Project Orion: A discussion of Science and Science Fiction

[Terwin]

9 hours ago, Spacescifi said:

The merits of Orion are multiple:

1. Can perform well both in atmosphere and space.

Orion only works in atmosphere if you are ok with melting the whole thing and irradiating your cargo while you do so. (Atmosphere can reflect both heat and radiation, space not so much.   This is not even considering the atmospheric shock-waves)

9 hours ago, Spacescifi said:

2. Much easier to make compared to fusion rocketry.

All of the hardest parts of fusion rocketry are also required for a pure fusion orion.  If anything they are made harder by having more space and an extended pusher-plate between the ignition sources and the ignition target.

9 hours ago, Spacescifi said:

3. Safer than the NSWR by Zubrin on any given day.

Fission is generally safer then fission, yes, but you may still have more radiation because your nuclear reaction is not inside of any sort of containment vessel.

[kerbiloid]

If take several antigrav repulsors and put them around the nozzle, we can use pure fusion by squashing the pellets with antigravity.

[Spacescifi]

1 hour ago, Bej Kerman said:

That's besides the fact that Orion drives will be older than stone tablets when we figure out how to manipulate gravity.

 

Quite right.

 

An alternative to Orion is a type of antigravity light ray drive.

 

So long the drive is charged it generates an invisible gravity canceling field around the vessel, but the nozzle can also emit antigravity rays to propel the vessel which depletes the drive's charge.

 

Long story short is that the ship is immune to gravity and must rely on it's antigrav ray for propulsion until it's charge is fully depleted, upon which gravity will pull on the ship again.

 

With the drive depleted it is useless until it is recharged of the local strength of a gravitation field multiplied by the drive's max g-force rating. It can accelerate at lower rates but it does not effect the charge depletion time like normal rockets.

 

Type 3 would multiply antigravity ray acceleration by 3 max for 3 hours of charge. You cannot recharge until fully depleted of tge previous charge.

 

Scenario: Fly into space, you cannot truly orbit as gravity no longer pulls you, you accelerate and coast to mars and retro thrust to slow down. Eventually using all your charge up so you could get there quickly as possible but also 'refuel'.

You refuel at with mars gravity for a few hours.

Result: Mars surface gravity scceleration multiplied by 3 for 3 hours.

 

[Bej Kerman]

3 minutes ago, Spacescifi said:

antigravity rays

I'm not sure why bother thinking a lot about the hard-science aspects if we're just gonna resort to soft-scifi gibberish like "antigravity rays". You can only pick one lane, there's no reason whatsoever to overthink the physics of everything if in the end you're gonna throw any realism in the bin.

Edited June 12, 2022 by Bej Kerman

[kerbiloid]

Why not just pull the Mars by the antigrav rays closer?

[Terwin]

10 minutes ago, Bej Kerman said:

I'm not sure why bother thinking a lot about the hard-science aspects if we're just gonna resort to soft-scifi gibberish like "antigravity rays". You can only pick one lane, there's no reason whatsoever to overthink the physics of everything if in the end you're gonna throw any realism in the bin.

Also, all of that extra detail is something that should only even exist if it will be a significant plot point.  With science fiction, the needs of the story drive everything else.  Everyone needs air to live, but how often does a story mention a character breathing?  Only when it illustrates or extends something directly important for the story, the rest of the time, it is a useless side-bar that usually detracts from the story as a whole.

If pusher-plates come up as a critical dramatic point in the story, then you have pusher-plates, even if they make no technical sense.  If they do not serve as a critical dramatic point, then the reader should be completely ignorant of those drive details.

If the story requires that an apollo stack can get to alpha centari in less than 5 years, then it can.

If the story does not come first, then nothing else matters because no one will read it.

[Spacescifi]

 

Picture this.... a large belly lander SSTO, using reusable chemical rockets for VTOL to get in the air, and the it starts to  nearly flip backward before firing it's main rear engine which has a single, thick bodied nozzle.

