The Engine Core (also referred to as "The Reactor", the "Main Engines" and simply "The Engines") is located in the central-rear part of the city-sized JMC mining spaceship Red Dwarf, and provides the main power and propulsion for the space freighter.
The Engine Core has yet to be seen in the television series, although it has been described in the novels.
A form of fusion reactor, the Engine Core was designed to last indefinitely in the ship's eternal quest around the Galaxy. It uses as fuel traces of hydrogen from the interstellar winds, which are sucked in through the Front Ramscoop. The Waste from the reactor is blasted back out through the ship's rear thrusters, providing propulsion. (Infinity Welcomes Careful Drivers)
Cadmium II was part of the coolant system of the Engine Core, and the Drive Plate kept this radiation safe from the human-occupied regions of the ship. When the grossly inept Arnold Rimmer, Second Technician in charge of Z Shift, was sent to make a major repair on the Drive Plate by Captain Hollister, it resulted in an explosive radiation leak that turned all of the crew into radioactive dust except for Dave Lister, who was in stasis at the time. Despite the radiation leak, the Engine Core was still functional, and Holly presumably fixed the Drive Plate with the help of the skutters. (Pilot episode)
Although the ship had solar panels, Diesel Decks and various battery back-ups for emergency power, Red Dwarf could only last a few weeks without the Engine Core. The gang discovered this three million years later when Holly was forced to off-line herself and the Engine Core after a failed "intelligence compression" experiment. Although the gang had artificial gravity and air for the time being, Kryten noted they would have been dead after a few weeks. This timeline was erased when Dave Lister played "pool with planets" and blocked up the White Hole which had been spewing time into the Universe. ("White Hole", Series IV)
When the Triplicator malfunctioned, the triplication field went outwards instead of in, encasing the entire ship and created two copies of Red Dwarf. However, the immense power involved in doing this caused the Engine Core of the original Red Dwarf to go to critical mass, and exploded the ship. The gang had escaped in a Starbug, and were able to recreate the original Red Dwarf by getting the triplicators from both ships, and merging the "high" and "low" versions of the ship. ("Demons & Angels", Series V)
When the nanobots recreated and updated Red Dwarf, they included a Karaoke Bar, ship-wide bio-organic networking, and also updated the Engine Core to a quark-level matter/anti-matter generator. ("Back in the Red", Series VIII)
- Noises from the Engine Core can be heard when Lister enters Supply Pipe 28 looking for the Cat in the Series I episode "Waiting for God", since Supply Pipe 28 ran close to the Engine Core. This reveals that the normal background hum of Red Dwarf sounds like clapped-out banging closer to the three-million-year-old engines.
- It is unclear what purpose the Diesel Decks served aboard Red Dwarf, although it could have generated the emergency or back-up power.