A Sea Launched/landing Super Heavy SSTO?

[Spacescifi]

Often it is fun to say that many spacecraft that have not been built are merely engineering problems, not something that known science will prohibit.

So what are the practical design challenges of taking the nuclear pulse orion concept and fusing that with a submarine?

For a basic proof of concept, let's say the proposed vessel will carry the same payload as the Sea Dragon project, 550 tons.

The concept I have in mind is to build the vessel in a shipyard, and then have it use onboard nuclear reactors to propel itself through the water from the sea docks until it is far enough away to launch.

Once it is it tilts it's nose upward above the water and detonates a bomb below the pusher plate for the inital launch.

Getting to orbit using nuclear pulse is arguably the easy part.

Getting back? Possible, but only by using water propellant and nuclear thermal rocketry to land on the ocean.

I suspect air augmentation intakes added to the rocket would also help, perhaps placed downward? So that as the vessel fell from the sky it's intakes would gulp or suck up the air before feeding it to the nuclear water thermal rocket sea landing engines.

What do you have to say on this?

Wait a minute... is it not possible to do an NTR underwater propelled sub?

It sounds feasible, not sure how practical that is for thrust over just using propeller blades underwater instead.

Edited August 3, 2020 by Spacescifi

[kerbiloid]

I suggest a supersubmarine carrying 24 Orions. Then they need just one reactor.

P.S.
But we need antimatter.

P.P.S.
And sleds, to not scratch the oceanic bottom.

Edited August 3, 2020 by kerbiloid

[RCgothic]

The problem with using nuclear pulse propulsion to leave an inhabited planet is what the inhabitants of that planet will do to you if they catch you.

Probably preemptively.

[Codraroll]

You'll also be taking a rocket nozzle and submerging it in salt water to a depth equal to the length of your ship. That ought to give the valve designers quite a few problems.

[SOXBLOX]

Pretty sure air intakes generally need to divert the airflow by less than, say, 90°, to achieve any kind of efficiency. Oh,and if you're thinking about mixing water vapor and air containing oxygen in a superheated reactor made of metal, the metallurgy department will come screaming after you with torches and stuff.

Also, if you want this submerged to any great depth, you will need two (at least) pressure hulls. One for compression loads, from the water, and one for hoop stress loads, from the atmosphere inside (assuming this is manned).

Maybe this could work, but it will be a committee -designed horse, workable, but not optimized for anything, and performing all jobs poorly. Well, all jobs besides giving local sea life cancer, that is.

[Spacescifi]

2 hours ago, SOXBLOX said:

Pretty sure air intakes generally need to divert the airflow by less than, say, 90°, to achieve any kind of efficiency. Oh,and if you're thinking about mixing water vapor and air containing oxygen in a superheated reactor made of metal, the metallurgy department will come screaming after you with torches and stuff.

Also, if you want this submerged to any great depth, you will need two (at least) pressure hulls. One for compression loads, from the water, and one for hoop stress loads, from the atmosphere inside (assuming this is manned).

Maybe this could work, but it will be a committee -designed horse, workable, but not optimized for anything, and performing all jobs poorly. Well, all jobs besides giving local sea life cancer, that is.

90 degrees? Then make it 90 degrees. Problem solved.

Why is the heat/water vapor/ oxygen a problem?

It can still be engineered away.

Just separate the water into LOX and LH in orbit through electrolysis. Into separate tankage. It's ONLY for landing, with the clear objective of ocean refueling after landing.

This is arguably the one most viable realistic SSTO I can think of that we can do with current technology.

As for the nozzle, it can be retracted into the main ship hull as needed once underwater, so it won't stay underwater for a long time.

8 hours ago, Codraroll said:

You'll also be taking a rocket nozzle and submerging it in salt water to a depth equal to the length of your ship. That ought to give the valve designers quite a few problems.

 

Why?

Edited August 3, 2020 by Spacescifi

[Codraroll]

6 minutes ago, Spacescifi said:

Why?

Several atmospheres of hydrostatic pressure bearing on moving parts of plumbing designed for fluids to flow the other way. You need to shut the water out while also pumping super-hot exhaust gases. The thermal gradients between the sea water and the exhaust gas will do nasty stuff to the metal parts you keep between, assuming you manage to avoid a steam explosion in the process. And then there's all the radioactivity. This is almost as stupid an idea as that two-meter cylinder spacecraft with spin gravity you touted some months ago.

