If you think it’s a pain to get cell reception when you visit your relatives in another state, just imagine trying to communicate with people who are at least 40 million miles away and are constantly moving relative to you. That’s what we’ll have to deal with if we plan to send humans to Mars, when communications won’t just be important – they’ll be vital.
To find out how to create a communications network that covers Mars and beyond, and how current systems are being upgraded to meet the challenge of ever-increasing amounts of data, we spoke to two experts who work on NASA’s current communications system – one on the Earth side and one on the Mars side.
This article is part of Life On Mars, a 10-part series that explores the cutting-edge science and technology that will allow humans to occupy Mars
Reaching out into the solar system with the Deep Space Network
In order to communicate with current missions like the Perseverance rover on Mars or the Voyager missions that are heading out into interstellar space, NASA has a network of antennae built all around the planet called the Deep Space Network, or DSN.
The DSN has three sites in California, Spain, and Australia, which hand over communications duties between one another each day. That way, there is always a site pointed in the direction that’s needed, regardless of how the Earth rotates or wobbles on its axis. At each site, there are a number of radio antennas up to 70 meters in size that pick up transmissions from space missions and relay the data to wherever it needs to go on Earth.
International cooperation in communications
The DSN is used for NASA missions, but there are other global networks used by different space agencies such as the European Space Agency (ESA). In a remarkably forward-thinking way, all these different networks follow the same international standards for their communications, so space agencies can use each other’s networks if the need arises.
“It’s a fairly small community. There are only a few nations that have the capability to send spacecraft to Mars, as an example,” Les Deutsch, the deputy director for the Interplanetary Network, which runs the Deep Space Network, told Digital Trends. “It’s growing, but it’s still a small number. And it behooves us all, as it’s a small community of very expensive missions, to try to do this together.”
That means that in addition to agencies that NASA works closely with, like ESA, even agencies which it doesn’t have a relationship with, like China’s space agency, still follow the same standards.
“Even China subscribes to a set of international standards that we’ve helped to develop over the years, so that all deep space missions communicate in the same way,” he said. “The spacecraft have similar radio formats and the ground stations have similar kinds of antennas and interfaces. So we can track each others’ spacecrafts through these agreements. They’re all built to be interoperable.”
Talking to Mars
So that’s how we receive transmissions on Earth. But how do you send transmissions from Mars? To send communications over such a great distance, you need a powerful radio. And missions like rovers need to be small and light, so there isn’t room to strap a huge antenna to them.
To circumvent this issue, Mars has a system for relaying communications, called the Mars Relay Network, or MRN. It consists of different orbiters that are currently traveling around the planet and which can be used to pick up transmissions from missions on the surface (like rovers, landers, or, eventually, people) and relay this data back to Earth. You can actually see the current position of all the craft in the MRN using this NASA simulation.
The majority of orbiters around Mars do double duty. In addition their science operations, they also work as relays – that’s the case with NASA’s Mars Atmospheric and Volatile EvolutioN (MAVEN) spacecraft and Mars Reconnaissance Orbiter, and ESA’s Mars Express. “Most of our missions that we’ve sent [to Mars] are at low-altitude orbits, so they’re somewhere between 300 and 400 kilometers above the surface. And those are really great!” MRN manager Roy Gladden told Digital Trends. “Those are great places to be, because it’s nice and close, and you can transmit quite a bit of data between a landing asset and an orbiter in that environment.”
Not every mission can be added to the relay network, though. If an orbiter is at a very high altitude, or if it has a very elliptical orbit where sometimes it is close to the planet and other times it is further away, it might not be suitable to be a part of the MRN. The United Arab Emirates’ (UAE) Hope mission, for example, is at a very high altitude so it can study Mars’s upper atmosphere. But that means it’s too far away from the surface to be useful as a relay.
Future missions to Mars, such as NASA’s Mars Ice Mapper or the Japan Aerospace Exploration Agency’s (JAXA) planned mission, will include communications hardware as well, so the more missions we send there, the more the network can be built out.
The importance of timing
One of the challenges of relaying communications from Mars is the fact the planet is always rotating, and that all of NASA and the ESA’s orbiters are moving around it. That’s not a problem if your rover needs to send communications twice a day, for example – the chances are high that several orbiters will pass overhead at some point. But when you need to track a specific event at an exact time, it gets more tricky.
For example, landing a rover on the planet’s surface is the most difficult part of a mission, so NASA always wants to have eyes on a landing. For the landing of the Perseverance rover, the orbiters in the MRN had their orbits tweaked to ensure they’d be in the right place at the right time to capture the landing. But to save on precious fuel, they could only make small adjustments to their trajectories, so the process of getting everything in the right place began years before the landing occurred.
One way to make this process more efficient is to use dedicated relay satellites to record key events like landings. When the InSight lander landed on Mars in 2018, it was accompanied by two briefcase-sized satellites called MarCOs, for Mars Cube One, which acted as relays. These small satellites followed InSight on a flyby of Mars, monitored and relayed data about the landing, and then headed off into space. “We were able to target them to where we wanted them to be so they could do that recording to capture that critical event telemetry,” Gladden said, “and then after the event was over, they turned over and pointed their antennas back to Earth and transmitted that data.”
