Of course this got me to wondering… could someone skydive from space? How far outside the atmosphere do you have to start falling from before you arrive fast enough to slam into the atmosphere and heat up as you brake to terminal velocity? And that’s assuming that you are stationary WRT to the ground; adding orbital velocity would definitely increase the potential crisped-like-a-meteor factor…
Has anyone researched this? Say, thrown something out of the cargo hold of the space shuttle and watched it all then way down?
The skydiving altitude record is a bit over 100,000 feet, from a high-altitude balloon. Beyond that, bailing out becomes a rather tricky proposition. The air is so thin that stability is a problem- a falling body can develop a fatal spin, unless some kind of stabilizing drogue chute is used. IIRC, for the X-15 rocket plane, the bailout procedure called for the pilot to stay strapped into his ejection seat until reaching lower altitude. Similarly, most plans for ballistic capsules call for the crew to ride the capsule down to lower altitude.
If you just threw something out of the shuttle, it wouldn’t fall all the way to the ground. It would just go into an orbit close to that of the shuttle itself. You could fire a gun (or just something to propel an object very quickly) backwards along your course of travel, but whatever you shot would be receding so quickly I don’t think you’d be able to see it fall.
The closest parallel might be the solid rocket motors and the external tank that the shuttle jettisons during launch. NASA’s web site might have some information on altitudes and velocities for those objects (the solid rockets are recovered by parachutes, the tank burns up in the atmosphere). NASA also revised the emergency procedures after the Challenger explosion, including the possibility of bailing out during the launch. You might be able to find the maximum planned altitude for that contingency.
And from what I’ve read about the development of ejeciton seats for jet aircraft, engineers were very concerned about injuries from the air blast when ejecting at just five or six hundred miles per hour. It’s not a pretty thought, but I think high speed skydiving would tear a human body apart before heat became a major problem.
I believe there is no provision for bailing out of the Space Shuttle. The first couple of flights had ejection seats for pilots, but only because they were considered test flights, not operational flights. There are plans for aborting a flight and flying the orbiter to a landing strip, but if the orbiter is disabled after launch, there is basically no hope of survival.
If you want to do a sky dive from space, one problem is, where do you jump from? If you step out of a Shuttle you just float there in orbit. The standard way of leaving orbit is to fire a rocket to slow down the spacecraft by a tiny bit. Just enough so that the spacecraft hits the upper atmosphere, gets slowed down even farther and fall to the ground. Problem is, the spacecraft in orbit is flying at something like Mach 25, and all that kinetic energy must be lost due to friction with air. That’s a huge amount of heat. It would be extremely difficult to build a spacesuit that can withstand this heat.
Another possibility is to get launched on a sounding rocket. These rockets can up to 100 mile altitude or more, but after that they just fall down. Since it never attains orbital speed, they hit the atmosphere much more slowly than orbital spacecraft. So with a properly designe spacesuit, you can probably survive reentry. Of course, there is the small problem of surviving the launch - most sounding rockets have extremely high acceleration at launch, tens of Gs or more. Still, there is no reason you can’t build a slower sounding rocket. In fact, Gus Grissom (sp?)'s flight was a sub-orbital flight.
you would need some type of force (rocket?) to propel you towards Earth’s gravitation pull.
You would also require some pretty heavy armor to protect against re-entry. If such an armor for a single human being exists then I do not know of it. It seems to me you would be nice and broiled.
If you can survive all that, you could theoretically design a parachute that would allow you to survive the remainder of the fall.
There was extensive discussion of “space diving” a while ago on slashdot.org at:
after an article appeared on space.com described new technologies being developed for recreational space diving. Unfortunately, the original article on space.com seems to be gone. Why oh why can’t sites maintain a proper archive of their past stories? It isn’t that hard…
I was aware of the orbital-velocity thing… so let’s assume that the jumper is stationary with respect to the surface of the Earth.
Being stationary with respect to the earth’s surface is the same as being in a geosynchronous orbit (at the equator, at least).
You can do this in free fall at an altitude of (I think) 35 800 km. At any other altitude, you need to provide support, such as the thrust of a rocket, to maintain a geosynchronous orbit. At altitudes below 35 800 km, without that support, you would fall back to earth. At altitudes greater than 35 800 km, without that support, you wwould be flung outwards into space.
The design of the “beanstalk” or orbital tower takes advantage of this. Unsing a very strong cable, you connect the surface of the earth to an asteroid in a non-free-fall geosynchronous orbit (far beyond the 35 800 km distance). The tension that keeps the asteroid from flying away supports the cable close to the earth.
With such a tower, you could simply step off a balcony anywhere below the 35 800-km level and start falling to earth.
So… how far up would you have to start falling from to be inconvenienced by re-entry heating? We know that we can start falling from a balloon at 103,000 feet (just under 31.4 km) without problem. However, by definition, that balloon was still within the atmosphere.
What happens to something falling from 50 km? 100 km? 1000 km? From what height does the falling object gather enough speed above the atmosphere to be heated by its deceleration to terminal velocity in the atmosphere?
I don’t believe you have a correct understanding of orbital motion. It is really irrelevant whether one is in a geosyncronous orbit or not. In other words, it doesn’t actually matter whether or not the jumper is stationary with respect to the ground.
What matters is that his angular velocity and tangential velocity is zero with respect to the center of the Earth. Tangential velocity is sometimes called “orbital velocity.”
If you have a “beanstalk” geosyncronous tower, the end of the tower has a tangential velocity of over 3.0 km/s. If you “step off a balcony” you will NOT start falling to the Earth. Because you have a large tangential velocity, you will simply put yourself into orbit.
<thinking about this a bit…>
Oh! So from a true stationary position above the equator, you’d see the earth rolling by beneath you, and every 24 hours the Beanstalk would sweep majestically past. Okay. I think I get this a bit better.
So for a true free fall straight down, you’d have to step off the balcony of the orbital tower, or our of your spacecraft, blast backwards to cancel its orbital motion, and blast downwards as well to cancel the incipient fall until you were ready.
Then you could take the Long Dive To Earth.
Why do I sense that this will be one of the Great Sports of the mid-21st century? Where’s Richard Branson to give this some funding?
I remember an SF story where they did this at a state funeral, only it was with respect to the sun. Yep. The coffin fell 150 000 000 km straight down “like a falling safe”…
Not quite. If your angular velocity was zero with respect to the center of the Earth, you are no longer in orbit. You would then indeed fall straight down. Assuming you are still relatively near the Earth, it would not take long before you burned up in the atmosphere or hit the ground.
Note that it takes a tremendous amount of energy to slow an object in a solar orbit such that it will fall into the Sun. It’s an interesting result that it actually takes more energy to slow such an object so that it falls into the Sun, than to put it on an escape trajectory away from the Sun.