Gamma Radiation Absorbent Propellant Scifi Scheme....

[Spacescifi]

Another scifi propulsion scenario:

 

Gamma Rods: Are your energy source. Gamma rods are metallic and have properties on par with steel including it's melting point with one very important exception.... they can totally absorb gamma radiation without heating or compressing... at least up to a point.

Gamma rods can absorb a maximum of gamma radiation that equals their mass... if it's mass was converted TOTALLY into energy.

Trying to pump more gamma rays into it from that point would result in an RUD of the rod... as it releases ALL of it's stored gamma ray energy at once with a boom.

Propellant: Any that will readily absorb gamma rays as heat so it can be used for propulsion.

Gamma rod usage: Gamma rays can be induced to shoot out either end preferred as a graser (gamma laser beam). This is how gamma rays are extracted from the rod that stores them. It does not take much energy to extract gamma lasers from the rod... anymore than it does turn the spigot on jug laden with water for it to pour out. Unlike normal lasers gamma rods produce zero waste heat on itself compared to how much they put out. A user literally extracts the gamma energy level they type in based on however much energy is stored.

You would have the choice of extracting all the gamma ray energy from a rod in one mighty zap, or gradually over a constant use or gradually in pulses or a mix.

 

Hazards: Since other than their special gamma absorption and graser use gamma rods have the properties of steel... they can melt just like steel. If a gamma rod is melted while possessing stored gamma rays it will explode... even if only partially melted. Releasing all it's stored gamma rays.

Questions:

 

1. Would this scifi tech be energetic enough to pull off heavy scifi SSTOs via thermal rocketry (100 ton at least)? I think so... since rods can hold their mass in gamma rays or less. So all you need is enough gamma rod mass with enough absorbed gamma and you are good.

2. What propellant is best for absorbing gamma radiation for thermal rocketry?

3. What is the optimal way of of getting the graser into the reaction chamber to mix with propellant?

4. QUESTION EDITED OUT as I just realized the rod can be can induced to produce a gamma ray beam without a lens. It does not need a lens... especially since at higher power levels the laser would destroy it anyway.

 

My conclusions: With enough engines (a lot) I reckon one could SSTO with it. The exhaust would have gamma rays in the exhaust plume but gammas are safer than neutrons so that it is OK enough.

Edited January 5, 2023 by Spacescifi

[farmerben]

I didn't follow your scheme precisely but gamma ray reflection is a huge problem.  It is a problem especially for antimatter engines where there is no effective reflector.  Supposing you had a tungsten rocket chamber of considerable thickness.  The high energy gamma rays from an antimatter interaction would often go through the chamber or be absorbed at some depth and radiated eventually as heat in all directions.

 

Edited January 5, 2023 by farmerben

[Spacescifi]

2 hours ago, farmerben said:

I didn't follow your scheme precisely but gamma ray reflection is a huge problem.  It is a problem especially for antimatter engines where there is no effective reflector.  Supposing you had a tungsten rocket chamber of considerable thickness.  The high energy gamma rays from an antimatter interaction would often go through the chamber or be absorbed at some depth and radiated eventually as heat in all directions.

 

 

Ah but that is what my scheme solves! Instead of gamma rays going every which way they leave the end of the rod as a focused gamma ray beam.

Whatever propellant used would have to dense enough to absorb the gamma rays efficiently to work the thermal rocket.

Gamma ray reflectors we have in the setting by the way... that's only fair... and not anywhere as cheaty as say... antigravity.

 

So gamma ray scattering in the fuel reaction chamber could be redirected to fly out the chamber as it should rather than just heat up the ship.

[kerbiloid]

And while it great ISP (literally, a photon rocket), its thrust is pathetic.

Also it's a nuke-powered X-ray laser.

[KSK]

1.  Yes

2.  Anything with heavy elements in - the heavier the better. Tungsten is good.  Heavy elements pretty much suck as propellants though for a variety of reasons.