[Guest]

This design is a rampant violation of one of the most important principles of good engineering: KISS. Which stands for "Keep It Simple, Stupid". Perfect engineering would be when you have the simplest machine possible that does what you want it to do. Good engineering tries to come as close as possible to this ideal. Very elaborate arrangements are almost never the best choice, and the only time they are is when the requirements are so broad that you need that complexity just to accommodate all of them (Space Shuttle was the prime example).

If you want your tech to be realistic, keep it simple. On the rare occasion these Rube-Goldberg contraptions get built, they rarely work right, if at all. 

[Spacescifi]

11 minutes ago, Dragon01 said:

This design is a rampant violation of one of the most important principles of good engineering: KISS. Which stands for "Keep It Simple, Stupid". Perfect engineering would be when you have the simplest machine possible that does what you want it to do. Good engineering tries to come as close as possible to this ideal. Very elaborate arrangements are almost never the best choice, and the only time they are is when the requirements are so broad that you need that complexity just to accommodate all of them (Space Shuttle was the prime example).

If you want your tech to be realistic, keep it simple. On the rare occasion these Rube-Goldberg contraptions get built, they rarely work right, if at all. 

 

A rapid repeat launch SSTO kind of needs this for Earth worlds.

Like... if you land on land, it will take arguably longer to refuel unless you purposely land by the ocean or a river.

Also gives you less mobility.

The way I see it, complex though it may be, it is the closest we can ever to this...

 

Spoiler

 

Assuming we were exploring Earth worlds so common in scifi.

[Guest]

If you bothered doing the maths, you'd find out that a normal fusion engine with air augmentation would be sufficient for that. Air as propellant in atmosphere, deuterium as fusion fuel, hydrogen as propellant in space. Don't overcomplicate this. 

Also, don't try to copy Star Trek, you'll never get there with realistic technology. Spaceflight will never look exactly like Star Trek, it might be just as common, but many things will be different.

[Spacescifi]

17 minutes ago, Dragon01 said:

If you bothered doing the maths, you'd find out that a normal fusion engine with air augmentation would be sufficient for that. Air as propellant in atmosphere, deuterium as fusion fuel, hydrogen as propellant in space. Don't overcomplicate this. 

Also, don't try to copy Star Trek, you'll never get there with realistic technology. Spaceflight will never look exactly like Star Trek, it might be just as common, but many things will be different.

 

Normal fusion engine?!

What normal fusion engine? Since when did we get fusion rockets? It can hardly be sustained fusion reactions since the engine will melt.

If you are talking pulse fusion rockets... that's some descendant of the orion project... boom boom.

Which my drive already uses as pulse fusion against the plate to reach orbit.

Also, Star Trek is not my guide. I was showing that. exploring new Earths could actually be done using current tech.

The warp drive is total plot needium, yet I also find real workable tech more fascinating than arbritrary rules for fantasy tech. 

And either way, using your or my suggestions REQUIRES landing near a body of water if not on it.

ABSOLUTELY NECESSARY.

Otherwise you cannot go anywhere.

Land. Refuel.

No water or ice on that planet? Forget it! Leave that to the mining drone ships and robots.

EDIT: The heavier an SSTO vessel is the less likely air alone is going to work as propellant.

Not enough thrust.

I don't care what energy source you have. That's the difference between melting your engine or not.

That is the primary advantage of liquid propellants. They take away engine heat more efficiently than air does.

 

Edited August 4, 2020 by Spacescifi

[SOXBLOX]

No. 90° won't work. If your intake is pointed downwards, then diverting the airflow 90° puts it at right angles to your descent. To point the exhaust stream down, you have to divert by ~180°. And superheated steam and oxygen is doubly corrosive. You really don't want to try to find an alloy to compromise between steam, O2, and radiation resistance. 

And Orion is "realistic" the way the Nuclear Death Water Rocket is; that is, it is only realistic if you ignore the fact that A) no military leaders in their right minds would let anyone move nukes out of a secure facility and B) no one wants this flying over their heads.

