper. Key elements of the CPT include a liquid hydrogen (LH2) propulsion stage with “extended life” RL10C-X engines, an in-line liquid oxygen (LO2) tank assembly, and an inflatable habitat module carrying the crew, passengers, and their consumables. Mounted to the front end of the habitat module is a forward observation gallery with eight large viewing windows. The gallery connects the CPT’s forward docking port to the inflatable habitat module located behind it. Paired MegaFlex solar arrays and radiator panels located on the habitat module’s power bus provide the electrical power and thermal control for the habitat module’s key subsystems. Passengers would board the CPT at either a commercial LEO station, or directly in LEO, delivered there by a commercial launch provider. The CPT would then depart LEO, fly passed the Moon at altitudes of ~300 to 6000 km, then return to Earth capturing back into LEO. Between missions, the CPT is resupplied with propellants and consumables at a commercial LEO Space Transportation Node (STN) that provides both a cargo transfer and propellant depot function. Once established in polar and equatorial lunar orbits as well, these strategically positioned STNs will become important transportation hubs for a variety of lunar transfer vehicles operating in cislunar space. Like their LEO counterpart, lunar STNs will provide convenient staging locations where cargo and passengers will be transported to and from the lunar surface by reusable, surfaced-based lunar landing vehicles (LLVs). Lunar STNs will also provide convenient “ports of call” for stopover orbital missions where tourists will have time to view the Moon up close and personal while the CPT is refueled for its return trip to LEO. Refueling with lunar-derived propellants will be essential to ensuring CPTs of reasonable size and mass. Lunar resource extraction facilities employing “24/7” megawatt-class fission power systems will produce LO2 and LH2 propellants and other important solar-wind-implanted volatiles (like hydrogen and helium-3) using regolith and volcanic glass from the Moon’s polar and mare regions as feedstock material. Using a variety of mining and processing techniques (e.g., in-situ thermal mining enclosures, excavation-haulers supplying lunar oxygen (LUNOX) production plants, and mobile volatile miner-processors), extracted resources would then be delivered to the STN by autonomously-operated “tanker” LLVs stationed at these production facilities. The paper quantifies the operational characteristics of key in-space and surface systems, and provides conceptual designs for the space transportation and infrastructure elements discussed within the paper.