After yesterday’s SpaceX announcement of having booked two customers for a Apollo-8 style mission around the Moon and back, using Falcon Heavy and Dragon V2, I got thinking about ways to take the next step in lunar tourism–surface missions. Now, this “White Dragon” mission around the Moon makes a lot of sense for SpaceX even though Elon doesn’t care that much about the Moon:
- Hardware-wise, there really might not need to be much new work beyond what they’re already doing for Falcon Heavy and Dragon V2. The flight is short enough relative to a worst-case ISS delivery that with 2 passengers instead of 7, the ECLSS is probably already adequate. The heat shield, due to minimum gauge issues with PICA-X, is way overbuilt for LEO return, and thus is likely more than adequate for lunar return.1 The Falcon Heavy should have the throw-mass to do the mission. So they can do this without likely requiring dramatic hardware development beyond what they need for normal FH and crewed Dragon V2 flights.
- It’s revenue–even if it costs say $170M/flight (take a ~$140M cost for a four-person ISS delivery, subtract 60M for the Falcon 9 and add 90M for the Falcon Heavy), they can still get takers at a price of ~$85M each. Heck, even if they’re selling it through Space Adventures for $100M each (with the $15M delta being Space Adventure’s cut), this is still a good deal for SpaceX. They only have to convince two people, and they get double the revenue of a Falcon Heavy flight. That’s not quite as good as selling a several flight campaign for Iridium, but it’s not too shabby, especially if Space Adventures or someone like them is bringing the passengers.
- There’s a good chance it could turn into a steady stream of revenue. As I’ve previously discussed here, one of the main limitations on space tourism has been availability of spare Soyuz seats, not the price. And when you add the novelty of a lunar mission, I wouldn’t be surprised if they could get a steady White Dragon mission every year or every other year at worst. Even if the price doesn’t come down much over time.
- It gets them experience they want for future deep-space operations. Testing reentry heatshield wear, ECLSS behavior on long missions, how their electronics hold up outside the magnetosphere, etc.
So for all those reasons, it makes sense for Elon to say yes to White Dragon missions, even if he doesn’t care at all about the Moon. If someone wants to give you money like that, and it doesn’t cost you much to service them, why the heck not?
But as soon as you start talking about lunar landing missions, the situation changes. Now you’re talking significantly more complicated missions that are going to take non-trivial amounts of new hardware, that will unlikely be directly relevant to Mars missions. Barring someone dropping a bunch of money in Elon’s lap, I’m not sure it would make sense for SpaceX to do the mission by themselves. But, it might be an intriguing joint mission for SpaceX and ULA, assuming for sake of argument that Elon would be willing to work with his closest competitor, and that Boeing and LM wouldn’t torpedo something that could be seen as a direct competitor to SLS/Orion.
So, assume away the political challenges for a second. Could you realistically make a lunar landing mission work with a combination of SpaceX and ULA hardware? After running the numbers, I’d say tentatively yes.
Here’s what the SpaceX stack would look like:
- Falcon Heavy
- Large LOX/LH2 tanker (~39.4mT of prop, ~7.2mT dry)
- Dragon V2 on top
The ULA stack would look like:
- Vulcan/ACES 546, with the ACES having a Xeus landing kit (~1mT)
- Small short-duration two-person crew cabin (estimated ~2mT)
Falcon Heavy would launch first, placing the crew and tanker in orbit. Vulcan/ACES would then launch shortly thereafter, with ACES performing a rendezvous with the SpaceX stack, transferring ~39.4mT of prop over (basically filling the ~70mT ACES stage). The Dragon would then separate from the tanker, and connect to the ACES/Xeus stage. The ACES Xeus stage would do a TLI burn for the stack, followed by an insertion into LLO. Dragon would then be left in orbit while the astronauts are flown down to the lunar surface by the Xeus stage, hang out for a while, and then they get flown back up to LLO by the same Xeus stage. The Xeus stage would then dock with Dragon and perform the LOI burn, sending the whole stack back to earth.
Using these assumptions, it looks like the concept closes (here’s the first-pass analysis spreadsheet: WhiteDragon-XeusCalcs), but without as much margin as you would want, and without enough propellant to propulsively capture Xeus back into LEO.
Here are some ways that the concept could be improved:
- Be more aggressive on the lander cabin design–2mT is actually half the dry mass of a Dragon Capsule, in spite of not needing anywhere near the capabilities–no need for a trunk or a reentry shield, no need for RCS engines (ACES and Dragon V2 both have plenty of maneuverability). So you might be able to whittle that down a bit.
- Use chilled propellants–between the Vulcan/ACES 546 leftover propellant and the Falcon Heavy tanker propellants, there’s actually more propellant than will fit into a stock ACES stage at normal boiling point densities. Chilling the propellant would both surpress boiloff losses, and would also allow you to cram a bit more propellant into the stage. This is already something SpaceX does for Falcon 9, so it isn’t that crazy.
- Stage in EML2 and have the Dragon V2 perform the earth return burn leaving Xeus at EML-2. The question is how much propellant is needed for rendezvous, reentry, and landing. By my BOTE calcs, assuming a 320s Isp on the regular Dracos, you should be able to get ~620m/s of delta-V out of Dragon V2, and you’d only need ~150m/s for the earth return/powered swingby maneuver. But you’d now be talking about a much, much longer mission.
- Jettison the lander cabin and/or Xeus kit prior to the earth return burn.
- Have the lander cabin actually be a separate lander/ascent stage. Have the ACES stage not have a Xeus kit, but do an uncrasher maneuver where the crew cabin stage separates right before landing. the ACES stage returns to lunar orbit w/o the ascent stage, and reconnects with the Dragon capsule. The ascent stage lands, the crew hangs out for a bit, and then launches again back up to the waiting Dragon and ACES stages. The crew cabin/ascent stage is left in LLO before ACES takes Dragon back to Earth.
- Down the road adding refueling in LLO or EML2 or on the lunar surface would make the whole thing tons easier–you’d need another launcher, but that would all of the sudden give you the margin needed to do much more ambitious missions if you didn’t have to haul the prop all the way from LEO and back.
There are probably other variations on the theme. But the interesting thing is that this concept comes close to closing using Falcon Heavy, a stock Dragon V2, with the main pieces of new hardware being a propellant tanker section for Falcon Heavy2, the Xeus kit for ACES, the fuel transfer hardware, and the crew cabin.
If you assume $150M for the Vulcan/ACES 546 flight ($90M for the bare Vulcan/ACES plus six strapons at $10M/ea), $170M for the FH + Dragon V2, $20M for the tanker/transfer hardware, and $30M each for the Xeus kit and the crew cabin, you get about $400M/mission, or about $200M/person (plus markup if your brokering it through Space Adventures). Call it an even $250M/person ticket price. That’s about 1/3 of what Golden Spike was targeting…
Anyhow, rockets aren’t legos, who knows if Elon and ULA can play nice with each other, I have no idea how ULA would get its parents to go along with a scheme that enables lunar landings without needing SLS/Orion. But the concept comes really close to closing, so I thought I’d put it out there.
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- And frankly we know a ton more about lunar return reentry heating and how to simulate/test for it than we did at the time of the Apollo program, so I’m not too worried about the heat shield not holding up.
- This will likely look weird, since you’d probably want to leverage ACES tankage for the job, which would have the Falcon Heavy looking like a weird cross between the spacecraft version and the Dragon V2 version.
Apollo 8 didn’t fly a free return. It went into orbit. I know the free return sort of looks like an 8, but they didn’t fly that.