HiPotOk1978 to map orbital pertubations around the Earth

[HiPotOk1978]

Some to all of you may know that turning on nonspherical gravity sources causes objects into LEO to undergo what is called nodal regression. This affect can be visualized if you place for example a space station in the same ground track of the moon and allow time to progress. What happens is that your orbit drifts to the west if your in a prograde orbit or east if you are in a retrograde orbit. Nodal regression is not always a bad thing. For example, if you wanted to place a satellite that has a view of the sun 24 hours a day 365 days out of the year, nodal regression could help you correct for the 1 degree of change the Earth's orbit around the sun will introduce into your orbit.

Why am I doing this?
The first I am curious how accurate Dr Martin simulated this effect. The other reason is to have a chart of this phenomena for use in Orbiter. Nodal regression is not a fixed number for every orbit. Depending on your semi-major axis and inclination, you will experience various ammounts. My plan is to launch various objects into various circular orbits of various inclinations and monitor them for a total of 48 hours. The simulations will be ran at 1x time. Every 12 hours starting with Zero hour when the device is deployed the Latitude of the decending node will be noted. The current plan is to fly these satellites from 150km to 800km, at 50km intervals and at various inclinations from 0 degrees to 100 degrees latitude at 5 degrees intervals. Once this data is compiled, I will present a chart for the Orbiter community at orbithanger. A total of 154 different orbits will be measured so this will take some time. I hope this data will be of use to others and I know it will be use to me

 

[Urwumpe]

The first I am curious how accurate Dr Martin simulated this effect.

Not very accurate, if I remember correctly. Orbiter uses only the first coarse functions for modeling the equatorial bulge, if I remember correctly. You can download a file with over 400 constants for modeling the gravity of Earth from the GRACE project.

 

[Andy44]

There is a simple equation that approximates the effects of nodal regression based on your orbial elements. It's in Sellers' text book. When I find the book I'll post back. I got it laying around here somewhere, in the small black hole I use as a filing system.

 

[tblaxland]

There is a simple equation that approximates the effects of nodal regression based on your orbial elements. It's in Sellers' text book. When I find the book I'll post back. I got it laying around here somewhere, in the small black hole I use as a filing system.

Such an equation is also contained in Martin's docs, see Orbiter\Doc\Technotes\gravity.pdf, equation 7.

 

[Zatnikitelman]

This could also relate to studying the numerical accuracy of various propagators see hrere: http://www.orbiter-forum.com/showthread.php?t=6630

 

[HiPotOk1978]

well it sounds like the information already exists... I will look into this further before I continue with my experiments