How fast do rockets go to leave Earth

To maintain a circular orbit just above Earth’s atmosphere, a spacecraft must move at about 8 kilometers (5 miles) per second. Increasing the spacecraft’s launch velocity will make it swing farther from Earth. Increasing it to 11 kilometers (7 miles) per second will make the spacecraft escape from the Earth altogether.

Elon Musk's private rocket company SpaceX announced Monday that it plans to launch two paying customers around the moon in late 2018.

How hard will that be to accomplish, exactly?

Gravity makes it possible for us to live on Earth, but it also makes it pretty hard to leave.

Satellites fight gravity by going just fast enough to free-fall around the planet indefinitely, like the International Space Station, with many traveling at speeds of more than 17,500 mph.

But if you want to leave this planet, you have to go faster. This speed is called the escape velocity.

It takes a lot of fuel to reach that speed, which is why early rockets, like Apollo's Saturn V, were so big: They had to carry enough fuel to get to the moon. SpaceX's rockets are a little bit smaller than the Saturn V, but they'll have to go even further to take humans around the moon and back.

Musk has got to be relieved he's not launching from Jupiter yet. Because other planets in our solar system have different gravitational strength, they each have different escape velocities.

On Jupiter, you'd have to reach an unthinkable 135,000 mph because the planet is twice as massive as all the other planets put together. That high speed is the only way you could launch a rocket into space and not have it get pulled back.

Here's how fast you'd have to go to leave every planet in the solar system — in one tidy, animated GIF:

Any rocket can achieve a very high speed if it accelerates for a long time. A conventional rocket has a hard time doing this because a huge amount of fuel must be carried into space in order for this to happen. This may make the rocket too heavy to lift off. Conventional rockets are generally designed to meet the speeds necessary for them to go where they need to go, and not go much faster.

Generally, a conventional rocket has to be going about 17,000 mph for it to achieve orbit; otherwise known as LEO -- Low Earth Orbit. This is the minimum speed for a spacegoing rocket. The farther from the Earth, the faster it needs to go. We list some other velocities for comparison:

Flight Plan

With increasing speed it becomes harder and harder to gain another mile per hour. This is because the amount of fuel one has to carry becomes really big, and it becomes difficult and expensive to lift that much fuel into space. Solar escape velocity is nearing the practical limit of how fast one can move with conventional rockets.

NASA's fleet of space shuttles operated in Earth orbit between the years 1981 and 2011. There were five space shuttle orbiters in total, and together they entered Earth's orbit more than 130 times. The massive velocity of the space shuttle meant that it left Earth's atmosphere incredibly quickly.

Space Shuttle Launch

The space shuttle used approximately 1.1 million pounds of rocket propellant per booster, as well as additional fuel in its external tank, to accelerate into space. It took just 8.5 minutes to propel the space shuttle from ground level to the orbital height of at least 185 kilometers (115 miles). As it entered space, the space shuttle reached an orbital velocity of 27,875 kilometers per hour (17,321 miles per hour). The space shuttle is set to be replaced by the Orion multipurpose vehicle in 2014.

References

• NASA: Ask The Mission Team - Question and Answer Session
• NASA: Orion

Writer Bio

Samuel Markings has been writing for scientific publications for more than 10 years, and has published articles in journals such as "Nature." He is an expert in solid-state physics, and during the day is a researcher at a Russell Group U.K. university.

If a rocket is launched from the surface of the Earth, it needs to reach a speed of at least 7.9 kilometers per second (4.9 miles per second) in order to reach space. This speed of 7.9 kilometers per second is known as the orbital velocity, it corresponds to more than 20 times the speed of sound.

A rocket reaching the orbital velocity (1st cosmic velocity) will enter into orbit around the Earth (C), higher speed will lead to an elliptical trajectory (D). When the escape velocity (2nd cosmic velocity) is attained, the rocket will move away (E).

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