A Reusuable Sea Launched Two Stage? Better Than Spacex?

[Spacescifi]

So most regular commenters in this part of the forum will agree that two-stage rockets beat SSTO's at putting max payload or cargo in orbit.

Whereas in scifi SSTO's tend to take precedence... it's a trope of sorts that is followed kind of without thinking about it

Because of the success of Spacex, I thought of a new 2-stage rocket that could be more efficient... but also more expensive and risky.

 

The Idea: A two-stage booster launched from the sea.

 

First stage fills itself with water from the ocean, and uses nuclear reactor power plus airbreathing rocketry to accelerate the 2-stage up to a height where separation occurs and the second stage takes flight.

 

The first stage falls back to the ocean but makes a powered landing with reserve water.

To fly anywhere else to a waiting ocean carrier ship is as simple as water refueling, and then making more powered water landings if not close enough to the carrier to land.

Beats flying over land where rapid refueling is not an easy option.

 

This idea has obvious advantages, but it would be more expensive and risky than Starship.

 

Also some have mentioned before that superheated steam tends to erode nuclear reactors.... which is not good. Surely there are engineering solutions that can be found, but my gut feeling is that the solution will be with technology we have yet to engineer.

Something truly new.

 

Your thoughts?

To me it's like the wannabe child of Sea Dragon and Spacex.... with Zubrin as the godfather who both sides try to quiet whenever he begins to speak of uranium salts...

 

 

[wumpus]

"Nuclear reactor power plus airbreathing rocketry" with ... water?  

[snip]

Launched from the sea:

The whole idea is to use a huge rocket and reduce infrastructure costs, this helps in launching the rare huge rocket (see Sealaunch).

Nuclear rocket: high-cost, likely requires a high cadence.  Only reason not to use ground launch is nuclearphobia.

Nuclear thermal rockets heat the propellant and expel it out the back.  There is essentially no reason not to use all water or all air.  And if you do use water (I think that's the right choice), make sure you purify it (probably reverse osmosis) before heating to rocket exhaust temps in your heating chamber.

Assuming stage 1 is nuclear, the big issue is getting enough thrust to get in space.  Almost certainly not going to happen, but if you want a spaceplane this  is the easiest way to justify it (you never need thrust > weight).

Assuming stage 1 is nuclear, there is no reason to drop the first stage.  Just switch "fuel" tanks to hydrogen and use that for your "second stage" to orbit (or beyond).

And while cracking water to hydrogen is inefficient, if you happen to have your nuclear reactor nearby *and* a strong hydrogen "fuel" tank handy cracking the water wouldn't be all that dumb (although you might eventually want turn around times high enough to crack the stuff at your launch base instead of waiting to refuel while doing the ISRU thing on Earth).

Isp of NTR/water is going to be lower than a SSME (same exhaust, and SSMEs and any reactor would melt running at the temperature of a SSME combustion chamber), but NTR/H₂ was achieving 800s in the early 1970s and should get a bit higher.

 

Edited July 21, 2021 by Vanamonde

[MKI]

I can't see directly integrating raw sea water into a launch system being a good idea.

Isn't Starship going to launch/land from ocean platforms anyways? So isn't this idea the same, except integrating Sealaunch tech?

16 hours ago, Spacescifi said:

Because of the success of Spacex, I thought of a new 2-stage rocket that could be more efficient... but also more expensive and risky.

I don't actually see anywhere this is more efficient. Its known sea water increases wear and tear as its corrosive, and thus will increase maintenance and decrease reliability. Its why SpaceX didn't originally want to land Dragon into the water, and rather wanted to land it on land. So putting your rocket in the ocean kills the whole idea. Now if you used some kind of barge, and just used the location on/next to the ocean as the "fuel" sure... but then you need to argue the rest of the system is more efficient than a traditional rocket. 

 

15 hours ago, wumpus said:

Do you use a randomizer to come up with these questions?

One element always seems to be nuclear powered first stages for some reason. Maybe they have the Dr. Evil checkbox marked. 

