The Eagle II – Conceptual Design of an Alternative Lunar Lander Vehicle and Lunar Landing Architecture to Return Americans to the Moon

This paper presents a conceptual design of a lunar lander vehicle and lunar landing architecture as an alternative to the current Artemis lander architectural element, which utilizes lunar landers from commercial contractors that are propelled by cryogenic liquid methane and liquid oxygen propellants. These landers must be refueled in low Earth orbit (LEO) by multiple propellant tankers using as-yet unproven technology to transfer cryogenic propellants between tankers and landers. A refueled lander would perform trans-lunar injection, coast for five days on a lunar trajectory, and perform orbit insertion into a near-rectilinear halo orbit (NRHO) where it would rendezvous and dock with the crewed Orion spacecraft. The crew would transfer to the lander and perform (1) orbital transfer from NRHO to a low lunar orbit (LLO), (2) descent to the surface, (3) a one-week surface stay, (4) ascent to LLO, (5) orbital transfer to NRHO, and (6) rendezvous, docking, and crew transfer with Orion in NRHO. These landers will experience boiloff of cryogenic propellants while in LEO, during the outbound transit to the moon, while in lunar orbit, and while on the lunar surface. Strict coordination of multiple launches will be necessary to minimize the amount of cryogenic propellant boiloff experienced by the lander vehicle during refueling. The combination of zero-g cryogenic propellant transfer needing multiple successful tanker flights coupled with continuous cryogenic propellant boiloff and precise mission timing and launch coordination represents significant risk to the successful completion of a lunar landing mission. Use of cryogenic propellants opens the possibility of stranding astronauts on the lunar surface due to excessive boiloff of propellants needed for the return flight. The Eagle II lander design presented in this paper is designed to be a “plug and play” substitution for the current NASA Artemis lunar landing architectural element. It will be a simpler, more reliable, and safer option that will require no modifications to the current Orion and SLS elements of the Artemis architecture. The Eagle II lander would utilize storable hypergolic propellants and simple, pressure-fed engines like the Apollo Lunar Module, resulting in a much simpler design approach with no propellant boiloff possible. This approach would need only two SLS launches to complete a moon landing mission: the first launch will inject the Eagle II into a trans-lunar trajectory on an SLS Block 2 Cargo launch vehicle. The second launch will inject the crewed Orion spacecraft into a trans-lunar trajectory on an SLS Block 2 Crew launch vehicle. The Orion would rendezvous and dock with the Eagle II in NRHO, and the Eagle II would provide round-trip transportation for the four crew members between NRHO and the lunar surface. Storable propellants used by the Eagle II lander would permit extended loiter in NRHO and allow larger launch windows for the crewed Orion SLS that could accommodate launch delays without jeopardizing the success of the landing mission. This concept of operations is much simpler and would possess higher inherent reliability than the current Artemis approach: no cryogenic propellant transfer in LEO, no cryogenic propellant boiloff, and a very simple lander propulsion system utilizing pressure-fed engines and hypergolic propellants. The Eagle II lander vehicle would utilize proven technology and incorporate current NASA habitability requirements and would provide radiation shielding for the crew.