When President John Nixon tried to control the weather on Earth by exploding thermonuclear devices close to the sun, he inadvertently weakened the sun's gravitational attraction. Realising that the Solar System would have to be evacuated, Nixon employed Dr. Robert Sabinsky and Professor Michael Longman (and his two clones) to come up with a solution. They used genetic engineering to create viruses that would terraform planets, change the Human genome and create hardened life forms that could tame the new planet in the Andromeda galaxy. These included several species of GELF, Simulants, Mechanoids, Symbi-morphs and Holograms.
A small Human crew was selected to take the mission to Andromeda aboard the Mayflower. During the long voyage, Lt. Col. Michael McGruder woke from Deep Sleep and was tricked by Symbi-morphs into releasing the non-humans who had been de-animated by a power failure. They mutinied, killing the other Humans and causing the ship to drift into the Omnizone.
Passing into another dimension, the Mayflower crash landed into a volcanic moon and became immersed in magma. In order to save the ship, the GELFs released one of the viruses, turning the magma into water and creating an ocean under the surface. The crew then abandoned the Mayflower in escape pods, tearing a map that showed the ship's location into four parts. Each part was taken by a different GELF species to prevent any one group from finding the ship.
Many years later, the crew of a Starbug from that dimension managed to piece together the map. The Lister from that dimension realised that the genetic technology aboard the Mayflower would make him immensely powerful and almost immortal, so he killed his shipmates to get the map. He was forced to flee the damaged Starbug without the map because his Kryten had managed to keep it from him.
When the Starbug from the original dimension came across the crashed Starbug, they found the map and were persuaded by Lister to locate the Mayflower, not knowing that he was not their version of Lister. After Kryten had given Lister's doppelganger to the Kinitawowi, Starbug managed to find the Mayflower. They began to strip it of supplies and the many viruses, including the terraforming and Luck viruses. After Rimmer was transformed several times into various creatures, Kryten used the DNA modifier to make himself human, but soon regretted his decision.
When they tried to use the modifier to restore Kryten's mechanoid body, they realised it was missing from the database. One of the three versions of Michael Longman had taken Kryten's genome because his own chromosomes had "given up" after being modified so many times. He and his clones were falling apart and needed new bodies. They attacked the crew, but Kochanski used the Luck virus to defeat them. After Kryten was restored, Starbug left the Mayflower behind to search for their Lister. (Last Human)
The Mayflower was shaped like a corkscrew and had a large ramscoop at the bow to collect space debris for fuel, allowing it to fly through space indefinitely. It was as large as "a three-day music festival" and had a hundred thousand portholes.
The ship was propelled by a negative gravity drive and had enough room aboard for thousands of passengers in Deep Sleep. There were also enough escape pods for everyone aboard to evacuate. The stores aboard the ship were extensive, necessary for terraforming a new homeworld for humanity.
The ship's genetic laboratories were highly advanced, allowing the manipulation of any life form and providing viruses that would assist the terraformers.