Chapter 1: The Whisper from the Void

Look skyward. Beyond our solar system, where temperatures plummet and darkness prevails, an electrical charge emits a faint radio signal. This barely perceptible blip, generating roughly 22 watts—similar to a standard refrigerator bulb—originates from Voyager I. Its 12-foot antenna reaches out to us from the depths of space.

After a remarkable journey of over 20 hours, this fragile wave finally reaches Earth, but by then, its strength has diminished significantly to about 0.1 billion-billionths of a watt. Although the signal's traverse through our solar system has concluded, its mission to convey our most distant origins is only just beginning. The challenge now lies not just in its journey but in deciphering the subtleties embedded within the message.

Interpreting such a minuscule fragment of information requires a cadre of skilled experts. For the Voyager missions, this expertise is housed in three colossal, 21-story dishes—each spanning 230 feet and weighing close to 3,000 tons—strategically placed around the globe. These dishes are purpose-built for deep-space communication, ever-vigilant for the probes' daily updates.

One of these giant antennas, known as DSS-14, towers over a secluded stretch of California's Mojave Desert, about 60 miles from the nearest road. It rests in a small valley surrounded by ancient volcanic hills. Accessing this site involves passing through multiple security checkpoints at Fort Irwin military base. Visitors here share the landscape with unexploded munitions, various rattlesnake species, camel spiders, scorpions, and roving packs of feral donkeys, which may attempt to nibble on unsuspecting guests out of sheer curiosity.

As you approach DSS-14, it emerges from behind a bend, standing tall like a guardian, casting a long, warped silhouette across the sunlit desert. Above, turkey vultures glide effortlessly on thermal currents, and aside from the wind's whispers and the crunch of sand underfoot, there exists another sound—one that lies far beyond human perception, mingling with the vast hum of the universe.

The complex situated at Fort Irwin, which NASA's Jet Propulsion Laboratory has dubbed Goldstone after a long-gone mining settlement, includes about a dozen smaller antennas. The first of these became operational in 1958 and even features a decommissioned Apollo antenna. Similar installations exist in the Australian outback near Canberra and in Robledo de Chavela, close to Madrid, established in 1965. Since the Mercury IV mission in 1964, these three arrays have maintained our connection with every craft launched beyond low Earth orbit.

Strategically placed, these antennas are separated by longitudes (120 degrees apart for complete 360-degree coverage) and unified by their remoteness. This isolation is crucial, as it prevents powerful space signals from interfering with terrestrial communications like air traffic control chatter.

Together, these facilities form the Deep Space Network, managed from JPL headquarters in Pasadena, California. The system is constantly attuned to signals from and commands to approximately 40 probes, satellites, spacecraft, and rovers—ranging from those as near as the Moon to distant travelers like Juno, orbiting Jupiter, and New Horizons, which famously buzzed Pluto in 2015. Among these, the Voyagers I and II, launched in 1977 to investigate Jupiter and Saturn, remain the longest-operating missions overseen by NASA or JPL.

The data transmitted from these two probes provides invaluable insights into the sparsely populated realm of interstellar space, including observations of low-energy charged particles, magnetic fields, and the plasma that constitutes the majority of our universe. This information is conveyed as strings of ones and zeros at a mere 160 bits per second—equivalent to one-fifteenth of the slowest fax machine connection. Analyzing this data has enabled physicists to map the contours of the heliosphere, the protective magnetic bubble enveloping our solar system, and assess the speed of solar winds.

As NASA explores faster, more efficient light-based communication systems, it might be tempting to believe that radio will soon become obsolete. However, both methods will coexist. The Voyager probes, pushing the boundaries of technology, remind us of the unique insights gleaned from radio waves throughout their journey. The noise they collect as they traverse planets, moons, and asteroids offers a glimpse into our cosmic neighborhood; in some cases, this static proves just as valuable as the actual messages.

The first video, "Decoding and Signal Processing - A Sign in Space Workshop with Wael Farah and Daniel Estévez," elaborates on how we extract meaningful data from cosmic signals, providing a deeper understanding of the processes involved.

