Having a rocket that can fly very fast and / or very high isn't very useful if passengers can't survive the trip. Therefore we need to build some type of mechanical device that can help us ensure our passengers safe return to earth.
The most advanced and safest machines on the planet today is the automobile. Thousands of car accidents happen daily, yet very few people become victims of those accident. Over the years, pressure from customers and companies like the National Highway Insurance Institute have pushed the automobile industry to build vehicles with the highest level of safety in case of an accident. (planes on the other hand have very high safety standards in order to avoid the accident all together)
Engineers have designed and tested thousand of cars and systems over the years. Each year, new cars are put on the road and each time that new car is safer than its predecessor.
Also known as a crush zone, crumple zones are areas of a vehicle that are designed to deform and crumple in a collision. This absorbs some of the energy of the impact, preventing it from being transmitted to the occupants.
Seat belts are design to keep you in place. Most people don't know this but your seatbelt is actually designed to pull you tight against the seat in order to prevent any side to side motion in the even of an accident. The seatbelt uses pre-tensioner to do this.
Together with the seat belt, airbag help reduce the deceleration force during an accident.