Voyager 1 is the most-distant human object...

Voyagers are leaving the Solar System


Voyagers set to enter interstellar space »
More than 30 years after they left Earth, NASA's twin probes are now at the edge of the Solar System.

Voyager's golden record »
NASA's Voyager probes carry messages for extraterrestrial civilizations:
greetings from humans and whales, some of Earth's greatest music, brainwaves of a woman in love.

NASA artist concept of the Voyager 1 and Voyager 2 spacecraft
Click to enlarge NASA artist concept of Voyager 1 and 2
NASA's Voyager 1 spacecraft is the most distant human-made object in the universe.

Its twin, Voyager 2, has traveled to more planets than any other in history.

The spacecraft twins, Voyager 1 and Voyager 2, were launched by NASA during the summer of 1977 from Cape Canaveral, Florida.

Barring any fatal equipment failures, the Voyager twins are likely to survive and relay data from beyond the outer planets for many decades into the 21st century.

Today, in a dark, cold, vacant neighborhood at the very edge of our Solar System, NASA's Voyager 1 deep space probe holds the record as the Earth explorer that has traveled farthest from home.

Voyager 1

When Voyager I was launched in 1977 to study and photograph the giant outer planets of the Solar System, the robot ship was expected to survive just four years. However, like the battery advertising icon, the Energizer Bunny, the little spacecraft kept on going.

For 25 years, the Pioneer 10 spacecraft led the way outbound, pressing the frontiers of exploration, but in 1998 the baton was passed from Pioneer 10 to Voyager 1, according to NASA's Jet Propulsion Laboratory (JPL), Pasadena, California.

Voyagers Timeline
  The Mariner Jupiter/Saturn 1977 mission is renamed Voyager
Aug. 20 Voyager 2 spacecraft launched from Kennedy Space Flight Center, Florida
Sept. 5

Voyager 1 spacecraft launched from Kennedy Space Flight Center, Florida

Voyager 1 sends the first spacecraft photo of Earth and the Moon

Mar. 5 Voyager 1 flies by Jupiter in its closest approach to that planet
July 9 Voyager 2 makes its closest fly-by of Jupiter
Nov. 12 Voyager 1 flies by the planet Saturn

With no more planet fly-bys in its plan, Voyager 1 begins its trip out of the Solar System
Aug. 25 Voyager 2 flies by Saturn
  NASA's Deep Space Network upgrades two 85-ft. antennas to 112-ft. diameter to be better able to receive weak radio signals from the Voyager spacecraft
Jan. 24 Voyager 2 completes the first-ever spacecraft encounter with the planet Uranus

NASA's Deep Space Network expands 210-ft. antennas to 230-ft. diameter for improved reception of weak signals from the very distant Voyager spacecraft
  Voyager 2 observes the faraway stellar explosion known as Supernova 1987A
  Voyager 2 sends to Earth the first color images of the planet Neptune
Aug. 25 Voyager 2 is the first spacecraft to observe Neptune

