Hydrogen Peroxide Monopropellant Thruster

Hydrogen Peroxide Monopropellant Thruster (propulsion/rocket/hydrogen-peroxide-monopropellant-thruster)

Use when the task is sizing and assessing a hydrogen peroxide monopropellant thruster for spacecraft reaction control: high-test hydrogen peroxide (HTP) decomposes catalytically over a silver catalyst bed and the hot steam-oxygen product gas expands through a nozzle to produce a small thrust for attitude control. This leaf implements the peroxide station model in pure Python, stdlib only: the decomposition products and the net decomposition heat release at a documented peroxide concentration w with the water dilution, the adiabatic decomposition (chamber) temperature from the Hess-law energy balance, and the frozen-composition isentropic expansion of the steam-oxygen product mixture to the vacuum exhaust velocity, the vacuum specific impulse and the propellant mass flow at the thrust point, plus an advisory silver-catalyst-bed band verdict. It pairs with propulsion/rocket/hydrazine-monopropellant-thruster as the other catalytic station model in the pack and with propulsion/rocket/rocket-engine-cycle for the feed system that supplies the peroxide. The boundary is strict: this leaf is the decomposition station math, not a feed cycle model, not a nozzle hardware sizer, not a tank sizer and not an attitude control law.

Domain quick reference

• Decomposition: 2 H2O2(l) -> 2 H2O(g) + O2(g), exothermic. At peroxide mass concentration w (H2O2 fraction in water), the dilution water carried in the feed vaporizes into the products: n_w = (1-w)/w * M_H2O2/M_H2O moles of liquid dilution water per mole of H2O2 fed; products n_h2o = 1 + n_w and n_o2 = 0.5, total moles n_tot = 1.5 + n_w. Product mass closes on the feed mass at every w.
• Net heat release (Hess-law balance at 298.15 K, products all vapor): Q(w) = Q_BASE - n_w * DELTA_H_VAP_H2O_298, with Q_BASE = 54046.4 J/mol the gas-product decomposition release. Linear and strictly increasing in w: 44814.925553 J/mol at w = 0.90, 54046.4 J/mol (Q_BASE exactly) at w = 1.0.
• Heat capacities: quadratic fits cp(T) = a + bT + cT^2 in J/(mol K) through reference points (298.15, 1000, 2000 K): H2O(g) (33.59, 41.27, 51.20), O2(g) (29.38, 34.86, 37.75).
• Adiabatic decomposition temperature T_c: the root of product sensible heat from T_REF to T_c equaling Q(w), where the sensible heat integrates the mixture heat capacity; the monotone left side makes the bisection on [298.15, 2600] K close the unique root.
• Mixture gas: M_mix = feed mass per mole H2O2 / n_tot, R_mix = 8314.462618 / M_mix J/(kg K), and the isentropic exponent gamma = cp_mix / (cp_mix - R_univ) with cp_mix the mole-fraction-weighted frozen mixture heat capacity, evaluated at the chamber state.
• Vacuum expansion (fully expanded, p_e = 0): v_e = sqrt(2 gamma/(gamma -
  1. R_mix T_c), vacuum specific impulse Isp = v_e / g0 with g0 = 9.80665 m/s^2, and propellant mass flow at the thrust point mdot = F / v_e (the vacuum thrust F = mdot * v_e carries no exit-pressure term).
• Concentration domain (documented, enforced): w in [0.85, 1.0], the published silver-catalyst HTP monopropellant service range (85 to 98 percent by weight); below 0.85 the dilution-water vaporization load dominates the release and the model refuses.
• Silver-catalyst-bed operating band (reference-only, advisory): 823.15 to 1234.93 K (550 C to the 961.78 C silver melting point), published reference data, never enforced.
• Units are SI throughout: K, J/mol, g/mol, J/(kg K), m/s, s, N, kg/s.
• ECSS frames the spacecraft propulsion context; the relations above are standard engineering methodology, summary-only.

