# Generating TLEs with STK Using SGP4 Propagator;

STK has two methods for generating TLEs; Trajectory Sampling method and Single Point method.

I have read the differences both of them at http://help.agi.com/stk/index.htm#stk/tools-10.htm but I am still confused about the difference between them.

How might TLEs generated using the two methods differ? Are there guidelines for how to decide which method to use, or which is more accurate?

• I've made some adjustment to the wording of your question to help it fit the Stack Exchange format. Please feel free to edit further or roll back. Welcome to Space! – uhoh Sep 9 '19 at 4:38

And there are two ways of doing so, one is to solve the nonlinear equation $$(r,v)=\text{SGP4}(TLE, t_0)$$, with $$(r,v)$$ a single, known point in the trajectory at time $$t_0$$ (since the TLE's epoch). Thus, you get a TLE that provides you the exact position and velocity you've used as reference at that given epoch. Often, this is good enough, but while this allows you to fit the mean orbital elements in the TLE message, it wouldn't allow you to fit the ballistic coefficient associated with atmospheric drag.
• Great answer! +1 I made a small edit adding a link to Wikipedia, feel free to roll back. Should BSTAR be mentioned as well? Will a non-zero BSTAR come out of the trajectory sampling method? – uhoh Sep 9 '19 at 14:05