Author Topic: ITS for the Moon  (Read 14621 times)

Online Steven Pietrobon

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ITS for the Moon
« on: 11/23/2016 08:04 AM »
Here's a little study I recently did of using the SpaceX Interplanetary Transport System (ITS) for missions to the Moon.

I first had a look of using ITS directly to Moon (after filling up with 1950 t of methane/LOX propellant from five tanker flights).

For the landing burn on Earth, looking at the YouTube technical broadcasts the burn was about 25 seconds for JCSat 16 and 31 seconds for SpX-9. Lets take the average of 28 seconds. We'll also assume Th = 14 seconds at full thrust and Tl = 14 seconds at minimum thrust of 55% as given below

http://spaceflight101.com/spacerockets/falcon-9-ft/

This results in a landing delta-V of 719 m/s. Data is below showing how I calculated this. This results in a negative cargo mass of -36.7 t, which means Lunar Direct will not work with ITS.

One idea I had was to use Lunar orbit propellant transfer. On the first flight, we bring cargo to the surface, but reach Lunar orbit with no propellant left in the tank. That brings a huge 180.6 t to the Lunar surface!

Waiting in Lunar orbit is another ITS, which transfers 107.2 t of propellant to the returning ITS. The second ITS then lands on the Moon bringing 105.1 t of cargo! The process then repeats. This works because we don't bring down and up again the return propellant from Lunar orbit, which is a huge penalty.

Attached is my Pascal program used to work out the payload.

Falcon 9 landing Delta-V calculation
------------------------------------

ms = 22.2 t
ves = g*282 = 2765.48 m/s
Fs = 845 kN
Rp = Fs/ves = 0.306 t/s
Th = 14 s
Tl = 14 s
mp = (Th + Tl*0.55)*Rp = 6.63 t
margin = 2%

We need to solve these two equations where mpr is the residual propellant.

dv = ves*ln(1+mp/(ms+mpr))
margin*dv = ves*ln(1+mpr/ms)

margin*ln(1+mp/(ms+mpr)) = ln(1+mpr/ms)
mpr = ms*(exp(margin*ln(1+mp/(ms+mpr)))-1)

This is a non-linear equation which we solve iteratively. This gives

mpr = 0.116 t
dv = ves*ln(1+mp/(ms+mpr)) = 719 m/s.

Check second equation

margin*dv = 14.4 m/s
ves*ln(1+mpr/ms) = 2765.48*ln(1+0.116/22.2) = 14.4 m/s

ITS Direct Cargo Calculation
----------------------------
Delta-V values are

dv1 = 3180 m/s (TLI)
dv2 = 960 m/s (LOI)
dv3 = 28 m/s (PDI)
dv4 = 2041 m/s (Lunar Descent)
dv5 = 1850 m/s (Lunar Ascent)
dv6 = 1169 m/s (TEI)
dv7 = 719 m/s (Earth landing)
marginl = 2%
margine = 1%
ve = g*382 = 3746.14 m/s (Raptor exhaust speed)
ves = g*334 = 3275.42 m/s (Sea Level exhaust speed)
ms = 150 t (ITS empty mass)
mp = 1950 t (propellant mass)

dvm = (1+margine)*(dv1+dv2+dv3+dv4) = 6271 m/s (delta-V to Lunar surface)
dve = (1+margine)*(dv5+dv6) = 3049 m/s (delta-V back to Earth)
dvl = (1+marginl)*dv7 = 734 m/s (delta-V landing on Earth)

Need to solve these three equations where mc is the cargo mass and mpe is the propellant to get to Earth and mpl is the landing propellant.

dvm = ve*ln(1+(mp-mpe-mpl)/(ms+mpe+mpl+mc))
dve = ve*ln(1+mpe/(ms+mpl)))
dvl = ves*ln(1+mpl/ms))

Solving the equations from last to first gives

mpl = ms*(exp(dvl/ves)-1) = 37.7 t
mpe = (ms+mpl)*(exp(dve/ve)-1) = 235.9 t
mpm = mp-mpe-mpl = 1676.5 t
mc = mpm/(exp(dvm/ve)-1)-ms-mpl-mpe = -36.7 t

Unfortunately, the negative value for mc means that this won't work.