Workflow

1. Fix the duty point: the required vacuum thrust F in N and the peroxide concentration w in [0.85, 1.0] (the water dilution).
2. Decompose: dilution_water_moles(w) gives the dilution water, product_mole_numbers(w) the steam-oxygen product moles and total_product_moles(w) the mixture total.
3. Energy release: decomposition_heat_released(w) gives the net decomposition heat release at the reference state, J per mole H2O2 fed.
4. Chamber temperature: decomposition_temperature(w) solves the peroxide decomposition energy balance by bisection for the adiabatic decomposition temperature T_c in K; product_heat_capacity(w, t_k) and product_sensible_heat(w, t_k) sample the mixture heat capacity and sensible heat at any temperature.
5. Composition: product_mole_fractions(w) and product_mass_fractions(w) give the steam-oxygen mixture composition.
6. Mixture gas: mixture_molar_mass(w), mixture_gas_constant(w), and mixture_gamma(w, T_c) give the frozen-composition isentropic exponent at the chamber state.
7. Expand to vacuum: vacuum_exhaust_velocity(w) gives v_e, then vacuum_specific_impulse(w, g0) the vacuum specific impulse and propellant_mass_flow(F, w) the peroxide flow at the thrust point.
8. Advisory check: within_silver_catalyst_bed_band(T_c) reports whether the decomposition temperature sits inside the documented silver-catalyst-bed band.
9. Confirm the deterministic checks and the domain guards with the contract test scripts/test_hydrogen_peroxide_monopropellant_thruster.py.

Worked example

A 1 N RCS thruster at peroxide concentration w = 0.90, the same design at 22 N, and the query-2 concentration-limit points at w = 0.85 and w = 0.98.

• 1 N point, w = 0.90: per mole of H2O2 fed, dilution water n_w = 0.209789072881 mol; products 1.209789072881 mol H2O + 0.5 mol O2 (n_tot = 1.709789072881 mol; mole fractions 0.707566267717 H2O and 0.292433732283 O2; mass fractions 0.576669249865 H2O and 0.423330750135 O2); net heat release Q = 44814.925553 J/mol; mixture molar mass 22.1045329441 g/mol with R_mix = 376.1428770760 J/(kg K); decomposition temperature T_c = 1024.2354582656 K; gamma at the chamber state 1.2656230167; vacuum exhaust velocity v_e = 1916.0668272739 m/s; vacuum specific impulse Isp = 195.3844408920 s; propellant mass flow at 1 N mdot = 0.000521902465 kg/s (0.521902465 g/s); silver-catalyst-bed band verdict True.
• 22 N point, w = 0.90: identical station numbers (n_w, products, Q, M_mix, R_mix, T_c, gamma, v_e, Isp, verdict), with propellant mass flow mdot = 22 / 1916.0668272739 = 0.011481854227 kg/s (11.481854227 g/s).
• Concentration-limit points at 22 N: w = 0.85 gives T_c = 901.7013222428 K, v_e = 1785.8078417405 m/s, Isp = 182.1017209486 s and mdot = 0.012319354572 kg/s, verdict True; w = 0.98 gives T_c = 1221.3719212069 K, v_e = 2109.8144943685 m/s, Isp = 215.1412046283 s and mdot = 0.010427457039 kg/s, verdict True. The 98 percent point leaves about 13.6 K of margin below the silver melting ceiling.
• Pure-peroxide heating-only bound, w = 1.0: no dilution water; Q(1.0) = 54046.400000 J/mol equals Q_BASE exactly; T_c = 1271.0022500679 K, v_e = 2155.7580276312 m/s, Isp = 219.8261412033 s, and the band verdict is False (above the silver melting ceiling, which is why service concentration on silver beds is capped near 98 percent).
• Read-off: the 1 N duty needs 0.521902465 g/s of 90 percent HTP at an ideal vacuum Isp of 195.3844408920 s with a 1024.235 K decomposition temperature inside the reported silver-bed band; the sweep shows T_c and Isp rising monotonically from 901.7 K / 182.1 s at 85 percent to the pure-peroxide bound 1271.0 K / 219.8 s at 100 percent, with the chamber gamma falling mildly from 1.2745 to 1.2509 as the mixture dries. The ideal-model impulses sit at or above the published real-engine vacuum class of roughly 150 to 190 s because real thrusters carry nozzle efficiency and finite-expansion losses this leaf's fully expanded ideal vacuum form does not model; the published class stays reference-only.

