[table=head]Altitude [km]|50|150|1000
2006 Legacy model|0.000055|0.000056|
J71G model|0.000289|0.0015|0.0020
NRLMSISE-00 model|0.00384|0.0266|0.0146[/table]
Table 1: Timing comparison between atmosphere models: Times for 1000 model evaluations at different altitudes.
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For a real-time application like Orbiter, the computational efficiency of the atmosphere model is important. Atmosphere data are queried at each timeframe by each vessel within the atmosphere range limit of a given celestial body. For densely populated simulation scenarios, a complex atmosphere model may adversely affect performance.
Timing results for the three atmosphere models are shown in Table 1. They show the times for 1000 evaluations of model evaluation at different altitudes. It can be seen that the NRLMSISE-00 model is significantly more expensive than the J71G model by approximately an order of magnitude, and both models are substantially more expensive than the trivial Orbiter legacy model.
It should however be noted that for moderately loaded simulation scenarios, even the more expensive models may not significantly degrade performance. For a test scenario with 50 vessels in the atmosphere, the application of the NRLMSISE-00 model resulted in a drop in frame rate from 130 to 114 frames per second.
