How did Phoenix manage to orientate itself E-W when Landing Options

[Sandro]

Hi together

During the hot phase of the EDL-sequence with thrusters active, phoenix made automatically many different attitude controls. Among them was the orientation of phoenix's arm to the north. I wondered how phoenix found out his actual orientation and where north was. Since Mars does not have a strong dipol magnetic field like earth, I assume there must have been some other way to figure out the current orientation?!

I thought of maybe using the sun? But this would have been not easy at all!

Does anyone know how this was done?

Many thanks in advance!

Regards,
Sandro

[jmknapp]

I wondered how phoenix found out his actual orientation and where north was.

That pirouette was a nice flourish! At one stage during the EDL coverage it was mentioned that PHX was turning off the star tracker and going on gyros for guidance, so that would be a good guess.

[ugordan]

Are you sure propagation of IMU data is good enough to land within 0.6 degrees of E-W alone after several minutes of tumbling through the atmosphere? I'm curious as to how it was oriented as well. I thought a Sun sensor of some kind was used.