The Ship was the official last hope for the distant human colony of Sarath after its moon threatened to destroy the planet.
For centuries, the people of Sarath had little interest in space travel, developing advanced medical technologies instead as their planet's moon was too distant to inspire a genuine interest in space travel. When an asteroid strike sent the moon into a descending orbit, Professor Tovel Jarrasen, a member of the Functionary class in the city of Arkhaven, proposed the construction of the Ship to evacuate the people of Arkhaven to the nearby planet Mirath. (PROSE: City at World's End)
Extending upwards to over a hundred stories high, the Ship was a vast silver structure officially powered by nuclear engines. It was intended to carry the population of Arkhaven, the tools and supplies they would need to colonise a new world, and some space for extra cargo. Officially, all storage capacity had been calculated before the last refugees from other cities arrived in Arkhaven, and any new attempts to enter the city or those who objected to the current situation were sentenced to the NC2- Non-Citizen, Non-Conformist- camp, where they would be left behind to die once the Ship launched.
The upper body of the Ship was also a lunar lander that would carry out reconnaissance on Mirath and find a suitable landing site, as the main body of the Ship was a simple brute-force lifter and cargo pod that would only be able to make one journey and not take off again. If a suitable landing site for the Ship could not be found, the Lander would thus be used to ferry the "crew" and cargo down in smaller groups, although its limited reaction mass capacity meant that it would need to be remotely controlled to lift off completely unladen after each such trip and be refuelled in orbit.
The Ship's interior included modularised pods and cartons secured for flight, vast tanks of water and oxygen, pumping systems and air-purification equipment, and couches stacked three in a row where all but essential crew would be lightly sedated during the flight to minimise demands on life support. (PROSE: City at World's End)
When the TARDIS landed on Sarath a month before the moon was scheduled to crash into the planet, the crew were separated in a meteor strike. Having established his credentials as an alien with advanced scientific knowledge, the First Doctor agreed to assist Jarrasen and the people of Arkhaven in offering his own insight into the Ship's systems. Although Jarrasen asked the Doctor to focus on helping him with the Lander, arguing that the main Ship was the simpler device that he was reasonably confident would work while also being too large to modify in such a short time, the Doctor's visit to the Ship allowed him to make some mental calculations based on his estimations of its dimensions and mass, structural weight, engine thrust and likely payload. Combined with his earlier suspicions when Mayor Brantus Draad had stated that the ship had been designed before a war with the neighbouring Taklarians killed almost ninety percent of Arkhaven's population, yet there were still concerns about the overall passenger capacity, the Doctor realised that the Ship was a monstrous deception without the power to lift itself even once inch off the ground.
In reality, Jarrasen's lack of funding prior to the destruction of the moon had caused him to make mistakes in his calculations, only realising after construction of the Ship began that he was only able to create an engine with a thrust capacity two or three orders of magnitude less than what was needed to power the Ship. As a result, while construction of the Ship continued to serve as a public symbol to maintain morale, members of the Functionary class created a genuine Lunar Lander to carry five hundred survivors directly to Mirath, with a new launching system constructed to boost it into space. This flight would take six weeks rather than the ten days that the Ship would have done if it was real, but it was the only chance they could find. (PROSE: City at World's End)
When Zero Day was declared after the moon broke in half a month ahead of schedule, the surviving Taklarians attempted to take the Ship themselves after most of the Arkhavians had been "evacuated" into the Ship and sedated before the flight began. However, when Taklarian Prince Keldo attempted to confront Mayor Draad in the Ship's control room, he was only confronted with a video phone, Draad informing Keldo that the Taklarians' presence on board simply made it that little bit easier for Draad to destroy the fake ship and kill the now-sedated Arkhavians along with the Taklarians. Despite the city's controlling A.I. Monitor attempting to stage a coup with specially-built androids to preserve his own existence, he was defeated and his function on the Lander was replaced by Monitor's own android duplicate of Susan. After the Doctor donated a "life pod" from the TARDIS to provide the Lander with extra volume but no additional mass so that it could take on extra survivors, the reunited TARDIS crew programmed the Lander's launch sequence, departing in the TARDIS after the Lander had left for Mirath. (PROSE: City at World's End)