And you don't have to refuel after landing in order to lift off again; its just that if you don't, you can't land again under NTR power.

[Spacescifi]

1 hour ago, SOXBLOX said:

No. 90° won't work. If your intake is pointed downwards, then diverting the airflow 90° puts it at right angles to your descent. To point the exhaust stream down, you have to divert by ~180°. And superheated steam and oxygen is doubly corrosive. You really don't want to try to find an alloy to compromise between steam, O2, and radiation resistance. 

And Orion is "realistic" the way the Nuclear Death Water Rocket is; that is, it is only realistic if you ignore the fact that A) no military leaders in their right minds would let anyone move nukes out of a secure facility and B) no one wants this flying over their heads.

And you don't have to refuel after landing in order to lift off again; its just that if you don't, you can't land again under NTR power.

 

OK... what if the intakes are opposite the downward thrust?

No diversionary problems... it's just that we are falling down, so that I am not sure the intakes will gulp enough air to really warrant them being useful.

Intakes work best when starting from a stop or when flying headfirst with little to no air diversion.

As for refueling... without the water NTR, the said vessel cannot safely land on an Earth world.

What's it going to slow with?

Nuclear detonations LOL?

In space this is still risky... but more doable.

Like I would not recommend landing in the moon via nuclear pulse detonation... unless you could do it safely without tipping over like Scott Manley did in a Kerbal vid once.

[SOXBLOX]

You just repeated everything I said!!! We agree!

[KSK]

Lots to dig into here. Lets start with the nuclear pulse propulsion (NPP) system.

Project Orion did a lot of solid work on this (as folks here probably know) but there's still a long way between 'works on paper and no, lighting a nuke off under the spaceship won't actually vaporize it' and a working system. Building a shock absorber that can handle being repeatedly whacked with a kiloton atomic hammer remains an engineering challenge, as does designing a system capable of firing out the pulse units (bombs) at the required speed and accuracy and reliability. NPP drives are not famed for their engine-out capability and having a pulse unit jam in the first few moments of flight is likely to be a Bad Thing that means you will Not be Going to Space Today. For that matter, building a system that can recoat the pusher plate with ablative grease after every few detonations (as a number of Orion designs required) doesn't strike me as an easy problem to solve, especially for large pusher plates.

Then there's the fairly fundamental question of whether the basic physics of an NPP drive will actually hold underwater. I honestly don't know the answer to that but I can imagine that a nuclear explosion propagating underwater is a very different beast to a nuclear explosion propagating through air. Then there's the follow up question of whether all the moving parts of that NPP drive will work properly underwater. Firing a pulse unit through air is considerably easier than firing it through water for example, and a shock absorber that's tuned to work in air might not work so well in a more viscous environment. Incidentally, I would think that you have to fire the pulse units - just dropping them out the back of the ship wouldn't be fast enough, given that you'll be lighting one off every few seconds or less.

But lets assume that the NPP drive really is the easy bit. What next? In no particular order, I can think of at least the following challenges. They may all be solvable (again, I don't know, not being an Actual Engineer) but I imagine that they're challenges nonetheless.

