totm nov 2023 SpaceX Discussion Thread

[cubinator]

38 minutes ago, Mad Rocket Scientist said:

The Case For Mars talked about using some feedstock hydrogen hauled from earth to make CH4 and H2O, then splitting the H2 off and recycling it through the process. It used 6 tons of hydrogen to make 108 tones of CH4-O2 propellant, and avoided needing ice mining the moment you arrive.

That seems like a workable plan.

[IncongruousGoat]

1 hour ago, Mad Rocket Scientist said:

The Case For Mars talked about using some feedstock hydrogen hauled from earth to make CH4 and H2O, then splitting the H2 off and recycling it through the process. It used 6 tons of hydrogen to make 108 tones of CH4-O2 propellant, and avoided needing ice mining the moment you arrive.

Well, sure, but now you're stuck hauling hydrogen all the way out to Mars, which is pretty tricky very difficult (as in, we don't have a good way to do it). If you're going that route it would be easier to go the Andy Weir route and bring hydrazine, which you then decompose to get hydrogen out. But then you're stuck hauling hydrazine out to Mars. Bringing the hydrogen as methane is problematic, since methane pyrolysis isn't the cleanest process ever, and bringing it as water is very mass-inefficient.

Edited June 11, 2018 by IncongruousGoat

[Mad Rocket Scientist]

3 minutes ago, IncongruousGoat said:

Well, sure, but now you're stuck hauling hydrogen all the way out to Mars, which is pretty tricky very difficult (as in, we don't have a good way to do it). If you're going that route it would be easier to go the Andy Weir route and bring hydrazine, which you then decompose to get hydrogen out. But then you're stuck hauling hydrazine out to Mars. Bringing the hydrogen as methane is problematic, since methane pyrolysis isn't the cleanest process ever, and bringing it as water is very mass-inefficient.

I think the book said it was something like an extra 15% for boiloff. It seems like around 0.1%-0.5%/day, depending on how heavily insulated the tanks are, is normal. That seems good enough for initial operations.

[AVaughan]

Is there any reason they couldn't just capture the hydrogen boil off, and re-liquify it?  (Although it might be easier/more efficient to just use insulated tanks, manage ship orientation to help keep the hydrogen tanks as cool as possible, and bring extra hydrogen to deal with the remaining boil off). 

This sort of process (hydrogen + carbon dioxide -> methane + water, with the water then split into hydrogen + oxygen) could be run in a plant that was installed in an automated BFR that was sent on a conjunction before a manned mission.  That way they could demonstrate that everything the plant was working, and that fuel would be available for the return leg of a manned mission.  By not relying on extracting water from Martian soil, there should be less that could go wrong for an automated fuel generation mission.  (By my math, 80 tons of hydrogen would make about 960 tons of methane + liquid oxygen. which is close to full tanks for a BFR cargo ship.  That would mean such a BFR could still bring about 70 tons of fuel production plant or other cargo.  Since a fuel production plant would already need the equipment to liquify oxygen, maybe it's not too much of a stretch to also include the ability to liquify hydrogen). 

Water extraction from the Martian soil could wait for a manned mission.  

Edited June 11, 2018 by AVaughan

[sevenperforce]

5 hours ago, AVaughan said:

Is there any reason they couldn't just capture the hydrogen boil off, and re-liquify it?  (Although it might be easier/more efficient to just use insulated tanks, manage ship orientation to help keep the hydrogen tanks as cool as possible, and bring extra hydrogen to deal with the remaining boil off). 

Heat rejection becomes problematic when you're trying to cool something as cool as liquid hydrogen. The mass of your radiators rapidly outpaces any propellant stock boil-off savings.

 

[kerbiloid]

2 hours ago, sevenperforce said:

8 hours ago, AVaughan said:

Is there any reason they couldn't just capture the hydrogen boil off, and re-liquify it?  (Although it might be easier/more efficient to just use insulated tanks, manage ship orientation to help keep the hydrogen tanks as cool as possible, and bring extra hydrogen to deal with the remaining boil off). 

Heat rejection becomes problematic when you're trying to cool something as cool as liquid hydrogen. The mass of your radiators rapidly outpaces any propellant stock boil-off savings.

And that hydrogen is also a champion of heat capacity.

Spoiler

P.S.
Plan B. Bring to Mars methane, extract hydrogen from it , make ISRU methane....

Btw, both methane and oxygen are cryogenic, too. And they will be boiling off while being produced. Poor, poor idea.