 

 

[Rakaydos]

Rule of thumb: if something is "better than SpaceX", and not already on SpaceX's roadmap, there's some kind of hidden drawback. Usually in the form of "the benifits are too small for the extra headaches (political, economic, material engineering, ect) to be worthwhile."

[jimmymcgoochie]

Using sea water for a NTR is not the same as a nuclear salt water rocket!

Nuclear reactors are large and heavy so it would be next to impossible to make one generate enough thrust to lift a) itself, b) all the reaction mass, c) the rest of the rocket’s structural mass and d) the payload on top. You can’t just switch a nuclear reactor on and off at the drop of a hat either, it takes time to ramp up or down the fission rate which doesn’t work for a propulsive landing where rapid changes are required.

[Rakaydos]

8 minutes ago, jimmymcgoochie said:

Using sea water for a NTR is not the same as a nuclear salt water rocket!

Nuclear reactors are large and heavy so it would be next to impossible to make one generate enough thrust to lift a) itself, b) all the reaction mass, c) the rest of the rocket’s structural mass and d) the payload on top. You can’t just switch a nuclear reactor on and off at the drop of a hat either, it takes time to ramp up or down the fission rate which doesn’t work for a propulsive landing where rapid changes are required.

If this was supposed to be a NSWR, the OP has COMPLETELY misunderstood the concept. A NSWR "salts" water with highly enriched radioactives, in a solution just below critical mass. Sodium Floride is REALLY not going to cut it.

[kerbiloid]

57 minutes ago, Rakaydos said:

Rule of thumb: if something is "better than SpaceX", and not already on SpaceX's roadmap, there's some kind of hidden drawback.

Rule of another hand thumb. If it is on SpaceX roadmap, there's still some kind of hidden drawback.

[Rakaydos]

1 minute ago, kerbiloid said:

Rule of another hand thumb. If it is on SpaceX roadmap, there's still some kind of hidden drawback.

If it's worth doing anyway, we call those "engineering trades."

[jimmymcgoochie]

@Rakaydossea salt is sodium chloride, not fluoride  but either way it isn’t fissile and would probably just melt and either clog up the inside of the reactor or pebbledash the engine nozzle with globs of semi-molten salt. And possibly fish…

[Vanamonde]

The world is full of people who don't know much about science. Why make fun of the ones that discuss it to learn more? 

Some comments removed. 

[sevenperforce]

13 minutes ago, Vanamonde said:

The world is full of people who don't know much about science. Why make fun of the ones that discuss it to learn more? 

I will say, very humbly, that there are people who do not know much about science and discuss it to learn more...

...and there are people who refuse to learn.

[Vanamonde]

47 minutes ago, sevenperforce said:

I will say, very humbly, that there are people who do not know much about science and discuss it to learn more...

...and there are people who refuse to learn.

And who gains by mocking them? 

[wumpus]

11 hours ago, sevenperforce said:

I will say, very humbly, that there are people who do not know much about science and discuss it to learn more...

...and there are people who refuse to learn.

I have to wonder just how many of these questions wouldn't be needed if somebody sat down and played KSP until they could reach another planet.  This one might be an edge case, as KSP has a limited range of nuclear rockets (the only one included matches the only one ever test fired) and you might not realize that the Isp of NTR/Water < hydrolox (for virtually all cases).  But a surprisingly large number would, especially the orbital mechanics ones.  Anything regarding TSTO might require the realism overhaul mod, but I'd recommend that for anyone who needs correcting on "things KSP doesn't cover/covers badly".

[Spacescifi]

On 7/19/2021 at 11:47 AM, MKI said:

I can't see directly integrating raw sea water into a launch system being a good idea.

Isn't Starship going to launch/land from ocean platforms anyways? So isn't this idea the same, except integrating Sealaunch tech?

I don't actually see anywhere this is more efficient. Its known sea water increases wear and tear as its corrosive, and thus will increase maintenance and decrease reliability. Its why SpaceX didn't originally want to land Dragon into the water, and rather wanted to land it on land. So putting your rocket in the ocean kills the whole idea. Now if you used some kind of barge, and just used the location on/next to the ocean as the "fuel" sure... but then you need to argue the rest of the system is more efficient than a traditional rocket. 

