HPOP Force Models: Solar Radiation Pressure

The SRP tab of the HPOP Force Model Properties window provides a variety of options for modeling solar radiation pressure. To model solar radiation pressure (SRP) for an HPOP trajectory calculation, select Use SRP.

Model

The SRP models that are available for use with HPOP are described in the following table:

Model Description
GPS_BlkIIA_AeroT20 Aerospace T20 solar radiation pressure model for GPS block IIA.1
GPS_BlkIIR_AeroT30 Aerospace T30 solar radiation pressure model for GPS block IIR.1
GPS_BlkIIA_GSPM04a Bar-Sever GPS Solar Pressure Model 04a for block IIA.2
GPS_BlkIIR_GSPM04a Bar-Sever GPS Solar Pressure Model 04a for block IIR.2
GPS_BlkIIA_GSPM04ae Bar-Sever GPS Solar Pressure Model 04ae for block IIA.3
GPS_BlkIIR_GSPM04ae Bar-Sever GPS Solar Pressure Model 04ae for block IIR.3
Spherical SRP Solar radiation pressure model that assumes a spherical satellite.

1. O’Toole, James W., "Mathematical Description of the OMNIS Satellite Orbit Generation Program (OrbGen)", NSWCDD/TR-02/118, May 2004.

Fliegel, H.F., Gallini, T.E., Swift, E.R., "Global Positioning System Radiation Force Model for Geodetic Applications", Journal of Geophysical Research, Volume 97, No. B1, January 1992.

Fliegel, H.F., Gallini, T.E., "Solar Force Modeling of Block IIR Global Positioning System Satellites", Journal of Spacecraft and Rockets, Volume 33, No. 6, November-December 1996.

2. Bar-Sever, Y., Kuang, D., "New Empirically Derived Solar Radiation Pressure Model for Global Positioning System Satellites", IPN Progress Report 42-159, November 15, 2004.

3. Bar-Sever, Y., Kuang, D., "New Empirically Derived Solar Radiation Pressure Model for Global Positioning System Satellites During Eclipse Seasons", IPN Progress Report 42-160, February 15, 2005.

GPS SRP Model Parameters

The following parameters pertain to GPS SRP models:

Parameter Description
K1 Defines the K1 (scale) value.
K2 Defines the K2 (Y bias) value.

Spherical SRP Model Parameters

The following parameters pertain to the Spherical SRP model:

Parameter Description
Cr Defines the solar radiation pressure coefficient.
Area/Mass Ratio Defines the area-to-mass ratio to be used in SRP calculations.

General SRP Parameters

The following parameters pertain to all SRP models:

Parameter Description
Shadow Model

A shadow model accounts for the reduction in SRP caused by an eclipsing body as it obscures the sun. Select the level of precision that you want to apply to computing this effect.

    None- No model. Shadowing of the satellite will not be considered.

    Cylindrical - The cylindrical model assumes that the Sun is at an infinite distance from the satellite. All light coming from the Sun moves in a direction parallel to the Sun to satellite vector.

    Dual Cone - The dual cone model uses the actual size and distance of the Sun to model regions of full, partial (penumbra), and zero (umbra) sunlight. The visible fraction of the solar disk is used to compute SRP during penumbra.

The primary central body is always considered as an eclipsing body except for the case where the primary central body is the Sun. Extra central bodies to be evaluated for shadowing effects are determined using parent, child, and sibling relationships. The hierarchical order in the solar system consists of the Sun, which is the parent of the planets, which in turn are the parents of their moons. The set of eclipsing bodies contains the parent of the primary body (unless the parent is the Sun), the siblings of the primary body (unless the parent is the Sun) and the children of the primary body (unless the primary is the Sun). For example, if either the Earth or the Moon is the primary body then both the Earth and Moon are considered as eclipsing bodies.
Use Boundary Mitigation When the satellite crosses a shadow boundary during an integration step, the sudden change in SRP may result in a computation error for that step. Select this option if you want STK to correct for these errors.
Method to Compute Sun Position This specifies the direction of the Sun for SRP computations. Select one of the following options:
  • Apparent Sun to True CB -- takes into account the time required for light to travel from the sun to the central body.
  • Apparent -- takes into account the time required for light to travel from the sun to the position of the satellite.
  • True -- assumes that light from the sun reaches the satellite instantaneously.
Atmospheric Altitude for the shape of the central body for Eclipse

A simple model that accounts for attenuation and refraction of solar radiation through the atmosphere.

When computing SRP, STK accounts for penumbra and umbra regions of eclipse. These regions are the result of the Earth's obstruction of the Sun from the satellite’s position.

By default, STK uses the Earth’s surface shape, which corresponds to an atmospheric altitude of 0.0 km. Thus, attenuation and refraction of solar radiation through the atmosphere is not accounted for. You can increase the shape of the earth by its altitude height. Enter the altitude that you want to apply. The most common altitude used for this kind of modeling is 23 km.

Eclipsing Central Bodies

The Eclipsing Bodies lists allow you to select the planets and moons that may eclipse solar radiation pressure or albedo in the force model. The list of available bodies includes all the central bodies defined in the Component Browser. Select a body in the Available list and click or double-click the body to move it to the Assigned list. To remove a body from the Assigned list, select it and click or double-click it.