Waiting for a Pump-Fed Methalox Lunar Descent Engine

[jongoff]

And, if that isn't crazy enough, you could "exchange" landers, have one coming and one going, sharing an uncrasher stage's propulsion all at once on the same trip. No room at all for contingencies, however, for cargo/resupply this might be possible albeit quite a tour de force.

I don't know if I ever ran the numbers on that scenario, but it was an idea I mentioned at the end of this blogpost back in 2013:

http://selenianboondocks.com/2013/09/centaur-uncrasher-stages-for-simplified-lunar-landings/

One of my few regrets about running a startup is not having the time to run numbers on crazy ideas like this. Maybe some day we'll be profitable enough that I can afford hiring someone or sponsoring some grad students just to run simulations for me. :-)

~Jon

[TrevorMonty]

Liked your depot fiso talk, pity you run out of time for more Q&A.

When I did rough calculations on uncrasher stage (OTV might be better description) I was thinking of human landers. Your idea of using for small cargo landers has lots of possibilities. In some ways it is better than a XEUS lander as payloads only need to handle forces in one direction.
If lander attaches to OTV and it's LV via it's base all major forces are in downward direction. With XEUS launch and orbital burns are horizontal compared to landed position.

Having propulsion the lander can rendezvous with OTV after being dropped off by LV.

The OTV dry mass can be less than ACES US as it doesn't need to handle launch stresses with payload. Plus development costs are lot less than XEUS. Lander should be straight forward and low cost, especially for likes of Moon Express and Masten. With refuelling at LEO and EML1 a 30t OTV could land close to 20t.

[sevenperforce]

The ITS is planned to use 10-tonne metha(l)ox-gas thrusters for RCS, fed from the autogenous pressurization coolant loop of the Raptor.

The dev Raptor is smaller than the final design, at around 1000 kN SL thrust; I'd project around 1150 kN vacuum-optimized thrust.

If you built a methalox upper stage for Falcon Heavy based around two of the dev Raptors and gave it a few of those gas thrusters (dual thrust-axis lander design), then refueled it in cislunar space, it could perform most of the landing burn using its main engines and just use the gas thrusters for the last little bit of the burn. It would have no trouble carrying enough fuel along with it to return to lunar orbit, or even to an Earth entry trajectory.

[spacenut]

If worried about batteries, a landing could be done at the begining of the 2 week solar cycle, and lift off near the end, with limited battery needed.  It would allow for about a 1-1/2 week stay before getting back into lunar orbit and docking with mother ship or moon station. 

[Steven Pietrobon]

Secondly, I reject any proposal that abandons its descent stage and engines. The propellant required to send a new descent stage from Earth to LLO far exceeds the propellant required to return that stage from the Lunar surface to LLO.

You're forgetting the extra LM propellant and the extra stage mass required to hold the extra propellant that you need to send from Earth. That extra two or three tonnes of stage mass that you "save" from not sending from the Earth requires an extra 10 to 15 tonnes of propellant that you need to send from Earth into low Lunar orbit (LLO). That is the extra amount of propellant that is required to reuse the whole LM (plus you now got the problem of your ascent engines possibly being damaged during landing). At say $25,000 a kg into LLO, that works out to $200M to $300M extra that you need to pay. That's probably about the same price for a separate descent stage. Just reusing the ascent stage makes more sense and should make operations easier, since you just plugin in a new descent stage with its payloads to your ascent stage and have the descent stage refuel the ascent stage.