Project Orion: A discussion of Science and Science Fiction

[Spacescifi]

[Moderator Note:  Thread Title has been changed to reflect the megathread nature]

 

I know why it has both.

Just curious if you were already in space and wanted to retrofit a spacecraft to be a an Orion minus the pistons or shock absorbers would that be viable?

I don't think (hope) the g-force from the nuke going off will kill the crew, if the spacecraft is heavy enough anyway.

So release bombs behind spacecraft and let the directed blast hit the rearend continually.

Any advantages or disadvantages over the original design?

Advantage? Less mass because no pistons or shock absorbers, equals greater thrust.

Disadvantage? More uncomfortable but not dead crew...I hope?

 

Your thoughts?

Edited April 7, 2022 by Gargamel
Title

[sevenperforce]

1 hour ago, Spacescifi said:

I know why it has both.

Just curious if you were already in space and wanted to retrofit a spacecraft to be a an Orion minus the pistons or shock absorbers would that be viable?

I don't think (hope) the g-force from the nuke going off will kill the crew, if the spacecraft is heavy enough anyway.

So release bombs behind spacecraft and let the directed blast hit the rearend continually.

Any advantages or disadvantages over the original design?

Advantage? Less mass because no pistons or shock absorbers, equals greater thrust.

Disadvantage? More uncomfortable but not dead crew...I hope?

 

Your thoughts?

The first blast will liquefy the crew.

[kerbiloid]

If the alien race can withstand repeatable 10 000 g pulses, no problem.

[magnemoe]

7 hours ago, kerbiloid said:

If the alien race can withstand repeatable 10 000 g pulses, no problem.

Even for an unmanned orion I think the stresses especially on the bomb magazines will be an serious issue. That thing is basically an gigantic auto-loader. 

[kerbiloid]

1 hour ago, magnemoe said:

Even for an unmanned orion I think the stresses especially on the bomb magazines will be an serious issue. That thing is basically an gigantic auto-loader. 

Coca-Cola (whose trading machine was the prototype) would be shocked pretty badly if they ordered a cola ATM withstanding 10 000 g overload.

The Fallout designers have lost such significant part of epoch.

[Spacescifi]

18 hours ago, sevenperforce said:

The first blast will liquefy the crew.

 

10 hours ago, kerbiloid said:

If the alien race can withstand repeatable 10 000 g pulses, no problem.

 

2 hours ago, magnemoe said:

Even for an unmanned orion I think the stresses especially on the bomb magazines will be an serious issue. That thing is basically an gigantic auto-loader. 

 

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.

Spoiler

I am partial to using gravity based drives that harness the gravity fields surounding them generated from planets to fly in whatever direction they wish at whatever strength the gravity field is.

This decreases with distance obviously, so in deep interplanetary space you need something else...thus the orion.

 

Edited December 19, 2020 by Spacescifi

[RealKerbal3x]

16 minutes ago, 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.

So, uh... you want to compensate for the lack of shock absorbers by making your vessel more massive? (by the way, mass is the correct terminology to use here as it refers to how much matter there is in an object, whereas weight is a force due to the pull of gravity on the object).

Making your vessel massive enough to have survivable acceleration per pulse is going to decrease your dV significantly, to the point where it's a way better idea just to add shock absorbers. If you have the capability to modify a vessel to survive a nuclear bomb going off behind it every few seconds, you probably have the capability to install shock absorbers to efficiently manage the acceleration as well.

Edited December 19, 2020 by RealKerbal3x

[Rakaydos]

The problem is, each munition in an Orion drive only releases a single pulse, which passes over your entire spacecraft at almost the speed of light. That means your change in velocity per pulse, is however many meters per second, times an insanely small fraction of a second.

Basically if you don't have a piston on the back of the spacecraft, your passenger's legs have to be the piston,to absorb the spacecraft suddenly moving when it wasn't before.

It also means that there is no acceleration between bomb pulses. That means there's nothing to hold you against the ground, so the next time the bomb pulses, you're going to fall against the back wall, based on how much you bounce off of it the last time it went off.

 

The piston isn't to moderate the acceleration. Is to moderate the change in acceleration... Meters per second per second per second, which is technically called jerk.

Edited December 19, 2020 by Rakaydos

[Rakaydos]

And because this author is notorious for not getting the point let me give an example with numbers.

You're floating in your cabin and the captain says they're about to engage the Orion drive, so you float over to the back wall. There's a countdown, and when it reaches zero the entire room seems to suddenly start moving. The back wall impacts you at 3.6 km an hour, and you bounce away from it because you're still in zero g.

One second later, the room jerks forward again, and you impact at another 3.6 km an hour. This happens again once per second for about 10 minutes.