Chapter 2: The Science of Noise in Space

Embedded within the Jet Propulsion Lab's facility is a plaque stating "The Center of the Universe." Every signal dispatched from our solar system's objects passes through this hub. The so-called Dark Room, illuminated by the glow of numerous monitors, operates around the clock, having been staffed since the inception of the Deep Space Network. Rarely does anything halt operations here—not rain, not most earthquakes, and certainly not even a fire. During a past blaze, engineers managed to operate terminals remotely through smoke, ensuring no call from the cosmos was missed.

Currently, two engineers sit at a pair of monitors, intently observing a stream of numbers and colored lines. This downlink originates from the Juno probe, which has been orbiting Jupiter since 2016. Mike Levesque, who oversees the network's operations, explains the process: "Those are the data systems operators," he gestures toward the engineers. "Their responsibility is to extract spacecraft information"—including temperature, fuel levels, and operational status—and relay it to mission support. For instance, of the 160 bits sent by Voyager I, only about 10 are relevant to its internal status.

The remaining data packets primarily go to scientists rather than engineers. Scientists focus on what the instruments reveal about the environment surrounding the probe, as opposed to the probe itself. The engineers running the screens utilize programs to clean up the data stream, though they occasionally save the noise, recognizing its significance. When a signal travels through a medium, facing atmospheric or gravitational influences, the alterations in the wave can unveil truths about space. "When a craft passes through something intriguing, the noise becomes the data we seek," Levesque notes. In such instances, "the signal's noise can turn into valuable scientific information."

This noise is then analyzed by Kamal Oudrhiri, who leads JPL's Planetary Radar & Radio Sciences Group. To grasp his field better, he offers an analogy involving a school bus full of children. The driver’s goal is to safely transport all the kids. However, if you were more interested in the bus itself rather than the children, you could glean insights into the journey by examining the vehicle's markings and imperfections.

In Oudrhiri's analogy, the children represent the data carried by the signal, while the bus symbolizes the signal itself. Engineers and mission control staff prioritize the data, akin to focusing on the kids, but radio scientists delve deeper into the signal's nuances, discovering the journey it has undertaken.

Many foundational radio-science experiments were accidental. In 1971, when the Mariner 9 probe traversed Mars, its signal passed through the planet's atmosphere, altering the wave. While telecom experts viewed it as interference, others recognized that analyzing this distortion could reveal atmospheric density, pressure, and temperature on Mars—marking the inception of radio science.

Since that time, careful examination of space-borne noise has enriched our comprehension of the solar system. For example, disturbances in the Cassini probe's transmissions suggested that Saturn's vibrant rings formed much later than the planet itself—between 10 million and 100 million years ago, compared to the planet's age of 4.5 billion years. NASA's GRAIL lunar mission in 2012 employed two spacecraft to exchange radio waves, investigating the Moon's interior by analyzing how gravity fields affected the transmissions, ultimately revealing that much of the lunar crust is less dense than previously believed.

Oudrhiri appreciates radio science for its straightforwardness. A signal consists of a wave characterized by amplitude (the highs and lows), phase (the arrangement of peaks and troughs), and frequency (the number of oscillations in a given timeframe). Distortions in these attributes are easy to detect. Recognizing how the ripples should generally appear allows for the identification of changes—similar to noticing a smoke signal dissipating before you can decipher its pattern, indicating an unseen breeze.

A vital aspect of the Voyager probes' cosmic hum includes an acoustic phenomenon called the Doppler effect, which subtly stretches the signal's wavelength as the spacecraft hurtles through space at 38,000 miles per hour—much like how the sound of a siren changes as an ambulance speeds past. This transformation informs ground control about how far Voyager has traveled between check-ins and the 20 hours it takes for signals to reach Earth, aiding in tracking the probe's path.

With the primary missions of each probe complete, the new objective is to maximize their longevity. "How can we extend their operational life as long as possible?" asks Suzanne Dodd, project manager for Voyager and head of JPL's Interplanetary Network Directorate.

Delivering commands to these interstellar explorers—while managing dwindling opportunities for deep-space insight—primarily revolves around power management. All redundant systems onboard have been disabled, leaving the probes generating minimal heat in the frigid depths of interstellar space, which raises concerns about hydrazine propellant freezing in the fuel lines. Mission control carefully cycles through systems to identify which ones may be worth keeping operational to maintain warmth in the lines. It's a temporary solution for some of the oldest technology still functioning.

