Follow this link to go to the text only version of
NASA - National Aeronautics and Space Administration
+ Visit
+ Home
Are we there yet?
Why do astronauts eat tortillas instead of bread?
How would your body change in space?
How can we travel faster in space?
What will replace the Space Shuttle?
Why do robots travel places before people?
Why return to the Moon before going to Mars?
Why do we want to study and travel to Mars?
Where would a space explorer find water and oxygen?
What would you find on the Moon’s surface?
What would you hear in a weather report from Mars?
How will your imagination help you become an explorer?
NASA - 21st Century Explorer Banner

Subject Matter Expert: Joseph Trevathan, Dan Woodard, and Victoria Friedensen

Since early times, people have looked into space and wondered about its mysteries. The vastness of space has opened our minds, but its size has limited our search. We want to explore distant worlds, but how can we travel faster so we can go farther into space?

Jet speed certainly isn’t the answer. Imagine traveling by jet to the moon from Earth, about 386,000 km (240,000 miles). A jet traveling at 1,600 km/h (1,000 mph) would take about 240 hours or about 40 days to reach the moon.

Scientists and engineers clearly knew from the start that the only way to get into space is to use rockets and rocket propulsion. The vehicles and propulsion systems developed for the Apollo program were designed to reach the moon. Using a chemical propulsion system, it took the Apollo astronauts about 2.5 days to get to the moon, traveling at speeds faster than 39,000 km/h (more than 24,000 mph).

The space shuttle uses a chemical propulsion system based upon both liquid and solid propellants. It combines the features of a rocket, aircraft, and glider and is designed to carry astronauts, satellites, and other cargo into Earths’ orbit. Traveling at approximately 29,000 km/h (18,000 mph) the shuttle orbits Earth every 90 minutes.

By using current technology and a spacecraft powered by chemical rocket engines, a trip to Mars could take between six to nine months. Because of the alignment of Mars and Earth, our best chance to launch occurs every 26 months.

We need to find other ways to travel to Mars and beyond, and we are currently considering alternative propulsion systems.

Nuclear thermal propulsion allows a spacecraft to travel faster by providing a more efficient, and light weight system. We would not use nuclear propulsion systems until the spacecraft was far from Earth. Spacecraft would still be launched from Earth with chemical rocket engines or be built and launched in space. A nuclear thermal propulsion system could potentially be over 100 times more powerful than chemical systems of comparable weight. A system like this could easily cut down the time needed to travel to Mars and other places in our solar system.

NASA is studying a plasma-based propulsion system called project VASIMR (Variable-Specific-Impulse Magnetoplasma Rocket). Franklin R. Chang-Diaz, the first Hispanic astronaut, is studying this system. VASIMR works by using a large electric power source (such as nuclear power) to then utilize hydrogen as a rocket propellant. Hydrogen is plentiful in the solar system, possibly allowing a VASIMR-powered spacecraft to be launched with only enough propellant to reach its destination. When it arrives, it could pick up more hydrogen to use as propellant for the return trip. According to NASA, a VASIMR flight to Mars could take a little over three months, compared to the six to nine months required by a conventional chemical rocket. Shorter flight times lessen an astronaut’s time in reduced gravity and decreases the time an astronaut is exposure to space radiation.

There is much that we want to see and explore in our Solar System and beyond. New propulsion systems will help us get there faster.

+ QuickTime Video High
+ With Captions
+ Download Video
+ QuickTime Video Low
+ With Captions
+ Download Video
Song Title
+ 21st Century Theme Song
+ Educator Section
+ Student Section
+ Glossary
+ Books and Web Sites
+ Quiz
The 21st Century Explorer Education package is undergoing beta-testing. Please use the following link to submit any questions or comments.
+ Feedback
National Science Education Standards (NSES)

The following National Education Standards are addressed in this educational package.

Science (NSTA/NRC)
Mathematics (NCTM)

For an alignment see the Educator Section.