Quote from: Steven Pietrobon on 11/25/2016 03:57 AMQuote from: brickmack on 11/25/2016 01:57 AM(estimates I've seen before being ~30 tons to the lunar surface with only refueling in LEO, ~350 tons with refueling in lunar orbit after ascent, even the first of which is well beyond what previous studies indicated necessary to build a base)Is there a reference for that 30 t value? My calculations show that a Direct Lunar mission (using refueling in LEO) gets a cargo mass of -36.7 t, which means the scheme won't work since you need a have a payload with negative mass!https://www.reddit.com/r/spacex/comments/55k1f4/its_moon_landing_payloads_and_costs/ he finds 38 tons direct, 380 tons with lunar orbital refueling, I rounded down a bit to accommodate some safety margin and slight underperformance. Odd inconsistency here though. I'm trying to figure out where both of you got the delta v numbers from, neither matches up well with charts I've seen before. The guy on reddit has a higher delta v for "earth orbit to moon orbit" than you have for TLI+LOI, lower delta v for ascent and descent, lower for TEI, and higher for earth EDL, but the total delta v values only differ by about 500 m/s (9.7 km/s for the reddit post, 10.2 for yours), which isn't enough to explain such a huge discrepancy in payload capacity. And it looks like you're using the same mass and ISP values. He doesn't give his full calculations though, just spreadsheets

Quote from: brickmack on 11/25/2016 01:57 AM(estimates I've seen before being ~30 tons to the lunar surface with only refueling in LEO, ~350 tons with refueling in lunar orbit after ascent, even the first of which is well beyond what previous studies indicated necessary to build a base)Is there a reference for that 30 t value? My calculations show that a Direct Lunar mission (using refueling in LEO) gets a cargo mass of -36.7 t, which means the scheme won't work since you need a have a payload with negative mass!

(estimates I've seen before being ~30 tons to the lunar surface with only refueling in LEO, ~350 tons with refueling in lunar orbit after ascent, even the first of which is well beyond what previous studies indicated necessary to build a base)

Quote from: A_M_Swallow on 11/24/2016 04:11 AMSpace stations, tankers and propellant depots in lunar orbit will need station keeping. A set of ion thrusters should be able to supply this.Too small for two thousand tonne tankers. Fully loaded ITS tanker is 5-6x ISS mass, and lunar orbits are unstable for most part. Fine for Orbital Outpost (maybe 100 tonnes) in high orbit or EML-1/2.

Space stations, tankers and propellant depots in lunar orbit will need station keeping. A set of ion thrusters should be able to supply this.

I think "for the most part" is important. There are a small number of stable "frozen" lunar orbits that can be used for longer duration missions with very little station keeping. [See discussion of Frozen Orbits here: https://science.nasa.gov/science-news/science-at-nasa/2006/06nov_loworbit ]

OMG, Pascal. I am old enough to have a few stacks of punchcards encoding batch FORTRAN code I wrote back when Pascal was a spiffy new programming language, all the rage for use as a teaching language, all clean and strict about good programming technique.

Anyway, just to make sure to have something on-topic, I did want to highlight the general concept you employ: The exponential nature of the rocket equation delta-V budgets can be a killer for out-and-back missions, but you can sometimes soften the requirements by caching propellant at one or more stops partway out, in the mode of basecamps for mountaineering, where each expedition helps the ones that come after.

https://www.reddit.com/r/spacex/comments/55k1f4/its_moon_landing_payloads_and_costs/ he finds 38 tons direct, 380 tons with lunar orbital refueling, I rounded down a bit to accommodate some safety margin and slight underperformance. Odd inconsistency here though. I'm trying to figure out where both of you got the delta v numbers from, neither matches up well with charts I've seen before. The guy on reddit has a higher delta v for "earth orbit to moon orbit" than you have for TLI+LOI, lower delta v for ascent and descent, lower for TEI, and higher for earth EDL, but the total delta v values only differ by about 500 m/s (9.7 km/s for the reddit post, 10.2 for yours), which isn't enough to explain such a huge discrepancy in payload capacity. And it looks like you're using the same mass and ISP values. He doesn't give his full calculations though, just spreadsheets

I was just about to post my own numbers when I saw this. Working through the numbers, I think the difference is whether you go to lunar orbit first or straight to the lunar surface (obviously a more risky approach but maybe worth it for lower-value payloads) and how much you budget for Earth EDL. Using the numbers from the Wikipedia page on delta-V budgets for a direct landing (5.93 km/sec from LLO to Lunar surface, 2.80 km/sec from Lunar surface to C3=0, 0.75km/sec EDL) gives a total dV of 9.48, for a mass fraction of 12.61, and a payload of 18t. (Adding Steven's 2% margin, gives 9t). Still, you can do a lot better with Steven's LLO propellant transfer scheme.

Here is my spreadsheet.https://docs.google.com/spreadsheets/d/15kgq-0x6BKnNXGO9WFKfjhtE42WJncbpZHq3VHoQ3OA/edit#gid=081 tonnes payload delivered to the moon.

Quote from: MikeAtkinson on 11/27/2016 01:27 PMHere is my spreadsheet.https://docs.google.com/spreadsheets/d/15kgq-0x6BKnNXGO9WFKfjhtE42WJncbpZHq3VHoQ3OA/edit#gid=081 tonnes payload delivered to the moon.Thanks for putting this together; it is very easy to understand!But just to clarify the obvious: is the requirement that ITS must eject 81 tonnes of mass at the lunar surface for the mission to "close?"

I used the spreadsheet provided by MikeAtkinson as the basis for a look into whether propellant transfer between ITS ships in an orbit used by a deep space habitat could enable delivery of cargo to both the hab and then subsequently to the lunar surface.

What would the numbers look like, if assuming ISRU LOX from lunar surface? Somewhat better I assume, but how much?

Quote from: J-V on 11/30/2016 12:24 PMWhat would the numbers look like, if assuming ISRU LOX from lunar surface? Somewhat better I assume, but how much?Without numbers, a lot better, given that LOX is most of propellant by mass. They could land empty of LOX. Somehow it feels like a waste though to process water to LOX and release the hydrogen for lack of CO2. Also water would imply the poles.I have recently seen there is work to produce oxygen from SiO2. A process that would extract the oxygen using electrolysis at very high temperatures provided by concentrating sunlight. This could be done everywhere on the moon.I like the concept of Steven Pietroban leaving return propellant in orbit more though. No massive ISRU needed and still more than 100t payload to the surface.