Project Orion: A discussion of Science and Science Fiction

[Shpaget]

Haven't you already proposed a conventional explosives orion?

Ditto re: pure fusion bomb.

The first does away with the only reedeming quality of orion, the second doesn't exist.

[Spacescifi]

1 hour ago, Shpaget said:

Haven't you already proposed a conventional explosives orion?

Ditto re: pure fusion bomb.

The first does away with the only reedeming quality of orion, the second doesn't exist.

 

This is a hybrid... high explosives are merely to gain some altitude without buring VTOL rocket propellant.

 

Pure fusion bombs are at least theoretically possible and there are various ways of making them... from HE mixed with strong electromagnetic fields to initate pure fusion in fusion fuel, to using small amounts of antimatter as a catalyst for pure fusion reactions.

 

It's not a show stopper from a scifi perspective at least.

[Gargamel]

Overlapping threads have been merged again.   

[sevenperforce]

6 hours ago, Spacescifi said:

8 hours ago, Shpaget said:

Haven't you already proposed a conventional explosives orion?

Ditto re: pure fusion bomb.

The first does away with the only reedeming quality of orion, the second doesn't exist.

This is a hybrid... high explosives are merely to gain some altitude without buring VTOL rocket propellant.

That is absolutely the worst possible use of reaction mass.

Rocket propellant in a rocket engine is specifically designed to exit precisely opposite the intended thrust vector with maximal efficiency. Rocket engines are a marvel of engineering. They are ridiculously efficient for what they do.

Blowing up high explosives against a pressure plate "merely to gain some altitude without buring [sic] . . . propellant" is like trying to propel a racecar by stuffing hand grenades in the tailpipe to avoid burning fuel.

A racecar has a perfectly good engine capable of burning perfectly good fuel at maximal efficiency; there is absolutely no reason to waste dry mass on hand-grenade starters.

6 hours ago, Spacescifi said:

Pure fusion bombs are at least theoretically possible and there are various ways of making them... from HE mixed with strong electromagnetic fields to initate pure fusion in fusion fuel, to using small amounts of antimatter as a catalyst for pure fusion reactions.

Any science fiction situation where pure fusion can be harnessed to energize reaction mass, you will be able to downscale to produce a pure fusion throttleable engine.

The only reason the Orion idea ever existed is because fission bombs require a minimum pulse thanks to the critical mass rule.

[Spacescifi]

8 hours ago, sevenperforce said:

That is absolutely the worst possible use of reaction mass.

Rocket propellant in a rocket engine is specifically designed to exit precisely opposite the intended thrust vector with maximal efficiency. Rocket engines are a marvel of engineering. They are ridiculously efficient for what they do.

Blowing up high explosives against a pressure plate "merely to gain some altitude without buring [sic] . . . propellant" is like trying to propel a racecar by stuffing hand grenades in the tailpipe to avoid burning fuel.

A racecar has a perfectly good engine capable of burning perfectly good fuel at maximal efficiency; there is absolutely no reason to waste dry mass on hand-grenade starters.

Any science fiction situation where pure fusion can be harnessed to energize reaction mass, you will be able to downscale to produce a pure fusion throttleable engine.

The only reason the Orion idea ever existed is because fission bombs require a minimum pulse thanks to the critical mass rule.

 

My thinking was that although pure fusion is far less toxic than fission nukes, it still is toxic.

 

So I thought high explosive could save fuel gaining altitude while also reducing the radiation polution on the launch site.

 

Turns out chemical rocketry would be best and then flipping to engage pure fusion orion.

 

My thinking also was that a pure fusion orion is easier to build than an actual pure fusion rocket. Since instead of trying to contain a pure fusion reaction which is.... hard to say the least, it would most likely work by injecting pure fusion fuel into the reaction chamber and igniting it.

 

Less powerful than a pure fusion orion reaction which is so energetic you would either need a giant reaction chamber or risk blowing it up outright.

Edited June 7, 2022 by Spacescifi

[sevenperforce]

17 minutes ago, Spacescifi said:

My thinking was that although pure fusion is far less toxic than fission nukes, it still is toxic.

It is not. A pure fusion reaction produces no heavy nucleotides.

17 minutes ago, Spacescifi said:

I thought high explosive could save fuel gaining altitude while also reducing the radiation polution on the launch site.

