TLE(5)								File Formats Manual							    TLE(5)

NAME

       tle - extension for files containing NORAD two-line orbital element sets.

DESCRIPTION

       The file extension ".tle" commonly designates a list of elements of orbiting satellites in the two-line format of NORAD.

       The  positions  and  velocities	of  satellites	are updated periodically by NORAD, and provided to users through their bulletin boards and
       anonymous ftp sites.  A variety of models may be applied to these element sets in order to predict the future position and  velocity  of  a
       particular  satellite.  However, it is important to note that the NORAD output data are mean values, i.e., periodic perturbations have been
       removed.  Thus, any predictive model must be compatible with the NORAD models, in the sense that the same terms must  be  canceled.   There
       are several models which accomplish this goal.

       Data for each satellite consists of three lines in the following format:

000000000111111111122222222223333333333444444444455555555556666666666
123456789012345678901234567890123456789012345678901234567890123456789

AAAAAAAAAAAAAAAAAAAAAA

1 NNNNNU NNNNNAAA NNNNN.NNNNNNNN +.NNNNNNNN +NNNNN-N +NNNNN-N N NNNNN
2 NNNNN NNN.NNNN NNN.NNNN NNNNNNN NNN.NNNN NNN.NNNN NN.NNNNNNNNNNNNNN

       These lines are encoded as follows:

   LINE 0
       A line containing a single 22-character ASCII string giving the name of the satellite.

   LINE 1
       Column Description

       01-01  Line Number of Element Data, in this case, 1.

       03-07  Satellite Number.  Each time a satellite is launched NORAD assigns a number to that satellite.  Vanguard 1 is the earliest satellite
	      whose elements can currently be found (all earlier birds must have reentered by now). It was launched on 3/17/58 and carries "00005"
	      as a NORAD Catalog number.

       10-11  International  Designator--the last two digits of the year the satellite was launched.  This number is for reference only and is not
	      used by tracking programs for predictions. Thus it may be omitted in some element sets.

       12-14  International Designator--the number of the launch for that year.  This number does not give any indication as to  when  during  the
	      year the bird went up just its ranking among its fellow launches for that year. This number is for reference only and is not used by
	      tracking programs for predictions. Thus it may be omitted in some element sets.

       15-17  International Designator--piece of launch.  On many launches there are more than one payload.  This number is for reference only and
	      is not used by tracking programs for predictions. Thus it may be omitted in some element sets.

       19-20  Epoch Year--The last two digits of the year when the element set was measured.

       21-32  Epoch Day--The Julian Day and fractional portion of the day when the element set was measured.

       34-43  First Time Derivative of the Mean Motion or Ballistic Coefficient-- depending on ephemeris type.

       45-52  Second Time Derivative of Mean Motion (decimal point assumed; blank if N/A)

       54-61  BSTAR  drag  term if GP4 general perturbation theory was used.  Otherwise, radiation pressure coefficient.  (Decimal point assumed.)
	      This number usually refers to atmospheric drag on a satellite. However, at times satellites are strongly affected  by  the  gravita-
	      tional  pull of bodies other than the Earth (ie: Sun and Moon). While it seems unlikely, drag can actually be a negative number thus
	      indicating an increase in orbital energy rather than a decrease. This happens when the Sun and Moon combine to pull the  satellite's
	      apogee to a higher altitude.  However, this condition of negative drag is only valid for as long as the gravitational situation war-
	      rants it. So, some folks like to zero out negative drag factors for smoother orbital calculations.

       63-63  Ephemeris type.  This code indicates the type of model used to generate the element set.	Allowed  values  and  their  corresponding
	      models are:

		  1 = SGP
		  2 = SGP4
		  3 = SDP4
		  4 = SGP8
		  5 = SDP8

	      The models designated "SG*" are used for near-earth satellites (i.e., those with periods less than 225 minutes), and the models des-
	      ignated "SD*" are used for deep-space satellites (those with periods equal to or greater than 225  minutes).   Atmospheric  drag	is
	      more  important  for  near-earth	satellites, while tidal effects from the sun and moon are more important for the deep-space satel-
	      lites.

