Born at the height of the Cold War, Pine Gap was presented to the Australian public in 1966 as a space research facility. But behind the scenes, the station was run by the C.I.A. to collect information from American spy satellites about the Soviet Union’s missile program.
Since then, American spies, engineers, cryptologists and linguists have flocked to Alice Springs, the small town closest to the base, to work at the facility. At least 599 Americans lived there in 2016, according to the latest census. Though their presence in town is low-key, there are some telltale signs: a baseball diamond at a local sports complex, Oreo cookies and Dr Pepper in the supermarket, and beef brisket on sale at a butcher shop.
“Americans, from the time they came here, have never been isolated from the rest of the community,” said Damien Ryan, the mayor of Alice Springs, who could remember a time when Americans in left-hand-drive cars were frequently seen on the town’s roads. “They’ve been part of the community the whole time.”
The base is reached by a dead-end road, marked with a sign warning away visitors. Without clearance, the only way to see Pine Gap is by air, or by climbing the craggy ridges of the MacDonnell Ranges that surround the site.
Photos taken from the air show a sprawling campus punctuated by white geodesic domes that look like giant golf balls. Inside these spheres, called radomes, are antenna systems that send and receive information from satellites in constant orbit above the earth.
The staff at Pine Gap was predominantly American until the 1980s, when the two governments, responding in part to public pressure here, made it about half Australian. Today, more than 800 people from both countries are believed to work at the base. But the United States is firmly in control.
“Pine Gap has changed and developed enormously,” said Richard Tanter, a senior research associate at the Nautilus Institute and honorary Melbourne University professor who has investigated and criticized the base for years.
In documents leaked by Edward Snowden, the American intelligence contractor turned whistle-blower, Pine Gap is described as playing “a significant role in supporting both intelligence activities and military operations.”
What that actually means, Professor Tanter said, is that the station is involved in real-time contributions to the United States’ global military operations in Afghanistan, Iraq and Syria.
Pine Gap, he added, also “contributes data for C.I.A. drone operations in countries in which the United States is not at war — Yemen, Somalia, Pakistan and so forth. It is also critically important in whatever the United States is going to do on the Korean Peninsula.”
Professor Tanter has gleaned information about the secret site from unexpected public records, including the LinkedIn profiles of Pine Gap contractors and satellite photos that reveal new construction at the site.
Professor Tanter, who is president of the Australian board of the International Campaign for the Abolition of Nuclear Weapons, said he wanted the government to “make a very clearheaded assessment” of whether it is in Australia’s best interest to contribute data for drone assassinations and targeting nuclear weapons.
Other experts, however, said that hosting a base like Pine Gap helps maintain the country’s alliance with the United States, and that other partners of the Americans carry considerably larger burdens.
Australians are “not doing a lot of things that our allies are doing,” including permanently hosting American nuclear weapons and soldiers, said Stephan Frühling, a professor at the Strategic and Defense Studies Center of the Australian National University.
Last year, in the early hours of a cold, dark September morning, Ms. Pestorius, Mr. Dowling and three other “peace pilgrims,” as they call themselves, breached Pine Gap’s security perimeter.
As the activists scrambled up a rocky hill to get closer to the base, and with the police moving in, Ms. Pestorius picked up her viola. Another protester strummed his guitar. As they played a lament for those killed in war, Mr. Dowling held up a large, laminated photograph showing a bloodied young woman with her foot missing.
A sixth activist, Paul Christie, 44, carried out his own protest at Pine Gap days later; he was tried separately and convicted last week, charged, like the others, with entering a prohibited area. During the activists’ back-to-back trials this month, a modest band of supporters gathered at the courthouse. Many were members of the country’s antiwar movement, parts of which are religion-infused.
A Quaker knitted flower brooches. A Buddhist brewed coffee from the back of his van. A collection of colorful banners tied to fences read “Close Pine Gap” and “End the U.S. Alliance and Pine Gap Terror Base.”
Mr. Dowling, who said he had been arrested 50 to 100 times, was found guilty once before of trespassing at Pine Gap, in 2005. The conviction was later overturned.
One of his co-defendants this time was his 20-year-old son Franz, the guitar player at the protest last year. The younger Mr. Dowling and two other defendants — Andrew Paine, 31, and Timothy Webb, 23 — live together in a Dorothy Day Catholic Worker House in Brisbane, where they regularly take in homeless people.
All five were found guilty of entering a prohibited area, and Mr. Paine was convicted of an additional charge of possessing a photographic device.
During the trial, the five — who acted as their own attorneys — tried to argue that they had acted in the defense of others, but Justice John Reeves did not allow it.
Pine Gap has “to bear a big responsibility for all the murder and mayhem that has taken place in Iraq and Afghanistan,” said Jim Dowling, who appeared in court barefoot.
Mr. Dowling seemed unperturbed by how few activists had traveled to remote Alice Springs to support him and the others.
“There’s not a huge number engaged in nonviolent resistance in the name of their faith, but numbers don’t matter, do they?” he said. “Just follow your conscience, you know?”
An earlier version of this article misstated the age of Timothy Webb, one of the activists who were convicted on Friday. He is 23, not 26.