• Making your NPP drive seaworthy. Is dousing those moving parts in salt water going to damage them? Will the climb to orbit give the drive time to dry out? If not, what happens when the trapped water freezes when the ship gets high enough?
• Making your ship controllable as a submarine. An NPP drive strikes me as being approximately as seaworthy as a brick and a brick with a decidedly skewed mass distribution at that. Getting the ship to point its nose at the sky before launch might not be a problem compared to stopping it sinking like a rock and/or being steerable on the way to the launch site. It's not even so much that making something work like a submarine is difficult in principle, it's more that the ballast and/or flotation systems add another layer of complexity to the design.
• For an NPP powered ship with nuclear-thermal landing engines - where do you put the engines? It's unlikely that you're going to be putting them at the bottom because that's where the pusher plate goes. Unless you're going full crazy  with a Medusa sail of course, but that adds a whole bunch of other problems.  Wherever you put the engines, you need to make sure that their exhaust isn't impinging on the rest of the ship (please do not fire rocket at the nuclear veapons!), which means they're likely to be pointing out an angle. Which means cosine losses for reduced efficiency (yay!) and bits sticking out from your ship that won't do much to improve its already lackluster aerodynamics.
• More to the point, for an NPP powered ship that's intended to land, how does that work? Are you relying on aerobraking, in which case how does your thermal protection system work? Are you using the pusher plate as a heatshield and does that work? Most heatshields that I'm aware of are convex in the direction of travel. A pusher plate might be flat or even concave in the direction of travel (since it's designed as a reflector). Does this matter? Can you even design a pusher plate that also works as a heat shield?
• If you're relying on a powered descent instead then you're using a lot of propellant and possibly doing some of the braking with your NPP drive. Now, I don't know about you, but to my mind, riding an NPP drive to space requires a certain amount of faith in your engineering. However, at least you're flying away from the nuclear explosions! Flying backwards into the explosions takes that faith to a whole other level.
• As for propellant for your NTR landing engines, let's put the mass requirement to one side for the moment and consider where we're actually going to put the propellant tanks. Again, putting them at the bottom of the ship doesn't work so well because that part is full of pusher-plate and shock absorber. Putting them higher up might work but what does that do to your center-of-mass and aerodynamic stability during reentry. Flying backwards into the nuclear explosions isn't terribly appealing but it beats flying the Great Atomic Lawn Dart. 
• Also bear in mind that even with that shock absorber, you've still been whacking on your landing engines and propellant tanks with that aforementioned kiloton atomic hammer, which is a very different kind of dynamic load than rocket engines and propellant tanks are normally required to deal with.

Now, all of this might be solvable, or I might be blowing some parts (hah) out of all proportion. But I figure that this is pretty top-level stuff and, as with most things about spaceflight, the more you get into the details, the more challenges you'll find.

Edited August 6, 2020 by KSK

[Spacescifi]

3 hours ago, KSK said:

Lots to dig into here. Lets start with the nuclear pulse propulsion (NPP) system.

Project Orion did a lot of solid work on this (as folks here probably know) but there's still a long way between 'works on paper and no, lighting a nuke off under the spaceship won't actually vaporize it' and a working system. Building a shock absorber that can handle being repeatedly whacked with a kiloton atomic hammer remains an engineering challenge, as does designing a system capable of firing out the pulse units (bombs) at the required speed and accuracy and reliability. NPP drives are not famed for their engine-out capability and having a pulse unit jam in the first few moments of flight is likely to be a Bad Thing that means you will Not be Going to Space Today. For that matter, building a system that can recoat the pusher plate with ablative grease after every few detonations (as a number of Orion designs required) doesn't strike me as an easy problem to solve, especially for large pusher plates.

Then there's the fairly fundamental question of whether the basic physics of an NPP drive will actually hold underwater. I honestly don't know the answer to that but I can imagine that a nuclear explosion propagating underwater is a very different beast to a nuclear explosion propagating through air. Then there's the follow up question of whether all the moving parts of that NPP drive will work properly underwater. Firing a pulse unit through air is considerably easier than firing it through water for example, and a shock absorber that's tuned to work in air might not work so well in a more viscous environment. Incidentally, I would think that you have to fire the pulse units - just dropping them out the back of the ship wouldn't be fast enough, given that you'll be lighting one off every few seconds or less.

But lets assume that the NPP drive really is the easy bit. What next? In no particular order, I can think of at least the following challenges. They may all be solvable (again, I don't know, not being an Actual Engineer) but I imagine that they're challenges nonetheless.

