KPL/PCK Asteroid Bennu P_constants (PcK) SPICE kernel file =========================================================================== This text PCK contains rotational and ellipsoidal shape constants for asteroid Bennu. Version and Date -------------------------------------------------------- Version 1.3 -- February 3, 2019 -- Michael Nolan, LPL/UofA Updated rotational constants based on shape modelling in [4] along with the acceleration determined in [5]. It matches the solution in [4] at 2019 Jan 01 12:00:00 TDB Version 1.2 -- January 11, 2019 -- Michael Nolan, LPL/UofA Boris Semenov, NAIFJPL Updated prime meridian location (W0) and rotation terms (W1, W2) based on [2], [3], and Bennu lightcurve observations in flight. Updated ellipsoid parameters based on shape modelling in [3]. Version 1.1 -- October 22, 2018 -- Michael Nolan, LPL/UofA Boris Semenov, NAIF/JPL Updated prime meridian location (W0) and rotation terms (W1, W2) based on [2] and Bennu lightcurve observations in flight. Version 1.0 -- November 4, 2014 -- Boris Semenov, NAIF/JPL Initial version released for official use by OSIRIS-Rex project, containing values for the pole direction, rotation period and shape from [1]. Disclaimer -------------------------------------------------------- This constants file may not contain the parameter values that you prefer. Note that this file may be readily modified by you or anyone else. NAIF suggests that you inspect this file visually before proceeding with any critical or extended data processing. NAIF requests that you update the ``by line'' and date if you modify the file. Sources -------------------------------------------------------- The sources for the constants listed in this version of this file are: 1) (101955) Bennu Design Reference Asteroid, Document Number: OREX-XLSX-04.00-00001, Rev_10, Version: 2014 October 10 (OREX-XLSX-04.00-00001_Rev_10_Bennu_DRA_Final.xlsx) 2) M.C. Nolan et al. (2018). Detection of YORP on Bennu using HST Lightcurve Observations. Submitted to Geophysical Research Letters. 3) O.S. Barnouin et al. (2019) Exploring the Shape of (101955) Bennu with OSIRIS-REx. Submitted to Nature. 4) Product report for OSIRIS-REx shape model v020 5) C.W. Hergenrother at al. (2019). Photometric Properties, Rotation State, and Operational Environment of Asteroid (101955) Bennu from OSIRIS-REx Observations. Submitted to Nature Communications. Orientation constants for asteroid Bennu -------------------------------------------------------- The inertial reference frame for the Bennu rotation constants is J2000; this is the default reference frame for PCK orientation data. The epoch of the Bennu rotation constants is J2000; this is Julian ephemeris date (JED) 2451545.0. The NAIF integer code for Bennu is 2101955. See the NAIF_IDs required reading for further information on NAIF integer codes. The LONG_AXIS keyword providing the offset between the longest axis of the triaxial ellipsoid used to model Bennu and the Bennu prime meridian is not used by SPICE geometry software. It is considered deprecated and provided solely for backwards compatibility. Values in the Version 1.0 The pole direction, prime meridian location, and rotation period in this version are set to the following values from [1]: " 3.1.1 Rotation Period 4.297461 hours 3.1.6 Pole Position (J200 RA/DEC) (+86.6388, -65.1086) deg 3.1.7 Location of Prime Meridian 89.6456 deg (epoch J2000) " The rotation rate (W1) below was derived from the period and is provided in degrees/day. The corresponding keywords were set as follows (saved in comments for trace-ability, lower-cased to prevent accidental use): body2101955_pole_ra = ( 86.6388 0. 0. ) body2101955_pole_dec = ( -65.1086 0. 0. ) body2101955_pm = ( 89.6456 2010.4894494679531 0. ) body2101955_long_axis = ( 0. ) Values in the Version 1.1 The pole direction in this version is the same as in the version 1.0, based on [1]. The prime meridian location (W0) and rotation terms (W1 and W2) in this version are from [2], computed from fitting lightcurves, and adjusting W0 until the phase at 2005 Sep 14 (epoch of Radar model) matches the version 1.0 based on the phase difference between rq36.v.mod1002-submitted and rq36.p5.pdot30.mod models. The corresponding keywords were set as follows (saved in comments for trace-ability, lower-cased to prevent accidental use): body2101955_pole_ra = ( 86.6388 0. 0. ) body2101955_pole_dec = ( -65.1086 0. 0. ) body2101955_pm = ( 154.9182 2011.14576050637 1.5e-06 ) body2101955_long_axis = ( 0. ) Values in the Version 1.2 The pole direction in this version is from [3], based on the Nav solution from 2019 Jan 09. The rotation terms (W1 and W2) use the method of [2] but include data through approach. The prime meridian location (W0) was determined by fixing W1 and W2 and then adjusting W0 in ISIS until rendered Approach images visually showed the chosen Prime Meridian feature from [3] at 0 longitude. The corresponding keywords were set as follows (saved in comments for trace-ability, lower-cased to prevent accidental use): body2101955_pole_ra = ( 85.3400 0. 0. ) body2101955_pole_dec = ( -60.1600 0. 0. ) body2101955_pm = ( 146.8404 2011.146953279 1.5e-06 ) body2101955_long_axis = ( 0. ) Values in the current Version 1.3 The rotation terms and pole directon in this version are from [4], based on the Nav solution from 2019 Jan 16, OD90. These rotation coefficients were used in creating shape model v020. The rotation terms use the acceleration from [5] along with the rotation phase and rate from [4] recast to give the same rate and phase as [4] at 2019 Jan 01 12:00:00 TDB ("J2019"). [4] has rotation constants of ( 45.6089 2011.17201568 0 ). J2019 is 6940 days later than J2000. The T^2 term W2 from [5] is 0.000001815. W1 = 2011.17201568 - (2 * W2 * 6940) = 2011.14682348 W0 = 45.6089 + (2011.17201568 - 2011.14682348) * 6940 - 0.000001815 * 6940 * 6940 = 133.0258 \begindata BODY2101955_POLE_RA = ( 85.6474 0. 0. ) BODY2101955_POLE_DEC = ( -60.1697 0. 0. ) BODY2101955_PM = ( 133.0258 2011.14682348 1.815e-06 ) BODY2101955_LONG_AXIS = ( 0. ) \begintext Radii for asteroid Bennu -------------------------------------------------------- Values in Versions 1.0 and 1.1 The radii in this version are set based on following values from [1]: " 2.1.2 Polar Dimension 508 meters 2.1.3 Equatorial Dimensions 565 x 535 meters " The radii below are 1/2s of the polar and equatorial dimensions provided in kilometers. The corresponding keywords were set as follows (saved in comments for trace-ability, lower-cased to prevent accidental use): body2101955_radii = ( 0.2825 0.2675 0.254 ) Values in Version 1.2 and Current Version 1.3 The radii in this version are set based on following values from [3]: "The extent of the GDTM is (563.87 +/- 0.17) x (536.09 +/- 0.17) x (498.42 +/- 0.17) m." The radii below are 1/2s of the polar and equatorial dimensions provided in kilometers. \begindata BODY2101955_RADII = ( 0.281935 0.268045 0.24921 ) \begintext End of PCK file.