#3400 · Science & Engineering Tool

Satellite Link Power Budget Calculator

Estimate the spacecraft electrical capacity needed to operate a satellite communications link. Combine platform load, transmitter RF output, amplifier efficiency, contact duty cycle, sunlight availability, storage efficiency, and design margin to obtain average bus demand, minimum array output during sunlight, and battery energy for eclipse operation.

Calculator

Spacecraft communications power
W
Spacecraft load excluding the transmitter input.
W
Delivered radio-frequency power.
%
RF output divided by transmitter electrical input.
%
Fraction of the day transmitting.
%
Fraction of each cycle available for generation.
%
Energy retained through charge and discharge.
%
Capacity allowance on array and battery results.

How to use this calculator

  1. Enter the mission and hardware assumptions in consistent units.
  2. Use values for one clearly defined scenario or operating case.
  3. Select Calculate to update the engineering result.
  4. Review the secondary results and stated limitation before using the estimate.

Formula

Transmitter electrical input = RF output ÷ amplifier efficiency. Average bus load = platform load + transmitter input × duty. Array power = [sunlight energy + eclipse energy ÷ storage efficiency] ÷ sunlight fraction, then × (1 + margin).

What the result means

Minimum array output is the steady sunlight-period power needed to support the modeled daily cycle and storage losses. Battery energy covers the eclipse share of average demand with the selected margin.

This energy-balance model assumes loads are distributed uniformly at the stated duty cycle. Check peak transmitter power, eclipse timing, battery depth of discharge, degradation, and thermal limits separately.

Example calculation

For a 300 W platform, 80 W RF output, 40% amplifier efficiency, 25% transmitter duty, 60% sunlight, 85% storage efficiency, and 20% margin, average bus load is 350 W, minimum array output is about 749.41 W, and eclipse battery energy is 4,032 Wh.

Tips for better results

  • Check instantaneous transmitter input as well as daily average.
  • Use end-of-life solar-array capability for final sizing.
  • Apply allowable battery depth of discharge after this energy result.
  • Model eclipse and contact overlap when duty is not uniform.
  • Include converter and harness losses if not captured elsewhere.

Frequently asked questions

Why is transmitter electrical input higher than RF output?

The power amplifier is not perfectly efficient, so it draws more electrical power than the RF power it delivers.

How does satellite sunlight fraction affect array size?

Less sunlight leaves fewer hours to serve active loads and replace eclipse energy, increasing required sunlight-period array output.

Does battery energy include depth-of-discharge limits?

No. Apply allowable depth of discharge, aging, temperature, cell balancing, and redundancy when selecting actual battery capacity.

Is transmitter duty cycle averaged over the whole day?

Yes. This screening model treats it as a daily or representative-cycle average; use a time-profile model for clustered contacts.

Why is storage efficiency applied only to eclipse energy?

Energy used directly during sunlight avoids the modeled charge-discharge round trip, while eclipse energy must pass through storage.

Inputs and units

InputUnitRole
Platform continuous loadWSpacecraft load excluding the transmitter input.
Transmitter RF outputWDelivered radio-frequency power.
Power amplifier efficiency%RF output divided by transmitter electrical input.
Daily transmitter duty%Fraction of the day transmitting.
Sunlight per orbit%Fraction of each cycle available for generation.
Storage round-trip efficiency%Energy retained through charge and discharge.
Design margin%Capacity allowance on array and battery results.

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