compute_density_harrispriester#

namespace saltro
namespace orbits

Functions

bool compute_density_harrispriester(const Eigen::Matrix<double, 3, saltro::limits::MAX_LENGTH_TRAJ> &R, const Eigen::Matrix<double, 3, saltro::limits::MAX_LENGTH_TRAJ> &S, const int jtime_length, Eigen::Matrix<double, 1, saltro::limits::MAX_LENGTH_TRAJ> &rho)#

Compute atmospheric density using the Harris–Priester model.

Evaluates the atmospheric mass density along a spacecraft trajectory using the Harris–Priester empirical thermospheric density model. The model provides a simple representation of upper-atmosphere density as a function of altitude and solar position relative to the spacecraft.

For each trajectory sample \(k\), the density is computed as:

\[ \rho_k = \rho_{\mathrm{HP}}\!\left(\mathbf{R}_k, \mathbf{S}_k\right) \]

where:

  • \(\mathbf{R}_k\) is the spacecraft position vector (meters),

  • \(\mathbf{S}_k\) is the Sun direction vector relative to the spacecraft,

  • \(\rho_k\) is the resulting atmospheric density (kg/m³).

The Harris–Priester model accounts for the diurnal bulge in the atmosphere by interpolating between minimum and maximum density profiles based on the angle between the spacecraft position and the Sun direction:

\[ \rho_k = \rho_{\min}(h_k) + \bigl(\rho_{\max}(h_k) - \rho_{\min}(h_k)\bigr)\,f(\psi_k) \]

where \(h_k\) is altitude and \(\psi_k\) is the solar zenith angle. The weighting function \(f(\psi_k)\) models the day–night variation of density.

The output density is written as a row vector:

\[ \boldsymbol{\rho} = \begin{bmatrix} \rho_0 & \rho_1 & \cdots & \rho_{N-1} \end{bmatrix} \]

Parameters:

  • R – Spacecraft position vectors (meters). Each column corresponds to one trajectory sample in an Earth-centered frame.

  • S – Sun direction vectors (meters or unit vectors). Each column corresponds to the Sun direction at the matching trajectory sample.

  • jtime_length – Number of valid trajectory samples.

  • rho – Output atmospheric density values (kg/m³) for each trajectory sample.

Returns:

True if density computation succeeds for all samples, false otherwise.