A fusion-based rocket will produce no radiation pollution at the launch site. 

17 minutes ago, Spacescifi said:

Turns out chemical rocketry would be best and then flipping to engage pure fusion orion.

Not sure why flipping is at all necessary. 

17 minutes ago, Spacescifi said:

My thinking also was that a pure fusion orion is easier to build than an actual pure fusion rocket. Since instead of trying to contain a pure fusion reaction which is.... hard to say the least,

Pure fusion reactions are not difficult to contain; they are difficult to sustain. So pulse-based fusion engines are a good idea, like the Z-pinch. However, all these designs can be scaled down to minimal size. A pusher-plate approach is ridiculously inefficient and unnecessary.

[KSK]

Some real life numbers - or as close as they get for Orion. This is from a 1963-64, General Atomics study for NASA on a 10m diameter Orion craft designed to be launched on a Saturn V.

The ship is launched ‘dry’ (mass at launch is 100 tons) with propellant and crew (and presumably supplies) loaded on-orbit.

Departure mass is 600 tons, payload to Mars is 80 tons, with a round trip duration of 450 days. Artificial gravity created by slow tumbling of the ship in transit. 

Propellant requirement - 2782 kiloton yield pulse units weighing about 300 lb each

This is all taken from George Dyson’s ‘Project Orion’.

A couple of thoughts. Firstly, even with nuclear pulse propulsion, about 2/3 of the ‘wet’ vehicle mass is propellant. (We’ll ignore the political issues involved in launching nearly 3,000 kiloton yield weapons into space).

Secondly, a single pulse unit is equivalent to nearly  double the ‘wet’ vehicle mass of TNT.  Even accounting for the fact that modern high explosives are likely more performant than TNT (I have no knowledge on this point), the mass of explosives required seems to make an HE propelled Orion a non starter.

Thirdly, if one wanted to make this an SSTO as per the original post, a 600 ton vehicle would be… challenging to launch with reusable chemical boosters, whatever propellant combo one uses. In that regard hydrolox is a poor choice due to the low density of liquid hydrogen (although I agree that it’s probably the easiest choice for in-situ refuelling)  - witness the size of the main tank for SLS, which still requires a hefty SRB assist to get off the ground.

Edited June 7, 2022 by KSK

[Codraroll]

@Spacescifi, it appears to me like you are trying, on a conceptual level, to answer two questions:

1) Is there any use case that would justify using an Orion drive in hard sci-fi?

2) Would there be a way to improve the efficiency/effectiveness of the original concept?

However, it seems like the answer to 2) is quite clear every time: ditch the Orion drive and make a rocket. Practically any technology that could improve the Orion drive would also make it obsolete. It's like trying to make horseback riding faster by putting the horse on powered roller skates. Whatever propulsion method you come up with for the roller skates would make the horse no longer necessary.

I think this is basically what @sevenperforce is trying to find new ways to say every time.  Orion is an epitome of "cool, but impractical". In hard sci-fi, it could only be justified by having no better alternatives, and as soon as you make a better alternative, you no longer need the Orion. The pusher plate concept is literally the first thing that goes when you try to improve it. That, I think, is the essence of the answer you will get no matter how you formulate the question.

Come to think of it, something similar could probably be said about SSTOs, but maybe there are more nuances there.

[kerbiloid]

1 hour ago, KSK said:

2782 kiloton yield pulse units weighing about 300 lb each

What I like in 1950s.

59 minutes ago, Codraroll said:

Orion is an epitome of "cool, but impractical".

Humans have many times more than 3 000 nukes, but yet no Martian ship.

Looks not that impractical.

[Spacescifi]

2 hours ago, sevenperforce said:

It is not. A pure fusion reaction produces no heavy nucleotides.

A fusion-based rocket will produce no radiation pollution at the launch site. 

Not sure why flipping is at all necessary. 

Pure fusion reactions are not difficult to contain; they are difficult to sustain. So pulse-based fusion engines are a good idea, like the Z-pinch. However, all these designs can be scaled down to minimal size. A pusher-plate approach is ridiculously inefficient and unnecessary.

 

1. Okay.... I thought there was neutron radiation involved? So it would be safe to watch the laumch from a several kilometers away outside then?

