The low earth orbit is the region that starts from the Earth’s surface at sea level to an altitude of 2,000 km. Interestingly, major region of the low earth orbit lies within the Earth’s atmosphere. Most spacecraft and artificial satellites experience immense gravitational pull created by air molecules in the thermosphere (the last layer of the Earth’s atmosphere). Spacecrafts and satellites have to travel at extraordinary speeds to escape the pull of Earth’s gravitational force. Due to its nearness to earth, low earth orbit gives some of the most spectacular views.
Both military and aeronautical centers use low earth orbit for different purposes. Military rockets are launched in low earth orbit. When a missile is launched, it moves into a suborbital path using its engine. Later, the missile starts moving at cruising speed. In final stage, the earth's gravity brings it back towards it target. Usually, un-manned spacecrafts and satellite in low Earth orbit travels at a mean velocity of 26,000 km per hour. Remote sensing and weather satellites often travel in low earth orbits to observe our planet. These satellites capture very detailed images of Earth's surface. Due to its short round trip time (RTT), Low Earth Orbit satellites are used for Mobile Satellite Services (MSS). Typically, LOE satellites have a life expectancy of 5-7 years. Low Earth Orbit weather satellites also use X-ray sensors, thermal imaging, alpha detectors, high-energy proton detectors and energetic particle sensors.
According to the United States Space Command, the LEO environment is becoming very crowded. There are more than 8,000 objects in low earth orbit. All of these things are not working GEO satellites. There are thousands of pieces of metal from old satellites, broken shuttles, distorted rockets, and frozen sewage. There is every possibility of catastrophic collisions between satellites and other orbital debris. These phenomena are becoming more frequent. Untracked fragments of orbital debris are lethal for operational satellites.
The circular velocity of a GEO satellite in low earth orbit is approximately 17500 miles/hr. If the shuttle reaches twice the circular velocity, it will be manage to escape from earth orbit. The New Horizons spacecraft has left earth orbit at 16 km/s.
The International Space Station is also known as (ISS). It is a habitable artificial satellite located approximately 400km above the Earth. The International Space Station circles around the low earth orbit at a speed of 90 minutes per orbit. ISS is used as a space environment and microgravity research laboratory. Scientists conduct experiments in human biology, astronomy, physics and meteorology. Different spacecraft equipments used during missions to the Moon and Mars are tested at the International Space Station. On 20th November 1998, Russian Federal Space Agency launched the first modular structure of ISS. Remaining components were carried by the Russian Proton and Soyuz shuttles and American Space rockets. This massive space research center was completed in 2010.