3.  Cut hole in reaction chamber. Rivet gamma rod into hole. Make sure graser emitting end is pointing into chamber. Make sure not to weld gamma rod into hole in case it goes boom. Do not stare at grazer emitter with remaining eye.

Possible problem -  charging up gamma rods. From Wikipedia:

"When a uranium nucleus fissions into two daughter nuclei fragments, about 0.1 percent of the mass of the uranium nucleus[9] appears as the fission energy of ~200 MeV. For uranium-235 (total mean fission energy 202.79 MeV[10]), typically ~169 MeV appears as the kinetic energy of the daughter nuclei, which fly apart at about 3% of the speed of light, due to Coulomb repulsion. Also, an average of 2.5 neutrons are emitted, with a mean kinetic energy per neutron of ~2 MeV (total of 4.8 MeV).[11] The fission reaction also releases ~7 MeV in prompt gamma ray photons."

So about 3.5% of 0.1% or 0.0035% of the mass of a fissioning uranium nucleus appears as gamma rays.  Therefore to charge up a 1g gamma-rod, would require the equivalent of fissioning about 28.5 kg of uranium.

That's assuming a) that gamma-rods are perfect mass-energy converters, b) that all the gamma-rays from the fissioning uranium are captured and c) that no further gamma-rays are produced by decay of uranium fission fragments.

We can take (a) as read for this discussion and I don't have any idea about (c) off the top of my head. (b) is a significant issue though because the gamma rays from the fission reaction are going to be emitted in random directions. So to completely capture the gamma-ray output from a fission reactor would require a shell of gamma-rods to be constructed around the reactor core, and each individual gamma rod will only capture a small percentage of that gamma-ray output. 

Long story short - you're going to need to fission a lot more than 28.5 kg of uranium to charge up a single 1g gamma-rod. There are other sources of gamma-rays of course, but a fission reactor seems like the most controllable and dependable one. On a more positive note - have some free worldbuilding for your gamma-rod setting.  

 

 

 

[Spacescifi]

1 hour ago, KSK said:

1.  Yes

2.  Anything with heavy elements in - the heavier the better. Tungsten is good.  Heavy elements pretty much suck as propellants though for a variety of reasons.

3.  Cut hole in reaction chamber. Rivet gamma rod into hole. Make sure graser emitting end is pointing into chamber. Make sure not to weld gamma rod into hole in case it goes boom. Do not stare at grazer emitter with remaining eye.

Possible problem -  charging up gamma rods. From Wikipedia:

"When a uranium nucleus fissions into two daughter nuclei fragments, about 0.1 percent of the mass of the uranium nucleus[9] appears as the fission energy of ~200 MeV. For uranium-235 (total mean fission energy 202.79 MeV[10]), typically ~169 MeV appears as the kinetic energy of the daughter nuclei, which fly apart at about 3% of the speed of light, due to Coulomb repulsion. Also, an average of 2.5 neutrons are emitted, with a mean kinetic energy per neutron of ~2 MeV (total of 4.8 MeV).[11] The fission reaction also releases ~7 MeV in prompt gamma ray photons."

So about 3.5% of 0.1% or 0.0035% of the mass of a fissioning uranium nucleus appears as gamma rays.  Therefore to charge up a 1g gamma-rod, would require the equivalent of fissioning about 28.5 kg of uranium.

That's assuming a) that gamma-rods are perfect mass-energy converters, b) that all the gamma-rays from the fissioning uranium are captured and c) that no further gamma-rays are produced by decay of uranium fission fragments.

We can take (a) as read for this discussion and I don't have any idea about (c) off the top of my head. (b) is a significant issue though because the gamma rays from the fission reaction are going to be emitted in random directions. So to completely capture the gamma-ray output from a fission reactor would require a shell of gamma-rods to be constructed around the reactor core, and each individual gamma rod will only capture a small percentage of that gamma-ray output. 

