totm nov 2023 SpaceX Discussion Thread

[RedKraken]

42 minutes ago, Rakaydos said:

The engins dont HAVE to throttle as deeply at the moon, because the rocket (refueled in eliptical orbit) is still going to have half it's fuel when landing on the moon, lowering it's TWR.

Fair enough.

I had not considered elliptical refueling.

 

[harrisjosh2711]

Someone tell Elon I'm going to beat him to the punch. In all seriousness, I love what spaceX is doing and I'm glad to see as many people on here feel the same!

Edited September 30, 2017 by harrisjosh2711

[Julien Kerman]

20 hours ago, Nibb31 said:

What do you mean ?

Last year they presented us this:   

 

It was this insanely large rocket, 12m in diameter, 122m tall, 42 Raptor engines in the first stage and 3 times heavier than the Saturn V.

My question was if they cancelled this in order to build the smaller BFR vehicle.

[Rune]

2 hours ago, Rakaydos said:

The engins dont HAVE to throttle as deeply at the moon, because the rocket (refueled in eliptical orbit) is still going to have half it's fuel when landing on the moon, lowering it's TWR.

Yup. Besides, 85mT+150mT payload, already 235mT. In order to keep about two and a half km/s to get back, you need a Mr of about two, so over 400mT when it touches down on the Moon. That assumes you take the cargo back of course, which is stupid, but still, a minimum of 310mT on touchdown (85*2+150).

 

Rune. Add hoverslam software developed for F9, and it starts looking easy.

Edited September 30, 2017 by Rune

[kerbiloid]

34 minutes ago, harrisjosh2711 said:

Someone tell Elon I'm going to beat him to the punch. In all seriousness, I love what space is doing and I'm glad to see as many people on here feel the same!

Reserve your rights asap, before Space-X can use your designs!

[Nibb31]

22 minutes ago, Julien Kerman said:

My question was if they cancelled this in order to build the smaller BFR vehicle.

The design evolved from 12m diameter, which was impractical for many reasons, to 9m, but it's the same project.

You have to expect more changes. It's a work in progress.

 

[Cassel]

47 minutes ago, Nibb31 said:

The design evolved from 12m diameter, which was impractical for many reasons, to 9m, but it's the same project.

You have to expect more changes. It's a work in progress.

 

May I ask stupid questions, why it was impractical? Why 9m is better? And what is next smaller practical diameter?

Edited September 30, 2017 by Cassel

[magnemoe]

2 hours ago, Rune said:

Yup. Besides, 85mT+150mT payload, already 235mT. In order to keep about two and a half km/s to get back, you need a Mr of about two, so over 400mT when it touches down on the Moon. That assumes you take the cargo back of course, which is stupid, but still, a minimum of 310mT on touchdown (85*2+150).

Rune. Add hoverslam software developed for F9, and it starts looking easy.

Assume smaller payload for moon unless its to build an permanent base. Some rovers, perhaps an drill rig, still don't see it goes over 50 ton. 
You might want to bring tourists even on an science mission as you have room and they help pay for the bill, still they don't add much weight even if you have rovers for them too. 
 

[Grand Ship Builder]

I'll begone now.

[sevenperforce]

On the subject of landing on the Moon -- recall that one of the first things Elon talked about was engine redundancy on landing. The two landing engines are close enough together that each can gimbal its thrust through the CoM, enabling single-engine landings if the other engine fails.

A single SL raptor, downthrottled all the way, should be able to hover on the Moon with around 30-50% propellant loading.

12 minutes ago, tater said:

Being trapped inside my entire life would not make me feel excited, just trapped.

Read (or listen, I know I heard a podcast about people who live at the research base in Antartica--radiolab or TAL, maybe) about people in Antartica. They get a little kooky.

I think that people living on a suitable large torus habitat would have far better lives. They'd have an outside to walk around in shirtsleeves, they'd still be able to do "space" stuff, best of both worlds. Mars would be interesting to visit, but not to live.

I'm sure some people will feel that way and some people won't.

[Nightside]

8 hours ago, kerbiloid said:

1.
How many launchpads/landing zones will be built for the Big F. Hopper?

If 1..2, then you have to spend several hours getting to the nearest one,
then jump from one continent to another,
then several hours more to get from the LZ to your destination.
Instead of just sitting several hours in a regular plane from the nearest airport.

If many - how often would fly a hopper from any of them?
So, you have to wait several weeks to save several hours? Very fast way, indeed.

2.
How many Big F. Hoppers would be built?

If 1..2 - they are unique original product, very expensive.

If you are looking to repeat the performance of making a lot of money very quickly you need to be opening up new markets, not by slightly outperforming existing tech (F9 for example) in well established markets.

If the hopper plan were to work, it would be by opening up new routes. It would likely not be competive to a NYC-London airliner route.

