Thermal Ramjet Nozzle and Thermal Turbojet
Chemical-fueled rockets derive their thrust from a chemical reaction that produces heat and pressure inside the rocket nozzle. Instead of pumping fuel into the rocket nozzle like a typical chemical rocket, these rocket nozzles simply include a heat exchanger connected to a reactor ; they derive their thrust from the high temperature of the reactor.
As such, these rocket nozzles may produce almost innumerable combinations of thrust and specific impulse depending upon the reactor that they are connected to and the reaction mass you're using. All sizes of thermal nozzle and turbojet function exactly the same, but they will suffer a large penalty if attached to the wrong-sized reactor.
This part must be connected directly to a reactor or [Thermal Receiver](Microwave Power Transceivers) in order to function
The ISP of a thermal rocket is dependent on the temperature of the reactor. The hotter the reactor, the higher the ISP becomes. The amount of thrust a nozzle provides is dependant on both the thermal power of the reactor / thermal receiver and the ISP. The higher the thermal power, the more thrust it produces. The higher the ISP, the less thrust it produces. The exact relation is given by the equation P=1/2 * F * ISP * G0, where P is the power of the reactor/ thermal receiver, F is the thrust it provides, ISP is it's ISP, and G0 is the force of gravity at Earth's or Kerbin's surface (9.81 m/s^2).
Thermal rocket nozzles work best in a vacuum and will lose up to 60% ISP and thrust in atmosphere.
The thermal rocket nozzle can switch between different propellants on the fly. Each option provides different multipliers of thrust and ISP. They all obey the same formula given above, with the exception of LFO and MethaLOx. The thrust of these reactions is higher than normal due to the additional chemical reaction between the fuel and oxidizer. The available options are:
- Liquid fuel: Baseline
- LFO: Much higher thrust due to the chemical reaction at the expense of a somewhat lower ISP.
- MethaLOx: LqdMethane+Oxidiser, Highest thrust of all fuels and lowest ISP.
- Kethane: Higher thrust than liquid fuel, but less ISP. Less thrust and ISP compared to LFO.
- LqdMethane: Same as Kethane.
- Water: Higher thrust and lower ISP compared to Kethane or LqdMethane.
- Ammonia: Slightly lower thrust and higher ISP compared to Kethane or LqdMethane.
The thermal turbojet operates on a similar principle to the thermal rocket. However, instead of using an onboard reaction mass, it uses the atmosphere as propellant. Since they do not combust anything, they will function on any planetary body that has an atmosphere, regardless of whether it has oxygen. Thus, the thermal turbojet requires no fuel of it's own and can fly as long as the attached reactor has fuel, which can be several years in the case of a nuclear reactor. They will automatically throttle themselves based on the amount of intake air you are getting, so unlike regular turbojets they will not flame out under most conditions.
Thermal turbojets use integrated turbomachinery in order to compress the incoming atmosphere. This has the practical result of reducing the ISP but increasing the thrust. This means that even though a nuclear thermal rocket has very low thrust, a nuclear thermal turbojet will have enough thrust to comfortably fly in-atmosphere. The low ISP also means that the thermal turbojets do not function well at high altitudes, and thrust will drop off sharply as you run low on intake air.
The thermal turbojet can also be upgraded to a hybrid thermal rocket, at which point it is capable of toggling to an internal fuel source. In this mode, it functions identically to a thermal rocket nozzle. This makes it the thermal equivalent of a RAPIER engine and is ideal for spaceplanes.
