[Author’s Note: Back in summer of 2019, shortly after Mike Pence announced the goal of having NASA return astronauts to the lunar surface for the first time in over half a century, I had the idea of doing a blog post about the benefits of fully-reusable lunar landers, and then going over a few of my favorite unorthodox reusable lunar lander configurations. I got side-tracked at the time by my entrepreneurial day job1, and by the time I freed up from that, Altius was busy supporting one of the three Artemis HLS teams, so I felt a blog post like this might be impolitic. Now that we’re no longer actively supporting that team, and given that I no longer have running a startup as an excuse for not blogging, I wanted to finish fleshing out these ideas and at least get them out there for discussion.]
While traditionally most lunar landers and lander conceptual designs have been fully-expendable, many people, including NASA have begun to see some of the benefits of reusable lunar lander systems. Some of those benefits as I see them include:
- Lowers the cost of sending hardware to the Moon: This is the obvious one that people get about reusability, is that so long as it’s done right, it can significantly lower the per mission cost, especially if the lander can be reused many times over its lifetime.
- Makes the program easier to throttle up or down: One of the big challenges the Augustine Commission noticed for NASA Human Spaceflight missions was that they could rarely afford to both develop new capabilities while operating previous ones. With a fully-reusable lander system, especially one designed to not require a huge standing arm to support it, much of the cost of a given mission could be the marginal cost of launching new crew/cargo/propellant, which means it’s easier to throttle down temporarily without losing the capability.
- More amenable to non-critical-path international participation: With reusable landers, once they’re launched, incremental missions mostly require refueling, reprovisioning, and a crew swapout. Government space agencies typically don’t want to spend money outside of their country–they typically try to find a way where they can handle things through barter and no-exchange-of-funds agreements. For instance, in exchange for getting some of the ISS crew slots, Japan and ESA both developed cargo vehicles to bring some of the cargo that ISS needed. So they could spend their space agency money locally, and use that contribution to get ISS astronaut slots without having to develop their own crew launch capabilities2. Reusable lunar landers provide an easy barter option for international participation in NASA lunar missions — launching propellant and/or cargo. The nice thing is that if done wisely (say using a Low-Orbit HSF Depot in LEO), this might require minimal development cost for foreign countries, while allowing them to usefully contribute, but in a way where they’re not on the critical path, and they can throttle up or down their involvement as desired.
- Creates near-term demand for lunar ISRU: Once you have reusable lunar landers, the vast majority of the mass needed per mission is propellant. Being able to source that locally could significantly reduce the cost of missions3, and could increase the capability of landers by enabling them to be refueled both in orbit and on the surface4. With reusable landers, you have established demand at an established price point, which makes closing the business case for lunar ISRU easier, so long as you can truly extract it cheaper than shipping it from Earth5.
- Enables a much more ambitious exploration program: This should be obvious, but once you have reusable landers, you have tons more flexibility for doing things beyond simple flags-and-footprints missions. Things like lunar search and rescue, doing suborbital sorties from a bigger outpost to explore areas of economic or scientific interest, etc. become more feasible.
Anyhow, if you’re reading this blog, I’m probably preaching to the choir here, but I wanted to lay out some of my thoughts on why reusable lunar landers matter.
Unorthodox Reusable Lander Concepts
Given the desirability of fully-reusable lunar landers, it’s sad that most of the best-known reusable lander concepts have used a very similar landing configuration — tall skinny landers with the crew and cargo mounted on top.
In this series I wanted to highlight a few other potential fully-reusable lander configurations worth considering, some thoughts on variations on the themes, and their pros and cons. Only maybe one of these configurations is one I could claim to have invented, but I thought it would be worth highlighting some other good ideas that may or may not be as well known, especially to younger space engineers or enthusiasts.
In the following parts I’d like to discuss the following reusable lunar lander configurations:
- Bottom-loader SSTOs
- Horizontal-landing SSTOs
- Un-Crasher TSTOs
I may think of and add additional configurations later if time permits. But next up: Bottom-loader SSTO landers.
