Clever, I've never considered having the lander leave its return fuel in LLO.
Quote from: TrevorMonty on 11/23/2016 08:24 amClever, I've never considered having the lander leave its return fuel in LLO. I thought of this technique quite a long time ago. It was called Lunar orbit propellant transfer with the idea of transferring LOX produced on the Moon to the next craft coming in to land. I was a bit bummed when my paper got rejected by the BIS.
I love the idea of leaving propellant in orbit for the return flight. The problem with this is it only works in a constant chain of flights. Maybe the ITS would stay on the moon until the next mission. Like crew capsules on the ISS. I am not sure this is the best operation though. Conditions on the moon are harsh for a spaceship with the long days and long nights. Very different to LEO or deep space.Alternatively there could be a depot in lunar orbit. ITS fills it on the way down and takes the fuel back on the way up. The depot would not even need to be very large.
One important aspect is thrust levels while landing on the Moon. Here's the case using two of the vacuum Raptors which have 3.5 MN thrust each. I know Musk said that these are fixed, but for Lunar missions they could be made to swivel. I don't like the idea of switching from vacuum to inefficient sea level engines for the Lunar landing.
Quote from: Steven Pietrobon on 11/23/2016 08:28 amOne important aspect is thrust levels while landing on the Moon. Here's the case using two of the vacuum Raptors which have 3.5 MN thrust each. I know Musk said that these are fixed, but for Lunar missions they could be made to swivel. I don't like the idea of switching from vacuum to inefficient sea level engines for the Lunar landing.I don't see how gimballing can be implemented without making the nozzles a lot smaller. There isn't enough room for any movement. Its not necessary anyway, differential thrust plus RCS can provide sufficient control authority in all 3 axes with a smaller performance hit (which is how attitude control during TMI/TEI is planned, and most likely during Mars landing)
Space stations, tankers and propellant depots in lunar orbit will need station keeping. A set of ion thrusters should be able to supply this.
Quote from: brickmack on 11/23/2016 07:01 pmQuote from: Steven Pietrobon on 11/23/2016 08:28 amOne important aspect is thrust levels while landing on the Moon. Here's the case using two of the vacuum Raptors which have 3.5 MN thrust each. I know Musk said that these are fixed, but for Lunar missions they could be made to swivel. I don't like the idea of switching from vacuum to inefficient sea level engines for the Lunar landing.I don't see how gimballing can be implemented without making the nozzles a lot smaller. There isn't enough room for any movement. Its not necessary anyway, differential thrust plus RCS can provide sufficient control authority in all 3 axes with a smaller performance hit (which is how attitude control during TMI/TEI is planned, and most likely during Mars landing)This has been discussed elsewhere, but the lag inherent in differential thrust makes control a lot harder. Not undoable but gimballing makes avoiding overshoot a LOT easier.
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.
Might I suggest a simpler approach? A dedicated ITS lander with large on-board battery packs and which transits between the surface and a man-tended depot, where not only are gasses stored but battery maintenance and cargo transshipping occurs. Leave the solar arrays in orbit, too, or at the very least work out a schedule which will deliver batteries to the surface to allow overnight stays. Crews would travel uphill aboard a 'standard' ITS without Lunar landing capability, but also carrying cargo. Use the depot to offer a shirtsleeves cargo transfer facility without EVAs or manipulator arms, and build up a bespoke delivery service for third-party exploration and development.
I don't see how gimballing can be implemented without making the nozzles a lot smaller.
(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: AncientU on 11/24/2016 09:08 pmQuote 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.Steven Pietrobon only talked about leaving 105.1 t of propellant in lunar orbit.
Quote from: A_M_Swallow on 11/25/2016 12:38 amQuote from: AncientU on 11/24/2016 09:08 pmQuote 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.Steven Pietrobon only talked about leaving 105.1 t of propellant in lunar orbit.In OP, calculation with Lunar orbit refueling after ascent from surface delivered 180.6 tonnes, then 105.1 for the spaceship that supplied the on orbit fuel. (The second ship would need to be refueled like the first.)
Attached is my Pascal program used to work out the payload.
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!
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
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.
