| SCLK Required Reading |
Table of ContentsSCLK Required Reading Abstract Introduction References Support for New Missions Detection of Non-native Text Files The Basics SCLK rates SCLK kernels Partitions, briefly Converting between SCLK strings and ET or UTC Using encoded SCLK Encoded SCLK Ticks Partitions SCLK Conversion Functions Distinguishing Between Different Clocks Clock Types Clock type-specific functions Spacecraft-Specific Parameters The SCLK Kernel File Partition boundaries Clock type assignment Clock type-specific parameters Expanding the system: What NAIF must do An Example Using SCLK Functions SCLK01 Conforming spacecraft clocks Type 1 SCLK format Galileo SCLK format Mars Global Surveyor SCLK format Voyager SCLK clock format Type 1 SCLK conversion Conversion algorithms Type 1 SCLK functions The type 1 SCLK kernel file Kernel ID assignment Parallel time system code assignment SCLK type assignment Format constant assignments Time coefficients Partition boundaries Sample SCLK kernels Appendix: Document Revision History May 27, 2010 April 1, 2009 March 02, 2008 December 21, 2004 February 2, 2004 April 12, 1999 SCLK Required Reading
Abstract
Introduction
It is natural, then, that SCLK have an important role in the CSPICE system. In fact, all C-kernel pointing data are referenced to SCLK. CSPICE contains functions to convert between SCLK and other standard time systems, such as Ephemeris Time (ET) and Universal Time Coordinated (UTC). References
Support for New Missions
Detection of Non-native Text Files
The Basics
SCLK rates
The mapping that models the relationship between SCLK and other time systems is updated as a mission progresses. While the change in the relationship between SCLK and other systems will usually be small, you should be aware that it exists; it may be a cause of discrepancies between results produced by different sets of software. SCLK kernels
To use any of the SCLK conversion functions, your program must first load a SCLK kernel file. The code fragment
furnsh_c ( <name of the SCLK kernel file goes here> );accomplishes this. You must supply the actual name of the kernel file you want to load. In addition, you will usually need to load a leapseconds kernel. For some missions, conversions between SCLK and ET will require that both an SCLK and a leapseconds kernel be loaded. The code fragment
furnsh_c ( <name of the LEAPSECONDS kernel file goes here> );loads a leapseconds kernel. Leapseconds kernels are described in the TIME required reading document, time.req. Normally, you will load these kernels at just one point in your application program, prior to using any time conversion functions. Details concerning the kernel pool are covered in the KERNEL required reading document, kernel.req. Partitions, briefly
The fact that a spacecraft clock may regress raises the possibility that the clock may give the same reading at two or more different times. For this reason, SCLK strings in CSPICE are prefaced with partition numbers. The partition number is a positive integer followed by a forward slash, for example
4 /Any number of blanks are allowed on either side of the slash. An example of a Galileo SCLK string with a partition number is
1/100007:76:1Partition numbers serve to ensure that spacecraft clock readings can be interpreted unambiguously. Converting between SCLK strings and ET or UTC
To convert a SCLK string to a double precision ET value, you can use the function call
scs2e_c ( sc, clkstr, &et );To convert a SCLK string to a UTC string, you can use the code fragment
scs2e_c ( sc, clkstr, &et ); timout_c ( et, pictur, lenout, utc );where
The inverse conversion is performed by the code fragment
str2et_c ( utc, &et ); sce2s_c ( sc, et, lenout, clkstr ); Using encoded SCLK
You can obtain encoded SCLK values from SCLK strings via the function scencd_c. The code fragment
scencd_c ( sc, clkstr, &sclkdp );encodes the SCLK string `clkstr' as the double precision value `sclkdp'. Encoded SCLK values can be converted to strings using the code fragment
scdecd_c ( sc, sclkdp, lenout, clkstr );You can obtain continuous encoded SCLK values from ET via the function sce2c_c. The code fragment
sce2c_c ( sc, et, &sclkdp );encodes the ephemeris time ET as the double precision value `sclkdp'. SCLKDP need not be integral; even though non-integral tick values do not represent SCLK readings, they are permitted to avoid truncation error when representing ET as encoded SCLK. A parallel routine sce2t_c converts ET to encoded SCLK, rounding the result to the nearest integral tick. The inverse conversion is provided by the routine sct2e_c, which is called as follows:
sct2e_c ( sc, sclkdp, &et );SCT2E handles integral or continuous tick values as inputs. There is a special function that is used for encoding ``tolerance'' values for the CK readers. (See the CK Required Reading, ck.req, document for a discussion of the CK readers.) The code fragment
sctiks_c ( sc, clkstr, &ticks );produces an encoded tolerance value. sctiks_c takes SCLK strings WITHOUT partition numbers as inputs; this is because the strings indicate a delta time rather than an absolute time. All of the concepts used in this section are discussed in greater detail in the following sections of this document. Encoded SCLK
To convert a character representation of an SCLK count `sclkch' to its double precision encoding `sclkdp', use the function scencd_c (Encode SCLK):
scencd_c ( sc, sclkch, &sclkdp );The function scdecd_c (Decode SCLK) recovers the character representation of spacecraft clock from its double precision encoding.