That's 600 m per second of Delta v at an acceleration of 1 m per second per second. 1/10 of an earth gravity.

Edited December 19, 2020 by Rakaydos

[radonek]

Now that we have crew liquification covered, let's think about ship itself. If you just bolt pusher plate on ship that is not designed for it, you are essentially undergoing low frequency pogo from hell. Sooner or later, your ship will start to shed pieces and break up.  May take five rounds or five hundred, but break it will. Heavier ship will IMO just make stress greater.

I can imagine it as emergency  way to show something heavy out of way with a blast or two, especially if you dont care much about damage to moved object. As a propulsion, no.

[magnemoe]

3 hours ago, kerbiloid said:

Coca-Cola (whose trading machine was the prototype) would be shocked pretty badly if they ordered a cola ATM withstanding 10 000 g overload.

The Fallout designers have lost such significant part of epoch.

Heard about the coca cola thing but the loaders looks more like an artillery auto-loader for me.
However its closer to 100 g than 10K who is more like that an artillery shell experiences. 
Still you probably have to put more into making the ship keep together than you save on shock absorbers. 

On the other hand you could run an unmanned and single use orion much harder skimping a lot on the suspension. 

 

[Spacescifi]

3 hours ago, radonek said:

Now that we have crew liquification covered, let's think about ship itself. If you just bolt pusher plate on ship that is not designed for it, you are essentially undergoing low frequency pogo from hell. Sooner or later, your ship will start to shed pieces and break up.  May take five rounds or five hundred, but break it will. Heavier ship will IMO just make stress greater.

I can imagine it as emergency  way to show something heavy out of way with a blast or two, especially if you dont care much about damage to moved object. As a propulsion, no.

 

It would not be pogo because they would be strapped in.

Even so, as another said, the stress on the ship without pistoms or shock absorbers would be great, they did not mention the vibrations would rattle screws loose sooner or later as well.

Also, as one pointed out, my mass counter to g-force would cancel out the advantages I seek.

Coincidentally, the OP has unknowingly stumbled upon what thw crew would feel if they were broadsided with a shaped charge nuclear space missile.

 

Thank you.

[kerbiloid]

8 hours ago, magnemoe said:

However its closer to 100 g than 10K who is more like that an artillery shell experiences. 

100 times per piston stage, iirc. So, 10 000 → 1.

11 hours ago, Spacescifi said:

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

Heavier vessel - bigger nukes.

[wumpus]

Another thing you seem to miss in these continual questions about the Orion.

Pulse engines simply aren't a good system.

The reason the Orion was developed to use pulsed explosions was that nuclear explosives were the only known way to produce the energy needed for [interstellar] space travel without the fuel mass where that lets the rocket equation stop you from getting there.

There are [were] pulsed jets.  Think like a ramjet, only with pulses.  The V1 "buzz bomb" was such a thing.  But once the ramjet was developed, nobody would think of making such an inefficient design as a pulsed jet.  Likewise, if you simply increased the mass (and thus ruined the rocket equation), you could presumably build a de Laval nozzle to efficiently shape your exhaust velocity (it would have to be a massive nozzle to survive atomic explosions, but hey, you wanted to increase mass!).  Similarly, if you refused to use a piston, you would want to reduce the size of the explosion as much as possible, and possibly increase the frequency.  Perhaps something like laser ignition.  And you seem to like anti-matter based tricks.  But anything to have a reasonably efficient explosion that is much smaller than traditional.

I'm a huge fan of the original Orion.  But the whole point of the thing was that it could harness the fusion (or possibly just fission) that we already had in the 1960s to take us to space and possibly the stars (I'm not remotely convinced that the Isp is there for the delta-v I keep seeing for Orion).  But there really was no intention (or ability) to make the whole thing efficient.  There wasn't a real point: the nukes were simply so much more powerful than anything else humans could produce at the time (still are, although NTR are a something of a thing).

Finally, at some point you will just have to stop and play KSP.  It isn't on sale right now, so I'd suggest waiting a bit longer (steam should have plenty of post Christmas specials, but I have no idea if KSP will be one).  But to understand space you need to understand delta-v and ISP  (or at least the rocket equation), and KSP is easily the best way to learn that.  These discussions would go a lot better if you understood the rocket equation at roughly KSP-player level.

[kerbiloid]

Orion was "because", not "why".

They were researching directed blast nukes and realised that a direct blast looks viable for propulsion of something heavy in vacuum.

As the military doctrines of those days were focused on using thousands of nukes everywhere it's possible (every city with >25k population and any battlefield), the nukes were looking getting more cheap and available, so it was not a problem to spend from time to time a thousand or two for space flights.

[Scotius]

8 hours ago, Spacescifi said:

 

It would not be pogo because they would be strapped in.

