Complex sentence: The Phase 1 Mantis vehicle is powered by two Rolls-Royce Model 250 turboprop engines, although this is likely to change in later variants, and is intended to have at least 24-hour endurance.
Split into simpler sentences: The Phase 1 Mantis vehicle is powered by two Rolls-Royce Model 250 turboprop engines, although this is likely to change in later variants. The Mantis is intended to have at least 24-hour endurance.