What kinds of stress does the acceleration related to rocket launch and reentry produce on the human body?

Answer 1

When a rocket launches into orbit, it has to get up to over 18,000 miles per hour in order to move forward at exactly the same speed that it is falling towards the earth, which is what is referred to as "orbit". In order to get to this incredible speed, it has to accelerate sufficiently before the fuel itself runs out. This means that you have to get to that speed very fast - usually in just a few minutes. In a car, you notice when you first hit the gas, it pushes you back in your seat. This is an acceleration force. Acceleration forces are measured in g's - in which 1 g = the force that gravity has on you, that naturally weighs you down on earth. On a roller coaster, you experience everything from 4-8 g's to zero g to negative g's. Zero g's means you are free-flying with no g pressure. Negative g's are when the ride pulls you down faster than you would fall. You will trying to "come up out of your seat. The really hard curves and dips can generate up to 8 gs in some coasters. This is usually when you are moving downward very fast and all of a sudden the direction changes to up and you feel yourself being pushed very hard into your seat. You may feel light headed. The high g's you experience on a roller coaster are very brief. Usually no more than a second or two. If that is sustained for a longer period of time, you can esperience some very negative effects. All that force pushing down can cause the blood to rush down to your feet. And away from your head. Your heart simply can't keep up. Eventually you will blackout. Your vision goes blurry, then you pass out. Even just a few minutes of time spent at very high g's can cause death. This is often experienced by fighter pilots who may have to make radically steep dives and pull out of them very hard as part of their tactics. This is why pilots wear pressure suits. These suits monitor their pressure and actually squeeze the legs to limit blood back flow to the legs and help maintain some blood flow to the brain. They can withstand higher g forces because of the suit than they could without it. The opposite can happen in an "over-the-top" loop, and it's called a redout. High negative g forces are applied and too much blood rushes to the head. The pilot sees red before passing out. Imagine climbing very fast in a jet and then just pushing the stick forwar. The plane will loop over and down, and the pilot will be forced up against his shoulder harness. Again, the pressure suit helps control this. (But the pilot may roll over and "invert" when doing this turn to apply positive g's instead of negative ones.) The old Mercury, Gemini and Apollo rockets provided a great deal of thrust and acceleration and about 6-9 g's of force, so the crews needed pressure suits and needed to lie down while lifting off. The shuttle on the other hand is a bit slower and only puts about 6 g's on the crew as it's going to orbit. Coming back, a spacecraft has to slow down very rapidly. It starts it's descent by simply slowing to under 18,000 mph. This causes them to start to fall into the atmosplere. As they fall lower at 18,000 mph, the atmosphere becomes thicker and slows them sown - just like landing in water when you cannonball in. As they fall their speed rapidly declines from 18,000 mph to only 400 mph in just a few minutes. Again, the g forces are just like the roller coaster when it turns from going down before it turns up. The shuttle crew experiences quite a bit fewer g forces on the way back in because the shuttle comes in at an angle and glides in. But there is also more surface area, so the drag is greater. Hope this helps.