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153 lines
5.1 KiB
Plaintext
153 lines
5.1 KiB
Plaintext
KPL/LSK
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LEAPSECONDS KERNEL FILE
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===========================================================================
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Modifications:
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--------------
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2016, Jul. 14 NJB Modified file to account for the leapsecond that
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will occur on December 31, 2016.
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2015, Jan. 5 NJB Modified file to account for the leapsecond that
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will occur on June 30, 2015.
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2012, Jan. 5 NJB Modified file to account for the leapsecond that
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will occur on June 30, 2012.
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2008, Jul. 7 NJB Modified file to account for the leapsecond that
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will occur on December 31, 2008.
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2005, Aug. 3 NJB Modified file to account for the leapsecond that
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will occur on December 31, 2005.
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1998, Jul 17 WLT Modified file to account for the leapsecond that
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will occur on December 31, 1998.
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1997, Feb 22 WLT Modified file to account for the leapsecond that
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will occur on June 30, 1997.
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1995, Dec 14 KSZ Corrected date of last leapsecond from 1-1-95
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to 1-1-96.
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1995, Oct 25 WLT Modified file to account for the leapsecond that
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will occur on Dec 31, 1995.
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1994, Jun 16 WLT Modified file to account for the leapsecond on
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June 30, 1994.
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1993, Feb. 22 CHA Modified file to account for the leapsecond on
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June 30, 1993.
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1992, Mar. 6 HAN Modified file to account for the leapsecond on
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June 30, 1992.
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1990, Oct. 8 HAN Modified file to account for the leapsecond on
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Dec. 31, 1990.
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Explanation:
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------------
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The contents of this file are used by the routine DELTET to compute the
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time difference
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[1] DELTA_ET = ET - UTC
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the increment to be applied to UTC to give ET.
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The difference between UTC and TAI,
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[2] DELTA_AT = TAI - UTC
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is always an integral number of seconds. The value of DELTA_AT was 10
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seconds in January 1972, and increases by one each time a leap second
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is declared. Combining [1] and [2] gives
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[3] DELTA_ET = ET - (TAI - DELTA_AT)
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= (ET - TAI) + DELTA_AT
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The difference (ET - TAI) is periodic, and is given by
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[4] ET - TAI = DELTA_T_A + K sin E
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where DELTA_T_A and K are constant, and E is the eccentric anomaly of the
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heliocentric orbit of the Earth-Moon barycenter. Equation [4], which ignores
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small-period fluctuations, is accurate to about 0.000030 seconds.
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The eccentric anomaly E is given by
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[5] E = M + EB sin M
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where M is the mean anomaly, which in turn is given by
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[6] M = M + M t
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0 1
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where t is the number of ephemeris seconds past J2000.
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Thus, in order to compute DELTA_ET, the following items are necessary.
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DELTA_TA
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K
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EB
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M0
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M1
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DELTA_AT after each leap second.
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The numbers, and the formulation, are taken from the following sources.
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1) Moyer, T.D., Transformation from Proper Time on Earth to
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Coordinate Time in Solar System Barycentric Space-Time Frame
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of Reference, Parts 1 and 2, Celestial Mechanics 23 (1981),
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33-56 and 57-68.
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2) Moyer, T.D., Effects of Conversion to the J2000 Astronomical
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Reference System on Algorithms for Computing Time Differences
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and Clock Rates, JPL IOM 314.5--942, 1 October 1985.
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The variable names used above are consistent with those used in the
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Astronomical Almanac.
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\begindata
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DELTET/DELTA_T_A = 32.184
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DELTET/K = 1.657D-3
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DELTET/EB = 1.671D-2
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DELTET/M = ( 6.239996D0 1.99096871D-7 )
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DELTET/DELTA_AT = ( 10, @1972-JAN-1
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11, @1972-JUL-1
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12, @1973-JAN-1
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13, @1974-JAN-1
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14, @1975-JAN-1
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15, @1976-JAN-1
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16, @1977-JAN-1
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17, @1978-JAN-1
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18, @1979-JAN-1
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19, @1980-JAN-1
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20, @1981-JUL-1
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21, @1982-JUL-1
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22, @1983-JUL-1
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23, @1985-JUL-1
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24, @1988-JAN-1
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25, @1990-JAN-1
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26, @1991-JAN-1
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27, @1992-JUL-1
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28, @1993-JUL-1
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29, @1994-JUL-1
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30, @1996-JAN-1
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31, @1997-JUL-1
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32, @1999-JAN-1
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33, @2006-JAN-1
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34, @2009-JAN-1
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35, @2012-JUL-1
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36, @2015-JUL-1
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37, @2017-JAN-1 )
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\begintext
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