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Satellite Power Observation Time Estimator

The Satellite Power Observation Time Estimator calculates how long a spacecraft can support an observation when the payload and spacecraft bus are drawing from a finite usable battery-energy allowance. It is aimed at mission planning cases where an instrument run must fit within power-storage constraints, such as eclipse operations or temporarily power-limited attitudes.

The result is an energy-limited duration. It helps planners test whether a proposed observation fits inside the selected battery-use policy before adding other operational constraints such as thermal limits, data storage, visibility windows, or communications schedules.

Calculator inputs

Wh
%
%
W
W
Result
—
Energy-limited observation time
Usable observation energy—
Observation load—
Energy used per hour—

1. Enter battery energy
Use the battery energy capacity relevant to the planned operating condition.

2. Limit usable discharge
Set the fraction of nominal battery energy that mission rules allow for this activity.

3. Keep a reserve
Reserve part of the usable energy for contingency or post-observation operations.

4. Enter payload and bus loads
Use average electrical power during the observation, not only instrument nameplate power.

5. Review the duration
Treat the result as a power-limited upper bound and compare it with visibility and thermal constraints.

Usable observation energy = battery energy × usable depth of discharge × (1 − reserve fraction)
Observation load = payload power + bus power
Observation time = usable observation energy / observation load

The model assumes constant average power and does not model battery voltage, rate capability, temperature, degradation, converter efficiency, or other time-varying loads. Use energy values and power values that already reflect any losses you want included.

What the result means

This is the maximum continuous observation duration supported by the allocated battery energy at the entered average load.

Operational observation time may be shorter because of geometry, thermal, pointing, data, or communications constraints.

Given

  • Battery energy = 2,400 Wh
  • Usable depth of discharge = 30%
  • Reserve = 15%
  • Payload power = 420 W
  • Bus power = 310 W

Calculation
Usable energy = 2,400 × 0.30 × 0.85 = 612 Wh. Total load = 420 + 310 = 730 W. Time = 612 / 730 = 0.838 h = 50.3 min.

Result
Observation time ≈ 50.3 minutes.

Under the stated energy policy, a longer uninterrupted observation would exceed the allocated battery energy.

Why use usable depth of discharge instead of the full battery rating?

Mission operations usually protect battery life and maintain contingency energy by limiting how much nominal capacity is intentionally used. The usable percentage lets you reflect that policy.

Should bus power include heaters and communications?

Include any loads expected to be active during the observation. If a load is intermittent, use a defensible average or model separate operational phases.

Can the result exceed an orbital visibility window?

Yes. This calculator only sets an energy-based limit, so geometry, eclipse, ground contact, target visibility, thermal limits, and data capacity may produce a shorter practical observation.

What if payload power is zero?

The estimator can still calculate how long the spacecraft bus alone can operate from the allocated energy. At least one of payload or bus power must be greater than zero.

How does battery degradation affect the estimate?

Use the expected available battery energy at the mission age of interest rather than the beginning-of-life rating. That keeps degradation represented in the input instead of assuming a fixed percentage.