Thanks John for the link to the A_2017_U1.bsp file. Meanwhile I wrote the .ssc file etc for SPICE from scratch and added some comments about where the various parameters came from:
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"A2017 U1" "Sol"
{
Class "asteroid"
Mesh "asteroid.cms" # default
Texture "asteroid.jpg" # default
Orientation [ 90 1 0 0 ]
Radius 0.08 # educated guess
Albedo 0.1 # guess
OrbitFrame { EclipticJ2000 { Center "Sol" }}
Beginning "1900 01 01 00:00:00.000" # from 'brief' Spice utility
Ending "2101 01 01 00:00:00.000" # 'brief *.bsp'
SpiceOrbit
{
Kernel "A_2017_U1.bsp"
Target "3788040" # from 'brief *.bsp' command
Origin "0" # from 'brief -c *.bsp'
Period 0 # from celestia.Sci code to get aperiodic Spice trajectory
BoundingRadius 1 # not too big since used just for culling
}
UniformRotation
{
Period 6 # guess
}
}
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A few remarks: celestia.Sci and Celestia code expect Period = 0 for an aperiodic (hyperbolic) Spice trajectory. In one of the scholarly papers about A/2017 U1 some arguments are given for a relatively tiny size (0.16 km ) of the asteroid. Accordingly, the BoundingRadius (used for culling only) should be pretty small, too. Practically all other values came from using the 'brief' utility. As you can see, I used the default asteroid.cms and asteroid.jpg for now.
Here is a screenshot to show that things are working fine.
[by all means click on image and then hit F11 (Firefox)]Attachment:
a2017_u1.jpg [ 187.65 KiB | Viewed 759 times ]
Important tests I did were checking the various positions found by the official observers between Oct. 19 and Oct. 25.
http://www.minorplanetcenter.net/mpec/K17/K17UI3.htmlThe accuracy is generally quite OK.
Fridger