What it's like out there

If you want to design an experiment that the shuttle could take into space, you must consider the conditions your experiment would encounter:

Microgravity: Everything on earth is held to the planet by gravity. That's what keeps water in a cup and cars on the ground. There is almost no gravity on the space shuttle once it is in orbit. People call this "weightlessness," but scientists prefer to call it "microgravity." Many experiments study how this lack of gravity affects objects.

G-forces: Scientists measure the force of gravity in terms of "G's." Earth's gravity has a force of 1 G. During liftoff and landing, gravitational forces on the shuttle increase greatly - sometimes by three or four times. Even if an experiment does not explore G-forces, it must be designed to survive a force of up to 11 Gs.

Heat and cold: The air around the earth helps keep temperatures more even. In airless space, though, it is very hot when the sun is shining (140 degrees F.) and very cold (-4 degrees F.) when it is not.

Radiation: Some types of radiation - sunlight, X-rays, cosmic rays, gamma rays - are filtered out by the earth's atmosphere. Since the shuttle orbits above the atmosphere, more radiation hits the shuttle. Many experiments study the effects of cosmic radiation.

Extreme vibration: The shuttle shakes a lot when it takes off and lands. Dr. Ruthan Lewis of the Goddard Space Flight Center in Greenbelt, Md., tells students to take their experiments to a local paint store and test them in a paint shaker. If the project can survive the shaker, it will survive the shaking during its trip into space.