How to calculate MeanLongitude for planet

Marijn

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I am trying to create a planet for Orbiter. Actually, it's going to be an asteroid, but I assume the implementation of asteroids is no different than planets. I decided to use asteroid Bennu as an example.

Currently, the relevant part of my cfg file looks like:
; === Planetary Mean Orbits ===
Epoch = 2010.99931554
SemiMajorAxis = 168505699055.3255
Eccentricity = 2.037451084785423e-1
Inclination = 0.10532956489987094
LongAscNode = 0.03596892030325171
LongPerihelion = 1.191779504398578
MeanLongitude = 2.9668482563280243

When I select this body as a target in Orbiter's Orbit MFD, the shape and orientation of the orbit looks good to me. Except for the current position of the body in the orbit. That one is clearly wrong. I expect that there is a mistake in the calculation of the MeanLongitude. But I don't understand why.

Page 142 of the Orbiter Manual says:
Mean Longitude = Mean anomaly(ma) + Longitude of the periapsis.
Also, Longitude of the periapsis = Longitude of the ascending node(om) + Argument of periapsis(w).

When I do this math and convert it to radians, I end up with the 2.96 value above which must be incorrect. I got the epoch using the Orbiter Date utility.

Anybody who can help me to get it right?

The data I am working with:
[{
"epoch": 2455562.5,
"a": 1.126391025934071,
"e": 0.2037451084785423,
"i": 6.034939533607825,
"om": 2.060867329373625,
"w": 66.22306846088361,
"ma": 101.7039479473255
}]

Thanks
 

boogabooga

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Here, try this:

[ame="https://www.orbithangar.com/searchid.php?ID=1436"]MPC Database Asteroid Viewer and Exporter v2.0.3[/ame]

I had good results see for example:
[ame="https://www.orbithangar.com/searchid.php?ID=6814"]New Horizons Kuiper Belt Extended Mission[/ame]
 

Marijn

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Thanks. But it's throwing an error on startup:
---------------------------
MPC Database Viewer
---------------------------
Component 'COMDLG32.OCX' or one of its dependencies not correctly registered: a file is missing or invalid
---------------------------

The file is not missing. I am running Win8.1 without any trouble at the moment, so I don't think it's a good idea to mess with this now.
 

boogabooga

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Read the thread, I believe that orb gives a workaround for that.
 

Marijn

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Read the thread, I believe that orb gives a workaround for that.
I might do that later. It looks like I need to refresh the database as well when I would get it to work. The datafile is from 2008. My data includes Epoch 2010.999. I am sure that's possible, but I want to learn how to do these conversions myself anyway. It's just the last step, the position of the body in the orbit which I can't figure out at the moment.

Still thinking about your Mars launch scenario question as well :)

---------- Post added at 11:41 PM ---------- Previous post was at 04:11 PM ----------

It seems that the orbit of Bennu's which I posted above is correct after all. But I am not 100% sure.

Mean anomaly in the data source is 101.7. MnA displayed by Orbiter's Orbit MFD is 357.3

But the position seems correct so I think that's normal now.
 
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