Table of contents
sce2t_c ( ET to SCLK ticks )
void sce2t_c ( SpiceInt sc,
SpiceDouble * sclkdp )
Convert ephemeris seconds past J2000 (ET) to integral
encoded spacecraft clock (`ticks'). For conversion to
fractional ticks, (required for C-kernel production), see
the routine sce2c_c.
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
sc I NAIF spacecraft ID code.
et I Ephemeris time, seconds past J2000.
sclkdp O SCLK, encoded as ticks since spacecraft clock
sc is a NAIF integer code for a spacecraft whose encoded
SCLK value at the epoch specified by `et' is desired.
et is an epoch, specified as ephemeris seconds past
sclkdp is an encoded integral spacecraft clock value.
`sclkdp' is an encoded representation of the total
count of spacecraft clock ticks measured from the
time the spacecraft clock started to the epoch `et':
partition information IS reflected in the encoded
value. `sclkdp' is rounded to the nearest integral
double precision number.
1) If an SCLK kernel has not been loaded, does not contain all of
the required data, or contains invalid data, an error is
signaled by a routine in the call tree of this routine. The
output argument `sclkdp' will not be modified. This routine
assumes that that an SCLK kernel appropriate to the spacecraft
clock identified by the input argument `sc' has been loaded.
2) If a leapseconds kernel is required for conversion between
SCLK and `et' but is not loaded, an error is signaled by a
routine in the call tree of this routine. The output argument
`sclkdp' will not be modified. When using SCLK kernels that map
SCLK to a time system other than `et' (also called barycentric
dynamical time---`TDB'), it is necessary to have a leapseconds
kernel loaded at the time this routine is called.
The time system that an SCLK kernel maps SCLK to is indicated
by the variable SCLK_TIME_SYSTEM_nn in the kernel, where nn
is the negative of the NAIF integer code for the spacecraft.
The time system used in a kernel is TDB if and only if the
variable is assigned the value 1.
3) If the clock type for the spacecraft clock identified by `sc' is
not supported by this routine, the error SPICE(NOTSUPPORTED)
is signaled by a routine in the call tree of this routine. The
output argument `sclkdp' will not be modified.
4) If the input `et' value is not representable as an encoded
spacecraft clock value for the spacecraft clock identified by
`sc', an error is signaled by a routine in the call tree of this
routine. The output argument `sclkdp' will not be modified.
This function outputs discrete, encoded SCLK values. Since
continuous SCLK values are generally more useful, the newer
function sce2c_c (ET to continuous ticks) should normally be used
in place of this one. However, the functionality of this
routine is needed for converting ET to SCLK strings, and the
routine sce2s_c calls this routine for that purpose.
This function outputs encoded SCLK values. The advantage of
encoded SCLK, as opposed to character string representations of
SCLK, is that encoded SCLK values are easy to perform arithmetic
operations on. Also, working with encoded SCLK reduces the
overhead of repeated conversion of character strings to integers
or double precision numbers.
To convert ET to a string representation of an SCLK value, use
the CSPICE function sce2s_c.
See the SCLK Required Reading for a list of the entire set of
SCLK conversion routines.
1) Convert ET directly to an encoded SCLK value. Use both of
these time values to look up both C-kernel (pointing) and
SPK (position and velocity) data for an epoch specified by an
During program initialization, load the leapseconds and
SCLK kernels. We will pretend that these files are named
"leapseconds.ker" and "gllsclk.ker". To use this code
fragment, you must substitute the actual names of these
kernel files for the names used here.
Load leapseconds and SCLK kernels:
furnsh_c ( "leapseconds.ker" )
furnsh_c ( "gllsclk.ker" )
The mission is Galileo, which has spacecraft ID -77.
Let ET be the epoch, specified in ephemeris seconds
past J2000, at which both position and pointing data
Find the encoded SCLK value corresponding to ET.
sce2t_c ( -77, et, &sclkdp );
Now you're ready to call both ckgp_c, which expects the input
epoch to be specified by an encoded SCLK string, and
spkez_c, which expects the epoch to be specified as an
Find scan platform pointing cmat and s/c--target
vector (first 3 components of state) at epoch.
We assume that CK and SPK kernels have been loaded
already, via cklpf_c and spklef_c respectively.
ckgp_c ( scanpl, sclkdp, tol, refsys,
cmat, &clkout, &found );
spkez_c ( target, et, refsys, corr,
-77, state, < );
2) Convert UTC to an encoded Voyager 2 SCLK value.
Again, your initialization code must load the leapseconds
and SCLK kernels.
Load leapseconds and SCLK kernels:
furnsh_c ( "leapseconds.ker" );
furnsh_c ( "vgr2sclk.ker" );
Find the encoded Voyager 2 SCLK value sclkdp
corresponding to the given UTC time.
utc2et ( utc, &et );
sce2t_c ( -32, et, &sclkdp );
1) An SCLK kernel appropriate to the spacecraft clock identified
by `sc' must be loaded at the time this routine is called.
2) If the SCLK kernel used with this routine does not map SCLK
directly to barycentric dynamical time, a leapseconds kernel
must be loaded at the time this routine is called.
N.J. Bachman (JPL)
J. Diaz del Rio (ODC Space)
-CSPICE Version 1.0.3, 05-AUG-2021 (JDR)
Edited the header to comply with NAIF standard. Moved CK and SPK
required readings from -Literature_References to -Required_Reading
-CSPICE Version 1.0.2, 27-JAN-2004 (NJB)
Header was updated to remove comments indicating this routine
was deprecated. Minor changes were made to clarify both the
functionality of this routine and the difference between
this routine and sce2c_c. Examples were updated to use furnsh_c.
-CSPICE Version 1.0.1, 09-MAR-1999 (NJB)
Updated to reflect the introduction of continuous ticks and
the function sce2c_c.
Occurrences of "routine" were changed to "function" in the header.
-CSPICE Version 1.0.0, 08-FEB-1998 (NJB)
Based on SPICELIB Version 1.0.2, 10-APR-1992 (NJB) (WLT)
ephemeris time to spacecraft_clock ticks