What is the difference between Estimator and Propagator? or what is the diff. between the action of estimating and propagating in Orekit?

I am learning how to use Orekit for my research, and I got stuck on this question.

Thanks,

What is the difference between Estimator and Propagator? or what is the diff. between the action of estimating and propagating in Orekit?

I am learning how to use Orekit for my research, and I got stuck on this question.

Thanks,

Hi @psh0078 welcome,

Estimation is the process of determining what is the orbit from past measurements. Propagation is the process of evaluating position from an initial state.

In operational contexts, the right order of operations is to first estimate the orbit from measurements performed on the last few hours or days and then to propagate it in the future for anticipating where the spacecraft will be.

In mission analyses contexts, there are no measurements at all because the spacecraft may even not be built yet, so there is only propagation, starting from theoretical nominal states and optimization loops around propagation to tailor an orbit to some needs.

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Thank you for you help!