V1.1 Size Calculation (200 N)
February 5, 2026
After completing the V1.0 design with 150 N thrust, thermal analysis revealed a problem which the engine was too small for effective regenerative cooling. This entry documents the transition to V1.1. The previous design established basic sizing from CEA results. However, when we put these data into RPA, we find that the throat diameter is only 8 mm; to achieve acceptable wall temperatures (<900 K), channel width dropped below 0.5 mm and make them became unmachineable. We couldn’t even use liquid film cooling because the required orifice was simply too small.
New Solution
V1.1 increases both thrust and chamber pressure. This results in larger throat diameter which makes cooling channels manufacturable (>1 mm width). Higher chamber pressure provides two benefits: it improves $I_{sp}$, partially offsetting the mass flow increase, and it allows higher coolant pressure for better convective heat transfer.
From the throat area relation:
$$A_t = \frac{\dot{m} c^*}{p_c} \propto \frac{F}{p_c \cdot I_{sp}}$$
Increasing thrust faster than chamber pressure gives the needed geometric scaling for thermal management.
Report Links
- CEA report and structural report are collected here