[daniel_iversen]

Why does it have SPARC architecture CPUs as well I wonder? Any guesses?

[masklinn]

It's unclear whether you're asking why they have both SPARC and PPC chips, or what the SPARCs are used for.

For the former, different contractors for the features, with some contractors preferring RHPPC and other RHSPARC?

For the latter, one SPARCs controlled the thrusters and descent stage, the other controls the movement (it's the main chip of the motor controller).