What is a satellite?

1. What is a satellite?

2. Satellites • A satellite is any object that travels around another object in space • Examples • Natural: • Planets and moons • Man-made: (custom built) • Camera • Telescopes • GPS systems • Approximately 23,000 items of space junk -- objects large enough to track with radar that were inadvertently placed in orbit or have outlived their usefulness -- are floating above Earth.

3. What is their purpose • communication capabilities with Earth • a power source • a control system to accomplish its mission • Research • Military intelligence • Weather analysis

4. How do they work • Communicate with one or more ground stations. • Messages sent to the satellite from a ground station are "uplinked” • Many satellites are battery-powered, taking advantage of the sun. • Solar panels are prominent features on many satellites. • Other satellites have fuel cells that convert chemical energy to electrical energy, while a few rely on nuclear energy. • Energy is also required to provide climate control onboard for delicate instruments

5. What they transmit • Photograph a range of wave lengths. • Environmental satellites transmit data as numbers to a computer on Earth which translates this digital data into images. • Bright colors are often added to enhance the contrast to make details stand out or to allow us to see what was recorded in the infrared wavelength, beyond our visual range.

6. Examples • The Soviet Sputnik satellite was the first to orbit Earth, launched on October 4, 1957. • It contained: • Thermometer • Battery • Radio transmitter • Nitrogen gas pressurized the interior

7. Where is Sputnik today? • After 92 days, gravity took over and Sputnik burned in Earth's atmosphere. • Thirty days after the Sputnik launch, the dog Laika orbited in a half-ton Sputnik satellite with an air supply for the dog. • It burned in the atmosphere in April 1958.

8. Other examples • Skylab which was launched into orbit in 1973 • America's first experimental space station. • Issues during the launch caused temperature differences

9. What keeps them in orbit • Two factors: • velocity, or the speed at which it would travel in a straight line • it must travel a horizontal distance of 8000 meters before falling a vertical distance of 5 meters. • Since a horizontally-launched projectile falls a vertical distance of 5 meters in its first second of motion, a orbiting projectile must be launched with a horizontal speed of 8000 m/s. • When launched at this speed, the projectile will fall towards the Earth with a trajectory which matches the curvature of the Earth. • The projectile will fall around the Earth, always accelerating towards it under the influence of gravity, yet never colliding into it since the Earth is constantly curving at the same rate.

10. What keeps them in orbit • the gravitational pull between the Earth and the satellite. • Satellites never fall into the Earth this because Earth is round and curves travel in a circular path • Centripetal force: Center seeking • Newton’s Third Law helps explain why!