• Making your NPP drive seaworthy. Is dousing those moving parts in salt water going to damage them? Will the climb to orbit give the drive time to dry out? If not, what happens when the trapped water freezes when the ship gets high enough?
• Making your ship controllable as a submarine. An NPP drive strikes me as being approximately as seaworthy as a brick and a brick with a decidedly skewed mass distribution at that. Getting the ship to point its nose at the sky before launch might not be a problem compared to stopping it sinking like a rock and/or being steerable on the way to the launch site. It's not even so much that making something work like a submarine is difficult in principle, it's more that the ballast and/or flotation systems add another layer of complexity to the design.
• For an NPP powered ship with nuclear-thermal landing engines - where do you put the engines? It's unlikely that you're going to be putting them at the bottom because that's where the pusher plate goes. Unless you're going full crazy  with a Medusa sail of course, but that adds a whole bunch of other problems.  Wherever you put the engines, you need to make sure that their exhaust isn't impinging on the rest of the ship (please do not fire rocket at the nuclear veapons!), which means they're likely to be pointing out an angle. Which means cosine losses for reduced efficiency (yay!) and bits sticking out from your ship that won't do much to improve its already lackluster aerodynamics.
• More to the point, for an NPP powered ship that's intended to land, how does that work? Are you relying on aerobraking, in which case how does your thermal protection system work? Are you using the pusher plate as a heatshield and does that work? Most heatshields that I'm aware of are convex in the direction of travel. A pusher plate might be flat or even concave in the direction of travel (since it's designed as a reflector). Does this matter? Can you even design a pusher plate that also works as a heat shield?
• If you're relying on a powered descent instead then you're using a lot of propellant and possibly doing some of the braking with your NPP drive. Now, I don't know about you, but to my mind, riding an NPP drive to space requires a certain amount of faith in your engineering. However, at least you're flying away from the nuclear explosions! Flying backwards into the explosions takes that faith to a whole other level.
• As for propellant for your NTR landing engines, let's put the mass requirement to one side for the moment and consider where we're actually going to put the propellant tanks. Again, putting them at the bottom of the ship doesn't work so well because that part is full of pusher-plate and shock absorber. Putting them higher up might work but what does that do to your center-of-mass and aerodynamic stability during reentry. Flying backwards into the nuclear explosions isn't terribly appealing but it beats flying the Great Atomic Lawn Dart. 
• Also bear in mind that even with that shock absorber, you've still been whacking on your landing engines and propellant tanks with that aforementioned kiloton atomic hammer, which is a very different kind of dynamic load than rocket engines and propellant tanks are normally required to deal with.

Now, all of this might be solvable, or I might be blowing some parts (hah) out of all proportion. But I figure that this is pretty top-level stuff and, as with most things about spaceflight, the more you get into the details, the more challenges you'll find.

 

Haha... well I am glad you shared this, as it at least shows the challenges that need to be overcome.

Sounds like an easier route to a sea launched SSTO might be a seaplane/rocket hybrid, complete with air augmented rockets and likely shock cones for said rocket engine noses.

So you take this:

Add this: Air augmented rocket.

Plus nuclear reactors to heat the saltwater and we are in business!

Take that Elon! If he was or is even remotely aware of this he might just laugh.

Not without challenges, but a good deal easier than the near suicidal Orion idea guaranteed to cause radioactive death clouds at the very least.

The challenges to this are: Heating during reentry. Wings and hull need to survive well enough that SSTO plane can bank a few times to bleed off speed before attempting a landing on the ocean.

More challenges you may add. Oh yeah... radiation shielding, but that only adds weight.

At this point if it can fly, we are doing good.

Aerospikes might... I say might be useful here, assuming the heat did not damage then via warping them.

At any rate saltwater is a really good thing to conduct engine heat away to.

 

Edited August 6, 2020 by Spacescifi

[Arugela]

Actually I had an idea for such a thing. But instead of a pad you have a base launcher to drive it in the water and up into the air from underwater and then separate once slightly in the air. Basically a ballast based ICBM or sub missile that starts deep or move quickly in shallow water then goes up into the air to separate the real rocket. It could be reusable as it only jumps out of the water and relands and acts as a moveable landing pad for the real rocket. It could even try to use super cavitation or other exotic methods to make it more efficient. Maybe you could reduce some delta v by launching it with some inertia out of the water before ignition of the main rocket.

It could be unmanned and return to port or use various propulsions on top of actual ballast. It could be a reusable supercav missile base launcher. The supercav part could be on the real rocket or detached from the nose or something and collected. the ship could collect the part. Or navy or other vessels could collect.

And it could use different fuel sources or an electrical or other system to be as efficient as possible for the substage of the launch. Or any other exotic needed to produce the results.

The point would be to save energy on the upper stage. Or to give more launch sites. Or whatever else is useful.

Edited August 7, 2020 by Arugela

[SOXBLOX]

So now you want an air-augmented aerospike nuclear SSTO flying boat?!? What next, man?

