# Moving object in space

I am a learner in this field. I have a doubt after watching movie "Gravity". In that movie, an explosion occurs in a spacecraft and the particles of that vehicle move so faster than a bullet, (as mentioned by George in that movie) from a very long distance to the spot where the astronauts (actors) crew members are.

My question is will those objects (or parts of spacecraft) stops/slow down ever?

What I think right now is they don't stop because when Sandra (actress) goes into rotations, she just doesn't stop until George (actor) helps her out.

## 1 Answer

Each of the exploded debris will gain a given $\Delta$V based on the force from the explosion. This $\Delta$V will be comparatively small to the orbital velocity, typically you'd be looking at 100s of meters per second against 1000s. Objects in orbit stay in orbit ALMOST indefinitely. Drag is the best friend of gravity. Gravity stops these object escaping the Earth, they have to be moving a lot faster to get away from the gravity pull. But it keeps them in orbit going around and around the Earth. Each time a object orbits the Earth it might hit a few very sparsely spread atoms. These atoms collide with the debris and slow it down. Over a period of months, years, decades, etc all objects in orbit will eventually reenter the atmosphere. Low Earth orbit is a couple of months, or years. Geosynchronous orbit is more like millions and billions of years.

Short answer: Yes, eventually they will slow down and reenter the Earth's atmosphere.

• "Objects in orbit stay in orbit ALMOST indefinitely" -- Probably worth mentioning that isn't some special property of orbits, just plain old inertia. – called2voyage Apr 16 '14 at 13:04
• The fact that the Earth doesn't have a uniform gravity field will impact the orbit as well, but I don't know enough about that to speak in any more detail – Nickolai Apr 16 '14 at 13:50
• @called2voyage very true! The point I was trying to make is that things in orbit don't fall to the ground due to gravity. – ThePlanMan Apr 16 '14 at 15:03
• @Nickolai it will certainly have an impact on the orbit, but the effect is conservative so it wont decrease/effect the orbital life time! – ThePlanMan Apr 16 '14 at 15:04
• All objects in orbit eventually reenter the atmosphere? An object in geosynchronous orbit will re-enter the earth's atmosphere after millions and billions of years? I don't think this is right. – HopDavid May 14 '14 at 23:06