spkw10_c |

Table of contents## Procedurespkw10_c (SPK - write a type 10 segment ) void spkw10_c ( SpiceInt handle, SpiceInt body, SpiceInt center, ConstSpiceChar * frame, SpiceDouble first, SpiceDouble last, ConstSpiceChar * segid, ConstSpiceDouble consts [8], SpiceInt n, ConstSpiceDouble elems [], ConstSpiceDouble epochs [] ) ## AbstractWrite an SPK type 10 segment to the file specified by the input `handle'. ## Required_ReadingNAIF_IDS SPK ## KeywordsSPK ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- handle I The handle of a DAF file open for writing. body I The NAIF ID code for the body of the segment. center I The center of motion for `body'. frame I The reference frame for this segment. first I The first epoch for which the segment is valid. last I The last epoch for which the segment is valid. segid I The string to use for segment identifier. consts I Array of geophysical constants for the segment. n I The number of element/epoch pairs to be stored elems I The collection of "two-line" element sets. epochs I The epochs associated with the element sets. ## Detailed_Inputhandle is the file handle of a SPK file that has been opened for writing. body is the NAIF ID for the body whose states are to be recorded in an SPK file. center is the NAIF ID for the center of motion associated with `body'. frame is the reference frame that states are referenced to, for example "J2000". first, last are the bounds on the ephemeris times, expressed as seconds past J2000, for which the states can be used to interpolate a state for `body'. segid is the segment identifier. An SPK segment identifier may contain up to 40 characters. consts are the geophysical constants needed for evaluation of the two line elements sets. The order of these constants must be: consts[0] = J2 gravitational harmonic for Earth. consts[1] = J3 gravitational harmonic for Earth. consts[2] = J4 gravitational harmonic for Earth. These first three constants are dimensionless. consts[3] = KE: Square root of the GM for Earth where GM is expressed in Earth radii cubed per minutes squared. consts[4] = QO: High altitude bound for atmospheric model in km. consts[5] = SO: Low altitude bound for atmospheric model in km. consts[6] = RE: Equatorial radius of the earth in km. consts[7] = AE: Distance units/earth radius (normally 1). Below are currently recommended values for these items: J2 = 1.082616e-3 J3 = -2.53881e-6 J4 = -1.65597e-6 The next item is the square root of GM for the Earth given in units of earth-radii**1.5/Minute KE = 7.43669161e-2 The next two items define the top and bottom of the atmospheric drag model used by the type 10 ephemeris type. Don't adjust these unless you understand the full implications of such changes. QO = 120.0e0 SO = 78.0e0 The ER value is the equatorial radius in km of the Earth as used by NORAD. ER = 6378.135e0 The value of AE is the number of distance units per Earth radii used by the NORAD state propagation software. The value should be 1 unless you've got a very good understanding of the NORAD routine SGP4 and the affect of changing this value. AE = 1.0e0 n is the number of "two-line" element sets and epochs to be stored in the segment. elems is a time-ordered array of two-line elements as supplied in NORAD two-line element files. The i'th set of elements should be stored as shown here: base = i*10 elems[ base + 0 ] = NDT20 in radians/minute**2 elems[ base + 1 ] = NDD60 in radians/minute**3 elems[ base + 2 ] = BSTAR elems[ base + 3 ] = INCL in radians elems[ base + 4 ] = NODE0 in radians elems[ base + 5 ] = ECC elems[ base + 6 ] = OMEGA in radians elems[ base + 7 ] = M0 in radians elems[ base + 8 ] = N0 in radians/minute elems[ base + 9 ] = EPOCH the elements in seconds past ephemeris epoch J2000. The meaning of these variables is defined by the format of the two-line element files available from NORAD. epochs is an n-dimensional array that contains the epochs (ephemeris seconds past J2000) corresponding to the elements in `elems'. The i'th epoch must equal the epoch of the i'th element set. `epochs' must form a strictly increasing sequence. ## Detailed_OutputNone. The routine writes an SPK type 10 segment to the file attached to `handle'. ## ParametersNone. ## Exceptions1) If the structure or content of the inputs are invalid, an error is signaled by a routine in the call tree of this routine. 