How long can something orbit the Earth?
The period of a satellite, or how long it takes to orbit the Earth one time, is dependent on its orbital altitude. Satellites in LEO, like the International Space Station, take about 90 minutes to orbit the Earth. Satellites in MEO take about 12 hours to do the same.
The initial speed of the satellite maintained as it detaches from the launch vehicle is enough to keep a satellite on orbit for hundreds of years. A satellite maintains its orbit by balancing two factors: its velocity (the speed it takes to travel in a straight line) and the gravitational pull that Earth has on it.
Even when satellites are thousands of miles away, Earth's gravity still tugs on them. Gravity—combined with the satellite's momentum from its launch into space—cause the satellite to go into orbit above Earth, instead of falling back down to the ground.
No. The Earth has a lot of mass and moves extremely quickly in its orbit around the Sun; in science speak, we say its 'momentum' is large. To significantly change the Earth's orbit, you would have to impart a very great change to the Earth's momentum.
The first planet they land on is close to a supermassive black hole, dubbed Gargantuan, whose gravitational pull causes massive waves on the planet that toss their spacecraft about. Its proximity to the black hole also causes an extreme time dilation, where one hour on the distant planet equals 7 years on Earth.
As of May 2022, the Union of Concerned Scientists listed 5,465 operational satellites from a known population of 27,000 pieces of orbital debris tracked by NORAD.
If the earth were about 36,000 km in diameter with the same mass and length-of-day then the gravity at the equator would be zero. This is the altitude of geostationary orbits.
The key to understanding why satellites do not melt or burn up is the difference between temperature and heat. Temperature measures the thermal energy of particles, but as the air in the thermosphere is thin – as if it were a vacuum – there are not enough particles to transfer energy, causing low heat (here), (here).
The only gravity comes from its center, and it extends infinitely far away, getting weaker and weaker the further away you get. In order to get to that infinite point before you get pulled back by the Earth's gravity, you need to be going at least 11.2 km/s (25,000 mph). This speed is the escape velocity!
It is true that gravity is "unlimited" in the sense that it never turns off. Earth's gravity will never go away as long as it has mass. But since this is just a force and not an energy, the never-ending nature of gravity cannot be used to extract infinite energy, or any energy at all, for that matter.
Will gravity ever stop?
The Earth's gravitational field extends well into space it does not stop. However, it does weaken as one gets further from the center of the Earth.
Short-period comets take less than 200 years, and long-period comets take over 200 years, with some taking 100,000 to 1 million years to orbit the Sun. The short-period comets are found near the ecliptic, which means they are orbiting the Sun in same plane as the planets.
Long-period comets have orbital periods longer than 200 years. In addition, their orbits are often highly inclined to the ecliptic suggesting that they, like the short-period Halley-type comets originate in the spherical shell of icy bodies known as the Oort Cloud.
Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi) in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes 365.256 days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi).
Satellite orbit map. This diagram shows the relative distance from Earth of the three satellite orbits, with low earth orbit closest to the earth at 200 – 1,600km (373 – 932 miles), and geostationary orbit the furthest away, at 35,786 km (22,236 miles).