RAMA RETURNS

The great radar pulse generator Excalibur, powered by nuclear explo-sions, had been out of service for almost half a century. It had been designed and developed in a frantic effort during the months following the transit of Rama through the solar system. When it was first declared operational in 2132, Excalibur’s announced purpose was to give Earth ample warning of any future alien visitors: one as gigantic as Rama could be detected at inter-stellar distances—years, it was hoped, before it could have any effect on human affairs. That original commitment to build Excalibur had been made even before Rama had passed perihelion. As the first extraterrestrial visitor rounded the sun and headed out toward the stars, armies of scientists studied the data from the only mission that had been able to rendezvous with the intruder. Rama, they announced, was an intelligent robot with absolutely no interest in our solar system or its inhabitants. The official report offered no explana-tions for the many mysteries encountered by the investigators; however, the experts did convince themselves that they understood one basic principle of Raman engineering. Since most of the major systems and subsystems en-countered inside Rama by the human explorers had two functional backups, it appeared that the aliens engineered everything in threes. Therefore, since the entire giant vehicle was assumed to be a machine, it was considered highly likely that two more Rama spacecraft would be following the first visitor. But no new spaceships entered the solar neighborhood from the empty reaches of interstellar space. As the years passed the people on Earth con-fronted more pressing problems. Concern about the Ramans, or whoever it was that had created that drab cylinder fifty kilometers long, abated as the lone alien incursion passed into history. The visit of Rama continued to intrigue many scholars, but most members of the human species were forced to pay attention to other issues. By the early 2140s the world was in the grip of a severe economic crisis. There was no money left to maintain Excalibur. Its few scientific discoveries could not justify the enormous expense of assur-ing the safety of its operation. The great nuclear pulse generator was aban-doned.