The much-anticipated arrival of NASA’s Juno spacecraft at Jupiter is almost here. Juno will answer many questions about Jupiter, but at the cost of a mission profile full of challenges. One of those challenges is communicating with Juno as it goes about its business in the extreme radiation environment around Jupiter. Communications with Juno rely on a network of radio dishes in strategic locations around the world, receivers cooled to almost absolute zero, and a team of dedicated people.
The task of communicating with Juno falls to NASA’s Deep Space Network (DSN), a system of three facilities around the world whose job it is to communicate with all of the spacecraft that venture outside Earth’s vicinity. That network is in the hands of Harris Corporation, experts in all sorts of communications technologies, who are contracted to run these crucial facilities.
The person responsible is Sonny Giroux, DSN Program Manager at Harris. In an interview with Universe Today, Sonny explained how the DSN works, and describes some of the challenges the Juno mission poses.
“The network itself consists of three primary communication facilities; one in Goldstone, California, out in the middle of the Mojave Desert. The other facility is in Madrid Spain, and the third is in Canberra Australia. These three facilities are separated by about 120 degrees, which means that any spacecraft that’s out there is capable of communicating with Earth at any point in time,” said Giroux.
“Each facility has several antennae, the largest of which is 70 m in diameter, about the size of a football field. These antennae can be aimed at any angle. Then there are smaller antennae at 34 m in size, and we have a number of those at each complex.”
According to Giroux, the dishes can work independently, or be arrayed together, depending on requirements. At the DSN website, you can see which antenna is communicating with which of NASA’s missions at any time.
Juno is a complex mission with a dynamic orbit, and Jupiter itself is an extreme radiation environment. Juno will have to weave its way through Jupiter’s radiation belts in its polar orbit. According to Giroux, this creates additional communication problems for the DSN.
“As Juno goes into its orbital insertion phase, the spacecraft will have to turn away from Earth. Our signal strength will drop dramatically,” Giroux said. “In order to capture the data that Juno is going to send, we’re going to array all of our antennae at Goldstone and Canberra together.”
This means that a total of 9 antennae will be arrayed in two groups to communicate with Juno. The 4 dishes at the Canberra, Australia site will be arrayed together, and the 5 dishes at the Goldstone, California site will be arrayed together.
This combined strength is crucial to the success of Juno during JOI (Juno Orbital Insertion.) Said Giroux, “We need to bring Juno’s signal strength up to the maximum amount that we can. We need to know what phases Juno is in as it executes its sequence.”
“We’ve never arrayed all of our antennae together like this. This is a first for Juno.”
This combined receiving power is a first for the DSN, and another first for the Juno mission. “We’ve never arrayed all of our antennae together like this,” said Giroux. “This is a first for Juno. We’ve done a couple together before for a spacecraft like Voyager, which is pretty far out there, but never all of them like this. In order to maximize our success with Juno, we’re arraying everything. It will be the first time in our history that we’ve had to array together all of our assets.”
Arraying multiple dishes together provides another benefit too, as Giroux told us. “The DSN is able to have two centres view the spacecraft at the same time. If one complex goes down for whatever reason, we would have the other one still available to communicate with the spacecraft.”
The most visible part of the DSN are the antennae themselves. But the electronics at the heart of the system are just as important. And they’re unique in the world, too.
“We cool them
down to almost absolute zero to remove all of the noise out.”
“We have very specialized receivers that are built for the DSN. We cool them down to almost absolute zero to remove all of the noise out. That allows us to really focus on the signal that we’re looking for. These are unique to DSN,” said Giroux.
Juno itself has four different transmitters on-board. Some are able to transmit a lot of data, and some can transmit less. These will be active at different times, and form part of the challenge of communicating with Juno. Giroux told us, “Juno will be cycling through all four as it performs its insertion and comes back out again on the other side of the planet.”
“We just get the ones and zeroes…”
The DSN is a communications powerhouse, the most powerful tool ever devised for communicating in space. But it doesn’t handle the science. “DSN for the most part will receive whatever the spacecraft is sending to us. We just get the ones and zeroes and relay that data over to the mission. It’s the mission that breaks that down and turns it into science data.”
Juno will be about 450 million miles away at Jupiter, which is about a 96 minute round trip for any signal. That great distance means that Juno’s signal strength is extremely weak. But it won’t be the weakest signal that the DSN contends with. A testament to the strength of the DSN is the fact that it’s still receiving transmissions from the Voyager probes, which are transmitting at miniscule power levels. According to Giroux, “Voyager is at a billionth of a billionth of a watt in terms of its signal strength.”
Juno is different than other missions like New Horizons and Voyager 1 and 2. Once Juno is done, it will plunge into Jupiter and be destroyed. So all of its data has to be captured quickly and efficiently. According to Giroux, that intensifies the DSN’s workload for the Juno mission.
“Juno is different. We’ve got to make sure to capture that data regularly.”
“Juno has a very defined mission length, with start and stop dates. It will de-orbit into Jupiter when it’s finished its science phase. That’s different than other missions like New Horizons where it has long periods where its able to download all of the data it’s captured. Juno is different. We’ve got to make sure to capture that data regularly. After JOI we’ll be in constant communication with Juno to make sure that’s happening.”
The next most important event in Juno’s mission is its orbital insertion around Jupiter, and Giroux and the team are waiting for that just like the rest of us are. “Juno’s big burn as it slows itself enough to be captured by Jupiter is a huge milestone that we’ll be watching for,” said Giroux.
The first signal that the DSN receives will be a simple three second beep. “Confirmation of the insertion will occur at about 9:40 p.m.,” said Giroux. That signal will have been sent about 45 minutes before that, but the enormous distance between Earth and Jupiter means a long delay in receiving it. But once we receive it, it will tell us that Juno has finished firing its engine for orbital insertion. Real science data, including images of Jupiter, will come later.
“We want to see a successful mission as much as anybody else.”
All of the data from the DSN flows through the nerve center at NASA’s Jet Propulsion Laboratory. When the signal arrives indicating that Juno has fired its engines successfully, Giroux and his team will be focussed on that facility, where news of Juno’s insertion will first be received. And they’ll be as excited as the rest of us to hear that signal.
“We want to see a successful mission as much as anybody else. Communicating with spacecraft is our business. We’ll be watching the same channels and websites that everybody else will be watching with bated breath,” said Giroux.
“Its great to be a part of the network. It’s pretty special.”