Solar Radiation Pressure

Author: Tianjiang Says

Website: https://cislunarspace.cn

Definition

Solar Radiation Pressure (SRP) is the force exerted on a spacecraft by photons from the Sun. In cislunar space, where atmospheric drag is absent and the Earth's magnetic field has negligible influence, SRP becomes one of the primary environmental perturbations affecting spacecraft orbits.

Formula

The SRP acceleration is given by:

aSRP=kCRS0cAm(R0R)2n^a_{SRP} = k C_R \frac{S_0}{c} \frac{A}{m} \left(\frac{R_0}{R}\right)^2 \hat{n}

where:

  • kk: shadow factor (1 in sunlight, 0 in shadow)
  • CRC_R: reflection coefficient (1 for diffuse, 2 for specular reflection)
  • S0S_0: solar constant (≈1367\approx 1367 W/m²)
  • cc: speed of light
  • A/mA/m: area-to-mass ratio of the spacecraft
  • R0R_0: reference distance (1 AU)
  • RR: distance from the Sun
  • n^\hat{n}: unit vector from the spacecraft to the Sun

The solar radiation pressure at 1 AU is approximately 4.56 μN/m².

Effects on DRO Orbits

For spacecraft in DRO orbits:

  • Long-term perturbation: SRP causes gradual orbit evolution over time
  • Eclipse effects: Periodic entry/exit of Earth's shadow creates discontinuous perturbations
  • Area-to-mass sensitivity: Spacecraft with large solar panels are more affected
  • Station-keeping implications: SRP must be accounted for in orbit keeping strategies

References

  • Chen Yuju. DRO Orbit Design and Control Research for Cislunar Space Situation Awareness[D]. 2024.