Working with target of sky

[scsides]

When the target is not a NAIF body, but instead "sky" what is the plan? The current ISIS labels look similar, but a few things are obviously different (e.g. no POLE_RA, no valid body code for sky, ....)

[jessemapel]

I would assume we would set the target reference frame to J2000. What does a spiceinit'd ISIS cube look like with SKY as the target?

[krlberry]

I had a CaSSIS cube open anyway, so here are the differences between a spiceinited label with the original target (Mars) vs if I spiceinit with the TargetName in the Cube label set to Sky:

The following keywords are omitted from the NaifKeywords group in the Target=Sky label.

  BODY_CODE                       = 499
  BODY499_RADII                   = (3396.19, 3396.19, 3376.2)
  BODY_FRAME_CODE                 = 10014

And the BodyRotation table in the Target=Sky label is as follows:

Label:

Object = Table
  Name                = BodyRotation
  StartByte           = 2176779
  Bytes               = 64
  Records             = 1
  ByteOrder           = Lsb
  ConstantFrames      = (1, 1)
  ConstantRotation    = (1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 1.0)
  CkTableStartTime    = 533471602.76595
  CkTableEndTime      = 533471602.76595
  CkTableOriginalSize = 1
  FrameTypeCode       = 0
  Description         = "Created by spiceinit"
  Kernels             = ($tgo/kernels/tspk/de432s.bsp,
                         $tgo/kernels/tspk/mar097.bsp,
                         $tgo/kernels/pck/pck00010.tpc,
                         $tgo/kernels/pck/de-403-masses.tpc)
  SolarLongitude      = -1.79769313486231e+308

Contents:

tabledump fr=sky.cub name="BodyRotation"
J2000Q0,J2000Q1,J2000Q2,J2000Q3,AV1,AV2,AV3,ET
1.0,0.0,0.0,0.0,0.0,0.0,0.0,533471602.76595

Everything else was the same for this example CaSSIS cube.

[scsides]

Slight differences in the kernels group TargetPosition keyword: no mar097.bsp

InstrumentPointing is the same
InstrumentPosition is the same

BodyRotation
ConstantFrames = (1, 1)
ConstantRotation = (1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 1.0)
FrameTypeCode = 0

SunPosition is the same

NaifKeywords
Missing BODY_CODE, BODY499_RADII, BODY_FRAME_CODE

[jessemapel]

@scsides and I talked. Changing the target name to SSB should handle this. The rotation chain may break having the target reference frame be J2000, but the rest should work.

[krlberry]

SSB = Solar System Barycenter?

[jessemapel]

@kberryUSGS Yes