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How Do Space Rockets Work Without Air?

space-rocket
Without air to push against, how can a space rocket propel itself forward? (Image credit: <a href="http://www.shutterstock.com/gallery-805819p1.html">PRILL</a> / <a href="http://www.shutterstock.com/?cr=00&pl=edit-00">Shutterstock.com</a>)

In space, rockets zoom around with no air to push against. What's going on?

Rockets and engines in space behave according to Isaac Newton's third law of motion: Every action produces an equal and opposite reaction.

When a rocket shoots fuel out one end, this propels the rocket forward — no air is required.

NASA says this principle is easy to observe on Earth. If you stand on a skateboard and throw a bowling ball forward, that force will push you and the skateboard back. However, because your weight on the skateboard is heavier than that of the bowling ball, you won't move as far.

That's the challenge engineers face when designing space engines. Yes, a small amount of thrust does push the spacecraft forward, but it often takes a great deal of fuel to get going anywhere quickly. More fuel means more weight, which adds to the cost of a mission.

To save on money when shooting for far-away planets such as Jupiter, some spacecraft whip around a planet (say, Venus) and use its gravity to get a speed boost. This shortens the time it takes to get to other destinations.

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Elizabeth Howell
Elizabeth Howell is a regular contributor to Live Science and Space.com, along with several other science publications. She is one of a handful of Canadian reporters who specializes in space reporting. Elizabeth has a Bachelor of Journalism, Science Concentration at Carleton University (Canada) and an M.Sc. Space Studies (distance) at the University of North Dakota. Elizabeth became a full-time freelancer after earning her M.Sc. in 2012. She reported on three space shuttle launches in person and once spent two weeks in an isolated Utah facility pretending to be a Martian.