Table of contents
sce2c_c ( ET to continuous SCLK ticks )
void sce2c_c ( SpiceInt sc,
SpiceDouble * sclkdp )
Convert ephemeris seconds past J2000 (ET) to continuous encoded
spacecraft clock (`ticks'). Non-integral tick values may be
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
start. `sclkdp' need not be integral.
sc is a NAIF integer code for a spacecraft whose
encoded SCLK value at the epoch specified by `et' is
et is an epoch, specified as ephemeris seconds past
sclkdp is an encoded spacecraft clock value. `sclkdp' is
an encoded representation of the total number
of spacecraft clock ticks measured from the time
the spacecraft clock started to the epoch `et':
partition information IS reflected in the encoded
`sclkdp' may be non-integral: `sclkdp' is NOT
rounded to the nearest whole tick.
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 routine outputs continuous encoded SCLK values; unlike the
routine sce2t_c, the values output by this routine need not be
This routine supports use of non-integral encoded clock values in
C-kernels: non-integral clock values may be stored as pointing
time tags when a C-kernel is created, and they may be supplied
as request times to the C-kernel readers.
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 routine sce2s_c.
See the SCLK Required Reading for a list of the entire set of
SCLK conversion routines.
1) Convert ET directly to a continuous, 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.
sce2c_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 );
sce2c_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)
E.D. Wright (JPL)
-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, 09-NOV-2009 (EDW)
Corrected typo in header; j2000_c replaced with J2000. Mention of
the J2000 epoch in the previous header used the word "j2000_c" (wrong)
instead of "J2000" (correct).
-CSPICE Version 1.0.1, 14-AUG-2006 (EDW)
Replace mention of ldpool_c with furnsh_c.
-CSPICE Version 1.0.0, 18-JUN-1999 (NJB)
ephemeris time to continuous spacecraft_clock ticks