The main engine shoots out a long straight plume of bluish white fire in a single pulse, and despite the spaceship being large and heavy it literally shoots off with acceleration that is rapid..  like a tiny bottle rocket.

 

No slow rising here! This rocket engine has oomph to spare!

 

What is it?

 

Pure Fusion Pulse rocket: I basically considered what matterbeam wanted for a pure fusion orion and thought why not use that tech for a rocket?

 

What it would probably take to make:

 

Some sort of vacuum chamber lined with powerful super magnetic coils or devices. A pure fusion bomb would be inserted into a chamber and detonated, and the resulting fusion plasma would be shunted via magnetic fields into a reaction chamber where it would mix with the propellant as it leaves the nozzle.

Realistically I am not sure we have magnetic coils powerful enough and small enough that they do not need to be gigantic to pull off a feat of directing the plasma on par with a nuke for energy.

But we would need smaller more uber magnet tech to ever havs scifi SSTO's that take off like Star Wars on their bellies.

 

Unlike Star Wars I do not see constant flow pure fusion rocket SSTO's being a thing.

 

Why not?

Powerful high g pulsed acceleration is more fuel efficient than constant flow lower g acceleration.

 

High g pulsed acceleration does generate waste heat, but with sufficient ingenuity I don't see why that cannot be averted by dumping the heat into the propellant as it leaves the nozzle.

 

So... I think, if heavy SSTO's ever are made, they will be pure fusion pulsed rockets.

Using chemical rocketry to land.

 

Unlike project orion you do not have to lug around a heavy pusher plate and pistons, but I think the main advantage is that critical mass for a fission reaction no longer matters.

If I read correctly, pure fusion reactions can be scaled up or down as needed, which means if you want a smaller acceleration you can have it... not all your pulses need to be fusion death beams that leave a mini-mushroom dirt cloud where you launched from lol.

Edited June 13, 2022 by Spacescifi

[kerbiloid]

3 hours ago, Spacescifi said:

The main engine shoots out a long straight plume of bluish white fire in a single pulse, and despite the spaceship being large and heavy it literally shoots off with acceleration that is rapid..  like a tiny bottle rocket.

Like this one.

Spoiler

 

...and once it reaches several Machs in thick air, it gets white-hot and melts down, and the air drag starts totally eating its delta-V, because SSTO is not ABM, so its high-TWR pure-fusion engine mostly heats the air around rather than accelerates the rocket.

But happily, the cargo and the crew won't be fried, because first they will be squashed by overloads, as the total mass of the rocket is decreasing, so TWR grows together with the overloads.
Thus, the clever rocket starts decreasing thrus to keep TWR constant, and thus it's no sense in having TWR > 1.5..2 for a crewed/cargoed rocket at all.

[sevenperforce]

On 6/12/2022 at 1:43 AM, Spacescifi said:

We all know that the sheer amount of energy required to pull of feats in scifi is almost always greater than the ship could pull off without melting.

I do not understand why you think the primary problem in space flight is melting.

[sevenperforce]

13 hours ago, Spacescifi said:

Powerful high g pulsed acceleration is more fuel efficient than constant flow lower g acceleration.

No, it is not.

13 hours ago, Spacescifi said:

High g pulsed acceleration does generate waste heat, but with sufficient ingenuity I don't see why that cannot be averted by dumping the heat into the propellant as it leaves the nozzle.

If you use a constant-thrust engine rather than pulsing, then yes, you can dump the heat into the propellant as it leaves the nozzle.

13 hours ago, Spacescifi said:

I think, if heavy SSTO's ever are made, they will be pure fusion pulsed rockets.

Using chemical rocketry to land.

If you have a pure fusion engine then just use your pure fusion engine to take off and land. All other inquiries are unnecessary.

[wumpus]

2 hours ago, sevenperforce said:

I do not understand why you think the primary problem in space flight is melting.

