ALICE SPRINGS, Australia — Margaret Pestorius arrived at court last week in her wedding dress, a bright orange-and-cream creation painted with doves, peace signs and suns with faces.

“It’s the colors of Easter, so I always think of it as being a resurrection dress,” said Ms. Pestorius, a 53-year-old antiwar activist and devout Catholic, who on Friday was convicted of trespassing at a top-secret military base operated by the United States and hidden in the Australian outback.

From the base, known as the Joint Defense Facility Pine Gap, the United States controls satellites that gather information used to pinpoint airstrikes around the world and target nuclear weapons, among other military and intelligence tasks, according to experts and leaked National Security Agency documents.

As a result, the facility, dotted with satellite dishes and isolated in the desert, has become a magnet for Australian antiwar protesters. Over the past two weeks, Ms. Pestorius and five other Christian demonstrators were convicted in two separate trials of breaching the site’s security perimeter last year. They could face seven years in prison.