The use of the MarCOs was a test of a future capability, as satellites had never been used like this before. But the test was a success. “They did exactly what they were intended to do,” Gladden said. The MarCOs were a one-time-use item, as they didn’t have enough fuel to enter orbit. But such small satellites are relatively cheap and easy to build, and the MarCOs demonstrated that this is a viable way to monitor specific events without having to rearrange the entire Mars network.
Communications for crewed missions
For crewed missions, regular communications are even more important. There will always be a delay of up to 20 minutes in communications between Earth and Mars because of the speed of light. There’s absolutely no way around that. However, we can build out a communications network so that people on Mars would be able to talk to Earth more than a few times a day, with the aim to have as close to constant communications available as possible.
The upcoming Mars Ice Mapper mission “is kind of a step in that direction,” Gladden said. “Our intention is to send a small constellation of spacecraft that will be dedicated relay users with Ice Mapper.” This would be the first time a constellation has been used for Mars communications, and could be the building block of a larger relay network.
Such a project requires a lot of power to communicate over the large distances between planets, but it’s entirely technologically feasible.
A next-generation network around Mars
When it comes to envisioning the future of extraplanetary communications needs, “we’re trying to be forward-thinking,” Gladden said. “We’re trying to consider what we would need in the future. Especially knowing that eventually we want to send people there.”
Creating a futuristic Mars communications network might involve making it more similar to what we have on our planet, by adding more spacecraft to the network with increasingly more power. “On Earth, we solve our communications problem by sending up lots and lots of low-altitude spacecraft that are high-powered systems with big solar arrays, with highly complex radios that can do beam steering,” he said. “At Mars, we want the same thing.”
Technologically, it is possible to solve these problems and to set up a network around Mars comparable to the one we have around Earth.
There are complexities to creating a network that can handle long delays, and the creation of data standards that can be used by all Mars craft, but it’s possible. Such a communications network could theoretically be expanded to do more than just provide communications from Earth to Mars and back. It could be used as a positioning system to help with navigation across Mars or, with some modifications to the hardware, could provide communications across Mars as well.
But such capable spacecraft are large and heavy, which makes them difficult to launch. And they face another problem: Unlike satellites around Earth, which are protected by our planet’s magnetosphere, satellites in orbit around Mars would be bombarded with radiation. That means they need to be shielded, which requires more weight.
Technologically, it is possible to solve these problems and to set up a network around Mars comparable to the one we have around Earth. However, “how to get there is a big challenge,” Gladden said, “because somebody has to pay for it.”
Preparing communications for the future
Setting up a Mars communications network is one half of the puzzle for future communications. The other half is preparing the technology we have here on Earth.
Currently, the DSN is building more antennae so it can keep up with the ever-increasing number of deep space missions being launched. It also uses improvements in software to automate more of the network processes, so a limited number of staff can oversee more missions each.
But there’s another problem of limited bandwidth. Spacecraft now have more complex instruments that record huge reams of data, and transmitting all of this data over a slow connection is limiting – as anyone who’s ever been stuck with slow internet knows.
“From any particular spacecraft in the future, we want to be able to bring back more data,” Deutsch, the DSN deputy director, said. “That’s because as spacecraft progress in time, they’re carrying more and more capable instruments, and want to bring back more and more bits per second. So we have that challenge to keep up with that Moore’s law-like curve.”
The solution to this problem is to transmit at high frequencies. “If you increase the frequency at which you’re communicating, it narrows the beam which is transmitted from the spacecraft and more of it gets to where you want,” he explained. While early missions used 2.5 GHz, spacecraft have recently moved to around 8.5 GHz, and the very latest missions are using 32 GHz.
Higher frequencies can offer an improvement of around a factor of four in terms of bits per second, but even that won’t be enough in the long term. So the next big step in space communications is to use optical communications, also known as laser communications. This brings many of the same advantages of going to a higher frequency, but optical communications can offer an improvement of a factor of 10 over today’s state-of-the-art radio communications.
And the good news is that the DSN won’t need entirely new hardware to transition to optical communications. Current antennae can be upgraded to work with the new technology, and newly built antennae are designed to work on multiple frequency bands and be capable of receiving optical transmissions.
There are some limitations to optical communications, like clouds overhead that can block signals. But even allowing for that, the use of optical communications will increase the network’s overall capability considerably. And a long-term solution to this issue might involve putting receivers in orbit around Earth, where they would be above the clouds.
Where do we go from here?
The problems of communicating with another planet are deep and hard to solve. “Physics is immutable,” Gladden said. “It’s a long way away, so you lose signal strength. That’s a problem that we have to overcome when we think about trying to build a network for people.”
But we’re on the threshold of a new era in space communications. In the next decade, we’ll learn more about transmitting and receiving data from the upcoming Artemis mission to the moon, and the Mars Ice Mapper and its dedicated relay spacecraft.
“It’s going to be clumsy,” Gladden warns. “We’re just trying to figure this out.” He points to international debates about the use of standards, and the changing relationship between government space agencies and private companies. Decisions made now will determine how space exploration will progress over the next decades.
“It’s going to be both terrifying and fascinating to see what happens,” he said. “On one hand, there’s so much uncertainty about what’s going on. But on the other, this is high-tech stuff. We’re learning and doing things for the first time around another planet. That’s never been done before. That’s amazing.”
This article is part of Life On Mars, a 10-part series that explores the cutting-edge science and technology that will allow humans to occupy Mars
