Advanced Rocketry Seems More Wasteful From an ISRU Perspective Than Chemical Rocketry

[Spacescifi]

With advanced rocketry you are probably relying most on monopropellants since you neither need nor want oxidizer because antimatter or fusion etc is shooting the propellant out rather than a chemical reaction.

 

The price you pay at your industrial scale asteroid and moon bases is well illustrated below.

So you get several tons of hydrogen from ice.

Great. What are you going to do with all the leftover oxygen? Let it leak out into the void? You don't need it. Storing it for later use would just require continual enlargment of your storage facilities.

 

Chemical rocketry though uses both the oxidizer and the propellant so no waste.

 

Question: Would it even be wise to try to use liquid oxygen as a monopropellant?

 

I know oxidizer would wreck a nuclear reactor so that is not an option... might work with a fusion reaction though and antimatter works with everything.

 

Any way beyond using old chemical rocketry in the far future to make use of the excess oxygen instead of wasting it to the void?

 

Edited February 16, 2023 by Spacescifi

[magnemoe]

An fusion engine is monopropelant as in you don't add anything extra.  However its has an ISP who start with 40.000 s and can go up to hundreds of thousands. 
Now you could dump reaction mass into the plasma from the engine as an sort of afterburner, this would increase trust, it would also reduce you ISP but it you are injecting waste material its better than dumping it. 

But you are correct in that unless you can generate the fuel locally you are at an disadvantage. I can easy see this play out in KSP 2, you use an fusion or orion drive to go to and from Jool but you use chemical or nuclear thermal between the moons, as you don't need 300 km/s dv here  

[jimmymcgoochie]

If large-scale ISRU production of hydrogen from water (ice) is both scientifically and economically viable then there will also be a well-established market for oxygen so people living anywhere other than Earth can breathe and not die. Bottle it up and ship it out using that hydrogen propellant.

Chemical rockets tend to burn fuel-rich for a few reasons: hot oxygen is very reactive indeed and will corrode your engine(s) so excess fuel will ensure all the oxygen reacts with fuel and not engine; rocket fuel is generally lower molecular mass than oxygen, lower molecular mass = higher ISP so more fuel can lead to higher ISP even if unburnt- especially hydrolox which usually runs well above stoichiometric ratios of hydrogen to oxygen; and depending on the combustion cycle a rocket engine may need more fuel than oxidiser to run the turbopumps which is separate to the main combustion chamber that produces thrust. Suggesting that excess oxygen from a hydrolox ISRU should just be vented to space is complete nonsense, oxygen will be just as valuable- if not more so- than rocket fuel in space, especially colonies/settlements/anything not a ship.

TL;DR people still need to breathe.

Edited February 17, 2023 by jimmymcgoochie

[Spacescifi]

4 hours ago, jimmymcgoochie said:

If large-scale ISRU production of hydrogen from water (ice) is both scientifically and economically viable then there will also be a well-established market for oxygen so people living anywhere other than Earth can breathe and not die. Bottle it up and ship it out using that hydrogen propellant.

Chemical rockets tend to burn fuel-rich for a few reasons: hot oxygen is very reactive indeed and will corrode your engine(s) so excess fuel will ensure all the oxygen reacts with fuel and not engine; rocket fuel is generally lower molecular mass than oxygen, lower molecular mass = higher ISP so more fuel can lead to higher ISP even if unburnt- especially hydrolox which usually runs well above stoichiometric ratios of hydrogen to oxygen; and depending on the combustion cycle a rocket engine may need more fuel than oxidiser to run the turbopumps which is separate to the main combustion chamber that produces thrust. Suggesting that excess oxygen from a hydrolox ISRU should just be vented to space is complete nonsense, oxygen will be just as valuable- if not more so- than rocket fuel in space, especially colonies/settlements/anything not a ship.

TL;DR people still need to breathe.

 

You have a point... not gonna lie.

 

Yet without massive rotating habs or 100 meter long tethers for rotation I do not see any large populations living in space.

 

I am actually less fond of the idea from a scifi perspective, since it is far easier to colonize an Earth clone since those seem more common in scifi than reality.

 

Living in space is hard... since you have to recycle everything in a virtually closed ecosystem except for occasional supplies and constant shipments of LOX and LH.

 

So long Earth clones exist I do not see ever a large population living on any space station. Since Earth clone life is better.

[jimmymcgoochie]

2 hours ago, Spacescifi said:

 

You have a point... not gonna lie.

 

Yet without massive rotating habs or 100 meter long tethers for rotation I do not see any large populations living in space.

 

I am actually less fond of the idea from a scifi perspective, since it is far easier to colonize an Earth clone since those seem more common in scifi than reality.

 

Living in space is hard... since you have to recycle everything in a virtually closed ecosystem except for occasional supplies and constant shipments of LOX and LH.

 

So long Earth clones exist I do not see ever a large population living on any space station. Since Earth clone life is better.

Then why are you wasting time electrolysing ice? If you’re looking at interstellar levels of technology then gas giant harvesting is the obvious answer.

[Nuke]

this is why im a big fan of purely thermal engines, as you can use practically anything as propellant. isp will suck, but it will enable rock hopping. 

Edited February 17, 2023 by Nuke

[Shpaget]

3 hours ago, Spacescifi said:

So long Earth clones exist I do not see ever a large population living on any space station. Since Earth clone life is better.

Are we now talking FTL or generation ships?

If FTL is on the table, then who cares about propellant?

[Spacescifi]

3 hours ago, Shpaget said:

Are we now talking FTL or generation ships?

If FTL is on the table, then who cares about propellant?

 

I do not subcribe to the idea that a ship with the power to do FTL should ever land anywhere.

 

The safer thing to do is make a large FTL carrier that non-FTL ships dock with.

 

Then warp/hyperjump to the next system over, park the carrier in orbit about a light second away from the destination planet and let the docked vessels disembark.

 

Consider spaceships to be the solar system equivalent of drop ships, while the FTL carrier is what actually takes them between systems.

[darthgently]

If terraforming via mod or stock ever becomes a thing you probably would always be needing more oxygen

[Spacescifi]

31 minutes ago, darthgently said:

If terraforming via mod or stock ever becomes a thing you probably would always be needing more oxygen

What do you mean by mod or stock?

 

I do agree for colonizing dead, lifeless worlds you absolutely want lots of oxygen for crew habitats.

[darthgently]

2 hours ago, Spacescifi said:

What do you mean by mod or stock?

I forgot which forum I was in, thought it was KSP2 related, lol

[Nuke]

8 hours ago, Shpaget said:

Are we now talking FTL or generation ships?

If FTL is on the table, then who cares about propellant?

rock hopping + breeding = slow colonization. the oort cloud may go out a lightyear or two and may overlap with another star's cloud. so instead of one long hop its a bunch of little ones. granted we have to find a way to make human life sustainable at every colony, but if you can solve that problem, then it doesn't matter where we go so long as there are exploitable resources. in situations where propulsion technology catches up to the human frontier, you get a big boost in expansion.