The Hardest Part of Space Travel is Staying in Orbit

spacecraft in orbit

SpaceX owns over one-third of all satellites currently orbiting. Elon Musk’s International Space Station and weather forecasting satellites share low Earth orbit (LEO).

Spacecraft that need to stay in orbit require significant horizontal velocity; how do we achieve that goal?

Orbital Period

The orbital period measures the time required for an object to complete one complete orbit around another object, such as planets around stars; moons or celestial bodies around planets (binary stars); two or more spacecraft, rovers or probes orbiting around a single planet; or spacecraft in orbit around that planet.

Manmade satellites such as the International Space Station orbit in a sun-synchronous manner, maintaining their position relative to the Sun at all times and permitting scientists and those using satellite data to view a fixed portion of Earth at an identical time every day. This enables them to observe specific parts of our planet at precise moments each day.

Spacecraft travel at various speeds at different points of their orbit, which is measured using sector velocity. As they move faster, their proximity to their periapsis and apoapsis grows, which necessitates occasional rocket fuel boosting to maintain desired orbital positions.


Staying in space can be the hardest part of space travel, not getting there. Once a spacecraft enters orbit, its momentum allows it to remain there for years as gravity pulls downward on it.

Orbiting spacecraft remain stable due to moving so quickly that their path matches the curvature of Earth, leading to over 3,000 satellites to orbit Earth 16 times daily – which includes International Space Station!

Spacecraft can maintain their orbit by staying near points known as Lagrange points (L-points), which are distant from both Earth and Sun but close enough for observation or science missions to operate from there. Many ESA observational and science missions operate near Sun-Earth L1 and L2 points which enable us to study outer planets closely while Voyager probes have even farther-flung orbits beyond heliopause into interstellar space.


As spacecraft move through orbit they gain speed while running into debris slows them down – this can cause them to eventually fall back towards Earth if their speed falls too slowly and hit too many obstructions; escape velocity is necessary in this scenario to break free of Earth’s gravitational pull and fly into outer space – this term refers to this concept.

Spacecraft require considerable energy to reach their speeds. They also carry around mass that increases as speeds do; according to Special Relativity theory, as an object approaches light speed its mass gradually grows until it can no longer go any faster.

Rockets must be extremely powerful to change orbits with propulsive maneuvering; when returning from orbit, spacecraft need a way of decelerating without burning up, such as aerobraking (lowering its perigee into Earth’s atmosphere).


Scientists understood how to get things into space long before humans could actually launch anything there, but keeping them there proved more challenging. Orbits serve as “roadways in space,” and once a space vehicle has found an orbit it will remain there until something changes its trajectory.

Understanding acceleration physics is crucial, which describes the rate at which your spacecraft’s velocity changes over time. Acceleration is measured as a vector quantity with components in its radial direction (e), perpendicular to that radius vector (e2) and vertical direction (e3).

Think of gravity as pushing down on an otherwise weightless object rather than pulling it up; astronauts aboard the International Space Station appear weightless due to being in free fall, while sky divers take note: air resistance eventually overshadows gravity and pulls them back toward Earth.

Scroll to Top