|
Post by zuthal on May 14, 2017 12:14:01 GMT
Hmmm... well, not using HCs means compromising either propellant density (LH2) or exhaust velocity (ammonia, water)... though I guess ammonia wouldn't be too bad a propellant, density of 682 kg/m^3 at the boiling point, and the breakdown product has an average molar mass of 8.5 g/mol (assuming full recombination to N2 and H2, compared to 5.33 g/mol for methane with hydrogen recombination) to 4.86 g/mol (assuming the hydrogen stays dissociated, but the nitrogen recombines, compared to 3.2 g/mol for methane). As exhaust velocity is proportional to sqrt(1/[molar mass]), an ammonia NTR would be expected to have about 80% of the exhaust velocity of a comparable methane NTR - which for our NTRs would mean about 5.1 km/s, comparable to decane NTRs, with a propellant density only slightly less than that of decane.
Also, regaring chemically clearing the carbon soot: Would running hydrogen through at a temperature below the thermal decomposition temperature of methane work, hydrating the carbon deposites into methane?
|
|
|
Post by zuthal on May 14, 2017 8:51:37 GMT
I think there is a relative consensus on this forum that methane (and the higher hydrocarbons) are basically the best NTR propellants, with a good mix of density and exhaust velocity. However, IRL, there is a significant problem with using hydrocarbons in a sufficiently-hot NTR: The thermal decompositions of hydrocarbons produces solid carbon, which can clog up the internal plumbing of the NTR.
Thus my question is, is there any way of preventing that coking, besides running the NTR cold enough that the hydrocarbons do not decompose?
|
|
|
Post by zuthal on May 10, 2017 10:13:39 GMT
I don't find this a big problem; it takes minutes to saturate an Amorphous Carbon radiator to operating temperatures, so some battlestars carrying only enough radiator to fire all lasers for 2 minutes instead of 5 is a perfectly valid design choice. True - so then have another warning if laser radiators are not enough to sustain full fire indefinitely, but as a yellow warning (so that it doesn't make the ship design invalid), and also display how long it takes to overheat assuming all lasers are firing, and how many lasers can fire indefinitely.
|
|
|
Post by zuthal on May 8, 2017 19:37:00 GMT
KInetic strikes have the advantage of being more targeted and producing no fallout, though - which is useful if you want to avoid collateral damage. Also, I think with the same total energy at impact/detonation, a kinetic strike is more penetrating than a ground-detonated nuke - due to having quite a lot of downwards momentum. For example, a 1 m diameter tungsten sphere (mass ~10 tonnes) entering Earth's atmosphere vertically at 30 km/s impacts at 16 km/s, delivering 304 tonnes TNT equivalent and making a crater 118 meters wide and 25.2 meters deep in crystalline rock. Air blast, thermal and seismic damage is negligible at 500 m distance - only windows will shatter.
To compare, a 304 tonne nuke surface burst will make, according to Nukemap, a negligible crater. The airblast will shatter windows out to 660 meters, the thermal flash will give people burns out to 820 m, and people will receive a more than 50% dose of radiation within 680 meters.
So, kinetics will be better than nuclear strikes, I think, against small, hard targets. Not to mention that a few tonnes of tungsten rod plus the energy to accelerate it is probably cheaper than a nuke, even a small one (IRL at least).
|
|
|
Post by zuthal on May 7, 2017 0:19:56 GMT
If you make a ship that uses multiple stacked lasers (using the "count" slider on the laser module), the waste heat display, including the radiators not removing enough heat warning message, will be displayed as if you only had one laser. If you size your radiators according to that, the result is that shortly after opening fire, most of your lasers overheat and stop firing.
A workaround until this bug is fixed consists in either calculating the total needed radiator area from the waste heat and temperature, or in sizing the radiator area for one laser, and then multiplying that by the number of lasers you have.
|
|
|
Post by zuthal on May 4, 2017 23:46:27 GMT
So, you are saying that ablative PTFE chamber/nozzle coatings for HF missile engines might actually work?
|
|
|
Post by zuthal on May 4, 2017 20:53:04 GMT
I don't even know which allotrope of boron is assumed in the game - and that may have significant implications for thermal stability. E.g. amorphous boron anneals at ~1275 K.
|
|
|
Post by zuthal on May 2, 2017 23:25:02 GMT
Maybe allow you to carry, in a cargo module, spare armour material, and then during time spent out of combat, armour is repaired at a certain rate (dependent on materials, extent of damage, excess crew and such)... also maybe make it so that only the innermost and the outermost layers can be repaired - as they are the ones that are easily accessible.
|
|
|
Post by zuthal on May 2, 2017 21:00:04 GMT
Is graphite aerogel better even when looking at the fact that a much larger gun (for the same degree of protection) results in a much larger turret, which is a lot heavier?
|
|
|
Post by zuthal on May 1, 2017 19:50:13 GMT
The thing is, cosmic rays are individual, very-near-c particles with low overall intensity - opposed to that, a casaba-howitzer's plasma beam is a relatively dense, cohesive plasma, with an average particle velocity from what I have read on the order of 1000 km/s. So, I think that with a casaba-howitzer, the density is high enough and the particle energy is low enough that you cannot, as the comparison to cosmic rays does, treat it just as a collection of individual particles flying in close formation, but have to apply fluid dynamics.
|
|
|
Post by zuthal on May 1, 2017 18:45:46 GMT
This purports to be a video of fluorine reacting with boron - so the result of trying to store fluorine in a tank made of boron should be a very bright flame. In general, afaik the only materials that are not destroyed by fluorine are ones that either form a hard, solid, impermeable fluoride upon exposure, prevent the rest of the material from reacting, or the ones that aren't attacked by fluorine at all, e.g. teflon.
|
|
|
Post by zuthal on Apr 30, 2017 18:56:10 GMT
Tasil Aerospace Inc. presents the DDL-1 Hermes laser destroyer. Using the newest in dubious experimental materials, she boasts eleven 2.5 MW Ce:LLF extreme UV lasers, with an unparalleled efficiency of 29%! DDL-1 Hermes.txt (20.63 KB) Mod dependencies: Ce:LLF, Silicon/Silcion Dioxide/Platinum Mirrors, Molten Aluminum/Gold/Lead/Tin, Uranium Tantalum Carbide (all can be gotten from here)
|
|
|
Post by zuthal on Apr 9, 2017 2:12:15 GMT
Change order-of-magnitude of unit displayed/number of sigfigs? Yes, I would very much agree with that (as well as an "auto" option for people who just don't want to mess with those options).
Change units to non-SI units, on the other hand? NEVER!
|
|
|
Post by zuthal on Apr 6, 2017 11:45:40 GMT
Yield strength is where material starts to deform plastically, and ultimate tensile strength is where a material fractures - the difference between the two is a rough measure how far a material will deform plastically before it fractures, e.g. tungsten carbide has equal yield and ultimate strength, both 530 MPa, so it will shatter immediately upon starting to deform plastically.
|
|
|
Post by zuthal on Apr 5, 2017 10:35:02 GMT
The nozzle was staying nearly perfectly straight - and that would lose even less delta-V with the missiles, as those use differential thrust.
And you are right, cosine losses are by far not enough to explain the loss - a loss of 50% would require the thrust vector to be pointed at 60° to the velocity vector, on average.
|
|