Range with respect to?!

Good afternoon,

I am currently trying to perform some orbit determination of ILRS targets using Orekit and the ILRS network data (published through their API). I noticed that their data have extremely low uncertainties for the single normal points’ noise (in the range of a few cm). This sounds great if you want to perform OD, but only if you know where the laser beam is reflected on the satellite.
And here comes my question: the Range (or the RangeBuilder) class does not allow us to specify where the range is measured in the Spacecraft body-fixed frame. Does it assume that they are measured with respect to the satellite centre of mass?

Thank you in advance for the answer,
Edoardo.

The PhaseCentersRangeModifier is intended for this. The name is misleading as you are using retroreflector and not an anteann with a phase center, but the idea is the same.

Thank you @luc. Just to clarify, I would therefore have to define the satellite’s FrequencyPattern? Can the station’s FrequencyPattern not be defined or is it required for both if I want to use the modifier?
And the input “eccentricities” would need to be the 3D position vector of my retroreflector in the satellite-fixed frame with respect to its centre of mass. Did I get this right?

Thank you again,
Edo.

Yes, you need to define a frequency pattern. You can use null for the phaseCenterVariationFunction if you just need a fixed offset does does not depend on line of sight direction.
The eccentricity (a very strange name that comes from GNSS world) is the 3D position of the retroreflector.

1 Like

Perfect, thank you!