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What's pushing an Orion drive spacecraft? From what I know, the only reason a nuke will blow things away is because the heat causes air to expand and push objects. But there's no air in space, so the only thing that could be propelling the spacecraft is the small amount of mass in the bomb itself and the light energy.

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1 hour ago, LHACK4142 said:

What's pushing an Orion drive spacecraft? From what I know, the only reason a nuke will blow things away is because the heat causes air to expand and push objects. But there's no air in space, so the only thing that could be propelling the spacecraft is the small amount of mass in the bomb itself and the light energy.

Ah, you missed a key feature. The Orion drive units are CASABA-HOWITZER shaped nuclear charges firing a blast of hypervelocity tungsten plasma in a cone about 22⁰ wide, aimed at the launching spacecraft.

high-thrust-pulse-unit.png

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7 hours ago, LHACK4142 said:

What's pushing an Orion drive spacecraft? From what I know, the only reason a nuke will blow things away is because the heat causes air to expand and push objects. But there's no air in space, so the only thing that could be propelling the spacecraft is the small amount of mass in the bomb itself and the light energy.

The Orion propulsion ammo is an emasculated two-stage thermonuke consisting of in two chambers, primary (with a fission primer) and secondary (where the fusion charge is removed and replaced with a prosthesis of a nozzle shape).

Both chambers are surrounded with a metal casing covered with a heavy metal liner inside.
(Thec picture says "uranium", but it's obviously a bull sheep, as they dpn't need more energy splashed around. So, it's almost for sure lead.)
This forms an Xray thermos in which the other events happen.

The chambers are separated with a beryllium collimator/hohlraum (metallic, or oxide, or maybe carbide, who knows) to reflect back the neutrons 
It protects the content of the second chamber from preliminary elimination by the primer radiation, reflect the neutrons back to the primer, but let the primier Xrays pass through and make it focused on the secondary chambers walls to heat them.

When the primer blasts, most part of its energy is released in form of Xrays and warm the casing up to millions kelvins,

The casing starts emitting heat photons itself, and due to its temperature it radiates mostly Xrays.
A half of them outside, a half inside.
This makes the casing work like an Xray mirror bottle even when Xrays can't be reflected. This emulates the reflection by Xray heat radiation.

***

Normally (not in Orion) the secondary chamber normally contains a secondary charge full of lithium deuteride in metal sphere/cylinder, to be shrunk and fused.
And the empty space between the fusion ball and the casing is filled with plastic foam (or in 'Murican nukes with the secret aerogel named Fogbank) rich with hydrogen.
The plastic slows down the neutrons of the primer to prevent neutron irradiation of the unshrunk fusion charge. Because both H and C are effective neutron moderators.

When the casing emits enormous amounts of heat Xrays, the pressure of the Xray photons (i.e. photonic gas) starts compressing the fusion charge.
Radiation implosion.

The plastic foam gets fully ionized and turns into a mixture of electronic, protonic, and carbonic gases.
While thr protons and the carbonx keep moderating the incoming neutrons, the electronic gas, due to its enormously timy atomic mass (0.5 MeV vs 940 MeV of hydrogen) creates enormous pressure between the casing and the fusion charge, exceeding the Xray pressure for an order of magnitude.
It starts compressing the secondary charge even faster.
Ionization implosion.

The charge metallic case start evaporating at all over the surface, and the metal gas exhaust escapes radially, forming a spherical rocket jet, like a spherical rocket is compressing the charge ball.
The pressure of the ablation gas exceeds everything previous for an order of magnitude more, and shrinks the secondary charge from pumpkin to orange, making its internal fission charge to explode.

Two spherical shockwaves (contracting and expanding) meet in the middle, exactly in the thin layer of the compressed fusion fuel, heat it up by adiabatica compression, and light tthe fusion.
While the lithium deuteride doesn't provides much neutrons (only som amount of parasite ones from D+D reactions), it makes slow neutrons from uranium fission fast, and bombs the remains of the internal uranium charge, totally splitting them and getting from it as much neutrons as possible, tpo split the lithium into tritium and fuse.

Finally, a half of LiD releases its energy, and the plasma ball expands as an explosion.

