So, what about space jumps?
A few days ago, Felix Baumgartner flew in a Helium-filled balloon to an altitude of 39 kilometers and then jumped out. The data is being pored over by the FAI to get the exact figures, but he did indeed perform the highest to date manned ascent in a balloon and highest parachute jumped, achieved supersonic velocity while free-falling, and the longest recorded free fall distance, but not longest free fall time- that record still belongs to Joseph Kittinger, the first man to do a sky dive from the stratosphere in 1960. Kittinger also served as the ground-based adviser to Baumgartner today, a nice passing the torch moment.
Baumgartner's jump was a nifty Red Bull project, a daredevil stunt and good tv (hey I liked it loads). Back in Kittinger's day, there was another concern- would an astronaut be able to bail out of a malfunctioning craft and get to ground safely?
Aye, those were the early days of the space program, when all ideas were new and fresh and wacky. Stuff does break down, after all, wouldn't it make sense to have a way out if possible? So could it work?
The devil's in the details of what 'it' means. Jumping from a balloon up on high will work. It's not easy- one needs to take care of thermal insulation against both the cold air and any heat resulting from re-entry, ensuring an adequate oxygen supply to prevent loss of consciousness of the astronaut, and controlling the descent to avoid entering a death spin.
Jumping from a space ship in orbit will result in ... well, nothing spectacular actually. The astronaut would just hover around, also in orbit, finding themselves doing something I've covered before. Turns out that once in space it's very easy to throw yourself at the ground and miss.
Incidentally, that's not because Earth is so far away that it's gravity is barely felt. In fact, the gravity experienced by astronauts in (low Earth) orbit is almost the same as that we feel on the Earth's surface. The math- force is mass times acceleration (Newton's second), and (Newton's law of gravity) the force of gravitational attraction is the product of a gravitational constant, the masses of the two bodies (astronaut and Earth, say) divided by the square of the distance between their centers. So the formulas would be
where m is the mass of the astronaut, M is the mass of the Earth, R is the radius of the Earth and h is the height of the orbit above the surface. G is some constant, and gs, go are gravitational accelerations on the Earth surface/in orbit, respectively. It's now easy to see how many times smaller go is than gs:
If we plug in the values for the Earth radius (about 6400km) and height of a low Earth orbit (let's say, 200km), the result is that go is 94% of gs.
So why the weightlessness? Same thing happens, briefly, in a descending elevator, and for a bit more time, in one of those parabolic flights: free fall. Everything in an orbiting ship is falling, with the same speed and the same acceleration, towards the object it orbits around. But while the acceleration is toward that object, the velocity is sideways, and the relationship between its magnitude and that of the acceleration is such that the object stays in orbit.
From Newton's first law, unless a force acts on something, it will move in a straight line with constant velocity. An orbit around the Earth is circular, so a force must act to bend the object's trajectory. That force, of course, is gravity. How fast then does something need to move, so that it stays in orbit, can be (under simplifying assumptions: circular orbit of a body that's much less massive than what it orbits around) estimated like this. Since the centripetal acceleration experienced by an object in uniform circular motion of radius R with velocity is
and since that acceleration is simply our dear old gravitational acceleration, one finds the orbital velocity to be
For example, an orbit of radius 6400 kilometers (so, right on the Earth's surface) needs 8 kilometers/second of velocity. Low Earth orbits need just slightly lower values. So 8km/s aka 28800km/h is a good enough value for a bit of guesstimation. For comparison, Baumgartner's top speed towards the Earth surface was about 1340km/h.
Our supposed astronaut leaping from orbit and wanting to get to Earth in one piece needs to get rid of (most of) that speed of 28800km/h, which means getting rid of a lot of kinetic energy. They'd also have a lot of gravitational potential energy to leave behind. The only option we have, so far, is to dissipate that energy as heat.
The space shuttle uses an entire layer of heat shielding, and not all of it is meant to survive atmospheric re-entry. Chances of installing something similar on a human-wearable suit are slim.
One may think of longer trajectories- spending more time in the atmosphere in a spiral trajectory that goes around the Earth a few times for instance. That way, drag would first occur in the rarefied upper layers of the atmosphere and be smaller. Which is ok, because if the braking force acts for a longer time it doesn't need to be as big, so there's less heat produced each second, so dissipating it before it fries our space jumper becomes easier.
But there's an obvious problem with that. Such a spiral trajectory, if it were possible, would take several hours at the least. And the jumper needs to breathe for all that time. Strapping on several kilos of compressed air and other equipment in the heat of disaster- unlikely.
Which doesn't mean however that some bail out isn't possible at various stages of a space mission, in particular when the shuttle isn't too far away from take-off or landing. This possibility came to haunt NASA in the wake of the Challenger disaster. The crew were alive after the explosion, and death occurred at the impact with the water. They could have been saved, possibly, by an ejection system, but no such system was used because the shuttle was deemed reliable enough. Ok, that may sound callous, but given that there wouldn't be bailout from space, it had better been true.
