Global Reference Atmospheric Model (GRAM)

The Global Reference Atmospheric Model (GRAM) Suite is an engineering-oriented atmospheric model that provides estimates of mean values and statistical variations of atmospheric properties for various planetary bodies. GRAM is used for modeling and simulations to provide atmospheric properties that are then used for trajectory and vehicle performance predictions. GRAM has been one of most widely used engineering models of the atmosphere since development started in the 1990’s with updates and new atmospheric models being released in timely increments since then. Since FY2018, SMD has been providing funding support to continue enhancements of GRAM to support operations for several planetary missions and create atmospheric models of planetary models not available. In 2023, the new GRAM Suite was an Honorable Mention for NASA Software of the Year.

GRAM provides atmospheric properties, such as pressure, temperature, density, winds, atmospheric composition, speed and sound, and some other details as a function of local time, planetary location, and planetary season (parametrized by solar longitude). For some planetary bodies, such as Earth and Mars, the atmospheric model fidelity is even higher, and the modeling accounts for specific locations on the planet, such as a frequent launch or landing site, and contains historic data from these locations. A key feature of GRAM is the perturbation model which allows users to estimate the uncertainty around the mean atmospheric models, and capture effect of phenomenon such as atmospheric turbulence or gravity waves on planetary atmosphere. GRAM has been the key atmospheric model for many NASA and industry applications in atmospheric flight, such as launch, entry, descent, and landing (EDL), aerobraking, and aerocapture. GRAM is often the only available atmospheric model in early phase of mission development and has been used for site selection and characterization for Mars missions, launch and landing site analysis for Earth ascent and re-entry missions, and for operations use in aerobraking missions at planetary destinations. With the additional upgrades being undertaken in the GRAM code, new planetary destinations of highest science priority, such as Uranus, Neptune, and Saturn, will have models that encompass the current state-of-the-art knowledge of these planet’s atmosphere. In addition, GRAM models for existing planetary bodies, such as Earth, will be able to cross-couple GRAM’s perturbation apparatus with forecast models and user-provided localized atmospheric data, thus enhancing the modeling and simulation capabilities of many tools. The GRAM project holds a yearly workshop for the user community to disseminate the latest changes in the GRAM software while soliciting user ideas for future upgrades. Some recent changes that have come from user recommendations include APIs for scripting languages, such as Python and MATLAB, and customizing of ephemerides models.

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