It is fairly significant.  As far as I know, keeping combustion chambers from melting has a small limit on the Isp of chemical rockets (true at least for shuttle engines, and they have amazing Isp).  Of course, the real problem is always mass.  And bringing along a power supply that might cause the ship to melt is going to be heavy, too heavy to bring to space (although the kilopower project might give us hope for a somewhat lighter and less solar dependent power supply).  But there is also a known solution: radiators.  The ISS has a set of radiators that are about 1/10th the size of the solar panels, but they are there and needed.  For any reasonable power needs, you just scale them up.  I once calculated (for one of spacescifi's space battle threads) that the upper limit for an ISS-sized array was 60MW, an that you would have to scale up from  that (and that said radiator would make an ideal target in a space battle).  But in reality, you'd just keep building bigger radiators.

Melting is a huge issue for re-entry, and the entire reason we lost the Columbia.  On the other hand, the larger the vehicle landing, the less of an issue this is (although you'll pay later with a higher terminal velocity).  I'd assume that any "commercial trips to orbit" would have sliding "wings" that would increase the surface area of the returning ships by a significant multiple, and that this would make it much easier to return from orbit.  See also inflatable heat shields (no idea how to reuse such a shield). 

But looking at all the examples, the only reason "melting" is an issue is that the real question is "what is the least amount of mass we can spend to avoid melting".  The real issue is always mass.

[sevenperforce]

5 minutes ago, wumpus said:

3 hours ago, sevenperforce said:

I do not understand why you think the primary problem in space flight is melting.

It is fairly significant.  As far as I know, keeping combustion chambers from melting has a small limit on the Isp of chemical rockets (true at least for shuttle engines, and they have amazing Isp).

It is a significant problem, yes, but mass is always the primary problem.

My comment is aimed at oft-expressed sentiments like "we can't make science-fiction spaceships too large because it's impossible to get that much thrust without melting the engine" which doesn't really make sense. Active cooling of engines is one of the less complicated aspects of rocket science.

[Spacescifi]

12 hours ago, sevenperforce said:

No, it is not.

If you use a constant-thrust engine rather than pulsing, then yes, you can dump the heat into the propellant as it leaves the nozzle.

If you have a pure fusion engine then just use your pure fusion engine to take off and land. All other inquiries are unnecessary.

 

 

High thrust and efficiency are hard to pair together with rocketry.

 

I reckon that mixing propellant with pure fusion bomb plasma rapidly again and again via pulse would require both a level of complexity and power the world has not seen.

 

So let's make it simpler... somewhat.

 

Instead of using liquid propellant at all for the pulse rocket, just detonate a high yield pure fusion bomb inside a  vacuum super high compression magnetic chamber with a hole leading to the exit nozzle.

 

Let's presume the bombs are on par with nukes.

So what you end up with is a rocket with better performance than project orion because of the nozzle pointing the plume only rearward... with the side effect of leaving mushroom clouds in it's wake during launch.

At least the radiation is less than nuclear.

 

Now when I say efficiency I mean less bombs per ton need to be expended to reach orbit (because more energetic) than the tons upons tons of chemical propellant that would be required otherwise.

 

Ultimately the way we currently know physics, any Star Trek adventures would be at LEAST two spaceships.

 

1. A large SSTO.... basically it is the shuttle to anywhere and back.

2. The orbiter. With rotating arms for crew to live in. They would live here and only transfer to the SSTO when they wanted to explore.

The main difference between commonly depicted media scifi and this is that instead of a small accessory of tiny shuttlecraft, you get one large SSTO spaceship that no one lives in until they need to try to land anywhere.

 

It is too hard and also unrealistic to try to get an SSTO to do all the things an orbiter needs to do with rotational gravity.

 

It always pays to optimize.

 

 

Edited June 14, 2022 by Spacescifi

[kerbiloid]

39 minutes ago, Spacescifi said:

just detonate a high yield pure fusion bomb inside a  vacuum super high compression magnetic chamber with a hole leading to the exit nozzle.
<...>
the nozzle pointing the plume only rearward...

