Tool · efficiency to cost

What one percent of efficiency weighs.

Every watt a discharge stage does not deliver becomes heat. Heat needs a path and a radiator, which are mass; mass is launch cost; and the same heat raises component temperature, which shortens life. Move the sliders. Every parameter is an estimate you can replace with your own.

Inputs

Power delivered to the thruster's discharge.
The design under evaluation.
What you compare against. vidyut's discharge-stage design target is 98%.
Heat path plus radiator. Spacecraft radiators reject roughly 200–350 W/m² at 5–10 kg/m², i.e. 0.015–0.05 kg/W before margins.
Hot-case margin, end-of-life coating degradation, structure and mounting, worst-case sun angle. 1.3–2.0 is common.
Rideshare to LEO ~$6,000/kg; dedicated or GEO delivery far higher.
The thermal design choice. Heat above the reference design is either radiated away by added mass (left) or accepted as a hotter unit (right). 100% mass holds temperature and life; 0% holds mass and pays in life.
°C rise at the hottest component per watt of stage loss that is not radiated away, through the baseplate and mounting.
Expected life of the reference design. Lifetime is taken to halve for every 10 °C the hotspot runs above the reference (the common Arrhenius rule of thumb).
Value of the unit and its share of the mission, $ M. The fraction of expected life lost is priced against this, so the life cost is bounded by it.
heat generated by the stage
thermal mass carried (path + radiator × margin)
launch cost of that mass
hotspot temperature change versus the reference design
expected lifetime at that temperature
value of life lost versus reference
loss = P·(1−η)/η  ·  extra = loss − lossref  ·  mass = (lossref + f·extra) · kg/W · X  ·  launch = mass · $/kg
ΔT = (1−f)·extra · θ  ·  life = life₀ · 2^(−ΔT/10)  ·  life cost = unit value · (1 − life/life₀)  ·  f = share of extra heat radiated

Illustrative model, not a flight thermal analysis. It ignores radiator view factors, heat sharing with other subsystems and the thruster's own thermal load, and it treats the hotspot rise as linear in loss. Its purpose is the shape of the trade: at kilowatt scale, efficiency is paid for in kilograms and years. See the technical note for the sources on efficiency, mass and heat.

Back to the technical note