ITS Lunar Orbit Propellant Transfer First Flight
------------------------------------------------

dvm = (1+margine)*(dv1+dv2+dv3+dv4) = 6271 m/s (delta-V to Lunar surface)
dva = (1+margine)*dv5 = 1869 m/s (delta-V to Lunar orbit)

Need to solve these two equations where mc is the cargo mass and mpa is the propellant to get to Lunar orbit.

dvm = ve*ln(1+(mp-mpa)/(ms+mpa+mc))
dva = ve*ln(1+mpa/ms))

Solving the equations from last to first gives

mpa = ms*(exp(dva/ve)-1) = 97.0 t
mpm = mp-mpa = 1853.0 t
mc = mpm/(exp(dvm/ve)-1)-ms-mpa = 180.6 t

Check

dvm = 3746.14*ln(1+1853.0/(150+97.0+180.6)) = 6271 m/s
dve = 3746.14*ln(1+97.0/150)) = 1869 m/s

ITS Lunar Orbit Propellant Transfer Subsequent Flights
------------------------------------------------------

dvo = (1+margine)*(dv1+dv2) = 4181 m/s (delta-V to Lunar orbit)
dvd = (1+margine)*(dv3+dv4) = 2090 m/s (delta-V to Lunar surface)
dva = (1+margine)*dv5 = 1869 m/s (delta-V to Lunar orbit)
dvt = (1+margine)*dv6 = 1181 m/s (delta-V to Earth)
dvl = (1+marginl)*dv7 = 734 m/s (delta-V landing on Earth)

dvo = ve*ln(1+(mp-mpd-mpa-mpt-mpl)/(ms+mpd+mpa+mpt+mpl+mc))
dvd = ve*ln(1+mpd/(ms+mpa+mc))
dva = ve*ln(1+mpa/ms)
dvt = ve*ln(1+mpt/(ms+mpl))
dvl = ves*ln(1+mpl/ms))

From before we have

mpl = 37.7 t
mpa = 97.0 t

The fourth equation gives us

mpt = (ms+mpl)*(exp(dvt/ve)-1) = 69.5 t

The second equation gives

ms+mpa+mc = mpd/(exp(dvd/ve)-1)

which we subsitute into the first equation

mp-mpd-mpa-mpt-mpl = (exp(dvo/ve)-1)*(mpd+mpt+mpl+mpd/(exp(dvd/ve)-1))

Let

ao = exp(dvo/ve)-1
ad = exp(dvd/ve)-1

Then

mp-mpa-mpt-mpl = mpd+ao*(mpd(1+1/ad)+mpt+mpl)
mpd = (mp-mpa-mpt-mpl-ao*(mpt+mpl))/(1+ao*(1+1/ad))
mpd = (mp-mpa-(1+ao)*(mpt+mpl))/(1+ao*(1+1/ad)) = 262.9 t
mpo = mp-mpd-mpa-mpt-mpl = 1482.8 t

From the second equation we get

mc = mpd/ad-ms-mpa = 105.1 t

Check

dvo = 3746.14*ln(1+1482.8/(150+262.9+97.0+69.5+37.7+105.1)) = 4181 m/s
dvd = 3746.14*ln(1+262.9/(150+97.0+105.1)) = 2090 m/s
dvt = 3746.14*ln(1+69.5/(150+37.7) = 1181 m/s

Transfer propellant = mpt+mpl = 107.2 t
« Last Edit: 11/23/2016 08:16 AM by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline TrevorMonty

Re: ITS for the Moon
« Reply #1 on: 11/23/2016 08:24 AM »
Clever, I've never considered having the lander leave its return fuel in LLO.
Just down rough calculations on ACES lander doing round trip from EML1- lunar surface - EML1, I got 10% fuel saving leaving return fuel in LL0.
« Last Edit: 11/23/2016 08:47 AM by TrevorMonty »

Online Steven Pietrobon

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Re: ITS for the Moon
« Reply #2 on: 11/23/2016 08:28 AM »
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.