So anyway. Cheers for Baumgartner, Kittinger and Red Bull. And may future planned attempts at jumps from even higher levels of the atmosphere be similarly smooth in their proceedings.
Baumgartner's jump was a nifty Red Bull project, a daredevil stunt and good tv (hey I liked it loads). Back in Kittinger's day, there was another concern- would an astronaut be able to bail out of a malfunctioning craft and get to ground safely?
Aye, those were the early days of the space program, when all ideas were new and fresh and wacky. Stuff does break down, after all, wouldn't it make sense to have a way out if possible? So could it work?
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| A photo from Joseph Kittinger's 1960 jump. Placed in the public domain by the US gov. |
Jumping from a space ship in orbit will result in ... well, nothing spectacular actually. The astronaut would just hover around, also in orbit, finding themselves doing something I've covered before. Turns out that once in space it's very easy to throw yourself at the ground and miss.
Incidentally, that's not because Earth is so far away that it's gravity is barely felt. In fact, the gravity experienced by astronauts in (low Earth) orbit is almost the same as that we feel on the Earth's surface. The math- force is mass times acceleration (Newton's second), and (Newton's law of gravity) the force of gravitational attraction is the product of a gravitational constant, the masses of the two bodies (astronaut and Earth, say) divided by the square of the distance between their centers. So the formulas would be
where m is the mass of the astronaut, M is the mass of the Earth, R is the radius of the Earth and h is the height of the orbit above the surface. G is some constant, and gs, go are gravitational accelerations on the Earth surface/in orbit, respectively. It's now easy to see how many times smaller go is than gs:
If we plug in the values for the Earth radius (about 6400km) and height of a low Earth orbit (let's say, 200km), the result is that go is 94% of gs.
So why the weightlessness? Same thing happens, briefly, in a descending elevator, and for a bit more time, in one of those parabolic flights: free fall. Everything in an orbiting ship is falling, with the same speed and the same acceleration, towards the object it orbits around. But while the acceleration is toward that object, the velocity is sideways, and the relationship between its magnitude and that of the acceleration is such that the object stays in orbit.
From Newton's first law, unless a force acts on something, it will move in a straight line with constant velocity. An orbit around the Earth is circular, so a force must act to bend the object's trajectory. That force, of course, is gravity. How fast then does something need to move, so that it stays in orbit, can be (under simplifying assumptions: circular orbit of a body that's much less massive than what it orbits around) estimated like this. Since the centripetal acceleration experienced by an object in uniform circular motion of radius R with velocity is
and since that acceleration is simply our dear old gravitational acceleration, one finds the orbital velocity to be
For example, an orbit of radius 6400 kilometers (so, right on the Earth's surface) needs 8 kilometers/second of velocity. Low Earth orbits need just slightly lower values. So 8km/s aka 28800km/h is a good enough value for a bit of guesstimation. For comparison, Baumgartner's top speed towards the Earth surface was about 1340km/h.
Our supposed astronaut leaping from orbit and wanting to get to Earth in one piece needs to get rid of (most of) that speed of 28800km/h, which means getting rid of a lot of kinetic energy. They'd also have a lot of gravitational potential energy to leave behind. The only option we have, so far, is to dissipate that energy as heat.
The space shuttle uses an entire layer of heat shielding, and not all of it is meant to survive atmospheric re-entry. Chances of installing something similar on a human-wearable suit are slim.
One may think of longer trajectories- spending more time in the atmosphere in a spiral trajectory that goes around the Earth a few times for instance. That way, drag would first occur in the rarefied upper layers of the atmosphere and be smaller. Which is ok, because if the braking force acts for a longer time it doesn't need to be as big, so there's less heat produced each second, so dissipating it before it fries our space jumper becomes easier.
But there's an obvious problem with that. Such a spiral trajectory, if it were possible, would take several hours at the least. And the jumper needs to breathe for all that time. Strapping on several kilos of compressed air and other equipment in the heat of disaster- unlikely.
Which doesn't mean however that some bail out isn't possible at various stages of a space mission, in particular when the shuttle isn't too far away from take-off or landing. This possibility came to haunt NASA in the wake of the Challenger disaster. The crew were alive after the explosion, and death occurred at the impact with the water. They could have been saved, possibly, by an ejection system, but no such system was used because the shuttle was deemed reliable enough. Ok, that may sound callous, but given that there wouldn't be bailout from space, it had better been true.
So anyway. Cheers for Baumgartner, Kittinger and Red Bull. And may future planned attempts at jumps from even higher levels of the atmosphere be similarly smooth in their proceedings.
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