scdecd_c ( sc, sclkdp, lenout, sclkch );The first argument to both functions, `sc', is the NAIF integer ID for the spacecraft whose clock count is being encoded or decoded (for example, --32 for Voyager 2). Each spacecraft may have a different format for its clock counts, so the encoding scheme may be different for each. Later chapters describing clock types give complete details on clock string formats for spacecraft clocks supported by the CSPICE Toolkit. Ticks
An analogy can be drawn with a standard wall clock, showing hours, minutes, and seconds. One tick for a wall clock would be one second. And a wall clock time of
10:05:50would represent
10(3600) + 5(60) + 50 = 36350ticks. As in the case of the wall clock, the length of time associated with a tick varies as the clock rate varies. Since not all spacecraft clocks are the same, the particular time value for one tick varies from spacecraft to spacecraft. For Mars Global Surveyor, for instance, one tick is equivalent to approximately four milliseconds. For Galileo, it's about 8 1/3 milliseconds. In addition to representing spacecraft clock readings, ticks can be used to represent arbitrary epochs. In order to minimize discretization error, ``continuous'' (non-integral) tick values are supported: ephemeris times may be converted to non-integral ticks via the function sce2c_c. Conversion of spacecraft clock strings to ticks always produces integral tick values. Partitions
Any time one of these discontinuities occurs, we say that SCLK time has entered a new partition. The partitions must be accounted for when encoding and decoding SCLK. To continue our analogy, say our wall clock was being used to keep time throughout an entire day. Then 10:05:50 is ambiguous, because we don't know if it falls in the morning or evening ``partition.'' So we append the indicators ``a.m.''\ or ``p.m.''\ to be clear. We handle SCLK similarly. Instead of just converting a clock count to ticks (10:05:50 to 36350), we take into account the partition that the count falls in, and compute the number of ticks since clock start (10:05:50 a.m. to 36350; 10:05:50 p.m. to 36350 + 12(60)(60) = 79550). When you pass a SCLK string to scencd_c, it is normally prefixed with a number indicating the partition in which the count falls. Sample SCLK strings for Voyager 2, including partition numbers, are given in an example program later in this document. The presence of the partition number is not always required. If it is missing, scencd_c will assume the partition to be the earliest one possible that contains the clock string being encoded. It's good practice to always include the partition number in SCLK strings. To convert to ticks since clock start, scencd_c processes the partition number. It has to know how many ticks were in all preceding partitions, and what the start and stop clock values were for each. This information is stored in a SCLK kernel file for that spacecraft. The SCLK kernel file is described in detail in a later section. New partitions may occur at any time throughout the course of active missions. The responsible mission operations team must update the SCLK kernel file to include new partitions as they occur. In converting encoded SCLK back to an equivalent clock string, scdecd_c must also use the SCLK kernel file. Note, however, that you only have to load the SCLK kernel file once in your program, no matter how many calls to scencd_c and scdecd_c are made afterwards. See the KERNEL required reading file, kernel.req, for information about ``loading'' miscellaneous kernel files into the kernel pool. scdecd_c always returns a clock string prefixed by a partition number and the '/' character, for example
2/2000:83:12If you want to read partition start and stop times for yourself, use the function scpart_c:
scpart_c ( sc, nparts, pstart, pstop ); SCLK Conversion Functions
CSPICE contains the following functions to convert between encoded and character SCLK, ET and UTC. Note that the names of the functions involving SCLK are all prefixed with `sc', for Spacecraft Clock.
