In Rendezvous with Rama, the alien spacecraft is named Rama. It is a vast, perfectly smooth cylindrical starship that enters the Solar System in Arthur C. Clarke’s 1973 science-fiction novel.
Human astronomers first detect the object in 2131 and initially designate it 31/439. They later name it Rama after the Hindu god. A crew aboard the Endeavour intercepts the object and discovers that it is not a natural asteroid but an immense artificial vessel, approximately 50 kilometres long and 20 kilometres in diameter.
Inside Rama, the explorers find a rotating cylindrical world with artificial gravity, a sea, city-like geometric structures, and biological-robotic machines called biots. The ship’s creators, known as the Ramans, never appear, and the vessel’s purpose remains largely mysterious.
Discovery, Hermes, and Endeavour are easy to confuse with the answer. Endeavour is the human exploration ship sent to investigate Rama; Rama is the alien vessel itself. The novel was the first in Clarke’s Rama series and won several major science-fiction awards.