I guess this is like Lindburgh wondering if the fly in his plane affected his fuel.
When astronauts move inside a capsule, or even sneeze, does it jar the whole thing?
On the one hand, action and reaction will balance out, but on the other hand, not necessarily at the same time.
So if he tosses a ball at the wall, he will move one way and the ball the other, but I’m thinking one of them wil hit the capsule first and then the other, causing a 1-2 punch.
I know they have automatic course correction, that’s not the issue.
Also, would it be different if he were on a space walk? Say he threw a paperwad at the ship and it stuck, so there was nothing leaving the craft, would his motion and the wad’s balance exactly or create a wobble?
Basically, if the system stays closed - if momentum (which in this case pretty much amounts to mass) doesn’t arrive or depart - there is no net effect on the capsule’s course.
A closed system does not assure the absence of “wobble”. If you throw a ball, the mass-velocity product (momentum) is conserved, and the center of gravity of the entire ship is conserved, but the center of gravity may not be in the same place (relative to the the hull) that it was before.
A battery-powered vibrator is a closed system, yet a vibrator on the Space shuttle, will float free with a hellacious wobble. I’m sure someone must have done this and taken video. It’s just too good a science demo to skip, even for strait-laced NASA – but I bet they didn’t call it a “vibrator”.
The wobble, in this case, is typically from a off-center mass attached to a motor. As the mass moves, the rest of the vibrator moves in the other direction. The path of teh vibrator through space, however remains fixed.
In the case of an astronaut on an EVA, the “life line” would introduce more opportunities for complex wobbles. It is flexible, not rigid, and is usually not under tension, so there could be a delay before it transmitted the “equal and opposite” reaction of the astonaut to the ship. Ropes are good for pulling, not pushing, and they can only pull after they’ve exhausted all heir slack.
True. But as you note, wobble doesn’t affect the course.
[I actually think it would be possible to show that enough wobble *would* affect the course. But the effect would be almost unmeasureably small for any wobble that could be produced in an actual spacecraft.]
I’m not sure I understand you here. Let’s call it a “personal massager”. How would it’s behavior be different in a weightless environment, than on Earth? Assume that we’re in a breathable atmosphere (after all, without that, what would be the point?). I can imagine the massager floating freely in the air, but why would it’s vibrating effect be any more pronounced? It’s still a whirling mass on a shaft. (Now, isn’t that a pretty picture?)
According to this article , the recent Sumatran earthquake affected the Earth’s rotation in a measurable way. No mass was lost to the whole system (the planet), but the mass was rearranged. Wouldn’t this be an even greater effect on a spacecraft, since the passenger’s body is a greater percentage of the mass of the whole vehicle? The spacecraft’s course may not change, but it’s attitude would. If the bumping of a few techtonic plates can affect an entire planet, surely the bumping of a few astronauts can affect a spacecraft.
Rotation speed changes as mass moves closer to the center of rotation, but the path of the Earth in orbit around the Sun doesn’t change. The effect of the earthquake was like an ice-skater pulling in her arms; it spins faster, but it doesn’t change course.
Take an extreme example; the closed system consists of a spacecraft and a tethered external mass; the astronauts suit up and hurl the tethered mass away from the capsule; the mass travels in one direction, the astronauts and capsule in another (action and reaction) the rope goes taut and rebounds and the mass heads back toward them (and they toward it) - overall, everything is still going along the same path.
What I can’t quite work out is whether there would be any real change in course if the tethered mass, at its furthest extent, happened to experience acceleration due to passing deeper into a nearby gravity well than it would otherwise have done - on the one hand, the capsule and crew are now passing further out of the gravity gradient, but on the other hand, the gradient isn’t linear, so there might be a real imbalance. I dunno.
Did NASA use gyros (esp. early-on)? This would compensate for the astronauts’ movements, wouldn’t it? That “closed system” argument may be valid, too. It always fools me, like that science puzzle showing a jeep, lets’ say with a pole sticking out front and a super-powerful magnet aimed at the front of the jeep. I guess one would argue that the pull of the magnet is canceled by the equal and opposite reaction force, right? Such science puzzles always gave me pause to ponder…
Well, the thing that counts about the path seems to me to be the position of the center of mass of the capsule. Suppose that we are in a circular orbit with the astronaut exactly at the center of mass. Now if the astronaut moves toward the earth the center of mass is in a slightly lower orbit and one which is too low for the velocity. So it looks to me like the orbit would now become very slightly elliptical.
So I guess my WAG would be that yes, movements within the capsule change the orbital path to a small extent. I would think that with the shuttle, when a payload is released from the cargo bay thus changing the center of mass there would have to be an adjustment of the orbit.
Can someone who really knows for sure come in, please?
Except that the astronaut can change the position of the centre of mass only in relation to the capsule itself; when he moves toward the Earth, he does so by exerting force on the inner surfaces of the capsule and as he moves toward the Earth, the capsule moves away a bit; the position of the centre of mass in relation to the Earth is not changed, just the way in which that mass is distributed.
Notwithstanding possible gradient effects as previously mentioned.
Oh yeah. I think you’re correct in this. Which brings up a further question. When the shuttle releases a payload is it done by slightly changing the shuttle orbit with maneuvering jets for by pushing the payload away from the shuttle?
I think you mean momentum wheels. (Gyros measure attitude change; momentum wheels cause attitude change.) Momentum wheels can compensate for rotation if, for example, a motor starts running and the spacecraft starts to spin slightly in the opposite direction. But it won’t compensate for movement of an astronaut. For that you need a moving counterweight - perhaps three sliding weights on rails, or one weight attached to a robotic arm capable of motion in 3 directions.
I’m pretty sure “orbit” is the path of the center of mass, not the physical center of the object. So the astronaut can’t change the orbit. But he/she can cause the spacecraft to wobble relative to the orbit.
Deployable payloads are usually mounted on a tilt table that tilts it mostly out of the payload bay. Then explosive bolts separate the payload from the tilt table, and a spring-loaded mechanism gives it enough push to clear the payload bay. Another method is to grab the payload with the robitic arm and move it out of the payload bay. In either case the “push” is very slight. The Shuttle then changes orbit to move away from the payload, or the payload fires its own thrusters to get into a new orbit.