Project Orion: A discussion of Science and Science Fiction

[Spacescifi]

55 minutes ago, KSK said:

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.

 

 

That does it! I want the powers that be to make an Expanse like show with Orion....not some goofy fictional Epstein drive.

Going to Saturn and back is fair enough for an Expanse setting.

[sevenperforce]

9 hours ago, Spacescifi said:

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.

No, because you can just bring more RCS propellant.

The whole  point of Orion is that you have as much payload as you want.

Including as much RCS propellant as you want.

These threads remind me of the car I tried to design at age 8 which propelled itself by a gear that attached the steering wheel to the powertrain, so the "driver" would just turn the steering wheel around really fast to go. And then I needed to figure out steerng.

[Rakaydos]

13 hours ago, Spacescifi said:

OK...you got me there.

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

Congratulations, you just added a piston system, one that only works for the heads of crew members who are strapped in at the time. The entire point of the Orion piston system is to be a pillow for the whole spacecraft at once. A really well designd pillow, that allows higher useful acceleration by dampening the detonation pulse into a continuous stroke of acceleration.

Edited December 21, 2020 by Rakaydos

[kerbiloid]

As I had calculated here a couple of years ago, the amount of former cooling water returned from the pusher plate as steam, would be comparable to the minimal RCS characteristics of real ships.

So, it probably could be used to keep Orion on course on acceleration and deceleration, when it isn't maneuvering.

Though, afaic_anu_nderstand, the real Orion authors were just far from  these minor problems, being focused totally on propulsion.

"I'll think about it tomorrow."

***

Also (my guessing), as the pusher plate needs to be massive and (due to the pistons) retractable, maybe they could use it for aerobraking, still using the cooling water steam for attitude control.

For fine orbital mechanics they still need some chemical RCS or a nuclear boiler (the latter is better, because it's atompunk, not a moleculepunk).

[mrfox]

58 minutes ago, Rakaydos said:

A really well designd pillow, that allows higher useful acceleration by dampening the detonation pulse into a continuous stroke of acceleration.

Sorry... pet peeve. 
It’s damping. Dampening is adding moisture - making something wet.

carry on...

 

[KSK]

1 hour ago, mrfox said:

Sorry... pet peeve. 
It’s damping. Dampening is adding moisture - making something wet.

carry on...

 

I think Orion has you covered either way. Even with a good damping system, riding a series of nukes to orbit would be plenty dampening for me.

 

[Nuke]

figure as a way to move asteroids it would work. you would just be heating the surface rock, preferably as evenly as possible so as not to rip it to pieces with thrust asymmetries. you might use multiple nuclear shape charges all going off at various times such that the radiation hits the surface all at the same time.  keep in mind the warheads never actually touch the asteroid, jsut used as high powered nuclear flashlights.  a few coordinated blasts ought to be enough to deflect the asteroid away from or towards earth, whatever your desired outcome may be.

Edited December 21, 2020 by Nuke

[Scotius]

51 minutes ago, Nuke said:

figure as a way to move asteroids it would work. you would just be heating the surface rock, preferably as evenly as possible so as not to rip it to pieces with thrust asymmetries. you might use multiple nuclear shape charges all going off at various times such that the radiation hits the surface all at the same time.  keep in mind the warheads never actually touch the asteroid, jsut used as high powered nuclear flashlights.  a few coordinated blasts ought to be enough to deflect the asteroid away from or towards earth, whatever your desired outcome may be.

Aliens, living peacefully in a system several lightyears away: WTH are they doing to their own planetary system? Those barbarians must wage truly horrifying war! Nope, we are not going there!

TL;DR - "Let's nuke it!" is not the best answer to 95% of problems.

[kerbiloid]

1 hour ago, Scotius said:

Aliens, living peacefully in a system several lightyears away: WTH are they doing to their own planetary system?

They come in peace, didn't you watch?

Spoiler

Our endorphins  are that what they need.