2.  Flipping is necessary because the orion is a belly lander. It lifts off and lands with dual side resuable rocket boosters. I assumed chemical would be powerful enough to lift a heavy orion but apparently not without being really inefficient with payliad to propellant ratios. Besides the fact that hydralox would be a weak choice anyway. It is a belly lander because I prefer easier egress/getting on/off the ship once landed. Starship is a tail lander and must use a kind of elevator to get up and down. A belly lander only needs to let down a short ramp and crew can walk on out or ship cargo in or out as well. Also the fact that landing on your pusher plate like a tail lander means that lift off involves reusable rocket exhaust blowing past pistons... pistons you depend on to work that have flaming exhaust blowing all over them. It just seems like a great way to mess up the pistons. That is why I say belly lander. The original orion tail sitter was not designed to land at all and certainly not SSTO like a shuttle back and forth to a planet. Also as a belly lander it is easier to reach pistons for maintenanence. Lets say you land somewhere so cold the pistons freeze over? Yes I guess a tail sitter would be better in that instance since rocket exhaust would melt the ice. So maybe tail lander is better in that one scenario. Certainly not better at egress.

3. Sustained pure fusion reactions are difficult to contain because it is like trying to hold a star in a jar... if you did the heat would blow up jar. Stronger materials would melt before vaporizing.

4. What is Z-pinch? Because if is magnetic based SSTOing with it may... I say may be problematic because air conducts heat and magnets do not like excess heat or else they malfunction.

Z-pinch may work great when already up in space, but I am discussing an SSTO capable heavy launch vessel on par with project orion for payload and mass.

Are there any pure fusion pulse rockets that are on par with the abilites of project orion and it's ability to SSTO massive payloads? If not then project orion... especially with pure fusion is not exactly obsolete if you want a go anywhere and back kind of scifi SSTO that can carry heavy payloads.

Even if pure fusion pulse rockers are scaled down it won't matter if their thrust lower and their fuel consumption is higher than project orion is with pure fusion bombs.

EDIT: Likely pure fusion boosted chemical reusable rocketry would be needed for VTOL... while the rear pusher plate would use pure fusion bombs.

Edited June 7, 2022 by Spacescifi

[kerbiloid]

15 minutes ago, Spacescifi said:

and magnets do not like excess heat or else they malfunction.

And that's why thou shalt not make a nuclear ship on constant magnets.

[wumpus]

3 minutes ago, Spacescifi said:

1. Okay.... I thought there was neutron radiation involved? So it would be safe to watch the laumch from a several kilometers away outside then?

2.  Flipping is necessary because the orion is a belly lander.

Z-pinch may work great when already up in space, but I am discussing an SSTO capable heavy launch vessel on par with project orion for payload and mass.

 

First, being near an Orion launch would be as safe as being near multiple nuclear explosions.  Take your pick.

Orion simply doesn't land.  The whole point is to make the pusher plate sufficiently massive to absorb a nuclear explosion.  The rest of the craft in turn has to be sufficiently massive to absorb the momentum of the pusher plate.  So what you wind up with is a spacecraft the size of a battleship.  It simply doesn't land.   It would take 5000 Apollo F1 engines to match gravity for an Iowa class battleship, which tends to defeat the whole point of an Orion in the first place (on the other hand, the shear size and strength of the pusher plate makes re-entry  a breeze except for the issue that terminal velocity won't slow you down a whole lot.  Orion needs to scale up big (because making big nuclear explosions is as expensive as making small nuclear explosions)  and "scaling up big" and "landing from space" simply don't go together.

If you are committed to SSTO, you need magic Isp (probably at least 1000 or more) and a TWR>1.  Doesn't matter what you call it.  Nuclear rockets can get the Isp, Orions have both but have the weird scaling issues.  Learn how the rocket equation works and you won't have to keep asking stupid  questions about how to make an SSTO.