With no more planet fly-bys in its plan, Voyager 2 begins its trip out of the Solar System, traveling below the ecliptic plane
  During their "Grand Tour" of the planets Jupiter, Saturn, Uranus and Neptune, the Voyagers sent home nearly 80 thousand images and more than 5 trillion bits of data.
Jan. 1 NASA starts the Voyager Interstellar Mission
Feb. 14 The Voyager 1 cameras had been dormant since that spacecraft had left the vicinity of Saturn. NASA turned the cameras on to look back where the two spacecraft had come from and transmit its last Images – a portrait of the Solar System
  Spacecraft electrical systems generated 470 watts of power at launch. Now, the power generated by Voyager 1 has dropped to 334 watts and Voyager 2 to 336 watts.
Feb. 17 Voyager 1 passed Pioneer 10 to become the most distant human-made object in space.
  The 25-year-old Voyager 1 was more than 7.8 billion miles away from Earth. Radio signals required 12 hours to reach the probe. NASA sent commands to activate a spare sun sensor and star tracker to help the craft locate its position.
Aug. 1 Voyager 1 reported that high-velocity electrically-charged particles – electrons and ions – around the spacecraft increased 100 times from Aug. 1 to Feb. 5, 2003. The solar wind speed appeared to slow down. It wasn't clear whether the probe had crossed the Solar System "termination shock."
Apr. 15± Voyager 2 detected a shock wave from October 2003 solar storms. Powerful flares had hurled billion-ton clouds of gas across the Solar System. Voyager 2 measured its speed, composition, temperature and magnetism.
Jan. 5 It has been 10,000 days since Voyager 2's launch. The probe is nearly 7 billion miles (11 billion kilometers, 75 AU) away from Earth. It is heading in a northerly direction out of the Solar System.
Jan. 21 It has been 10,000 days since Voyager 1's launch. The spacecraft is nearly 9 billion miles (14 billion kilometers, 94 AU) from Earth in a dark, cold, vacant neighborhood at the very edge of our Solar System. Voyager 1 holds the record as the explorer from Earth that has traveled farthest from home. It is heading in a southerly direction out of the Solar System.
  Voyagers 1 and 2 still are returning valuable science data. Each probe's cosmic ray detector, magnetometer, plasma wave detector and low-energy charged particle detector are operational. The ultraviolet spectrometer on Voyager 1 and the plasma science instrument on Voyager 2 continue to send home data. Since the beginning of the interstellar part of their mission in 1990, the two deep space probes have returned an additional 65 billion bits of data.
  The Voyagers have sufficient electrical power and thruster fuel to operate at least until 2020 when Voyager 1 will be 12.4 billion miles from the Sun and Voyager 2 will be 10.5 billion miles.
  Voyager 1 will float by within 1.6 light years (9.3 trillion miles) of a star known as AC+79 3888 in the constellation Camelopardalis.
  Voyager 2 will sail within 4.3 light years (25 trillion miles) of Sirius, which today is the brightest star in Earth's sky.
On Feb. 17, 1998, the Voyager 1 spacecraft cruised beyond the Pioneer 10 spacecraft and become the most distant human-created object in space. At that time, it was 6.5 billion miles from Earth. Pioneer 10 and Voyager 1 are headed in almost opposite directions away from the Sun.

The twins, Voyager 1 and 2, opened new vistas for the human race by expanding our knowledge of Jupiter and Saturn. Voyager 2 then extended our great planetary adventure when it flew by Uranus and Neptune, becoming the only spacecraft ever to visit these worlds. (None has ever visited Pluto.)

Voyager 1, now the most distant human-made object in the Universe, and Voyager 2, close on its heels, continue their ground-breaking journey with their current mission to study the region in space where the Sun's influence ends and the dark recesses of interstellar space begin.

Voyager 1 is almost 70 times farther from the Sun than the Earth. Out there, the Sun is only 1/5,000th as bright as here on Earth. It is extremely cold, and there is little solar energy to keep the probe warm and to provide electrical power.

The probe can continue to operate at such great distances from the Sun because it has radioisotope thermal electric generators (RTGs) that create electricity. The fact that the spacecraft is still returning data is a remarkable technical achievement.

Voyager flight path. Voyager 1 was launched from Cape Canaveral on Sept. 5, 1977. It flew by Jupiter on March 5, 1979, and then Saturn on Nov. 12, 1980. Because its trajectory was designed to fly close to Saturn's large moon Titan, Voyager 1's path was bent northward by Saturn's gravity. That sent the spacecraft out of the Solar System's ecliptic plane -- the plane in which all the planets, except Pluto, orbit the Sun.

On Feb. 17, 1998, Voyager 1 was departing the Solar System at a speed of 39,000 miles per hour. At the same time, Voyager 2 was 5.1 billion miles from Earth and was departing the Solar System at a speed of 35,000 miles per hour.

Voyager 2 is heading in the opposite direction of Voyager I and traveling at a slightly slower speed.

Pioneer 10 had been launched earlier, on March 2, 1972. Its official mission ended on March 31, 1997. However, NASA's Ames Research Center, Moffett Field, CA, intermittently receives science data from Pioneer as part of a training program for flight controllers.

Low power. Voyager 1 was so far from Earth in 1998 that it took 9 hours 36 minutes for a radio signal traveling at the speed of light to reach Earth. Voyager's signal, produced by a 20 watt radio transmitter, is so faint that the amount of power reaching NASA's antennas is 20 billion times smaller than the power of a digital watch battery.

Deep space environment. Having completed their planetary explorations, Voyager 1 and its twin, Voyager 2, are studying the environment of space in the outer Solar System. Although beyond the orbits of all the planets, the spacecraft still are well within the boundary of the Sun's magnetic field -- the heliosphere.

