What If The Expanse TV Show Had RBOD Laser Cannons?

[Spacescifi]

Against space stations with limited manuverability you really can just overwhelm them with missiles. Against a moving spaceship it's a different story though.

Especially if spaceships use high efficiency torchdrives as seen in The Expanse.

Honestly common lasers make a much bigger difference if you have low efficiency drives like chemical rockets... since you cannot dodge much and lasers have all the time in the world to cook you.

 

However what if The Expanse actually used the infamous Ravening Beam Of Death from Winchell Chung's Atomic Rockets site?

How would the show change then? People often try to say the reason The Expanse did not use laser weapons was because they were impractical or require too much power. But a RBOD only needs 10 MW, and we already know Epstein drives put out way more MW than that.

 

Here is a refresher on the infamous Ravening Beam Of Death (RBOD) from Atomic Rockets web site:

 

The ever useful Atomic Rockets site has a great section on laser weaponry, but the conclusion is far different than what you seem to be implying. Rather than have a multitude of laser weapons or optical systems, the ultimate aim is to create a Ravening Beam of Death (RBoD) and attack targets from as great a distance as possible.

For practical reasons, this turns out to be one light second (just under the distance from the Earth to the Moon), since you can see the target, aim and make corrections in such a short time frame that the target cannot move an appreciable distance. The massive Free Electron Laser (or actually Xaser, since it is fired in the x-ray frequencies) near the end of the section can vaporize metal, ceramic and carbon in milliseconds at that range, and if you are on an unpowered orbit or on an asteroid, the beam is still lethal at a light minute and dangerous even a light hour away.

    Let's take a 10 MW ERC pumped FEL at just above the lead K-edge. This particular wavelength is used because lead is pretty much the heaviest non-radioactive element you can get, and at just above the highest core level absorption for a material you can get total external reflection at grazing angles - so no absorption or heating of a lead grazing incidence mirror. We will use a 1 meter diameter mirror. The Pb K-edge x-ray transition radiates at 1.4E-11 m. This gives us a divergence angle of 1.4E-11 radians. At 1 light second, we get a spot size of 5 mm, and an intensity of 5E11 W/m2.

    Looking at the NIST table of x-ray attenuation coefficients, and noting that 1.4E-11 m is a 88 keV photon, we find an attenuation coefficient of about 0.5 cm2/g for iron (we'll use this for steel), 0.15 cm2/g for graphite (we'll use this for high tech carbon materials) and 0.18 cm2/g for borosilicate glass (a very rough approximation for ceramics). Since graphite has a density of 1.7 g/cm3, we get a 1/e falloff distance (attenuation length) of 4 cm. Iron, with a density of 7.9 g/cm3, has an attenuation length of 0.25 cm. Glass, density 2.2 g/cm3, has an attenuation length of 2.5 cm.

    At 1 light second, therefore, the beam is depositing 2E12 W/cm3 in iron at the surface and 7E11 W/cm3 at 0.25 cm depth; 1.2E11 W/cm3 in graphite at the surface and 5E10 W/cm3 at 4 cm depth; and 2E11 W/cm3 in glass at the surface and 7E10 W/cm3 at 2.5 cm depth. Using 6E4 J/cm3 to vaporize iron initially at 300 K, we find that iron flashes to vapor within a microsecond to a depth of 0.9 cm. The glass, assumed to take 4.5E4 J/cm3 to vaporize (roughly appropriate for quartz) will flash to vapor within a microsecond to a depth of 4 cm within a microsecond. Graphite, at 1E5 J/cm3 for vaporization, will flash to vapor to a depth of 0.7 cm within a microsecond (the laser performs better if we let it dwell on graphite for a bit longer, we get a vaporization depth of 10 cm after ten microseconds).

    Net conclusion - ravening death beam at one light second.

    Now lets look at one light minute. The beam is now 30 cm across. This is much deeper than the attenuation length in all cases, so we will just find the radiant intensity and the equilibrium black body temperature of that intensity. We have an area of 7E-2 m2, and an intensity of 1.4E8 W/m2. You need to reach 7000 K before the irradiated surface is radiating as much energy away as heat as it is receiving as coherent x-rays. The boiling point of iron is 3023 K, the boiling point of quartz is 2503 K, and the sublimation temperature of graphite is 3640 K. All of these will be vaporized long before they stop gaining heat. At this range, the iron is subject to 5.6E8 W/cm3 at the surface, the graphite to 3.3E7 W/cm3 at the surface, and the glass to 5.6E7 W/cm3 at the surface. Using the above values for energy of vaporization, we get about 0.1 milliseconds before the iron starts to vaporize, 0.8 milliseconds before the glass starts to vaporize, and 3 milliseconds before the graphite begins to vaporize (because of its long attenuation length, once it begins to sublimate, graphite sublimates rapidly to a deep depth, while you essentially have to remove the iron layer by layer).

    Net conclusion - still a ravening death beam at one light minute.

    What about at one light hour? The beam is 18 meters across. The equilibrium black body temperature is 900 K. This is well below the melting point of most structural materials. Ten megawatts, however, is a lot of ionizing radiation. Any unhardened vehicle will be radiation killed at these ranges.