 

One element always seems to be nuclear powered first stages for some reason. Maybe they have the Dr. Evil checkbox marked. 

 

 

 

There are two ways I am aware of that increase thrust.

 

1. Increase propellant flow or mass.

2. Increase exhaust speed.

 

Number 1 has no limits if you don't mind staging to infinity.

Number 2 is limited by heat/energy available and the engine's tolerance for it.

I knew nuclear had better ISP, and I had assumed one could get thrust on par with chemical rockets if engineered sufficiently. Someone here mentioned nuclear dumbo rocket project that was aimed at doing that. LANTR is repeatedly mentioned as being capable of that as well.

 

I have heard twice that nuke reactors are cooler than the SSME (spaces shuttle main engine) rockets.

 

The main problem is not so much weight, but TWR. Nuclear TWR would need to be increased.

So perhaps cracking LOX and LH is more practical.

 

Perhaps just use a nuke reactor forthe cracking on earth, regular chemical for launch, and swtich to nuclear in space.

 

Granted that would be a complex machine that could switch over it's main engine to NTR from chemical midflght.... but it could be done.

 

Not cheaper than spacex, all it really grants is DIY way to orbit without any help but your own spaceship on Earth.

That's is it's main advantagem

Edited July 21, 2021 by Spacescifi

[MKI]

45 minutes ago, Spacescifi said:

The main problem is not so much weight, but TWR. Nuclear TWR would need to be increased.

And the dangers of radiations from a nuclear propulsion in the atmosphere right?

[Spacescifi]

1 hour ago, MKI said:

And the dangers of radiations from a nuclear propulsion in the atmosphere right?

 

There are ways to make an NTR not shoot out high levels of radiation.

 

Yet from what I have seen, such measures often require reducing either mass flow, heat/energy, or both.

I wonder if a non-nuclear two stage that cracks it's own LOX and LH from the ocean might be feasible instead?

[Beccab]

6 hours ago, Spacescifi said:

I wonder if a non-nuclear two stage that cracks it's own LOX and LH from the ocean might be feasible instead?

What should be the advantage with that? Refuelling normally from a tank works just fine, and doesn't require carrying the weight of the machinery of separating LOX and LH from the ocean

[kerbiloid]

And feeds the electrolyser with H and O from the electrolyzed water.

(As no nuke on board.)

[jimmymcgoochie]

2 hours ago, kerbiloid said:

And feeds the electrolyser with H and O from the electrolyzed water.

(As no nuke on board.)

Perpetual energy much?

Electrolyse the water, to them recombine it and produce power, to then split the water again? This isn’t KSP’s magic fuel cells, where you can produce enough LF/Ox to run the fuel cells that power LF/Ox production in an ISRU- this is reality, where electrolysing water requires a great deal more energy than you’ll get from putting the resulting hydrogen/oxygen through a fuel cell and where things like sea salt will quite happily get in the way, producing chlorine gas and sodium (hydroxide, since sodium metal reacts immediately with water) rather than water and oxygen unless you run it through a desalinisation process first which requires even more power.

Nuclear engines aren’t suited for use on launch vehicles, where conventional rockets are more than up for the job, but excel in vacuum where their lower TWR doesn’t matter, having huge propellant tanks isn’t a problem for aerodynamics etc. and also helps limit boiloff by reducing the surface area to volume ratio and long burn times can be used instead of having to switch the reactor on and off repeatedly.

[kerbiloid]

And that's why the H-O engine needs an external source of energy like a nuke or anything else.

[Spacescifi]

15 hours ago, Beccab said:

What should be the advantage with that? Refuelling normally from a tank works just fine, and doesn't require carrying the weight of the machinery of separating LOX and LH from the ocean

 

The booster will carry the  nuckear reactor solely for cracking LOX/LH from sea water. Chemical rocketry will propel it.

 

The second stage is also chemical,but has a reserve nuclear reactor that can be used in orbit or for interplanetary where high thrust is not required but efficiency helps more.

