Moon Starship

[TrevorMonty]

You can also look at this the other way round.  If all your O2 is a byproduct of the solar panel plant you will not launch many spaceships.

This is a minor optimization barely worth mentioning, not an example of an integrated manufacturing system using every part of the pig but the squeal.

I am not looking at it that way. I am looking at LOX production. Si is just a sideproduct that may or may not be useful.

Large quantities of surplus O will be a byproduct of most ISRU actitities. Hydrolox engines burn fuel rich mixture so they don't need all the O from electrolysis process. Reduction of iron oxides by applying heat and H results in Fe and H20. The H is recycled by electrolysis resulting in surplus O.

[KelvinZero]

Some comments from Dr. Zubrin below.  I'm not too concerned about ejecta as I'm assuming they'll eventually have prepared landing pads by the time a base exists.  And with on-orbit refueling, SpaceShip should be able to get back to Earth without lunar ISRU.
....

Yeah relaunching the initial starships sound hard especially with their TPS still in tip top condition.. so we probably will just not do that. First landings unmanned and one way.. so also these first landings can have wings and TPS omitted.

If even that was somehow problematic, which I doubt.. well the starship hopper was sometimes called a flying watertower. We could almost literally land a water-tower on the moon. Having no atmosphere we could build a large framework instead of legs keeping the rocket thrust well away from the surface, and perhaps suggesting a future purpose literally as a water tower or similar.. though of course the main purpose is initial cargos to deploy the landing pad for future manned missions.. and all this equipment could be attached to the bottom of the "water tower" legs/struts for immediate trivial deployment to the surface.

[guckyfan]

You can also look at this the other way round.  If all your O2 is a byproduct of the solar panel plant you will not launch many spaceships.

This is a minor optimization barely worth mentioning, not an example of an integrated manufacturing system using every part of the pig but the squeal.

I am not looking at it that way. I am looking at LOX production. Si is just a sideproduct that may or may not be useful.

Large quantities of surplus O will be a byproduct of most ISRU actitities. Hydrolox engines burn fuel rich mixture so they don't need all the O from electrolysis process. Reduction of iron oxides by applying heat and H results in Fe and H20. The H is recycled by electrolysis resulting in surplus O.

Producing hydrogen fuel requires water which is available at the poles. Maybe all lunar activity will concentrate at the poles. But maybe they want a base away from the poles. My suggestion was for ISRU that would work everywhere on the moon.

[khg]

I have seriously been lurking here since November last year.

Before there are dedicated landing platforms on the Moon I think that the last propulsion system used for the Moon descent should have an Isp below 100.
That way larger particles or gravel will not be blown into an orbit or even to exceed the Moon escape velocity.

Maybe starship could have an almost parallel decent until near the surface, then make a maximum gimbal maneuver for the Raptor to start the rotation of the starship then shut it off.
Now let the low Isp propulsion system (cold gas?) take over during the last descent to the Moon.

Almost the same procedure during liftoff from the Moon except this time it is the Low ISP thrusters that rotate the starship before Raptor ignition.
What do you say, could this be a way to mitigate the risk of polluting space around the Moon?

Back to lurking... 

[Yggdrasill]

It's certainly a way to mitigate the consequences. But I'm not sure that it isn't a solution in search of a problem. It hasn't been proven that landing a Starship on the moon would be very problematic. More analysis is needed.

But if it turns out to be an issue, I think it would be easier simply to land in a small crater. That would cut down on particles making it into orbit pretty much entirely. Then you could deploy some sort of tractor, level out and compact a landing area and deploy a basalt fiber mat (or similar) for taking the brunt of the next landing burn.

[TrevorMonty]

I'm not SS could land on moon using Raptor as SS is 1/6 weight on moon. Raptor would need to throttle to 1/6 of its earth landing power setting.

Placing smaller landing engines near top of SS and have them point out at angle would help reduce issue with debris being kicked up.

[speedevil]

I'm not SS could land on moon using Raptor as SS is 1/6 weight on moon. Raptor would need to throttle to 1/6 of its earth landing power setting.

Then F9  can't land on earth, as the thrust of one merlin is considerably more than the 20 tons dry weight of the booster.

[Yggdrasill]

Then F9  can't land on earth, as the thrust of one merlin is considerably more than the 20 tons dry weight of the booster.

Exactly. You only need to be able to throttle really low if you want to be able to hover. Which is completely unnecessary.