Verification

• Confirm dilution_water_moles(0.90) returns 0.209789072881, decomposition_heat_released(0.90) returns 44814.925553 J/mol and decomposition_temperature(0.90) returns 1024.2354582656 K.
• Confirm mixture_molar_mass(0.90) returns 22.1045329441 g/mol, mixture_gas_constant(0.90) returns 376.1428770760 J/(kg K), and mixture_gamma(0.90, 1024.2354582656) returns 1.2656230167.
• Confirm vacuum_exhaust_velocity(0.90) returns 1916.0668272739 m/s, vacuum_specific_impulse(0.90) returns 195.3844408920 s, and propellant_mass_flow(1.0, 0.90) returns 0.000521902465 kg/s.
• Confirm the product mass closes on the feed mass at every w (rel err at or below 2.047e-16), the sensible-heat residual at each solved T_c is below 1e-9 J, and decomposition_temperature(0.90) is bit-identical on repeated calls (deterministic, no RNG).
• Confirm every w outside [0.85, 1.0] or not finite, every non-positive sample temperature, g0 and thrust, and every non-finite band temperature raises ValueError, and that the endpoints T_c(0.85) = 901.701 K and T_c(1.0) = 1271.002 K plus the advisory band verdicts reproduce the published class without enforcing it.
• Run the contract test offline: python3 scripts/test_hydrogen_peroxide_monopropellant_thruster.py (30 tests, deterministic).

Related leaves

• propulsion/rocket/hydrazine-monopropellant-thruster: the other catalytic decomposition station in the pack, N2H4-specific end to end with a different energy balance and product mixture.
• propulsion/rocket/rocket-engine-cycle: the feed cycle that supplies the peroxide; its monopropellant row is a hydrazine feed-table entry only.
• propulsion/rocket/nozzle-design and the nozzle leaves: the expansion hardware, throat area solve and exit pressure terms this leaf does not do.
• propulsion/rocket/cold-gas-thruster: the inert gas RCS alternative, no catalytic chemistry.
• propulsion/electric/electrothermal-thruster: the electrically heated propellant alternative (NH3, N2, H2, He), a different energy source.
• propulsion/rocket/propellant-selection: the propellant-family classification that lists H2O2 as a storable bipropellant oxidizer, a different context from this decomposition station model.

Pitfalls

• Solving for the peroxide concentration: w is a documented input, never solved; this model performs no chemical-equilibrium composition iteration.
• Treating the mixture as a constant-gamma gas: gamma is evaluated at the chamber state from the mole-fraction-weighted frozen composition heat capacity and falls mildly from 1.2745 (water-rich, w = 0.85) to 1.2509 (pure peroxide, w = 1.0).
• Adding an exit-pressure thrust term: the exhaust velocity here is the fully expanded vacuum form of the decomposed steam-oxygen gas only; nozzle sizing, area ratio and any (Pe - Pa) * Ae term belong to the nozzle leaves.
• Quoting the ideal impulse as a real engine performance: real thrusters run near 150 to 190 s vacuum because of nozzle efficiency and finite-expansion losses; the ideal frozen values (182 to 220 s across w) are the loss-free account and the published class stays reference-only.
• Treating the silver-catalyst-bed band as an enforced limit: the band verdict is an advisory boolean report; the pure-peroxide point at 1271.002 K sits above the reported silver melting ceiling, which is exactly why service concentration on silver beds is capped near 98 percent.
• Using the model beyond its boundary: this leaf is the peroxide decomposition station model, not a feed-cycle power balance, not a tank sizer and not a nozzle hardware sizer.

Behavior contract (gate 3)

Run the deterministic contract test (stdlib unittest, offline):

python3 scripts/test_hydrogen_peroxide_monopropellant_thruster.py

The test covers the worked-example contract (dilution, products, heat release, decomposition temperature 1024.235 K at w = 0.90 and 901.701 K at w = 0.85, mixture gas constant, isentropic exponent, exhaust velocity 1916.067 m/s, vacuum specific impulse 195.384 s, mass flow 0.000521902 kg/s at 1 N), the mass-closure and mole/mass-fraction-sum identities, the monotone five-point concentration sweep, the Hess-law energy-balance residual closure, the term-by-term exhaust-velocity identity and the finite-pressure isentropic form against the vacuum limit, the frozen mass-flow linearity, the band-verdict semantics at the worked points and closed boundaries, determinism, the 16-function public API with no sibling-leaf outputs, and ValueError rejection of non-physical concentrations, temperatures, gravity and thrust values. The suite passes under the stdlib-only interpreter with no exact-float equality asserts on computed sums.

Compliance

• Standards referenced, not reproduced: ECSS E-ST-35 is a free ESA download (ecss.nl/standards); the peroxide decomposition relations above are standard engineering methodology with published reference data, summary-only per standards-map.yaml.
• compliance: STANDARDS-REF, gated: false.