At 3am on a Monday morning as most of Australia slept, a small CSIRO team was wide awake and hard at work at Canberra's deep space tracking station.
On October 14, NASA's largest and most expensive spacecraft, the Europa Clipper, launched from Cape Canaveral, Florida on its mission to Jupiter's fourth-largest moon.
The early local hour and agency's 'Follow the Sun' operations model meant Goldstone, the Canberra Deep Space Communication Complex's (CDSCC) sister site in California, was monitoring the Deep Space Network (DSN).
But the mission milestone — or Level One Critical Point — meant extra hands and eyes were necessary, so the CDSCC was tasked with making "first contact" with the spacecraft after it separated from its launch rocket.
CDSCC's education and public outreach manager Glen Nagle said the station had to make sure it could stay in contact with the spacecraft.
"The spacecraft never sleeps so neither do we," Mr Nagle explained.
"We had to make sure we could contact [with it and] if we failed … at the expected time, it could just mean a small glitch in the system somewhere, so we'd do all the troubleshooting … to establish that communication."
The CDSCC is one of three NASA tracking stations roughly 120 degrees apart in longitude and collectively called the Deep Space Network (DSN), with the other two stations in Goldstone, California, and near the Spanish capital of Madrid.
The four giant antennas and 90 staff just outside Australia's capital city provide continuous communication coverage to about 40 spacecraft, representing 27 nations.
In the almost 25 years he's worked at the CDSCC, Mr Nagle has tracked plenty of spacecraft signals, or "heartbeats".
"We don't listen for a spacecraft; we watch for the radio signal," he said.
"It's a particular little wave on the screen taking off at just the right moment, at the very specific frequency that we're expecting."
So it was a relief for the Canberra team, when the "acquisition of signal" came through from the solar-powered robotic Europa Clipper, as it started its five-and-a-half year, USD$5 billion mission.
CDSCC has been involved in hundreds of space missions since 1965, when it received the first close-up pictures of the surface of Mars from Mariner 4.
"Without us, nobody goes anywhere in the solar system," Mr Nagle said.
"It's a great testament to the professionalism and reliability of the Canberra team, that many missions actually plan for their key events to take place when it's Canberra providing the coverage."
'Good strong signal' with Europa Clipper
Europa Clipper's launch was a "a happy, textbook flight", Mr Nagle said.
"Immediately, as soon as the spacecraft came up over our resolve, we had contact," he said.
Mr Nagle said "a good, strong signal" was also relayed back to the NASA Jet Propulsion Labs in California.
Before the rest of the CSIRO team picked up tracking and communicating with Europa Clipper when their shift officially started later that morning, the "volume" of Canberra's antennas had to be turned down.
"When the spacecraft switches on, its transmitter is designed to transmit from a huge distance, hundreds of millions of kilometres from the Earth, when it's only a few hundred kilometres above the Earth," Mr Nagle explained.
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"Shortly after launch, it's like it's shouting down at us [so] we have to get the antennas out [and] tune them down," Mr Nagle said.
"It's kind of like muffling them, so the signal from the spacecraft doesn't overwhelm our receivers."
The team has been busy ever since, ahead of Europa Clipper's next mission milestone in February.
"We'll make a close flyby of the planet Mars, getting a gravity assist from that planet to slingshot it back into the inner solar system to flyby Earth later in 2025," Mr Nagle said.
"In both of those encounters, the spacecraft will use its instruments to take photos, measure magnetic and gravitational fields, and radar studies as well. All the sorts of things that it will do once it finally gets out to the Jupiter system in April of 2030," Mr Nagle said.
"Over the next few years … we're going to be monitoring the spacecraft and ensuring that it's on course, that all the data is flowing back, that this instrumentation is working correctly and sending up any commands that the mission team needs to do."
Understandably, Mr Nagle expects to spend this festive season a little differently.
"If something breaks at 3 o'clock in the morning on Christmas Day, believe me — we'll be right there fixing it." he said.
Contacting Voyager 1 and Voyager 2
While Europa Clipper's signals were straightforward to track, NASA's deputy associate administrator for space communications and navigation Kevin Coggins said not every spacecraft is as easy to stay in contact with.
"We do get silence, or at least we think it's silent," Mr Coggins said.
"Then, our engineers must get to work to try to find the signal in the noise."
Voyager 2 has required plenty of engineers' attention lately, and Canberra is the only site of the three able to help it "phone home".
Voyagers 1 and 2 launched in August 1977, with the second probe responsible for the first close-up images of Europa more than 40 years ago during the pair's so-called grand tour.
Now on an extended mission to interstellar space, both spacecraft are outside the heliosphere, "the protective bubble of particles and magnetic fields generated by the Sun".
"It's an area … that we never imagined that we'd have a spacecraft flying," Mr Coggins said.
With a diminishing power supply, and "radiation and all kinds of interesting things that it's measuring and going through", Mr Coggins said Voyager 2 had experienced lots of problems over the past year.
"Sometimes [the antennas] don't point just right, or sometimes the data comes in garbled," he said.
And, because signals take 22.5 hours to transmit each way, at a rate of just 160 bits per second, Voyager's "heartbeats" are whisper quiet.
"It's a 45-hour round trip just to get a, 'Hello? Are you there?'. 'Yes, I'm here!'," Mr Coggins said.
Even so, some of Mr Nagle's most memorable moments with the CDSCC involve the twin spacecraft.
Like the "recovery of communications from the depths of interstellar space" with Voyager 1 after an onboard computer glitch in November 2023; and with Voyager 2 three months earlier, "when its antenna was almost fatefully turned away from Earth".
