What is Reentry Velocity?

Reentry velocity is the speed at which a spacecraft or celestial object enters a planet's atmosphere from space. For Earth, this typically occurs at the "Entry Interface," which is conventionally defined at an altitude of approximately 100 to 120 kilometers (the Karman Line). Understanding this velocity is critical for aerospace engineering, as it determines the amount of kinetic energy that must be dissipated as heat through friction and compression.

How to Use the Reentry Velocity Calculator

This tool uses the principles of conservation of orbital mechanical energy to estimate the change in speed as a craft descends toward the atmosphere. To use the tool, follow these steps:

• Initial Altitude: Enter the starting height of the object in kilometers (e.g., 400km for the ISS).
• Initial Velocity: Provide the speed of the object at that starting altitude in km/s.
• Entry Interface: Define the altitude where you consider atmospheric entry to begin (standard is 120km).
• Planet Radius: While defaulted to Earth (6371 km), you can adjust this for other celestial bodies.

The Physics Behind the Calculation

The calculator utilizes the Vis-viva equation logic. In a vacuum, as an object loses altitude (potential energy), it must gain speed (kinetic energy) to maintain energy conservation. The formula used is based on the gravitational parameter (μ) and the radii from the planet's center. As a spacecraft drops from a higher orbit to the entry interface, the Earth's gravity accelerates it, significantly increasing its velocity before atmospheric drag becomes the dominant force.