Data Set Overview
  =================
    This data set presents the basic tri-axial ellipsoid shape model of
    comet 81P/Wild 2, as derived from the Stardust Navigation camera images
    that were obtained around the time of closest approach to the comet.
    Additional details and information about the model can be found in
    Duxbury et al. J. Geophys. Res., Vol. 109, No. E12, E12S02
    10.1029/2004JE002316 (2004) [DUXBURYETAL2004].
 
    On 2 January 2004, the STARDUST spacecraft flew past comet 81P/Wild 2
    and took 72 images. In these images, the phase angle started at 70 deg
    during the approach, dropped to 3 deg near closest approach, and then
    increased to 110 deg during the departure.  Most images were obtained
    within a range of 2,000 km, with the closest at 237 km.  The camera
    took the images using a broadband filter and a CCD that had an angular
    resolution of 57 microrad/pixel.  These images are archived in the PDS
    Stardust NAVCAM Data for comet Wild 2 (Data_Set_Name: STARDUST NAVCAM
    IMAGES OF WILD 2, Data_Set_ID: SDU-C-NAVCAM-2-EDR-WILD2-V1.0)
 
    A tri-axial ellipsoid model was fit to the limb and terminator in
    all the Wild 2 nucleus images.  The model was constrained by the fact
    that the viewing geometry changed by 180 degrees during the encounter
    and essentially the entire illuminated hemisphere of Wild 2 was viewed
    in these images (or ~50% of the surface, since there was no noticeable
    rotation during the few minutes that the images were taken).
 
    The axial dimensions determined from the visual fit of the model to
    the limb and terminator were 1.65 x 2.00 x 2.75 km +/-0.05 km (1
    sigma).  The illuminated limb is reasonably smooth, with the exception
    of a few large depressions.  It is understood that half of the surface
    was not illuminated and that these unseen surfaces could deviate from
    the model derived from the illuminated regions.  However the model fit
    to the terminator, even though quite rough due to topographic
    variations, does give some evidence that the model probably
    extrapolates to the unseen part of the nucleus to at least a km or
    better.
 
    A body-fixed coordinate system was established with the shortest axis
    assumed to be the rotation pole and the longest axis used to define the
    prime meridian.  The posigrade axis is defined to match the
    corresponding poles determined by Sekanina (2003) [SEKANINA2003] and
    Farnham and Schleicher (2005) [FARNHAM&SCHLEICH2005].
 
    Author
    ------
    The descriptions in this file were written by Tony Farnham.

Confidence Level Overview
  =========================
    A visual fit was used to match the model to the observations.
    Uncertainties were estimated by changing the parameters until an
    overlay of the model clearly deviated from the corresponding images.
    Estimated errors are 0.05 km in the axial dimensions, and 3 degrees in
    the angular measurements.
 
  Review
  ======
    This data set was peer reviewed on Oct 15, 2004 and accepted pending
    a few minor corrections and additions, which have been applied.