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I have two TLE, the drag term for the first TLE is -26868-1, which I suppose equals to -0.026868. But on the second TLE, we have 00000+0. What does the "+" symbol represents here?

COSMOS 2549             
1 47546U 21008A   21040.52165678 -.00037182  00000-0 -26868-1 0  9998
2 47546  67.1483  54.1721 0006757 284.8888  75.1223 13.96668399   985

TJS-6

1 47613U 21010A   21036.34392819  .00000403 -56594-6  00000+0 0  9998
2 47613  28.3962   6.0839 7309460 180.1054 196.4507  2.28168883    27
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  • My guess is that you place the decimal point towards the right. For example, 12345+1 will give 1.2345 opposed to 12345-1 which gives 0.012345. – Star Man Feb 09 '21 at 20:18

1 Answers1

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While this was too rushed out question, in the mean time I managed to find an answer while playing with already existing TLE parsers.

The main difference between the + and - sign is that - multiplies whatever is left of the sign with 10 to the negative value, while the + multiplies whatever is left of the sign with 10 to the positive value.

Example:

If we have the drag term -26868+1, the extracted value is -2.6868. But if we have the drag term -26868-1, the value is -0.026868.

From Celestrak's What is the format for the two-line element sets?:

Fields 1.10 and 1.11 have a somewhat different format that the other fields. In particular, they use a modified exponential notation with an implied leading decimal point. This convention is inherited from FORTRAN where all such numbers range from 0 to less than 1. The first six columns of each field represent the mantissa and the last two represent the exponent. For example, the value -12345-6 corresponds to -0.12345 × 10-6. Each of these two fields can be blank, corresponding to a value of zero.

From NASA Spaceflight's Definition of Two-line Element Set Coordinate System:

Second Derivative of Mean Motion

(00000-0 = 0.00000) The second derivative of mean motion is a second order drag term in the SGP4 predictor used to model terminal orbit decay. It measures the second time derivative in daily mean motion, divided by 6. Units are revs/day^3. A leading decimal must be applied to this value. The last two characters define an applicable power of 10. (12345-5 = 0.0000012345).

Drag Term

(67960-4 = 0.000067960) Also called the radiation pressure coefficient (or BSTAR), the parameter is another drag term in the SGP4 predictor. Units are earth radii^-1. The last two characters define an applicable power of 10. Do not confuse this parameter with "B-Term", the USSPACECOM special perturbations factor of drag coefficient, multiplied by reference area, divided by weight.

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