Astronaut saftey in freefall

Factual Questions
21

See, the problem is that most people don’t have a good mental model for what’s going on with orbits.

It’s not that you’ll float a little bit away. We have an intuitive sense from our experience and evolutionary history of living on the ground, that if you move something it moves a little bit, and then stops. If there’s nothing under you, you fall. And so on.

Except, when you change the environment, those things turn out not to be true.

Things stop moving here on Earth because of friction. So you throw a baseball, and it flies through the air, and then hits the ground and stops moving. But with no ground to hit, it’s going to keep moving. With no air to slow it down, it keeps moving exactly as fast as it did before.

So if you’re up in orbit, you absolutely can climb out of your spaceship and sit on the nose-cone. And you can’t fall off and plummet to your death, because you’re already falling at exactly the same rate as the spaceship. You and the spaceship are actually moving very fast, but since you’re both moving at the same rate you don’t move away from each other.

But suppose you’re sitting on the nose cone and give yourself a little bump, and start floating away. Well, if that happens on Earth you expect to fall back pretty fast to the surface, and you’re back sitting on the ship, or falling to the ground. Except, since you’re both in orbit, that won’t happen. You give yourself a nudge away from the ship, and you keep moving away. Newtonian physics. If you nudge yourself away at 1 ft/sec, you keep moving away. So after a minute you’re 60 feet away, after an hour you’re 3600 feet away.

But of course, you and the ship aren’t really stationary to begin with, you were just stationary with respect to each other. You’re actually both orbiting the Earth. There’s still plenty of gravity up there, and if you were stationary you’d plummet back to Earth. But to get into the orbit, you’ve given yourself a sideways vector. You’re actually falling towards the earth at the exact same speed as if you were stationary. You fall towards the Earth, but you keep missing.

Think about how it would be if you were just sitting up in space at the height of a space shuttle orbit. There’s the Earth below you. You start to fall. Pretty soon you’re going to smack into the Earth, although it’s going to be a long fall (Project Excelsior - Wikipedia). OK, but suppose you were going at some speed–you’d be falling towards the Earth at some speed, but if you had a fast enough sideways speed the falling and the sidewaysing would be equal, and after falling for 1 second you’d still be the same height above the earth. This is called an orbit. This is why the Moon goes around the Earth, and the Earth goes around the Sun.

So if you’re sitting on the nose cone of your spaceship, and push away gently, you don’t drift away forever, because what you’ve really done is put yourself in a slightly different orbit around the Earth. Your orbit is elliptical, which means that no other forces act on you, you’ll return to the exact same spot above the Earth after one orbit. Of course, the Earth will be rotating below you, but that doesn’t matter, the Earth and you and the spaceship will be orbiting the sun, but that doesn’t matter because you and Earth have the same orbit around the sun, and the Solar System will be orbiting the galactic core, but that doesn’t matter because you and the Earth and the Sun have the same orbit. What matters is that you’ve got a different orbit than the spaceship. And when you return to the same spot after orbiting the Earth once, the spaceship will also be orbiting the Earth. It will return to exactly the same spot–except at a different time.

22

I recall one of the Gemini astronauts sitting on the capsule during a spacewalk and admiring the view. :slight_smile:

23

But of course he’s not quite sitting “on” the capsule, he’s floating next to the capsule. But yeah, you can position yourself such that your buttocks are pressed against the capsule, if you’ve got something to hold on to.

24

Here’s a good picture. File:EdWhiteFirstAmericanSpacewalker.1965.ws.jpg - Wikipedia

Notice that he’s floating next to the capsule, not plummeting to his death.

25

I stand corrected.
Hey, the NASA book I had on Project Gemini when I was a kid said he was sitting on the capsule. You gonna argue with NASA? :slight_smile:

26

What you really want is one of these suits: Orbital skydiving | Memory Alpha | Fandom

27

Not really - if the rocket is still accellerating, he’s still going to be subjected to all sorts of g-forces, making it very difficult to do this (let alone move). The atmosphere doesn’t have anything to do with that. If you meant “once in stable orbit” then yes.

28

So, can you tell me you can’t just fly in a straight line through space? Why is it all about orbits?

29

You could fly a straight line through space, and you would, except if you are acted upon by an outside force. Like, say the force of the Earth’s gravity, or the Moon’s gravity, or the Sun’s gravity, or Jupiter’s gravity, or the galactic core’s gravity.

If you get far enough away from an object, you can treat their gravitational attraction as zero, because it drops away to pretty near zero. But the more massive the object, the more gravity it creates. This is why the Earth orbits the Sun instead of Venus. Venus exerts a gravitational attraction on the Earth, but it is so tiny compared to the Sun’s gravity that we typically treat it as zero, except when we’re doing very very very very precise calculcations.

