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26. DSN - Radio Science | NASA's The Invisible Network Podcast

Season 1Episode 26Jun 30, 2022

In this fourth episode in the fifth season of NASA's "The Invisible Network" podcast, we discuss the unique type of radio science empowered by Deep Space Network antennas.

The Invisible Network Podcast Graphic

Artist's concept of the Juno spacecraft orbiting Jupiter overlaid with elements from The Invisible Network podcast promotional graphics.

Audio collage begins.


We have an amazing telecom department with experts in radio science.


We had a lot of science we had in mind when we got there. And our picture of course has changed when we got data and saw Jupiter different in a thousand ways from what was expected.


We’re really at the forefront of planetary exploration by observing one asteroid at a time. And quite often we’re the first people in the world to see what these small worlds look like, and it’s tremendously exciting.


We turn the combination of the spacecraft and the DSN into a solar system-scale laboratory, if you will. And in order to do these kinds of experiments, it’s really every aspect of the DSN needs to be understood or, in some sense, controlled.

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While the bread and butter of NASA’s Deep Space Network is communicating with and tracking distant spacecraft, there are other services and capabilities they can offer missions. DSN mission interface manager Kathleen Harmon:


In addition to our… regular services, which tend to be TTC, which stands for telemetry, tracking, command ­– those are what most missions use to talk back and forth to Earth –…the DSN also provides other services like radio science and Juno [uses] that quite extensively…

We have an amazing telecom department with experts in radio science.


In this episode we’ll dive into the scientific inquiry that the Deep Space Network empowers through radio science. We’ll also learn about the network’s role in characterizing nearby celestial objects like comets and asteroids.

I’m Danny Baird. This is “The Invisible Network.”

A collage of historical audio


We choose to go to the Moon in this decade…


That’s one small step for man…

COMMENTATOR(Voyager Launch)

We have ignition, and we have lift off!


Hello from the children of planet earth…

COMMENTATOR(Cassini Launch)

Three… two… one… and liftoff, of the Cassini spacecraft…

COMMENTATOR(Perseverance Landing)

Touchdown confirmed, Perseverance safely on the surface of Mars…

Theme music fades.


My name is Joseph Lazio. Everybody knows me as Joe Lazio. And [my] formal title is Interplanetary Network Directorate scientist. And the Interplanetary Network Directorate at the Jet Propulsion Laboratory/California Institute of Technology is the organization that manages the Deep Space Network for NASA.


Running a communications network is largely in the realm of engineers, so Joe’s role as a network scientist is particularly interesting.


It’s largely about trying to get more science off the Deep Space Network… which has two angles:

One is: I’m always looking for ways to, for instance, get more data off spacecraft and to scientists. How can we effectively increase the data rate? Or increase the amount of data… the number of megabytes or number of gigabytes actually delivered to scientists?

And then the other way is, how can the large antennas of the Deep Space Network be used for science beyond just receiving data from spacecraft?

But there are two aspects… They’re both fun, and there’s a certain complementarity to them, too.


A core question for Joe is, “What is radio science?”


It’s an interesting term. It’s sometimes a bit plastic because people will use it for slightly different meanings. For instance, some people call radio astronomy, radio science.

In the context that several of us use radio science, it’s the technique of using the DSN antennas to track a spacecraft precisely. And the objective of doing that is:…Either you can tell very subtle differences or deviations – very subtle changes – in how the spacecraft is moving, that you can then use to infer some property of, say, the planet that it’s orbiting. Or you can measure the changes as the signal passes from the spacecraft to the antenna and through anything in between it, and then learn something about what is between you and the spacecraft.


As a discipline, radio science in the manner that Joe describes has been around for quite some time. He harkens back to 1964 and one of the earliest interplanetary missions, Mariner 4.


Mariner 4 was a flyby of Mars. And what they noticed was as the telecommunications signal – so the signal that they were using to receive data from Mariner 4 – as Mariner 4 passed behind Mars, the signal passed through the atmosphere of Mars.

Now from a communications perspective, that could be worrying, right? Your signal is passing through the atmosphere, the atmosphere might distort it, or somehow interfere.

To a scientist, you can turn that around and ask the question, “Can I understand how the Martian atmosphere is affecting the spacecraft signal?” If I can understand the effects of the Martian atmosphere, then I’ve learned something about the Martian atmosphere.

…That technique of tracking the spacecraft signal, and then getting science out of it has been around since the early 60s. It’s been an integral part of many, many, many missions – primarily planetary science ones. But it’s also done things such as help study aspects of the Sun, and even probe Einstein’s theory of general relativity…

Both Voyager 1 and Voyager 2, made their flybys of the four outer planets… As the Voyager went behind one of the giant planets, the signal was transmitted through the planet’s atmosphere… these remain some of the defining ways or defining measurements of the atmospheres of Uranus and Neptune. And that was back in the 80s.

