Reaction Control Thruster Calculator

A "bang-bang" maneuver reaches the target angle efficiently by accelerating for the first half of the turn and then decelerating for the second half, so the spacecraft arrives exactly at the target angle with zero leftover angular velocity rather than overshooting or needing a separate braking maneuver. Both the acceleration and deceleration burns consume propellant, which is why burn time in this calculator covers the entire maneuver, not just the first half.

Specific impulse measures how efficiently a thruster converts propellant mass into thrust over time -- a higher Isp means the same thrust can be sustained longer per unit of propellant, or equivalently, less propellant is needed for the same total impulse. Since propellant consumed is inversely proportional to Isp in the rocket equation, doubling Isp roughly halves the propellant needed for the same maneuver, which is why thruster chemistry (monopropellant hydrazine versus bipropellant systems) is such a significant design choice.

Computing a real moment of inertia requires knowing a spacecraft's actual mass distribution and geometry, which isn't available from just a total mass and a thruster moment arm. The uniform-sphere approximation (I = 2/5 × mass × radius²) gives a reasonable order-of-magnitude estimate for early sizing using only those two inputs, but a detailed spacecraft design should substitute the vehicle's actual computed or measured moment of inertia for a precise propellant budget.

The 1,000-maneuver figure is an illustrative mission-life assumption to translate a per-maneuver propellant cost into a rough total propellant budget, not a prediction of your specific mission's actual maneuver count. Real RCS propellant budgets are sized against the mission's actual planned attitude maneuvers, station-keeping burns, and margin for contingencies, which can be far more or fewer than 1,000 depending on mission duration and pointing requirements.