Have you ever been in the middle of designing your latest Mars mission in STK
when it strikes you that, although there are about a dozen detailed models for the Earth’s atmosphere, the red planet only gets a simple exponential model? Perhaps you then asked yourself “Where’s the love? Surely NASA or someone has a better model. Why can’t I have it in STK?” I know I have!
Well it turns out that NASA indeed has a better model called the Mars Global Reference Atmospheric Model, or MarsGRAM for short. The atmosphere of Mars is quite different than Earth. Though the atmospheric density at the surface is only about 0.5% that of Earth, differences in composition, temperature and local gravity mean the scale height is actually greater. Mars’ atmosphere is not only “fluffier,” but it can be much more sensitive to thermal, seasonal and local or regional weather (e.g. dust storms) variations. Even without dust storms, the density at high altitudes has been seen to change by a factor of 5 based on season and time of day! MarsGRAM can model these kinds of effects. It has been used operationally and continually refined since at least the Mars Odyssey mission, and is in use today for things like planning of the next Mars orbiter MAVEN.
Until recently, this model was carefully controlled by NASA. But now it is considered public domain. In response, AGI is releasing a special integration of the MarsGRAM models for use with STK/Astrogator
. You can download it today from here
. Users are also encouraged to register with NASA
. Be sure to read the included documentation carefully to set them up and make use of the many inputs unique to MarsGRAM. Once placed in the right location, you can use them as you would any other atmospheric model as an STK/Astrogator propagator function. In addition to computing drag on a satellite, you can also report or graph atmospheric density, pressure and temperature along your satellite’s orbit.