Question About Fixed Rotation Sequence in Rugged


#1

i’m using the rugged to do some simulation about Agile Remote Sensing Satellite mission which have fixed ration both in roll and pitch aim to target on earth surface.

in my computation,the “roll” fixed ration around x axis is going first,and followed by “pitch”(my satellite also work as this).

but when i build the line of sight in rugged, it will get wrong geodetic location if i add the roll first and add the pitch after roll in the los.addtransform().

then i made another try, if i switch the roll and pitch (add pitch first), the result will looks good.

why? no doc saying this ,is this a bug


#2

The FixedRotation LOS-transform uses the Hipparchus library Rotation class to model the
3D rotation to apply to LOS. Hipparchus does allow two opposite conventions to specify a
rotation, using an enumerate RotationConvention which can take either the value VECTOR_OPERATOR
or FRAME_TRANSFORM. However, Rugged design choice (almost arbitrary, mostly due to our
work habits) was to use VECTOR_OPERATOR. This choice has two consequences:

  1. it has an effect of the meaning of angle sign
  2. it has an effect on composition of rotations

What you see is most certainly due to different conventions between Rugged/Hipparchus/your satellite. There is no ultimate truth, these are only conventions and they may well be different. So when trying to
implement one satellite specification into a Rugged model, you may be enforced, due to different conventions, to either change angles signs, or change rotations composition order, or both.

So I would conclude by saying that it is not a bug, but as you already found that exchanging rotation order lead to the correct result, you have already found the proper conversion between your satellite and Rugged conventions.


#3

Thanks for your reply.

i’m new to your orekit and rugged,you and your team doing a really great job.

in the java world , I think orekit is the best library about astrodynamic.

I am learning and trying to apply orekit and rugged in my application in the right way.

thanks again!!!

youngcle

from Beijing