Complex sentence: By December 2002, he was claiming a working prototype with a total thrust of about 0.02 newtons powered by an 850 W magnetron but it was later reported that the device could only operate for a few tens of seconds before the magnetron failed, due to overheating.
Split into simpler sentences: By December 2002, he was demonstrating a working prototype, reporting a total thrust of about 0.02 newtons powered by an 850 W magnetron. It was later reported that the device could only operate for a few tens of seconds before the magnetron failed, due to overheating.