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?I think in this case the numbers are easy. Every kg of propellant you transfer aboard while on the lunar surface is a kg of propellant you didn't have to bring down to the lunar surface. So it frees up a kg of down-mass payload capability. Yes?
sdsds: You have 100 m/s margin for lunar landing and another 100 m/s margin for earth... are those additive at all? If you don't use all the margin at luna, do you leave that propellant in lunar orbit? Or do you take it back to earth, increasing the margin there but also impacting everything else (because you have a bit more mass to take)?
Second: his proposal allows each mission to target a different lunar surface location, so long as each ascending ship can make rendezvous with the incoming ship.
Quote from: sdsds on 12/02/2016 02:10 amQuote 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?I think in this case the numbers are easy. Every kg of propellant you transfer aboard while on the lunar surface is a kg of propellant you didn't have to bring down to the lunar surface. So it frees up a kg of down-mass payload capability. Yes?Its a bit more complicated than that. Assuming a 3.5 to 1 oxidiser to fuel mixture ratio, the saved 97.0*3.5/4.5 = 75.4 t of oxidiser mass increases payload mass by 75.4 t to 107.2+75.4 = 182.6 t. This also means that there is 75.4 t of extra propellant mass to bring extra payload down to the Lunar surface. Would have to crunch through the numbers to work out what that would be. A smaller increase could be further made by bringing some coal from Earth and combining that with hydrogen from Lunar water to make methane.
What if you also transfer lunalox to the landing ITS on the orbit from the ascending ITS?
Quote from: J-V on 12/02/2016 07:17 amWhat if you also transfer lunalox to the landing ITS on the orbit from the ascending ITS? You're trading extra methalox required to lift the LOX with the LOX that is brought up. I'd need to crunch the numbers but there might be a benefit. With hydrolox I know there is a benefit as I've studied this before (see my Lunar orbit propellant transfer paper on the first page). The lower Isp and mixture ratio of methalox might not have that advantage.
Waiting to see the numbers. Thank you!
IAC 2017 conference Ran some numbers for the new version of BFS for Lunar landing using Steven's method. Looks like it can deliver about 20 t cargo to the Lunar surface. However I did not include boil off.Any idea what the boil off rate would be? In LEO, LLO, Lunar surface, on way to and from moon. If anyone would like to run their own calculations that would be great.
Quote from: RocketmanUS on 10/04/2017 05:51 amIAC 2017 conference Ran some numbers for the new version of BFS for Lunar landing using Steven's method. Looks like it can deliver about 20 t cargo to the Lunar surface. However I did not include boil off.Any idea what the boil off rate would be? In LEO, LLO, Lunar surface, on way to and from moon. If anyone would like to run their own calculations that would be great.Is that with propellants fill up to full from a tanker after the Moon bound BFS departed LEO?
Quote from: Zed_Noir on 10/04/2017 09:22 amQuote from: RocketmanUS on 10/04/2017 05:51 amIAC 2017 conference Ran some numbers for the new version of BFS for Lunar landing using Steven's method. Looks like it can deliver about 20 t cargo to the Lunar surface. However I did not include boil off.Any idea what the boil off rate would be? In LEO, LLO, Lunar surface, on way to and from moon. If anyone would like to run their own calculations that would be great.Is that with propellants fill up to full from a tanker after the Moon bound BFS departed LEO?Fully fuel in LEO by tankers before TLI burn.
Quote from: RocketmanUS on 10/04/2017 11:32 pmQuote from: Zed_Noir on 10/04/2017 09:22 amQuote from: RocketmanUS on 10/04/2017 05:51 amIAC 2017 conference Ran some numbers for the new version of BFS for Lunar landing using Steven's method. Looks like it can deliver about 20 t cargo to the Lunar surface. However I did not include boil off.Any idea what the boil off rate would be? In LEO, LLO, Lunar surface, on way to and from moon. If anyone would like to run their own calculations that would be great.Is that with propellants fill up to full from a tanker after the Moon bound BFS departed LEO?Fully fuel in LEO by tankers before TLI burn.Ah! But Musk said they'd refuel in high, elliptical orbit for lunar missions. (I actually mentioned this possibility many months ago.)
