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Hi, Back in KSP 1.05, I did a cut n' paste job of the RAPIER engine config file. By splicing in stuff from the Juno and the NERV, I was able to make a nuclear turbojet with two operating modes : Mass 4T (one tonne heavier than the base NERV to allow for the turbomachinery). Includes built in RTG, 5 EC/Sec whether engine on or off Mode 1 (Air breathing) Used the Juno atmosphere and velocity curves, max thrust 80kn instead of 20kn. Acting as a nuclear turbojet, this mode requires no fuel, only intake atmosphere and can work in places like Duna and Eve where there is no oxygen. Mode 2 (Nuclear Thermal) Acting as the NERV, with the exception that Vacuum ISP is down to 776 but Sea Level ISP up to 660. I'm assuming that rather than a pure vacuum nozzle such an engine would use some kind of full range nozzle like the aerospike (or real world shuttle engine/proposed SABRE engine). I'm thinking of doing the above again, but is there a way to make an engine with more than two modes, by only editing the engine config file itself? The reason is, it seems plausible, technologically, to give the above engine a couple more operating modes - Mode 1.5 (Air Breathing - Afterburning) Like the base Air Breathing mode , this runs off intake atmosphere and uses jet engine Atmosphere and Velocity curves. They should probably be a similar shape to the Juno's. However, by injecting liquid fuel into the tail pipe, 50% more thrust is produced. ISP would probably be similar to the Panther in wet mode. This mode would require that the the atmosphere contains oxygen to work. The rationale is that in straight turbojet mode, power is limited by how much air the turbomachinery can handle, and how much heat the reactor can put into that air stream before temperatures get too high for the reactor or the first stage turbine. By burning fuel after the turbine, the temperature limits of the reactor and turbine can be ignored and more thrust produced with the same volume of air. Mode 2.5 (Nuclear Thermal - Afterburning) Operating in Nuclear thermal mode, max power is limited by reactor thermal output and the propellant can't be heated any higher than the reactor's max safe operating temperature. By injecting oxidizer into the liquid fuel that has been heated in the reactor, combustion occurs producing extra thrust at the cost of ISP.

I'm running an install that has Neartea's cryogenic engines and kerbal atomics installed, with the LH2-NTR option active. So the stock LV-N has been switched over to using hydrogen. Curious to use LF in an NTR engine, I have been fiddling around with a modded engine that attempts to emulate an issue that an NTR using kerosene propellant would probably encounter: carbon buildup. To attempt this, I have made the engine bimodal. One mode is high thrust, ~600 isp, uses LF and produces carbon buildup. (actually ablator, as I'd rather use existing resources) The other mode is low thrust, ~200 isp, and uses Oxidizer and the buildup/ablator. My intent is to have an engine that can use the dense LF, rather than LH2, but suffers because of it, having less stellar isp, and requiring periodic cleanings/flushings using Oxidizer to burn away carbon-rich buildup from thermally broken down kerosene. I have used a method to cause buildup that I know to be faulty: both modes have ablator as a propellant, but in the LF mode, its ratio is negative. So as the engine burns LF, the amount of ablator increases, as it burns Oxidizer, it decreases. However, I have run into an issue. Once the ablator reaches the maximum amount storable in the engine, it doesn't shut off, as I would like. I know that this is because using a negative ratio for propellant is a no-no, and it's not checked when a propellant runs max, only when it runs out. Does anyone have any tips on how I can get the engine to run only until the buildup is at the maximum amount, and shuts off once there?