***

In the Orion charge the secondary is removed from its chamber, and replaced with a nozzle-like structure of secret shape, fakely depictured as a typical de Laval nozzle filled with beryllium (or beryllium oxide).

It's unknown what's actually inside this secondary chamber,, but as it was being designed as a directed blast warhead for the secret Casaba howitzer, it's obviously something providing high gas pressure to kick ot the end cap forming a projectile plasma jet.

The expensive beryllium filler looks making not much sense except for its low atomic mass. 
Probably, it's the same hydrogen-rich plastic filler left from the thermonuke design, packed into a bell-like open envelope compressed in the way described above and blowing its content from the end.
It's possible that it gets a nozzle shape at the ends, and maybe its has it from the beginning, but probably it's shaped somewhat more tricky.

Also, it could be that a beryliium compound indeed fills it inside to let the elctronic gas from around compress the nozzle without counteraction.
So, beryllium could be chosen as the inner propellant exactly for its weaker pressure.

Anyway, when the orionic charge primer explodes, it heats the Xray thermos  liner, the liner's X-ray heat emission ionizes the plastic filler around the "nozzle" and compresses it with all mechanisms of the fusion nuke secondary.
The radiation, ionization, and ablation pressure compress the nozzle and ionize its content, and the whole ionic gas and electronic gas mixture directly (thanks to the compressed nozzle) hits into the end cap.

So, the charge actually works like normal atomic rocket, just the jet is directed at the ship, not from it.

***

The end cap is a thin tungsten membrane.
Being tungsten, it's very dense and high-atomic, absorbs Xray very well, and thus is a part of the Xray whole thermos.
So, to the moment of the jet hitting, it's a thin and dense cloud of tungsten plasma long ago.

It's thin because a thick membrane plasma cloud quickly expands radially and form a spherical cloud instead of the required directed one.
The thin one is kicked forward before it has time to expand radially. So a thin membrane on a strong kick forms a conical jet, which stays more or less narrows first hundred of meters.

Thus, when the thin and flat tngsten plasma cloud is kicked out by the secondary chamber filler electronic gas pressure, it runs directly at ~100..200 km/s velocity (for low-yield charges).

***

Originally, in its maiden Casaba howitzer sense, it (as it can be understood from the word "howitzer", absolutely nonsense in space zero-G), this should shape the shockwave of the howitzer shell  aerial blast down, at the target direction, instead of unifornly spreading it around.
Of course, in air the tungsten jet should pass throw the much greater mass of air between it and the aim.

Say, the membrane is 25 cm in diameter (orienting on the popular 280 mm nuke caliber) and 2 mm thick. Density is 19.25 g/cm3.
The jet mass = (pi * 252  / 4) * 0.2 * 19.25 ~= 2 kg.
The Orion plate is 10..20 m in diameter, so lets take that the hit spot is 10 m wide at 100 m distance.
The mass of the air inside the 10 m wide amd 100 m high cone is ~(pi * 102 / 4 / 3) * 100 * 1.225 ~=3 200 kg.

So, in air, in its original purpose, the 2 kg of 100 km/s fast tungsten plasma jet would collide with 3.2 t of air (1 600 greater mass).

Of course it means that there can be no shard plasma jet in air, but a normal firecall with a hump at the jet direction.

So, on the battlefield it just can make the fireball shockwave somewhat stronger at the target direction, but not pierce it with a plasma jet.
And that was its original purpose.

Also the 100 m working distance means that it makes no sense to make it yielder than few kilotons or less, so it's a pure artillery or tactical rocket warhead.

Also this means that trying to use it for Orion propulsion in low atmosphere is a bad idea, because instead of thin cone of tungsten plasma the ship will be hit but weaker and bulky shockwave.
So not so much propelled, but hit.

***

But as the Plumbbob / Pascal B nuclear test had shown, a metal plate can survive the shockwave/plasma jet hit of a low-yield (less than a kiloton) nuke at 150 m distance, and stay intact.

(The charge was at the bottom of a narrow 150 m deep shaft, in a small chamber, with a concrete collimator on the charge top).

So, if take a proper plate for proper yield, and attach cargo, this directed blast Casaba-like gunshell can be used for propulsion.