[tater]

Leaving these here for reference.

150 tons in LEO (dunno if that is an eccentric LEO or not) means they can fly upper stages with GEO comsats, and not have to leave LEO. With a single tanker they can bring north of 100 tons to GEO.

[tater]

So here's an idea.

Make a tug capable of lifting a pretty large sat to GEO as economically as possible---I'd give it ions, but perhaps some hypergolic as well for higher thrust needs. This thing can be pretty large, and can have many tons of propellant. 10s of tons at the very least.

Launch BFS to LEO, rendezvous with a tug. Tug is docked with customer sat, and heads to GEO. Tug might in addition to a docking ring have a grapple. It could head back to LEO, or it could grab a defunct GEO sat and head back to LEO on ions again. At some point it uses hypergolics to lower perigee to reenter the junk, lets go, then raises perigee to LEO again. Rinse, repeat. BFS can refuel this thing as needed as a comanifest thing.

Edited September 30, 2017 by tater

[Spaceception]

12 minutes ago, tater said:

So here's an idea.

Make a tug capable of lifting a pretty large sat to GEO as economically as possible---I'd give it ions, but perhaps some hypergolic as well for higher thrust needs. This thing can be pretty large, and can have many tons of propellant. 10s of tons at the very least.

Launch BFS to LEO, rendezvous with a tug. Tug is docked with customer sat, and heads to GEO. Tug might in addition to a docking ring have a grapple. It could head back to LEO, or it could grab a defunct GEO sat and head back to LEO on ions again. At some point it uses hypergolics to lower perigee to reenter the junk, lets go, then raises perigee to LEO again. Rinse, repeat. BFS can refuel this thing as needed as a comfiest thing.

That might be something else the BFS could do on the Moon, mine the regolith, and refill those tugs, they could receive fuel from Earth, but hey, another reason for a Moon base.

EDIT: or just use the cargo version of BFR, and do above, to save costs in developing another vehicle, and keeping everything integrated easily.

EDITEDIT: they could slightly redesign the front for spaceship tug purposes, but the fuel/engine part would stay the same.

Edited September 30, 2017 by Spaceception

[IncongruousGoat]

1 minute ago, Spaceception said:

That might be something else the BFS could do on the Moon, mine the regolith, and refill those tugs, they could receive fuel from Earth, but hey, another reason for a Moon base.

Mine the regolith... for what, exactly? Ions need xenon, or cesium, or other heavy stuff you don't exactly find in lunar regolith. Hypergolics are even worse-they're nitrogen compounds, and you're definitely not going to find nitrogen in the lunar regolith. About the only thing that has any utility as a propellant that you'll find in the lunar regolith is oxygen trapped in oxides and silicates, and even that's no good without an appropriate fuel to burn.

[sevenperforce]

13 minutes ago, tater said:

So here's an idea.

Make a tug capable of lifting a pretty large sat to GEO as economically as possible---I'd give it ions, but perhaps some hypergolic as well for higher thrust needs. This thing can be pretty large, and can have many tons of propellant. 10s of tons at the very least.

Launch BFS to LEO, rendezvous with a tug. Tug is docked with customer sat, and heads to GEO. Tug might in addition to a docking ring have a grapple. It could head back to LEO, or it could grab a defunct GEO sat and head back to LEO on ions again. At some point it uses hypergolics to lower perigee to reenter the junk, lets go, then raises perigee to LEO again. Rinse, repeat. BFS can refuel this thing as needed as a comfiest thing.

Absolutely.

I would say to make the tug quite large -- just large enough that it can fit inside the BFR on a nominal launch. No need for ions; just give it a single Raptor Vacuum and large propellant tanks. Send it up ahead of time.

Instead of selling single launches and sometimes dual-manifesting or having secondary payloads, SpaceX would begin to sell "slots" on group GTO launches. Schedule well in advance. Cargo BFR would take several (up to 10 or 15, perhaps) large comsats up to LEO at once, then rendezvous with the tug. The tug takes the comsats up individually or one-at-a-time, depending on  mission requirements, then uses upper-atmosphere aerobraking passes to come back to LEO, either to take the next comsat up, or to wait for the next mission.

The tug can refuel from the cargo BFR each time they rendezvous, since the BFR will virtually always have excess propellant for comsat missions.

After several dozen missions, the tug can simply rendezvous with the BFR one last time, dock inside the payload bay, and return to Earth for servicing and refurbishment.

It works because a big tank and a single Vac Raptor can take comsats MUCH further with a given amount of fuel than the BFR cargo can, simply because it doesn't have nearly as much dry mass to contend with.