et2utc_c (et, format, prec, lenout, utc) (Convert ET to a
utc string)
CSPICE also contains two functions that can encode and decode relative, or ``delta'' SCLK times. These are SCLK strings without partition numbers that represent time increments rather than total time since clock start. Such strings are encoded as tick counts. The functions are:
sctiks_c ( sc, clkstr, ticks ) (Convert delta SCLK to
ticks )
Distinguishing Between Different Clocks
The differences are handled by the SCLK software at two levels: High-level differences are managed in the code itself through ``clock types.'' More detailed spacecraft-specific differences are handled using parameters in a SCLK kernel. Clock Types
A spacecraft clock data type has two components: a format defining the set of acceptable spacecraft clock (SCLK) strings, and a method of converting SCLK strings to a standard time representation, such as ephemeris or UTC seconds past J2000. For example, a type 1 clock consists of some number of cascading integer counters. An individual counter can increment only when the immediately preceding counter reaches its maximum expression and ``rolls over.'' Our wall clock is an example: the counters are hours, minutes and seconds. One tick for a type 1 clock is defined to be the value of the least-significant component increment. Clock type 1 uses a piecewise-linear interpolation process to convert between SCLK and other time systems. The chapter ``SLCK01'' describes clock type 1 in detail. It includes the specific SCLK string formats for each of the type 1 spacecraft clocks supported by the CSPICE Toolkit. SCLK functions determine the clock type for a particular spacecraft from the SCLK kernel file (described in the next section). Clock type-specific functions
sctkcc_ (sc, clkstr, ticks, len_clkstr ) (SCLK string to ticks,
type cc)
sctkcc_ and scfmcc_ are called by sctiks_c and scfmt_c, respectively. Each clock type is supported in the time conversion process by two functions:
sctecc_ (sc, sclkdp, et) (Encoded SCLK ticks to ET, type cc)
Spacecraft-Specific Parameters
The SCLK Kernel File
Before calling any of the functions to encode or decode SCLK, or convert between SCLK and other time systems, an application program must load the contents of the SCLK kernel file into the kernel pool, using the function furnsh_c (load pool):
furnsh_c ( "name_of_SCLK_kernel_file" );An application must also load the leapseconds kernel file if there are any conversions to be performed between ET and UTC. This is typically done in the initialization section of your program. The SCLK kernel file you use should contain values for the particular spacecraft you are dealing with. The variables expected to be found in the file are all prefixed with the string
SCLK_These variables include partition boundaries, clock type, and several other parameters associated with the clock type. These are described below. Partition boundaries
SCLK_PARTITION_START_ss = ( .....
.....
.....
..... )
SCLK_PARTITION_END_ss = ( .....
.....
.....
..... )
where --ss is the spacecraft ID code. These variables are arrays
containing one element per partition. The nth element of
SCLK_PARTITITION_END_ssis considered to be the ``first tick'' of the (n+1)st partition. Mathematically speaking, partitions may be thought of as intervals that are closed on the left and open on the right. Clock type assignment
SCLK_DATA_TYPE_ss = ( cc )where cc is the clock type. New clock types will be developed as needed. Note that multiple spacecraft ID codes can be associated with the type 1 SCLK data type at one time. Since the spacecraft codes are included in the SCLK variable names, there will be no naming conflicts. (We don't expect this feature to be used much, if at all, but it's there should you need it.) Clock type-specific parameters
Expanding the system: What NAIF must do
If a new clock fits into the framework of clock type 1, then the clock can be accommodated simply by producing a new kernel file for that spacecraft clock. For the new clock, a new set of kernel variables corresponding to those described above, and those in the chapter ``SCLK01,'' could be added to an existing SCLK kernel file. Alternatively, an entirely new SCLK kernel file containing the new parameters could be created --- this is the more likely approach. Once this is done, all existing SCLK functions will function, without modification, using the spacecraft ID. If a new clock does not fit into the clock type 1 framework, then NAIF will design a new clock type. This will involve writing new versions of the four clock type-specific functions described earlier:
sctkcc_ scfmcc_ sctecc_ sceccc_where cc is the new clock type number. New cases will have to be added to the code of the following higher-level SCxxx conversion functions to call the new, type-specific functions:
scfmt_c sctiks_c sct2e_c scs2e_c sce2c_c sce2t_c sce2s_cIt will probably be necessary to design new SCLK kernel file variables to accommodate the new type, and augment the standard variables described above. Adding a new clock type does not change the calling sequence of any of the high-level conversion functions. Thus, once you've learned how to use the SCLK conversion functions, you won't have to re-learn just because a new spacecraft clock has been introduced. An Example Using SCLK Functions
/*
Request pointing from a C-kernel file for a sequence of
pictures obtained from the Voyager 2 narrow angle camera.
Use an array of character spacecraft clock counts as input.