| Fission (Uranium) | Thermal Power /MW | Thrust /kN | Specific Impulse /s | Reactor Mass /t | Nozzle Mass /t | TWR |
|---|---|---|---|---|---|---|
| 62.5cm (Basic) | 1.5 | 0.33 | 915 | 0.34 | 0.11 | 0.08 |
| 62.5cm (Upgraded) | 4.5 | 0.33 | 2793 | 0.34 | 0.11 | 0.07 |
| 1.25m (Basic) | 40 | 8.9 | 915 | 2.5 | 0.4 | 0.31 |
| 1.25m (Upgraded) | 120 | 8.75 | 2793 | 2.5 | 0.4 | 0.31 |
| 2.5m (Basic) | 500 | 111.25 | 915 | 14 | 1.5 | 0.73 |
| 2.5m (Upgraded) | 1500 | 109.37 | 2793 | 14 | 1.5 | 0.72 |
| 3.75m (Basic) | 3000 | 667.52 | 915 | 43 | 3 | 1.48 |
| 3.75m (Upgraded) | 9000 | 656.21 | 2793 | 43 | 3 | 1.45 |
| Fission (Thorium) | Thermal Power /MW | Thrust /kN | Specific Impulse /s | Reactor Mass /t | Nozzle Mass /t | TWR |
|---|---|---|---|---|---|---|
| 62.5cm (Basic) | 2.07 | 0.42 | 994 | 0.32 | 0.11 | 0.1 |
| 62.5cm (Upgraded) | 6.21 | 0.42 | 3032 | 0.32 | 0.11 | 0.1 |
| 1.25m (Basic) | 55.2 | 11.31 | 994 | 2.34 | 0.4 | 0.42 |
| 1.25m (Upgraded) | 165.6 | 11.12 | 3032 | 2.34 | 0.4 | 0.41 |
| 2.5m (Basic) | 690 | 141.42 | 994 | 13.04 | 1.5 | 0.99 |
| 2.5m (Upgraded) | 2070 | 139.02 | 3032 | 13.04 | 1.5 | 0.97 |
| 3.75m (Basic) | 4140 | 848.53 | 994 | 40 | 3 | 2.01 |
| 3.75m (Upgraded) | 12420 | 834.14 | 3032 | 40 | 3 | 1.98 |
| Particle Bed | Thermal Power /MW | Thrust /kN | Specific Impulse /s | Reactor Mass /t | Nozzle Mass /t | TWR |
|---|---|---|---|---|---|---|
| 62.5cm (Basic) | 3.5 | 0.93 | 766 | 0.35 | 0.11 | 0.2 |
| 62.5cm (Upgraded) | 5.8 | 0.82 | 1432 | 0.35 | 0.11 | 0.18 |
| 1.25m (Basic) | 85 | 22.59 | 766 | 1.83 | 0.4 | 1.03 |
| 1.25m (Upgraded) | 142 | 20.19 | 1432 | 1.83 | 0.4 | 0.92 |
| 2.5m (Basic) | 770 | 204.67 | 766 | 9.72 | 1.5 | 1.86 |
| 2.5m (Upgraded) | 1285 | 182.7 | 1432 | 9.72 | 1.5 | 1.66 |
| 3.75m (Basic) | 4500 | 1196.14 | 766 | 30.29 | 3 | 3.66 |
| 3.75m (Upgraded) | 7500 | 1066.32 | 1432 | 30.29 | 3 | 3.27 |
| Fusion (D/T) | Thermal Power /MW | Thrust /kN | Specific Impulse /s | Reactor Mass /t | Nozzle Mass /t | TWR |
|---|---|---|---|---|---|---|
| 62.5cm (Basic) | 20.9 | 1.87 | 2281 | 0.28 | 0.11 | 0.49 |
| 62.5cm (Upgraded) | 62.7 | 2.38 | 5376 | 0.28 | 0.11 | 0.62 |
| 1.25m (Basic) | 166.25 | 14.85 | 2281 | 2.25 | 0.4 | 0.57 |
| 1.25m (Upgraded) | 498.75 | 18.9 | 5376 | 2.25 | 0.4 | 0.73 |
| 2.5m (Basic) | 2163.15 | 158.11 | 2786 | 9.21 | 1.5 | 1.51 |
| 2.5m (Upgraded) | 6489.45 | 193.64 | 6825 | 9.21 | 1.5 | 1.84 |
| 3.75m (Basic) | 17305.2 | 1264.88 | 2786 | 38.11 | 3 | 3.14 |
| 3.75m (Upgraded) | 51915.6 | 1549.15 | 6825 | 38.11 | 3 | 3.84 |
| AIM | Thermal Power /MW | Thrust /kN | Specific Impulse /s | Reactor Mass /t | Nozzle Mass /t | TWR |
|---|---|---|---|---|---|---|
| 3.75m (Basic) | 14793 | 967.04 | 3116 | 12.79 | 3 | 6.24 |
| 3.75m (Upgraded) | 44379 | 1545.71 | 5847 | 12.79 | 3 | 9.98 |
| Antimatter | Thermal Power /MW | Thrust /kN | Specific Impulse /s | Reactor Mass /t | Nozzle Mass /t | TWR |
|---|---|---|---|---|---|---|
| 1.25m (Basic) | 5000 | 556.18 | 1831 | 2 | 0.4 | 23.62 |
| 1.25m (Upgraded) | 15000 | 364.6 | 8379 | 2 | 0.4 | 15.49 |
| 2.5m (Basic) | 40000 | 2972.08 | 2741 | 16 | 1.5 | 17.31 |
| 2.5m (Upgraded) | 120000 | 1706.17 | 14324 | 16 | 1.5 | 9.94 |
| 3.75m (Basic) | 135000 | 8117.6 | 3387 | 54 | 3 | 14.52 |
| 3.75m (Upgraded) | 405000 | 4586.8 | 17983 | 54 | 3 | 8.2 |
To modify for LFO - multiply thrust by 3.7 and multiply Isp by 0.6
To modify for MethaLOx - multiply thrust by 6.61 and multiply Isp by 0.34
To modify for Kethane or LqdMethane - multiply thrust by 1.79 and multiply Isp by 0.56
To modify for Water - multiply thrust by 2.13 and multiply Isp by 0.47
To modify for Ammonia - multiply thrust by 1.59 and multiply Isp by 0.63