Nuclear Rocket Turbopump Cycle Calculator
NTP Engine Systems Engineering: Model turbopump shaft power balance, closed expander vs hot bleed cycle thermodynamics, and net specific impulse efficiency.
Engine Cycle & Operating Pressures
Turbopump Power Balance & Specific Impulse
Recommended Tools & Equipment
Tested hardware and components for high reliability
Nuclear Thermal Propulsion Turbopump Cycles
Turbopumps feed low-pressure liquid hydrogen from cryogenic storage tanks into the nuclear reactor core at high pressure. Selecting the thermodynamic drive cycle determines maximum engine Isp and mechanical complexity.
1. Turbopump Power Balance
The shaft power generated by the gas turbine must match the hydraulic power demanded by the liquid hydrogen centrifugal pump:
P_shaft = ( ṁ_total · ΔP_pump ) / ( ρ_LH2 · η_pump ) = ṁ_turb · c_p · ΔT_turb · η_turb
where $\dot{m}_{turb} = \dot{m}_{total}$ for closed expander cycles, or $\dot{m}_{turb} = \text{bleed} \cdot \dot{m}_{total}$ for bleed cycles.
Frequently Asked Questions
Why does a liquid hydrogen turbopump require immense shaft power?
Because liquid hydrogen has an exceptionally low density (~71 kg/m³, 14 times lighter than water), delivering high chamber pressure (45–60 bar) requires enormous volumetric flow rates. A 30 kg/s flow rate requires pumping over 420 liters per second of cryogenic fluid, demanding 2 to 5 Megawatts of turbopump shaft power.
What is the key advantage of the Closed Expander Cycle over the Hot Bleed Cycle in nuclear rockets?
The Hot Bleed cycle dumps approximately 3% to 4% of total hydrogen propellant overboard through auxiliary turbine exhaust nozzles, penalizing engine specific impulse by 25 to 40 seconds. The Closed Expander cycle heats 100% of the hydrogen in reactor core tie-tubes and regeneratively routes all turbine exhaust back into the reactor core, preserving maximum vacuum Isp (~900 s).
What are reactor core "tie-tubes" in expander-cycle nuclear engines?
Tie-tubes are structural non-fueled moderator elements containing zirconium hydride ($ZrH$) that structurally support the hexagonal fuel bundle against vibration and drag forces. In an expander cycle, cryogenic hydrogen flows through these tie-tubes first, acting as a heat exchanger to pick up 300–400 K of heat to drive the turbine before entering the fueled core.