Complex sentence: The embedded computer systems that are on board the various Mars rovers sent to Mars by NASA have to withstand the high radiation levels and large temperature changes in space and for this reason their computational resources are limited compared to current computer systems commonly used on Earth.
Split into simpler sentences: The embedded computer systems on board the Mars rovers sent by NASA must withstand the high radiation levels and large temperature changes in space. For this reason their computational resources are limited compared to systems commonly used on Earth.