Landing mass is ms+mc+mpa = 150+105.1+97.0 = 352.1 t. Lunar gravity is 1.622 m/s giving a landing weight 352.1*1.622 = 571 kN. If the vacuum engines could throttle down to 571.1/(2*3500) = 0.0816 or about 8%, that could work. There are no flow separation issues, since the engine will be working in a vacuum. Its just a matter of if they can get their pumps to work effectively at that low flow rate. Isp will be reduced due to the lower chamber pressure (2.5 MPa versus 30.4 MPa), but should not be as great as for the sea level engines. It also means landing on the Moon can be performed with the vehicle perfectly vertical.
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Online Steven Pietrobon

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Re: ITS for the Moon
« Reply #3 on: 11/23/2016 08:31 AM »
Clever, 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.
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Offline Lar

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Re: ITS for the Moon
« Reply #4 on: 11/23/2016 02:47 PM »
Clever, 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.
That's the other direction though, yes? 

I guess it all depends on where propellant is abundant. Early missions? Earth. Later missions when ISRU is up and running well on Luna? Luna.

I love this idea of the next ship passing propellant to the previous ship. Need to think through failure modes though...
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"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline guckyfan

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Re: ITS for the Moon
« Reply #5 on: 11/23/2016 03:52 PM »
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.

Offline Lar

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Re: ITS for the Moon
« Reply #6 on: 11/23/2016 03:55 PM »
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.

Could be a tanker that was fully amortized and at end of life (for launches, but not for staying in orbit)... such a tanker might need some mods such as active cooling but those might have already been developed, since they are needed in some CONOPS for Mars (multiple tankers fill one, that one loiters till filled, meaning active cooling, at least potentially, then the crewed ship refills from it)
« Last Edit: 11/23/2016 03:57 PM by Lar »
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Online brickmack

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Re: ITS for the Moon
« Reply #7 on: 11/23/2016 07:01 PM »
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.

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)

Offline Lar

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Re: ITS for the Moon
« Reply #8 on: 11/23/2016 07:18 PM »
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.

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.
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Offline A_M_Swallow

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Re: ITS for the Moon
« Reply #9 on: 11/24/2016 04:11 AM »
Space stations, tankers and propellant depots in lunar orbit will need station keeping. A set of ion thrusters should be able to supply this.

Online AncientU

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Re: ITS for the Moon
« Reply #10 on: 11/24/2016 09:08 PM »
Space 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.
« Last Edit: 11/24/2016 09:09 PM by AncientU »
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Re: ITS for the Moon
« Reply #11 on: 11/24/2016 09:15 PM »
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.

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.

Differential throttling has its place, but it isn't in the final seconds before touchdown.  I suspect vacuum raptors to do the decent burn and gimballed engines for landing.  Not really interested in performance on landing burn, just about control.
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Offline Bob Shaw

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Re: ITS for the Moon
« Reply #12 on: 11/24/2016 09:35 PM »
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.

Offline A_M_Swallow

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Re: ITS for the Moon
« Reply #13 on: 11/25/2016 12:38 AM »
Space 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.

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Re: ITS for the Moon
« Reply #14 on: 11/25/2016 01:57 AM »
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.

The problem I see here is that it requires at least one dedicated ship only for Lunar use. Ideally each spaceship should be usable for any type of mission with minimal modification. Do a lunar surface flight, bring it back home and swap out cargo, do a LEO tourist flight, bring it back and swap out cargo, do a Mars flight, repeat. An ITS will cost hundreds of millions of dollars and likely several months to build, time and money better spent on building general purpose craft than unique ones. There had better be a damned good reason to make such a vehicle, and in the case of the moon its not necessary to do those sorts of performance optimizations anyway since the standard spacecraft is already so capable (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)

Online Steven Pietrobon

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Re: ITS for the Moon
« Reply #15 on: 11/25/2016 03:57 AM »
I don't see how gimballing can be implemented without making the nozzles a lot smaller.

If all the engines are gimballed, the four vacuum engines not being used can be gimballed sideways to leave room for the two vacuum engines to gimbal freely.

(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!
« Last Edit: 11/25/2016 04:01 AM by Steven Pietrobon »
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Online AncientU

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Re: ITS for the Moon
« Reply #16 on: 11/25/2016 11:02 AM »
Space 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.)
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Re: ITS for the Moon
« Reply #17 on: 11/25/2016 02:16 PM »
Space 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.)

So you end up needing about 15 NEXT ion thrusters for station keeping.