       65-68  Element number (modulo 1000).  Each time a satellite's orbit is determined and an element set created the element set is assigned  a
	      number.

       69-69  Checksum	(Modulo 10).  Letters, blanks, periods, plus signs = 0; minus signs =1.  The last number in each of the 2 lines of an ele-
	      ment set is a checksum.  This number is calculated by assigning the following values to each character on the line. A number carries
	      it's  own  value, a minus (-) sign carries a value of one (1), and letters, blanks and periods (decimal points (.)) carry a value of
	      zero (0).

   LINE 2
       01-01  Line Number of Element Data, in this case, 2.

       03-07  Satellite Number.

       09-16  Inclination (in degrees), i.e., the angle formed by the orbit to the equator. The inclination must be a positive number  of  degrees
	      between 0 and 180. A zero angle of inclination indicates a satellite moving from west to east directly over the equator. An inclina-
	      tion of 28 degrees (most shuttle launches) would form an angle of 28 degrees between the equator and the	orbit  of  the	satellite.
	      Also,  that  satellite will travel only as far north and south as +- 28 degrees latitude. On it's ascending orbital crossing (moving
	      from south to north) of the equator, the satellite will be moving from southwest to northeast. An inclination of	90  degrees  would
	      mean that the satellite is moving directly from south to north and will cross directly over the north and south poles. Any satellite
	      with an inclination greater than 90 degrees is said to be in retrograde orbit. This means the satellite is  moving  in  a  direction
	      opposite	the rotation of the earth. A satellite with an inclination of 152 degrees will be moving from southeast to northwest as it
	      cross the equator from south to north. This is opposite the rotation of the Earth. This satellite will move as far north	and  south
	      of the equator as 28 degrees latitude and be in an orbital direction exactly opposite a satellite with an inclination of 28 degrees.

       18-25  Right  ascension of ascending node (RAAN or RA of Node).	In order to fix the position of an orbit in space it is necessary to refer
	      to a coordinate system outside the earth coordinate system. Because the Earth rotates latitude  and  longitude  coordinates  do  not
	      indicate	an  absolute  frame  of  reference. Therefore it was decided to use astronomical conventions to fix orbits relative to the
	      celestial sphere which is delineated in degrees of Right Ascension and declination. Right ascension is similar to longitude and Dec-
	      lination	is  similar  to  latitude. When an element set is taken Right Ascension of the ascending Node is computed in the following
	      manner. As a satellite moves about the center of the earth it crosses the equator twice. It is either in ascending node, moving from
	      south  to north or descending node moving from north to south. The RAAN is taken from the point at which the orbit crosses the equa-
	      tor moving from south to north. If you were to stand at the center of the planet and look directly at the location where the  satel-
	      lite  crossed  the equator you would be pointing to the ascending node. To give this line a value the angle is measured between this
	      line and 0 degrees right ascension (RA). Again standing at the center of the earth 0 degrees RA will always point to the same  loca-
	      tion on the celestial sphere.

       27-33  Eccentricity.   In  general,  satellites	execute elliptical orbits about the Earth.  The center of the ellipse is at one of the two
	      foci of the ellipse.  The eccentricity of the orbit is the ratio of the distance between the foci to the major axis of the  ellipse,
	      i.e.,  the  longest  line  between  any two points.  Thus the ellipticity is 0 for a perfectly circular orbit and approaches 1.0 for
	      orbits which are highly elongated.

       35-42  Argument of Perigee (degrees).  The orbital position corresponding to closest approach  of  a  satellite	to  the  Earth	is  called
	      perigee.	 The  argument	of  perigee  is the angle measured from the center of the Earth between the ascending node and the perigee
	      along the plane of the orbit (inclination). If the Argument of perigee is zero (0) then the lowest point of the orbit of that satel-
	      lite  would be at the same location as the point where it crossed the equator in it's ascending node.  If the argument of perigee is
	      180 then the lowest point of the orbit would be on the equator on the opposite side of the earth from the ascending node.

