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Post by tessfield on Nov 19, 2016 16:51:30 GMT
It would be pretty cool if we could figure out what the cutoff point is for Chemical Engines, ship weight wise.
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erik
New Member
Posts: 34 
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Post by erik on Nov 19, 2016 17:19:23 GMT
Are we sure that decane is the best fuel for resistojets? What are the relevant properties? I mean, my first and without a doubt unoptimized try at a resistojet for a hydrogen deuteride tanker came out like this:  edit: looks like several fuels can hit 12+ km/s pretty easily. Not without penalty to trust per power ratio though. |
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Post by apophys on Nov 19, 2016 17:45:43 GMT
From my early testing, the weight of the reactor + radiators associated with a resistojet make it just slightly worse than an NTR that would give the same dV for the ship. That might have changed, as I developed better reactors since then. Also, I didn't try every propellant.
Edit: I meant in terms of total ship mass and cost.
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erik
New Member
Posts: 34
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Post by erik on Nov 19, 2016 18:53:54 GMT
From my early testing, the weight of the reactor + radiators associated with a resistojet make it just slightly worse than an NTR that would give the same dV for the ship. That might have changed, as I developed better reactors since then. Also, I didn't try every propellant. Its true for acceleration, my methane NTR provides 1800 N/kg(no gimbal). Resistojet + NTR + radiator only about 16 N/kg. Both could be made a bit better, but still. However, those resistojets' reactors could also power the ships weaponry(for a ship where you want high thrust) or you could sacrifice 99 % of acceleration to maintain propulsion system's mass fraction but to increase dV. In case my of my methane engines, 6.25 km/s to 7.53 km/s would make 20 % increase in dV. Majority of the system weight is in reactor and radiators, so if you're going to have them any way for weaponry, resistojets have almost triple the thrust to weight ratio of the NTR, 4950 N/kg! I think resistojets have the potential to be very useful on ships with large lasers or unarmed/unarmored ships that don't need to get too close to massive bodies and aren't in a hurry. I need to build at least ethane, hydrogen and hydrogen deuteride engines too and see how they compare and just what kind of system masses are required to match thrust, and at what mass ratios is it worthwhile to swap from NTR to resistojet or back. |
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Post by someusername6 on Nov 19, 2016 19:35:25 GMT
I think the main use case of resistojets is that its power can be shared with other modules (like weapons) when they are not in use, while the power of NTRs can't. I use them mostly for turning around in tactical combat.
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Post by someusername6 on Nov 19, 2016 19:45:55 GMT
Here's the 1.33 kW "snickers" reactor, by kaiserwilhelm on the reactors thread. |
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Post by zuthal on Nov 19, 2016 22:13:16 GMT
I think the main use case of resistojets is that its power can be shared with other modules (like weapons) when they are not in use, while the power of NTRs can't. I use them mostly for turning around in tactical combat. Also, resistojets do not pose any radiation hazard, unlike NTRs - meaning that you can put them in places that are not behind a shadow shield. |
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Post by apophys on Nov 20, 2016 6:30:02 GMT
Reposted from the reactor thread - a 25GW reactor. We need moar power! | Name | Author | Power | Temp. | Price | Mass | Shielded | | 25GW Standard II | apophys | 25.1 GW | 2400K | 12.3 Mc | 269t | Yes |
ThermoelectricFissionReactorModule 25.1 GW Thermoelectric Fission Reactor
ReactorCoreDimensions_m 0.33 0.49
NuclearReactor
Coolant Sodium
Moderator Boron Nitride
ModeratorMass_kg 0
Fuel U-233 Dioxide
FuelMass_kg 251
FuelEnrichment_Percent 0.97
ControlRodComposition Boron Nitride
ControlRodMass_kg 303
NeutronReflector Diamond
ReflectorThickness_m 0.5
AverageNeutronFlux__m2_s 2.2e+020
InnerTurbopump
Composition Diamond
PumpRadius_m 2.6
RotationalSpeed_RPM 460
ThermocoupleInnerDimensions_m 30 30
Thermocouple
PTypeComposition Tungsten
NTypeComposition Tantalum
Length_m 0.001
ThermocoupleExitTemperature_K 2400
OuterCoolant Sodium
OuterTurbopump
Composition Boron
PumpRadius_m 1.1
RotationalSpeed_RPM 580
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Post by kaiserwilhelm on Nov 20, 2016 13:07:23 GMT
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Post by ash19256 on Nov 24, 2016 1:27:49 GMT
Here's a revamp of the 10 MW LRR that produces slightly more power. Only had to drop the output temperature by 100 K, from 2500 K to 2400 K.  |
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Post by apophys on Nov 24, 2016 1:54:29 GMT
That's nearly 50% heavier than the currently listed 2500K 10MW reactor, and about double the price. Not an upgrade in any way, as far as I can see.
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Post by ash19256 on Nov 24, 2016 2:35:10 GMT
That's because I was using the 10 MW Long Rod Reactor designed by tessfield as a base. Here's the version created when I took the currently listed reactor and changed the output temperature.  |
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Post by targetx on Nov 24, 2016 10:05:49 GMT
You can get 4.5km/sec exhaust velocity from semi heavy water and its very dense. The only trouble seems to be when the tanks get hit by something extremely hot, the propellent boils off all at once nearly, chucking the spacecraft into a new orbit. Maybe that's a bug, Im not sure
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Post by tessfield on Nov 24, 2016 23:20:35 GMT
Thanks for the upgraded reactor ash19256! I'll update it now Thanks for the tip targetx! I'll add it too! |
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Post by ash19256 on Nov 26, 2016 2:00:55 GMT
Thanks for the upgraded reactor ash19256 ! I'll update it now Thanks for the tip targetx ! I'll add it too! You should probably hang onto the reactor I used as a base for that one, and just add a note saying to change the output temperature. That's the only change I made, and it's a pretty simple tweak to do when recreating the listed reactor. |
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