APOGEE STAFF
They’re among the oldest of the so-called “zombie” spacecraft, human-made celestial objects that fly well past their prime: Famed observational or “flyby” spacecraft, Voyager 1 and 2 are part of a narrow class of satellites that continue to fulfill at least some of their mandate, even decades after their liftoff. The twin satellites, launched in the late 1970s, still relay data back to Earth. But a time is approaching when the probes will no longer contribute to our understanding of outer space and end up drifting lifelessly through the cosmos.
NASA reports that Voyager 1 is using backup thrusters to keep its antennae pointed toward Earth, and that its instrumentation might cease working altogether in 2025. In early October 2024, scientists announced the shutdown of Voyager 2’s plasma science instrument, which measures the density and direction of ionized particles, to conserve electrical power. They hope this enables Voyager 2 to continue its mission into the 2030s. Both satellites use radioisotope thermoelectric generators (RTG) to create electrical power from heat generated by the decay of plutonium-238. The thrusters are powered by hydrazine.
When the Voyagers finally exhaust their energy supplies, they’ll meet the fate of forebears Pioneer 10 and 11, which launched earlier in the 1970s with a similar aim of gathering information about Jupiter and Saturn. The Pioneer probes have long stopped communicating with Earth and are believed to be floating somewhere beyond the heliosphere of our solar system, NASA said.
Before they encounter the same end, Voyager 1 and 2 will have achieved a distinction no other spacecraft can claim: They’ve traveled farther than any spacecraft in history. The Voyager probes are believed to have sailed past our solar system and are now moving through interstellar space. Voyager 1, the more distant of the two, is estimated to be about 24.6 billion kilometers from Earth. Although no longer relaying images to NASA, the spacecraft continue to transmit bits of data. However, the moment is approaching when both vehicles exhaust power and shut down. That point will mark the end of a journey begun almost 50 years ago.
Mission
The Voyager satellites launched in 1977 with the aim of exploring Jupiter and Saturn. In addition to capturing images of the planets and their moons, they studied plasma waves, magnetic fields and various particles near the planets. Traveling aboard a Titan-Centaur rocket, Voyager 2 lifted off from Cape Canaveral in Florida 16 days before Voyager 1 and arrived at the rings of Saturn in August 1981, nine months after its sister satellite. The probes encountered Jupiter two years earlier.
After a series of discoveries — including active volcanoes on Jupiter’s moon Io and details about Saturn’s rings — the Voyager mission was extended. Voyager 2 went on to explore Uranus and Neptune and is the only spacecraft to have visited those outer planets. Together, the two satellites have visited all the giant planets of our solar system — Jupiter, Saturn, Uranus and Neptune — 48 of their moons, and the planets’ unique rings and magnetic fields. Their current mission, Voyager Interstellar Mission, is to explore the outermost edge of the sun’s domain. The probes left the solar system at different times and follow different trajectories. Voyager 1 entered interstellar space in August 2012, while Voyager 2 crossed over in November 2018. Both spacecraft continue to send scientific information about their surroundings through the Deep Space Network. Scientists hope the data helps them understand more about interstellar space.
Discoveries
A NASA website describing the Voyager mission calls it “probably the most scientifically productive mission ever.” The satellites retrieved the first detailed profiles of the atmospheres of Saturn, Uranus and Neptune and improved scientists’ understanding of the intricacies of Jupiter’s atmosphere. The satellites uncovered details about Saturn’s rings, discovered the rings of Jupiter, and provided the first detailed images of the rings of Uranus and Neptune. Voyager also photographed Earth’s moon and discovered 23 new moons at the outer planets.
According to NASA, the satellites made “significant improvements in the measurements of the magnetospheres at Jupiter and Saturn and provided the first measurements of the magnetospheres at Uranus and Neptune. The significance of the Voyager is the vast amount of new knowledge about our outer solar system it provided and the interest in further exploration it generated. That interest has resulted in the Galileo mission to Jupiter and the Cassini mission to Saturn,” as well as the discovery of three new moons of Saturn using Earth-based instruments.
The greatest surprise, NASA said, was the discovery of active volcanoes on Io, the innermost of Jupiter’s four large moons. This marked the first time that active volcanoes had been seen on another body in the solar system, and it appears “that activity on Io affects the entire Jovian system,” the system of moons around Jupiter.
About Voyager
The Voyager satellites launched aboard Titan III E/Centaur rockets. The twin spacecraft are about the size and weight of a subcompact car. Including fuel, each weighed about 816 kilograms at launch. NASA now estimates the weight of Voyager 1 at 733 kilograms and Voyager 2 at 735 kilograms. The difference is the amount of hydrazine remaining in the satellites. Hydrazine is used to control the spacecrafts’ attitude, or position relative to a specific object in space. Without its various booms, Voyager is compact enough to fit inside a 4-meter cube. Measurements of the different structures connected to Voyager include:
- The high gain antenna is 3.7 meters across (diameter).
- The magnetometer boom is 13 meters long.
- The two planetary radio astronomy and plasma wave antennae are 10 meters long.
- The radioisotope thermoelectric generator boom is
3.7 meters long. - The science instrument boom is 3 meters long.
- The bus housing electronics is about 1.8 meters in diameter.
- Voyager’s Golden Record
In addition to its instruments, Voyager contains another intriguing item: an electroplated phonograph, or “Golden Record,” designed to serve as a kind of welcome note for extraterrestrial beings. The record’s cover includes a map that depicts our solar system and instructions for playing the record. Listeners would hear a Bach concerto, the Louis Armstrong song “Melancholy Blues” and other pieces of music from around the world. Also included is a verbal exchange between a mother and baby, a kiss and various mechanical sounds, including a train whistle, a tractor and a car.