Re: [Orekit Users] multiple thrust calibration

[MAISONOBE Luc <luc.maisonobe@c-s.fr>]

"RHONE, Quentin" <quentin.rhone@airbus.com> a écrit :

> Hi all,

Hi Quentin,

> I need to perform a single orbit determination which covers several  
> maneuvers. I want to calibrate the thrust of each maneuver  
> separately  but I cannot find the way to do it with the  
> ConstantThrustManeuver class.
> The thrust parameterDriver name  is declared "final static" so the  
> estimator considers that all maneuvers have the same thrust. It  
> eventually creates several rawDrivers that have the same value (even  
> if the maneuvers initially have different thrust levels). Am I right  
> or did I miss something ?

You are right ... and Orekit is wrong. Not being able to use different
maneuver configurations is indeed a really stupid error I can be blamed
for!

The fact the values are identical as soon as the same parameter name
appears in several differents model is however a feature and not a bug.
It was designed for example for central gravity coefficient, as this
coefficient should be the same despite it appears in different force
models (Newtonian attraction, spherical harmonics, relativity...). So
the bug is that we are not able to specify different names, not that
similar names are merged as one parameter only in the estimator.

Could you open a ticket on the forge so we do not forget to solve
the issue?

> I bypassed this problem by re-defining another maneuver class taking  
> a ConstantThrustManeuver and a maneuver name as attributes and  
> implementing AbstractForceModel but I don't find it satisfactory. Is  
> there a better way to do it ?

No, I thing this is roughly the way to go. Perhaps we should use a
thruster name rather than a maneuver name, so if thruster "1A" is
used for maneuvers 1, 2 and 4 and thruster "2C" is used for maneuver 3,
then we could have 2 parameters to be estimated rather than 4.

I think we will add a new constructor with a thruster name parameter
in the existing class, the name being used as a prefix. So if users
use the existing constructor without thruster name the parameter
driver will be "thrust", but if they use the new constructor with
a name "1A" the parameter name will be "1A-thrust".

Thanks for the report.
Luc

> Thank you in advance for your answer,
>
> Quentin
>
>
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