Dr. Moses said the team fired the laser only at night and did maintenance and equipment upgrades during the day. “This is a 24/7 facility,” he said.

The previous night, he said, the laser had been fired in an effort to improve coordination and timing. The 192 rays have to strike the target as close to simultaneously as possible.

The individual beams, he said, have to hit “within a few trillionths of a second” of one another if the fuel is to burn, and be pointed at the target with a precision “within half the diameter of your hair.”

The control room, modeled on NASA’s mission control in Houston, was buzzing with activity, even though some consoles sat empty. Phones rang. Walkie-talkies crackled. The countdown to firing the lasers, Dr. Moses said, took three and half hours, with the process “pretty much in the hands of computers.”

The operations plan for NIF, he added, is to conduct 700 to 1,000 laser firings per year, with about 200 of the experiments focused on ignition. There is no danger of a runaway blast, he said. Fusion works by heat and pressure, not chain reactions. Moreover, the fuel is minuscule and the laser flash extraordinarily short. During a year of operations, Dr. Moses said, “the facility is on for only three-thousandths of a second,” yet will generate a growing cascade of data and insights.

Next on the tour, after more sticky pads, was the holy of holies, the room surrounding the target chamber. It looked like an engine room out of a science-fiction starship. The beam lines  now welters of silvery metal filled with giant crystals that shifted the concentrated light to higher frequencies  converged on the chamber’s blue wall. Its surface was dotted with silvery portholes where complex sensors could be placed to evaluate the tiny blasts.

“When it’s running,” Dr. Moses said, “there’s a lot of stuff at the chamber’s center.”

Despite the giant banner outside and its confident prediction, it is an open question whether NIF’s sensors will ever detect the rays of a tiny star, independent scientists say.