2) If any file access error occurs, the error is signaled by a routine in the call tree of this routine. 3) If any of the `frame' or `segid' input string pointers is null, the error SPICE(NULLPOINTER) is signaled. 4) If any of the `frame' or `segid' input strings has zero length, the error SPICE(EMPTYSTRING) is signaled. ## FilesNone. ## ParticularsThis routine writes a type 10 SPK segment to the SPK file open for writing that is attached to `handle'. The routine getelm_c reads two-line element sets, as those distributed by NORAD, and converts them to the elements in units suitable for use in this routine. ## ExamplesThe numerical results shown for this example may differ across platforms. The results depend on the SPICE kernels used as input, the compiler and supporting libraries, and the machine specific arithmetic implementation. 1) Suppose that you have collected the two-line element data for a spacecraft with NORAD ID 18123. The following example code demonstrates how you could go about creating a type 10 SPK segment. Use the meta-kernel shown below to load the required SPICE kernels. KPL/MK File name: spkw10_ex1.tm This meta-kernel is intended to support operation of SPICE example programs. The kernels shown here should not be assumed to contain adequate or correct versions of data required by SPICE-based user applications. In order for an application to use this meta-kernel, the kernels referenced here must be present in the user's current working directory. The names and contents of the kernels referenced by this meta-kernel are as follows: File name Contents --------- ------------------------------------ naif0012.tls Leapseconds geophysical.ker geophysical constants for evaluation of two-line element sets. The geophysical.ker is a PCK file that is provided with the SPICE toolkit under the "/data" directory. \begindata KERNELS_TO_LOAD = ( 'naif0012.tls', 'geophysical.ker' ) \begintext End of meta-kernel Example code begins here. /. Program spkw10_ex1 ./ #include "SpiceUsr.h" int main( ) { /. Local parameters. ./ #define PNAMLN 3 #define SPK10 "spkw10_ex1.bsp" #define TLELLN 70 /. The SPK type 10 segment will contain 18 two-line elements sets for the NORAD spacecraft 18123 with respect to the Earth (ID 399) in the J2000 reference frame. As stated in the naif_ids required reading, for Earth orbiting spacecraft lacking a DSN identification code, the NAIF ID is derived from the tracking ID assigned to it by NORAD via: NAIF ID = -100000 - NORAD ID code ./ #define TLESSZ 9 #define BODY -118123 #define CENTER 399 #define FRMNAM "J2000" /. Local variables. ./ SpiceChar * ifname; SpiceChar * segid; SpiceDouble consts [8]; SpiceDouble elems [10*TLESSZ]; SpiceDouble epochs [TLESSZ]; SpiceDouble first; SpiceDouble last; SpiceInt handle; SpiceInt i; SpiceInt n; SpiceInt ncomch; /. These are the variables that will hold the constants required by SPK type 10. These constants are available from the loaded PCK file, which provides the actual values and units as used by NORAD propagation model. Constant Meaning -------- ------------------------------------------ J2 J2 gravitational harmonic for Earth. J3 J3 gravitational harmonic for Earth. J4 J4 gravitational harmonic for Earth. KE Square root of the GM for Earth. QO High altitude bound for atmospheric model. SO Low altitude bound for atmospheric model. ER Equatorial radius of the Earth. AE Distance units/earth radius. ./ SpiceChar noadpn [8][PNAMLN] = { "J2", "J3", "J4", "KE", "QO", "SO", "ER", "AE" }; /. Define the Two-Line