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Author Topic: Orbital Altitude Fluctuation...  (Read 895 times)
jc121081
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« on: November 06, 2007, 01:17:39 AM »

Just curious,

Looking though several other Orbiter forums before I've been aware of the now-existent nonspherical gravity perturbations in earth orbit. What I was wondering, however, was if anybody here is using Orbit Stabilization and what kind of detrimental or positive effects it may have for NASSP?

The reason I ask is that during much of my testing I have noted my orbital altitudes fluctuating in the three tools I use for monitoring Apoapsis and Periapsis (vAGC V82, Orbit MFD and Apollo MFD) I know these altitudes should shift because of the nonspher. gravity necessary for proper vAGC simulation, but I think to a much higher degree than normal. For example...

My intended orbit was 194.1nm by 123.0nm, however the V82 (and after proper use of both manual SV Updates and the new ApolloTelemetry MFD) and the ApolloMFD both fluctuated around 13nm in Apogee higher and then lower than the desired Apogee. After reading several other topics in the Orbiter forums, it was noted that these fluctuations shouldn't be more than 10 kilometers from the "true" orbit.

My other question is if anybody is using Orbit Stabilization, what do you have your settings under the Extra ----> Orbit stabilization parameters set to?

Here are mine, and please, somebody tell me if I'm wrong here...

Orbit Step Limit: 1%
Gravitational Field Perturbation Limit: 5%
Target orbit step: 2%
Max Steps: 10
Perturbation Model: 5%

Complex Flight Model: On (I remember reading I had to have this on, forget why, though...)
Damage & Failure Sim: Off (I suppose I could turn this on, hmmm)
Limited Fuel: On
Nonspherical gravity sources: On (Needed for vAGC)
Gravity-gradient Torque: Off (Makes SIVB stable after seperation)

Now, I read on another forum that setting the Orbit Step Limit to 0.012% greatly lessens the effect of perturbation. Would this be a bad thing, in any way?

And another thing, and a little off the topic, but I remember reading before that IMFD could work with vAGC scenarios using the SPS. I may be wrong though. Right now I'm only using IMFD's BaseApproach feature for deorbit burns. I tried turning the SIG COND switches off, and IMFD oriented the CSM properly, but the SPS did not ignite. Is there something more than the SIG COND switches, or does it not work at all for vAGC scenarios? If it's not possible, it's not too big a deal, just a little bit of a pain have to pan the screen over to the SPS Ignition switches and then back and forth once the time to ignition reaches zero.

Sorry for making this so long, had a hard time thinking of a way to explain this...  Duh!
« Last Edit: November 06, 2007, 06:10:56 PM by jc121081 » Logged
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