I did some tweaking of my Lunar Much Sooner architecture. The latest numbers are available here. The original post about this architecture can be found here. I’m still basing this on existing rockets and stages (with the only modification being a partially developed “Lunar Mission Kit” for the stock Centaur stage), as with previous versions. The lunar lander is still sized for the Sundancer delivery mission (with some modifications described below), with the 2-man missions using a lander that has substantial propellant offloaded from it.
The main changes were:
- I increased the weight allotment per crew + seats to 250lb each from the 150lb each original assumed. That should open up missions to a wider range of people.
- I assumed a much higher delta-V required for WSB trajectories. I’m still not familiar enough with these trajectories to be too comfortable with them, and at least one source I saw seemed to imply that the lower WSB delta-Vs were for insertion into a highly elliptical lunar orbit. And that once you added in the burn to drop down to lunar orbit, you’d be looking at ~3.7-3.8km/s total Delta-V.
- The constraint of using only existing launchers, with no propellant transfer, and only using existing stages (ie no Wide Body Centaur derived stages) forced me to assume that the Sundancer for use with this architecture is “offloaded” a bit for the landing. Some of the Sundancer weight quoted in the original Space.com article is for subsystems that wouldn’t be needed for a lunar base Sundancer. There are also some subsystems and consumables and stores that don’t implicitly have to be shipped with the Sundancer, but could be loaded/installed at a later date. When I was on my tour of Bigelow Aerospace two years ago, they mentioned the fact that a decent chunk of the mass for a station module could be sent up on a second flight if absolutely necessary. In order to make the numbers work with a little bit of margin, I needed to cut it down to about ~15klb. That means that somewhere around 5000lb of cargo from the first cargo lander would be needed to fit out the station.
- Since I no longer needed a lander to bring the full Sundancer station down from LUNO, I decided to shrink the lander itself by a similar percentage (going to an 1800lb dry, 12klb wet lander stage–ie still using the 15% dry fraction assumed previously).
- The lighter lander stage allowed for more mass on the manned missions to be allocated to the capsule section as well as to the “light crew cabin” section, while still maintaining margins similar to what was discussed previously. Now the capsule mass is within a couple hundred pounds of the mass assumed for the Early Lunar Return missions.
All in all, I think the exercise is still relatively useful, even if there is almost no chance that NASA would be interested in this approach. I think the rough sizing for the lander is probably in the ballpark of what would be desirable for commercial/multinational projects, and there are several important lessons I’ve learned so far. Here are a few thoughts of how this idea could be improved substantially:
- One of the two most annoying constraints for this strawman architecture has been sticking with existing upper stages as the base for the lunar transfer stage. Both Centaur and the DIVH upper stage are just a little too small for practical purposes. Using existing Centaur stages without propellant transfers makes everything a lot lower-margin, and requires everything to be more weight-optimized.
- Once you have propellant transfer capabilities, there isn’t a single element of this mission that couldn’t be launched on a stock Atlas V 401/402, Falcon IX, Zenit, and many of the components could be launched on Delta-IVMs if push came to shove.
- Wide Body Centaur technologies make everything in this architecture a lot easier. With a 1.5x WBC derived transfer stage, you don’t need to offload anything from the Sundancer lunar base module (and can go with the slightly bigger lander). WBC derived modules should have much lower boiloff losses, which is one of the areas that I think this architecture is likely to have the biggest challenges with. A WBC derived transfer stage could take a Dragon/”Human-Rated-Atlas-Capsule” all the way to LUNO, and then provide a Trans-Earth-Insertion burn.
- The lander (whether the 75% sized one assuming a normal Centaur transfer stage, or the full-blown one with a WBC stage) is big enough to land a much larger “crew cabin” if you top the tanks all the way up. Depending on which lander size you’re looking at, you could transport up to 6-8 people at a time to and from the lunar surface using a bigger crew module. You’d have to use either a LUNO way station, or a split mission (ie you send the lander and the crew separately), or use propellant depots, etc.
- A reusable lunar lander has enough performance to ship itself (and a decent amount of cargo) to lunar orbit from LEO (the required Delta-Vs are very similar).
Anyhow, that’s just the technical thoughts I had. I’ve been mulling over the best way to proceed on such a project, if one were looking at it from a fully commercial approach, and it is obvious that the path is quite a bit different than if you were trying to do things as part of a publicly funded project (or one funded by a very rich philanthropist who didn’t care about ROI). For a commercial lunar architecture, each step has to be developed incrementally, and if at all possible needs to be financially self-supporting. Figuring out exactly how to do this (ie what sequence of technologies and markets to take, how to finance things at different points, etc) makes the CM power-up problem shown in Apollo 13 seem like childsplay in comparison. I may try to work up some of my thoughts on the problem for the ISDC conference (which it is now looking like I’ll be able to attend–Thanks to all of those who’ve tossed money in the tip jar!), but until then, I’ll try to toss out random thoughts, and pieces of the solution as I go along.