Keplerian Elements Formats
Keplerian element sets are generally distributed in one of two
formats, usually called NASA format and
AMSAT format.
NASA Format
This is the format used by NASA to distribute satellite elements in their
NASA Prediction Bulletin. The origin of the format is unknown.
Some old NORAD reports refer to this as T-card format. NASA
documents often call it the "2-line" format.
As used in the amateur community, the format consists of groups of
3 lines: One line containing the satellite's name, followed by the
standard Two-Line Orbital Element Set Format identical to that used
by NASA and NORAD. Tracking programs are generally unforgiving of
anything that doesn't fit this format.
NASA format files look like this...
Each number is in a specified fixed column. Spaces are significant.
The last digit on each line is a mod-10 check digit, which is checked by
the program. The program also checks the sequence numbers (first column),
and checks each orbital element for reasonable range. This is a very good
set of checks, so this format is very safe, and robust.
There seems to be some disagreement about how the "+" character is
figured into the check digit. If you have trouble with checksum
failures on element sets with "+" signs in them, try replacing all
the "+" signs with spaces.
Data for each satellite consists of three lines in the following format:
Column Description
01-01 Line Number of Element Data
03-07 Satellite Number
10-11 International Designator (Last two digits of launch year)
12-14 International Designator (Launch number of the year)
15-17 International Designator (Piece of launch)
19-20 Epoch Year (Last two digits of year)
21-32 Epoch (Julian Day and fractional portion of the day)
34-43 First Time Derivative of the Mean Motion divided by 2.
or Ballistic Coefficient (Depending of ephemeris type)
45-52 Second Time Derivative of Mean Motion divided by 6. (Blank if N/A)
54-61 BSTAR drag term if GP4 general perturbation theory was used.
Otherwise, radiation pressure coefficient.
63-63 Ephemeris type
65-68 Element number
69-69 Check Sum (Modulo 10)
(Letters, blanks, periods = 0; minus sign = 1; plus sign = 2)
All other columns are blank or fixed.
Note that the International Designator fields are usually blank, as
issued in the NASA Prediction Bulletins.
Line 3
Column Description
01-01 Line Number of Element Data
03-07 Satellite Number
09-16 Inclination [Degrees]
18-25 Right Ascension of the Ascending Node [Degrees]
27-33 Eccentricity (decimal point assumed)
35-42 Argument of Perigee [Degrees]
44-51 Mean Anomaly [Degrees]
53-63 Mean Motion [Revs per day]
64-68 Revolution number at epoch [Revs]
69-69 Check Sum (Modulo 10)
All other columns are blank or fixed.
AMSAT Format
There are several very similar formats generated by several different
people that seem to be called "AMSAT" format. Tracking programs
generally try to read all of them. This format is very
user-friendly, and can be easily read and/or edited by humans. Spaces
are not significant. Each orbital element must appear on a separate
line. The order in which orbital elements appear is not significant,
except that each element set should begin with a line containing the
word "satellite". This file format does not contain any check digits
or other error detection techniques.
AMSAT format elements as distributed by AMSAT look like this:
Satellite: AO-13
Catalog number: 19216
Epoch time: 94311.77313192
Element set: 994
Inclination: 57.6728 deg
RA of node: 221.5174 deg
Eccentricity: 0.7242728
Arg of perigee: 354.2960 deg
Mean anomaly: 0.7033 deg
Mean motion: 2.09727084 rev/day
Decay rate: -5.78e-06 rev/day^2
Epoch rev: 4902
Checksum: 312