       44-51  Mean Anomaly (degrees).  The mean anomaly fixes the position of the satellite in the orbit as described above. So far we	have  only
	      talked  about  the shape and location of the orbit of the satellite. We haven't placed the satellite along that path and given it an
	      exact location. That's what Mean Anomaly does. Mean Anomaly is measured from the point of perigee. In the Argument of perigee  exam-
	      ple  above  it  was stated that an Arg of Perigee of zero would place perigee at the same location as the Ascending node. If in this
	      case the MA were also zero then the satellite's position as of the taking of the element set would also located  directly  over  the
	      equator  at  the	ascending node. If the Arg of Perigee was 0 degrees and the MA was 180 degrees then the satellite's position would
	      have been on the other side of the earth just over the equator as it was headed from north to south.

       53-63  Mean Motion (revolutions per day).  The mean motion of a satellite is simply the number of orbits the satellite makes in	one  solar
	      day (regular day, common day, 24 hours, 1440 minutes, 86400 seconds etc.). This number also generally indicates the orbit altitude.

       64-68  Revolution  number  at  epoch (revs).  Theoretically, this number equals the number of orbits the satellite has completed since it's
	      launch, modulo 100,000.  Some satellites have incorrect epoch orbit numbers.  Oscar 10 is just such a case. However, this number	is
	      provided more for reference purposes than orbital calculation. And so, its accuracy or lack thereof doesn't affect the accuracy of a
	      prediction.

       69-69  Check Sum (modulo 10).  As with Line 1, this number is provided to check the accuracy  of  the  element  set.  It's  calculation	is
	      described above.

EXAMPLES

       This is an example using an element set for the Oscar 10 amateur radio satellite:

000000000111111111122222222223333333333444444444455555555556666666666
123456789012345678901234567890123456789012345678901234567890123456789

OSCAR 10
1 14129U 83 58	B 91312.44187316 -.00000072  00000-0  99998-4 0  7762
2 14129  25.9057 115.4097 6067273 291.5986  16.1497  2.05882356 35213

       Oscar  10 has the catalog number 14129, and was the 58th satellite launched in 1983.  The element set given above corresponds to the second
       ('B') item deployed from the launcher.  It was measured in 1991 on the 312th day of the year. The decimal portion of  the  number  reflects
       the  fraction  of  the  day since midnight.  If this decimal were .5 it would be noon UTC. If it were 10:36:17 UTC. Remember that all epoch
       times are in UTC (GMT) time.

       {Does that do it for you?}

       [Need more explanation here.]{about?}

       In the Oscar 10 element set above the checksum calculation would start out like this for line one of the set. In column one is  the  number
       one (1).  So, so far the checksum is one (1). In column two is a blank space. That carries a value of zero (0), so the checksum remains one
       (1). In column three is the number one (1). Add this to the accumulated checksum so far and the new checksum value is two  (2).	In  column
       four is the number four (4). Add four to the checksum value and the new value is six (6). If you continue along through the entire line you
       will end up with a value of 172.  Only the last digit of this number is used. So the checksum of this line is two "2". DO NOT ADD the  last
       figure in column 69 as that is the actual checksum. When programs verify Checksums they perform the above calculations. If the value of the
       calculated checksum disagrees with the very last (69th column) number then the element set fails the checksum test and is considered a  bad
       element set.

SEE ALSO

       seesat5(1), seesat5(7), SEESAT5.INI(5), cr(1)

NOTES

       Availability

       NORAD two-line orbital element sets are available from:

BBS
	    Celestial BBS *(205) 904-9280*   updated several times weekly.
FTP
	    archive.afit.af.mil (129.92.1.66) pub/space    updated weekly.
FTP
	    spacelink.msfc.nasa.gov various paths good source for shuttle tle.

       Additional Information

IT.DOC - The doc file for Instant Track. Antonio describes these parameters
in concise terms easily understandable to all.

"The Satellite Experimenter's Handbook" by Martin Davidoff. Available from
the Amateur Radio Relay League, 225 Main St, Newington, Connecticut 06111
and probably most stores that sell amateur radio gear.

"Fundamentals of Astrodynamics" by Roger Bate, Donald Mueller, and Jerry
White. Publisher: Dover Publications, NYC, NY Copyright 1971.

Debian GNU Linux						   16 January 96							    TLE(5)