So if you were in interstellar space light years from any star or other object, you’d travel in a pretty good approximation of a straight line. Except you’d be orbiting around the galactic core, which is many many many times more massive than the sun, although it is also much much much much further away than the sun. It takes the solar system something like 200 million years to orbit the galaxy, and stars and objects are can be thrown out of the galaxy due to various mishaps, although it might take millions of years before you’d notice.

30

Of course you can fly in a straight line. But we tend not to do that with astronauts, because there aren’t any places to go that don’t take millions of years to get to. And when you do get there, they’re usually out of parking spots.

Because orbits keep us in outer space, but still really close to home.

31

The other big thing is that we’re really traveling pretty fast, what with the Earth revolving and orbiting the Sun, and so on. Especially compared with the ability of a rocket to accelerate and change velocity. You’ve only got so much rocket fuel in a rocket, and that rocket fuel can only change your velocity by a certain amount. And the speed at which we orbit the sun, or the speed it takes to orbit the earth, is pretty large compared to the ability of a rocket to change velocities. So it’s really hard to use a rocket to orbit the Earth, because the amount of energy it takes is very large compared to the output of a rocket, and adding more fuel just makes it worse, because you have to burn fuel just to move around your fuel tank.

So pointing your rocket at the stars and turning the engines on full won’t make you travel in a close approximation of a straight line, because your rocket engine isn’t very powerful when measured against the speeds and distances of interplanetary space.

32

Mostly because applying a continuous thrust with a rocket is very expensive. To do it, you’ve got to continuously throw a lot of reaction mass in the other direction to the direction you’re accelerating; and for that acceleration to be significant, you either need to be throwing it really, really fast (costing lots of energy), or throwing a lot of it (which means you quickly run out of stuff to throw).

The only practical means humans currently have to move through space is to make short, powerful blasts to adjust your path in a manner that’s calculated to put you on a free-fall path that gets you where you want to go. And since there’s nowhere within millions of miles that doesn’t have significant gravitational fields in play (from planets, moons, and/or the sun), that means your free-fall path is some kind of orbit of something. Either a closed ellipse around a nearby body, a hyperbolic orbit (usually as a path from body A to body B), or a parabolic orbit (colloquially known as ‘crashing’–have your parachute ready!).

33

To revisit the toolbag issue; You have a toolbag with you and you find yourself drifting away from the shuttle or space station, say about 10 or 15 feet. You manage to get your back to the shuttle and push the bag away from you with force (using both hands), it would propel you back to the mothership. Yes or no?

34

Yes. This is straight Newtonian physics. Every action has an equal and opposite reaction. So you throw your 1 kg toolkit at 10 m/s, and your 100 kg body travels in the opposite direction at 0.1 m/s.

Of course, that is added to your existing vector away from the spaceship. So if you were traveling at .1 m/s away, you’d stop traveling away. If greater than .1 m/s, you’d still be moving away, just not as fast. If less than .1 m/s you’d start moving towards the spaceship. This is assuming you can throw accurately enough to throw the toolkit directly away from the spaceship and not set yourself tumbling, etc.

Note that this is exactly how rockets work–throw hot gas one way, and you move the opposite way.

35

Quoth SCSimmons:

Parabolic orbits are not colloquially known as “crashing”. You can also crash with a hyperbolic or elliptical orbit, and you can be on a parabolic orbit without crashing. There’s no particular relationship there.

36

Wait, how can you be on a parabolic orbit without crashing? If you don’t crash, aren’t you by definition in either an elliptical or hyperbolic orbit? Parabolic means you go up-up-up, and then you go down-down-down and then kersplat. If you miss the kersplat then where are you?

37

A parabolic orbit is just an elliptical orbit that has one end stretched out to infinity.

38

OK, I get it. Hyberbolic means you start at infinity and end at infinity. Parabolic could end at infinity too—you shoot your cannonball up, and it could miss coming down–if you shoot it hard enough.

39

Hyperbolae, Parabolae, ellipses/circles are just different kinds of conic sections.

40

Well, yes, I do have some missing info on orbits and space and such. Not being in the loop, I was under the impression there is still some atmosphere even though you are technically in space. I also did think it would take a terribly large chute to cause enough drag to bring you down. It is not a terrible stretch of the imagination to think that even with two tethers, a human being cannot make a mistake and wind up separated from the ship. They lost a tool bag and many other items to smaller mistakes. It isn’t a matter of if it will happen, but when.

So they do have a “fishing line” to cast out and attempt to retrieve a lost soul, what if they miss, or the astronaut is unconscious and too far away to safely retrieve.

Here is a scenario, astronaut #1 is working near an O2 tank, misreading a wiring diagram, he causes a small non-lethal explosion pushing him away from the ship and dislodging his tether.

He is floating away, the damage to the ship is mitigated by emergency equipment, but it will have to abort it’s mission soon.

the other astronaut #2 retrieves a casting pole and manages to put the weighted end right in front of #1’s face, but he makes no attempt to grab it, nor any indication of struggle.

They can tell by his suits monitors that he is still alive, but unresponsive.
Is there a way to grab him and haul him back?