Hast thou gone mad?

Edited August 7, 2020 by SOXBLOX

[tater]

Boeing, 1976. 228t to LEO.

[kerbiloid]

46 minutes ago, tater said:

Boeing, 1976. 228t to LEO.

Too easy. I vote for Orion-propelled air-augmented winged submarines, releasing sublaunchers in flight.

[Spacescifi]

1 hour ago, SOXBLOX said:

So now you want an air-augmented aerospike nuclear SSTO flying boat?!? What next, man?

Hast thou gone mad?

 

I really want an SSTO so.... yes?

Does that include doing whatever it takes in scifi short of making it all up if I can find another way?

You bet I am!

 

It is also worth noting that given the scifi trope of exploring alien Earth worlds with no preexistent infrastructure for landing spacecraft... a kind of water landing SSTO shuttle would fill this niche nicely.

May as well make good use of all that saltwater.

Or would you rather spend a day or days sucking up water and then using electrolysis to extract hydrogen and oxygen?

One of these flight propellants takes a lot of time to enable departure, the other only requires filling up and filtering out any fishes or rocks. Whereas the hydrogen/oxygen route requires doing that and MORE to the Nth degree before you can ever even fly.

Propellant matters.

Edited August 7, 2020 by Spacescifi

[Codraroll]

6 hours ago, Spacescifi said:

One of these flight propellants takes a lot of time to enable departure, the other only requires filling up and filtering out any fishes or rocks. Whereas the hydrogen/oxygen route requires doing that and MORE to the Nth degree before you can ever even fly.

At this point you might as well just say the engine can be fueled using the rocks as well. Compared to the other engineering challenges you're banking on being solved here, it's not that much more difficult.

[kerbiloid]

And why filter out the fishes?

Maybe just bones, but the flesh is water and hydrocarbons.

[SOXBLOX]

9 hours ago, Codraroll said:

At this point you might as well just say the engine can be fueled using the rocks as well. Compared to the other engineering challenges you're banking on being solved here, it's not that much more difficult.

Yep.

The complexity of this system is so massive, and the requirements for it are sorta opposed to each other.

16 hours ago, Spacescifi said:

 

I really want an SSTO so.... yes?

Does that include doing whatever it takes in scifi short of making it all up if I can find another way?

You bet I am!

 

It is also worth noting that given the scifi trope of exploring alien Earth worlds with no preexistent infrastructure for landing spacecraft... a kind of water landing SSTO shuttle would fill this niche nicely.

May as well make good use of all that saltwater.

Or would you rather spend a day or days sucking up water and then using electrolysis to extract hydrogen and oxygen?

One of these flight propellants takes a lot of time to enable departure, the other only requires filling up and filtering out any fishes or rocks. Whereas the hydrogen/oxygen route requires doing that and MORE to the Nth degree before you can ever even fly.

Propellant matters.

So...at this point, you ARE making it all up. And one or two days can't be all that long compared to interstellar transit times. I see no reason the crew would need to hurry.

[Spacescifi]

4 hours ago, SOXBLOX said:

Yep.

The complexity of this system is so massive, and the requirements for it are sorta opposed to each other.

So...at this point, you ARE making it all up. And one or two days can't be all that long compared to interstellar transit times. I see no reason the crew would need to hurry.

 

Let me let you in on a little secret... I don't argue merely for the sake of 'winning'. I don't even care about 'winning' online arguments.

In this case, I wonder if the extra large LH tanks and the complicated setup of LOX/LH would be worth the trouble as opposed to water tanks which can afford to be smaller without the complications required when piping LOX and LH?

Less tank... more payload to orbit... sound fair?

Piping water is easier. And nuclear reactors are compact and robust.

It just seems that not only does the LH/LOX setup take longer, it has arguably more parts and is more susceptible to combustion failure (BOOM).

Water does not have that problem, as nuclear reactors provide the energy for water propulsion, not chemical combustion.

Also nuclear exhaust can be designed to be fairly safe too.

Now if you can convince me that a nuclear SSTO seawater NTR will likely always be necessarily heavier than an LH/LOX incarnation SSTO... then you might persuade me.

I doubt that is the case though....

Edited August 8, 2020 by Spacescifi