Rocketdoc Notes – Week of October 25, 2020

Best Transportation System for Lunar Development

In my last note I did an in-depth analysis of the Space-X Starship and what it offers for future Low Earth Orbit (LEO) and Mars developments. The Starship appeared to be a real solution for LEO and Mars developments, but unfortunately, it did not look to be economical for Lunar economic development. Hence, this week I dug in and did an in-depth analysis of the best way to development lunar resources and what this could mean for human space settlements. I think you will find this both interesting and intriguing.

If you remember, I used a tool called BLAST to define and cost out a hypothetical Starship operating in a reasonable space transportation market. I assumed we built a fleet of 50 Starship 2nd stages and 40 Heavy Lifter 1st stages (Starships spend years away on Mars missions). The BLAST tool calculated that for 1500 launches per year the average operating cost/flight is about $3.5 M/flight for the booster and $2.4 M/flight for the Starship 2nd stage (all in 2020 dollars). If we amortize the average unit cost for the hardware over each flight assuming 100 flights/stage and 200 flights/engine I get approximately $3.4 M per flight to depreciate the hardware (2020 $). Therefore, our total cost per flight is $3.5 M+ $2.4 M + $3.4 M = $9.31 M. Assuming Space-X wants to make profit on each Starship launch, I added a Return on Investment (ROI) of about 28% for profit and that indicates Space-X could sell flights for $12M each and meet their ROI goal. This works out to about $100/kg, assuming an average 120 mT payload to LEO which is equivalent to an average load factor of 0.80 (about average for volume-constrained launch vehicles). So far so good. $100/kg is an excellent launch cost to enable profitable LEO business parks and tourist facilities. Once the requirement for low-cost access to orbit is satisfied, the Industrialization of Space will happen in three waves. Those three waves will be industrialization of Low Earth Orbit (LEO), industrialization of the moon, and industrialization of the asteroids. I believe Colonization of Mars will be concurrent with wave three. These waves may be months to decades apart, but logic says they will be sequential. The first wave, the industrialization of LEO will be as covered below.

Industrialization of LEO

Once low-cost access to LEO is available, what happens next? LEO markets development will be driven by adventure tourism and businesses exploring and exploiting zero-gravity. There are numerous new materials that can be made in zero-gravity (no dispersions due to density variations), and processes that require totally clean surfaces can take place in the hard vacuum of space behind a space station. With respect to tourism, many of the well-to-do have visited the majority of the highlights on Earth, but they haven’t seen Earth from space, or experienced activities in zero-gravity. As we showed during CSTS (Chapter 5), that market is huge once the transportation price gets under $500/kg. I would expect hundreds of hotels, adventure parks, and business parks in LEO by 2030. The business parks will cater to zero-gravity research, but also to extraterritoriality (i.e. earth laws don’t apply in LEO, so businesses there don’t have to pay taxes, or follow usury laws). I foresee some interesting times as significant business moves up to LEO. The initial users of LEO Business Parks will be tourists and specialty manufacturers. Some products can be built better in zero gravity and some things can only be built or tested in zero gravity. This market will become huge (hundreds of Billions of dollars per year), but the next step, mining the moon, has orders of magnitude more growth potential.

The primary driver for lunar development is probably global warming. Global warming is key because the most readily available, and the most lucrative materials to mine off-world, are also those which are very critical for producing and using green-energy. Therefore, no matter what your position on global warming is, it could play an important part in future space industrialization. For myself, I believe that Climate Change is a historical process that has been overwhelmed by the enormous burning of fossil fuels in the last 100 years to support the advancement of humankind. i.e., the current global warming is real and must be addressed by; switching to alternative “green” energy sources, capturing and sequestering Carbon Dioxide, and increasing Earth’s albedo to reduce surface temperatures. I believe all three approaches are necessary in the short run to prevent the ice melt caused global flooding severe enough to disrupt humanities technical progress. This is a very political subject, so I won’t dwell, but the technologies to support all three approaches exist or are in advanced development, so all three should be pursued to increase our chances for a happy outcome.

That brings us back to why Global Warming could benefit space. The first approach is limiting carbon-dioxide production by switching to “green energy generation” which should slowdown the warming and give more time to establish “a happy equilibrium”. Improving technologies for generating and storing massive amounts of solar and wind energy requires metals that are hard to obtain on the Earth’s surface. Specifically, we need an affordable supply of Platinum Group Metals (PGMs) and Rare Earth Metals (REMs). The six platinum-group metals are ruthenium, rhodium, palladium, osmium, iridium, and platinum. The PGMs are very rare on Earth’s surface and are used primarily as catalysts for chemical reactions (reducing pollution) and for fuel cells (converting O2 plus H2 into water and electricity). There are seventeen REMs, too many to cover here, but three, Praseodymium, Neodymium and Samarium are used in Rare-Earth permanent magnets, and one Yttrium, is used in high-temperature superconductors. These new magnets are much more powerful than any other known magnets and have taken over in the wind energy and electric motor/generator businesses. Both applications are vital to meeting the current global warming goals. Fortunately, although scarce and expensive to mine on Earth, both PGMs and REMs are relatively abundant on the moon, and the PGMs are especially abundant on asteroids.