New Horizons: same idea. How the signal passed through the atmosphere of Pluto has been used to study the atmosphere of Pluto.

The grand finale of Cassini, when it dipped between the planet and the rings… by tracking the orbit of the spacecraft very precisely – which in effect means measuring the frequency of the signal very precisely – some investigators… could estimate what the mass of the rings of Saturn is.

That was actually interesting, because their mass suggests that the rings have to be a fairly young feature of Saturn. Saturn has not always had those rings, or they’ve come and gone over time.


There are a couple qualities that a radio antenna needs to be considered a good radio science telescope.


We turn the combination of the spacecraft and the DSN into a solar system-scale laboratory, if you will. And in order to do these kinds of experiments, it’s really every aspect of the DSN needs to be understood or, in some sense, controlled. So, it’s large antennas. They’re equipped with receivers that are operating only a few degrees above absolute zero.


Beyond the sensitivity of the antenna, an accurate timekeeping device is critical.


All of the DSN complexes have… hydrogen masers. And hydrogren masers: you can think about them as a very precise clock – as an exceptionally precise clock. So, these are the kinds of clocks that over the course of 30 million years, they’ll lose about only a second.

And we use that because the precision of the clock affects how well you can measure the frequency with which you’re receiving the signal. And in turn,…how much you can infer about, say, what the signal is passed through, or how much change in the spacecraft path or the spacecraft orbit has happened…


The Juno mission is a prime example of how radio science contributes to deep space science and exploration. Juno reached Jupiter, our solar system’s largest planet, in 2016 and has been studying the gas giant ever since.

Steve Levin, who has worked on the mission since before launch, can describe how radio science observations and measurements from Juno instruments have led to exciting new discoveries.


My name is Steve Levin, and I’m the project scientist for Juno.

When I came to JPL in 1990, I thought I would stick around for a year or two and look for a university position that involved teaching as well, because I like that. And then JPL was just too much fun to leave. So, I’ve been there for 30 years, and we have the best toys to play with…

Long-term, the project that’s been the most fun to work on has been Juno, because it’s been consistently interesting and exciting, and a great team of people to work with…

Juno launched August 5, 2011. It took us five years to get to Jupiter. Arrived at Jupiter, depending on which time zone you’re in, on Fourth of July, 2016. And it’s been orbiting Jupiter ever since…


And what has Juno been up to in the last six years?


Well, we had a few main goals. I’d say probably the most important was to try to understand the origin of Jupiter in order to understand the origin of the solar system. So how did our solar system form? How do planets form?

Jupiter is the largest in the planet in the solar system by far and it formed first, so understanding Jupiter is a key factor in understanding how the solar system formed. To do that, that requires: trying to understand about the interior of Jupiter – ­the interior structure and composition; trying to understand the deep atmosphere of Jupiter, in particular how much water there is in Jupiter is a key piece to understanding the formation.

Then, on top of that sort of origin of Jupiter story, we also are looking at the atmospheric dynamics because it’s this giant atmosphere with complicated weather patterns and things to try to understand. We’re looking at the magnetosphere and the aurora of Jupiter, where Jupiter has these enormous northern and southern lights – the strongest in the solar system – and complicated physics and magnetospheric dynamics to try to understand…We’re using gravity science to learn about the shape and the structure of Jupiter’s interior.

We had a lot of science we had in mind when we got there. And our picture of course has changed when we got data and saw Jupiter different in a thousand ways from what was expected.


Assuring that Juno had all the tools it needed to accomplish its science objectives took plenty of forethought and some clever engineering.


Obviously, everything on this spacecraft relies on the Deep Space Network for communication to the Earth. But anytime you put a radio out in space and communicate with the Earth, you’ve also – by the very nature of the radio – put a sensitive instrument in space that can do things like measure the speed of the spacecraft.

So, on Juno – unlike some spacecraft – that was not an afterthought of, “What can we do with the radio science, since we have to put a radio on board anyway?” it was an important major experiment that was on our spacecraft, because we want to measure the gravity field of Jupiter…

We went to Jupiter with a suite of instruments:

A microwave radiometer to see beneath the clouds because most of what you see from a distance at Jupiter is the tops of the clouds.

A gravity science experiment – so, using the radio on our spacecraft to very accurately measure the speed of the spacecraft, which tells us about the gravity – which tells us about the interior because gravity comes from the whole planet.

A magnetometer to measure the magnetic field, which also comes from deep inside the planet, from an ocean of liquid metallic hydrogen, deep inside Jupiter. That generates the bulk of the magnetic field…

And, then aside from those big three – the microwave instrument, gravity science, and the magnetometer – we have a whole suite of fields and particles instruments.