Even so, as another said, the stress on the ship without pistoms or shock absorbers would be great, they did not mention the vibrations would rattle screws loose sooner or later as well.

Also, as one pointed out, my mass counter to g-force would cancel out the advantages I seek.

Coincidentally, the OP has unknowingly stumbled upon what thw crew would feel if they were broadsided with a shaped charge nuclear space missile.

 

Thank you.

Squishy bits inside of humans don't like such sudden pulses of acceleration. Especially the brain, almost free floating inside the braincase. It is a slow, unpleasant way to brain injury via repeated concussions. Strapping in won't help you there.

[mikegarrison]

16 hours ago, RealKerbal3x said:

So, uh... you want to compensate for the lack of shock absorbers by making your vessel more massive? (by the way, mass is the correct terminology to use here as it refers to how much matter there is in an object, whereas weight is a force due to the pull of gravity on the object).

Making your vessel massive enough to have survivable acceleration per pulse is going to decrease your dV significantly, to the point where it's a way better idea just to add shock absorbers. If you have the capability to modify a vessel to survive a nuclear bomb going off behind it every few seconds, you probably have the capability to install shock absorbers to efficiently manage the acceleration as well.

The core concept of Project Orion is actually that you do in fact want a more massive spaceship. The more massive the better. The ISP is so high that delta-v is not really an issue. And since there is a minimum size to a nuclear weapon, a more massive Orion is actually capable of more fine control. But of course it has issues with things like maneuvering thrusters, which would have to be full-size rockets being used for RCS.

But this lack of concern for extra mass is also why it makes no sense to skip all the shock-absorbing stuff.

If the thought is using some of of jury-rig propulsion system rather than a purpose-built Orion, all you would do is destroy your ship and probably irradiate anyone that wasn't directly killed.

15 hours ago, radonek said:

Heavier ship will IMO just make stress greater.

Sorry, but this is not how stress works.

5 hours ago, wumpus said:

The reason the Orion was developed to use pulsed explosions was that nuclear explosives were the only known way to produce the energy needed for [interstellar] space travel without the fuel mass where that lets the rocket equation stop you from getting there.

This is not true. Dyson primarily envisioned it for interplanetary travel, not interstellar travel. He figured this was basically the only practical method for getting past Mars, and I don't think he really thought getting to Mars via chemical rockets was a good idea either.

[mikegarrison]

5 hours ago, wumpus said:

Pulse engines simply aren't a good system.

There are [were] pulsed jets.  Think like a ramjet, only with pulses.  The V1 "buzz bomb" was such a thing.  But once the ramjet was developed, nobody would think of making such an inefficient design as a pulsed jet. 

Pulse propulsion is not inherently inefficient. V1-style pulse jets are inefficient because of their design. (They are also cheap and reliable for a single flight because of their design, which was what Germany really needed for a terror weapon. They didn't need accuracy or even a lot of damage and they certainly weren't concerned about efficiency. They just needed to flood the skies with them and instill fright.)

[Spacescifi]

7 hours ago, Scotius said:

Squishy bits inside of humans don't like such sudden pulses of acceleration. Especially the brain, almost free floating inside the braincase. It is a slow, unpleasant way to brain injury via repeated concussions. Strapping in won't help you there.

OK...you got me there.

Yet I also think being pulled into a headrest pillow repeatedly won't be so bad.

Brain rattling in the skull? Yeah...bad.

A sapient bird derived race coincidentally may retain the biology that allows smaller birds to survive high g forces...but I digress. Like woodpeckers..no concussion despite being living wood jackhammers. Biology is awesome.

Humanoids? Bad for that kind of thing. Not designed for it.

4 hours ago, mikegarrison said:

The core concept of Project Orion is actually that you do in fact want a more massive spaceship. The more massive the better. The ISP is so high that delta-v is not really an issue. And since there is a minimum size to a nuclear weapon, a more massive Orion is actually capable of more fine control. But of course it has issues with things like maneuvering thrusters, which would have to be full-size rockets being used for RCS.

But this lack of concern for extra mass is also why it makes no sense to skip all the shock-absorbing stuff.

If the thought is using some of of jury-rig propulsion system rather than a purpose-built Orion, all you would do is destroy your ship and probably irradiate anyone that wasn't directly killed.

Sorry, but this is not how stress works.

This is not true. Dyson primarily envisioned it for interplanetary travel, not interstellar travel. He figured this was basically the only practical method for getting past Mars, and I don't think he really thought getting to Mars via chemical rockets was a good idea either.