The nozzle is strong. A nuke explodes inside, but it doesn't even melt.

A lot of good knives can be forged out of this nozzle if capture the ship.
Though, a trouble: how to melt the nozzle to forge them.

Irl. Heat radiation evaporates the rocket together wirh nozzle and turns everything into a fireball.

The hypothetical pulse engines either burn the fusion pellets at low rate, or explode the nuke far away from the ship (Orion) and receive the energy as a prolonged plasma jet.

And the magnetic nozzle is anyway just a metal truss.

48 minutes ago, Spacescifi said:

At least the radiation is less than nuclear.

Unless it's an aneutronic fusion, the radiation can easily exceed the nuclear (i.e. fission) one, due to much greater amount of neutrons activating the ground.

50 minutes ago, Spacescifi said:

with the side effect of leaving mushroom clouds in it's wake during launch.

Just one. But immediately.

[Vanamonde]

I suspect that a magnetic field strong enough to contain and direct a fusion explosion would have deleterious side effects, such as pulling the iron out of the crew's blood. 

[Terwin]

15 hours ago, Spacescifi said:

So let's make it simpler... somewhat.

 

Instead of using liquid propellant at all for the pulse rocket, just detonate a high yield pure fusion bomb inside a  vacuum super high compression magnetic chamber with a hole leading to the exit nozzle.

 

Let's presume the bombs are on par with nukes.

Why?  This gives you all the complexity of pure fusion(which can scale down to single fusion events) with the scaling problems of fission(minimum impulse size limited by critical mass).

Instead of a single large impulse every X seconds, do 100 impulses of 1% of the large impulse at a rate of 100 per x seconds.  This lets you reduce the strength of just about everything involved by at least two orders of magnitude, greatly reducing engine weight and improving TWR.  Take this to the logical extreme and you have a drive that is either continuous or has very small discrete fuel 'pellets' igniting many times per second. 

Also, with fusion, you do not need pre-packaged pure-fusion bombs, but can instead use the same ignition source and just pump in the hydrogen you want to ignite(possibly in a magnetic bottle or some such).

15 hours ago, Spacescifi said:

So what you end up with is a rocket with better performance than project orion because of the nozzle pointing the plume only rearward... with the side effect of leaving mushroom clouds in it's wake during launch.

Why would this form of engine create mushroom clouds when other engines that also shoot out super-hot gas do not?  There is no huge fireball to ascend into the sky and provide that mushroom shape(unless something goes very wrong, and at that point your ship is no longer reusable). 

 

15 hours ago, Spacescifi said:

Now when I say efficiency I mean less bombs per ton need to be expended to reach orbit (because more energetic) than the tons upons tons of chemical propellant that would be required otherwise.

With fusion, you do not want discrete bombs, you have a single reusable means of igniting the fusion that you use either continuously for a torch drive, or for small discrete packages of fuel for a pulse drive.  Ideally, your fuel is a large tank of hydrogen that you can refuel anywhere with easily accessible hydrogen.

 

[KSK]

5 hours ago, Vanamonde said:

I suspect that a magnetic field strong enough to contain and direct a fusion explosion would have deleterious side effects, such as pulling the iron out of the crew's blood. 

I don’t know about a fusion explosion but the ITER central solenoid  apparently produces a 13 Tesla field, which is comfortably lower than the field strengths used by modern (600Mhz +)  NMR spectrometers. Those will have a safety line around them which you shouldn’t cross if you’re wearing a pacemaker (or are carrying credit cards - ask me how I know…) but the ‘danger’ zone around the magnet is not large.

So I’m not sure that fusion rocket magnetic fields would be a particular problem, especially if you put it at a decent distance from the crew compartment.

 

[mikegarrison]

1 hour ago, KSK said:

 (or are carrying credit cards - ask me how I know…)

Yeah, I visited a magnet lab one time and was told that all of the regular workers had been in trouble with their banks for repeatedly needing their ATM and credit cards fixed/replaced.