What makes the Orion so cool is that it showed how to build a craft the size of say, the Starship Enterprise, and launch it around the solar system with nothing  more than 1960s technology.  Possibly even go interstellar, but I haven't seen the math showing how it gets million second Isp.  The whole point was to harness nuclear bombs for power.  The pusher plate is a kludge, but *anything* that could take the power of a nuclear bomb and turn it into useable energy was going to be overpowered regardless of inefficiency.  But as tech moves on, the Orion appears more and more like a dinosaur, and nobody even uses that kludge (the pusher plate) to launch rockets with fuel-air explosions (too much mass and not enough efficiency).  And it is even worse if you try to force it to do things it would be really bad at, like landing.

[Spacescifi]

57 minutes ago, kerbiloid said:

And that's why thou shalt not make a nuclear ship on constant magnets.

 

You can if it is a space-only ship. Vacuum is not a heat conductor like atmosphere.

[Terwin]

42 minutes ago, Spacescifi said:

You can if it is a space-only ship. Vacuum is not a heat conductor like atmosphere.

And this is why you cannot launch using ORION: anything strong enough to get it off the ground will melt your ship to slag.

A pusher-plate will *not* shield you from atmospheric heating. 

[Spacescifi]

5 minutes ago, Terwin said:

And this is why you cannot launch using ORION: anything strong enough to get it off the ground will melt your ship to slag.

A pusher-plate will *not* shield you from atmospheric heating. 

 

I can accept that with rockets... inasmuch even Scott Manley admitted even if we had metallic hydrogen it would melt the rocket engine if we used pure metallic hydrogen.

 

 

I had no intention of using a pusher plate for reentry shielding.

My idea has been a T-shaped cylindral bodied SSTO vessel that is a belly lander with the pusher plate at the tail.

 

During reentry it goes headfirst (the hammerhead front cylinder) which is fine since it has heat shielding on it.

 

To slow for landing it would flip and ignite a few pure fusion bombs before going horizontal to engage rocket engines to slow for landing.

 

But the way matters look it seems rocketry is a matter of go lightweight or stay home... if you want an SSTO anyway.

Multi-staging is where rockets really do their best work If you want to heavy lift.

 

Preferably reusable multistaging.

 

[Spacescifi]

So I guess heavy payload SSTO's really are science fiction and will remain so since the energy required to VTOL them means that even of you did you are landing in lava  walled craters.

 

Canceling out the force of gravity would work, but that would break reality as we know it.... at least what we currently know.

Edited June 7, 2022 by Spacescifi

[Terwin]

2 hours ago, Spacescifi said:

I had no intention of using a pusher plate for reentry shielding.

I was referring to liftoff, but an atmospheric retro-burn would likely be at least as bad, especially once you get sub-sonic.

[sevenperforce]

9 hours ago, KSK said:

Even accounting for the fact that modern high explosives are likely more performant than TNT (I have no knowledge on this point), the mass of explosives required seems to make an HE propelled Orion a non starter.

Modern solid high explosives can be up to around double the specific energy of TNT.

For a HE-based pulse pusher plate propulsion system, you would want an explosive with maximal specific energy. For the highest specific energy, you’ll probably want a mixture of ammonium perchlorate and powdered aluminum. You’ll also need something to bind it together into a putty of some kind, like polybutadiene acrylic acid acrylonitrile prepolymer, which also burns well with ammonium perchlorate and increases specific energy.

One advantage of this high explosive mixture is that you can make very small “pulse” units and therefore extract more of their energy by detonating them against a conical pusher plate. In fact, if you really want to extract the maximum energy, you can detonate them inside a sphere with an opening on one end so that all of the gases from the explosion flow out of that opening in a straight line.

If you’re very very clever you can make the pulse units very small — only a few molecules each — and detonate many of them continuously in a giant cylinder with a hole on one end.

7 hours ago, Spacescifi said:

I thought there was neutron radiation involved? So it would be safe to watch the laumch from a several kilometers away outside then?

The first all-up launch of the Saturn V knocked ceiling tiles loose at a distance of three miles, if I recall correctly. You don’t want to be anywhere near any rocket of any kind while it is launching.

The neutron activation radiation range of a pure fusion reaction is measured in centimeters.

[Bej Kerman]

On 12/19/2020 at 5:28 PM, Spacescifi said:

How heavy the vessel is DOES affect how strong the g-force is.

Basically, the heavier it is, the less g-force will bother the crew. Can autoloader withstand repeated 4g pulses? Perhaps.

If not...all we have to do is make the vessel heavier.

