Explained

Reporting, analysis, and reference material from across this subject.

NASA's NSTAR ion thruster doing a test fire in a vacuum chamber at the Jet Propulsion Laboratory

What is Specific Impulse (ISP)?

Specific impulse (Isp) measures how efficiently a rocket engine uses propellant. Learn how it works, compare the RS-25 and F-1 engines, and explore the tradeoffs behind chemical, ion, and nuclear propulsion.

What is Delta-V?

What is Delta-V?

Delta-V is the hidden limit behind every space mission. It’s the budget that decides how far a spacecraft can go, and what it can afford to do.

ISS long-exposure image showing Earth’s horizon and colorful star trails created by orbital motion above the atmosphere.

What Are Orbital Mechanics? A Beginners Guide

Orbital mechanics is the foundation of spaceflight. It explains how satellites stay in orbit and how spacecraft travel between worlds. This guide breaks down the core principles in a clear, practical way.