A hoverslam/suicide burn at full throttle is the most efficient way to land. It means you're working against gravity for the least amount of time. It's unlikely SpaceX would choose such an aggressive strategy, but they could choose to land using two of the vacuum raptors throttled almost as low as they go. Means you would accelerate at something like 6 moon-Gs (1 earth-Gs) upwards if you cut the engines too late. Luckily you have some leeway. The LEM cut propulsion at 1.6 meters, and fell the rest of the way. Starship could do something similar, depending a bit on the landing legs.

[ncb1397]

I'm not SS could land on moon using Raptor as SS is 1/6 weight on moon. Raptor would need to throttle to 1/6 of its earth landing power setting.

Placing smaller landing engines near top of SS and have them point out at angle would help reduce issue with debris being kicked up.

It needs to be at minimum ~260 t(120 t dry, 140 t fuel) to get back to earth but with 20% throttle(390 kN), it only needs to be 240 t or higher for a 1:1 thrust to weight ratio. I know that 20% to 100% was shown at IAC 2016. Anybody have more recent information?

edit: vacuum thrust is actuallly 220 t, so 20% would be 431 kN and so minimum mass for 1:1 would be 266 t. It still basically lines up with what you need to get back to earth.

[Yggdrasill]

I wouldn't expect throttling much below 50%.

https://twitter.com/elonmusk/status/1107369149431341057?lang=en

[JonathanD]

Why would you need the vacs to throttle anyway?  Once in orbit you can control with burn time.

[ZChris13]

Why would you need the vacs to throttle anyway?  Once in orbit you can control with burn time.

Managing maximum acceleration.

[Barley]

You can also look at this the other way round.  If all your O2 is a byproduct of the solar panel plant you will not launch many spaceships.

This is a minor optimization barely worth mentioning, not an example of an integrated manufacturing system using every part of the pig but the squeal.

Large quantities of surplus O will be a byproduct of most ISRU actitities. Hydrolox engines burn fuel rich mixture so they don't need all the O from electrolysis process. Reduction of iron oxides by applying heat and H results in Fe and H20. The H is recycled by electrolysis resulting in surplus O.

There will not be large quantities of O2 as a by product.  Only small quantities.  If you want large quantities it has to be the primary product.

Most of the possible ISRU activities will result in comparable quantities of O2 and reduced material such as iron.  It is much easier to use hundreds or thousands of tonnes of O2 (and H2 or Ch4) to refuel than it is to use hundreds of tonnes of materials for other purposes.

You're not going to use 120 tonnes of iron to build another Starship.  Even crude use of materials such as rolling one inch iron plates and building double walled pressure vessels as living quarters are going to take vastly more work than pumping the same amount of O2 into a tank; and will quickly become pointless -- additional fitting out will consume far less material and far more labor.

Until a settlement is almost self sufficient most fuel and oxidizer will produced as fuel and oxidizer.  Anything left over will be mostly be waste, only a small a fraction of the waste can be used as byproducts.

[raketa]

I will try to clarify my idea by picture.
1/Moon Starship weight during launch time will be same as regular SS.
2/The only modification required is moving bulkheads  several feet  up, eating up a little bit crew space.
3/Increase refuel capacity will be used just on LEO
4/Save on refueling trips, since right now refueling will have happen in high elliptical orbit, decreasing tanks capacity for refueling.
Here is picture

[envy887]

I will try to clarify my idea by picture.
1/Moon Starship weight during launch time will be same as regular SS.
2/The only modification required is moving bulkheads  several feet  up, eating up a little bit crew space.
3/Increase refuel capacity will be used just on LEO
4/Save on refueling trips, since right now refueling will have happen in high elliptical orbit, decreasing tanks capacity for refueling.
Here is picture

But refueling higher is pretty simple and more effective. In fact, for maximum efficiency you want to refuel in low lunar orbit rather than elliptical Earth orbit. This means sending 2 ships, but they don't have to be fully refueled in LEO.

[rakaydos]

I will try to clarify my idea by picture.
1/Moon Starship weight during launch time will be same as regular SS.
2/The only modification required is moving bulkheads  several feet  up, eating up a little bit crew space.
3/Increase refuel capacity will be used just on LEO
4/Save on refueling trips, since right now refueling will have happen in high elliptical orbit, decreasing tanks capacity for refueling.
Here is picture

"The most common mistake experienced engineers make, is optimizing something that doesn't need to exist." -Elon Musk

[speedevil]

I will try to clarify my idea by picture.
1/Moon Starship weight during launch time will be same as regular SS.
2/The only modification required is moving bulkheads  several feet  up, eating up a little bit crew space.
3/Increase refuel capacity will be used just on LEO
4/Save on refueling trips, since right now refueling will have happen in high elliptical orbit, decreasing tanks capacity for refueling.
Here is picture

But refueling higher is pretty simple and more effective. In fact, for maximum efficiency you want to refuel in low lunar orbit rather than elliptical Earth orbit. This means sending 2 ships, but they don't have to be fully refueled in LEO.

