The Soviet Union was the first country in the world to launch the world’s first artificial satellite Sputnik I into space in 1957 and space race is born after that. This satellite was only the size of a beach ball, but it made history.
2,271 satellites have been sent to space according to the Goddard Space Flight Center. 1,324 are Russian satellites while 658 have been launched by the U.S. There are so many satellites roaming over the earth and mostly freely then why don’t collide with each other and simply burn?
A standard collision avoidance procedure has been established by space agencies to avoid any such accident. a Collision On Launch Assessment (COLA) is performed when the satellite is launched. To make sure that the space vehicle trajectory does not take it too close to any other object in space, the launch window is set such that it has COLA blackout period, the intervals during which the spacecraft does not lift.
The purpose of COLA is to avoid the collision after launch. To avoid any debris or spacecraft collision while in orbit, the satellite performs collision avoidance maneuver also called Debris Avoidance Maneuver (DAM). The collision avoidance maneuver is usually performed to raise or lower the orbit of the craft by a few kilometers. Read more about how the Hubble Space Telescope conducts it to avoid space debris hits.
With every precaution is in place satellite collisions in space have occurred not frequently but they do collide. There are about 1,000 pieces of space debris greater than 10 cm, and these collisions are exactly where those came from.
While small space debris hits to satellites are frequent, on February 10th, 2009, the first accidental hypervelocity collision between two satellites in the Earth’s orbit occurred. The two satellites were the Iridium 33 and Kosmos-2251 that collided above the Taymyr Peninsula in Siberia, at an altitude of 789 km and the speed of 42,120 km/h.
The Kosmos-2251 was a Russian satellite owned by Russian Space Forces, that was launched in June 1993. The satellite went out of service just two years later having no propulsion system. It stayed in orbit as space debris as it was not actively controlled anymore. The Iridium-33 was owned by Iridium Communications Inc. and was operational at the time of the collision. Both the satellites were completely destroyed in the accident leaving a massive 1510 kg of debris in orbit. (The Kosmos-2251 weighed 950 kg, Irridium-33 weighed 560 kg).
In 2007, the Chinese government launched a missile into space to destroy a satellite just to show off and to make a point that they can shoot down satellites. This left another mess of debris in the low earth orbit, and piece of that mess even hit a Russian satellite in 2013.