How Do We Measure Spacecraft Speed?

spacecraft speed

Spacecraft require vast amounts of energy to move, far beyond what can be provided from burning rocket fuel like you use in your car.

Parker Solar Probe currently holds the record for heliocentric speed; however, as its mission extends further away from Earth our frameworks for measurement deteriorate and ascertaining their speed becomes increasingly challenging.


Spacecraft are vehicles capable of traveling through outer space using rocket engines to power acceleration to reach orbit and continue their mission. Spacecraft may be either manned or unmanned and may serve important functions like scientific advancement, national security enhancement and critical services like communications or weather forecasting.

The Parker Solar Probe recently set a record speed and distance record when travelling at 70 km/s relative to our star.

However, this spacecraft still cannot escape Earth’s gravitational pull – to reach this speed it would require approximately 15,000 times more energy than is carried in its rocket propellant mix – but is nonetheless the fastest man-made object ever constructed and provides invaluable insight into our universe. As it moves into solar radiation fields with weaker gravitational fields it will eventually encounter Pluto but this feat stands as testament to such a small craft’s accomplishment.


Space travel involves measuring spacecraft velocity based on acceleration. Earth observation satellites often follow orbits with consistent acceleration that allow us to keep tabs on their locations as well as distance from Earth.

NASA’s Parker Solar Probe currently holds the record for speed in space travel, moving towards our sun at 200 kilometers per second – or 0.067% the speed of light! At such an impressively fast rate, NASA hopes that their probe can get close enough to our star and better understand its unique weather system – something which could impact everything from astronaut safety to aurora displays.

In theory, it may be possible to accelerate a spacecraft even faster; however, doing so could expose its crew members to dangerous levels of radiation exposure. Therefore, real-world spacecraft must decelerate gradually as they reach their destinations, according to relativity principles.

Orbital velocities

Orbital velocity refers to the required speed at which a spacecraft must travel in order to remain orbiting around a planet or celestial body, such as Earth or another celestial body. Its orbital path, either elliptical or circular, displays how inertia keeps it on an even path while gravity pulls downward on it – with more massive central bodies necessitating greater orbital velocities at certain altitudes.

Rockets typically launch vertically to quickly reach above Earth’s atmosphere and their desired orbital velocity, before transitioning into horizontal motion to maintain this velocity for their trajectory.

Orbital velocities are closely tied to Earth’s rotational velocity, which explains why space agencies prefer launching rockets from launch points nearer the equator. As Earth rotates faster, its orbital velocity rises at that location – this process is known as Hohmann transfer and represents one of the most efficient methods of moving satellites between orbits.

Relative velocities

Spacecraft that wish to leave Earth’s gravity and travel toward other planets or moons must reach what is known as escape velocity – at least 4.9 miles per second or 11.2 kilometers per second – in order to evade gravity and travel faster.

ExoMars/TGO mission animation from YouTube illustrates how much relative velocities of spacecraft can change as it orbits around and away from the Sun, starting out at around 30 km/s but gradually decreasing with gravity assists from Jupiter and Mars. On launch day, its speed was about 30 km/s but then reduced below 20 km/s after being gravity assisted at these locations.

As New Horizons travels further into space, its relative heliocentric speed should decrease further and eventually surpass that of our Sun’s ever-weakening gravitational pull to enter interstellar space – an impressive accomplishment for an intelligently constructed machine!

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