Long story short - you're going to need to fission a lot more than 28.5 kg of uranium to charge up a single 1g gamma-rod. There are other sources of gamma-rays of course, but a fission reactor seems like the most controllable and dependable one. On a more positive note - have some free worldbuilding for your gamma-rod setting.  

 

 

 

 

Thanks... my worldbuilding idea was that the civilization had antimatter factories where they annihilated it with a bit of mass inside massive vacuum chambers shaped like a parabolic reflector... because the chamber reflects gamma rays. At the opposite end are the gamma rods absorbing it.

 

So yes... this is one of those scifi technologies that is so advanced that we could only make partial use of it with today's tech... which is why gamma rods are only super useful if you already have scifi gamma ray mirrors and profitable antimatter industry production.

 

As bonus... gamma rods make great laser weapons for space too... just do NOT have yours get zapped... since if it does and it melts... kaboom!

Edited January 5, 2023 by Spacescifi

[KSK]

That makes sense.  Use the horribly unstable antimatter to make an energy source that gives you most of the bang for your buck but is substantially safer.

As an aside, have you read Andy Weir's Project Hail Mary?

Spoiler

It had an... interesting take on mass-energy conversion and using it for propulsion. I enjoyed the book but the attempts to explain its more speculative elements with actual science didn't quite work for me. To be honest I prefer your gamma-rods.

 

[Spacescifi]

Actually I think just about any solid rocket propellant would work great... we do not need tungsten.

Throttling is as simple as not zapping the solid propellant with grasers.

 

Not sure how to arrange gamma rods to light up solid propellant but I think it's doable.

2 minutes ago, KSK said:

That makes sense.  Use the horribly unstable antimatter to make an energy source that gives you most of the bang for your buck but is substantially safer.

As an aside, have you read Andy Weir's Project Hail Mary?

  Hide contents

It had an... interesting take on mass-energy conversion and using it for propulsion. I enjoyed the book but the attempts to explain its more speculative elements with actual science didn't quite work for me. To be honest I prefer your gamma-rods.

 

 

Never heard of it but will check it out.

 

And yes.... I desperately wanted a safe-ish propellant system.

 

Gamma ray boosted exhaust being what it is... I suppose crew would be advised to wait a while after landing so the radiation can dissipate.

Edited January 5, 2023 by Spacescifi

[KSK]

The problem is that most materials don't absorb gamma rays terribly well, which will limit how efficiently a gamma-rod engine can convert gamma rays to heat and therefore to thrust.  Whilst a sufficiently thick block of conventional solid propellant would certainly absorb the gammas, I'm not sure how evenly it would heat up, which might make it difficult to use in practice.

In space, I guess you could dispense with propellant entirely and go with a pure photon rocket - you're not going to be short of photons with gamma-rods - but a photon rocket isn't much good for lifting stuff out of a gravity well, unless the photon source is intense enough to create a whole bunch of other 'interesting' problems.

So for an SSTO, I would think you need a propellant that is reasonably good at absorbing gamma-rays both for ease of creating enough thrust and for making the exhaust safer. 

I wonder if a 'candy cane' propellant block would work? Layers of tungsten to at least partially absorb the gamma rays, sandwiched between thicker layers of a more easily vaporised material.  Tungsten absorbs gamma rays, gets hot, vaporises rest of propellant. Or a block of propellant doped with tungsten particles might work better.

Edited January 5, 2023 by KSK

[Spacescifi]

1 hour ago, KSK said:

The problem is that most materials don't absorb gamma rays terribly well, which will limit how efficiently a gamma-rod engine can convert gamma rays to heat and therefore to thrust.  Whilst a sufficiently thick block of conventional solid propellant would certainly absorb the gammas, I'm not sure how evenly it would heat up, which might make it difficult to use in practice.

In space, I guess you could dispense with propellant entirely and go with a pure photon rocket - you're not going to be short of photons with gamma-rods - but a photon rocket isn't much good for lifting stuff out of a gravity well, unless the photon source is intense enough to create a whole bunch of other 'interesting' problems.