Decode the output clock counts and print the input and
output clock strings. Also print the equivalent UTC time
for each output clock time.
Note that the SCLK kernel file must contain VGR 2 clock
information.
*/
#include <stdio.h>
#include "SpiceUsr.h"
void main()
{
/*
Local constants:
*/
#define NPICS 4
#define TIMLEN 25
#define LINLEN 80
/*
Names of C kernel and SCLK kernels:
*/
#define CK "VGR2NA.BC"
#define SCLKKER "SCLK.KER"
#define LSK "LSK.KER"
/*
The instrument we want pointing for is the Voyager 2
narrow angle camera. The reference frame we want is
J2000. The spacecraft is Voyager 2.
*/
#define INST -32001
#define REF "J2000"
#define SC -32
/*
Local static variables:
*/
static SpiceChar clktol [ TIMLEN ] = "0:01:001";
static SpiceChar sclkin [ NPICS ] [ TIMLEN ] =
{
"2/20538:39:768",
"2/20543:21:768",
"2/20550:37",
"2/20564:19"
};
/*
Local automatic variables:
*/
SpiceBoolean found;
SpiceChar sclkout [ TIMLEN ];
SpiceChar utc [ TIMLEN ];
SpiceDouble cmat [3][3];
SpiceDouble et;
SpiceDouble timein;
SpiceDouble timeout;
SpiceDouble tol;
SpiceInt i;
SpiceInt sc;
/*
Load the appropriate files. We need
1) A CK file containing pointing data.
2) The SCLK kernel file, for the SCLK conversion functions.
3) A leapseconds kernel, for ET-UTC conversions.
*/
furnsh_c ( CK, );
furnsh_c ( SCLKKER );
furnsh_c ( LSK );
/*
Convert the tolerance string to ticks.
*/
sctiks_c ( SC, clktol, &tol );
for ( i = 0; i < NPICS; i++ )
{
scencd_c ( SC, sclkin[i], &timein );
ckgp_c ( INST, timein, tol, REF, cmat, &timeout,
&found );
scdecd_c ( SC, timeout, TIMLEN, sclkout );
sct2e_c ( SC, timeout, &et );
et2utc_c ( et, "D", 3, TIMLEN, utc );
if ( found )
{
printf ( "\n"
"Input s/c clock count: %s\n"
"Output s/c clock count: %s\n"
"Output UTC: %s\n"
"Output C-Matrix: \n"
"\n"
"%f\t %f\t %f\t\n"
"%f\t %f\t %f\t\n"
"%f\t %f\t %f\t\n"
"\n",
sclkin[i],
sclkout,
utc,
cmat[0][0], cmat[0][1], cmat[0][2],
cmat[1][0], cmat[1][1], cmat[1][2],
cmat[2][0], cmat[2][1], cmat[2][2] );
}
else
{
printf ( "\n"
"Input s/c clock count: %s\n"
"No pointing found.\n",
sclkin[i] );
}
}
}
The output from this program looks like this:
Input s/c clock count: 2 / 20538:39:768 Output s/c clock count: 2/20538.39.768 Output UTC: 79-186/21:50:23.000 Output C-Matrix: <first C-matrix> Input s/c clock count: 2 / 20543:21:768 Output s/c clock count: 2/20543.22.768 Output UTC: 79-187/01:35:57.774 Output C-Matrix: <second C-matrix> Input s/c clock count: 2 / 20550:37 Output s/c clock count: 2/20550.36.768 Output UTC: 79-187/07:23:57.774 Output C-Matrix: <third C-matrix> Input s/c clock count: 2 / 20564:19 Output s/c clock count: 2/20564.19.768 Output UTC: 79-187/18:22:21.774 Output C-Matrix: <fourth C-matrix> SCLK01
Conforming spacecraft clocks
Type 1 SCLK format
Type 1 SCLK strings have the form
pppp/<time string>where pppp is a partition number between 1 and 9999 inclusive, and
<time string>is a time representation that conforms to the type 1 SCLK format. The partition specification (number and slash character) is optional; SCLK strings without partition numbers are assumed to refer to times in the first partition in which the specified clock count occurred. It's good practice to always include the partition number. An example of a type 1 SCLK string (for Galileo) is
3 / 10110007:09:6:1The number ``3'' is the partition number, the slash is a delimiter, and the rest of the string is a ``time string.'' With this example in hand, we're ready to define the type 1 SCLK format. The partition number is a positive integer followed by a forward slash, for example
4 /Zero or more blanks are allowed on either side of the slash. A type 1 SCLK time string consists of a series of one or more fields, each of which contains an integer. All fields but the leftmost are optional. The fields of a time string represent modular counts of time units. (A ``mod n'' count increments from zero to n-1, and then cycles back to zero.) The values for a given field may be offset by some fixed integer, so that they range from m to m+n, where m is non-negative. The moduli of the various fields are not necessarily the same. The time unit associated with a given field, multiplied by the modulus for that field, gives the time unit for next field to the left. For each field but the first, values may exceed the modulus for the field. For example, the modulus of the fourth field of a Galileo SCLK string is 8, but the digit ``9'' is allowed in that field. So