Spoiler

Never understood why "Dolph Lundgren" when the main character is obviously Matthias Hues' "

 

 

Edited December 21, 2020 by kerbiloid

[sevenperforce]

6 minutes ago, Scotius said:

1 hour ago, Nuke said:

figure as a way to move asteroids it would work. you would just be heating the surface rock, preferably as evenly as possible so as not to rip it to pieces with thrust asymmetries. you might use multiple nuclear shape charges all going off at various times such that the radiation hits the surface all at the same time.  keep in mind the warheads never actually touch the asteroid, jsut used as high powered nuclear flashlights.  a few coordinated blasts ought to be enough to deflect the asteroid away from or towards earth, whatever your desired outcome may be.

Aliens, living peacefully in a system several lightyears away: WTH are they doing to their own planetary system? Those barbarians must wage truly horrifying war! Nope, we are not going there!

TL;DR - "Let's nuke it!" is not the best answer to 95% of problems.

Nuking asteroids is, in fact, one of the best ways to deflect them.

Sometimes I think that what the Earth really needs is a nice big serious asteroid scare. It would bring us together in a way that the pandemic clearly didn't. You'd have all the best nuclear physicists and rocket scientists in the world coming together. Plus it would be a peaceful reason to build REALLY big nukes...which are exciting for boom boom reasons. And it would force rocket science to improve and expand.

[Scotius]

You just love to poke Murphy with a stick, don't you?

[magnemoe]

1 hour ago, sevenperforce said:

Nuking asteroids is, in fact, one of the best ways to deflect them.

Sometimes I think that what the Earth really needs is a nice big serious asteroid scare. It would bring us together in a way that the pandemic clearly didn't. You'd have all the best nuclear physicists and rocket scientists in the world coming together. Plus it would be a peaceful reason to build REALLY big nukes...which are exciting for boom boom reasons. And it would force rocket science to improve and expand.

Agree, its one of the few cases there nuking it is the best option. I assume you will use something like an orion drive charge here as it will give an pretty even push on one side of the asteroid. 
Benefits 1) its the most force we can deliver in an small package. 2) you do not need to match velocity with the asteroid. 3) Not much new technology, an deep space probe and an nuclear bomb, granted the orion drive charge is probably not tested well but the have some ideas and you can always test some over the moon surface to get something good enough. 

Downsides: not so good against gravel heap asteroids but few things are, yes you could use an gravity tractor or some mass driver technology but realistically this will require starship as an bare minimum and decades to set up. 
Blowing it up might work better. 
Flyby with an multi megaton nuke who work like an sharped charge so 50% of blast goes in one direction  should have some impact. Landing and digging in would much better but also much harder. 
Main problem is to get in for secondary shots, you can however drop off wifle shield armor as it does not need to be part of probe and you wait some weeks. 

[Entropian]

2 hours ago, sevenperforce said:

Sometimes I think that what the Earth really needs is a nice big serious asteroid scare.

So glad I'm not alone.

[sevenperforce]

1 hour ago, magnemoe said:

Agree, its one of the few cases there nuking it is the best option. I assume you will use something like an orion drive charge here as it will give an pretty even push on one side of the asteroid. 
Benefits 1) its the most force we can deliver in an small package. 2) you do not need to match velocity with the asteroid. 3) Not much new technology, an deep space probe and an nuclear bomb, granted the orion drive charge is probably not tested well but the have some ideas and you can always test some over the moon surface to get something good enough. 

Downsides: not so good against gravel heap asteroids but few things are, yes you could use an gravity tractor or some mass driver technology but realistically this will require starship as an bare minimum and decades to set up. 
Blowing it up might work better. 
Flyby with an multi megaton nuke who work like an sharped charge so 50% of blast goes in one direction  should have some impact. Landing and digging in would much better but also much harder. 
Main problem is to get in for secondary shots, you can however drop off wifle shield armor as it does not need to be part of probe and you wait some weeks. 

So you don't actually want to impact the asteroid; rubble pile or not, it's always easier to deal with one object rather than many. No need for an Orion-style tungsten shaped charge. Rather, you want a very big blast, as big as possible so that you can detonate it from a significant distance. The x-ray and gamma flux to the surface of the asteroid will vaporize the first 12-14 centimeters of regolith, causing it to expand in the opposite direction and produce relatively gentle, distributed thrust. 

Then you rinse and repeat. You'd want to send up 20 or 30 bombs, both to spread out the thrust over time and to give yourself plenty of margin in case a bomb fails to detonate or is lost during launch.