***

So, the idea of Orion is to throw 1..4 times per second a Casaba howitzer shell (or other similar nukes in various cases) to hit the rear end of the ship with tungsten plasma jet.
In vacuum it would be a cone 10..20 m in diameter and 100..200 m long.

The hit receiving end of the ship propulsion unit is a massive steel pusher plate. Can be covered with a replaceablr protective layer of carbon or so.
The other part of the ship is attached to the plate via a two-stage pneumopiston system.

On every shot a system of sprinklers spread some substance referred as "oil" on the plate surface.

On approach of the tungsten plasma jet, the "oil" evaporates, gets ionized, and turn into carbon-hydrogen plasma cloud between the plate and the tungsten plasma.

The oil plasma cushion softens the tungsten plasma hit to protect the steel plate.

***

As the plate is flat, all plasma escaped radially from behind, so the only mechanical stress for the ship is axial.
It lets to avoid using massive radial elements like nozzles and their frames.

As the energy gets released at hundred(s) of meters away, and the charge is low, no elements of the ship receive much heat from it.
So, the ship doesn't need high-power cooling system and huge radiators.

As unlike the rockets it doesn't have a chamber surrounding the reaction zone, there is no temperature limit making to reduce the power to protect the chambers and nozzles.
The black body luminosity per area is ~ R2T4.
So any contained fission/fusion engines can have only very limited power, because they can't be cooled by the chamber/nozzle heat radiation, they either have to be very low-power, or need a superfast cooling system and enormously huge radiators.
So, the nuke/thermonuke rocket engines can have either high thrust and low ISP, or vice versa.
This makes them more fancy than practical.

While Orion provides high thrust and high ISP at once, and this makes it the design of choice.
No other known possible designs can provide this,

As a result, the ship is mich lighter and smaller than if it was a rocket, and can carry heavy cargo fast.

***

When the pusher plate gets hit by the tungsten jet, it jumps towards the ship at 10 000 g acceleration.

Simultaneously, it gets cooled by a portion of water from the syringe of ship, which takes waste heat, evaporates and gets thrown out.

It's not specified by the Orion authors, but my estimation calculation shows that this steam can provide an attidude control acceleration of weak (compared to the mass) RCS, not enough to effectively maneuver, but enough to keep the ship on course while it's accelerating.

***

The plate is attached to the ship via the two-stage cascade of pneumatic energy accumulators.

The not specified inert gas in the cylinder gets adiabatically compressed by incoming piston and stores the hit energy for milliseconds.

Then it starts expanding and pushing out the piston, and at once pushing the cylinder forward.

The cylinder pushes the attached piston of the second stage of cascade, and presses it into the second cylinder.

The things work same well, and the expanding inert gas in the second cascade stage pushes forward the engine frame.

The cargo (for example, a space ship) is attached to the frame.

Each stage of the piston cascade decreases the acceleration 100 times.

So, while the pusher plate jumps up at 10 000 g, the piston interstage only at 100 g, and the ship itself at 1 g.

***

The space and ballistic rockets second stages provide 0.8 .. 1.2 initial T/W, and 1 g of the Orion is required not for making the travel comfy, but to match the upper stage T/W requirement of ~ 1 g.

So, after being lifted up by launch boosters and starting nuking, it just follows the normal trajectory of any rocket.

This means that it will reach LEO in ~10 minutes, providing 6 km/s of delta-V.

This also means that for another 6 km/s required for Mars it needs 10 minutes more.

So, the total work time of Orion engine required for Mars is about 20 minutes, and has nothing common with pictures of artificial gravity and long nuke blasting acceleration.

These 20 minutes the crew can spend like sardines in a tiny radshelter in the command center of the ship, so the radprotection of the Orion crew is much simpler and lighter than of any constant acceleration nuclear rocket ship which needs its reactor to be on for hours, days, or weeks.

***

The Orion nuke hazard and requirements are highly overestimated.

It needs charges of 0.1..1 kt yield.

As the Upshot-Knothole / Ruth & Ray tests had shown, about 10 kg of uranium hydride with no plutonium is enough to provide 0.2 kt.
(It's a problem to get much greater yield).

As the nukes since late 1950s are DT-boosted, the amount of fissiles for a 0.1 .. 1 lt nuke is hundreds of grams to several kilograms.