0:0:0:9is a valid Galileo SCLK string and represents the same time as
0:0:1:1On input to CSPICE functions, the fields of a type 1 SCLK string may be separated by any of the delimiter characters
- . , : <blank>On output from CSPICE functions, the delimiter characters will be those defined by a parameter in the SCLK kernel, described later. Consecutive delimiters containing no intervening digits are treated as if they delimit zero values. Note that all fields in time strings represent integers, not decimal fractions. So, the strings
11000687:9 11000687:90do not represent the same time value: in the former, the second field indicates a count of 9; in the latter, 90. Galileo SCLK format
16777214:90:9:7Numbering the fields from left to right, the time units and moduli of the fields are:
Field Time unit Modulus
----- --------------------------- --------
1 60 2/3 sec. 16777215
2 2/3 sec. (666 2/3 ms) 91
3 1/15 sec. ( 66 2/3 ms) 10
4 1/120 sec. ( 8 1/3 ms) 8
Fields 1--4 are known as: ``Real time image count'' (RIM), ``mod 91
count,'' ``mod 10 count'' or ``real time interrupt count'' (RTI), and
``mod 8 count.'' The values in all fields normally range from zero to
the modulus of the field, minus one.
The maximum time value that the Galileo spacecraft clock can represent (16777214:90:9:7) is approximately 32 years. Mars Global Surveyor SCLK format
4294967295.255Numbering the fields from left to right, the time units and moduli of the fields are:
Field Time unit Modulus
----- ---------------------- ----------
1 approximately 1 sec. 4294967296
2 1/256 sec. 256
Field 1 is known as the ``sclk_secs count.'' Field 2 is known as the
``sclk_fine word.'' The values in the first and second fields normally
range from zero to the modulus of the field, minus 1.
The maximum time value that the Mars Global Surveyor spacecraft clock can represent (4294967295.255) is approximately 136 years. Voyager SCLK clock format
65535.59.800Numbering the fields from left to right, the time units and moduli of the fields are:
Field Time unit Modulus
----- ------------------ ---------
1 2880 sec. 65536
2 48 sec. 60
3 0.06 sec. 800
Fields 1--3 are known as: ``Mod 16 count'' (actually mod 2**16), ``mod
60 count,'' and ``mod 800 count.'' The values in the first and second
fields normally range from zero to the modulus of the field, minus 1.
The range of the third field is from 1 to 800. The ``offset'' for the
third field is 1, so values in this field normally range from 1 to 800
rather than from 0 to 799; values above 800 are allowed and treated as
described above.
The maximum time value that the Voyager 1 and Voyager 2 spacecraft clocks can represent (65535:59:800) is approximately six years. Type 1 SCLK conversion
Since CSPICE also contains functions that convert between any of a variety of standard time systems, including ET, UTC, Terrestrial Dynamical Time (TDT), TAI, TDB Julian date, TDT Julian Date, and UTC Julian Date, conversion between SCLK strings and any other time system supported by CSPICE requires at most two function calls. Conversion algorithms
The standard time system used for the conversion is referred to here and in the CSPICE SCLK functions as the ``parallel'' time system. Normally, the CSPICE Toolkit will use only one parallel time system for any given spacecraft clock. Conversion from TDB to encoded SCLK follows the reverse path: first, TDB values are converted, if necessary, to equivalent values in the parallel time system; next, those parallel time values are converted to encoded SCLK. For each type 1 spacecraft clock, encoded SCLK is related to the parallel time system for that clock by a piecewise linear function. The function is defined by a set of pairs of encoded SCLK values and corresponding values in the parallel time system, and by a set of ``rate'' values that apply to the intervals between the pairs of time values. The rate values give the rate at which ``parallel time'' increases with respect to encoded SCLK time during the interval over which the rate applies. The rates in a type 1 SCLK kernel have units of
parallel time system units
----------------------------
most significant clock count
The units of the currently supported parallel time systems TDT and TDB
are seconds measured in those respective systems. So clock rates may be
TDT or TDB seconds per most significant clock count. For example, for
the GLL orbiter spacecraft clock, the rate unit is ``TDB seconds per
RIM.''