[kerbiloid]

5 hours ago, KSK said:

10 hours ago, Vanamonde said:

I suspect that a magnetic field strong enough to contain and direct a fusion explosion would have deleterious side effects, such as pulling the iron out of the crew's blood. 

I don’t know about a fusion explosion but the ITER central solenoid  apparently produces a 13 Tesla field

According to https://physics.stackexchange.com/questions/269410/what-is-the-relationship-between-the-magnetic-units-oersted-and-tesla

Quote

Therefore a 1 Oe corresponds to 10⁻⁴ T in non-magnetic materials.

As I had read in childhood, 500 kOe field slows the blood speed by two times,  2 MOe field stops it.

So, >50..200 T is a lethal range.

[Spacescifi]

On 6/14/2022 at 11:49 AM, Terwin said:

Why?  This gives you all the complexity of pure fusion(which can scale down to single fusion events) with the scaling problems of fission(minimum impulse size limited by critical mass).

Instead of a single large impulse every X seconds, do 100 impulses of 1% of the large impulse at a rate of 100 per x seconds.  This lets you reduce the strength of just about everything involved by at least two orders of magnitude, greatly reducing engine weight and improving TWR.  Take this to the logical extreme and you have a drive that is either continuous or has very small discrete fuel 'pellets' igniting many times per second. 

Also, with fusion, you do not need pre-packaged pure-fusion bombs, but can instead use the same ignition source and just pump in the hydrogen you want to ignite(possibly in a magnetic bottle or some such).

Why would this form of engine create mushroom clouds when other engines that also shoot out super-hot gas do not?  There is no huge fireball to ascend into the sky and provide that mushroom shape(unless something goes very wrong, and at that point your ship is no longer reusable). 

 

With fusion, you do not want discrete bombs, you have a single reusable means of igniting the fusion that you use either continuously for a torch drive, or for small discrete packages of fuel for a pulse drive.  Ideally, your fuel is a large tank of hydrogen that you can refuel anywhere with easily accessible hydrogen.

 

 

I think what you are saying is with an uber magnetic field with the right configuration, it can be used to literally squeeze liquid hydrogen until it fuses and then spit it out magnetically for a rocket plume.

 

 

Using small pellets I know works by using magnetic nozzles, and I would love to think a magnetic nozzle would work fine in atmosphere.... but IRL I think the magnetic truss shaped like a cone would be blown up from the air pressure wave which is not magnetic.

 

Unless the magnetic field is SO uber that it deflects the air blast wave as well.

 

This is in theory possible, but at that point you may as well have a solid magnetic nozzle since the heat won't conduct to it anyway.

[kerbiloid]

A magnetic "nozzle" (which is actually a chamber) would not work in atmosphere because it's a quasispherical grid of conductors, to minimize its irradiated area.
So, everything fusing/being fused inside would be blown away by wind before the nozzle.

And that's exactly what gives to the Orion scheme its advantage. It doesn't surround the reaction zone with something heatable or destroyable. It  has released the energy far behind, but then focused on its enforced reflector (the pusher plate).
So, it doesn't need to care about the pressure and temperature, but can't work in atmosphere, too, just for other reasons.

It its turn, the magnetic nozzle scheme is limited by its material nature, and can't produce high thrust, because high thrust provided by light particles and cores requires a lot of energy due to high energy-to-momentum ratio.
This will cause significant heating of surrounding structures (the magnetic nozzle), what makes to make it a grid of flat trusses, but any grid size is limited mechanically by the strength of materials.

So, non-Orion schemes are low-thrust (unless they heat some heavy-atom substance on atmospheric flight, which turns them into a low-ISP rocket).

That's why there is no visible alternatives to the Orion-like design based on the known physical principles.
Just the classic, mechanical Orion scheme is obsolete (though probably workable), and MiniMag Orion with Z-pinch fusion and magnetic reflector instead of the pusher plate is appropriate for high-thrust and high ISP, but also not for atmospheric flights.