[Spaceception]

9 minutes ago, IncongruousGoat said:

Mine the regolith... for what, exactly? Ions need xenon, or cesium, or other heavy stuff you don't exactly find in lunar regolith. Hypergolics are even worse-they're nitrogen compounds, and you're definitely not going to find nitrogen in the lunar regolith. About the only thing that has any utility as a propellant that you'll find in the lunar regolith is oxygen trapped in oxides and silicates, and even that's no good without an appropriate fuel to burn.

True. And I made a couple edits

[sevenperforce]

14 minutes ago, Spaceception said:

That might be something else the BFS could do on the Moon, mine the regolith, and refill those tugs, they could receive fuel from Earth, but hey, another reason for a Moon base.

EDIT: or just use the cargo version of BFR, and do above, to save costs in developing another vehicle, and keeping everything integrated easily.

EDITEDIT: they could slightly redesign the front for spaceship tug purposes, but the fuel/engine part would stay the same.

Really no fuel on the moon.

Much better to do a dedicated single-engine tug than to redesign the cargo BFR as a tug. You REALLY don't need that much thrust for sending comsats to GTO.

Being able to choose whether you put comsats in GTO or GEO is big, too. Pay a little extra for the extra tug-fuel to circularize your big comsat in GEO, and you don't have to worry about self-circularizing. The tug burns retrograde, aerobrakes down to LEO, and is none the worse for wear.

[kerbiloid]

KSPI-E includes a hybride Aluminium-LOX engine, both components are to be produced from the regolith.

[IncongruousGoat]

36 minutes ago, kerbiloid said:

KSPI-E includes a hybride Aluminium-LOX engine, both components are to be produced from the regolith.

Aluminum and LOX? Build me such a thing IRL, and then we can talk about the manufacturing difficulties. Which are extensive.

Aluminum is manufactured by the Hall-Heróult process, which involves electrolysis of an alumina-cryolite molten salt bath. Have fun pulling that off on the Moon, where power would be at a serious premium. Not to mention the effort required to extract oxygen from oxygen and silicates in the regolith.

EDIT: Apparently, Al/LOX has been made to work in an engine, so that at least isn't a problem.

Edited September 30, 2017 by IncongruousGoat
Updated information

[kerbiloid]

5 minutes ago, IncongruousGoat said:

Aluminum is manufactured by the Hall-Heróult process, which involves electrolysis of an alumina-cryolite molten salt bath. Have fun pulling that off on the Moon, where power would be at a serious premium. Not to mention the effort required to extract oxygen from oxygen and silicates in the regolith.

Yes, a lot of energy. But if one extracts (by pure physics, as there are no coke or so on the Moon, too) oxygen from regolith, metals (including Al) would remain as bonus.
(I know, that Al cannot be extracted chemically, I've mentioned the coke because lunar oxygen is contained in iron oxides, too.)

Edited September 30, 2017 by kerbiloid

[sevenperforce]

7 minutes ago, IncongruousGoat said:

Aluminum and LOX? Build me such a thing IRL, and then we can talk about the manufacturing difficulties. Which are extensive.

Aluminum is manufactured by the Hall-Heróult process, which involves electrolysis of an alumina-cryolite molten salt bath. Have fun pulling that off on the Moon, where power would be at a serious premium. Not to mention the effort required to extract oxygen from oxygen and silicates in the regolith.

Not undoable, perhaps, but definitely outside the realm of autonomous, readily-reusable liquid-fueled rockets with regular propellant transfer.

[tater]

Al-lox was worked on decades ago, I have the papers on it.

[IncongruousGoat]

2 minutes ago, kerbiloid said:

Yes, a lot of energy. But if one extracts (by pure physics, as there are no coke or so on the Moon, too) oxygen from regolith, metals (including Al) would remain as bonus.
(I know, that Al cannot be extracted chemically, I've mentioned the coke because lunar oxygen is contained in iron oxides, too.)

Er... what? "By pure physics"? How do you propose to do this, exactly?

[kerbiloid]

4 minutes ago, IncongruousGoat said:

Er... what? "By pure physics"? How do you propose to do this, exactly?

Er... Not that I propose, I am not the mod maintainer.

But as you have said yourself,

50 minutes ago, IncongruousGoat said:

About the only thing that has any utility as a propellant that you'll find in the lunar regolith is oxygen trapped in oxides and silicates, and even that's no good without an appropriate fuel to burn.

So, if somebody can extract the "oxygen trapped in oxides", this means that he can split the oxides into oxygen and metals.
And as unlikely he had brought cryolite, coke, lime or anything else, probably he does this not chemically, but non-chemically. I.e. by some physical process (you had mentioned the oxygen extraction, btw, not me).

Personally I can imagine (and consider this as a future mainstream) only heating any piece of rock and junk up to ionization temperature and separating ions of different elements by a magnetic trap, getting metal powders of pure Fe, Al, Ti, etc.
But, this is, of course, a more or less far future, not BFR level.

So, I just mean that if somebody can get O, he automatically gets Al as junk.