The vessel would be heavy enough that a pulse blast is merely 4g, or if still heavier 2g.

Nevrermind about how to get something that heavy in space....since let's assume the vessel already is in space to begin with.

So, to save weight, you're gonna alter the design of the craft to add much more weight than is taken by removing the shock absorbers? Wouldn't we save weight by replacing millions of tons with a little shock absorber?

[sevenperforce]

7 hours ago, Spacescifi said:

I assumed chemical would be powerful enough to lift a heavy orion but apparently not without being really inefficient with payliad to propellant ratios.

Chemical rockets have very high TWR so if all you need is getting off the ground, they are your drug of choice.

7 hours ago, Spacescifi said:

the fact that landing on your pusher plate like a tail lander means that lift off involves reusable rocket exhaust blowing past pistons... pistons you depend on to work that have flaming exhaust blowing all over them.

The pistons are able to handle close proximity nuclear explosions.

7 hours ago, Spacescifi said:

The original orion tail sitter was not designed to land at all and certainly not SSTO like a shuttle back and forth to a planet.

That’s because the Orion concept is 100% not useful as a shuttle. It’s for lifting very massively heavy things into a trajectory that requires ridiculous dV.

7 hours ago, Spacescifi said:

Also as a belly lander it is easier to reach pistons for maintenanence. Lets say you land somewhere so cold the pistons freeze over?

Conveniently, nuclear explosions are known to generate a great deal of heat.

I would be much more concerned about landing somewhere without a convenient source of refueling. I don’t know of any place where I can casually pick up a few hundred nuclear weapons.

7 hours ago, Spacescifi said:

Sustained pure fusion reactions are difficult to contain because it is like trying to hold a star in a jar... if you did the heat would blow up jar.

Well I don’t advise trying to hold a fusion reaction in a jar. I don’t advise holding any rocket fuel combustion in a jar. That is an inefficient path to propulsion. If you want propulsion, put a hole on one end of the jar and then it will produce thrust. 

[Bej Kerman]

8 minutes ago, sevenperforce said:

It’s for lifting very massively heavy things into a trajectory that requires ridiculous dV.

It can lift anything from anywhere if you have as much disregard for the environment as all billionaires. Ideally you wouldn't want to use it anywhere near a planet lest you mess with the electronics on the ground or irradiate nearby satellites.

[sevenperforce]

7 hours ago, Spacescifi said:

What is Z-pinch? Because if is magnetic based

Z-pinch uses a chemically-induced magnetic flux collapse to trigger a fusion pulse. It’s ideal in a vacuum but it can be done anywhere, really. There are no actual magnets involved. 

7 hours ago, Spacescifi said:

Are there any pure fusion pulse rockets that are on par with the abilites of project orion and it's ability to SSTO massive payloads? If not then project orion... especially with pure fusion is not exactly obsolete if you want a go anywhere and back kind of scifi SSTO that can carry heavy payloads.

There is no pure fusion . . . anything. There are no pure fusion bombs. If there was a way to directly harness pure fusion fuel then you could make it into a rocket engine but at no point would you ever remotely consider a pusher-plate design.

I don’t know why you think a pusher plate design has special SSTO capabilities.

Pound for pound, for a given a fuel type, a pusher plate will always be the least efficient design. If you want more payload, just build a bigger rocket.

If you want to write a science fiction story in which a pusher plate design is common place, for whatever reason, just make it so. Say that fissile material is extremely accessible and so everyone has nukes laying around. Say whatever you want. But know that the only possible universe where you would ever consider using a pusher plate is the universe where it is the absolute last resort.

7 hours ago, Spacescifi said:

Even if pure fusion pulse rockers are scaled down it won't matter if their thrust lower and their fuel consumption is higher than project orion is with pure fusion bombs.

They won’t be.

By basic rocket science definition, the propellant consumption and TWR of a rocket engine will always be better than a vehicle which uses the same fuel in a pusher plate design.

A Project Orion design is wildly inefficient and has abysmal TWR and abysmal specific impulse for the type of energy it is harnessing. The only reason anyone would ever consider using pusher plates is if they have an energy source like nuclear bombs, which are so wildly energetic that you can afford to waste 90% of the energy but have a minimum size. 

