Space Science with Python - Part 12: Ceres' Orbit

After covering the orbital elements in our last "Concepts" session, we start now to work on some actual data. For starters, as a gentle introduction, we warm up with the orbital elements of the dwarf planet / major asteroid: (1) Ceres.

Ceres is known since 200 years and was also visited by the spacecraft Dawn back in 2015. The trajectory is well known and understood and a perfect starting point to get a feeling for:

- Semi-major axis
- Perihelion
- Eccentricity
- Inclination
- Longitude of ascending node
- Argument of perihelion

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Content
0:00 Introduction / Ceres
1:30 Code preparation & required kernels
6:10 Let's code!
19:30 Comparison with the Minor Planet Center
27:10 Summary & Outlook

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There is a lot to do and to learn and I hope you will join the journey. Meanwhile, if you have questions or ideas, reach out to me via:

Or drop a comment!

Talk to you later,
Thomas

[iankelley]

We're finally all caught up! This is such a nice tutorial, and you're going faster than me, meaning I'll have a backlog! Incredible channel and content!

[philwebb]

8:49 print(mat.round(2)) aligns rows and columns.

[philwebb]

I noticed you didn't print out all the parameters returned from spiceypy.oscltx(), so I checked the missing ones. It calculates the gravitational parameter of Ceres as 132.71 km^3/sec^2, which is 2.11-times larger than the value Wikipedia gives, 62.6325 km^3/sec^2, which is 6.67e-20 km^3/kg⋅sec^2 * 6.26e10 kg (the mass of Ceres). Playing further, if you reduce gm_sun by 2.11 to 6.26e10, then you get the Wikipedia value for Ceres mu. Strange that G*M for Ceres is somehow proportional to G*M of the sun. I wonder if Newton knew about this. I didn't see any notes on the oscltx_c docs page to explain what's happening.

Update: So, how does spiceypy.oscltx() figure out the gravitational parameter for a body from it's state vector? Playing with that question, I plugged several bodyid's into spiceypy.spkgeo() to get several state vectors and discovered that spiceypy.oscltx() always returns the value 132.71 km^3/sec^2 in the 8th position, elts[7], regardless of what state vector you feed it, whenever you set mu=gm_sun. And the value, elts[7], scales with whatever you set mu equal to. So, I'm not sure what that parameter is trying to tell us.