Spacecraft in Orbit

Spacecraft in orbit serve as our entryway into our solar system, galaxy and beyond. They carry instruments ranging from cameras and telescopes to radar and spectrometers – offering access to information in multiple dimensions.

To achieve orbit, a rocket must travel high above most of Earth’s atmosphere in an elliptical path around our planet – this way it counteracts gravity’s pull and keeps its craft circling our planet.


Orbit is the path a spacecraft follows to orbit an object such as Earth or another celestial body. Orbits may be natural – like Earth’s moon – or artificial like that of the International Space Station. Placing satellites in orbit is both costly and challenging; only large countries with advanced space programs can afford such ventures.

Orbits can either be circular or elliptical in shape. To form an orbit, an object’s force of gravity must be perfectly balanced with its forward momentum in order to enter an orbit; otherwise it will either pass by without entering, or it will be pulled downward and crash into something.

Most artificial satellites operate in low-Earth orbit (LEO), approximately 160 kilometers or 100 miles above Earth’s surface. A full orbit in LEO takes 90 minutes, while at higher altitudes a satellite could remain in orbit for centuries before returning into our atmosphere and burning up; although even at these heights they may encounter occasional atmospheric drag.


Altitude refers to the height a spacecraft reaches above Earth. As satellites ascend higher in altitude, they fly through thinner layers of atmosphere with reduced drag – however as they reach more of Earth’s upper atmosphere they increase their chances of collapsing back down towards us and being consumed by its atmosphere and burning up in it.

An orbit’s altitude determines its coverage at any given moment, while its inclination affects how far north and south it travels.

Global Positioning System (GPS) satellites occupy a mid-Earth orbit (MEO). Their signals enable tracking the locations of ships, airplanes and automobiles; however, their signal sensitivity decreases with increasing apoapsis; as such, GPS satellites must boost their orbit’s apogee by using onboard rocket thrusters when at periapsis to increase its altitude.


There are over half-a-million objects orbiting Earth, from paint flecks to full satellites. All are moving rapidly toward our planet but, due to its curvature, will never actually collide.

Low Earth Orbit (LEO) satellites encircle our planet very closely, completing one orbit every 90 minutes. LEO satellites are among the most widely-used for communication and observation satellites – accounting for an estimated 80% of commercial communications satellites as well as all NASA science exploration satellites in LEO orbit. Unfortunately, satellites in close orbits may run into Earth’s atmosphere which causes drag, decaying their orbit further until finally returning towards our planet again.

To increase their distance from Earth, satellites may be placed into polar orbits that pass over different areas with each revolution – for instance ESA’s Mars Express and Venus Express satellites both operate in such orbits that allow them to map all four poles of rotation on both planets.


Finding the optimal speed for an orbital path is of critical importance for any spacecraft’s success. Like throwing a ball out the window of a tall building, initial thrust gives its initial velocity while Earth’s gravitational pull keeps tugging it along its orbital path.

If the satellite deviates too greatly from its set speed, gravity will take over and it will spiral toward Earth; but if its velocity increases drastically enough to escape Earth’s orbit.

Engineers use rocket thrusters onboard spacecraft to maintain its target orbital speed. At both periapsis (closest approach to planet) and apogee (furthest away), engineers can fire rocket thrusters to remove energy from its path at both points – or they may use aerobraking, first used with Magellan radar-mapping spacecraft at Venus before later used by Voyager probes at Saturn for saving rocket propellant. Or they may simply wait for satellites to slow themselves by flying through planets’ thin atmospheres or waiting for satellites to do it themselves!

Scroll to Top