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How can Voyager, despite its vast distance, transmit signals that we can still receive more than 20 years after its launch?

Rather than asking how Voyager sends a strong enough signal, it’s more insightful to consider how Earth manages to receive such a weak signal. Voyager’s signal, when it leaves the spacecraft, is only about six times more powerful than that of an average cell phone. By the time it reaches Earth, it is incredibly faint.

NASA operates the Deep Space Network (DSN), which consists of large antenna complexes in California, Spain, and Australia, spaced 120 degrees apart in longitude to provide global coverage. These complexes feature massive dish antennas, ranging from 85 to 230 feet in diameter. The parabolic shape of these antennas ensures that incoming signals are focused towards a central point, amplifying them.

Voyager

This network is so sensitive that it can pick up even the faintest signals from Voyager. The antennas are capable of detecting Voyager’s transmissions, which could continue for another century, though the spacecraft’s power supply is expected to dwindle by around 2025. Voyager is powered by the heat from the radioactive decay of plutonium, which initially produced about 450 watts of power. Today, it’s less than 250 watts.

When Voyager sends a signal using its high-gain antenna, aimed precisely at Earth, the signal starts at about 19 watts. After traveling for 16 hours at the speed of light, the signal weakens to about 10^-16 watts by the time it reaches the DSN antennas. Voyager transmits at a high frequency (X-band 8.4 GHz), a range not commonly used on Earth, reducing the chance of interference from terrestrial sources like cell phones, TV, and GPS.

Despite the DSN’s capabilities, it faces challenges due to underfunding and aging equipment, which can lead to outages and missed data. Additionally, even rain bouncing on the dish can disrupt the signal reception.

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