Several Falcon Heavy launches could send an Orion and lunar lander to the Moon. (credit: SpaceX)

Returning humans to the Moon without SLS and NRHO

by Ajay Kothari
Monday, January 13, 2025

Recent media reports suggest that the incoming Trump Administration may seek to cancel the Space Launch System. We must then look at other options to put Americans on the Moon as soon as possible. One method described here may be the least costly and the safest, with margins, and be the quickest method to counter China.

We must look at other options to put Americans on the Moon as soon as possible. One method described here may be the least costly and the safest, with margins, and be the quickest method to counter China.

Mike Griffin and Lisa Porter proffered an interesting and promising solution for returning Americans to the Moon more quickly than the present Artemis schedule. It describes sending a lander and Orion separately over a week to LLO (Low Lunar Orbit), docking there and landing two astronauts on the lunar surface using a lander like Apollo. This author feels that SLS is neither a sustainable nor a cost-effective approach for boosters, hence here we intend to modify it by using Falcon Heavy instead of SLS as booster. The rest of the ideas, including the maneuvers for human landings on the Moon, remain the same, except that the upper stages taken to the lunar surface offer an additional repurposing potential.

Starship offers potential for large payloads delivered to lunar surface but it is not human-rated yet, which may take a few years. Another issue is a large refueling need (from 8 to 16 to 20 flights, according to numbers from SpaceX, GAO, and NASA respectively, which makes its reliability questionable at best, as described in the Griffin/Porter paper. The reason is the very high dry mass (DM) of Starship (the upper stage) at almost 100 tons.

From Griffin and Porter

With Blue Origin’s Blue Moon Mark 2 Lunar lander in the 45-ton range (wet mass), which can take four astronauts to Lunar surface from near rectilinear halo orbit (NRHO) and hence from LLO, it offers an enticing possibility of these two space companies partnering for the sake of the country. Four flights of Falcon Heavy with its upper stages docked in LEO would give enough delta-V for translunar injection (TLI) and lunar orbit insertion (LOI). Blue Moon, though, rests on Blue Origin successfully developing a solar-powered liquid hydrogen refrigeration scheme to have the cryogenic propellants, especially the liquid hydrogen storage near 20 kelvins for the period mentioned by them, 30 days. Also, there would be no need for a tug or refueling at NRHO.

China’s Chang’e-4 landed on the far side of the Moon in January 2019. Chang’e-5 did so in December 2020 and returned samples from Moon surface. Now, Chang’e-6 last year returned the samples from near the south pole, a very attractive site for any future habitation and in situ resource utilization, with possible indication of copious amounts of water ice, a crucial element for any lunar program. China will establish a permanent presence on Moon through the International Lunar Research Station (ILRS) shown here in the 2030s, with taikonauts on Moon likely sooner than that. Would China stake a claim to the entire South Pole as some have mentioned? No, but they can and will do so for the most promising regions there.

Starship is a very promising possibility, but with two caveats. The dry mass of the Starship upper stage is too large for lunar missions while being necessary for the Mars mission, its primary intention. Its reusability for the Artemis 3 mission is not of primary importance, neither is that of the Super Heavy booster. The problem here is the dry mass at nearly 100 tons. This requires between 8 and 20 refueling tanker flights for the delta-V requirements of TLI, LOI, and landing. Refueling in LEO will require many test flights to increase the technology readiness level to a satisfactory level, whereas docking in LEO, as proposed here, has been done since 1965 in both manual and automatic modes. If SpaceX were to develop a smaller version of the upper stage for the Moon and cislunar space, it would be appropriate to look at that option but, at this stage, we need to look at other possibilities.

That option would be using Falcon Heavy instead, a proven vehicle with eight of eight successful flights under its belt. The computed numbers below prove that this is quite feasible with margins to spare. Although three dockings in LEO would be required for the Orion, there is no refueling need and it is a much smaller number than the Starship HLS refueling estimates. If SpaceX designs an upper stage with a much lower dry mass, it will change its potential for use as a lunar lander, which will significantly improve its potential as HLS. With China making big strides, the time also become of essence.