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Re: ITS for the Moon
« Reply #18 on: 11/26/2016 02:26 PM »
Thanks for this clever concept! I do enjoy working through the numbers on these, which will take me a bit more time, but I can't resist the OT observation that caught my eye:
Attached is my Pascal program used to work out the payload.
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. I reminds me of the adage that real grizzled old programmers can write FORTRAN code in any programming language! [Semi on topic is that IRL, I rarely any more draw the sharp, austere blade of C, my weapon of choice from when by brain, too, was clean and sharp, rather dallying in the more easy-going lands of Python, but I have been using the ideas in this forum as a fun incentive to get up with the times and learn Swift. When I get around to making a little app to do delta-V estimates on your smart watch, I post it to NSF!]
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.

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Re: ITS for the Moon
« Reply #19 on: 11/26/2016 03:49 PM »
(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

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Re: ITS for the Moon
« Reply #20 on: 11/26/2016 04:55 PM »
(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 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.

Offline DrRobin

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Re: ITS for the Moon
« Reply #21 on: 11/26/2016 05:10 PM »
Space 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.

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 ]

Offline laszlo

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Re: ITS for the Moon
« Reply #22 on: 11/26/2016 05:51 PM »
Isn't leaving the return fuel in lunar orbit what the Apollo lander did? ;)

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Re: ITS for the Moon
« Reply #23 on: 11/26/2016 05:57 PM »

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 ]

But are such stable orbits suitable for a fuel depot? I think it needs to be in low lunar orbit. Steven Pietoban may correct me if I am wrong.

But I don't think it would be a big problem. Make that depot only as large as needed. Just above 200t if we assume 2 landed ITS at the same time. 100 if we assume only one. ITS would not stay over night so be on the ground for maybe 10 days. During that time stability should not be the issue. For the empty depot some ion thrusters could do the station keeping.

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Re: ITS for the Moon
« Reply #24 on: 11/27/2016 07:45 AM »
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.

We must be of similar age as I also have stacks of punchcards written in Fortran. :-) Us students would write the code (80 characters to a line) and secretaries would punch out the cards for us! Any mistakes and we would punch the correction ourselves. Running the software involved submitting the punched cards, waiting a while while the technicians ran the program, and then collecting the printed output, hopefully without any errors, otherwise the whole process would have to be repeated. Just seems so archaic, but we accepted this method as pretty normal at the time.

Quote
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.

That sort is similar to what I'm doing, except instead of basecamps (or propellant depots in this case) we have back and forth travellers passing what they need to each other.
« Last Edit: 11/27/2016 07:48 AM by Steven Pietrobon »
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Re: ITS for the Moon
« Reply #25 on: 11/27/2016 07:56 AM »
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

Looks like he gets his delta-V values from Wikipedia, not the most reliable of sources. I got most of my delta-V values from "Apollo: The Definitive Sourcebook" by Orloff and Harland.
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Re: ITS for the Moon
« Reply #26 on: 11/27/2016 08:02 AM »
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.

Yes, that's what I was thinking for the difference. With a direct landing and ascent the delta-Vs are lower which would make a significant difference to the payload mass. My understanding is that only certain areas of the Moon can be reached using direct landing.
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Re: ITS for the Moon
« Reply #27 on: 11/27/2016 08:55 AM »
It's an excellent concept!

I would appreciate thoughts on a modification of the idea. Suppose there were and additional something else at the rendezvous orbit. A deep space habitat in need of cargo resupply, for example. Could an ITS-like system earn revenue by delivering some of that cargo and then like Cygnus has just demonstrated proceed on to a secondary mission? For the ITS-like system that secondary mission would be a trip down to the lunar surface and back. Would this work with non-negative payload masses even if the habitat were in lunar DRO or NRO?
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Offline MikeAtkinson

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Re: ITS for the Moon
« Reply #28 on: 11/27/2016 01:27 PM »
Here is my spreadsheet.

https://docs.google.com/spreadsheets/d/15kgq-0x6BKnNXGO9WFKfjhtE42WJncbpZHq3VHoQ3OA/edit#gid=0

81 tonnes payload delivered to the moon.

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Re: ITS for the Moon
« Reply #29 on: 11/28/2016 01:43 AM »
Here is my spreadsheet.

https://docs.google.com/spreadsheets/d/15kgq-0x6BKnNXGO9WFKfjhtE42WJncbpZHq3VHoQ3OA/edit#gid=0

81 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?"
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Offline MikeAtkinson

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Re: ITS for the Moon
« Reply #30 on: 11/28/2016 07:55 AM »
Here is my spreadsheet.

https://docs.google.com/spreadsheets/d/15kgq-0x6BKnNXGO9WFKfjhtE42WJncbpZHq3VHoQ3OA/edit#gid=0

81 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?"