This depends on how you define efficiency.
Maximum efficiency in terms of payload out per fuel in means reducing effective dry mass, which means filling up all the way is always better if you have a use for propellant at your destination and can transship cargo - or your propellant is your cargo.

A minimal number of SS launches (10) gets you 10 tons on the moon. (1t/launch)
Approximately double the number of launches to 20, and you get 100 tons. (5t/launch)
Double it again to 40, and you get 800 tons. (20 tons/launch)
At this point diminishing returns kick in - doubling again will only get you to ~25 tons/launch.

As sketched earlier in the thread.

[raketa]

I will try to clarify my idea by picture.
1/Moon Starship weight during launch time will be same as regular SS.
2/The only modification required is moving bulkheads  several feet  up, eating up a little bit crew space.
3/Increase refuel capacity will be used just on LEO
4/Save on refueling trips, since right now refueling will have happen in high elliptical orbit, decreasing tanks capacity for refueling.
Here is picture

But refueling higher is pretty simple and more effective. In fact, for maximum efficiency you want to refuel in low lunar orbit rather than elliptical Earth orbit. This means sending 2 ships, but they don't have to be fully refueled in LEO.

-No because you have to speed up to high elliptical orbit not just fuel but also dry weight of tanker.

1/LEO Refueling
-Tanker could deliver 150 t fuel to LEO
-In LEO you need 11 refueling mission 11*150 = 1650t
-This 11 mission will fill bigger tank(by 30%) but will be able to fly to Moon and back
-To fly from LEO to Moon you need delta ~10km/s
-SS on LEO        1650t
-SS on Moon     ~300t (delta v 6.4 km/s)
-SS back LEO    ~150t (delta v 2.3 km/s)

2/High elliptical orbit 10km/s
-required delta v 2.3km/s
-SS tanker on LEO 100+150t= 250t
-SS tanker on HEO 250t - 115t = 135t
- 22 * 35 = 800t(fuel)
You need 22 refueling missions

Fly from HEO to Moon and back you need 7.5kms
-SS on HEO          ~900t
-SS on Moon        ~300t (delta v 4.1km/s)
-SS back on LEO   ~200t (delta v 2.3 km/s)

It will required 50% less refueling missions, if SS tank could be stretch internally by 30%, just using crew space.

[rakaydos]

I will try to clarify my idea by picture.
1/Moon Starship weight during launch time will be same as regular SS.
2/The only modification required is moving bulkheads  several feet  up, eating up a little bit crew space.
3/Increase refuel capacity will be used just on LEO
4/Save on refueling trips, since right now refueling will have happen in high elliptical orbit, decreasing tanks capacity for refueling.
Here is picture

But refueling higher is pretty simple and more effective. In fact, for maximum efficiency you want to refuel in low lunar orbit rather than elliptical Earth orbit. This means sending 2 ships, but they don't have to be fully refueled in LEO.

-No because you have to speed up to high elliptical orbit not just fuel but also dry weight of tanker.

1/LEO Refueling
-Tanker could deliver 150 t fuel to LEO
-In LEO you need 11 refueling mission 11*150 = 1650t
-This 11 mission will fill bigger tank(by 30%) but will be able to fly to Moon and back
-To fly from LEO to Moon you need delta ~10km/s
-SS on LEO        1650t
-SS on Moon     ~300t (delta v 6.4 km/s)
-SS back LEO    ~150t (delta v 2.3 km/s)

2/High elliptical orbit 10km/s
-required delta v 2.3km/s
-SS tanker on LEO 100+150t= 250t
-SS tanker on HEO 250t - 115t = 135t
- 22 * 35 = 800t(fuel)
You need 22 refueling missions

Fly from HEO to Moon and back you need 7.5kms
-SS on HEO          ~900t
-SS on Moon        ~300t (delta v 4.1km/s)
-SS back on LEO   ~200t (delta v 2.3 km/s)

It will required 50% less refueling missions, if SS tank could be stretch internally by 30%, just using crew space.

Now calculate how many flights will be nessesary to recoup the development costs.

