Here's why:
* Gravity decreases with distance: Gravity weakens as you move further away from the Earth's center.
* Space shuttle altitude: The Space Shuttle orbited at an altitude of around 200-600 kilometers (124-373 miles). This is a relatively small distance compared to the Earth's radius (6,371 kilometers).
* Slight decrease: At that altitude, the gravitational force is about 90% of what it is on Earth's surface. This means an astronaut in the Space Shuttle would experience about 90% of their weight on Earth.
* Weightlessness: The reason astronauts appear weightless in orbit is due to freefall - they are constantly falling towards Earth but also moving forward at a very high speed, causing them to miss the Earth. It's like being on a constantly descending roller coaster, but with no track to follow.
In conclusion: While gravity is slightly weaker at the altitude of the space shuttle, it is not significantly different from the gravity on Earth's surface. The apparent weightlessness experienced by astronauts is due to their constant freefall around the Earth.
