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Eclipse Time

CurrentModule = SatelliteAnalysis

using SatelliteAnalysis

The eclipse time is the period the satellite does not receive sunlight due to the Earth shadow. This information is paramount for mission design since it directly interferes in the power and thermal subsystems.

We can compute the eclipse time of a satellite using the function:

eclipse_time_summary(orbp::OrbitPropagator; kwargs...) -> DataFrame

This function computes the eclipse time summary for the orbit propagator orbp. The summary is computed as the total time the object stays in the sunlight, penumbra, and umbra regions per orbit at each day. The algorithm was adapted from [1].

The following keywords are available:

  • num_days::Number: Number of days in which the analysis will be performed. (Default = 365)
  • step::Number: The step in which the propagation will occur. Notice that this function has a crossing estimation to accurately estimate the transition between the regions. However, if this step is very large, we may miss some small regions. If it is negative, it will be selected as the time in which the mean anomaly advances 0.5°. (Default = -1)
  • unit::Symbol: Select the unit in which the results will be generated. The possible values are:
    • :s for seconds (Default);
    • :m for minutes; or
    • :h for hours.

The function returns a DataFrame with three columns:

  • sunlight: Total sunlight time per orbit at each day [unit].
  • penumbra: Total penumbra time per orbit at each day [unit].
  • umbra: Total umbra time per orbit at each day [unit].

The unit of each column is stored in the DataFrame using metadata.

!!! note

If we want to verify the current lighting condition in a satellite (sunlight, umbra, or
penumbra), see the function [`lighting_condition`](@ref).

Examples

We will compute the eclipse time of the Amazonia-1 mission for one year. The first thing we need to do is define the orbit:

jd₀ = date_to_jd(2021, 1, 1)

orb = KeplerianElements(
    jd₀,
    7130.982e3,
    0.001111,
    98.405 |> deg2rad,
    ltdn_to_raan(10.5, jd₀),
    π / 2,
    0
)

The next step is to define the desired propagator:

orbp = Propagators.init(Val(:J2), orb)

Now, we can use the function eclipse_time_summary to obtain the eclipse time information for each day of the year:

df = eclipse_time_summary(orbp; unit = :m)

Finally, we can use the DataFrame to analyze the result. For example, the maximum eclipse time in an orbit is:

maximum(df.penumbra .+ df.umbra)

i.e., 34.66 minutes.

References

  • [1] Longo, C. R. O., Rickman, S. L (1995). Method for the Calculation of Spacecraft Umbra and Penumbra Shadow Terminator Points. NASA Technical Paper 3547.