Skydivers normally wear a backup parachute. Apollo 15 survived with two out of three parachutes working properly. But wouldn't it be great to have a second deployment option, like skydivers do? The deployment maneuver itself must be a huge part of the risks with parachute landings from space. AFAIK reserve parachutes have never been used in space travel. Is the mass penalty of an independent secondary parachute system so big that it is easier to instead make sure it works every time?