[envy887]

I will try to clarify my idea by picture.
1/Moon Starship weight during launch time will be same as regular SS.
2/The only modification required is moving bulkheads  several feet  up, eating up a little bit crew space.
3/Increase refuel capacity will be used just on LEO
4/Save on refueling trips, since right now refueling will have happen in high elliptical orbit, decreasing tanks capacity for refueling.
Here is picture

But refueling higher is pretty simple and more effective. In fact, for maximum efficiency you want to refuel in low lunar orbit rather than elliptical Earth orbit. This means sending 2 ships, but they don't have to be fully refueled in LEO.

This depends on how you define efficiency.
Maximum efficiency in terms of payload out per fuel in means reducing effective dry mass, which means filling up all the way is always better if you have a use for propellant at your destination and can transship cargo - or your propellant is your cargo.

A minimal number of SS launches (10) gets you 10 tons on the moon. (1t/launch)
Approximately double the number of launches to 20, and you get 100 tons. (5t/launch)
Double it again to 40, and you get 800 tons. (20 tons/launch)
At this point diminishing returns kick in - doubling again will only get you to ~25 tons/launch.

As sketched earlier in the thread.

I'm skeptical of orbital cargo transfer due to volume constraints. 150 kg/m3 is already pretty dense for anything except bulk liquids.

However, I think you can hit 10 landed tons per launch with only 15 launches: 10 for the cargo lander and 5 more for the tanker.

I will try to clarify my idea by picture.
1/Moon Starship weight during launch time will be same as regular SS.
2/The only modification required is moving bulkheads  several feet  up, eating up a little bit crew space.
3/Increase refuel capacity will be used just on LEO
4/Save on refueling trips, since right now refueling will have happen in high elliptical orbit, decreasing tanks capacity for refueling.
Here is picture

But refueling higher is pretty simple and more effective. In fact, for maximum efficiency you want to refuel in low lunar orbit rather than elliptical Earth orbit. This means sending 2 ships, but they don't have to be fully refueled in LEO.

-No because you have to speed up to high elliptical orbit not just fuel but also dry weight of tanker.

1/LEO Refueling
-Tanker could deliver 150 t fuel to LEO
-In LEO you need 11 refueling mission 11*150 = 1650t
-This 11 mission will fill bigger tank(by 30%) but will be able to fly to Moon and back
-To fly from LEO to Moon you need delta ~10km/s
-SS on LEO        1650t
-SS on Moon     ~300t (delta v 6.4 km/s)
-SS back LEO    ~150t (delta v 2.3 km/s)

2/High elliptical orbit 10km/s
-required delta v 2.3km/s
-SS tanker on LEO 100+150t= 250t
-SS tanker on HEO 250t - 115t = 135t
- 22 * 35 = 800t(fuel)
You need 22 refueling missions

Fly from HEO to Moon and back you need 7.5kms
-SS on HEO          ~900t
-SS on Moon        ~300t (delta v 4.1km/s)
-SS back on LEO   ~200t (delta v 2.3 km/s)

It will required 50% less refueling missions, if SS tank could be stretch internally by 30%, just using crew space.

Landing and returning 150 t does require 22 refueling launches of 150 t each: 7 each to load two tankers, and 8 to fuel a loaded cargo landing ship. All three burn for TLI, transfer fuel to the cargo ship while en route to the Moon, tankers free return to LEO, cargo ship lands and then returns with the full 150 t of cargo to LEO.

But I'm pretty sure that landings will be initially be dominated by cargo downmass, and return mass will be quite small. After all, not everything you bring to the Moon needs to come back to Earth. For 15 refueling launches you can land 150 t of cargo, and return 30 t:

Lets say the "elliptical orbit" we choose to refuel in is TLI. 15 refueling launches of 150 t each will fill up both the tanker ship and the cargo ship in LEO. Both ships burn for TLI and rendezvous during transit to the Moon. The tanker does a free return and aerobrakes into LEO (~50 m/s), so it only needs to mass 122 t after transferring off prop. It starts at 1200 t of prop + 120 t dry mass, and burns down to 560 t total mass in TLI. So it can offload 562-122=440 t of props to the cargo vehicle. The cargo ship fills up to 1470 t total mass in LEO and has burned down to 625 t total mass in TLI. It takes on 440 t of prop form the tanker and thus has a total mass of 1065 t before starting lunar orbit insertion. After 3 km/s for insertion and landing, it has a total mass of 475 t on the lunar surface. It has to offload 120 t of cargo, but can bring 30 t back through the 3 km/s return to aerobrake into LEO.

Even better, only takes 12 launches to land and return 30 t, which is about the mass of a fully stocked Bigelow BA330 with 10+ crew inside.

This is all assuming refueling in highly elliptical Earth orbit (aka TLI). I think LLO refueling is slightly more efficient.