Voyager 1 and Voyager 2 are two robotic spacecraft launched by NASA in 1977 to explore the outer Solar System. Their missions took advantage of a rare alignment of the giant planets that made a multi-planet Grand Tour possible. The spacecraft returned the first close-up views of Jupiter, Saturn, Uranus, Neptune, and many of their moons.
They changed astronomy by showing that the outer Solar System is active, diverse, and full of surprising worlds.
The Voyagers used gravity assists to gain speed and redirect their paths without carrying huge amounts of fuel. Each spacecraft carried cameras, fields and particles instruments, plasma detectors, radio science equipment, and a gold-plated phonograph record containing sounds and images from Earth. Voyager 1 is now in interstellar space, while Voyager 2 is the only spacecraft to have visited all four giant planets.
The Golden Record turns the mission into both a scientific expedition and a message from humanity to any future finder.
Key Facts
- Voyager 1 launched on September 5, 1977, and Voyager 2 launched on August 20, 1977.
- A gravity assist changes a spacecraft speed and direction by stealing a tiny amount of orbital energy from a planet.
- Average speed can be estimated with v = d/t.
- Radio signal time is found with t = d/c, where c = 3.00 x 10^8 m/s.
- Voyager 2 flew by Jupiter, Saturn, Uranus, and Neptune, completing the only close-up Grand Tour of all four giant planets.
- The Golden Record contains 115 images, natural sounds, music, greetings in many languages, and instructions for playback.
Vocabulary
- Gravity assist
- A maneuver in which a spacecraft uses a planet's motion and gravity to change its speed and direction.
- Grand Tour
- A mission path made possible by a rare planetary alignment that allowed one spacecraft to visit several outer planets using gravity assists.
- Heliopause
- The boundary where the solar wind from the Sun is slowed and pushed back by the interstellar medium.
- Interstellar space
- The region between stars where particles and magnetic fields are no longer dominated by the Sun.
- Golden Record
- A gold-plated copper record carried by each Voyager spacecraft that contains sounds and images representing Earth and human culture.
Common Mistakes to Avoid
- Thinking Voyager 1 visited Uranus and Neptune. Voyager 1 flew by Jupiter and Saturn, while Voyager 2 continued on to Uranus and Neptune.
- Treating gravity assists as free energy from nowhere. The spacecraft gains or loses energy by exchanging a tiny amount of energy and momentum with the moving planet.
- Assuming the Golden Record was meant for quick communication with aliens. It is a long-term symbolic message that might only be found far in the future, if ever.
- Confusing leaving the Solar System with leaving the Sun's gravity completely. Voyager 1 crossed the heliopause into interstellar space, but it is still influenced by the Sun's gravity.
Practice Questions
- 1 A radio signal travels at 3.00 x 10^8 m/s. If Voyager is 2.40 x 10^13 m from Earth, how many seconds and hours does a one-way signal take to arrive?
- 2 Voyager 2 traveled from Earth to Neptune in about 12 years, a distance of roughly 4.5 x 10^9 km. Estimate its average speed in km/s over that part of the journey.
- 3 Explain why a rare alignment of the outer planets made the Voyager Grand Tour possible, and why the same mission would have required much more fuel without gravity assists.