Metal Sludge Gossip Board

SeminiferousButtNoid wrote: ↑Sun May 10, 2020 12:57 pm

I am falling from 900,000 feet. I have no parachute nor a backup parachute. If I was able to make my landing in the ocean, could I survive?

Skip Reith wrote:
Let’s say that it is some time in the future and you are on a station part of the way up (900,000 ft) a space elevator
. Some nefarious people brought outside with misinformation and pushed you over the edge. Can you survive?

For the first 700,000–800,000 feet (210–250 km) you fall like a rock. Or like a feather - there is no atmosphere worth mentioning so everything accelerates at the same speed - 32 ft/sec/sec or 9.8 m/sec/sec.

Just about 220 seconds after the big push you will hit the upper atmosphere and you are traveling at 7,150 feet/second (4,875 MPH or 7,850 kph). At 100,000 feet, that speed is about 8–10 times the speed of sound. At that height, there is only a little air (just over 1% of that a sea level). That small amount of air will do little to slow you down, but at least your acceleration would drop. The problem is a spacesuit is not designed for atmospheric entry. The atmospheric drag will hit some parts more than others and you will start to spin. Unless you are an expert at high altitude sky diving you probably will never come out of the spin and that spin alone will kill you.

If you manage to keep stable you will continue to accelerate some more until you hit about 80,000 feet or so when air pressure starts to be felt powerfully.



Once you hit about 70,000 feet the friction becomes seriously noticeable as you begin to slow down. At first, the slowing isn’t bad, but soon it gets quite uncomfortable. You won’t hit terminal velocity until about 10,000 feet (well, actually, you will hit terminal velocity a few milliseconds after hitting the water). At 75,000 feet you are starting to slow down due to atmospheric friction. The slowdown will increase rapidly once you pass 60,000 and will continue until you hit about 10,000 feet.

You hit a maximum speed of about 8200 ft/sec (or 5590 MPH or 9,000 kph) at around 75,000 feet. That speed is still about 8 or 9 times the speed of sound because of the speed of sound increases as the air pressure increases.

During the drop from 100,000 ft to 10,000 ft your space suit get hot. The heating increases very quickly as the atmosphere tries to slow you down. By about 10,000 ft you will have slowed down to terminal velocity (and terminal has multiple meanings here). How much energy did you have to dissipate to slow you down? You started the slow down at 2,500 meters/second (I am using m/s for energy calculations). You end the slowdown at about 60 m/s. Using the calculation of

Energy = (mass x (start vel - end vel.)^2 )/ 2

We see that the amount of kinetic energy that is applied to your suit to slow you down is 45.4 megajoules. The time to go from 100,000 ft to 10,000 ft is about 21.5 seconds. You will average about 11 Gs of force (11 times the force of gravity at the surface) although you may peak at around 15 Gs. That is a lot of force and could cause some internal bleeding and organ damage. It can kill a lot of people. The space shuttle starts its slowdown much higher in the atmosphere because of its large surface area and its terminal velocity is much higher than a dropping body.

The power your suit has to deal with is around 2 megawatts. Each square foot of your suit will have to try to dissipate 71,000 watts. If your suit could somehow dissipate that energy it will be glowing white-hot by the time you hit about 20,000 feet. At that point, it will begin to cool. The last 10,000 feet will be the most exciting as the details of the water grow very quickly.

You will have about a minute to enjoy the view. When you hit the water you will decelerate extremely quickly. Pretty much all of your energy will be absorbed by the water in under 10 feet of depth, but we will give you the full 10 feet just because we can. If you throw something towards the water that hits the water before you, that will break up the surface tension some and make the landing just a little bit less traumatic.

The problem with hitting the water at 125 miles per hour is that you end up stopping in one-tenth of a second. To do that, your body experiences 52 Gs. That is enough force to turn pretty much a body into a pizza.

Your only hope is to go in feet first, toes pointed after you threw something in front of you to break up the water. Then, you may experience only about 10–15 G’s. Of course, your legs will be up into your stomach somewhere, but you might just live long enough to drown.

Guy Snelling wrote: That was the long answer. The short answer is no.

Skip Reith wrote: Brevity was never my strong suit.

dmbrocker wrote: ↑Wed May 27, 2020 10:14 am