There are plenty of other instruments as well: the Jovian Infrared Auroral Mapper, or JIRAM, JunoCam, the Ultraviolet Imager/Spectrograph, and the Stellar Reference Unit.

However, the gravity science experiment is most linked with DSN radio science. It requires a specially-designed system that met both science and communication requirements.


So, our radio to communicate with the Earth is designed to be especially good at also measuring the Doppler signature…


The Doppler signature is a measurement of the Doppler effect, the apparent change in frequency of a wave as it moves toward or away from an observer. You can hear the effect in passing sirens or horns when stationary at the side of a road.


So, we can measure the radio signal at two different frequencies. And that helps us eliminate some of the foreground errors that are caused by the atmosphere of the Earth and the plasma in between the Earth and Jupiter…

What we do then… is very accurately measure the frequency of the signal that we’re getting from our spacecraft compared to the signal that we’re transmitting to the spacecraft… And the change in frequency is caused by the speed of the spacecraft along your line of sight. So, that lets us measure very accurately the speed of the spacecraft, which means we can deduce very accurately the gravitational field of Jupiter as we orbit it. And that tells us a lot about the interior of the planet.


Exactly how did observations of the spacecraft orbiting Jupiter tell us more about the planet’s structure?


If you think about this giant planet Jupiter – 300 times the mass of the Earth – rotating every 10 hours – more than twice as fast as the Earth does – and it’s fluid, right? It’s made out of mostly hydrogen and helium, which are gases here on the Earth and… at the intense temperature and pressure on Jupiter they’re liquid. So, as the planet rotates, it’s going to bulge out near the equator, and flatten at the poles because of the rotation.

And if you think about what happened with the interior structure of the planet, if there were a dense core down in the center, it would bulge out and flatten in a different way than the less dense material exterior to it…

Then, if you look at the planet from the outside, from what we see at Earth, we see these belts and zones. They’re jet streams moving in opposite directions at hundreds of miles an hour. So, if those jet streams are dense and deep, they will have a different signature than if they’re less dense or shallow.


Measuring the change in frequency of signals returned by Juno as it orbits Jupiter can provide evidence of the gas giant’s internal structure. This method of radio science has led to some really interesting discoveries:


What we found was that – unlike the expectation, which was a dense core, near the center of Jupiter, somewhere between say three and 20 times the mass of the Earth – What we found is something that looks fuzzy. It looks like maybe there’s a denser core, but it stretches out to perhaps as much as half the radius of Jupiter.


Using these radio science measurements of Jupiter alongside those taken by other instruments also provides scientists like Steve a more complete picture of the planet.


Juno made the discovery that we can actually see variation in Jupiter’s magnetic field. So, Jupiter’s magnetic field turned out to be much more complex and asymmetric than expected. And it includes what we call the Great Blue spot, which is a place near the equator where the magnetic field is sort of intense… And the northern hemisphere of Jupiter looks much more complicated than the southern hemisphere, so we have this whole complicated picture.

And, superimposed on that picture – if you compare with measurements from decades ago –…we have enough information now to see that the magnetic field has actually changed a little bit. And it looks like it’s being affected by the flow of the atmosphere… The magnetic field lines are drifting in connection with the flow of Jupiter’s atmosphere.

So that whole picture of the magnetic field, and the belts and zones, and the deep interior – our ability to measure that with the gravity science experiment and compare with what we see with the magnetometer – is giving us a more complete picture of Jupiter. And there’s a synergy in doing this set of measurements together.


Radio science isn’t limited to work at distant planets. In fact, NASA can use Deep Space Network antennas to better understand the asteroids and comets that we detect in close proximity to Earth.


My name is Lance Benner, I’m Principal Scientist in the… small bodies group in the science division, formerly asteroids, comets and satellites. We specialize in radar observations of near-Earth asteroids: asteroids that closely approach the Earth. We also, from time to time, observe comets that get relatively close to Earth, and occasionally main belt asteroids…

And we are now doing all of these radar observations using the 70-meter… antenna out of the Goldstone Deep Space Communications Complex. Previously, we also use the Arecibo Observatory in Puerto Rico, but unfortunately, it is no longer available.

Radar is a very powerful tool… because we can make the most precise measurements available short of going there with the spacecraft, certainly more precise than any other ground-based technique… We measure their velocities and their distances, and we can shrink the uncertainties in our knowledge of their orbital parameters and thus compute their motion, decades – in some cases, even centuries ­– farther into the future than we could have otherwise…

From a practical perspective ­– and the perspective that the public often finds most interesting ­–­ it’s simply protecting the planet from being hit by asteroids, and to a lesser extent, comets. It’s a very rare event that… one of these objects large enough to do some damage actually hits us, but it certainly behooves us to… find all these objects and to track them so that we can tell well in advance whether there’s any risk.

