Table of contents
SPKW10 (SPK - write a type 10 segment )
SUBROUTINE SPKW10 ( HANDLE, BODY, CENTER, FRAME, FIRST, LAST,
. SEGID, CONSTS, N, ELEMS, EPOCHS )
Write an SPK type 10 segment to the file specified by
the input HANDLE.
DOUBLE PRECISION FIRST
DOUBLE PRECISION LAST
DOUBLE PRECISION CONSTS ( * )
DOUBLE PRECISION ELEMS ( * )
DOUBLE PRECISION EPOCHS ( * )
VARIABLE 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.
HANDLE is the file handle of an SPK file that has been opened
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
FRAME is the reference frame that states are referenced to,
for example 'J2000'.
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(1) = J2 gravitational harmonic for Earth.
CONSTS(2) = J3 gravitational harmonic for Earth.
CONSTS(3) = J4 gravitational harmonic for Earth.
These first three constants are dimensionless.
CONSTS(4) = KE: Square root of the GM for Earth where
GM is expressed in Earth radii cubed
per minutes squared.
CONSTS(5) = QO: High altitude bound for atmospheric
model in km.
CONSTS(6) = SO: Low altitude bound for atmospheric
model in km.
CONSTS(7) = RE: Equatorial radius of the earth in km.
CONSTS(8) = AE: Distance units/earth radius
Below are currently recommended values for these
J2 = 1.082616D-3
J3 = -2.53881D-6
J4 = -1.65597D-6
The next item is the square root of GM for the Earth
given in units of earth-radii**1.5/Minute
KE = 7.43669161D-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 = 120.0D0
SO = 78.0D0
The ER value is the equatorial radius in km of the Earth
as used by NORAD.
ER = 6378.135D0
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 = 1.0D0
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-1)*10
ELEMS( BASE + 1 ) = NDT2O in radians/minute**2
ELEMS( BASE + 2 ) = NDD6O in radians/minute**3
ELEMS( BASE + 3 ) = BSTAR
ELEMS( BASE + 4 ) = INCL in radians
ELEMS( BASE + 5 ) = NODE0 in radians
ELEMS( BASE + 6 ) = ECC
ELEMS( BASE + 7 ) = OMEGA in radians
ELEMS( BASE + 8 ) = M0 in radians
ELEMS( BASE + 9 ) = N0 in radians/minute
ELEMS( BASE + 10 ) = EPOCH of 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
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
The routine writes an SPK type 10 segment to the file attached to
1) If the structure or content of the inputs are invalid, an
error is signaled by a routine in the call tree of this
2) If any file access error occurs, the error is signaled by a
routine in the call tree of this routine.
This routine writes a type 10 SPK segment to the SPK file open
for writing that is attached to HANDLE.
The routine GETELM reads two-line element sets, as those
distributed by NORAD, and converts them to the elements in units
suitable for use in this routine.
The 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
Use the meta-kernel shown below to load the required SPICE
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
geophysical.ker geophysical constants for evaluation
of two-line element sets.
KERNELS_TO_LOAD = ( 'naif0012.tls',
The geophysical.ker is a PCK file that is provided with the
SPICE toolkit under the "/data" directory.
End of meta-kernel
Example code begins here.
C SPICELIB functions.
DOUBLE PRECISION SPD
C Local parameters.
PARAMETER ( NAMLEN = 40 )
PARAMETER ( PNAMLN = 2 )
PARAMETER ( SPK10 = 'spkw10_ex1.bsp' )
PARAMETER ( TLELLN = 69 )
C The SPK type 10 segment will contain 18 two-line
C elements sets for the NORAD spacecraft 18123 with
C respect to the Earth (ID 399) in the J2000 reference
C As stated in the naif_ids required reading, for Earth
C orbiting spacecraft lacking a DSN identification code,
C the NAIF ID is derived from the tracking ID assigned to
C it by NORAD via:
C NAIF ID = -100000 - NORAD ID code
PARAMETER ( TLESSZ = 9 )
PARAMETER ( BODY = -118123 )
PARAMETER ( CENTER = 399 )
PARAMETER ( FRMNAM = 'J2000' )
C Local variables.
CHARACTER*(PNAMLN) NOADPN ( 8 )
CHARACTER*(TLELLN) TLE ( 2 * TLESSZ )
DOUBLE PRECISION CONSTS ( 8 )
DOUBLE PRECISION ELEMS ( 10 * TLESSZ )
DOUBLE PRECISION EPOCHS ( TLESSZ )
DOUBLE PRECISION FIRST
DOUBLE PRECISION LAST
C These are the variables that will hold the constants
C required by SPK type 10. These constants are available
C from the loaded PCK file, which provides the actual
C values and units as used by NORAD propagation model.
C Constant Meaning
C -------- ------------------------------------------
C J2 J2 gravitational harmonic for Earth.
C J3 J3 gravitational harmonic for Earth.
C J4 J4 gravitational harmonic for Earth.
C KE Square root of the GM for Earth.
C QO High altitude bound for atmospheric model.
C SO Low altitude bound for atmospheric model.
C ER Equatorial radius of the Earth.
C AE Distance units/earth radius.
DATA NOADPN / 'J2', 'J3', 'J4', 'KE',
. 'QO', 'SO', 'ER', 'AE' /
C Define the Two-Line Element sets.