Element sets. ./ SpiceChar tle [2*TLESSZ][TLELLN] = { "1 18123U 87 53 A 87324.61041692 -.00000023" " 00000-0 -75103-5 0 00675", "2 18123 98.8296 152.0074 0014950 168.7820 " "191.3688 14.12912554 21686", "1 18123U 87 53 A 87326.73487726 .00000045" " 00000-0 28709-4 0 00684", "2 18123 98.8335 154.1103 0015643 163.5445 " "196.6235 14.12912902 21988", "1 18123U 87 53 A 87331.40868801 .00000104" " 00000-0 60183-4 0 00690", "2 18123 98.8311 158.7160 0015481 149.9848 " "210.2220 14.12914624 22644", "1 18123U 87 53 A 87334.24129978 .00000086" " 00000-0 51111-4 0 00702", "2 18123 98.8296 161.5054 0015372 142.4159 " "217.8089 14.12914879 23045", "1 18123U 87 53 A 87336.93227900 -.00000107" " 00000-0 -52860-4 0 00713", "2 18123 98.8317 164.1627 0014570 135.9191 " "224.2321 14.12910572 23425", "1 18123U 87 53 A 87337.28635487 .00000173" " 00000-0 10226-3 0 00726", "2 18123 98.8284 164.5113 0015289 133.5979 " "226.6438 14.12916140 23475", "1 18123U 87 53 A 87339.05673569 .00000079" " 00000-0 47069-4 0 00738", "2 18123 98.8288 166.2585 0015281 127.9985 " "232.2567 14.12916010 24908", "1 18123U 87 53 A 87345.43010859 .00000022" " 00000-0 16481-4 0 00758", "2 18123 98.8241 172.5226 0015362 109.1515 " "251.1323 14.12915487 24626", "1 18123U 87 53 A 87349.04167543 .00000042" " 00000-0 27370-4 0 00764", "2 18123 98.8301 176.1010 0015565 100.0881 " "260.2047 14.12916361 25138" }; /. Load the PCK file that provides the geophysical constants required for the evaluation of the two-line elements sets. Load also an LSK, as it is required by getelm_c to perform time conversions. Use a metakernel for convenience. ./ furnsh_c ( "spkw10_ex1.tm" ); /. Retrieve the data from the kernel, and place it on the `consts' array. ./ for ( i = 0; i < 8; i++ ) { bodvcd_c ( CENTER, noadpn[i], 1, &n, consts+i ); } /. Convert the Two Line Elements lines to the element sets. ./ for ( i = 0; i < TLESSZ; i++ ) { getelm_c ( 1950, TLELLN, tle[i*2], epochs+i, elems+(i*10) ); } /. Define the beginning and end of the segment to be -/+ 12 hours from the first and last epochs, respectively. ./ first = epochs[0] - 0.5 * spd_c(); last = epochs[TLESSZ-1] + 0.5 * spd_c(); /. `ncomch' is the number of characters to reserve for the kernel's comment area. This example doesn't write comments, so set to zero. ./ ncomch = 0; /. Internal file name and segment ID. ./ ifname = "Test for type 10 SPK internal file name"; segid = "SPK type 10 test segment"; /. Open a new SPK file. ./ spkopn_c ( SPK10, ifname, ncomch, &handle ); /. Now add the segment. ./ ## RestrictionsNone. ## Literature_References[1] F. Hoots and R. Roehrich, "Spacetrack Report #3: Models for Propagation of the NORAD Element Sets," U.S. Air Force Aerospace Defense Command, Colorado Springs, CO, 1980. [2] F. Hoots, "Spacetrack Report #6: Models for Propagation of Space Command Element Sets," U.S. Air Force Aerospace Defense Command, Colorado Springs, CO, 1986. [3] F. Hoots, P. Schumacher and R. Glover, "History of Analytical Orbit Modeling in the U. S. Space Surveillance System," Journal of Guidance, Control, and Dynamics. 27(2):174-185, 2004. [4] D. Vallado, P. Crawford, R. Hujsak and T. Kelso, "Revisiting Spacetrack Report #3," paper AIAA 2006-6753 presented at the AIAA/AAS Astrodynamics Specialist Conference, Keystone, CO., August 21-24, 2006. ## Author_and_InstitutionN.J. Bachman (JPL) M. Costa Sitja (JPL) J. Diaz del Rio (ODC Space) B.V. Semenov (JPL) W.L. Taber (JPL) ## Version-CSPICE Version 1.0.2, 05-NOV-2021 (JDR) (MCS) Edited the header to comply with NAIF standard. Added complete code example based on existing example. Added NAIF_IDS to the list of required readings. Added relevant reports and papers to -Literature_References. -CSPICE Version 1.0.1, 30-OCT-2006 (BVS) Deleted "inertial" from the FRAME description in the -Brief_I/O section of the header. -CSPICE Version 1.0.0, 29-JUN-1999 (NJB) (WLT) ## Index_Entrieswrite a type_10 SPK segment |

Fri Dec 31 18:41:13 2021