The specific method by which pairs of time values and rates are used to map encoded SCLK to parallel time values is explained in detail below. In the following discussion we'll use the name ``PARSYS'' to refer to the parallel time system. We'll use the name MSF to indicate the number of ticks per most significant SCLK field. We can represent the data that define the SCLK-to-PARSYS mapping as a set of ordered triples of encoded SCLK values (in units of ticks since spacecraft clock start), their equivalents in PARSYS time, and the rates corresponding to each pair of times:
( s/c_clock(1), parsys(1), rate(1) )
.
.
.
( s/c_clock(n), parsys(n), rate(n) )
The mapping of SCLK values to PARSYS times is carried out as follows: If
the sclk time ``clock'' satisfies
sclk(i) < clock < sclk(i+1)
-
then the corresponding PARSYS time is
parsys(i) + ( rate(i)/MSF ) * ( clock - sclk(i) )If
clock > clock(n)
-
the formula still applies, with i = n.
To convert PARSYS time values to SCLK, we use an analogous method. If ``time'' is the value to be converted, and
parsys(i) < time < parsys(i+1)
_
then the corresponding continuous encoded SCLK value is
time - parsys(i)
sclk(i) + ----------------
rate(i)/MSF
If
time > parsys(n)
-
the formula still applies, with i = n.
Note that this method will not handle rate values of 0 parallel time system units per tick. When the function described by the pairs of time values and rates is continuous, then all rates except for the last one are redundant, since
parsys(i+1) - parsys(i)
rate(i)/MSF = ------------------------
sclk(i+1) - sclk(i)
If the mapping from encoded SCLK to the parallel time system is not
continuous, then the mapping will not be strictly invertible: if an
encoded SCLK value is mapped to a parallel time value, then mapping that
parallel time value to encoded SCLK may not yield the original encoded
SCLK value. However, the capability of supporting non-continuous
mappings is provided in case it is needed to implement the mapping
provided by a flight project.
In order for CSPICE SCLK conversion functions to work, the information represented by the ordered triples described above must be loaded via the kernel pool. See the section ``The spacecraft clock kernel file'' below for details. Type 1 SCLK functions
The type 1 SCLK functions are
scfm01_ (sc, ticks, clkstr, len_clkstr) (Convert
ticks to a
type 1 SCLK
string)
The type 1 SCLK kernel file
SCLK_Variables that are applicable only to type 1 spacecraft clocks start with the string
SCLK01_An SCLK kernel file makes the following assignments for each spacecraft whose clock values are to be treated as ``type 1'' by the CSPICE SCLK functions: Kernel ID assignment
SCLK_KERNEL_IDThis identifier is normally a UTC time string, preceded by the character '@', for example,
@04-SEP-1990If you have loaded multiple SCLK kernels into the kernel pool, the identifiers for these kernels should be distinct. Parallel time system code assignment
SCLK01_TIME_SYSTEM_ss = ( nnn )where nnn is a numeric code designating the time system that the coefficients in the kernel map encoded SCLK to. The time systems and codes currently in use are:
SCLK type assignment
SCLK_DATA_TYPE_ss = ( 1 )Note that multiple mission ID codes can be associated with the type 1 SCLK data type at one time. Since the mission codes are included in the SCLK variable names, there will be no naming conflicts. Format constant assignments
SCLK01and end with the string
_sswhere --ss is the NAIF mission ID code. This allows the type 1 SCLK functions to find the correct constants for each mission ID associated with the first SCLK data type. The format constants that must be assigned are
SCLK01_N_FIELDS_ss SCLK01_MODULI_ss SCLK01_OFFSETS_ss SCLK01_OUTPUT_DELIM_ssHere are sample assignments of values to the variables describing the format of type 1 SCLK strings. The values shown apply to the Galileo SCLK format. Number of fields:
SCLK01_N_FIELDS_77 = ( 4 )Modulus of each field:
SCLK01_MODULI_77 = ( 16777215 91 10 8 )Offsets for field values. Offsets are listed for each field in left-to-right order:
SCLK01_OFFSETS_77 = ( 0 0 0 0 )Code for delimiter to be used in output strings. The codes and corresponding delimiters are:
Code Delimiter
1 .