Obviously, the ideas of "close, medium and far" ranges have very different meanings in a space war context. The only way to effectively deal with a weapon like that is to have several weapons of similar power in your constellation, or be prepared to fill the sky with tens of thousands of kinetic kill vehicles (referred to in Rocketpunk Manifesto as Soda Cans of Death or SCoDs). With an overwhelming number of targets, the individual laser will eventually not be able to track and kill every target, and of course other factors like the service cycle (how often you might have to stop and cool down the system), or the speed the laser mirror can swivel to track incoming targets reduces the absolute number of targets you can service even with a RBoD.

 

Main Questions: What would The Expanse be like if it used RBOD laser cannons? Would it change the show so much it would be unrecognizable lol?

 

 

 

 

 

Edited Tuesday at 12:29 AM by Spacescifi

[ColdJ]

Might be time to have a thread with a subject that changes each week? Just a thought.

Now we are mixing real world with fantasy. Nobody will ever be completely happy with any answer.

Having seen "The Expanse" series and read the books before seeing the series, I just need to say, that even though they got closer than most to real world conditions, they still cheated many times, in order to move the story along.

Ok, lets consider bomb pumped X-ray lasers (You might want to read the Honor Harrington book series.)

Let us assume for a sec that all the war ships in "The Expanse" somehow could meet the energy requirements. There is still a lot of complicated engineering, that requires constant maintenance to keep them running. Add to that the quick and massive heat build up while floating somewhere that does not easily radiate heat. In air or water you have somewhere for heat to radiate into, not so much in space.

Under ideal conditions, the target does not move and you have perfectly calculated so that the beam is focused tightly when it hits the hull. Hopefully you hit something vital, because due to heat build up you only get a few shots before a long cool down period. After which you have to perform maintenance incase something shifted slightly or broke.

Less than ideal conditions, the target knows what weapon you have and makes random touches of the RCS that constantly throw off your targeting LIDAR. it also has ablative plating designed to sacrifice itself to stop you reaching the vital. You don't hit something vital and it sprays heavy slugs in your general direction in the hopes that something hits.

Space battles are rarely up close and where you can see your targets face. They are usually hundreds of kms apart.

Try hitting a moving pea at 10 kms away.

Quick quiz question and answer.

Q: What is the difference between Star Wars and Star Trek?

A:You rarely ever see the people who maintain the ships in Star Wars (How many times do you remember seeing the engineering section of a Star Destroyer?) While you see engineering in Star Trek all the time.

[Spacescifi]

  On 3/18/2025 at 4:30 PM, ColdJ said:

Might be time to have a thread with a subject that changes each week? Just a thought.

Now we are mixing real world with fantasy. Nobody will ever be completely happy with any answer.

Having seen "The Expanse" series and read the books before seeing the series, I just need to say, that even though they got closer than most to real world conditions, they still cheated many times, in order to move the story along.

Ok, lets consider bomb pumped X-ray lasers (You might want to read the Honor Harrington book series.)

Let us assume for a sec that all the war ships in "The Expanse" somehow could meet the energy requirements. There is still a lot of complicated engineering, that requires constant maintenance to keep them running. Add to that the quick and massive heat build up while floating somewhere that does not easily radiate heat. In air or water you have somewhere for heat to radiate into, not so much in space.

Under ideal conditions, the target does not move and you have perfectly calculated so that the beam is focused tightly when it hits the hull. Hopefully you hit something vital, because due to heat build up you only get a few shots before a long cool down period. After which you have to perform maintenance incase something shifted slightly or broke.

Less than ideal conditions, the target knows what weapon you have and makes random touches of the RCS that constantly throw off your targeting LIDAR. it also has ablative plating designed to sacrifice itself to stop you reaching the vital. You don't hit something vital and it sprays heavy slugs in your general direction in the hopes that something hits.

Space battles are rarely up close and where you can see your targets face. They are usually hundreds of kms apart.

Try hitting a moving pea at 10 kms away.

Quick quiz question and answer.

Q: What is the difference between Star Wars and Star Trek?

A:You rarely ever see the people who maintain the ships in Star Wars (How many times do you remember seeing the engineering section of a Star Destroyer?) While you see engineering in Star Trek all the time.

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Rule of space combat 1: The faster the speed the weapon strikes effectively, the longer the range of combat becomes.

Edited Wednesday at 12:11 AM by Spacescifi

[Nuke]

i think the reason the expanse doesn't use lasers outside of communications and targeting is because lasers really suck compared to bullets and missiles. though with advances in diode pumped lasers i figure that would have been a solved problem by the 23d century. i dont think lasers will ever be efficient enough for fusion let alone weaponry.

Edited Wednesday at 03:46 PM by Nuke

[magnemoe]

  On 3/19/2025 at 3:39 PM, Nuke said:

i think the reason the expanse doesn't use lasers outside of communications and targeting is because lasers really suck compared to bullets and missiles. though with advances in diode pumped lasers i figure that would have been a solved problem by the 23d century. i dont think lasers will ever be efficient enough for fusion let alone weaponry.

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Now laser cannons starts to become an thing. Its benefit is light of speed travel and easy aiming, downside is hitting power.  But that is not so important against drones, missiles is a bit harder. 
So it would be useful against missile swarms. at least as close in weapons.