Quote from: Robotbeat on 10/05/2017 12:31 amQuote from: RocketmanUS on 10/04/2017 11:32 pmQuote from: Zed_Noir on 10/04/2017 09:22 amQuote from: RocketmanUS on 10/04/2017 05:51 amIAC 2017 conference Ran some numbers for the new version of BFS for Lunar landing using Steven's method. Looks like it can deliver about 20 t cargo to the Lunar surface. However I did not include boil off.Any idea what the boil off rate would be? In LEO, LLO, Lunar surface, on way to and from moon. If anyone would like to run their own calculations that would be great.Is that with propellants fill up to full from a tanker after the Moon bound BFS departed LEO?Fully fuel in LEO by tankers before TLI burn.Ah! But Musk said they'd refuel in high, elliptical orbit for lunar missions. (I actually mentioned this possibility many months ago.)Robobeat, I know what he said, but that is not the concept of Steven's for this thread. Could you please run the numbers to see if this new version can bring cargo to the Lunar surface per this concept and if so how much?
@ ciscosdadNot having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.@envy887Thanks, what I needed was the number of payload mass using Steven's concept. So what you got was 23 t payload.Any ides on how much unused propellant mass there would be? That is the unused in the engines and that used to pressurize the tanks.
Quote from: RocketmanUS on 10/05/2017 04:11 am@ ciscosdadNot having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.@envy887Thanks, what I needed was the number of payload mass using Steven's concept. So what you got was 23 t payload.Any ides on how much unused propellant mass there would be? That is the unused in the engines and that used to pressurize the tanks.Steven's OP had two concepts, you'll have to clarify which you meant:1) Refuel in LEO, direct lunar landing and return to Earth surface (this had negative payload), and 2) Refuel in LEO, land on lunar surface, ascend to LLO rendezvous for return fuel, then direct return and landing on Earth (105 t payload landed).I slightly modified these concepts to:3) Refuel in LEO, direct landing and return to LEO with aerobraking, refuel in LEO before landing on Earth surface (10 t payload for full round trip), and4) Refuel in LEO, boost to EEO, top off before TLI, descent to LLO and lunar landing, drop off 150 t payload, return to LLO empty, pick up fuel for TEI, aerobrake into LEO, pick up fuel for Earth landing.My mission profiles trade some operational complexity for a lot more payload; I get 43% more payload to the lunar surface despite 38% less IMLEO, by having 10 rendezvous instead of 7. One additional rendezvous is in LEO, and the other 2 in low elliptical Earth orbit, apogee ~3500 km.
Quote from: envy887 on 10/05/2017 03:30 pmQuote from: RocketmanUS on 10/05/2017 04:11 am@ ciscosdadNot having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.@envy887Thanks, what I needed was the number of payload mass using Steven's concept. So what you got was 23 t payload.Any ides on how much unused propellant mass there would be? That is the unused in the engines and that used to pressurize the tanks.Steven's OP had two concepts, you'll have to clarify which you meant:1) Refuel in LEO, direct lunar landing and return to Earth surface (this had negative payload), and 2) Refuel in LEO, land on lunar surface, ascend to LLO rendezvous for return fuel, then direct return and landing on Earth (105 t payload landed).I slightly modified these concepts to:3) Refuel in LEO, direct landing and return to LEO with aerobraking, refuel in LEO before landing on Earth surface (10 t payload for full round trip), and4) Refuel in LEO, boost to EEO, top off before TLI, descent to LLO and lunar landing, drop off 150 t payload, return to LLO empty, pick up fuel for TEI, aerobrake into LEO, pick up fuel for Earth landing.My mission profiles trade some operational complexity for a lot more payload; I get 43% more payload to the lunar surface despite 38% less IMLEO, by having 10 rendezvous instead of 7. One additional rendezvous is in LEO, and the other 2 in low elliptical Earth orbit, apogee ~3500 km.Option #2 please for the 2017 version of BFR/BFS.
