Complex sentence: During deployment, the slider slides down from the canopy to just above the risers, the slider is slowed by air resistance as it descends and reduces the rate at which the lines can spread and therefore the speed at which the canopy can open and inflate.
Split into simpler sentences: During deployment, the slider slides down from the canopy to just above the risers. It is slowed by air resistance as it descends and reduces the rate at which the lines can spread and therefore the speed at which the canopy can open and inflate.