#propulsion

Specific impulse (Isp) is the single most important performance metric in rocket propulsion. What it means physically, how it derives from exhaust velocity, why it governs mission architecture, and how every propulsion type compares — from cold gas to ion drives.

Nuclear thermal propulsion achieves twice the fuel efficiency of the best chemical rockets. How NERVA demonstrated the technology in 1968, why it was cancelled, and what DRACO and Centaur Z mean for the next generation of deep-space missions.

How do spacecraft reach the outer planets without carrying impossible amounts of fuel? The physics of Hohmann transfers, gravity assists, and the Oberth effect — why orbital mechanics is the art of doing more with less.