Table of Contents

Environment: Thermosphere NRLMSISE-00

Description

The NRLMSISE-00 atmosphere module uses an external module to accurately determine the temperature and density of the atmosphere evaluated at some coordinate. The model is developed by NASA Goddard Space Center and is publicly available. The model takes in the current epoch from the simulation universe and space weather parameters can be added to the model to predict the temperature and density fluctuation at a given point in time. Assuming that the location is in geodetic coordinates \(\{\theta, \phi, h\}\), then the model is able to compute these parameters about the Earth. This model is strictly available for the Earth only and will not work for any other celestial body in the system.

Additionally, the model averages observed behaviour of temperature, 8 species densities, and mass density via a parametric analytic formulation. The model inputs are location, day of the year, time of day, solar activity, and geomagnetic activity. The model couples thermosphere species densities to the entire column, via an effective mass profile that transitions each species from the fully mixed region below ~70 km altitude to the diffusively separated region above ~200 km. Other changes include the extension of atomic oxygen down to 50 km and the use of geopotential height as the internal vertical coordinate.

Example Use Cases

  • Use a computationally efficient model for quickly assessing the effect of atmospheric drag on the decay of a spacecraft's orbit.
  • Find the amount of propellant needed to compensate for drag over a mission sequence.
  • Determine the temperature of the atmosphere at particular locations around a body.
  • Implement space weather forecasts with the temperature and density fluctuations within the thermosphere.

Module Implementation

NRLMSISE-00 depends on space weather parameters, including \(Ap\), \(Kp\) and \(F_{10.7}\) (the 81-day average of the solar flux intensity). The \(Ap\) index is a measure of the strength of geomagnetic disturbances caused by solar activity, such as solar flares and coronal mass ejections. It ranges from 0 to over 400, with higher values indicating more significant geomagnetic activity. The NRLMSISE-00 model uses the \(Ap\) index to account for the effects of geomagnetic storms on the atmosphere. The \(Kp\) index is a measure of the global magnetic activity level over a 3-hour period. It ranges from 0 to 9, with 0 being very quiet and 9 being highly disturbed. The \(Kp\) index is calculated based on the observed variations in the Earth's magnetic field at several geomagnetic observatories around the world. Given some location about the surface, \(\vec{r} = \{\theta, \phi, h\}\), where \(\theta\) is the latitude, \(\phi\) is the longitude and \(h\) is the height above the Earth’s surface according to the standard meridian in an ECEF frame, the model will output the temperature \(T\) and the density \(\rho\) of the atmosphere at that point. The inner mathematics of the model can be found by observing the publicly available source code written in Fortran.

Assumptions / Limitations

  • The atmosphere is defined everywhere and all spacecraft will read an atmosphere value if they are within the atmosphere defined.
  • Unless a component is added, the dynamic effects of the atmospheric drag will not contribute to the dynamic orbit of the spacecraft by default.
  • An exponential atmosphere and an MSIS atmosphere cannot be added to the Earth at the same time.
  • At present, all nonexponential models are Earth-specific. NRLMSISE-00, specifically, is highly dependent on “space weather parameters” such as Ap, Kp, and F10.7, among others. The outputs of this model can vary greatly with the selected parameters.

References

[1] David Vallado. Fundamentals of Astrodynamics and Applications. Microcosm press, 4 edition, 2013 [2] Tianyu Gao et al. Calibration of Atmospheric Density Model based on Gaussian Processe. Department of Mechanical and Aerospace Engineering, 2019.