So for an SSTO, I would think you need a propellant that is reasonably good at absorbing gamma-rays both for ease of creating enough thrust and for making the exhaust safer. 

I wonder if a 'candy cane' propellant block would work? Layers of tungsten to at least partially absorb the gamma rays, sandwiched between thicker layers of a more easily vaporised material.  Tungsten absorbs gamma rays, gets hot, vaporises rest of propellant. Or a block of propellant doped with tungsten particles might work better.

 

Lead works but somehow I don't think exhaust plumes of lead gas is a good idea for the local biosphere.

I think the problem with uneven heating can be mitigated with a larger reaction chamber than normal... a vacuum chamber with gamma rods lining the walls... as well as number of movable gamma rod turrets.

 

Solid fuel is loaded from a separate fuel bay and multiple grasers can be used to precisely zap the solid fuel in such a way that it burns evenly.... if that even makes sense lol.

 

The sandwhich idea I fear my cause a reverse tungsten plume backfiring into the gamma rods... since any uber laser zap makes a rocket plume on just about anything solid.

[Spacescifi]

Maybe if I made them ultra-violet rods instead? Ultra-violet radiation is readily absorbed by propellant right?

Only issue then is to find a powerful source of UV to charge the UV rods.

Edited January 7, 2023 by Spacescifi

[KSK]

Sunlight should do the job for UV, especially if you put your rod charging facility up in space.  If you want to go full on sci-fi, build a Dyson Sphere around a star and use its entire output for charging UV-rods.  Or optical-rods, or infrared rods.  The solar spectrum is here - spectra for other stars will obviously vary.

Infrared rods might be pretty decent energy sources and I would think most propellants would absorb infra-red radiation to some extent, given that infra-red spectroscopy is a pretty standard technique for fingerprinting molecules, particularly organic molecules. Heck you can see two big absorption bands for water in that diagram I linked to - both in the infra-red.

[Spacescifi]

1 hour ago, KSK said:

Sunlight should do the job for UV, especially if you put your rod charging facility up in space.  If you want to go full on sci-fi, build a Dyson Sphere around a star and use its entire output for charging UV-rods.  Or optical-rods, or infrared rods.  The solar spectrum is here - spectra for other stars will obviously vary.

Infrared rods might be pretty decent energy sources and I would think most propellants would absorb infra-red radiation to some extent, given that infra-red spectroscopy is a pretty standard technique for fingerprinting molecules, particularly organic molecules. Heck you can see two big absorption bands for water in that diagram I linked to - both in the infra-red.

 

Um... building a dyson sphere around a star using the output for UV rods sounds dangerous.

As for infrared yes it is great for heating but there are so many sources of infrared heat that I think you would have to store it in a cold and dark place to prevent a random overcharge detonation.

Shorter wavelengths are not as easily absorbed as they are more penetrating but longer wavelengths absorb easily.

 

Which is problematic since infrared radiation can be conducted (correct me if wrong), so a mere change im degrees from cold to warm in the IR rod storage chamber and boom!

 

It's more hazardous to deal with than shorter wave lengths since common heat sources can be absorb and trigger a detonation if the rod is fully charged.

 

At least with UV rods you either need to melt them or overcharge it with UV.

 

With an IR rod simply holding a fully charged rod in your hand could trigger a detonation due to IR rays conducting from your hand to the rod lol.

https://www.erchonia.com/blog-news/visible-vs-infrared-lasers/

 

As for UV absorbing propellant... anything dark works.

 

Dirty water anyone?

*water with high mineral/iron content*

 

Coincidentally this is great for ISRU, since all you need is ice and minerals to make propellant you barely need to process... no splitting of elements required here.

 

 

In space mirrors could be used to focus sunlight for charging UV rods, which would be stored when charged enough.

 

I doubt rods will ever be fully charged much to to the overcharging detonation risk.

