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) This function assumes that that an SCLK kernel appropriate
to the spacecraft clock identified by the input argument sc
has been loaded. If an SCLK kernel has not been loaded,
does not contain all of the required data, or contains
invalid data, error diagnoses will be performed by functions
called by this function. The output argument sclkdp will not
2) 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 function is called. If a leapseconds kernel is required
for conversion between SCLK and ET but is not loaded, the
error will be diagnosed by functions called by this function.
The output argument sclkdp will not be modified.
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 function, the error
SPICE(NOTSUPPORTED) is signaled. 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', the error will be diagnosed by functions called by this
function. 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.
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.
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 function is called.
2) If the SCLK kernel used with this function does not map SCLK
directly to barycentric dynamical time, a leapseconds kernel
must be loaded at the time this function is called.
 CK Required Reading
 SPK Required Reading
N.J. Bachman (JPL)
-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