Keplerian Elements Formats 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... OSCAR 10 1 14129U 88230.56274695 0.00000042 10000-3 0 3478 2 14129 27.2218 308.9614 6028281 329.3891 6.4794 2.05877164 10960 GPS-0008 1 14189U 88230.24001475 0.00000013 0 5423 2 14189 63.0801 108.8864 0128028 212.9347 146.3600 2.00555575 37348 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: AAAAAAAAAAA 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 Line 1 Line 1 is a eleven-character name. Line 2 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 The checksum is defined in ???. Feedback to KB5MU.

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