TLE Checksum

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This TLE Checksum equation computes the checksum of a line (a card) of the Two Line Element set (TLE), allowing you to verify the checksum.

You simply copy paste the entire card (one of the two lines of TLE) into the input field and the TLE Checksum equation computes the checksum integer value.

Click HERE for a lits of terms and acronyms related to orbital elements, orbitology and satellites.

Computing the value

TLE Checksum equation computes the checksum value by performing these steps:

The checksum sums the numeric value of all the numeric characters in the string that is the TLE card (so 123 would sum to 6)
The checksum ignores non-numeric characters except the minus sign ("-")
- The checksum assigns the value 0 to the alpha characters (so basically ignores the alpha characters)
- The checksum assigns the value 0 to periods and blanks (so basically ignores the periods and blanks)
- The checksum assigns the value 0 to '+' signs (so basically ignores plus signs)
The checksum assigns the value 1 to '-' signs and sums their assigned value (so each minus sign has a value 1)

The TLE Checksum equation then takes modulo 10 of the total of numeric values and the 1's for the minus signs.

Example

If you had the following TLE:

1 27831U 03028B 17074.62687020 -.00000167 +00000-0 +00000-0 0 9999
2 27831 000.0302 175.3600 0002592 186.4728 193.2334 01.00271880050427

If you pasted the first line into the input field of the TLE Checksum equation, you would get 9 as the resultant checksum.

If you pasted the second line into the input field of the TLE Checksum equation, you would get 7 as the resultant checksum.

Satellite Position and Attitude

Two-line element sets (TLE) are used as an encoded data format for orbital elements for objects in Earth orbit. TLEs are often used as input for orbit propagation algorithms that compute the ephemeris of orbiting bodies over time. Ephemeris is a time tagged list of orbital positions. The positions are 3D vectors in an Earth centered frame (ECF - Earth Centered Fixed or ECI - Earth Centered Inertial).

In parallel with the satellite's position is the satellite's orientation, also known as attitude. Satellite attitudes are usually indicated by a time tagged series of quaternions that can be used to show the difference between local satellite axis frame and the axis of an universal coordinate frame (ECF or ECI).

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