8 hours ago, Spacescifi said:

Likely pure fusion boosted chemical reusable rocketry would be needed for VTOL... while the rear pusher plate would use pure fusion bombs.

Nooooooo. If you have pure fusion ANYTHING it will be better than a pusher plate. 

[Gargamel]

32 minutes ago, sevenperforce said:

Chemical rockets have very high TWR so if all you need is getting off the ground, they are your drug of choice.

As long as you’re comfortable with a rocket the size of a large skyscraper.   We need to carry the fuel to land and takeoff again to make this anywhere a viable ssto.   And if we want to be picky, calling it a ssto means we’re not dropping any boosters, so we have to lift all that dead weight, and now that’s a rocket the size of a few skyscrapers.  
 

And we can’t say we’ll just refuel in orbit.   That completely defeats the purpose, as you can detach and land a shuttle from the main craft.   
 

Designing a ssto Orion craft is like putting wheels on a super tanker to deliver oil directly to Iowa.  

[Spacescifi]

1 hour ago, Gargamel said:

As long as you’re comfortable with a rocket the size of a large skyscraper.   We need to carry the fuel to land and takeoff again to make this anywhere a viable ssto.   And if we want to be picky, calling it a ssto means we’re not dropping any boosters, so we have to lift all that dead weight, and now that’s a rocket the size of a few skyscrapers.  
 

And we can’t say we’ll just refuel in orbit.   That completely defeats the purpose, as you can detach and land a shuttle from the main craft.   
 

Designing a ssto Orion craft is like putting wheels on a super tanker to deliver oil directly to Iowa.  

 

I see, so any more realistic SSTO will be smaller than any navy ship.

 

More like a large airplane at best, which would require a type of fusion rocket anyway to reap such high thrust and efficiency with less fuel.

Which means it coukd carry a little over 100 tons cargo like a 747.

 

I think even if we had fusion, heavy lift SSTO's on the scale of project orion would not be practical.

 

So SSTO's will always be glorified shuttles, designed for shuttling back and forth and little else.

 

Rather than full on spaceships that do interplanetary trips too.

 

 

Edited June 8, 2022 by Spacescifi

[Gargamel]

48 minutes ago, Spacescifi said:

 

I see, so any more realistic SSTO will be smaller than any navy ship.

No.  
 

There is no realistic size for an Orion SSTO.  Size isn’t the main issue though.   Mass is.     
 

48 minutes ago, Spacescifi said:

More like a large airplane at best, which would require a type of fusion rocket anyway to reap such high thrust and efficiency with less fuel.

Which means it coukd carry a little over 100 tons cargo like a 747.

This is like comparing apples and iguanas.    
 

Ones is designed to stay in orbit, permanently.   The other uses air pressure to create lift and carry that heavy load.   
 

48 minutes ago, Spacescifi said:

 

So SSTO's will always be glorified shuttles, designed for shuttling back and forth and little else.

Somewhat    

An SSTO is any craft that reaches orbit in a single stage.  Single Stage To Orbit.  It can be a rocket, a plane, or any vessel that doesn’t dump stages.   You could literally take an apple to the summit of Olympus Mons and throw it hard enough to enter orbit.   That apple is now an SSTO.   

If we want to talk spaceplanes (which may or not be SSTO), then we can do that.  We can keep taking about SSTO’s too if you’d like, but I think part of the issue is getting the nomenclature right.   

There is nothing stopping stopping you from making an SSTO that rendezvous with an asteroid, mines it, and returns the ore to a planet or another craft, aside from it being highly inefficient.  All those tanks that used to carry fuel are now dead weight, and that hurts your fuel efficiency, forcing you to carry less ore on the way back.   
 

Is that a realistic proposition? Absolutely not, as it is highly inefficient and unnecessarily complicated.   It is far better to have specialized components of a mission  that do one thing, and do it very well.   
 

So yes, the theoretical best use for an SSTO is some sort of passenger or cargo transport that meets up with an orbital platform of some sort, and then returns for a quick turnaround.   However, SpaceX has shown that it might be easier to get the best of both worlds.     They have a booster platform that can get a sizable payload to space, and then return to launch site for a very quick turn around, which allows the upper stage to be that specialized vessel that is required for the specific task.   
 

Apologies if this sounded a bit heavy handed.