Questions on field propagation with uncertainties in force parameters

[bogdan.udrea]

Dear Colleagues,

I am working on a simulation to propagate uncertainties of a spacecraft/ orbit due to imperfect knowledge of its initial state vector and disturbance force parameters. I am doing this in OREKIT 11.0

So far i have reproduced the FieldPropagation available in the GitLab tutorials but I changed it from a Keplerian orbit to a Cartesian orbit.

First of all, I would like to include the effect of uncertainties in the acceleration due to drag through the drag coefficient. My understanding, from a post of 2018 vintage from @luc is that I have to do the following:

1. Define a custom acceleration method that “takes a FieldSpacecraftState and an array of Field elements that correspond to the current value of the force model parameters.”
2. “Before propagation start you will have to set up the parameters for the force model…” as shown by @Luc in the reply.

I am stuck because I don’t know how to implement step 1 in general and in particular for the acceleration due to drag. The IsotropicDrag class has methods that calculate both regular acceleration and a field one. Should I start by rewriting it?

Thank you for your help.

Bogdan

[bcazabonne]

Hi @bogdan.udrea

In order to accomplish what you want in an orbit propagation context, you will have to create fielded versions of the drag force. I strongly recommend you to look at Maxime’s answer on the following post.

Partial derivatives w.r.t Maneuver objects

Hi @ChristopheL, The way the maneuver models are designed right now, it does not seem possible to do what you want easily. That is if you are really bound to use a FieldPropagator. In that case I think you will have to design your own “Fielded” maneuver model. I’m talking about this a bit more below. If it is ok for you to use a classical numerical propagator, there are two options: Propagate the state transition matrix and extract the Jacobian of the maneuver’s parameter drivers. For thi…

Maxime gives an example of what you would like to do but with Maneuvers force model. You can follow his recommendations and his example to help you with drag.

If you have additional questions, don’t hesitate

Best regards,
Bryan

[bogdan.udrea]

@bcazabonne thank you for the prompt reply. I will take a look at Maxime’s advice, maneuvers were next on the list.
Bogdan