Photograph of Atlantis lift-off.
Click on image for full size
The average person can jump about 2 feet off the ground, and few of us can throw a baseball higher than even fifty feet in the air. It seems as if there is some force that "pulls" everything on the Earth down to the ground.
This "pull" is due to gravity, a force of attraction which exists between any two objects, but depends on their size. Since our planet is so massive, we experience a strong pull toward its center.
Space travel is only possible is if we can escape Earth's gravity. However, for a spacecraft to do so it must be launched with a speed of 39,600 km/hr (nearly 25,000 mph). .
It was only by the middle of the twentieth century that mankind finally understood enough about rockets to be able to reach such high speeds. After leaving Earth, spacecraft use small on-board thrusters to navigate through space and explore the universe.
Shop Windows to the Universe Science Store!
Learn about Earth and space science, and have fun while doing it! The games
section of our online store
includes a climate change card game
and the Traveling Nitrogen game
You might also be interested in:
A new museum exhibit shows that some of the robots, vehicles and devices from the Star Wars films are close to the types of things scientists have developed to use in space. The exhibition--at the Science...more
The Hubble Space Telescope (HST) is really neat! It was first launched in 1990, but scientists started building it in the 1970's! We have found all kinds of objects like stars, nebulae and galaxies. The...more
Apollo 11 was the first mission that landed a person on the moon. On July 16, 1969, the U. S. rocket Saturn 5 was launched carrying the lunar landing module Eagle. The Eagle was released and it reached...more
Apollo 12 was launched on Nov. 14, 1969 and arrived at the Moon three days later. Astronauts Charles Conrad and Alan Bean descended to its surface, while Richard Gordon remained in lunar orbit aboard the...more
Apollo 15 marked the start of a new series of missions from the Apollo space program, each capable of exploring more lunar terrain than ever before. Launched on July 26, 1971, Apollo 15 reached the Moon...more
NASA chose Deep Impact to be part of a special series called the Discovery Program. This program is for cheap, scientific projects. In May 2001, NASA said it was ok to start with mission development for...more
Galileo was a spacecraft that orbited Jupiter for eight years. It made many discoveries about Jupiter and its moons. Galileo was launched in 1989, and reached Jupiter in 1995. The spacecraft had two parts....more