Quote from: RocketmanUS on 10/05/2017 04:50 pmQuote from: envy887 on 10/05/2017 03:30 pmQuote from: RocketmanUS on 10/05/2017 04:11 am@ ciscosdadNot having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.@envy887Thanks, what I needed was the number of payload mass using Steven's concept. So what you got was 23 t payload.Any ides on how much unused propellant mass there would be? That is the unused in the engines and that used to pressurize the tanks.Steven's OP had two concepts, you'll have to clarify which you meant:1) Refuel in LEO, direct lunar landing and return to Earth surface (this had negative payload), and 2) Refuel in LEO, land on lunar surface, ascend to LLO rendezvous for return fuel, then direct return and landing on Earth (105 t payload landed).I slightly modified these concepts to:3) Refuel in LEO, direct landing and return to LEO with aerobraking, refuel in LEO before landing on Earth surface (10 t payload for full round trip), and4) Refuel in LEO, boost to EEO, top off before TLI, descent to LLO and lunar landing, drop off 150 t payload, return to LLO empty, pick up fuel for TEI, aerobrake into LEO, pick up fuel for Earth landing.My mission profiles trade some operational complexity for a lot more payload; I get 43% more payload to the lunar surface despite 38% less IMLEO, by having 10 rendezvous instead of 7. One additional rendezvous is in LEO, and the other 2 in low elliptical Earth orbit, apogee ~3500 km.Option #2 please for the 2017 version of BFR/BFS.Using Steven's delta-v figures and the #2 mission profile, I get 57 tonnes for the 2017 BFR vs. 105 tonnes for the 2016 architecture.
Did you off load the return propellant before Lunar descent into another BFS that just came up from moon for return trip back to Earth? The number you have ( 57 t ) would be for the first BFR landing I believe , all the other BFR's would have a lower payload mass. Keep in mind that at around 20 t payload that payload also returns back to Earth ( this assumes crew missions ).
OK, ran my software for the new BFR. First flight payload mass is 90.5 t, with subsequent flights having a payload of 47.6 t. Transfer propellant in LLO is 62.0 t. Would need seven refuelling flights (or eight flights altogether) for each mission! For the first flight we have propellant mass of 7x150 + 150-90.5 = 1109.5 t, just over the 1100 t capability of BFS. Software attached.
Quote from: Steven Pietrobon on 10/08/2017 01:37 amOK, ran my software for the new BFR. First flight payload mass is 90.5 t, with subsequent flights having a payload of 47.6 t. Transfer propellant in LLO is 62.0 t. Would need seven refuelling flights (or eight flights altogether) for each mission! For the first flight we have propellant mass of 7x150 + 150-90.5 = 1109.5 t, just over the 1100 t capability of BFS. Software attached.Thanks.That is with the cargo left on the moon.What I was doing was bringing the cargo back. I did this to see how much return payload mass could be available for a crewed mission. That is the crew mass , their suits, ect.Edit:Ran the numbers for payload round trip from LEO ( refueled ) to Lunar surface and back to Earth. This is with estimated unusable propellant ( 8,000 kg ), Still would need an expert answer for better estimate. Finding was 12 t payload round trip picking up return propellant in LEO from incoming BFS before return trip to Earth.
Quote from: RocketmanUS on 10/09/2017 05:09 amQuote from: Steven Pietrobon on 10/08/2017 01:37 amOK, ran my software for the new BFR. First flight payload mass is 90.5 t, with subsequent flights having a payload of 47.6 t. Transfer propellant in LLO is 62.0 t. Would need seven refuelling flights (or eight flights altogether) for each mission! For the first flight we have propellant mass of 7x150 + 150-90.5 = 1109.5 t, just over the 1100 t capability of BFS. Software attached.Thanks.That is with the cargo left on the moon.What I was doing was bringing the cargo back. I did this to see how much return payload mass could be available for a crewed mission. That is the crew mass , their suits, ect.Edit:Ran the numbers for payload round trip from LEO ( refueled ) to Lunar surface and back to Earth. This is with estimated unusable propellant ( 8,000 kg ), Still would need an expert answer for better estimate. Finding was 12 t payload round trip picking up return propellant in LEO from incoming BFS before return trip to Earth.Picking up return propellant in LLO or LEO? It should be possible to do both, which combined with a tanker top-off in low EEO gives a round-trip payload of over 50 tonnes.
...After TEI how much propellant is needed to brake into EEO?
Quote from: RocketmanUS on 10/12/2017 07:58 pm...After TEI how much propellant is needed to brake into EEO?If you are braking into orbit it makes more sense to go to LEO, not EEO.But it doesn't really matter for this calculation. An aerobrake orbit will dip into the atmosphere with a perigee of around 60-80 km. Pulling the perigee up to ~300 km so you don't reenter on the next orbit takes about 55-65 m/s at apogee.Compare this to landing which takes 500 to 800 m/s, and this fuel has to go at least to LLO and back, and you can see why it helps the payload a lot.