[Spacescifi]

12 minutes ago, kerbiloid said:

A magnetic "nozzle" (which is actually a chamber) would not work in atmosphere because it's a quasispherical grid of conductors, to minimize its irradiated area.
So, everything fusing/being fused inside would be blown away by wind before the nozzle.

And that's exactly what gives to the Orion scheme its advantage. It doesn't surround the reaction zone with something heatable or destroyable. It  has released the energy far behind, but then focused on its enforced reflector (the pusher plate).
So, it doesn't need to care about the pressure and temperature, but can't work in atmosphere, too, just for other reasons.

It its turn, the magnetic nozzle scheme is limited by its material nature, and can't produce high thrust, because high thrust provided by light particles and cores requires a lot of energy due to high energy-to-momentum ratio.
This will cause significant heating of surrounding structures (the magnetic nozzle), what makes to make it a grid of flat trusses, but any grid size is limited mechanically by the strength of materials.

So, non-Orion schemes are low-thrust (unless they heat some heavy-atom substance on atmospheric flight, which turns them into a low-ISP rocket).

That's why there is no visible alternatives to the Orion-like design based on the known physical principles.
Just the classic, mechanical Orion scheme is obsolete (though probably workable), and MiniMag Orion with Z-pinch fusion and magnetic reflector instead of the pusher plate is appropriate for high-thrust and high ISP, but also not for atmospheric flights.

 

Alright feel free to correct me if I am wrong.... thanks for the info... you and everyone else.

 

Why cannot  a pure fusion Orion work in the atmosphere?

The reasons I suspect you are going to say are:

1. While you could do it it would cause neutron activation and therefore radiation if the blast wave occurs near the ground. It's not a show stopper but does mean that you will have to watch the last of the first stage rocketds be blown to smithereens by the pure fusion blast. The first set of the first stage rockets could in theory be reusable and land on their own. You would need plenty of altitude to avoid neutron activation before you engage the orion drive.

2.  Obviously landing an Orion is a no go... too heavy. Sure you could slow it down with pure fusion blasts, but the heat from the air I reckon would mess up the pistons over time since you are falling into inferno clouds again and again.

 

Ironically.... the only way I can even see an Orion as a viable safe SSTO is if it could generate gravity suspension field bubbles around the ship.

 

I know, I know, scifi super tech meets the obsolete, but it woumd still work.

 

With gravity no longer in play making spacecraft get to space would be easy

 

We could spin launch the thing and wait an hour for it to drift into space, and also spinlaunch a 100 meter radius habitat ring to attach with it in space as well.

[kerbiloid]

8 minutes ago, Spacescifi said:

Why cannot  a pure fusion Orion work in the atmosphere?

No Orion can work in atmosphere. Because it's a nuclear explosion in a hundred or two of meters behind.

An aerial fireball radius is (59 _{68 for on-ground} * yield^0.4) in meters.
So, the orion can stay away from the 8 000 K hot zone and survive.

But the air shockwave is several Machs fast, and it will hit the ship and mechanically destroy it.
In vacuum there is no shockwave in surrounding air.

Edited June 16, 2022 by kerbiloid

[Gargamel]

As this thread has yet again devolved into Orion SSTO’s, it has been merged with the master thread. 

[Spacescifi]

28 minutes ago, kerbiloid said:

No Orion can work in atmosphere. Because it's a nuclear explosion in a hundred or two of meters behind.

An aerial fireball radius is (59 _{68 for on-ground} * yield^0.4) in meters.
So, the orion can stay away from the 8 000 K hot zone and survive.

But the air shockwave is several Machs fast, and it will hit the ship and mechanically destroy it.
In vacuum there is no shockwave in surrounding air.

 

Are you sure?

Did not the designers intend the Orion to detonate bombs in atmosphere part way to space?