Have you seen satellites zipping across the sky, taking minutes to travel from horizon to horizon? They appear tranquil but in reality are moving at hundreds of kilometers per second!
Just as different seats in a theater offer different viewpoints of an event, different Earth orbits provide satellites with varied perspectives of our planet. Some satellites may appear to remain stationary over a single location while others zoom all around it quickly covering many regions within a day.
Between low-orbit and geostationary (GEO), satellites can be found in a medium-Earth orbit (MEO). MEO satellites offer the ideal balance for coverage area and data transmission rates while being less susceptible to space debris that flies through other orbits.
Navigation and communication satellites employ MEO for navigation and communication purposes, with Global Positioning System being one of the best-known examples. The US Space Force operates 24 GPS satellites in this orbit along with European Union Galileo and China BeiDou systems to transmit signals that receivers on Earth triangulate to determine their position, velocity and time data; additionally these systems offer sensors which monitor weather phenomena as well as natural events.
LEO satellites are much closer to Earth, making transmission easier. Their speeds and latency rates are therefore faster, with lower latency levels; however, more LEO devices must be launched to cover any given region.
Spacecraft in this orbit usually travel over the polar regions or are placed into Sun-synchronous orbit (SSO), keeping their bodies aligned with the sun so that they can observe a specific spot on earth each day – providing vital weather and traffic monitoring capabilities.
Satellites orbit the Earth quickly – one complete orbit takes just 90 minutes – which allows them to be launched more cost effectively and rapidly, but exposes them to atmospheric drag that degrades their orbital energy over time. Therefore, it’s vital for satellite operators to have plans in place for safe deorbiting or reentry at the end of their operational lives in order to minimize space debris buildup.
Geostationary orbits ensure that satellites always pass over a specific point on Earth’s surface and have zero eccentricity or inclination; their path follows Earth’s rotational direction precisely.
Geostationary satellites are ideal for transmitting communications signals between Earth and its satellites, with one orbital position covering nearly three quarters of the globe in just one line-of-sight path – which explains why telecom companies often launch multiple such satellites simultaneously.
Weather satellites often orbit in geostationary orbit, as this allows them to continuously observe one region of Earth. This is made possible through Lagrange points where Earth and Sun’s gravity combine, permitting satellites to remain fixed relative to Earth – such as those employed by NOAA’s two GOES systems (Geostationary Operational Environmental Satellite).
Highly Elliptical Orbit
Molniya orbits are highly elliptical orbits which follow an oval path around Earth. Moving more quickly at its closest approach – known as perigee – and more slowly when further from home – or its apogee. These types of orbits are common among communications satellites as it keeps them visible for extended periods and only out of reach for brief times during each orbital pass.
An ellipse is defined by its major and minor axes; distance from any point on an orbit to its center equals semimajor axis while from same point to apogee equals eccentricity (e). For HEO orbits, these values are respectively 0.55 for both parameters.