ISRU for propellant on the moon would make the whole BFS to the moon proposal much simpler. However it doesnt appear to be as straight forward as on Mars from what I read.
Quote from: corneliussulla on 10/18/2017 06:56 amISRU for propellant on the moon would make the whole BFS to the moon proposal much simpler. However it doesnt appear to be as straight forward as on Mars from what I read.ISRU for LOX only could make a lot of sense. After all LOX is ~80% of propellant mass. There is a concept worked on to produce LOX from SiO2 which is available everywhere on the moon. But worth it probably only when regular large payloads to the moon are needed.
Quote from: guckyfan on 10/18/2017 09:41 amQuote from: corneliussulla on 10/18/2017 06:56 amISRU for propellant on the moon would make the whole BFS to the moon proposal much simpler. However it doesnt appear to be as straight forward as on Mars from what I read.ISRU for LOX only could make a lot of sense. After all LOX is ~80% of propellant mass. There is a concept worked on to produce LOX from SiO2 which is available everywhere on the moon. But worth it probably only when regular large payloads to the moon are needed.Lunar ISRU trades against 3 or 4 tanker flights to LEO, to land a 150 tonne payload on the Moon and return empty, or landing 50 tonnes and returning 50 tonnes. Tanker flights have to be pretty expensive to make ISRU worthwhile (this is not the case form Mars since Mars is so much more difficult to return from).I haven't worked the numbers for landing 150 tonnes and returning 50 tonnes, but that's the limit of the BFR/BFS architecture unless you go to LEO payload transfer - and even then it's likely volume limited for most payloads. I don't think lunar ISRU fits well with BFS/BFR. But it does make sense to have it for at least an emergency backup O2 and H2O source if you have a lunar base.
Quote from: corneliussulla on 10/18/2017 06:56 amISRU for propellant on the moon would make the whole BFS to the moon proposal much simpler. However it doesnt appear to be as straight forward as on Mars from what I read.No, it'd make it far more complex. If you need a lot of payload on or off the Moon, it might still make sense cost-wise, but it's FAR simpler without lunar ISRU.
Some dispute about whether the CO results are trustworthy, apparently. We just have to go and look. It is definitely possible though. It is frustrating that such huge HSF architectures are being finalised without this basic information verified. This is not a SpaceX criticism.Jon Goff mentions some Paul Spudis doubt here:https://forum.nasaspaceflight.com/index.php?topic=39559.msg1612453#msg1612453
But primarily any significant source of carbon found would enable the creation of methane when combined with water and other O2 from oxides.
What I like about BFR is that it can land rovers with Tesla model S type batteries, than can probably roam thousands of km per week before returning to get charged. If we could land a few strategically placed charging solar stations before the main vehicle, then we probably could explore the whole moon in very little time, compared to now.
The next suggestion would be for NASA to scrap SLS and spend the money on this system.
But generally, NASA needs to get out of the launch business and focus on "boldly going". SpaceX will not have a commercial reason to develop a lunar lander - so maybe NASA needs to do it? Best still, NASA commissions lunar landers. And SpaceX design and build it.
Quote from: alexterrell on 03/04/2018 09:51 amBut generally, NASA needs to get out of the launch business and focus on "boldly going". SpaceX will not have a commercial reason to develop a lunar lander - so maybe NASA needs to do it? Best still, NASA commissions lunar landers. And SpaceX design and build it. This is the mentality we need to change. NASA has to start commissioning cargo and passenger capacity and service to the Moon. Commissioning a vehicle gets us back to the old situation.
Quote from: IRobot on 03/04/2018 10:13 amQuote from: alexterrell on 03/04/2018 09:51 amBut generally, NASA needs to get out of the launch business and focus on "boldly going". SpaceX will not have a commercial reason to develop a lunar lander - so maybe NASA needs to do it? Best still, NASA commissions lunar landers. And SpaceX design and build it. This is the mentality we need to change. NASA has to start commissioning cargo and passenger capacity and service to the Moon. Commissioning a vehicle gets us back to the old situation.For anything which has been done before - like launching mass from Earth to orbit - absolutely. Whether you can extend this to new stuff is a questionable. Let's say we want a capacity to land on Europa, penetrate the ice to the water below, and send back data. Can NASA commission that capability? Or does it need to commission the vehicle?