81 tonnes or less.

You could land an empty ITS and return with some payload, or land far less than 81 tonnes and return it. I perhaps should amend the spreadsheet to cover those cases.

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Re: ITS for the Moon
« Reply #31 on: 11/28/2016 08:30 AM »
Here is my spreadsheet.

https://docs.google.com/spreadsheets/d/15kgq-0x6BKnNXGO9WFKfjhtE42WJncbpZHq3VHoQ3OA/edit#gid=0

81 tonnes payload delivered to the moon.

Lunar escape velocity is 2.38 km/s. Both your Lunar descent and ascent delta-V's are 2.4 km/s. You have only included 20 m/s for gravity losses, equivalent to having a burn time of 20/1.622 = 12 seconds! Lets say there are about 200 m/s of gravity losses (about 2 minutes at 1.622 m/s).

Also, escape velocity will leave you in orbit at Lunar distance. Additional delta-V is required to lower your perigee. This varies from 790 to 903 m/s depending if you are at Lunar perigee or apogee. Assuming 0.8 km/s required to lower the perigee, that gives a total delta-V of sqrt(2.38+0.8)+0.2 = 2.71 km/s. Thus, you need to add about 0.3 km/s to your delta-V values.
 
A TLI of 3.2 km/s is plenty to get to the Moon. You don't need 3.5 km/s.

Your landing delta-V of 700 m/s should be OK. I used 733 m/s (including margin).
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Re: ITS for the Moon
« Reply #32 on: 11/29/2016 06:17 AM »
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.

It /seems/ to show each ITS mission could deliver both 35 t of cargo to the hab and something like 20 t of cargo to the lunar surface. This is enabled by transferring 63 t of propellant between departing and returning ITS ships.

I assumed the ships for this would be 25 t more massive in dry weight (175 t total) to provide for robust cargo handling equipment, performance margin, etc. My delta-v numbers are from https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019648.pdf, as best I understand it.
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Re: ITS for the Moon
« Reply #33 on: 11/30/2016 07:01 AM »
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.

You have 2400 m/s for Lunar descent from LLO. That's a bit high. Apollo was 2069 m/s. A value of 2100 m/s would be plenty.
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Re: ITS for the Moon
« Reply #34 on: 11/30/2016 07:19 AM »
Oh yikes, you're right! Looking closer it also seems I had an unreasonably low lunar ascent delta-v. Fixing that is going to hurt the payload performance, more than it is helped by fixing the descent delta-v error.
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Re: ITS for the Moon
« Reply #35 on: 11/30/2016 12:24 PM »
What would the numbers look like, if assuming ISRU LOX from lunar surface? Somewhat better I assume, but how much?

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Re: ITS for the Moon
« Reply #36 on: 11/30/2016 01:56 PM »
What 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.

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Re: ITS for the Moon
« Reply #37 on: 12/01/2016 03:48 AM »
Producing Lunar oxygen would be a future enhancement to increase payload mass. I think the best source is Lunar regolith instead of ice, since its so plentiful (although harder to extract). Here's a link various sources on the subject.

http://www.lunarpedia.org/index.php?title=Oxygen

The first 180 t payload could contain a Lunox factory.
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Re: ITS for the Moon
« Reply #38 on: 12/02/2016 12:03 AM »
What 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.

Actually 180 tonnes per Steven's calculations. If you park a tanker in Lunar orbit, a series of ITS-payloads could land, return to orbit/refueling, and then back to Earth. The tanker would return to Earth on its last 100 tonnes or so of fuel.

ISRU is much harder than this strategy... good for the long run, but not a pre-req to get going.
« Last Edit: 12/02/2016 12:05 AM by AncientU »
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Re: ITS for the Moon
« Reply #39 on: 12/02/2016 02:10 AM »
What 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?
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Offline Lar

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Re: ITS for the Moon
« Reply #40 on: 12/02/2016 02:23 AM »
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)? 

