martins
Orbiter Founder
Since Orbiter's atmosphere model has been discussed quite a bit recently, I finally decided to revisit and rewrite the Earth atmosphere model. I have selected a moderately complex model (L. G. Jacchia, Thermospheric Temperature, Density, and Composition: New Models, Smithson. Astrophys. Obs. Spec. Rept. No. 375, 1977) which covers the range from 90 to 2500km (using a static standard atmosphere model below 90km). The only model parameter (apart from altitude) is the exospheric temperature. I found a plausible model for the diurnal exosphere temperature variations (Montenbruck, Satellite Orbits), but I won't include any dynamic parameters that depend on observation data (geomagnetic activity, solar flux).
Once I've written up the details I'll present them here for disucssion. Also, once implemented, I will upload a new public beta.
In any case, the new model will be substantially different from the current one. Not only will it extend to more than 10x the current altitude, it will also be far denser in the range from ~120 to 200km. This is because the current model seriously underestimates the high-altitude temperature. As a result, long-term stability of LEO (physical and numerical) will become more of a challenge, so I thought I should drop an early warning. Possible problems include
- Launch autopilots. Anything that relies on the current atmosphere model may need to be rewritten. Increased drag will eat into the Delta-V budget, so reaching a given orbit will require tighter planning. Also, since the atmosphere has a diurnal oscillation, the autopilots will need to be adaptive, or take the time of day and season into account.
- Stations and satellites in LEO. They will either require autopilots with orbit boost capacities, or, in the worst case, fudge the drag effects (zero drag coefficients). However, ignoring drag could lead to other problems (pseudo-forces messing up docking operations).
Numerical stability at high time compression will be even more of a headache, but I guess this will be mostly my problem to solve.
So in short, operations in low orbit are bound to become more interesting.
Once I've written up the details I'll present them here for disucssion. Also, once implemented, I will upload a new public beta.
In any case, the new model will be substantially different from the current one. Not only will it extend to more than 10x the current altitude, it will also be far denser in the range from ~120 to 200km. This is because the current model seriously underestimates the high-altitude temperature. As a result, long-term stability of LEO (physical and numerical) will become more of a challenge, so I thought I should drop an early warning. Possible problems include
- Launch autopilots. Anything that relies on the current atmosphere model may need to be rewritten. Increased drag will eat into the Delta-V budget, so reaching a given orbit will require tighter planning. Also, since the atmosphere has a diurnal oscillation, the autopilots will need to be adaptive, or take the time of day and season into account.
- Stations and satellites in LEO. They will either require autopilots with orbit boost capacities, or, in the worst case, fudge the drag effects (zero drag coefficients). However, ignoring drag could lead to other problems (pseudo-forces messing up docking operations).
Numerical stability at high time compression will be even more of a headache, but I guess this will be mostly my problem to solve.
So in short, operations in low orbit are bound to become more interesting.
)
, THANKS!