Modern nuclear weapons designers could probably produce 100-200 megaton bombs at somewhere between 20 and 30 tonnes each. If the orbital mechanics and rocket scientists decided slightly smaller nukes would be better, you could produce a bunch of 10-megaton weapons at 3-4 tonnes each.  The United States no longer maintains its arsenal of W53 thermonuclear warheads, but it retained the casings and some associated parts to allow them to be rebuilt if they were ever needed for planetary defense. Detonated in-atmosphere, the W53 would have created a nuclear fireball up to 5 kilometers in diameter. 

A refueled, stripped-down Starship would probably be the best delivery system in any event.

[KSK]

19 hours ago, sevenperforce said:

Nuking asteroids is, in fact, one of the best ways to deflect them.

Sometimes I think that what the Earth really needs is a nice big serious asteroid scare. It would bring us together in a way that the pandemic clearly didn't. You'd have all the best nuclear physicists and rocket scientists in the world coming together. Plus it would be a peaceful reason to build REALLY big nukes...which are exciting for boom boom reasons. And it would force rocket science to improve and expand.

Given the general level of political competence currently on display, I’d really rather not test that theory with a Dinosaur Killer heading our way, thanks.

By the time we’d persuaded everyone that a) it wasn’t a hoax and b) that all the missiles will be aimed at the asteroid and nowhere else, I rather suspect our window for deflecting the asteroid will be long gone.

[sevenperforce]

1 hour ago, KSK said:

Given the general level of political competence currently on display, I’d really rather not test that theory with a Dinosaur Killer heading our way, thanks.

By the time we’d persuaded everyone that a) it wasn’t a hoax and b) that all the missiles will be aimed at the asteroid and nowhere else, I rather suspect our window for deflecting the asteroid will be long gone.

No Dinosaur Killer required -- I'm talking one of the intermediate-size city-killers. No one would be able to know for sure where it would impact and so everyone would want to work together.

[kerbiloid]

A single dinosaur killer.

[MatterBeam]

This is from the latest ToughSF blogpost: http://toughsf.blogspot.com/2021/01/moto-orion-mechanized-nuclear-pulse.html

Moto-Orion: Mechanized Nuclear Pulse Propulsion

The Orion nuclear pulse propulsion concept has been around for over six decades now. It is powerful and robust, but lacks the flexibility and features we expect from many more modern designs.

Can we give it those additional capabilities?

That cutaway is one of Matthew Paul Cushman’s amazing pieces.

Basic overview of Orion

William Black has plenty of great Orion artwork.

There is a lot of information on Project Orion, available mostly here and here. It is best to read through them to gain a complete understanding of how it works. We’ll only give a simple overview to start.

Project Orion’s design for a nuclear pulsed propulsion system was pretty simple. A physical plate of steel, protected with a thin layer of oil, faced a plasma jet from a nuclear shaped charge. The force of that blast was translated into useful thrust for the Orion spaceship.

In this manner, a propulsion system could tap into the immense power of a nuclear detonation while sidestepping the heat management issues that would normally come from handling such an output. Its thrust was huge, enough to lift thousands of tons into orbit, and so was its efficiency, with an effective Isp of 2,000 to 12,000s. That’s five to thirty times the specific impulse of a chemical rocket, with thrust and efficiency that only gets better as you scale it up. We call this combination of high thrust and high efficiency a ‘torch drive’; a term from ‘Golden Age’ science fiction where authors did not want to spend pages explaining things like deltaV limits and interplanetary trajectories to their readers. A torch drive lets you point at your destination and accelerate to get there. Even today, sci-fi loves this solution.  

It did have drawbacks though. The fissile fuel in each nuclear pulse charge is inefficiently used, with the majority being wasted. This was because each pulse had to be small, so as to not obliterate the pusher plate, and therefore could not produce the better burnup ratios of large nuclear charges. The rate at which these pulses were ignited could not be varied by much either. Timing the pulses with the motion of the pusher plate, so that the blast would meet the suspension system in the right position, was essential.

