Athom83, on 03 June 2017 - 03:47 PM, said:
My autocorrect screwed me there.
You'd be correct for a fission reactor. But with a fusion reactor, it honestly depends on how the reactor is hit. The sarna page explains this a bit better. Go to the last two paragraphs of the description;
http://www.sarna.net...i/Fusion_Engine Summary; It isn't the reactor that creates the explosion, but the quick intake of air before the superheated plasma is supercooled by the containment walls. Thermal expansion is a *****.
This is mostly due to the size and power of the laser requiring it to be focused properly. The standard laser in BT is simply designed to pump out enough light and heat to melt the targeted armor. All other forms of lasers are basically modifications to the application of that.
This is for a few reasons.
The ballistics range is cut short because they are basically howitzers firing HESH rounds. Battletech "missiles" are actually more like rockets. They had the dozens of km long ranged missiles, but they were far to expensive to maintain a stock of on a galactic scale. Also, they're euiped with basic fused to self destruct when they run out of fuel as hitting something important way off in the distance (like the General's pool) is not such a good thing
A tank is not able to pick things up to use them. A walking robit can. A tank cannot easily traverse obstructed terrain, even when it has equipment to do so. A mech can. A tank, even a massive one, does not have the same psychological impact of a 15m tall walking maching with cannons and missiles and lasers and whatnot bristling about it.
Unfortunately, most of these are examples where Battletech physics and real physics collide and a good background is needed in order to understand the issues.
1) Take proton-proton or H-H fusion for example.
http://www.fisicanuc...19-856264-0.pdf
page 11 - table of fusion reactions, energy released and cross-sections
p-p fusion has a cross section of 4e-22, releases 1.44MeV/reaction .. 0.27 of which is completely lost to a neutrino, and has D and an electron as reaction products which is problematic in terms of which particle gets most of the reaction energy.
Compare to D-T
D-T has a cross section of 1.2e4, releases 17.59MeV/reaction, has reaction products of He3 and a neutron, the neutron receives 14.1eV of the released energy so a reactor requires a blanket to capture the kinetic energy of the neutron.
The best choices for a science fiction reactor would be either D-He3 or p-Boron ... both release decent amounts of energy, have reasonable cross-sections and all their reaction products are charged particles which makes it feasible to consider MHD methods to extract the power since the charged particle may be constrained by the magnetic fields. However, fast ion and first orbit losses of these charged particles after the fusion reaction occurs is still an issue since the energy of the reaction product will typically be much higher than the plasma and so they will have a much larger gyro radius than plasma particles for a given magnetic field strength.
https://en.wikipedia...rtant_reactions
Most nuclear fusion references don't even mention p-p fusion since the reaction cross sections are so low. Even in the sun "At the temperatures and densities in stellar cores the rates of fusion reactions are notoriously slow." ... though the sun is a high pressure and relatively low temperature environment compared to a terrestrial fusion reactor.
As for "thermal expansion" :
http://www.sarna.net...i/Fusion_Engine
"There have been a number of cases of fusion engines being "over revved" and exploding with devastating force, but this is more akin to a boiler explosion than a true nuclear explosion. More often a destroyed engine will be punctured by weapons fire. Because the plasma is held in a vacuum chamber (to isolate the superheated plasma from the cold walls of the reactor; contact with the walls would super-chill the plasma below fusion temperatures), a punctured reactor can suck in air where the air is superheated. Normal thermal expansion of the air causes the air to burst out in a brilliant lightshow often mistaken for a "nuclear explosion". This thermal expansion damages anything within 90 meters of the destroyed 'Mech."
This is more Battletech physics hyperbole. Fusion reactors are extremely hot but operate at a very low density. There are about 2.5e25 particles in one cubic meter of air at standard temperature and pressure. Fusion reactor density is more like 1e20 ... lets say 1e21 for some futuristic reactor.
Fuel ions are hydrogen isotopes while the atmostpheric particles will be mostly nitrogen for an earth type atmosphere.
Lets assume a 10keV core temperature which is about 100,000,000K. If the reactor volume is 10m3 then the total stored energy in plasma particles (excluding the magnetic field which itself represents a fair bit of energy but will more likely dump into the material components ... runaway electrons etc).
