Follow watts from source to exhaust
List the source, storage, conversion electronics, RF or high-voltage stage, feed system, magnets and controls. Report power at each boundary. Comparing power measured at an RF generator with power measured at another engine’s discharge can quietly omit different losses. Our proposed comparison uses total input to the propulsion subsystem, with the spacecraft power-source mass reported separately.
The thrust and exhaust-speed trade
For a single ideal nonrelativistic jet, Pjet = ½ṁvₑ² and F = ṁvₑ. Therefore F = 2ηPinput/vₑ when η describes conversion of the selected input power into effective directed jet kinetic power. This is a screening relationship, not a universal thruster map. At fixed available power and efficiency, faster exhaust reduces thrust while saving propellant per unit impulse. Mission duration decides whether that exchange is useful.
Heat must reach a radiator
Not every watt outside the effective axial jet heats the spacecraft: some leaves as radiation or non-axial plume energy. Allocate the losses before sizing cooling. A radiator must be thermally connected to the components that produce heat. Good emissivity alone cannot fix a poor contact, a temperature-sensitive component or an obstructed view of space.
An explicit first estimate
For a uniform gray radiator facing an idealized environment with unit view factor, Q = εσA(T⁴ − Tenv⁴). Use kelvin, σ = 5.670374419 × 10⁻⁸ W m⁻² K⁻⁴ and actual emitting area. A two-sided panel has two emitting faces only if both have the assumed view. Sunlight, planetary infrared, albedo, self-viewing, temperature gradients and aging require a fuller thermal model. The calculator is an initial bound, not a flight design.
What earns a better design
Compare complete mass and operating limits at the same mission requirement. Include source degradation, eclipse operation, warm-up energy and power reserved for avionics. A proposed gain is worth pursuing if it persists after magnet mass, electronics, structure and cooling are included. Our research gate is a closed input-power ledger and a thermal allocation with stated uncertainty; no current Metric Flight hardware efficiency is implied.
A useful sensitivity study
Vary efficiency, allowed temperature and power-system mass independently. Record which input changes the mission conclusion most strongly. If the answer depends on an unmeasured efficiency near its ideal limit, that parameter becomes an early measurement priority. If cooling dominates mass over the whole plausible range, a slightly better engine nozzle may be less valuable than a different operating temperature or duty cycle.
PRIMARY SOURCES / FOLLOW THE EVIDENCE
Research behind the study
- NASA: Thermal Control, Small Spacecraft Technology ↗Radiators, heat transport and constrained spacecraft surface area.Institutional or primary research link · bibliographic details pending verificationConsult the linked record; no full-text access claim.
- ESA: Thermal Control ↗Spacecraft temperature depends on incoming environmental flux, internally generated heat and rejected heat.Institutional or primary research link · bibliographic details pending verificationConsult the linked record; no full-text access claim.
- NASA: Solar Electric Propulsion ↗Solar power, ionized propellant and advanced Hall propulsion development.Institutional or primary research link · bibliographic details pending verificationConsult the linked record; no full-text access claim.
References checked 24 October 2026. External research is not a Metric Flight result or an institutional endorsement. Source abstracts, records and accessible full text support this synthesis; individual links may require publisher access.