There were three parts to the suspension system. The first is the pusher plate itself. When struck at a precise angle, it could be accelerated at 50,000g or more without being bent or twisted. It first slams into a gas bag, that acts similar to how a car’s airbags are used in a car crash, to turn a sharp shock into a more gradual shove. Momentum from the plate is then transferred to a set of pistons at a much slower rate. These pistons are connected to rigid springs that convert the series of pushes into a continuous acceleration. When the timing is right, the literally well-oiled machinery is very strong. When the timing is off, things break down.

The suspension cycle, in short.

If one charge ignited too early, then only a fraction of the suspension length can be used to absorb the blast’s momentum, so it gets translated into a hard jolt. Ignited too late, and it would further accelerate an already retreating pusher plate, with potentially devastating consequences. A complete misfire isn’t great either. The suspension arms would only be partially compressed, and so would not reach full extension on the rebound and it would become unsafe to receive another nuclear blast. The Orion spaceship would have to wait for the suspension to wobble to a full stop, and then use a half-powered charge to restart it from a fully compressed state. Waiting to restart the suspension cycle isn’t a nice position to be in when launching off a planet. 

Another drawback was the inability to convert any of the nuclear pulse drive’s immense output into electrical power. The two-step suspension system simply acts as a fancy spring to transfer momentum between the nuclear blasts and the spaceship. Most of the time, this is not an issue.

Liftoff from a planet or moon’s surface does not take long, so stored power is sufficient. Cost-efficient interplanetary travel consists of short uses of the main propulsion system followed by long periods of coasting, during which solar panels can be deployed.

An Orion warship accelerating, from the sadly incomplete sequence here.

However, some of the more demanding applications require a lot of onboard power. Military spaceships especially want the ability to both accelerate out of harm’s way, while producing plenty of electrical power to feed lasers, RADARs and other energy-intensive equipment. Fulfilling this requirement means sacrificing payload capacity to mount an onboard nuclear reactor or some other heavy solution. It’s also a problem for very fast transports that want to use the Orion engine as much as possible; they can only extend tiny solar panels while accelerating as anything bigger would get burnt off by the nuclear blasts. 

Of course, there are many other problems too, that we won’t go into more detail this time. The fact that each nuclear charge is a fully functional nuclear warhead, for example, means that a crash-landing would spill out a full nuclear arsenal, worthy of arming a superpower.

Or that the main propulsion system of an Orion ship cannot be used to turn, so huge Reaction Control thrusters would be needed for every single maneuver.

We cannot ignore the existence of more modern and more refined nuclear pulse propulsion designs either. Orion was dreamt up in the 1960s and a lot has happened since then. 

Mini Mag-Orion.

Most notably, Mag-Orion and variants thereof. Instead of a physical pusher plate, a magnetic nozzle is used to capture the momentum of nuclear-generated plasma. Fully self-contained bombs are replaced by subcritical masses of uranium. They have to be detonated by external compression devices, such as a Z-pinch or a magnetic pulse. The result; they are completely safe in storage and gain a not-bomb-like-at-all quality. Generating electrical power is a simple repurposing of coils in a magnetic nozzle into Magnetohydrodynamic generators, and turning is accomplished by unequally deflecting the plasma within the nozzle one way or another. 

However, these more advanced designs cut away at the awesome potential of an Orion drive. The need for large magnets, cooling systems for the nozzle, capacitor banks for the ignition system, all add a lot of weight. Designs of this type have much lower thrust than the original Orion design. They can’t take off from large planets or even operate inside an atmosphere. They move away from that brutal, simple and resilient character that a nuclear Orion engine has, to become something flimsier and more complicated. Perhaps that is an unacceptable compromise, especially for someone seeking specific capabilities, or a sci-fi author aiming for a special aesthetic.  

Ad Astra Game's RocketPunk, seeking that aesthetic.

Could we solve some of the original Orion’s most glaring drawbacks without moving too far away from the image of an atomic piston engine from a bygone era?
Moto-Orion

We alter the 60 year old design by giving it a crankshaft. It won’t be directly connected to the pusher plate - it can be connected behind the main suspension arms, so that it doesn’t have to receive the shock from a nuclear blast directly and become unreasonably long and heavy as a result. 

