Celestia Forums

I've been looking at asteroid spin information at these two sites:
http://www.astro.amu.edu.pl/Science/Asteroids/Spindata/spin.pdf
http://www.bdl.fr/ephem/ephephys_eng/ephephys_constantes.html
From these its possible to put together some good rotation definitions for solarsys.ssc's four big asteroids, as follows.

CERES

PALLAS

JUNO

VESTA


There's information about most of the rest of the asteroids defined in solarsys.ssc at the second of these sites, but I'd like to look at it for a little longer - I need, for instance, to check whether the pole definitions used for Celestia's mesh objects agree with the pole definitions used in the table at that site.

Grant

i'll make sure to add these to my list!

I'll add the changes into solarsys.ssc for Celestia 1.2.6.

--Chris

I've been checking the parameters for Toutatis and Castalia.

TOUTATIS
Toutatis is a retrograde rotator, and appears to precess in the same direction as it spins (at least some of the time!) according to the animation at http://www.solarviews.com/cap/ast/toutspin.htm.
So its rotation parameters should read:


CASTALIA
I've found an error in the solarsys.ssc orbital period for Castalia, which prevents Celestia reproducing its close approaches to the Earth in 1989 and 2046. I've also corrected the orientation of the shape model relative to its spin axis, given it a polar orientation provided by http://www.astro.amu.edu.pl/Science/Asteroids/Spindata/spin.pdf, and revised the rotation period slightly in the light of the current data from that site and from Horizons.
The final definition I've come up with is:

(A single orbit definition is never going to reproduce the close approaches perfectly, but at least they now occur within a few days and a few million kilometres of the correct values.)

Grant

Solarsys Updated
good work as usual, keep it up grant.

Thanks

I've now made a sweep through the asteroids in solarsys.ssc.
Scott Hudson's shape models all need reorientated to get their poles on to the Celestia rotation axis. I've tracked down a rotation axis for all of them bar 1998 KY26 (which must have an axis somewhere to go with its shape model - if anyone finds it, let me know), and I've checked most of these against dated rotation animations or radar views, to make sure that the Celestia model is correctly orientated and rotating in the correct sense.
I've also picked up a couple of errors in the Celestia orbit definitions, and updated some rotation periods. Rather than carry on with piecemeal postings, I thought I'd provide a complete current set of definitions for the asteroids. Let me know if you spot any errors!

The above code requires my corrected Eros model, which you can download from Selden's site at http://www.lns.cornell.edu/~seb/celestia/hutchison/#4.2
It also works better with the corrected Ida model, again available from Selden's site at http://www.lns.cornell.edu/~seb/celestia/hutchison/#3. (Thanks again to praesepe for doing the smoothing on both these models.) When I've used on-line resources other than the ones I've previously credited, I've supplied an InfoURL in the above listing.

Oh, and belated thanks to Selden, who came up with an albedo for Dactyl!

Grant

Oops - meant to include albedos for the Big Four, all supplied by the JPL Horizons system. I've edited the previously posted code.

Grant

The final part of solarsys.ssc, with some updated rotational elements (a chaotic tumble for Halley, a good axis and rotation for Borrelly) from me, and a reminder of the previously-posted changes to orbital elements by JackHiggins (which I confess I trimmed of a few decimals).

although JackHiggins gave radii of 100km for both Varuna and Ixion, the original Celestia radii seem to be on a good footing, and I've therefore restored them in this version. I've also slipped the Borrelly shape model into the Halley definition, since it's of roughly the right proportions, although Halley's primary rotation is around its long axis, whereas Borrelly is in a relatively stable short-axis rotation.

Grant

PS: Edited on 9th February to correct the error detected by DarkMiss, below.

should Haley's Epoch be 449400.5 or 2449400.5

Darkmiss wrote:should Haley's Epoch be 449400.5 or 2449400.5 :?:

Oops, sorry. 2449400.5.
I just cut-and-pasted those parameters from JackHiggins' original post, so heaven alone knows how I managed to delete that "2"! I'll edit the original post.

Grant

All of these updates to solarsys.ssc are now checked into CVS, and will be in 1.2.6 (including that leading 2 )

--Chris

chris wrote:(including that leading 2 )

Gad, that's embarrassing. The worst thing, of course, is that I messed up someone else's data, not my own. Sorry, JackHiggins, if you're reading this!

Grant