It's time to stop thinking of single purpose spacecrafts, which are optimized for mass to orbit and not for price.
I watched the Spacex video of a BFS moon landing. Just like in the moon landing in “2001 A Space Odyssey” the dust kicked up by the landing burn billowed as if it was in an atmosphere. No biggie, but it got me wondering about what was hidden, and that was the landing gear! The narrow-stance legs shown in the Mars ITS videos are obviously only useful for a prepared landing site, and given the base width compared to the overall height, maybe even dicey for that. Remember, on landing with a payload, the tanks are going to be nearly empty, so a lot of the overall mass is going to be up near the nose/top! Doesn’t feel right, and certainly unsafe for unprepared landing sites like will be encountered in exploratory flights.
For lunar missions BFS could really benefit from depots and SEP tugs.If you could keep a depot at L1 or L2 the landed mass becomes the full 150 tons.
The landing ring addresss the “coffin corner” situation, where there is not a level enough or firm enough spot for the narrow and highly-loaded landing gear I have seen envisioned. Yes you can hover for a while, but it doesn’t matter - if you can’t land you don’t have the option to abort to orbit like Neil Armstrong had - you must land someplace!
Quote from: Patchouli on 03/04/2018 11:57 pmFor lunar missions BFS could really benefit from depots and SEP tugs.If you could keep a depot at L1 or L2 the landed mass becomes the full 150 tons.It really doesn't.You put a second BFS in LLO, and transfer TLI fuel to it before landing, and back after.This gets you a hundred tons or so on the moon every eight launches.It is questionable if you can even use Xenon with a free, massless SEP tug to move fuel cheaper than BFS. (Xenon is expensive).SEP tugs have very questionable value in a scenario where fuel is cheap until you get to several times the total exhaust velocity delta-v over which the fuel must be transported over.And even then, if your alternative can aerobrake some of the velocity off, that can be a massive advantage for it.
Yes, I agree that a landing abort is made possible by limiting cargo on the first landing at a new site. But as a matter of standard operating procedure, I would recommend that all sites be “improved” anyway. To me the best way to improve them is by providing a landing/launching ring. The use of a ring would probably have been mastered and standardized on Earth long before, and adopting the practice would allow your whole lunar fleet to dispense with landing gear altogether. Seems like a good safety practice that will also improve overall efficiency, no?
Yes, I agree that a landing abort is made possible by limiting cargo on the first landing at a new site. But as a matter of standard operating procedure, I would recommend that all sites be “improved” anyway. To me the best way to improve them is by providing a landing/launching ring.
A question. How would the BFS unload large monolithic cargos?This picture shows pallets and people...https://ourplnt.com/making-life-multiplanetary/spacex-bfs-lunar-base/But what if there's a 100 ton hab module with a cargo diameter of 8 metres?
Quote from: alexterrell on 03/06/2018 08:45 amA question. How would the BFS unload large monolithic cargos?This picture shows pallets and people...https://ourplnt.com/making-life-multiplanetary/spacex-bfs-lunar-base/But what if there's a 100 ton hab module with a cargo diameter of 8 metres?With the chomper and a crane.https://spaceflight101.com/spx/wp-content/uploads/sites/113/2017/09/IAC2017-Musk-26.jpgBut a BFS itself would make a good hab module, if you use a crane to tip it over, use cargo rovers to roll it into place, and then bury it under regolith. The hab section is 850 m^3, and you could vent/purge and then cut into the tanks and outfit them for an extra 1200 m^3 of habitable volume.
Is there any potential for problems from the lunar dust? It seems to have an almost supernatural ability to freeze up mechanical sliding mechanisms. Would there be any risk to BFR's engines? Doors? Any other hardware?
Regarding lunar ISRU propellant generation for BFR/ITS - there's not much carbon on the lunar surface. Where are you going to get it from? Earth? Asteroids? Or is there some cometary frozen methane ice in shadowed crater areas that could be tapped?