The Fastest Artificial Satellites Orbiting Earth

When discussing the fastest objects orbiting the Earth, the International Space Station (ISS) often takes the spotlight. As of the last update in August 2023, the ISS maintains an average speed of about 28,000 kilometers per hour (17,500 miles per hour). It travels at an altitude of around 400 kilometers (248 miles) around the Earth's surface. This incredible velocity is achieved while maintaining its orbit in a relatively stable, low Earth orbit (LEO).

However, if one is considering the fastest artificial satellite in terms of its orbital speed, satellites in low Earth orbit (LEO) or those on escape trajectories often lead the pack. For example, the Parker Solar Probe, while primarily focusing on its solar mission, has been designed to achieve astonishing speeds of over 700,000 kilometers per hour (430,000 miles per hour). Despite these incredible speeds, the Parker Solar Probe does not maintain a stable orbit around Earth; rather, it follows a trajectory that takes it closer to the Sun and back, with an elliptical path.

Orbital Speed and Altitude

The speed of a satellite in orbit is influenced by its orbital altitude. As a rule, the closer a satellite is to the Earth's center, the higher its velocity. This is because the satellite is affected by the Earth's gravitational pull more strongly at closer distances. The formula to determine the orbital speed (v) of a satellite at a distance (r) from the Earth's center is given by:

V sqrt(G * M_Earth / r)

Where:

V is the orbital speed. G is the gravitational constant. M_Earth is the mass of the Earth. r is the distance from the center of the Earth to the satellite.

For a satellite at the Earth's surface, where the radius (r) is approximately 6,371 km, the orbital speed is approximately 7.9 km/s. However, this speed is not possible for satellites in a stable orbit due to atmospheric friction. In a low Earth orbit (LEO) at an altitude of about 400 km, the average orbital speed is around 7.5 km/s.

The Moon, with an average orbital speed of about 1 km/s, moves more slowly compared to satellites in LEO. The variation in speed is key to understanding the dynamics of different orbital paths.

Factors Influencing Orbital Speed

There are several factors that influence the orbital speed of a satellite:

Orbital Altitude: The higher the altitude, the lower the orbital speed. In LEO, the satellite needs to travel faster to overcome the gravitational force. Eccentricity of Orbit: Satellites with more eccentric orbits (where perigee and apogee distances vary significantly) experience higher speeds at the closest point to the Earth (perigee). Direction of Travel: Whether the satellite travels eastward (along the Earth's rotation) or westward (against the Earth's rotation) affects its orbital efficiency.

For the most up-to-date information on satellite speeds and orbits, it is advisable to consult recent updates from space agencies and satellite tracking websites. These sources provide the latest data on various satellites, including those in LEO and those on deeper space missions like the Parker Solar Probe.