How does space junk get an orbit?

Question

Say an astrounaut throws a hammer out of a space craft. It will get some arbitrary orbit. Will this hammer remain in space or fall down through earths atmosphere? My take on this is, since earth has gravity it should get down. Also, how does the hammer get orbital propulsion to remain in orbit for whatever time it remains there?

Answer 1

The answer is the same for both the astronaut, the spacecraft, and the hammer. The conservation of angular momentum around the Earth keeps all of these in an orbit, at least originally. (The impulse given to the hammer is very small, and insufficient to make the hammer plunge to Earth right away. Likewise for the back reaction on the astronaut!) You can say initially, at the very start, that it's "inertia" that keeps them going, but viewed on an orbital timescale, that "inertia'" become responsible for the principle of the "Conservation of Angular Momentum."

No (new) propulsion power is needed at all on this initial orbital time-scale. Of course, their angular momentum at the start of your question was ultimately derived from the "propulsive power" that sent the spacecraft into orbit initially, some time earlier.

However, the subsequent, longer term answer is that they'll all fall to Earth in the end, but not JUST because of earth's gravity (which, after all, is actually KEEPING THEM IN ORBIT)!

The reason is that even up there, at the height where things are generally sent to orbit, there are still some vestiges of Earth's atmosphere. That provides a frictional drag, however small, that robs things of their angular momentum, as a result of which the height of their orbit is lowered.

There is an almost paradoxical situation here, however: as energy is removed from the orbit, the orbital speed slowly INCREASES! Despite that, the TOTAL ENERGY (gravitional plus kinetic) IS reduced by the friction, but the magnitudes of these two contributors to the total energy both get LARGER! Without providing energy to counter this frictional drag, I'm afraid that these objects will all finally encounter denser atmosphere until they burn up at higher speeds than their original orbiting speed, unless they have efficiently working heat shields.

We're so used to friction "slowing things down," that it initially seems very counter-intuitive that friction can also SPEED THINGS UP! It all happens because GRAVITY is a NEGATIVE ENERGY field. Things in slowly decaying orbits move faster and faster (and with that same friction present, also get hotter and hotter) as they move deeper in. It's because gravity is a negative energy field that the "burn-ups" as things enter the Earth's atmosphere in the last vestiges of still orbital motion happen with increasing ferocity (unless prperly shielded).

It's also the reason that the material collapsing to become a star gets hot: the material gets hottter through collisions, but that also helps to create some thermal pressure that (partly) resists the infall. Of course, if the material were transparent, all the heat would whoosh out as thermal radiation, meaning there'd be NO pressure (except for degeneracy, which I won't go into), almost immediately. (If the Sun were to suddenly become transparent, all the energy from it's center would be "outa there" in 2 1/3 seconds!)

But stellar material becomes opaque, and bottles that energy up; only then is the thermal pressure effective at slowing down or stopping the star's material from "falling together." Notice that thermal pressure itself isn't what stops a star collapsing (a common fallacy). Ultimately, it's the material's OPACITY that stops it! (Lots of books say "stellar material falls together until the pressure builds up to stop it" --- WRONG, WRONG, WRONG!)

Yes, stars are hot, not because they have nuclear reactions going on inside them, but because their original material fell together. It's because they're hot enough that nuclear reactions can start, and NOT the other way round. The nuclear reactions don't make stars hot, or make them shine --- they do however, enable them to shine for a VERY LONG TIME. (I've even known some professional physicists who aren't clear minded on this.)

Live long and prosper.

Answer 2

Of course, if some item is just tossed into space sufficiently close to Earth, then Earth's gravity will pull it down. The key here is that if the astronaut losing the hammer was already in orbit with his space station or spaceship, which seems likely, the hammer will go on on a similar orbit. In most scenarios this would be the case, as otherwise the astronaut would also be in danger of falling down towards Earth or flying into outer space.

Orbits that are sufficiently close to the Earth, for example one of the International Space Station, are not sustainable, the station has to be boosted by a spacecraft every now and then, as it is slowed down by friction with the upper traces of the atmosphere. Same would happen to a hammer thrown out of the station, and eventually it would enter the atmosphere and burn.

Higher orbits are of course more sustainable, for example the moon has remained up for a long time orbiting the Earth with nothing giving it a boost, and of course the Earth is revolving around the Sun with nothing particular driving it, besides it's existing intertia.

Even without friction to slow objects down, orbits can decay via magnetic drag, tidal forces, gravitational waves and such, but these are extremely weak forces and only come to play in very long time scales or where the forces involved are extraordinarily strong (say when considering situations involving black holes.)

Answer 3

Object in orbit will remain in orbit unless they are dragged down. In what is called low earth orbit, the one where the space shuttle and the space station are, a very slight drag exists becasue the atmosphere is not really totally zero there. But dragging something down until if gets slowed enough to completely fall can take decades.
As strange as it may seem, the hypothetical hammer of your example does get some propulsion from the light of the sun. However, in each orbit, it is as likely to push it up as push it down, and if the hammer spins (and unless deliberately stabilized, any object will slowly spin in space) the surface that gets this push will vary over time, making the trajectory very hard to anticipate.

Answer 4

It would eventually fall back to earth, because it does not have any way to keep it at the velocity required to keep it up. The space shuttle remains in orbit only because it is flying at the proper velocity for its altitude to remain orbiting around the earth. The shuttle makes "attitude adjustments" to maintain its orbit if it should start to drift.

If a hammer was thrown backwards, it would not have enough velocity to overcome gravity, and it will fall to earth. If it were thrown forwards, it would have too much velocity and it would create an irregular orbit which would send it crashing back to earth as well.

Maintaining an orbit is a function of altitude and velocity. For every altitude there is a corresponding velocity that must be achieved to maintain orbit. The lower you are, the higher the velocity needs to be, because the force of gravity is higher the closer you are to the center of the earth.

And, DUH, there is gravity in space, furthermore you can theoretically NEVER escape the earths gravitational pull, no matter how far you are. Take a physics class before you comment. Please!

Answer 5

Look at it this away ,every thing in orbit will probably stay there for a very long time. So if an astronaut was working and his hammer was floating there it will need no new energy to keep it there. The shuttle and hammer could orbit together for years if nothing hit either. There is almost nothing in space .

Answer 6

i get give you a specific example of something like this happening. in orbit around earth, in addition to other traditional bits of space debris the is are a camera and a glove. one of the astronauts was on a space walk and he lost hold of his camera and now it is in orbit. you ask about the orbital propulsion... the camera already had orbital propulsion as the astrounaut did who was holding it. the astronaut had orbital propulsion inherant int eh fact that he was orbiting and it transferred to the camera as he accidentally released it.

another way junk gets in to space is when certain nations empty thier trash from space stations.. open the hatch and let it out, it becomes orbital space debris

Answer 7

DOH! There's no gravity in space...that's how it stays out there DUH