The Epstein drive is a revolutionary fusion-based rocket engine from The Expanse that enables rapid interplanetary travel by allowing ships to continuously accelerate at high 'g' forces for extended periods. Invented by Dr. Solomon Epstein, the drive uses magnetic coils to accelerate plasma exhaust from a fusion reaction, allowing spacecraft to reach speeds near the speed of light. This allows for travel between Earth and Mars in just a few days, significantly shortening voyages to the outer solar system.