When we talk about robots, the first images that come to mind are often machines that move, sense, and act here on Earth. Voyager 1 and Voyager 2, twin spacecrafts launched in 1977, don’t fit that stereotype, but they share the same fundamental qualities. They are machines equipped with sensors, mechanisms for movement, decision-making routines, and the ability to act independently. In that sense, they are robotic explorers—though their mission takes place in deep space, billions of kilometers away.

Each Voyager spacecraft was designed to study the outer planets and then continue into interstellar space. To do this, they carry a suite of instruments that measure magnetic fields, charged particles, plasma, and other environmental conditions. They autonomously adjust orientation with thrusters, keep their antennas pointed toward Earth, and run programmed routines to protect themselves.

Let’s look at some key aspects of Voyager’s operation:

Power Management:

Power has always been the limiting factor for robots, and this is almost infinitely more pronounced for extremely long missions which we can only remotely interfere, such as the Voyagers’. Instead of solar panels, which are ineffective at far distances from the Sun, Voyager runs on a radioisotope thermoelectric generator. This device converts heat from decaying plutonium into electricity. The supply decreases every year, so mission controllers gradually turn off non-essential systems to keep the most important instruments running, which allowed these probes to last for so long.

Communication:

Each spacecraft transmits signals with just 20 watts of power (i.e. power of a light bulb). And now Voyagers are now so far away that, even at light speed, signals take almost a day to travel one way, (Voyager 1 is a little further away with about 25 billion km). That means any command sent from Earth, or data received back, involves almost a full day of delay. This low power signal and huge distance means a very, very weak signal when it reaches us.

Yet with the help of NASA’s Deep Space Network (DSN) — an array of giant radio antennas (up to 70 meters in diameter) located in California, Spain, and Australia, the faintest signals from across the cosmos can be detected and amplified.

How these weak signals are detected and meaningfully interpreted from billions of kilometers away is something one may wonder. Let’s try to explain briefly….

First, voyager autonomously keeps its antenna aligned toward Earth, otherwise the signal would not even reach to us.

Then, the robot sends the signal specifically using:

S-band (~2.3 GHz): Used in the early mission (close to Earth and the planets).

X-band (~8.4 GHz): Became the primary communication band for deep space, since it allows narrower beams and higher data rates with less noise.

These weak signals from billions of kilometers are picked up by NASA’s Deep Space Network we mentioned above. The antennas are very big because the signals become extremely faint when they reach earth —about 10^(-27) watts in comparison to about 20 watts when emitted from Voyager because the signal strength decreases in proportion to square of the distance from the source. A large dish antenna has a bigger “collecting area,” which gathers more of that weak energy. The big antenna also means, high signal-to-noise ratio (SNR). Space is noisy with natural radio emissions. To extract Voyager’s data (like scientific readings or engineering info), the antenna must maximize the useful signal while minimizing noise. A larger antenna improves the SNR. Another reason for big antennas is that the Voyager transmits in the X-band (~8 GHz). At these frequencies, a large dish provides a much narrower beam, improving sensitivity and reducing interference. And there is also the data rate limitations. Voyager can only send data at a few hundred bits per second. Without such big antennas, we’d get no usable data at all. In short: the farther the source and the weaker the signal, the bigger your “radio ear” has to be.

Once the signal is received, it’s amplified and filtered to remove background noise. The data is encoded as binary (1s and 0s) — sequences of tiny shifts in the radio wave’s phase or frequency. Specialized computers decode this binary stream back into engineering data (about the spacecraft’s status) or scientific measurements (from Voyager’s instruments).

We keep saying “signal” above but what do we mean by it exactly in Voyager’s case? Is it a 1 bit thing or something that carries a lot of information?

Voyager sends out a continuous radio wave — that’s the “signal” in its most basic sense. This wave is steady, like a tone, and travels through space at the speed of light.

To carry information, Voyager modulates (changes) the wave in tiny ways. It can slightly shift the wave’s frequency or phase to represent digital data. That digital data is basically bits (1s and 0s). A single bit doesn’t mean much — it’s just “on” or “off” but Voyager sends long sequences of bits that form data frames. These frames may contain:

-Engineering telemetry (temperatures, voltages, power levels, orientation data).
-Science data (measurements from instruments, like magnetic fields or plasma density).

So in other words, when we say “signal,” we mean the radio wave itself (the carrier) and the modulation of that wave that encodes long sequences of bits, which carry meaningful information once decoded.

The few hundred bits per second data rate which was normal when the probes were made in 1970s, is extremely low by today’s standards which also depends on distance and conditions. But over time, these trickles of data accumulate into huge scientific returns. Scientists and engineers translate these data streams into usable information. Engineering data tells NASA about Voyager’s health (temperature, power levels, orientation). Science data comes from instruments measuring density of plasma in interstellar space, measuring magnetic fields, track cosmic rays, record how solar wind interacts with galaxy beyond out solar system and so on, which are very valuable for scientists.

And you may also wonder how does Voyager manage to keep its antenna pointed towards earth?

Voyager does this using a clever mix of navigation tools and small course corrections. Since Earth is far too dim to track directly, the spacecraft orients itself by watching the Sun and the bright star Canopus, while gyroscopes track its movements in between. A computer compares this data to the desired orientation, then fires tiny hydrazine thrusters to nudge the craft back on target when it drifts. This keeps the high-gain antenna locked within half a degree of Earth’s position (which is like pointing towards a coin from thousands of km away), so faint signals can still make the 20-plus billion kilometer journey to NASA’s Deep Space Network. Because commands now take more than 22 hours to reach the spacecraft, most of these adjustments are handled autonomously. To conserve fuel, the system corrects its aim only occasionally rather than continuously, ensuring Voyager can keep talking to us for as long as possible.

Final Thoughts:

The endurance of Voyager is not just about the hardware. It reflects the genius and vision of the engineers who built them, anticipating problems and creating machines that could solve some of those problems themselves even with 1970s knowledge and technology. That balance between human foresight and robotic independence is part of why Voyager still works, decades after launch. It shows how even simple routines, when designed carefully, can extend a mission far beyond its expected lifetime.

Voyager 1 and 2 are reminders that robots don’t need to walk or talk to be extraordinary. Sometimes, the most remarkable robots are the ones that endure silently, sending back discoveries from the edge of the stars.

Post By: A. Tuter