One of the commenters on last night’s post wanted to see some more information on how I came up with the results I’ve been discussing. Well, I finally broke down and figured out how to use Google Spreadsheets, and here is the spreadsheet with the details.
The surprising thing I found was that if you assume LOX/LH2 for the lander using an RL10 as a baseline engine (since they are off-the-shelf, and have been used for throttling and VTVL applications before), that you can actually do a two-man sortie using only two EELV launches. I usually have done most of my analysis assuming the landers use LOX/Kerosene or LOX/Propane, as those are closer to my experience base with LOX/alcohol. However, I was trying to come up with an architecture that used existing boosters and stages as much as possible, and I found that LOX/LH2 for the landers actually makes that feasible.
The other thing that made this architecture possible was using Weak Stability Boundary trajectories for the unmanned landings. I first heard of WSB trajectories from the t/Space CE&R report. These rather complicated trajectories use multiple lunar encounters over a 3 month period to more or less eliminate the need for the Lunar Orbit Insertion burn. The required Delta-V from LEO to LUNO drops from ~4.2km/s using a normal 3-day Hohmann transfer to ~3.2km/s using a WSB transfer. While 3 Months in deep space is a long time, the Centaur guys at Lockheed have design ideas for keeping boiloff reasonable over that long of a period. This enables the cargo launches to also be two-vehicle missions.
The basic architectural blocks for this system are:
- The Single Engine Centaur: This is a stock SEC as used on the Atlas V launch vehicle, with a lunar-mission kit attached. This mostly consists of things like solar cells, long-duration navigation hardware (stuff like star-trackers), extra MLI on the tanks to reduce boiloff, and things like that. All of these have been under development there at LM.
- The Single-Stage Multi-Purpose Lander: This is a light, LOX/LH2 lander based around a similar construction technique to that proposed for the Wide Body Centaur. The lander can carry either a 5klb crew capsule on a round trip, drop-off a 15.5klb cargo pallet on the lunar surface (with the lander returning to orbit), or haul a full 19.9klb Sundancer module all the way to the lunar surface (with the lander staying on the surface either to be cannabalized, or to be refueled from a cargo landing). The lander itself is reusable, so eventually you only have to send propellants for it instead of having to ship the lander ever time.
- The Crew Capsule: This is a light, 5klb crew capsule. The Lunar Module Ascent stage weighed less than 4500lb, including the weight of the propellant and pressurization tanks, the main ascent engine, and a bunch of 60s era electronics and batteries. Using modern materials and electronics, this capsule can probably be quite a bit roomier than the LM was, though they will likely still be a bit cramped. This capsule includes some RCS engines, a reentry heat shield, and parachutes.
For each of the three mission sorts (manned, Sundancer landing, or cargo dropoff), a single Delta IVH places the fully fueled Centaur stage into orbit, and then an Atlas V launch (a man-rated 401 for crew, or a 531 for either Sundancer or cargo delivery) places the rest of the mission payload into orbit, where they rendezvous and dock. The Centaur then performs the TLI burn. In the case of the manned missions, the Centaur also performs the LOI burn, and the TEI burn after the crew returns from the surface. All of the missions were designed assuming at least some boiloff, and including some extra Delta-V to make up for contingencies.
This isn’t the absolute most perfect architecture in the world, but it’s an inexpensive and simple one that gives a lot of flexibility. The ideal architecture would probably use fully reusable landers that had multiply redundant engines, that used WBC derived reusable transfer stages, and that used both on-orbit propellant transfer and lunar ISRU derived propellants to continually drive costs down while driving performance up. But this is a simple, straightforward, low-risk, near-term feasible technical solution.
Between existing Atlas and Delta IVH capabilities, up to 10-12 missions per year could be accomplished without adding new pads or infrastructure. At that flight rate, a lunar sortie would cost about $300M for a manned or a cargo mission, and probably an extra $100-150M for a Sundancer mission. And that’s assuming no Wide Body Centaurs, no on-orbit propellant transfer, and no new lower-cost launchers. If on-orbit propellant transfer comes on-line, you can get rid of the Delta-IVH launches and extra Centaur stages and just refuel the Centaur used for launching the capsule and lander. That would cut the mission costs about in half to $160M for the manned and cargo missions and $260-310M for the Sundancer mission.
So, ignoring the on-orbit propellant transfer for a second, we find that for just the fixed annual costs of the ESAS architecture, you could put:
- Two Sundancer modules down at 1-2 locations
- Four Two-man teams at 1-4 outpost/sortie locations
- Three 7mT cargo pallets down at 1-3 different outpost/sortie locations
The coolest thing is that you only have two pieces of hardware that need to be developed for this architecture: the capsule and the lander. While they are a bit sophisticated, neither of them ought to take more than 2-3 years to field. Which means that you could start having lunar missions again this decade.
Mark Whittington likes to poke fun at a 2-man architecture calling it the “Incredible Shrinking Moon Mission”, but I kind of prefer it to the “Rapidly Receding Moon Mission Schedule” which promises Apollo-on-Steroids but keeps pushing the landing date out a year for every year of real time. When Bush announced it, the first landing was supposed to be in 2015. Then it was 2018. Now it’s possibly as late as 2020. So what started as an 11 year schedule when Bush proposed it is now a 14 year schedule in spite of the fact that it’s now two years later…Me, I’m a fan of Lunar Sooner (and Better).
Anyhow, whoever the anonymous commenter was, I hope he enjoys the spreadsheet.
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