Boiloff issue

Since this proposal uses the upper stage of Falcon Heavy using the Merlin engine, there would be no liquid hydrogen boiloff issue either, unlike if were to use Centaur 3 or BE-7 as offered by Blue Origin for Blue Moon and the tug. There would be a liquid oxygen boiloff issue, but it is much less severe compared to liquid hydrogen. Also, there would be no need for a separate LOI stage (Centaur 3) as described in “Returning Humans to Moon” by Griffin and Porter. The docked upper stages of the Falcon Heavy will do the work of TLI plus LOI.

From Griffin and Porter

Architecture (lander)

The lander would have to be built by NASA. It would be like the Apollo 17 Lunar Module, called Challenger, which carried two astronauts to the surface from LLO. It had a mass of 16.5 tons, so the new one here is bookkept at 18 tons wet mass, including higher consumable for a 6.5-day stay. This would require one to two years to have it ready. The Lander uses MMMH/N2O4 as propellants so there is no boiloff issue.

Lander first: The campaign would then start with first Falcon Heavy flight carrying the 18-ton lander to LEO and park it there. Two upper stages of Falcon Heavy dock in LEO after two flights of that rocket over perhaps one day.

Falcon Heavy LEO payload is 38/54/63 tons depending on fully reusable, partially reusable (the side boosters return with the core expended), and fully expendable. This analysis picked the partially reusable option.
One of the upper stages carries the lander as payload (~18 tons) whereas the second one would carry that much (54 tons) extra propellant, which will remain in it at LEO.
Thus, the PF is increased to what is required (0.7 for Merlin1Dv engine) for TLI plus LOI (3200+900 m/s) for the combination.
The upper stage dry mass is 4.5 tons for Falcon Heavy. Let us allow for beefing up the tanks (as we may use them for habitats on Moon also) and landing legs, thus adding another 1.5 tons to its dry mass.
Total propellant in LEO thus is (36.4+54.4)= 90.8 tons
The total mass in LEO will be (18+6*2+90.8)=120.8 tons
The propellant fraction of the combination thus is 0.75 which is sufficiently greater than needed for TLI+LOI (0.7).
The combination fires the two of the Merlin 1Dv engines to do TLI and LOI capture (any combination that makes sense can be allowed, to be determined).
The propellant used up will be 70 tons. Total leftover propellant in LLO is 20.8 tons, which is more than enough for landing the stages on the south pole. This maneuver takes three to five days.
The side upper stages (6 tons each) separate in LLO and each one lands on Moon using the landing legs, consuming ~5 tons of propellant (propellant fraction for the landing is 0.44 for 2000 m/s delta-V).
One could possibly postulate the use of upper stage tanks (already beefed up and with windows) as potential habitats. They can be vented to space first and can be later fitted with inflatable habitats
The lander remains in LLO waiting for the Crew module (Orion) to arrive.

Architecture (Orion)

The same procedure is repeated from Earth for the crew using Orion (28 tons) after the lander is safely in LLO, but this time with three Falcon Heavy flights over 48 hours.
Note that the TLI capacity this way is higher than that of SLS Block 2 (crew variant) and it would be easier and cheaper to do than SLS.
The lander and Orion dock in LLO and the two crew transfer to the lander, as in the Artemis 3 plan. The lander descent stage takes the crew to the lunar surface
After the anticipated stay (about one week), the ascent stage of the lander takes the crew back to LLO, where it docks with Orion and transfers the two crew to it. Orion performs TEI burn and heads to Earth with all four crew.
All remaining procedures would be same as what would have been done with SLS in Artemis III.

Cost

Five Falcon Heavy at ~$120 M each = ~$600 M (for partial reuse option)
Two SLS = ~$2B each (a NASA Inspector General figure which does not include Orion and Centaur 3), for ~ $4B. (The Inspector General estimate for all included is ~$4B for each flight)
The difference is substantial cost savings to NASA: almost 85%

This modus operandi is also suggested for our future. The combination/permutation with four degrees of freedom (number of flights, number docked versus refueled, payload sizes, and delta-V) needed for different destinations in the solar system provide hundreds of possible solutions with already developed and built rockets and engines. There is no need to redevelop new rockets for new aims except in specific cases.

Dr. Ajay Kothari is President and Founder of Astrox Corporation, an Aerospace R&D company located in suburban Washington, DC. His PhD and MS in Aerospace Engineering are from the University of Maryland and BSc in Physics from Bombay University. He is Associate Fellow of AIAA and member of AIAA Aerospace Power Technical Committee. He has over 40 professional publications and has been PI on more than 35 NASA and DOD contracts.

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