Spacecraft Mass Budget

Mass is the hardest currency in spacecraft design. Every kilogram has to be lifted to orbit, and the launch vehicle (or the rideshare port on it) sets a hard cap. A mass budget is the running ledger that tracks where every kilogram goes — subsystem by subsystem — so the team knows, at any point in the design, whether the spacecraft still fits.

This tool follows the standard first-order treatment from SMAD (Space Mission Analysis and Design, Ch. 14) and NASA / AIAA S-120 (Mass Properties Control for Space Systems). Each subsystem — structure, power, ADCS, propulsion, comms, payload, thermal, harness, avionics — carries its own dry-mass estimate plus its own contingency (also called mass-growth allowance, MGA). Contingency is a maturity-based reserve: a flight-proven box that has been built and weighed carries roughly 5%, an off-the-shelf or modestly-modified item carries roughly 10% nominal, and a new-development item whose design has not matured must reserve roughly 20%. The contingency-loaded subsystem mass is m × (1 + contingency / 100).

Summing the contingency-loaded subsystem masses gives the dry mass with contingency. Adding propellant — a sized quantity carrying no growth allowance, because it is not an estimate that can creep — gives the wet mass. The wet mass is what is checked against the launch-vehicle mass cap. The difference is the margin: margin = cap − wet mass. SMAD / AIAA S-120 margin philosophy holds that early in design — before Preliminary Design Review — a spacecraft should carry roughly 20% margin against its allocated mass, burning that reserve down as the design matures and estimates firm up. This tool flags whether the budget clears both the hard cap and that recommended reserve.

What this tool does not capture: mass properties beyond total mass (centre of gravity, moments of inertia, balance), the allocation flow-down from system to subsystem to component, separate dry / burnout / injected mass accounting against multiple launch milestones, or the formal mass-properties control board process. It is a fast trade-study roll-up for sizing and feasibility — not a substitute for a verification-grade mass-properties report.