The crankshaft is connected to a crank that turns a large wheel. Depending on the pulse rate of the Orion drive, this wheel will turn at 54 to 69 RPM. A gear train would be needed to increase the RPMs into the thousands, suitable for an electric generator. Also necessary is a counter-torque mechanism, such as a second wheel or even just a counterweight turning in the opposite direction. 

Please note that the depiction in the diagram above isn't perfect, as all these mechanisms have to find a place in between the springs, hydraulics and other machinery above the suspension arms. A different arrangement would take up less room, but be harder to read visually.

The concept is similar to a wind turbine and its generator, except the blades are replaced by a nuclear pulse-driven crank.

The power that can be extracted through the crankshaft will be a fraction of the mechanical energy delivered through the Orion drive’s suspension. This is already a small percentage of the nuclear energy released by the pulse charges. The USAF design for a 10m diameter nuclear spaceship has a fantastic 32.9 GW output, but this is only 0.78% of the energy released by 1 kiloton yield blasts every second. We’ll call this the Motorized Orion or Moto-Orion. 

In practice, the electrical power that can be derived from an Orion drive will depend on the mass of the electrical generator and the equipment needed to manage waste heat. A high performance generator would have an efficiency of over 95% and a power density in the tens of kW/kg. Waste heat will be the main obstacle to generating a lot of electrical power, especially as electrical generators tend to operate at lower temperatures. As discussed in a previous post, temperature is the biggest factor in allowing for lightweight heat management systems. 

A generator would typically want to operate at room temperature 300K, but this would mean huge (and heavy) radiators would be needed to handle their waste heat. We want the hottest generators possible. They are mainly limited by the decreased performance of their electrical insulators at higher temperatures. Commercially available motors are available at 570K, but applying research like this could create generators that operate at 770K. However, increased temperatures also increase electrical resistance and therefore cut into the efficiency of a generator. Based on some studies, high temperature efficiency can be held at above 90%. A generator is a motor in reverse, so we will use these same temperatures and efficiencies. 

Estimating the power density of an entire heat management system is quite difficult, but we can make some estimates. 1 m^2 of double-sided 2mm thick carbon fibre radiator fins would be 4 kg and radiate away 8.3 kW of heat at 520K.

Note how this is a slightly lower number than the operating temperature of the generators, as we need a temperature gradient throughout the heat management system to actually move heat from where it is created to where it is radiated away.

With reasonable figures for a silicone oil pump, a microchannel heat exchanger and a +20% margin for assorted pipes, valves and backups, it all averages out to 1.2 kW/kg. 

This seems like a low figure, but it only deals with the <10% of power that becomes waste heat. 1 MW of mechanical energy coming through the crankshaft would become 900 kW of electricity, handled by 45 kg of generators, and 100 kW of waste heat, requiring around 83 kg of cooling equipment. Altogether, this makes for an average power density of 7 kW/kg. This ignores the mass of the crankshaft, counterweight and other mechanisms, but they will be small compared to the rest. There is also the complication of radiator placement; they want to extend out from the hull, but also must stay within the shadow cone of the pusher plate to avoid being disintegrated by nuclear plasma. 

The original USAF 10m Orion had a payload capability of up to 225 tons (on certain missions). If a quarter of this was dedicated just to producing electricity, we could expect it to output 393 MW. That is a respectable amount! 

Here’s what a Moto-Orion derived from that design, with fully scaled radiators, would look like:

 

Though, it is only 1.2% of the drive power. You could imagine an Orion drive spaceship that extracts more of its output as electricity, but it is fundamentally limited by the difference between the power density of the propulsion system (on the order of 330 kW/kg) and that of the power extracting equipment (<10 kW/kg). Furthermore, equipment that consumes that electrical output will take up an outsized portion of the spaceship’s payload capacity, due to their even lower power density (<1 kW/kg).

There are other ways to generate electrical power.

A linear alternator should be an ideal option. A magnet is simply pushed through a series of conductive coils, producing current as it travels up and down. It is just as efficient as a rotating electric generator, and depending on the exact design used, can operate at the same high temperatures. Even better, it does not produce any sideways torque, is easier to fit in between the suspension arms and is more resilient to vibrations. However, their power density is far lower than that of rotating generators, with 1.49 kW/kg being the best figure mentioned anywhere.