[sevenperforce]

On 7/21/2021 at 4:27 PM, Spacescifi said:

There are two ways I am aware of that increase thrust.

1. Increase propellant flow or mass.

2. Increase exhaust speed.

Number 1 has no limits if you don't mind staging to infinity.

Number 2 is limited by heat/energy available and the engine's tolerance for it.

One of the challenges with allllll of these threads is that it’s really unclear what you are looking for. Are you creating a fictional universe where you want a reusable rocket that can land on a planet, refuel itself, and take off to orbit again? Or are you talking about a real world solution?

If the former, then seriously: just write it however you want. It is your fictional world. Bend the technology to fit your plot, not the other way around.

If the latter...well, that’s where things break down, because what you’re describing/suggesting/hypothesizing simply doesn’t reflect reality.

If you want a rocket to have increased thrust via “increas[ing] propellant flow or mass”, you need bigger turbopumps, full stop. The bigger the turbopump, the more propellant you can push through your engine. Don’t think in terms of total thrust. Think in terms of thrust-to-weight ratio. The goal is to have an engine which can lift 70X or more its own weight on Earth. Adding “more thrust” doesn’t do any good if your engine weight grows just as fast.

As for increasing exhaust velocity: increasing exhaust velocity does not necessarily increase thrust. For example, SpaceX could raise the specific impulse of the existing Raptor Vac just by narrowing the throat, which increases the expansion ratio but decreases thrust. And an “engine’s tolerance” for heat is really not a big deal. You can run an engine as hot as you want as long as you use film cooling or regenerative cooling.

The only time you run into problems with heat tolerance is certain solid-core nuclear thermal rocket designs, where the temperature is limited by the melting point of the nuclear fissile material. You can avoid that fairly easily (if anything in nuclear rocketry is easy) by enclosing the fissile material in tungsten or tantalum halfnium carbide and allowing the fissile material to melt inside it. 

On 7/21/2021 at 4:27 PM, Spacescifi said:

I knew nuclear had better ISP, and I had assumed one could get thrust on par with chemical rockets if engineered sufficiently. Someone here mentioned nuclear dumbo rocket project that was aimed at doing that. LANTR is repeatedly mentioned as being capable of that as well.

Don’t focus on thrust; focus on thrust-to-weight ratio. It doesn’t do you any good to build a nuclear engine with as much thrust as a Raptor if the darn thing weighs fifty tonnes. Playing KSP can really help give you a better intuitive sense of all this. I strongly recommend it.

You can build a nuclear engine with as much thrust as you want; there’s not really any meaningful upper limit. But the more thrust you want, the heavier your engine will become. Nuclear reactors are heavy; nuclear thermal rockets cannot achieve anywhere near the thrust-to-weight levels of a conventional chemical engine. It’s wildly, wildly disproportionate. For reference, NERVA produced four times its own weight in total thrust. The Space Shuttle Main Engines produced 78 times their own weight in total thrust. The Merlin 1D produces 200 times its own weight in total thrust.

DUMBO might have gotten up to 8-10 times its own weight in thrust, which is still just wildly too low to be used for liftoff.

LANTR (the LOX-Afterburning Nuclear Thermal Rocket) injects liquid oxygen into the nozzle of an ordinary nuclear thermal rocket, which burns with the hot hydrogen and multiplies thrust briefly at the expense of efficiency. Even so, it only produces about three times as much thrust, which still pales in comparison to even the least powerful chemical rockets.

On 7/21/2021 at 4:27 PM, Spacescifi said:

So perhaps cracking LOX and LH is more practical.

Again, here’s where it’s unclear what you’re going for. Are you proposing a real-world rocket or a fictional one?

[Spacescifi]

3 hours ago, sevenperforce said:

One of the challenges with allllll of these threads is that it’s really unclear what you are looking for. Are you creating a fictional universe where you want a reusable rocket that can land on a planet, refuel itself, and take off to orbit again? Or are you talking about a real world solution?

If the former, then seriously: just write it however you want. It is your fictional world. Bend the technology to fit your plot, not the other way around.

If the latter...well, that’s where things break down, because what you’re describing/suggesting/hypothesizing simply doesn’t reflect reality.

