when it wants to study another planet or come back to earth
The firing of a spacecraft's engine against the direction of motion to cut the spacecraft's orbital speed. The speed reduction places the spacecraft in a lower orbit. If this lower orbit passes through Earth's atmosphere, the spacecraft reenters.
Tim Peake traveled back to Earth aboard the Soyuz MS-01 spacecraft. After spending several months aboard the International Space Station, he and his fellow crew members completed a deorbit burn, leading to re-entry into Earth's atmosphere. The spacecraft then descended and eventually landed in Kazakhstan, where they were safely recovered by ground crews.
It takes about 3 days (72 hours) for a spacecraft to travel from Earth to the Moon.
It would take over 16,000 Earth days, or around 44 Earth years, for a spacecraft to travel from Earth to Neptune at its average distance from Earth. The actual time would depend on the speed and trajectory of the spacecraft.
The gravitational pull between earth and the spacecraft will become insignificant.
Traveling at the speed of light, it would take a spacecraft 40 years to reach a star located 40 lightyears away from Earth.
A spacecraft that is controlled from Earth is typically referred to as a teleoperated spacecraft. This means that it is being controlled by operators on Earth rather than operating autonomously.
The same reason why all spacecrafts have parachutes: During reentry into the Earth's atmosphere, the spacecraft goes extremely fast. And if there are people in the spacecraft and no parachute, they would slam into the water at that speed and it would be like hitting concrete. So without a parachute, everyone on the spacecraft would be killed.
9 years
Traveling at the speed of light, it would take a spacecraft 40 years to reach a star located 40 light-years away from Earth.
that isn't a question, but if it did it it would get pulled to earth by earth's gravity
No spacecraft from Earth has ever landed on Neptune.