So, a DT-boosted uranium-hydride charge can easily provide the yield required by Orion, contains a couple of kilograms of weapon-grade uranium and no disgusting plutonium,
It's almost not radioactive before the explosion, its fissile mass is much lower than critical mass in case if terrorists get one.
It can easily self-destroyed just by burning several grams of boosting tritium (and this will happen anyway if it falls from the sky).

The estimation shows that a Martian flighht needs ~20 t of weapon-grade uranium and ~20 kg of tritium.

Also, the tritium can be stored in a ship can and be injected into the charges before shooting them.

The DT-boosted yield is easily adjustable by the tritium dosing, so the thrust also can be regulated smoothly.

***

The primer implosion is obviouls of 2-point detonation system, melon-like, used since mid-1950s.
Maybe that's why it's called Casaba, a sort of melons.

So, no complicated electronics or shaped explosive lenses are requried.
And additionally this allows to make one-point detonation tests to ensure that the nukes are still intact, and to adjust the yield in addition to the amount of injected tritium.

As the American two-point detonation systems of that time were made by high-precision machines with estimated upper diameter limit of 40+ cm, and most of the known primers of that design (Swan, Swift, Swallow, Robin, Tsetse, Python) are of ~40 cm diameter, it is probably what the Orion designers were orienting on.

This design was of ~2:1 elongation, so the primer chamber length should be about a meter long.

As the secondary chamber probably had similar diameter, this makes to think that the internal nozzle-like thing was of (75%..80% of the casing) 30 cm diameter at the end, and thus the tungsten membrane ~25 cm in diameter.

As the nozzle presumably was folowing the de Laval nozzle shape, the secondary chamber length was probably about a half-meter.

 

So, we can presume that a typical Orion propulsion charge was a cylinder of dia 50 x 170 cm size.

***

So, the Orion technological simplicity together with absence of anything nuclear with thrust greater that 40 tf of Nerva, it raises the only question.
Which kind of the Orion designs will be the first at other planets.

***

Spoiler

Now this thread can be merged to the dedicated Orion thread.

 

Edited by kerbiloid
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On 10/6/2022 at 1:48 AM, Entropian said:

If you're doing it purely for yourself, all bets are off and you can do pretty much whatever you want with it.  If you're redistributing it, you need to check the relevant parts of the license.

Yes, that you do with your own game is up to you. So no issue removing parts you don't like. 
Who will stop you or know :) Now modifying mods, much the same but here you should be more careful with stuff like challenges or videos. 

Distributing, only with agreement with the mod creator unless stated otherwise. This is for copyright reasons and to keep one version of the mod. 

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19 hours ago, Rutabaga22 said:

Why are letters in math always times new roman font?

Depends. If you're seeing something typeset with TeX, they are most probably actually Computer Modern (the font family Donald Knuth designed to go with TeX). If not, they are probably Times New Roman because that is the widely available font which looks most similar to CM.

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10 hours ago, Rutabaga22 said:

Would the best orbit for an International space station(Not the real one) be polar? It would make it so every country can launch to it.

Dunno. That would require higher performance rockets probably as you don’t have the Earth’s turn to assist you on the way up.

Proton and Shuttle did just fine launching ISS modules into inclined equatorial LEO, not sure if they have the same payload capability to any polar orbits.

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31 minutes ago, SunlitZelkova said:

Dunno. That would require higher performance rockets probably as you don’t have the Earth’s turn to assist you on the way up.

Proton and Shuttle did just fine launching ISS modules into inclined equatorial LEO, not sure if they have the same payload capability to any polar orbits.

Yes, an polar orbit limit cargo capacity. You want an inclination who cover the northern of the relevant launch sites but not higher. 

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16 hours ago, Rutabaga22 said:

Would the best orbit for an International space station(Not the real one) be polar? It would make it so every country can launch to it.

But is there a relevant country that can't secure access to a launch site as close or closer go the equator than Baikonur?

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Anyone looked into 3d printing with regolith?

ESA - 3D-printed ceramic parts made from lunar regolith

 

I'm wondering what the binding agent is.  Guessing since cured with light, its some kind of resin based composite, like they use in teeth.  Question is; could we dump a dedicated rover on the moon and have it build anything with 3d printing tech?  Like a landing pad?  I'm guessing the binder is no small part of the whole; the payload would have to be full of the stuff.