Voyager mission control operates from a nondescript building situated a couple of miles from JPL, lacking visible signage and adorned with high windows—easily overlooked behind a wall of foliage. Next door sits a McDonald's, where a team of 12 works tirelessly to maintain the health of the most distant objects ever created by humanity.

Here, the focus remains on receiving signals, rather than noise. Spacecraft systems engineer Fernando Peralta is particularly attentive to the messages sent back by Voyagers I and II—he cares deeply about the "kids" on Oudrhiri's metaphorical bus. Any anomalies or interference troubles him. "When we receive the signal and observe fluctuations, I wonder, 'Why is it undulating?' It could indicate the spacecraft's health, or perhaps it’s just a cloudy or windy day. To us, excessive noise is catastrophic."

A distorted signal also poses a risk of obscuring the unique soundscape that only these probes can provide. Voyager I carries a digital eight-track recorder to capture plasma waves and fluctuating ions and electrons, generating a sort of oceanic current extending beyond the solar system's borders. This deck remains powered (partly due to its heat generation, which prevents freezing in the fuel lines) and records 48 seconds of ambient sounds three times weekly. When Voyager I transmits this data, antennas in either California or Spain dedicate at least four hours to download the ethereal, wave-like sounds from the far reaches of deep space.

Peralta navigates through a cluster of cubicles, passing under a small sign reading "Mission Control." Modern computers occupy space alongside a microfilm reader, where the team consults historical blueprints. He has overseen the shutdown of numerous systems on both Voyager probes, and each day he finds the craft has successfully communicated feels like an unexpected gift. "This is a unique place in space, one we might never revisit in our or any future lifetimes," he states. "The data is incredibly valuable. It connects us."

In a matter of months or years, that connection will come to an end. As the heat dissipates from either Voyager I or II, a fuel line may freeze, rendering the propellant unable to reach the thruster. Consequently, the craft will lose the ability to make slight course adjustments, steer its antenna toward Earth, and send greetings. While its messages may still drift through space, we will be unable to capture and interpret them. Dodd speaks plainly about this inevitability: "You'd lose the signal. And that would be the end."

Before Voyager II exhausts its fuel, the mission team is already strategizing for a period of disconnection. Due to the craft's trajectory, which dips below the solar system's plane, only the antenna in Australia will be able to receive signals. This dish will remain inactive for nearly a year while NASA equips it with new test arrays of mirrors and optical sensors, aiming to supplement radio communications with light. By allowing the probe to drift for 10 months without commands, the agency is making a calculated sacrifice: halt communication with Voyager II and its radio-only antenna to facilitate a new generation of spacecraft that can continue to transmit data long after the older probes fall silent.

For decades, NASA has explored this approach—employing laser pulses that can transmit exponentially more data, faster, to smaller receivers. This strategy addresses two key issues: the increasing congestion in space, which complicates radio communication scheduling, and the need to transmit significantly more video data in less time as we explore destinations like Mars. When it launches in 2022, NASA's asteroid-exploring Psyche probe will be one of the first to utilize optical communication systems.

Yet light does have its limitations. For example, clouds can obstruct and distort it, while radio waves can penetrate most atmospheric conditions. Additionally, the systems are relatively economical, especially considering that "mass in space comes with a heavy cost," as Oudrhiri notes. The technologies he relies on stem from equipment that has been integral to our earliest space missions, from Echo balloons to Apollo and beyond.

Deep-space communication via radio waves is not going anywhere because it is simple and effective. "People often overcomplicate solutions to complex problems," Oudrhiri comments. "However, often the answer lies in simplicity: just observe what we've learned by paying attention to how the signal varies."

It turns out we've learned a great deal: the Moon's density, the age of Saturn's rings, the boundaries of our solar system. The interplay of signal and noise enriches our understanding of our place in the cosmos—the intricate pathways and conditions surrounding our solitary blue planet.

The second video, "We've Been Receiving A Mysterious Signal Every 22 Minutes For 35 Years," delves into the enigmatic signals we have been capturing and the implications of these discoveries for our understanding of the universe.