When utilizing numerical method determines, how many points of gps(x, y, z, vx, vy, vz data are at least required ? If the Estimated reflection coefficient is negative, what could be the cause?Thank everyone!!!

Welcome to the Orekit forum.

There is just a theoretical minimum of observation. It corresponds to the number of estimated parameter. Because you need at least one equation per estimated parameter.

After that, the only rule is: the more observations you have, the more your optimizer appreciate

In order to help you and provide you more precise advice, could you tell us:

- The dynamical model you used to initialize the numerical propagator.
- The number of measurements.
- The type of measurements
- The measurement time span

The best would be a runnable test case in order to reproduce your issue and debugging it.

Best regards,

Bryan

Thank you so much！

- I’m using numerical estimated no numerical propagator.
- The number of measurements is around 500.
- The type of measurements：I don’t know.
- The measurement time span is 10 seconds.

You’re in trouble

What should be the normal range of cd and cr values?

Hi @hurricane313622,

They should be positive. “Classical” values for drag and reflection coefficient is around 2., so say between 0 and 5.

Classical value for

I see, thanks