Photo courtesy NASA
What Is a Satellite?
A satellite is basically any object that revolves around a planet in a circular or elliptical path. The moon is Earth's original, natural satellite, and there are many man-made (artificial) satellites, usually closer to Earth.
- The path a satellite follows is an orbit. In the orbit, the farthest point from Earth is the apogee, and the nearest point is the perigee.
- Artificial satellites generally are not mass-produced. Most satellites are custom built to perform their intended functions. Exceptions include the GPS satellites (with over 20 copies in orbit) and the Iridium satellites (with over 60 copies in orbit).
- 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. The actual number varies depending on which agency is counting. Payloads that go into the wrong orbit, satellites with run-down batteries, and leftover rocket boosters all contribute to the count. This online catalog of satellites has almost 26,000 entries!
Although anything that is in orbit around Earth is technically a satellite, the term "satellite" is typically used to describe a useful object placed in orbit purposely to perform some specific mission or task. We commonly hear about weather satellites, communication satellites and scientific satellites.
Whose Satellite Was the First to Orbit Earth?
The Soviet Sputnik satellite was the first to orbit Earth, launched on Oct. 4, 1957.
Because of Soviet government secrecy at the time, no photographs were taken of this famous launch. Sputnik was a 23-inch (58-centimeter), 184-pound (83-kilogram) metal ball. Although it was a remarkable achievement, Sputnik's contents seem meager by today's standards:
- Radio transmitter - changed the tone of its beeps to match temperature changes
- Nitrogen gas - pressurized the interior of the satellite
On the outside of Sputnik, four whip antennas transmitted on short-wave frequencies above and below what is today's Citizens Band (27 MHz). According to the Space Satellite Handbook, by Anthony R. Curtis:
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.
Sputnik is a good example of just how simple a satellite can be. As we will see later, today's satellites are generally far more complicated, but the basic idea is a straightforward one.