Space Environment

How does gravity work in space?

What is escape velocity?

Escape velocity is the speed that an object needs to be traveling to break free of a planet or moon's gravity well and leave it without further propulsion. For example, a spacecraft leaving the surface of Earth needs to be going 7 miles per second, or nearly 25,000 miles per hour to leave without falling back to the surface or falling into orbit.

A Delta II rocket blasting off. A large amount of energy is needed to achieve escape velocity. Photo from Jet Propulsion Laboratory's Planetary Missions & Instruments image gallery

Since escape velocity depends on the mass of the planet or moon that a spacecraft is blasting off of, a spacecraft leaving the moon's surface could go slower than one blasting off of the Earth, because the moon has less gravity than the Earth. On the other hand, the escape velocity for Jupiter would be many times that of Earth's because Jupiter is so huge and has so much gravity.


Escape Velocity in Kilometers/ Second

Escape Velocity in Miles/Hour
Ceres (largest asteroid in the asteroid belt)
1430.78 mph
The Moon
2.38 km/sec
5320.73 mph


11.2 km/sec

25038.72 mph

715,000,000,000,000,000,000,000,000 kg
59.5 km/sec
133018.2 mph
1,990,000,000,000,000,000,000,000,000 kg
618. km/sec
1381600.8 mph
Sirius B (a white dwarf star)
2,000,000,000,000,000,000,000,000,000 kg
5,200. km/sec
11625120 mph

One reason that manned missions to other planets are difficult to plan is that a ship would have to take enough fuel into space to blast off of the other planet when the astronauts wanted to go home. The weight of the fuel would make the spaceship so heavy it would be hard to blast it off of Earth!

What is gravity?
How do we put a spacecraft into orbit?
Once a ship is in orbit, do we have to do anything to keep it there?
How did DS1 get into space?
Could NASA use ion propulsion to put a ship into space?

What is mass?
Why is it a good idea to launch a ship into orbit from near the equator?
Why is mass important?
How does a multi-stage rocket like the Delta II work?
Why does it take so much energy to launch DS1?

Why do mass and distance affect gravity?
What's a gravity well?