Another option still is to use a high temperature superconducting generator. NASA has designs that aim for 60 kW/kg at the multi-megawatt scale. 

Efficiency is 99%, meaning that 1% of the power becomes waste heat. Thankfully, this heat is produced not in the superconducting magnet, but in the non-superconducting stator. It can reach 570K, so we can use similar heat-management equipment as described above. 1 MW of input power becomes 990 kW of electricity and 10 kW of heat, which are handled respectively by 16.5 kg of generator and 8.3 kg of cooling equipment, for an average power density of 40 kW/kg. 

The downside to using superconducting devices is having to mount the bulky and sensitive equipment needed to keep them in that state. A high-temperature superconductor needs to be kept in liquid nitrogen, which boils at 77K. About 0.01 to 0.1% of the power that a superconducting device handles is expected to become waste heat inside the cryogenic part through ‘AC losses’, where alternating currents create magnetic vortices within a conductor.

 

Progress is being made into megawatt scale superconducting generators/motors. This Honeywell 1 MW design achieves 8 kW/kg.

The passive solution to handling this heat load is to just let the liquid nitrogen boil. It can absorb 198 kJ/kg during vaporization, so for every kW a superconducting generator outputs, 5 milligrams per second of liquid nitrogen needs to be expended. 

Using the expendable liquid nitrogen solution, we can have the USAF 10m Orion dedicate 40 tons to electrical production, and 16.25 tons to liquid nitrogen reserves (adding up to a quarter of its 225 ton payload, as before). It would be able to output a whopping 1.6 GW of electricity, but only for 33.5 minutes before liquid nitrogen reserves run out. It’s not too bad; the spaceship would likely run out of pulse charges before it uses up all this coolant. 

The active solution is to use a cryocooler. It raises the temperature of the waste heat to a level where it can be disposed of using radiator panels of reasonable size. If the high temperature superconducting material operates at 100K, then it takes at least 4.7 Watt of cryocooler power to move 1 Watt of waste heat up the temperature gradient to 570K. A realistic cryocooler will achieve 30% of maximum Carnot efficiency, so we increase the power requirement to 15.7 Watts. We choose the 570K temperature target to keep using the cooling equipment from previous calculations (all the better to compare each solution). 

Cryocooler power density for aerospace applications is about 133 W/kg, but 300 W/kg is cited as an achievable goal. Putting these elements together, we have 1 MW of input power becoming up to 1 kW of cryogenic waste heat, which requires 15.7 kW of cryocoolers that mass 52 kg. The active solution brings down average power density to 12.9 kW/kg. It is a respectable figure, better than the non-cryogenic design’s 7 kW/kg, and especially interesting for missions with prolonged engine use with no opportunity to refill on liquid nitrogen..

A USAF 10m Orion that used an actively cooled superconducting generator massing 56.25 tons would produce 725.6 MW as long as the engine is running. 

There is a ‘catch’ to these cryogenic designs though. Superconducting magnets are not known to be resistant to radiation or damage of any kind. It is especially concerning when a nuclear pulse propulsion spaceship bathes itself with penetrating neutrons and high energy gamma rays repeatedly. The magnets cannot be placed too far away from the pusher plate and suspension system either, so they can’t hide in the relatively safe environment the crew enjoys at the other end of the spaceship.

Flexibility

There are two other major benefits to the Moto-Orion. 

The first is during start-up. The original Orion design relied on the suspension system being pre-compressed before the first full-strength nuclear charge could be used. It was the job of a half-strength bomb to get the suspension ready. While this use of fissile material is not too wasteful when compared to the hundreds of bombs that are regularly used, it is very inflexible. Start-up would only be possible a limited number of times, and only when the pusher plate is standing still… not at all comforting when space travel involves must-not-miss burns. It is even worse for a warship that needs multiple successive starts and stops to effect dodges from enemy fire. 

A Moto-Orion can use its electric generator in reverse, to produce torque while consuming energy from battery reserves. It can draw in the suspension arms to a compressed position, or time its pushes and pulls to bring a wobbling plate to standstill more quickly. The batteries can even be charged from another power source, such as solar panels, if battery reserves are depleted. 