I would think that if this wasn't a oneshot, if there was a continuous run of ships coming and going, whenever you have margin that you didn't use getting to a place, you leave the margin at that place, so that if another ship comes in that cut it close, you make it up from what you saved.. does that make sense?
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Re: ITS for the Moon
« Reply #41 on: 12/02/2016 03:24 AM »
Yes Lar it does make sense and I really like the idea. The general concept is that of caching resources you brought with you but ended up not consuming, thus making those resources available to others that follow. The lunar surface would be a great place to cache propellant, assuming the next mission will be returning to that same spot on the surface. It also assumes your architecture supports lunar surface propellant transfer.

There are at least two really nice aspects of Steven Pietrobon's proposal though that don't "play well" with lunar surface propellant caching. First: his proposal doesn't require any propellant transfer capability in cis-lunar space beyond what ITS will already require in LEO, i.e. ship-to-ship transfers. 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.

I definitely want to explore this line of thinking further, because I think it has implications for where the rendezvous (and thus propellant transfer) should take place. I think you want it to be in as high (energetic) an orbit as the ascending ship can reach with the propellant it has available. But I'm not sure of that. Maybe it is always better to rendezvous as low as possible?
« Last Edit: 12/02/2016 03:25 AM by sdsds »
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Re: ITS for the Moon
« Reply #42 on: 12/02/2016 04:16 AM »
What 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.
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Re: ITS for the Moon
« Reply #43 on: 12/02/2016 04:19 AM »
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)? 

Any margin you don't use up to Lunar orbit could be left in Lunar orbit. Otherwise, you could carry that margin all the way back to Earth. The margin is not a penalty since you just burn a little of that margin to make up for the extra propellant.
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Re: ITS for the Moon
« Reply #44 on: 12/02/2016 04:29 AM »
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.

Yes, there is no limit on where the next ship could land. The next ship would arrived at its desired inclination around the Moon, wait up to 14 days for the previous ship to be under the next ship at which point the next ship goes into Lunar orbit and docks with the next ship. The previous ship then waits up to 14 days for proper alignment with Earth and performs TEI. Similarly, the next ship waits up to 14 days to align with where they would want to go next. The 14 days is half the 28 day orbital period around the Earth of the Moon.

« Last Edit: 12/02/2016 04:29 AM by Steven Pietrobon »
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Re: ITS for the Moon
« Reply #45 on: 12/02/2016 07:17 AM »
What 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?

Btw, does anyone have any reference how heavy the equipment needed to extract oxygen from regolith would be in this scale? I'd like to know how many flights it would take to have more payload with oxygen production than without.

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Re: ITS for the Moon
« Reply #46 on: 12/02/2016 07:56 AM »
What 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.
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Re: ITS for the Moon
« Reply #47 on: 12/02/2016 07:37 PM »
What 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!

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Re: ITS for the Moon
« Reply #48 on: 12/03/2016 04:54 AM »
Waiting to see the numbers. Thank you!

I'll calculate them when ITS reaches the Moon. :-)
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Re: ITS for the Moon
« Reply #49 on: 10/04/2017 05:51 AM »
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.

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Re: ITS for the Moon
« Reply #50 on: 10/04/2017 09:22 AM »
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.

Is that with propellants fill up to full from a tanker after the Moon bound BFS departed LEO?

Offline RocketmanUS

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Re: ITS for the Moon
« Reply #51 on: 10/04/2017 11:32 PM »
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.

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.

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Re: ITS for the Moon
« Reply #52 on: 10/05/2017 12:31 AM »
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.

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.)
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Offline RocketmanUS

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Re: ITS for the Moon
« Reply #53 on: 10/05/2017 12:39 AM »
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.

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?

Offline ciscosdad

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Re: ITS for the Moon
« Reply #54 on: 10/05/2017 02:14 AM »
Some combination of Elliptical earth orbit and Lunar propellent exchange would also be of interest. Benefits of both and limit penetration of Van Allen belts.

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Re: ITS for the Moon
« Reply #55 on: 10/05/2017 03:09 AM »
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.

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?

My numbers below. Requires 8 tanker launches to get 150 tonnes to the lunar surface, after LEO refuel, boost to 200x3500 km EEO, topping off, and LLO rendezvous with a returning ship. I'm not accounting for boiloff, but have an extra half-tanker (almost 90 tonnes) of prop in LEO for margins, and for landing the ship after aerobraking back into LEO and final tanker rendezvous. If the cargo vehicle is lighter, it gains a 1:1 improvement in payload delivered for all dry mass reduced.