1e21 * 10,000 * 1.6 e-19 * 10 = 1.6e7 Joules of energy
https://en.wikipedia...gnitude_(energy)
This about the energy of combustion of 0.5m3 of natural gas or about the energy released by 2kg of TNT or about the kinetic energy of one high velocity armor piercing round. In addition, MOST of the energy will be contained within the reactor chamber being used to heat the walls/armor and other components.
Of course it is all still Battletech physics so this is mostly a moot discussion but the point I am making is that the hand waving justifications in the Battletech technical readout and the Sama webpage really don't make any sense from a physics perspective and some of it was specifically invented AFTER a particular Battletech author decided it would be cool for mechs to explode and the editors didn't know enough to catch the issue.
This doesn't make Battletech any less fun

... but it doesn't make it any more real either
2) One quick comment on lasers.
Lasers could have a fixed focal length that would increase the energy density at the focal point. However, this would then make them much more effective at the focal point than anywhere else ... either closer or farther away (though that depends to some extent on beam dispersion). Changing focal lengths in real time means changing the optics, it also requires focusing materials that can withstand the energy density of the beam at the point where it traverses the optics. However, in this case there is no practical reason that the effective focal distance would be limited to only a few hundred meters.
The other approach is a laser with a fixed cross-section where dispersion is the primary mechanism of beam energy loss. In this case, the range should be far larger than a few hundred meters.
Anyway, the distinct ranges used in Battletech are a game mechanic and not a physics constraint.
3) Ballistic weapons.
Another mostly fruitless discussion. You suggest that Battletech rounds are mostly HESH ... basically a projectile with a plastic explosive shaped charge.
https://en.wikipedia...ive_squash_head
"Since the 1970s, HESH ammunition has increasingly fallen out of favour as armour designs have trended towards layered composites of hard metal and heat-resistant materials. "
Unfortunately, the reasons highlighted in this sentence for the reason why HESH is not used so much any more actually corresponds to a good description of Battletech armor.
The following description is from the Technical Manual but captures some more of the Battletech physics in terms of material properties.
http://haveno.info/B...0TechManual.pdf
"The Layers
Standard BattleMech armor consists of multiple layers.Only two of these layers are armor in the truest sense. The
other two layers play supporting roles. The outer layer of armor is an extremely strong, extremely hard iron alloy...a steel. It is intended to fragment projec-tiles and/or—hey, have you heard anyone use “and/or” aloud before?—to fragment projectiles and/or ablate protectively in the face of energy attacks. The grains of this steel, that is, its crystals, are carefully aligned for maximum strength and radiation-treated to further hardness and strength. Though phenomenally strong and hard, the steel pays for these properties by being quite brittle. In fact, the steel is brittle enough that the second layer of armor that backs the steel is a ceramic, cubic boron nitride. The point of the boron nitride layer is to act as a catcher’s mitt for the fragments and plasma of the steel. Another very strong, very hard material with a brittleness problem, boron nitride is carefully processed to avoid any porosity and incorporates an additional web of artificial diamond fibers to make the ceramic a fine backstop for the steel outer layer."
Basically, the description here implies that Battletech armor is specifically designed to mitigate HESH type explosives.
In additon, I couldn't find data on typical effective ranges for HESH ammunition but anecdotally it appears to be on the order of miles rather than 270m for the AC20.
4) Both LRMs and Streak SRMs are guided missiles so they already have whatever tracking technology is needed. Range is just a function of fuel in the projectile. Fuel is usually cheap. Missiles already are equipped with everything they need for long range use except some extra fuel. Anyway, again no real justification for such limited ranges for missile weapon systems.
The bottom line to all of this is ... it's Battletech physics ... all the hand waving explanations the authors care to come up with won't change the reality which is that the game is science FICTION. Fun fiction, enjoyable fiction, cool fiction ... but fiction none the less ... which doesn't necessarily fit into the physics of our universe. (It may fit into the Battletech universe physics for all we know since it is made up

).
Edited by Mawai, 04 June 2017 - 09:29 AM.