Albedo radiation pressure modeling

[ChristopherRabotin]

High level description

Large spacecraft may be affected by albedo modeling. This is not currently supported in Nyx, but it should be and it's pretty straightforward.

Migrated from https://gitlab.com/nyx-space/nyx/-/issues/201

Requirements

What does the system need to do?

Test plans

• Test that there is an extra force upward when albedo modeling is enabled.
• Test that varying the albedo reflection coefficient will affect the orbit.

Design

A planet's albedo should be specified either as an average over the whole object or as a map returning the albedo value from the latitude and longitude of the spacecraft position. For initial data, use the values from Wikipedia

Algorithm is pretty straight forward:

• If disabled, do nothing
• Compute the sun elevation at nadir (the Sun-Planet-Probe angle should be greater than 90 degrees, else nadir is in the dark)
• Fetch the nadir pointed surface area (which is different than the normal SRP area)
• Fetch the albedo at this given location
• Compute the attenuation based on the frequency of sunlight (cf. https://www.perplexity.ai/search/Frequency-band-of-8xtYKb0AQjquLkdr6DBhaQ )
• Pass all of this data into the SRP computation module.

[ChristopherRabotin]

In the LRO OD example, I had to dramatically lower the gravity of the Moon to match the published OD solution. It's likely that the difference is actually the albedo! That would exert a negative R force in the RIC frame.