 

4 hours ago, mikegarrison said:

Pulse propulsion is not inherently inefficient. V1-style pulse jets are inefficient because of their design. (They are also cheap and reliable for a single flight because of their design, which was what Germany really needed for a terror weapon. They didn't need accuracy or even a lot of damage and they certainly weren't concerned about efficiency. They just needed to flood the skies with them and instill fright.)

 

Good points. You could write a story or a book on Orion spacecraft.

Ultimately intent decides all tech in scifi. Whereas physics and intent decides all tech IRL.

In scifi if you want an interstellar freighter that is owned by civillians that can make random detours you have little choice but to rely on fiction.

 

In real life Project Orion's biggest problem in space is the RCS. The amount of propellant burned for each course correction realistically brings hard lmits to where an Orion can actually go in a timely fashion in the solar system.

I mean..processing ice found on an asteroid for RCS propellant is doable, but that is risky and prolongs mission time.

 

My suggestion? On really massive Orions use high powered chemical bombs for pusher plate RCS.

Leading to a weird  Orion with a big rear pusher plate and somewhat smaller ones tacked on for RCS.

Sounds viable in my head anyway.

Edited December 20, 2020 by Spacescifi

[mikegarrison]

31 minutes ago, Spacescifi said:

You could write a story or a book on Orion spacecraft.

It's already been written, and I've read it.

https://www.amazon.com/Project-Orion-Story-Atomic-Spaceship/dp/0805059857

It was written by Freeman's son, George Dyson.

Or if you prefer fiction, here's another one I've read, this one by Poul Anderson.

https://www.amazon.com/dp/B005HRT8RM

Edited December 20, 2020 by mikegarrison

[Spacescifi]

7 minutes ago, mikegarrison said:

It's already been written, and I've read it.

https://www.amazon.com/Project-Orion-Story-Atomic-Spaceship/dp/0805059857

It was written by Freeman's son, George Dyson.

Or if you prefer fiction, here's another one I've read, this one by Poul Anderson.

https://www.amazon.com/dp/B005HRT8RM

Thanks.

What do you think about my pusher plate chemical bomb RCS vs using propellant?

 

Would that be more efficient in space?

Obviously getting all that into orbit will be hard and time consuming...but once there good right?

Edited December 20, 2020 by Spacescifi

[mikegarrison]

4 minutes ago, Spacescifi said:

What do you think about my pusher plate chemical bomb RCS vs using propellant?

No.

The whole point of Project Orion is that nuclear reactions are much more powerful than chemical reactions (and are the only way we know to get good ISP and also good thrust together at the same time). It was never that explosions pushing on plates are more effective than rockets. If you are going to use chemical reactions, just build chemical rockets.

Edited December 20, 2020 by mikegarrison

[Spacescifi]

16 minutes ago, mikegarrison said:

No.

The whole point of Project Orion is that nuclear reactions are much more powerful than chemical reactions (and are the only way we know to get good ISP and also good thrust together at the same time). It was never that explosions pushing on plates are more effective than rockets. If you are going to use chemical reactions, just build chemical rockets.

Well...that limits the options the does'nt it?

Real life spaceship Orions are like heavy trains that have a super long straight track and a limited amount of detour tracks.

Unless you make more detour track (asteroid ice refueling).

Makes little sense to mine any gravity well since the gravity fuel losses will cancel out the fuel spent to grab it unles...cannon.

A chemical powered cannon on the moon could be designed to shoot stuff into orbit around the moon.

And by stuff I mean bagged ice for the orbiting Orion to intercept and pick up.

The cannon could use hydrogen and oxygen from ice to power it to launch. the bulk of the ice inside bags to prevent sublimation from sun rays before the orbiting Orion catches them all.

Edited December 20, 2020 by Spacescifi

[Scotius]

No. Real life Orions are cars without engines. Instead they have anvils welded to rear bumpers. You propel them forward by pulling a pin from a hand grenade and throwing it out from the rear window. Then entire assembly gets propelled forward by the shockwave and cloud of shrapnel hitting the anvil. Sounds awesome, right?

[KSK]

From my own copy of Project Orion:

"An Advanced Interplanetary Ship powered by 15 kiloton bombs, with up to 4g acceleration and a takeoff mass of 10,000 tons was envisaged as 185 feet in diameter and 250 feet in height. It's payload to a 300 mile orbit was 6,100 tons; to a soft lunar landing 5,700 tons... to a landing on an inner satellite of Saturn and return to a 300 mile orbit, 1300 tons."

That's a lot of payload space to fit RCS propellant into. Yes, it will be a limitation but I don't think it would be a crippling one.

For comparison, the mass of a ready-to-launch Falcon 9 is about 549 tons, so the Advanced Interplanetary Ship could have hauled two fully fueled Falcon 9s out to Saturn and back, with payload capacity to spare.