How to Keep a Spacecraft in Orbit

As throwing something into the air causes it to follow a curving path, so too do satellites require an equal balance of momentum from their rocket and gravity in order to remain in orbit. Only when this equilibrium has been found can spacecraft remain stationary within their orbital path.

Some orbits, like those occupied by the Hubble Space Telescope and Global Positioning System satellites, are circular; others take an elliptical path with each revolution covering one or more polar regions – as is done with weather satellites or military surveillance satellites.


Orbits are the curved paths taken by objects in space (stars, planets, moons, satellites, asteroids and spacecraft) around another object due to gravitational force. When closer to its parent body it reaches its perihelion; when farther from it – its apogee. Closed orbits tend to be elliptical.

When solar activity is at its highest levels, its magnetic field generates rapid changes to upper atmosphere temperature and density which cause short-term temperature swings which increase drag on satellites in LEO, necessitating periodic maneuvers to counteract this increased atmospheric drag in order to keep their original orbital path unchanged.

ESA science missions often utilize Lagrange points – specific locations in space where the gravitational fields of Earth and Sun combine to form stable orbits which do not revolve directly around Earth – for their scientific missions. Examples of such points are SOHO, LISA Pathfinder, Herschel at Sun-Earth L1 points; Planck Ariel Euclid Gaia all orbit Earth-Sun L2 points.


Velocity refers to the speed at which an object moves along a path (tangential velocity, as opposed to centripetal velocity which moves in perpendicular directions). Furthermore, velocity increases proportionately with radius doubling: for instance doubling an object’s radius will double its speed by 2x!

Spacecraft must reach speeds sufficient to overcome gravity’s downward pull in order to stay on their orbital paths, hence why satellites require such high energy launches for launch into an orbit with high orbital velocity.

Once satellites reach space, their speed doesn’t need to remain as constant; nothing is pushing against them; but as they accelerate further towards Earth, their proximity with its atmosphere increases and drag causes it to start pulling them back towards its surface; hence why most orbital satellites use an elliptical path rather than circular orbits.


As satellite mass increases, so will its orbit. A more massive satellite will experience greater gravitational force when orbiting Earth or other celestial bodies.

However, it’s essential to recognize the distinction between weight and mass. A satellite will weigh less the farther it is from Earth due to gravity exerted upon it depending on where it lands on its path.

Physical scientists typically employ a balance that takes gravity into account to calculate an object’s weight. If you want your students to gain a deeper understanding of this concept, have them compare the accelerations of dropping two items from equal height – pencil vs wadded paper will fall faster due to air resistance!


Spacecraft traveling to distant planets and entering into orbit about them (such as the International Space Station ) require large propelling capabilities in order to decelerate them for correct orbital insertion. They must also adapt to solar occultations events, which obstruct power from its solar panels, extreme thermal variations, as well as Earth occultations events that block off uplink/downlink communications between earth and space.

Spaceships accelerate by throwing mass out the back — literally the exhaust from their rocket engines — while their passengers experience changes in acceleration despite moving at a constant velocity.

As spacecraft rise, their speed decreases due to gravity’s weakening effects, hence why satellites in elliptical orbits move faster nearer planet and slower when farther from it. But still need to slow enough before returning home; aerobraking and thrusting techniques help achieve this task.

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