General Question Atmospheric Drag

[romanasul]

I have a question regarding atmospheric drag in Orbiter. I've noticed that sometimes it works while other times it doesn't. For example, I was flying STS-4 in an alternate history scenario. I simulated an engine failure but have still managed to get into a 220x220 km orbit. After a few days i've noticed that my orbit was starting to decrease and eventually I was reentering the atmosphere after about a week. I tried to repeat this by loading the "on-orbit" scenario from the Shuttle Fleet/Atlantis folder. I placed it in the same altitude and waited. However, nothing hapenned. The altitude remained the same even after several months of high time acceleration. Has anybody experimented with this? Is there some way to enable atmospheric drag all the time?

 

[asbjos]

Did you use the Scenario Editor in the simulation? Orbiter has a tendency to freak out when you manipulate the simulation, and orbiter can suddenly ignore atmospheric drag or other modules show strange behavior.

If you flew up manually it can be your direction. More contact with air brakes you more, so if you faced prograde you can stay up in orbit way longer than if you not face forward.

 

[romanasul]

Did you use the Scenario Editor in the simulation? Orbiter has a tendency to freak out when you manipulate the simulation, and orbiter can suddenly ignore atmospheric drag or other modules show strange behavior.

If you flew up manually it can be your direction. More contact with air brakes you more, so if you faced prograde you can stay up in orbit way longer than if you not face forward.

Yes, I did use scenario editor for the second test. I'll try loading another scenario without manipulating the simulation using scenario editor.

 

[Urwumpe]

The 2010 version of Orbiter does also model exosphere drag, that atmosphere layer goes from about 80 km to maximal 1500 km (I think it ends in 600 km altitude in Orbiter)

 

[Cras]

I had found myself wondering this myself a few times, where my orbit didnt seem to be suffering from atmospheric drag, but rather I find the orbit height increasing over time. Yet other times, I clearly see the orbit degrading and I need to boost it to stay out of the atmosphere.

 

[martins]

I have a question regarding atmospheric drag in Orbiter. I've noticed that sometimes it works while other times it doesn't. For example, I was flying STS-4 in an alternate history scenario. I simulated an engine failure but have still managed to get into a 220x220 km orbit. After a few days i've noticed that my orbit was starting to decrease and eventually I was reentering the atmosphere after about a week. I tried to repeat this by loading the "on-orbit" scenario from the Shuttle Fleet/Atlantis folder. I placed it in the same altitude and waited. However, nothing hapenned. The altitude remained the same even after several months of high time acceleration. Has anybody experimented with this? Is there some way to enable atmospheric drag all the time?

Can this effect be repeated with a stock vessel? Orbiter doesn't keep a history how a spacecraft arrived at a given set of state vectors, so it shouldn't matter if it's flown to orbit or placed there by a scenario, unless the module itself does some trickery.

Can you also test the following: From the Orbiter Launchpad, go to Extra | Time propagation | Orbit stabilisation, and disable that. Then, under Linear state propagators, disable all stages except the first one, and set that to RK8. Does this have any effect on the behaviour?

The 2010 version of Orbiter does also model exosphere drag, that atmosphere layer goes from about 80 km to maximal 1500 km (I think it ends in 600 km altitude in Orbiter)

Earth's atmosphere ends at 2500km in Orbiter, unless you are using the 2006 legacy model (which ends at 200km).

 

[Urwumpe]

Earth's atmosphere ends at 2500km in Orbiter, unless you are using the 2006 legacy model (which ends at 200km).

Thats... far. There should be already no difference to the interplanetary medium in 1500 km during a solar maximum (less altitude during solar minimum)

 

[romanasul]

Can this effect be repeated with a stock vessel? Orbiter doesn't keep a history how a spacecraft arrived at a given set of state vectors, so it shouldn't matter if it's flown to orbit or placed there by a scenario, unless the module itself does some trickery.

Can you also test the following: From the Orbiter Launchpad, go to Extra | Time propagation | Orbit stabilisation, and disable that. Then, under Linear state propagators, disable all stages except the first one, and set that to RK8. Does this have any effect on the behaviour?


Earth's atmosphere ends at 2500km in Orbiter, unless you are using the 2006 legacy model (which ends at 200km).

Hello Dr. Martin, thanks for your reply. I have tested it with orbit stabilisation disabled and the linear propagators set to the highest. This time there seems to be atmospheric drag proportional to the altitude. However the problem now is my computer, which freezes for a few seconds while in time acceleration. Because of this the orbit jumps to a hyperbolic one.

Edit: I have also done a test with the stock Atlantis shuttle. When orbit stabilisation was enabled my orbit remained the same (even at 180 km). Without orbit stabilisation once again my computer froze for about two seconds and the shuttle jumped to a hyperbolic orbit. I then reset everything back to default and proceeded to fly the STS-9 mission. Once I got into an orbit of around 250 km I proceeded with the mission. Again, i noticed that my orbit was lowering very slowly, so I increased to 10000x, waited for about a week and stopped. My orbit was now 70 km lower.

---------- Post added 12-16-12 at 08:19 AM ---------- Previous post was 12-15-12 at 03:59 PM ----------

I've been experimenting more with this and I found that stock orbiter vessels seem to experience atmospheric drag while others don't. I'm guessing this could be due to their aerodynamic properties or maybe some other factors.