This gives the spaceship an unlimited number of restarts. It gains the flexibility to halt and ready its drive at any time. 

The second benefit is recovery after the pulse sequence goes wrong, whether it is late, early or missed completely. 

Accurate suspension cycle for an Orion craft, by ElukkaJ.

A Moto-Orion might be able to react quickly enough to adjust the position of the suspension system in case of a late pulse. Once the nuclear shaped charge moves past its designated ignition point, the spaceship’s motors would draw power to slow down the retreating pusher plate. This could prevent it from being accelerated into the suspension arms at an excessive velocity. 

 

When things go wrong, unpleasant, up to destructive, g-forces are generated.

An early detonation is especially troublesome. Not only does it erode the pusher plate, it cannot be predicted. The Moto-Orion’s crankshaft and generator can be turned into an additional suspension arm to absorb the unexpected shock, but it would usually be weaker than the massive steel springs the engine habitually relies upon. Still, it can assist in bringing the pusher plate velocity back in line and ready to receive nuclear plasma blasts again. 

When it comes to misfires, Moto-Orion can potentially add velocity to the slower pusher plate (as it did not receive the momentum from the missed pulse) and bring the drive sequence back into correct timing. It can avoid a complete halt by drawing energy from battery reserves, and if it is powerful enough, do so without skipping a beat. 

There are other forms of flexibility, gained indirectly from having access to huge amounts of electrical power. They might not be as flexible in this regard as a nuclear-electric ship could be, as power generation is tied to the use of the engine and not an independent reactor, but many possibilities open up. Orion nuclear spacecraft could deploy drones and beam power to them, by means of microwave emitters or laser beams. They could receive nuclear charges ‘on the fly’ using magnetic scoops. Electrical Reaction Control thrusters can be used, so that the spaceship can turn more efficiently. There are many more possibilities.

Consequences

An Orion spaceship staging off a aerobraking lander at Mars.

Moto-Orions are safer and more flexible than the original Orions. For a simple transport ship that only uses its engines briefly and wishes to maximize payload, the extra weight is unwelcome. Any craft that carries people might instead find that the additional capabilities and securities are a worthwhile trade-off. Warships would absolutely desire Moto-Orions. The huge amounts of electrical power turn them into terrifying attackers that can both unload with weapons energized by hundreds of megawatts of power while also performing multi-g evasive maneuvers. 

In a science fiction setting, Moto-Orions can deliver the retrofuturistic aesthetic of spacecraft riding on nuclear blasts while also making possible the use of exciting hardware like lasers and coilguns. One setting, RocketPunk, is in development by Ad Astra Games (and by Rick Robinson, who inspired ToughSF). It features Orion-propelled warships battling for Mars in an alternate Cold War future. More engaging action could be made possible with these motorized variants.

The fact that a Moto-Orion connects electrical output with drive power by a single-digit percentage ratio is an interesting feature by itself. We discussed how this avoids troublesome issues such as The Laser Problem, where overpowered lasers have excessive ranges and render maneuvering during ship-to-ship combat useless. Low electrical power and high drive power give room for dynamic combat that is more exciting for readers or viewers. Other types of ‘torch ship’, like a rocket with an immensely powerful fusion reactor, could have better performance than Moto-Orion, but would have proportionally more electrical power - this pushes combat ranges so far out that maneuvering is rendered pointless again. 

The military potential of Orion was always at the forefront.

Another bonus towards dynamic and interesting space combat is an Orion drive’s ability to continuously accelerate and outrun missiles that have less potent propulsion systems. Due to how poorly nuclear pulse propulsion performs when scaled down (burnup ratio and thrust efficiency drop dramatically), a missile would not be able to keep up with a full-sized Orion drive unless it had its own large and expensive pulse propulsion system. They would be excessively expensive, so only smaller and less powerful engines would be available to missiles. Consequently, Orion warships have a good chance of outpacing missiles.

It creates a situation where one side having more missiles than the other does not automatically guarantee a win. Instead, careful use of maneuvers and relative positioning to set up a shot with short-legged missiles is necessary. All the better to read about or play through!

The Project Orion battleship.

