Celestia Forums

I am working on updating an Excel spreadsheet that I have used to create systems. Part of the file is dedicated to calculating the anything from mean orbital velocity and period to surface area and density. I would like some feed back and help converting the template to the newer 1.6 format and if there are any excel wiz's out there help with the formatting. Anyway take a look.

File Updated/Simplified

Given Period, SemiMajorAxis, Eccentricity, Inclination, AscendingNode

how do you, or can you calculate the

ArgOfPericenter, LongOfPericenter, MeanLongitude, MeanAnomaly

If someone can walk me though it i would like to add it to my calc sheet.

Thanks

You can't calculate those quantities from the first set. They are extra parameters which are required to fully specify the orientation in 3D space, and also to specify the position of the planet on its orbit.

To orient the ellipse you need three numbers (these correspond to the Euler angles for the rotation). One of these is the inclination (i). The remaining two are chosen from the following set of three: longitude of the ascending node (AscendingNode, ?), argument of pericenter (ArgOfPericenter, ?) and longitude of pericenter (LongOfPericenter ?=?+?).

The position of the planet in its orbit at a given time (by default, J2000.0=JD2451545.0, this can be changed by specifying the Epoch parameter) is specified either by the mean anomaly (MeanAnomaly, M) or the mean longitude (MeanLongitude, L=M+?).

Mean anomaly is probably better than mean longitude if you wish to generate them randomly. Mean anomaly increases uniformly with time, and can thus be generated with RAND()*360, whereas mean longitude is dependent on the eccentricity and a simple RAND()*360 is insufficient to create a uniform distribution. Mean anomaly is equal to 0 at perihelion, and increases by exactly 360 degrees in a time equal to the Period.

I been meaning to get back to everyone one this, i was working on calculating the values after the second reply, but got stuck on the calculating the following.

Eccentricity Vector
http://en.wikipedia.org/wiki/Eccentricity_vector
Eccentric Anomaly
http://en.wikipedia.org/wiki/Eccentric_anomaly
Orbital state vectors
http://en.wikipedia.org/wiki/Orbital_position_vector

I update the document above to get rid of some of the garbage and simplify it. (Download from the first post) This is driving me a little bit loopy, it should be much easier then i am making it out. anyone will to take a stab. I also came across an interesting post on getting the precession rate of a planet http://www.sciforums.com/showthread.php?t=65185 naturally this assumes only a 2 body system, but the formula seems to work extremely well.

Thanks for the help