Author Topic: ITS for the Moon  (Read 15676 times)

Online 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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Offline sdsds

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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 »
-- sdsds --

Offline Steven Pietrobon

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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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Offline Steven Pietrobon

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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.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Steven Pietrobon

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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 »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline J-V

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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.

Offline Steven Pietrobon

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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.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline J-V

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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!

Offline Steven Pietrobon

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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. :-)
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 #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.

Offline Zed_Noir

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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.

Offline Robotbeat

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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.

Online envy887

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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 »

Offline RocketmanUS

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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 »

Offline RocketmanUS

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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.

Online envy887

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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 »

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