# AFSPC Standardized Astrodynamic Algorithm Library (SAAL)

The Standardized Astrodynamic Algorithm Library (SAAL) was developed to ensure interoperability for users of the Joint Space Operations JSpOC satellite catalog. In order to obtain the most accurate prediction, users need to apply the same propagator models that were used to generate the satellite catalog. The accuracy of a Standardized Astrodynamic Standard algorithm is primarily a function of its underlying physics model and the accuracy and compatibility of the data it uses. It is easy to understand that the "better" the underlying physics model or the more accurate the data, the more accurate the algorithm's calculation. However, it is not as intuitively obvious that the prediction model must also be compatible with those models generating the orbital data that it uses as input. The bottom line is, if you are a user of the JSpOC satellite catalog (either TLEs or Vector Covariance Messages (VCMs)), you should use the same propagators that were used to generate the TLEs or VCMs in order to get the most accurate prediction.

DSoft Technology is well-versed in using and integrating the Standardized Astrodynamic Algorithm Library, having worked with the standards and Air Force Space Command since 2003. Since then we have performed configuration management, testing, integration, and distribution of the Standardized Astrodynamic Algorithms and understand the complexity of their integration and use. We can assist authorized clients to integrate the standard DLLs into other applications using a C# wrapper.

The following describes each standard in more detail:

AOF (Area Overflight) |
AOF computes when overhead satellites can see a particular location on the earth. AOF uses both SGP4 and SP for ephemeris generation. |

BatchDC (Batch Differential Correction) |
Performs a least squares batch differential correction of orbital elements using tracking data and both the SGP4 and SP propagator. The BatchDC now combines the old SGP4DC and SPDC. |

COMBO (Computation of Miss Between Orbits) |
Computes close approaches between satellites using both SGP4 and SP for ephemeris generation. |

FOV (Field of View) |
FOV determines times in which orbiting satellites fly through a ground based observer's conical field of view. The field of view can be defined by a constant azimuth and elevation, a constant right ascension and declination, or as a line-of-site to another orbiting satellite. FOV uses both SGP4 and SP for ephemeris generation. |

GELCON (Generalized Element Conversion) |
Converts element sets or vectors of one of three theories (SGP4, SALT, or SP) to element sets or vectors of a selected theory (SGP4, SALT, or SP). |

IOMOD (Initial Orbit Generation; Name carried over from Initial Orbit Module) |
Computes an initial set of orbital elements from three observations. |

LAMOD(Look Angles Generation, name carried over from Look Angles Module algorithm) |
Computes sensor (ground based or space based) viewing opportunities (so-called "look angles") for earth centered satellites. LAMOD uses both SGP4 and SP for ephemeris generation. |

ROTAS (Report/Observation Association) |
Associates observations against satellite element sets. |

SALT (Semi-Analytic Liu Theory) |
Is a semi-analytic method of providing ephemerides and orbital lifetime analysis for satellites in earth-centered orbits. |

SeqDC (Sequential Differential Correction) |
Performs a series of least-squares differential corrections (DC). These differential corrections are computed in a sequential mode, which uses one or more observations or tracks while retrieving former covariance information from a prior DC. SEQDC uses both SGP4 and SP for ephemeris generation. |

SGP4 (Simplified General Perturbations #4) |
Is an analytic method of generating ephemerides for satellites in earth-centered orbits. |

SGP4DC (SGP4 Differential Correction) |
Performs a least squares differential correction of orbital elements using tracking data and the SGP4 propagator. |

SP (Special Perturbations) |
Is an algorithm, which uses numerical integration to generate ephemerides for satellites in earth-centered orbits. |

SPDC (SP Differential Correction) |
Performs a least squares differential correction of orbital elements using tracking data and the SP propagator. |

The Standardized Astrodynamic Algorithms that are available to the public are viewable here.

Having trouble deciding which algorithm to use? Contact us and we'll help you find the right one.