Low accuracy, long term predict earth PCK ========================================= Created by: Nat Bachman (NAIF/JPL) Creation date: 2025-08-26T19:44:31 Program version: WRTPEM Version 7.0.0, 02-JUN-2023 Original file name: earth_2025_250826_2125_predict.bpc Data Sources Input file: extended EOP created from JPL EOP file latest.long (Copied from WWW URL https://eop.jpl.nasa.gov/eop/latest.long) Source EOP metadata: $ JPL Earth Orientation Parameter File $ Last Data Point 26-AUG-2025 $ Predicts to 21-NOV-2025 $ EOPLBL='EOP. LAST DATUM 26-AUG-2025. PREDICTS->21-NOV-2025, UT1TYP=UT1. ' EOPFNG='Enter MAKE_EOP 26-Aug-2025 11:03:05 linked 09-Nov-2023 23:29:03 ' EOPUT1='UT1' EOPTYP='EOP' EOPTIM='26-Aug-2025 11:03:05 ' EOPTRF='ITRF93' EOPCRF='ICRF93' Input file: leapseconds kernel naif0012.tls Coverage ET Start time: 2025 JAN 01 00:01:09.183 TDB ET Stop time: 2125 NOV 22 00:01:09.182 TDB UTC Epoch of last datum: 2025 AUG 26 00:00:00.000 UTC Particulars This is low-accuracy predict PCK file giving the orientation of the Earth as a function of time for the interval shown above. This PCK file is made from an extended EOP file which consists of the JPL EOP file named above, with four extra records appended. These records are designed to add 100 years to the coverage of the EOP file without affecting interpolated data values for times within the coverage interval of the original EOP file. Data values of records in the extended interval are constant, with the exception of the TAI-UT1 offsets. Those are adjusted so that the corresponding values of TAI-UT1R are constant. The terrestrial frame whose orientation is given by this file is ITRF93; the inertial base frame is Ecliptic of J2000. Rotational effects included are: -Precession (1976 IAU model) -Nutation (1980 IAU model) -Nutation corrections -Rotation through true sidereal time -Polar motion Euler angles have been extracted from the Ecliptic-to-ITRF93 rotation matrix, and Chebyshev polynomials were fit to the Euler angles. The Chebyshev expansion degree was 49; the degree of the retained polynomials is 20. The coverage interval for each set of polynomials is 1 day or less. This file represents the same earth orientation as does the cited EOP file for the time range: 01-JAN-2025 UTC 21-NOV-2025 UTC That EOP file was extended as described below. The extended EOP file was used to create this binary PCK file. For epochs after the end of EOP coverage, polar motion and nutation corrections from the EOP file are held constant at values obtained by extrapolating 1 day from the last source EOP record. TAI-UT1 values are set so that the corresponding TAI-UT1R values at each epoch of the extrapolated records are equal. Details of the EOP extrapolation process are given below. Let n be the number of data records in the original EOP file. Let MJD(i) be the epoch of the ith record expressed as a modified Julian date. The added records have the following characteristics: Record n+1: Epoch is MJD(n) + 1. Nutation correction and polar motion values are obtained by extrapolating to the epoch a cubic Lagrange interpolating polynomial fitted to the corresponding data in records n-3 : n. TAI-UT1 is obtained by converting to TAI-UT1R the TAI-UT1 data in records n-3 : n, extrapolating an interpolating polynomial as for the other data, then converting the extrapolated TAI-UTR1 value to TAI-UT1. UTC string is consistent with the MJD epoch. Record n+2: Epoch is MJD(n) + 2. Nutation correction and polar motion values match those of record n+1. TAI-UT1 is set so that the corresponding value of TAI-UT1R at this epoch is that corresponding to TAI-UT1 at the epoch of record n+1. UTC string is consistent with the MJD epoch. Record n+3: Epoch is MJD(n) + 3. Data values are as described for record n+2, adjusted for this epoch. Record n+4: Epoch is MJD(n) + 27393. Data values are as described for record n+2, adjusted for this epoch. In all of the four records described above, the values of TAI-UT1 have been selected so the corresponding values of TAI-UT1R are constant and equal to the value resulting from extrapolating the cubic interpolating polynomial for TAI-UT1R, fitted to the final four values of TAI-UT1R derived from the original EOP file, to the epoch of record n+1. The expected behavior of the interpolation algorithm is as follows: Time range Interpolation characteristics ============ ============================= Epoch of record 1 to epoch of record n-1: Interpolation is identical to standard EOP file, up to round-off error and small differences in polynomial fitting errors. Orientation error relative to that provided by a binary PCK derived from the source EOP file is non-zero due to differences in the Chebyshev fitting process. Error is at the sub-nanoradian level. Epoch of record n-1 to epoch of record n: Nearly identical to standard EOP file; small round-off error will occur. Orientation error relative to that provided by a binary PCK derived from the source EOP file is at the sub-nanoradian level. Epoch of record n to epoch of record n+1: Some ringing of interpolated data will occur. This interval has duration 1 day. Orientation error, relative to actual Earth orientation, is estimated to be at the 3 microradian level. Epoch of record n+1 to epoch of record n+2: Some ringing of interpolated data will occur. This interval has duration 1 day. Orientation error, relative to actual Earth orientation, is estimated to be at the 3 microradian level. Epoch of record n+2 to epoch of record n+3: Ideally nutation corrections and polar motion will be constant, as will TAI-UT1R derived from TAI-UT1 values in the file. Some round-off error should be expected. This interval has duration 1 day. Orientation error, relative to actual Earth orientation, is estimated to be at the 3 microradian level. Epoch of record n+3 to epoch of record n+4: Data are as described for records n+2 to n+3. This interval has duration ~75 years. Orientation difference relative to the IAU_EARTH reference frame's rotation model ranges from the 1.5 milliradian level at the interval start to the 5.5 milliradian level at the end.