Complex sentence: As the LM descended towards the lunar surface the landing radar was then also switched on, the computer's duty cycle grew heavier than expected and a series of "1201" and "1202" alarms began signalling an executive overflow.
Split into simpler sentences: As the LM descended towards the lunar surface the landing radar was also switched on. Now processing data from two radars instead of only one as intended, the computer's duty cycle grew heavier than expected and a series of "1201" and "1202" alarms began signalling an executive overflow.