When unmanned spacecraft accelerate in space, what causes them to slow down?
The speeds of spacecraft are affected most strongly by the gravity of the planets and the Sun. For example, if you want to send a spacecraft from Earth to Jupiter, you first have to get it away from the Earth. If you just shoot it into space, the farther it gets from Earth, the slower it will go. If you don't start it out fast enough, it will eventually slow down to zero velocity, and then fall back toward the Earth, just like if you throw a ball into the air-- you can't throw it high enough to escape the Earth, so it falls back toward you. But if it has escape velocity it will never fall back.
Once the spacecraft is free of the Earth's gravity, you have to give it enough speed to get it out to Jupiter. As it moves away from the Sun, the spacecraft will slow down. If it doesn't have enough velocity, or enough rocket fuel to increase its velocity, it will never get all the way out to Jupiter.
Spacecraft in special situations can also be slowed down (or sped up or turned) by other effects, such as light pressure from the Sun, by drag from an atmosphere if they're close to a planet.
Get More 'Curious?' with Our New PODCAST:
- Podcast? Subscribe? Tell me about the Ask an Astronomer Podcast
- Subscribe to our Podcast | Listen to our current Episode
- Cool! But I can't now. Send me a quick reminder now for later.
- Do unmanned spacecraft like Voyager travel in straight lines?
- How do rockets move in space?
- If Mars is only about 35-60 million miles away at close approach, why does it take 6-8 months to get there?
- How do rockets work?
How to ask a question:
If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.
This page has been accessed 23226 times since September 16, 2002.
Last modified: November 10, 2005 5:24:14 PM
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.
Warning: Your browser is misbehaving! This page might look ugly. (Details)