2 :
3 -
4 ,
5 <space>
For Galileo, the code assignment would be:
SCLK01_OUTPUT_DELIM_77 = ( 2 ) Time coefficients
The time coefficients are assigned to the variable
SCLK01_COEFFICIENTS_sswhere --ss is the spacecraft ID code. The assigned values are triplets of SCLK values, corresponding parallel time values, and rates. The SCLK values are expressed in total ticks since clock start. The parallel time values may be expressed in a variety of units. The rate values have units that depend on the units used for the parallel time values: if we call these units
PARALLEL_TIME_UNITSthen the rate units are
PARALLEL_TIME_UNITS
----------------------------
most significant clock count
The term most ``significant clock count'' shown in the denominator
refers to the length of time associated with one count of the most
significant (leftmost) field of the formatted spacecraft clock string.
For example, for Voyager 2, the most significant field of a formatted
SCLK string is the ``mod 16'' field. For Galileo, the most significant
field is the ``RIM count.'' For Mars Global Surveyor, the most
significant field is the ``sclk_secs count.''
Partition boundaries
PARTITION_START_ss PARTITION_END_sswhere --ss is the spacecraft ID code. These variables are arrays containing one element per partition. Sample SCLK kernels
KPL/SCLK
\begindata
SCLK_KERNEL_ID = ( @04-SEP-1990//4:23:00 )
SCLK_DATA_TYPE_77 = ( 1 )
SCLK01_N_FIELDS_77 = ( 4 )
SCLK01_MODULI_77 = ( 16777215 91 10 8 )
SCLK01_OFFSETS_77 = ( 0 0 0 0 )
SCLK01_OUTPUT_DELIM_77 = ( 2 )
SCLK_PARTITION_START_77 = ( 0.0000000000000E+00
2.5465440000000E+07
7.2800001000000E+07
1.3176800000000E+08 )
SCLK_PARTITION_END_77 = ( 2.5465440000000E+07
7.2800000000000E+07
1.3176800000000E+08
1.2213812519900E+11 )
SCLK01_COEFFICIENTS_77 = (
0.0000000000000E+00 -3.2287591517365E+08 6.0666283888000E+01
7.2800000000000E+05 -3.2286984854565E+08 6.0666283888000E+01
1.2365520000000E+06 -3.2286561063865E+08 6.0666283888000E+01
1.2365600000000E+06 -3.2286558910065E+08 6.0697000438000E+01
1.2368000000000E+06 -3.2286557090665E+08 6.0666283333000E+01
1.2962400000000E+06 -3.2286507557565E+08 6.0666283333000E+01
2.3296480000000E+07 -3.2286507491065E+08 6.0666300000000E+01
2.3519280000000E+07 -3.2286321825465E+08 5.8238483608000E+02
2.3519760000000E+07 -3.2286317985565E+08 6.0666272281000E+01
2.4024000000000E+07 -3.2285897788265E+08 6.0666271175000E+01
2.5378080000000E+07 -3.2284769395665E+08 6.0808150200000E+01
2.5421760000000E+07 -3.2284732910765E+08 6.0666628073000E+01
2.5465440000000E+07 -3.2284696510765E+08 6.0666628073000E+01
3.6400000000000E+07 -3.2275584383265E+08 6.0666627957000E+01
7.2800000000000E+07 -3.2245251069264E+08 6.0666628004000E+01
1.0919999900000E+08 -3.2214917755262E+08 6.0666628004000E+01
1.2769119900000E+08 -3.2199508431761E+08 6.0665620197000E+01
1.3085799900000E+08 -3.2196869477261E+08 6.0666892494000E+01
1.3176799900000E+08 -3.2196111141061E+08 6.0666722113000E+01
1.3395199900000E+08 -3.2194291139361E+08 6.0666674091000E+01
1.3613599900000E+08 -3.2192471139161E+08 6.0666590261000E+01
1.4341599900000E+08 -3.2186404480160E+08 6.0666611658000E+01
1.5069599900000E+08 -3.2180337818960E+08 6.0666611658000E+01
1.7253599900000E+08 -3.2162137835458E+08 6.0666783566000E+01
1.7515679900000E+08 -3.2159953831258E+08 6.0666629213000E+01
1.7777759900000E+08 -3.2157769832557E+08 6.0666629213000E+01
3.3451599900000E+08 -3.2027154579839E+08 6.0666505193000E+01
3.3713679900000E+08 -3.2024970585638E+08 6.0666627480000E+01
3.3975759900000E+08 -3.2022786587038E+08 6.0666627480000E+01
5.6601999900000E+08 -3.1834234708794E+08 6.0666396876000E+01
5.6733039900000E+08 -3.1833142713693E+08 6.0666626282000E+01
5.6864079900000E+08 -3.1832050714393E+08 6.0666626282000E+01
8.9797999900000E+08 -3.1557601563707E+08 5.9666626282000E+01
8.9798727900000E+08 -3.1557595597007E+08 6.0666626282000E+01
8.9799455900000E+08 -3.1557589430307E+08 6.0666626282000E+01 )
\begintext
Below is a sample SCLK kernel file for Mars Global Surveyor. Note that
the text prior to the first
\begindatadirective is treated as a group of comment lines by the SPICELIB kernel readers. The labels shown in this comment area are examples and should not be construed as a correct specification.