TLE(1) = '1 18123U 87 53 A 87324.61041692 -.00000023'
. // ' 00000-0 -75103-5 0 00675'
TLE(2) = '2 18123 98.8296 152.0074 0014950 168.7820 '
. // '191.3688 14.12912554 21686'
TLE(3) = '1 18123U 87 53 A 87326.73487726 .00000045'
. // ' 00000-0 28709-4 0 00684'
TLE(4) = '2 18123 98.8335 154.1103 0015643 163.5445 '
. // '196.6235 14.12912902 21988'
TLE(5) = '1 18123U 87 53 A 87331.40868801 .00000104'
. // ' 00000-0 60183-4 0 00690'
TLE(6) = '2 18123 98.8311 158.7160 0015481 149.9848 '
. // '210.2220 14.12914624 22644'
TLE(7) = '1 18123U 87 53 A 87334.24129978 .00000086'
. // ' 00000-0 51111-4 0 00702'
TLE(8) = '2 18123 98.8296 161.5054 0015372 142.4159 '
. // '217.8089 14.12914879 23045'
TLE(9) = '1 18123U 87 53 A 87336.93227900 -.00000107'
. // ' 00000-0 -52860-4 0 00713'
TLE(10) = '2 18123 98.8317 164.1627 0014570 135.9191 '
. // '224.2321 14.12910572 23425'
TLE(11) = '1 18123U 87 53 A 87337.28635487 .00000173'
. // ' 00000-0 10226-3 0 00726'
TLE(12) = '2 18123 98.8284 164.5113 0015289 133.5979 '
. // '226.6438 14.12916140 23475'
TLE(13) = '1 18123U 87 53 A 87339.05673569 .00000079'
. // ' 00000-0 47069-4 0 00738'
TLE(14) = '2 18123 98.8288 166.2585 0015281 127.9985 '
. // '232.2567 14.12916010 24908'
TLE(15) = '1 18123U 87 53 A 87345.43010859 .00000022'
. // ' 00000-0 16481-4 0 00758'
TLE(16) = '2 18123 98.8241 172.5226 0015362 109.1515 '
. // '251.1323 14.12915487 24626'
TLE(17) = '1 18123U 87 53 A 87349.04167543 .00000042'
. // ' 00000-0 27370-4 0 00764'
TLE(18) = '2 18123 98.8301 176.1010 0015565 100.0881 '
. // '260.2047 14.12916361 25138'
C Load the PCK file that provides the geophysical
C constants required for the evaluation of the two-line
C elements sets. Load also an LSK, as it is required by
C GETELM to perform time conversions. Use a metakernel for
CALL FURNSH ( 'spkw10_ex1.tm' )
C Retrieve the data from the kernel, and place it on
C the CONSTS array.
DO I = 1, 8
CALL BODVCD ( CENTER, NOADPN(I), 1, N, CONSTS(I) )
C Convert the Two Line Elements lines to the
C element sets.
DO I = 1, TLESSZ
CALL GETELM ( 1950, TLE( (I-1)*2 + 1 ),
. EPOCHS(I), ELEMS( (I-1)*10 + 1 ) )
C Define the beginning and end of the segment to be
C -/+ 12 hours from the first and last epochs,
FIRST = EPOCHS(1 ) - 0.5D0 * SPD()
LAST = EPOCHS(TLESSZ) + 0.5D0 * SPD()
C NCOMCH is the number of characters to reserve for the
C kernel's comment area. This example doesn't write
C comments, so set to zero.
NCOMCH = 0
C Internal file name and segment ID.
IFNAME = 'Test for type 10 SPK internal file name'
SEGID = 'SPK type 10 test segment'
C Open a new SPK file.
CALL SPKOPN( SPK10, IFNAME, NCOMCH, HANDLE )
C Now add the segment.
CALL SPKW10 ( HANDLE, BODY, CENTER, FRMNAM,
. FIRST, LAST, SEGID, CONSTS,
. TLESSZ, ELEMS, EPOCHS )
C Close the SPK file.
CALL SPKCLS ( HANDLE )
When this program is executed, no output is presented on
screen. After run completion, a new SPK type 10 exists in
the output directory.
 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.
 F. Hoots, "Spacetrack Report #6: Models for Propagation of
Space Command Element Sets," U.S. Air Force Aerospace
Defense Command, Colorado Springs, CO, 1986.
 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,
 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.
M. Costa Sitja (JPL)
J. Diaz del Rio (ODC Space)
B.V. Semenov (JPL)
W.L. Taber (JPL)
SPICELIB Version 1.1.0, 04-NOV-2021 (JDR) (MCS)
Added IMPLICIT NONE statement.
Corrected the expected order of QO, SO and ER in the detailed
description of the input argument GEOPHS and the input element
names in ELEMS.
Added Spacetrack Report #3 to literature references and
NAIF_IDS to the list of required readings.
Edited the header to comply with NAIF standard. Added complete
code example based on existing example.
SPICELIB Version 1.0.2, 30-OCT-2006 (BVS)
Deleted "inertial" from the FRAME description in the $Brief_I/O
section of the header.
SPICELIB Version 1.0.1, 21-JUN-1999 (WLT)
Cleaned up the header.
SPICELIB Version 1.0.0, 05-JAN-1994 (WLT)