If you want a rocket to have increased thrust via “increas[ing] propellant flow or mass”, you need bigger turbopumps, full stop. The bigger the turbopump, the more propellant you can push through your engine. Don’t think in terms of total thrust. Think in terms of thrust-to-weight ratio. The goal is to have an engine which can lift 70X or more its own weight on Earth. Adding “more thrust” doesn’t do any good if your engine weight grows just as fast.

As for increasing exhaust velocity: increasing exhaust velocity does not necessarily increase thrust. For example, SpaceX could raise the specific impulse of the existing Raptor Vac just by narrowing the throat, which increases the expansion ratio but decreases thrust. And an “engine’s tolerance” for heat is really not a big deal. You can run an engine as hot as you want as long as you use film cooling or regenerative cooling.

The only time you run into problems with heat tolerance is certain solid-core nuclear thermal rocket designs, where the temperature is limited by the melting point of the nuclear fissile material. You can avoid that fairly easily (if anything in nuclear rocketry is easy) by enclosing the fissile material in tungsten or tantalum halfnium carbide and allowing the fissile material to melt inside it. 

Don’t focus on thrust; focus on thrust-to-weight ratio. It doesn’t do you any good to build a nuclear engine with as much thrust as a Raptor if the darn thing weighs fifty tonnes. Playing KSP can really help give you a better intuitive sense of all this. I strongly recommend it.

You can build a nuclear engine with as much thrust as you want; there’s not really any meaningful upper limit. But the more thrust you want, the heavier your engine will become. Nuclear reactors are heavy; nuclear thermal rockets cannot achieve anywhere near the thrust-to-weight levels of a conventional chemical engine. It’s wildly, wildly disproportionate. For reference, NERVA produced four times its own weight in total thrust. The Space Shuttle Main Engines produced 78 times their own weight in total thrust. The Merlin 1D produces 200 times its own weight in total thrust.

DUMBO might have gotten up to 8-10 times its own weight in thrust, which is still just wildly too low to be used for liftoff.

LANTR (the LOX-Afterburning Nuclear Thermal Rocket) injects liquid oxygen into the nozzle of an ordinary nuclear thermal rocket, which burns with the hot hydrogen and multiplies thrust briefly at the expense of efficiency. Even so, it only produces about three times as much thrust, which still pales in comparison to even the least powerful chemical rockets.

Again, here’s where it’s unclear what you’re going for. Are you proposing a real-world rocket or a fictional one?

Thanks for the information on nuclear. Clears things up concisely!

Definitely this is real world consideratation of solutions.

 

So guess the only good for nuclear is power, as it makes a lousy launch vehicle.

 

 

Even the infamous metallic hydrogen or AM would do better.... assuming tge protective mass did not lower TWR badly.

 

 

Perhaps their are other gases worth trying to make metastable other than hydrogen? As metals?

 

Assuming it is possible with current at all.

[Beccab]

7 hours ago, Spacescifi said:

The booster will carry the  nuckear reactor solely for cracking LOX/LH from sea water. Chemical rocketry will propel it.

Again, why would it do that? Is there literally any advantage that justifies carrying a nuclear reactor on board with all the related weight and high risks?

[Spacescifi]

6 minutes ago, Beccab said:

Again, why would it do that? Is there literally any advantage that justifies carrying a nuclear reactor on board with all the related weight and high risks?

 

If I were trying to sell the idea and I were rich like Elon, the only ones that would want DIY repeat launch ability from the ocean with no infrastructure would be the airforce.

It is simply too OP to jusify civillian use.

 

A single booster can launch mulitple second stages suppied by an ocean carrier.

 

Each time it launch, return to the earth and ress...

 

 

That's it!

 

Just make a two stage rocket launched from a carrier in the ocean. First stage lands in ocean.

 

The ocean carrier cracks LH/LOX all day long and has plenty to spare.

Fuels up first stage, attaches another second stage, launch again!

 

That would be faster repeat launches than normal.

 

At least until the carrier runs out of propellant and has to crack more.

Edited July 23, 2021 by Spacescifi