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Quote

As a next step, the parts will be tested to check their strength and mechanical properties

So, haven't been.

But the lunar colonists will have cups, teethbrush holders, and souvenirs for tourists in any case.

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On 10/9/2022 at 4:52 AM, SunlitZelkova said:
On 10/8/2022 at 6:23 PM, Rutabaga22 said:

Would the best orbit for an International space station(Not the real one) be polar? It would make it so every country can launch to it.

Dunno. That would require higher performance rockets probably as you don’t have the Earth’s turn to assist you on the way up.

Proton and Shuttle did just fine launching ISS modules into inclined equatorial LEO, not sure if they have the same payload capability to any polar orbits.

As others have pointed out, there are really no countries with launch sites at higher latitudes than Baikonur, so there's really no need for a higher inclination.

Also keep in mind that for everyone else, a higher inclination means a shorter launch window. A perfectly polar orbit means an instantaneous launch window for everywhere other than the poles. So that's annoying.

On 10/9/2022 at 10:04 PM, JoeSchmuckatelli said:

I'm wondering what the binding agent is.  Guessing since cured with light, its some kind of resin based composite, like they use in teeth.  Question is; could we dump a dedicated rover on the moon and have it build anything with 3d printing tech?  Like a landing pad?  I'm guessing the binder is no small part of the whole; the payload would have to be full of the stuff.

I've seen research that shows sintered regolith construction to be pretty promising. No binder needed.

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57 minutes ago, sevenperforce said:

shows sintered regolith construction to be pretty promising. No binder needed.

Isn't the energy requirements of sintering pretty high? 

 

I've looked into this a tiny bit; looks like an infrastructure project.  I.e. not small.

You'd need one rover to bulk scoop regolith and transport to a processing plant, that would then either sort or pulverize the regolith into a fine powder.  The fines could then be sent to another plant to sinter - apparently there's a slow process that's less energy intensive, but we're still talking relatively high temps.  Might need a warehousing / cooling unit.  Then you'd need another rover to take and process those to where you want them placed.

Quote

The driving force in the sintering process is the surface energy of the powder, which is closely related to the particle size of the powder. The effect of grain size of parent glass on crystallization and sintering has been discussed when preparing glass-ceramics by traditional glass-ceramics preparation methods [14], [15], [16], [17], [18]. Fine particles of parent glass imply low sintering temperature, high strength and smooth surface of the prepared glass-ceramics. However, in addition to Lu investigated the size influence of slag powders on the properties of glass-ceramics through direct sintering [19], Erol found the properties of the sintered material from coal fly ash were not only related to the sintering temperature and time, but also to the particle size of the raw material

...

Sintered glass-ceramics were successfully prepared through direct sintering from 100% coal fly ash powders labeled CFA, 20CFA and 40CFA. According to the results, the finer the coal fly ash particles are, the better the sintering effect is, the lower sintering activation energy is, and the better the performance of the sintered glass-ceramics is. When d50 of coal fly ash is less than 7.5 μm and the sintering temperature is higher than 1170 °C, the sintered glass-ceramics meeting the standards for building decoration can be prepared. 

The sintering kinetics and properties of sintered glass-ceramics from coal fly ash of different particle size - ScienceDirect

(Fly ash, not regolith)

 

I was hoping for something that could basically be sent out to scoop/flatten an area and poop out 3D printed bricks behind it, laying a 'pad' for something to land on.  Probably nothing that easy would work...

Edited by JoeSchmuckatelli
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2 hours ago, JoeSchmuckatelli said:

I was hoping for something that could basically be sent out to scoop/flatten an area and poop out 3D printed bricks behind it, laying a 'pad' for something to land on.  Probably nothing that easy would work...

One of the issues with a prepared landing surface is that you can end up making the problem worse if you’re not careful. As long as your landing site is sufficiently flat, your landing engine plume is **probably** only going to spew dust everywhere; there’s a risk of excavating larger pieces of debris but there’s also no guarantee there are any such pieces of debris to be excavated.

In preparing a pad, you’ve gotta be 100% certain that your preparation will result in a surface that’s truly impermeable to an exhaust plume, because otherwise you have basically just created a giant layer of potential shrapnel. 

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