Youtube channel ‘Let’s Do the Science’ examines the science behind the Epstein Drive as portrayed on The Expanse.

According to The Expanse Wiki, the Epstein Drive is a modified fusion drive invented by Solomon Epstein one hundred and fifty years before the start of Leviathan Wakes. It enabled humanity to travel from Earth and the inner planets, and colonize the Asteroid Belt and outer planets. The drive utilizes magnetic coil exhaust acceleration to increase drive efficiency, which enables spaceships to sustain thrust throughout the entire voyage.