We suggest going out and applying these calculations to bring motorized variants to other Orion designs. Huge spacecraft like the 4000 ton USAF 'battleship' could benefit immensely from this concept. 

You could also think about how Medusa could extract electrical power from its tether strokes, or even more outlandish ideas, such as a propulsion system where high velocity kinetic impactors strike a lump of propellant to create a jet of plasma that strikes a pusher plate, like a non-nuclear Orion. 

[mikegarrison]

Wait ... in that one drawing it says "350 rem per shot". 350 rem one time is a sometimes-lethal dose. Surely no crew would survive getting 350 rem per shot.

[kerbiloid]

5 rem/y for nuke personnel, 1000 shots per flight once per year → 0.005 rem/shot max appropriate.

ln(350/0.005)/ln(2) ~= 17 half-dose layers

Gamma, lead ~2 cm, steel ~3 cm.

So, if they put a 50..70 cm thick floor, they can live with it.

[mikegarrison]

41 minutes ago, kerbiloid said:

5 rem/y for nuke personnel, 1000 shots per flight once per year → 0.005 rem/shot max appropriate.

ln(350/0.005)/ln(2) ~= 17 half-dose layers

Gamma, lead ~2 cm, steel ~3 cm.

So, if they put a 50..70 cm thick floor, they can live with it.

You're saying you think the "350 rem" notation is outside the crew area, not the crew dose.

Does that much radiation activate the metal of the ship? Neutron flux, and all that.

[Scotius]

Nuclear powered crankshafts. Of course.

And this here is clearly the best project for car propulsion ever envisioned:

Yes. Those are legs. Because of course.

I'd ask we stop beating this long-deceased equine, trying to make Orion look not like a fever dream of a mentally unstable survivalist... But i doubt it would work for long. So, instead: Ridicule.

[kerbiloid]

41 minutes ago, mikegarrison said:

You're saying you think the "350 rem" notation is outside the crew area, not the crew dose.

I mean, it's inside the crew compartment  without additional protection, like a 0.5 cm thick armor floor.

41 minutes ago, mikegarrison said:

Does that much radiation activate the metal of the ship? Neutron flux, and all that.

It probably will activate the pusher plate.

11 minutes ago, Scotius said:

the best project for car propulsion ever envisioned

If add another pair at the opposite end, it can step over stones and bring the hull to another side.

On the plain places it can roll the hull by wheels, saving power.

Looks like a perfect idea for an extraterrestrial rover...

Edited January 10, 2021 by kerbiloid

[Scotius]

Like this?

I bet we'll see walking cars on the roads faster than we'll see Orions flying.

Again: Orion was a child of it's times. When:

A: We thought nukes are answers to everything. Want a canal? Dig it with nukes. Want to reach deep oil reservoir? Blast it open with a nuke. Want to flatten mountain top for a new observatory? Blast the sucker with a nuke!

B: Didn't knew better yet.

Today we know better than to repeatedly nuke our own home. Also, good luck getting politicians and environmentalists on your side (without Apocalypse looming over the Earth). It's a slow slog getting approval for sending nuclear reactors to space, or getting nuclear thermal engine project rolling - and you want Orion?

Not gonna happen'.

[mikegarrison]

2 hours ago, Scotius said:

Like this?

I bet we'll see walking cars on the roads faster than we'll see Orions flying.

Again: Orion was a child of it's times. When:

A: We thought nukes are answers to everything. Want a canal? Dig it with nukes. Want to reach deep oil reservoir? Blast it open with a nuke. Want to flatten mountain top for a new observatory? Blast the sucker with a nuke!

B: Didn't knew better yet.

Today we know better than to repeatedly nuke our own home. Also, good luck getting politicians and environmentalists on your side (without Apocalypse looming over the Earth). It's a slow slog getting approval for sending nuclear reactors to space, or getting nuclear thermal engine project rolling - and you want Orion?

Not gonna happen'.

Yes ... but no.

Nuclear power is still the only known practical energy source for getting beyond Mars, and there are some pretty good arguments that moving any significant amount of payload to Mars isn't terribly practical with chemical rockets either.

Is Orion the answer? Don't know. But if we ever really get serious about leaving the Earth, it's not going to be by using chemical rockets.