 

So larger rods would have larger UV energy before actually overcharging.

 

A kilogram of UV rod is a kilogram of mass converted into a total UV laser... or a UV blast if overcharged.

Edited January 7, 2023 by Spacescifi

[KSK]

Ahh, OK. 

I forgot about the overcharging part. I figured that provided the rods weren't hot enough to melt, they'd be fine.

On the other hand -  the rods can be made to release their energy in a single burst or gradually over time. Is there a lower limit to how gradual that release can be? Because I'm thinking that IR rods could be plugged into a safety system, which monitors their change in mass, and then causes them to 'vent' infra-red radiation if they get too massive.  The need for a safety system might make them a little more difficult to use for some applications, but it should at least prevent them overcharging from exposure to ambient IR radiation.

If you needed a technical explanation for the mass sensor, one way of  building one might be to use a torsion balance to measure the gravitational force between the rod and an accurately known test mass. There are probably more elegant ways of doing it, or you could just handwave the details away if they weren't important to the story.

Edited January 8, 2023 by KSK

[Spacescifi]

1 hour ago, KSK said:

Ahh, OK. 

I forgot about the overcharging part. I figured that provided the rods weren't hot enough to melt, they'd be fine.

On the other hand -  the rods can be made to release their energy in a single burst or gradually over time. Is there a lower limit to how gradual that release can be? Because I'm thinking that IR rods could be plugged into a safety system, which monitors their change in mass, and then causes them to 'vent' infra-red radiation if they get too massive.  The need for a safety system might make them a little more difficult to use for some applications, but it should at least prevent them overcharging from exposure to ambient IR radiation.

If you needed a technical explanation for the mass sensor, one way of  building one might be to use a torsion balance to measure the gravitational force between the rod and an accurately known test mass. There are probably more elegant ways of doing it, or you could just handwave the details away if they weren't important to the story.

 

No there is no lower limit to release of energy over time.

 

You could release it all at once but you would blow up your engine... and ship with it.

 

After considering all this... I think the original gamma rods would be best.

 

Why? Even though gamma rays require a lot of density to be absorbed, solid propellants are ideal for that.

With gamma reflecting mirrors such energy may be used to power uber magnetic fields... which in turn could power an uber plasma rocket.

 

So I guess I figured a way to make a safe rocket afterall.

 

Just internalize the gamma rods and gamma mirrors with absorbent materials  to generate power by converting gamma to electrical power somehow to create brief pulses of uber magnetic field.

 

So a gamma charged plasma pulse rocket?

 

No radiation! Yaay! Just do not crash it if you do not want a detonation on par with antimatter.

[Spacescifi]

I slept on this and had a revelation... merely shooting the graser beam into the reaction chamber, which would be filled with any chemical propellant... even water... would work.

 

It doea not matter that gamma rays do not absorb well... since this is a concentrated beam and the higher it's energy the more it will transfer it's thermal energy to the propellant.

 

We have no lack of power due to the gamma rods.

 

The only real cost here is twofold:

 

1. Less efficient use of the gamma rods since higher gamma ray intensity is required to heat the propellant it would normally sail through barely impeded. Plus we cannot forget the vital role gamma ray mirrors would play here... since instead of scattering ominidirectionally inside the reaction chamber they would be focused out along with the exhaust plume.... thanks to gamma ray mirrors lining the walls of the reaction chamber.

 

2. I can not overestimate how much anything BEHIND the exhaust is going to get a lethal dose of gamma rays.

 

Due to all of this... I think the safest SSTO would be a ssubmarinewith gamma ray thermal rocketry. Seawater is the propellant.

 

It would flip over and launch straight up in the water and land in the water the same way... on it's tail end where the rocket engines are.

In space it would be an orbiter, sending down shuttle craft with less lethal engines to land on actual land.

To return to earth the orbiter submarine would land in the ocean again.

Edited January 9, 2023 by Spacescifi