This assumes an empty return, but return payload trades at about with landed payload. So for the same flight profile and number of tankers:
Land 120 tonnes, offload 100 tonnes, return 20 tonnes, or
Land 90 tonnes, offload 50 tonnes, return 40 tonnes, or
Land 60 tonnes, offload 10 tonnes, return 50 tonnes.

All this complexity is not needed for initial missions though... fully refueled in 200 km LEO, the crew BFS could land 23 tonnes of payload on the Moon and return the same payload to Earth's surface directly.
« Last Edit: 10/05/2017 03:32 AM by envy887 »

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Re: ITS for the Moon
« Reply #56 on: 10/05/2017 04:11 AM »
@ ciscosdad
Not having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.

@envy887
Thanks, 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.

Online envy887

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Re: ITS for the Moon
« Reply #57 on: 10/05/2017 03:30 PM »
@ ciscosdad
Not having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.

@envy887
Thanks, 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), and
4) 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.
« Last Edit: 10/05/2017 03:32 PM by envy887 »

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Re: ITS for the Moon
« Reply #58 on: 10/05/2017 04:50 PM »
@ ciscosdad
Not having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.

@envy887
Thanks, 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), and
4) 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.

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Re: ITS for the Moon
« Reply #59 on: 10/05/2017 05:15 PM »
@ ciscosdad
Not having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.

@envy887
Thanks, 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), and
4) 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.
« Last Edit: 10/05/2017 05:17 PM by envy887 »

Offline RocketmanUS

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Re: ITS for the Moon
« Reply #60 on: 10/05/2017 07:38 PM »
@ ciscosdad
Not having crew spending unneeded time in the Van Allen belts is why I was looking at Steven's concept for this new BFS.

@envy887
Thanks, 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), and
4) 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.
Thanks.

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 ).

Online envy887

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Re: ITS for the Moon
« Reply #61 on: 10/05/2017 09:16 PM »
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 ).

Yes. 57 tonnes is for continuous operation, the first one would be slightly higher.

I'll run through again with a round trip payload, but I expect 20 tonnes will be about right.

BTW, for cargo missions I expect SpaceX will want to stage in EEO and aerobrake back to LEO as it more than doubles payload. The orbit will have sufficient inclination and a low enough apogee to avoid most of the inner Van Allen Belt. It might even be acceptable for crew.
« Last Edit: 10/05/2017 09:19 PM by envy887 »

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Re: ITS for the Moon
« Reply #62 on: 10/08/2017 01:37 AM »
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.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline RocketmanUS

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Re: ITS for the Moon
« Reply #63 on: 10/09/2017 05:09 AM »
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.
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 LLO from incoming BFS before return trip to Earth.

Edit:
Typo fixed , LEO to LLO
« Last Edit: 10/12/2017 07:53 PM by RocketmanUS »

Online envy887

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Re: ITS for the Moon
« Reply #64 on: 10/12/2017 05:30 PM »
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.
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.

Offline RocketmanUS

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Re: ITS for the Moon
« Reply #65 on: 10/12/2017 07:58 PM »
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.
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.
Typo fixed. Thanks for pointing out. That is LLO.

After TEI how much propellant is needed to brake into EEO?

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Re: ITS for the Moon
« Reply #66 on: 10/12/2017 09:17 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.
« Last Edit: 10/12/2017 09:18 PM by envy887 »

Offline RocketmanUS

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Re: ITS for the Moon
« Reply #67 on: 10/13/2017 04:51 AM »
...
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.
I ran some quick numbers and see what you mean. If I have time I'll run the numbers through to see how close I get to your payload mass round trip. For landing back on Earth will need deorbit burn propellant alwell. But that is brought up from Earth with the landing propellant and would not effect the round trip payload mass if done by LEO tanker.

Using both LLO and then LEO for adding propellant would be better than using elliptical orbits for Lunar departure.

Offline corneliussulla

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Re: ITS for the Moon
« Reply #68 on: 10/18/2017 06:56 AM »
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.

Offline guckyfan

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Re: ITS for the Moon
« Reply #69 on: 10/18/2017 09:41 AM »
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.

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.

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Re: ITS for the Moon
« Reply #70 on: 10/18/2017 05:27 PM »
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.