What is the best way to mine these lunar resources? In 2012 I was teaching the Senior Space Design Class for the Aeronautics and Astronautics Department at the University of Washington and my students and I dove into this problem. We based our transportation system on the same system NASA chose in 1989 for the Lunar portion of Space Exploration Program. Pictures of those elements are shown in figures 1, 2, & 3 below. Figure 1 is a picture of the Aerobraked Orbit Transfer Vehicle (ABOTV) transferring two containers of cargo to the Reusable Lunar Lander Vehicle (RLLV).

Figure 1 ABOTV transferring Containers to Reusable LLV

The 1989 version of this system shown here transferred propellants, people, and cargo to the RLLV on most missions, as shown in the artwork. The 2012 version only transferred cargo, liquid hydrogen fuel, and people occasionally. The 2020 version would only transfer cargo with all lander propellants generated on the moon and a separate lander system designated for people. Figure 2 below shows the RLLV landing on the lunar surface. The lunar base is not shown because it hadn’t been designed yet when the picture was painted. All three paintings were done by Jack Olson, a skilled artist/engineer I worked with at Boeing Aerospace.

Figure 2 RLLV landing on the lunar surface

Figure 3 ABOTVs returning from the moon to Earth Orbit

The ABOTV’s were designed to be assembled inside a reusable aerobrake permanently deployed and rigidized In LEO at the Space Operations Center (SOC). The rocket engines extended their nozzles and thrusted through a hatch in the aerobrake base. The Aerobrakes were designed to be reused ten times and then refurbished on orbit as required. The combined performance and costs for a LOX/LH2 fueled ABOTV/RLVV combination is shown in Figure 4 below.

Figure 4 Performance and Cost Comparisons for Various RLLV Refueling Options

I’m comparing three different lunar lander refueling options in figure 4. For each of these refueling options I have looked at three different payload masses so we can size the overall systems. The first three columns assume the RLLV is based and refueled in a 100 km Low Lunar Orbit (LLO). It receives the payload and propellants, deorbits, lands, unloads and returns to LLO each mission. This is the minimal lunar infrastructure model since it doesn’t require LOX and LH2 to be produced on the lunar surface. It is a good option since each lander can service multiple locations on the moon. Additional design requirements are imposed because 1) the orbit is unstable, and 2) the moon takes 27.3 days to rotate so consecutive landing opportunities are 13.65 days apart. This option is competitive.

The middle three columns assume the RLLV is based on the lunar surface and in situ propellants are generated for each roundtrip to LLO. This option requires the least mass in LEO for each kg landed on the lunar surface (best gear ratio from Chapter 5) but requires a LUNLOX plant (Ref 1) and a nuclear-powered Regolith Miner (Ref2) to be designed, built, tested, and operated at each landing site. More details are in Chapter 8 of the book. In effect this option trades better gear ratio for higher up-front costs and reduced operational flexibility.

The last three columns are a compromise system where RLLV LOX is produced on the moon and RRLV hydrogen is supplied from Earth. It eliminates the need and cost of a special purpose Regolith Miner to harvest hydrogen from the regolith, but that in turn greatly reduces the harvesting of water, CO, Carbon Dioxide, He3, Nitrogen, and other gases vital to a colony. We’ll see how this option racks up cost-wise relative to the other two options.

To compare Starship with our three ABOTV/RLLV options I will assume that we need to deliver multiple 20 mT payloads to ten various mining bases and/or research facilities scattered over the lunar surface. I picked 20 mT because my numbers say that is the maximum the Starship can deliver to the lunar surface and return to earth empty. I assume six visits to each facility each year with 20,000 kg down and 500 kg up. Over a twenty year period from starting the design of the lunar transportation systems and surface systems, through Design, Development and Test (5 years), initial deliveries to the moon (three years), and final exploitation of the moon (12 years) I get a total transportation cost of $17.5 B (2020 $) for option one (RLLVS based in LLO), $14.4 B for option 2 (All RLLV Propellants produced on the surface at each facility), and $13.4 B for option 3 (LOX produced at each facility and LH2 brought up from Earth. This compares to the all Starship delivery cost over twenty years of $68.2 B. The Starship costs are large because it takes six Starship tanker launches to refuel each Starship going to the moon. The gear ratio is lousy.

The bottom line from this study is that the ABOTV/RLLV combination is way more cost effective than Starship operating as a lunar transportation system all by itself. As to which of the three options shown is best, they all have their advantages and disadvantages. Option one is more flexible because a lander can land anywhere (provided some are in high inclination orbits) for rescue or to start new facilities. Option two makes bases more or less totally independent of constant Earth support, but costs more than option three which relies on Earth for hydrogen. I suspect the final system will be a mixture of these options with option one used early on and a gradual switch to option three and eventually to option two. Likewise, lunar payloads may start at 20 mT but I suspect a switch to 40 mT as ABOTVs and RRLVs evolve. Remember that Starship provides the Earth to Orbit (ETO) transportation for all of these options. Low cost launch is the key to the good ROIs predicted from lunar mining.


1. Eagle Engineering, Inc.,” Conceptual Design of a Lunar Oxygen Plant”, Lunar Base Systems Study (LBSS) Task 4.2, NASA Contract NAS9-17878, July 1, 1988.

2. Gajda, M.E., “A Lunar Volatiles Miner”, Master’s Thesis, Engineering Mechanics, University of Wisconsin, 2006.

Thanks for reading.

Dana Andrews


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