KPL/SCLK
Status
-----------------------------------------------
This file is a SPICE spacecraft clock (SCLK) kernel containing
information required for Mars Global Surveyor spacecraft
on-board clock to ET conversion.
Production/History of this SCLK files
-----------------------------------------------
This file was generated by the NAIF utility program MAKCLK,
version 3.3, from the most recent Mars Global Surveyor
spacecraft SCLK SCET file.
Usage
-----------------------------------------------
This file must be loaded into the user's program by a call to
the FURNSH subroutine
CALL FURNSH( 'this_file_name' )
in order to use the SPICELIB SCLK family of subroutines to
convert MGS spacecraft on-board clock to ET and vice versa and
to use MGS frames defined below as reference frames for
geometric quantities being returned by high-level SPK and
CK subroutines.
References
-----------------------------------------------
1. SCLK Required Reading file (sclk.req), NAIF document number 222
2. MAKCLK User's Guide, NAIF document number 267
Inquiries
-----------------------------------------------
If you have any questions regarding this file contact
MGS Spacecraft Operations Team (SCOPS)
Lockheed/Martin, Denver
Boris Semenov - NAIF/JPL
(818) 354-8136
bsemenov@spice.jpl.nasa.gov
SCLK DATA
-----------------------------------------------
\begindata
SCLK_KERNEL_ID = ( @1999-02-07/03:51:29.00 )
SCLK_DATA_TYPE_94 = ( 1 )
SCLK01_TIME_SYSTEM_94 = ( 2 )
SCLK01_N_FIELDS_94 = ( 2 )
SCLK01_MODULI_94 = ( 4294967296 256 )
SCLK01_OFFSETS_94 = ( 0 0 )
SCLK01_OUTPUT_DELIM_94 = ( 1 )
SCLK_PARTITION_START_94 = ( 1.3611133440000E+11 )
SCLK_PARTITION_END_94 = ( 1.0995116277750E+12 )
SCLK01_COEFFICIENTS_94 = (
0.0000000000000E+00 -9.9510252675000E+07 9.9999996301748E-01
8.3066265600000E+08 -9.6265476795000E+07 9.9999994844682E-01
1.9330583040000E+09 -9.1959244017000E+07 9.9999994927604E-01
2.7708477440000E+09 -8.8686629183000E+07 9.9999994213351E-01
4.0538009600000E+09 -8.3675093473000E+07 9.9999993609973E-01
4.7829370880000E+09 -8.0826905655000E+07 9.9999993275158E-01
5.2473643520000E+09 -7.9012736777000E+07 9.9999993064539E-01
5.4909818880000E+09 -7.8061105843000E+07 9.9999992770059E-01
6.7515176960000E+09 -7.3137138199000E+07 9.9999992410889E-01
7.9017973760000E+09 -6.8643858540000E+07 9.9999992038548E-01
8.9854187520000E+09 -6.4410962877000E+07 9.9999991689249E-01
9.9588085760000E+09 -6.0608659193000E+07 9.9999991330346E-01
1.1222619136000E+10 -5.5671899621000E+07 9.9999990916047E-01
1.2448517120000E+10 -5.0883236056000E+07 9.9999990447344E-01
1.3831336704000E+10 -4.5481597572000E+07 9.9999990051645E-01
1.5223486464000E+10 -4.0043513113000E+07 9.9999989497162E-01
1.7390367488000E+10 -3.1579135002000E+07 9.9999988993180E-01
1.7567130624000E+10 -3.0888654078000E+07 9.9999989100000E-01 )
\begintext
Appendix: Document Revision HistoryMay 27, 2010
April 1, 2009
March 02, 2008
December 21, 2004
February 2, 2004
April 12, 1999
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