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- That summer we were recruiting a full-time VP of Business Development for Altius, and then got sucked into several strategic investment/M&A conversations that ultimately led to Voyager majority-acquiring Altius. So yeah, life was kind of hectic
- One other approach I’ve seen is the concept of “offsets”, where say a foreign country agrees to buy some US aircraft in exchange for having the aircraft company establish some part of their production capability in that country to create local jobs. I haven’t seen that used in space applications as much so far, but it might be a palatable alternative to the barter approach used for space missions
- Yes, I know a lot of people think RLVs will magically make lunar ISRU irrelevant, but I don’t think that has to be the case. It’s a point for another blog post though.
- This benefit is amplified if you have a propellantless way of getting propellant into orbit, but once again, that’s a topic for another series
- Which I believe to be the case
At some point I need to post a few numbers on a layover concept. Tall skinny lands and after stable tips over on two legs with “landing rockets” in the nose to bring the velocity to zero at horizontal with another couple (or sets) of legs to catch it. For launch the “landing rockets” in the nose bring it back vertical before launch. Somewhere around 20 m/s V for the upper section depending on height and configuration.
Does reusable lunar lander land on pad or can also land “in the field”?
Musk is going to catch the first stage of starship.
I am sort of, ah we will see, but is needed to have reusable lunar lander be able to land anywhere on Moon or have limited to be able land in a spot which has prepared for it to land on. If it’s limited, then need another lunar lander which may not go orbit, but it can land anywhere on lunar surface.
A lift vehicle like Falcon uses might be attractive for a mid-sized or larger vehicle. Balancing side loads using thrusters would not be fun and the increased structural requirements might outweigh a crane/elevator arrangement even in low gravity.
It would depend entirely on the lander. A large base supply vehicle such as an unmodified Starship might want a pad but anything else should be fine without.
One thing I find interesting about Moonship is just how impractical the design really is due to the height but they still come out ahead because they aren’t crippled by launcher limitations. Even the NHRO foolishness isn’t a problem for it.
That said what I’d really like to see is a vehicle capable of Lunar P2P2P. (From any point on the lunar surface to any other and back again.) That would be the ideal setup for both field work and secondary outposts operated from an established primary base. I’m looking forward to seeing what these unconventional designs might offer here.
On the ISRU topic, I think RLVs are what make it relevant. You need a long-term presence in one location to make it worth the cost and RLVs are what make that possible. For infrequent short term missions it just isn’t practical.
I had an idle thought about this while considering the Dynetics Alpaca lander as a choice for hopper (lunar P2P). If it were up to me, I might want to resurrect the Golden Spike “lunar jetranger” lander (so called because it bears a passing resemblance to the Bell Jetranger helicopter of yesteryear). In addition to hopper duties from a moonbase, you could ship a pair of them to lunar orbit in the hold of a standard Starship, along with extra fuel, and deploy them for repeated sorties to various points on the lunar surface (maybe one making a sortie while the other stood by as a rescue vehicle). You could do a lot of preliminary exploration that way, both as a sortie lander and as a hopper.
What ever happened to the TSTO concepts that used an upper stage connected to the lander via rotating tether to drop local velocity of the lander on drop (and throw the upper stage higher), along with a catch op with fast reel in and upper stage boost back up to higher orbit for going up?
@N/A I proposed a tethered landing system for a group project this semester (we got the landing stage for free in the project, so it would have made our ascent stage free too), but alas we “needed” to launch by 2025 and I can’t prove the TRL for the system. I really believe in that concept though, and it would be so dang cool to watch: an elevator to the heavens
What a tease! It’s already April 2022.
I think the Dynetics ALPACA already covers configuration alternatives 1 and 2.
I take a shot at describing alternative 3, over at Space News.
I can’t even use the excuse of running a company getting in the way of my blogging anymore. Sorry. ALPACA is close to #1 and #2, but there are other variations on the theme I had wanted to consider.