Edited June 11, 2018 by kerbiloid

[RCgothic]

Also hydrogen can actually diffuse through solid tank walls, so even a perfectly refrigerated tank is going to lose some.

[sevenperforce]

4 minutes ago, RCgothic said:

Also hydrogen can actually diffuse through solid tank walls, so even a perfectly refrigerated tank is going to lose some.

And it will crack your tank over time as randomly migrating monatomic hydrogen atoms happen to meet up inside the metal lattice and mate.

6 hours ago, kerbiloid said:

Plan B. Bring to Mars methane, extract hydrogen from it , make ISRU methane....

YOU'VE GOT IT

Actually, let's bring kerosene and crack that into methane.

[Nefrums]

probably easier to launch a bunch of tanks with Hypergolic fuel into mars orbit and use that for landing/return  Even a falcon heavy could put close to 10 tons of fuel in mars orbit.

 

 

Edited June 11, 2018 by Nefrums

[Mad Rocket Scientist]

55 minutes ago, sevenperforce said:

YOU'VE GOT IT

Actually, let's bring kerosene and crack that into methane.

Bring coal, then make coal gas and liquefy to make a steampunk coal powered rocket engine. Brass fittings not included.

[sevenperforce]

4 minutes ago, Mad Rocket Scientist said:

Bring coal, then make coal gas and liquefy to make a steampunk coal powered rocket engine. Brass fittings not included.

Just bring carbon black. It's dense.

[CatastrophicFailure]

[kerbiloid]

6 hours ago, Mad Rocket Scientist said:

Bring coal, then make coal gas

 

6 hours ago, sevenperforce said:

Just bring carbon black. It's dense.

Gentlemen, haven't you forgotten that there is a lot of carbon on Mars? They need hydrogen.

The problem is how to deliver hydrogen, when any way of doing this, except local ice mining, means to bring several times more ballast than that hydrogen.

So, unless they just mine the ice in situ, Sabatier gives nothing good.

Edited June 12, 2018 by kerbiloid

[sevenperforce]

7 hours ago, kerbiloid said:

Gentlemen, haven't you forgotten that there is a lot of carbon on Mars? They need hydrogen.

Of course. That was the joke.

[kerbiloid]

Btw a dense proton beam can deliver as much pure hydrogen to Mars as you wish, with a near-light speed.
SpaceX should put proton traps on their ship, and catch the protons just before the methane manufacturing.

[KSK]

1 hour ago, kerbiloid said:

Btw a dense proton beam can deliver as much pure hydrogen to Mars as you wish, with a near-light speed.
SpaceX should put proton traps on their ship, and catch the protons just before the methane manufacturing.

That’s fine when you’ve only got one BFR at a time going to Mars. With multiple ships you need to be careful not to cross the streams.

Because crossing the streams is bad.

[magnemoe]

20 hours ago, kerbiloid said:

Btw a dense proton beam can deliver as much pure hydrogen to Mars as you wish, with a near-light speed.
SpaceX should put proton traps on their ship, and catch the protons just before the methane manufacturing.

Way more complex than just to mine for ice, note that ice would be very high on requirements for an base anyway.
You should be able to jump around on Mars pretty well with an BFS to once tanks is topped.  

[tater]

 

[tater]

Take away:

There are not enough boosters at, or OTW to the various launch sites to cover all the launches, so there will either be some delays in July, or they will refly some block 5 boosters pretty quickly.

[sh1pman]

1 hour ago, tater said:

or they will refly some block 5 boosters pretty quickly.

Well, that’s the whole point of Block 5, isn’t it?

[tater]

3 hours ago, sh1pman said:

Well, that’s the whole point of Block 5, isn’t it?

Yeah. Fingers crossed!

[CatastrophicFailure]

We have a date for the second Block 5 launch... but it’ll be a while. 

 

[tater]

 

[KSK]

Not going to repost the image but I'm getting goosebumps here - I think that news by @tater may even beat the Falcon Heavy launch. 

Why? Because this might be the point where SpaceX really start to live up to their name. Don't get me wrong - I like me a Falcon launch and booster recovery as much as the next space geek but there's more to space exploration than boosters. So seeing that they're working on space technologies other than boosters is... well see above.

Edited June 14, 2018 by KSK

[kerbiloid]

So, at the moment they hadn't started R&Ding the key component which may or may not make sense of the whole delivery system?

 

Edited June 15, 2018 by kerbiloid