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.

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Re: ITS for the Moon
« Reply #71 on: 10/18/2017 11:24 PM »
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.

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.

Have you taken into account ISRU machinery lasting about 10-15 years? This means it can make more fuel than it weighs.

Online Robotbeat

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Re: ITS for the Moon
« Reply #72 on: 10/19/2017 02:55 AM »
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.
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.
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Offline guckyfan

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Re: ITS for the Moon
« Reply #73 on: 10/19/2017 03:27 PM »
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.
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.

I agree it makes it more complex. But should be worth it for a major base that needs multiple thousands of tons payload to the moon.

May I point out that this discussion is in stark contrast to arguments, we need to produce propellant on the moon to facilitate Mars flights? I never thought lunar propellant makes a lot of sense for Mars but there is plenty of argument for it.

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Re: ITS for the Moon
« Reply #74 on: 10/19/2017 04:32 PM »
I was trying to find if it was possible to have frozen CO2 traped with the water at the Lunar pols. The temperatures are -237 degrees C. This looks to be cold enough for frozen CO2 but the value for temp of frozen CO2 in vacuum is seemingly not available. Also could the CO2 bond (not a chemical bond but there is also a possibility of C and O molecules performing bonds) with other items in the regolith allowing it to freeze at higher temps.

http://www.chemicalogic.com/Documents/co2_phase_diagram.pdf

I just looked it up but LCROSS detected carbon monoxide in the plume. So it could be possible to make some Metholox with the volatiles in the Lunar pol regolith.
« Last Edit: 10/19/2017 04:48 PM by oldAtlas_Eguy »

Offline KelvinZero

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Re: ITS for the Moon
« Reply #75 on: 10/19/2017 10:06 PM »
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
« Last Edit: 10/19/2017 10:08 PM by KelvinZero »

Online oldAtlas_Eguy

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Re: ITS for the Moon
« Reply #76 on: 10/20/2017 04:43 PM »
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. Unfortunately most of the surface, dark craters, and lava tubes have never been explored or tested for specific makeup of the contents. So we know our understanding from Apollo was not the whole picture of the Lunar resources. But we do not know what the resources extent or makeup is at this point, only educated guesses at what it could be.

Because BFR will not depend at least initially on any Lunar resources this will enable the ability to explore and develop resources which could then lower the costs of the transport to and from the Lunar surface. a bootstraping event which because of the massive transportation flow to the Moon there would be great incentive for others to develop capabilities on the Moon that would allow by selling products (propellant in some form) to the transporters that enables them to lower prices and increase volume which increases total revenue which increase profits. This is the essence of the bootstrap but in this case for a commercial services industry based on the development of Lunar resources. Growth of bases and capabilities would grow at an exponential rate which at first  would hardly be noticeable but at 10 20 years after BFR first landing on the Moon would be showing significant Lunar industry growth increases which itself would be doing at an increasing rate.

Online speedevil

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Re: ITS for the Moon
« Reply #77 on: 11/19/2017 05:03 PM »
But primarily any significant source of carbon found would enable the creation of methane when combined with water and other O2 from oxides.
I now wonder at what velocity you can hard-land coal on the moon, and have it remain in the general area at moderate concentration.
(I would be astonished if this was actually worthwhile)

Offline Bynaus

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Re: ITS for the Moon
« Reply #78 on: 11/19/2017 07:07 PM »
There's plenty of carbon in comets (e.g., measured in comas), up to 4% carbon in chondritic meteorites, and there are even some "ultracarbonaceous" interplanetary dust particles which are 80% C. Strong heating upon impact will primarily make CO and CO2 (depending on availability), which are then both easily trapped at the polar cold traps. There is every reason to expect large deposits of carbon in the polar craters. The LCROSS results fit in well with this expectation. Still, it needs to be confirmed on-site.

Offline lamontagne

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Re: ITS for the Moon
« Reply #79 on: 11/19/2017 09:09 PM »
How about this paper

https://www.hou.usra.edu/meetings/lpsc2016/pdf/1415.pdf

Proposing, I think, large amounts of meteorite impact carbon?  Doesn't quite seem convincing but it's an interesting possibility.

Offline lamontagne

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Re: ITS for the Moon
« Reply #80 on: 11/19/2017 09:12 PM »
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.

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