You know, in 2013, there was a small object – roughly 20 meters in diameter ­that exploded in the atmosphere above the Russian city of Chelyabinsk and it actually injured more than 1000 people. And that sort of thing, we think happens every few 100 years for something that size. So, it’s a very low frequency type of event, but high consequence when it happens.

But in the more general picture, we’re also very interested in these objects because they can tell us a great deal about how the inner solar system formed and also about its geologic history. Some of these objects are the targets of spacecraft missions. For example, the asteroid Bennu that was the target for NASA’s OSIRIS-REx mission. We were the first people to observe that with radar: at Goldstone in September of 1999. I was the person who led those observations. And we observed it with radar again in 2005. And those observations were instrumental – fundamental ­­– for NASA selecting that mission to go forward and actually happen.

We’ve observed a number of other – you know – targets for spacecraft missions, such as the asteroid Itokawa that was visited by Japan’s original Hayabusa mission. The asteroid Eros, that was the target of NASA’s near-Earth asteroid rendezvous mission. The asteroid Didymos, which is the target of NASA’s DART mission that just launched… and will impact an asteroid ­– well, a small moon of an asteroid – and the moon is called Dimorphos in late September.


Radio detection of asteroids is not a new innovation, but our ability to make these sorts of observations has greatly increased over the past half a century.


So, the first near-Earth asteroid observed with radar was an asteroid called Icarus, and that was in 1968. And, when I started doing asteroid radar work with Dr. Steven Austro in the fall of 1995, the number of near-Earth asteroids observed with radar was about 35.

In August, we observed the 1,000th, near-Earth asteroid with radar. Now, most of these objects, (about two-thirds of them) were observed with the Arecibo facility because it was –when it was operational – it was about 20 times more sensitive than Goldstone is. But we’ve also observed, well over 350. I think it’s around 370 Earth-approaching asteroids with Goldstone alone, and that number is increasing.

And so, in August, there was this small object that we observed, that had just been discovered a few days earlier. We had some time scheduled for a different asteroid, and we decided to try this new one. And it was number 1000, among the near-Earth asteroids observed with radar…

We’re observing around 30 to 40 a year with the Goldstone facility… If Goldstone weren’t used primarily for spacecraft communications, and if there were… unlimited resources, we could actually be observing… probably closer to 200. But… that’s not the primary purpose of the Goldstone facility.


Radar observations of asteroids and comets aids in a number of disciplines at NASA, including planetary science and planetary defense.


The work we do is intimately connected with a number of NASA missions. And we’re also… very interested in trying to understand the early history of the solar system and how things are continuing to evolve by studying one asteroid at a time.

The Invisible Network theme.


Radio science may seem like a discipline for doctoral research or senior scientists, but that isn’t the case. Stay tuned for next week’s episode, where we’ll meet students and teachers doing real radio science on Deep Space Network antennas.


It is not as daunting and as complicated as it seems… A lot of people see the scientific community – especially at NASA ­–…as, like, really scary. And there’s no way I’m ever going to infiltrate that. But… people notice if you’re really passionate about something. And, if you love it, that’s more than enough.


Thank you for listening. Do you want to connect with us? The Invisible Network team is collecting questions about NASA’s Deep Space Network from listeners like you! We’re putting together a panel of NASA experts from across the Space Communications and Navigation community to answer your questions.

If you would like to participate, navigate over to NASA SCaN on Twitter or Facebook and ask your question using the hashtag AskSCaN. That’s @ NASA SCaN, N-A-S-A-S-C-A-N, on social media, with the hashtag AskSCaN, A-S-K-S-C-A-N.

This Deep Space Network-focused season of “The Invisible Network” debuted in summer of 2022. Developed by NASA’s Jet Propulsion Laboratory in Southern California, the Deep Space Network is managed by JPL with funding and strategic oversight from the Space Communications and Navigation, or SCaN, program at NASA Headquarters in Washington, D.C.

This podcast is produced by SCaN at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with episodes written and recorded by me, Danny Baird. Editorial support is provided by Katherine Schauer and JPL’s Laurance Fauconnet. Our public affairs officer is Lora Bleacher.

Special thanks to Fall 2021 interns Julia Adde and Nate Thomas, Barbara Adde, SCaN Policy and Strategic Communications director, and all those who have lent their time, talent, and expertise to making “The Invisible Network” a reality. Be sure to rate, review, and follow the show wherever you get your podcasts.

For transcripts of episodes, visit To learn more about the vital role that space communications plays in NASA’s mission, visit For more NASA podcast offerings, visit There, you can check out “On a Mission,” the official podcast of NASA’s Jet Propulsion Laboratory.