Science instruments on both spacecraft sense signals that scientists believe are coming from the outermost edge of the heliosphere, known as the heliopause.

Heliosphere. The Sun emits a steady flow of electrically-charged particles called the solar wind. As the solar wind expands supersonically into space, it creates a magnetized bubble around the Sun -- the heliosphere. Eventually, the solar wind runs into the electrically-charged particles and magnetic field in the interstellar gas. The solar wind abruptly slows down from supersonic to subsonic speed, creating a termination shock. Before both spacecraft travel beyond the heliopause into interstellar space, they must pass through that shockwave. Voyager may pass through the termination shock sometime soon. Then, within ten years, Voyager should penetrate the heliopause -- the outermost edge of the Sun's magnetic field -- and enter into true interstellar space for the first time.

The low-energy charged-particle detectors aboard both Voyagers continue to detect ions and electrons accelerated by the Sun and huge shock waves, tens of astronomical units (AU) in radius, that are driven outward through the solar wind.

Using data sent to Earth by the Voyager cosmic ray detectors, NASA scientists are predicting the termination shock to be in the range of 62 to 90 AU from the Sun. They estimate the heliopause is located from 110 to 160 AU from the Sun. Most estimates are about 85 AU. Voyager 1 is moving outwards at 3.5 AU per year, so it may encounter the termination shock in the early 2000s.

Reaching the termination shock and heliopause will be major milestones for the mission because no spacecraft from Earth have been there before and the Voyagers will gather the first direct evidence of the termination shock and heliopause. Flying through the termination shock and heliopause have been long-sought goals for many space physicists. What space is like around the two boundaries is a mystery.

Receiving data. Science data from the Voyagers is returned to Earth in real-time to NASA's 34-meter Deep Space Network antennas in California, Australia and Spain. Both spacecraft have enough electricity and attitude control propellant to continue operating until about the year 2020. It is estimated that electrical power produced by the RTGs then will no longer support science instrument operation. At that time, Voyager 1 will be 150 times farther from the Sun than the Earth is -- almost 14 billion miles away.

Voyager 2

Voyager 2 was launched first, on Aug. 20, 1977, and Voyager 1 was launched shortly thereafter, on Sept. 5, on a faster trajectory.

Initially, both spacecraft were only supposed to explore two planets-Jupiter and Saturn. But the incredible success of those two first encounters and the good health of the spacecraft prompted NASA to extend Voyager 2's mission to Uranus and Neptune. Since 1989, when Voyager 2 flew by Neptune, both spacecraft have been studying the environment of space in the outer Solar System. Voyager 1 is now more than twice as far from the Sun as Neptune and their journey is only half over.

The planetary encounters

Voyager 1 at Jupiter. Voyager 1 encountered Jupiter on March 5, 1979, and Saturn on Nov. 12, 1980, and then, because its trajectory was designed to fly close to Saturn's large moon Titan, Voyager 1's path was bent northward by Saturn's gravity sending the spacecraft out of the ecliptic plane, the plane in which all the planets but Pluto orbit the Sun.

Voyager 2 at Jupiter. Voyager 2 arrived at Jupiter on July 9, 1979, and Saturn on Aug. 25, 1981, and was then sent on to Uranus on Jan. 25, 1986, and Neptune on Aug. 25, 1989. Neptune's gravity bent Voyager 2's path southward sending it also out of the ecliptic plane and on toward interstellar space.

Voyager science

As the spacecraft flew across the Solar System, remote-control reprogramming of their computers gave the Voyagers greater capabilities than they possessed when they left Earth. Four science instruments still are collecting data as part of the Voyager Interstellar Mission.

Faster solar wind. The plasma detectors, which measure the protons in the solar wind, observed a slow, year-long increase in the speed of the solar wind which peaked in late 1996. Now they are reporting a slow decrease in solar wind velocity. The velocity peak may have coincided with the recent solar minimum. As a new solar maximum arrives in the year 2000, the solar wind pressure may decrease. That might draw the termination shock and heliopause inward towards the Voyager spacecraft.

Weakest magnetic fields. The magnetometers onboard the Voyagers measure the magnetic fields carried out into interplanetary space by the solar wind. The Voyagers have measured the weakest interplanetary magnetic fields ever detected and those are responsive to charged particles that cannot be detected directly by any other instruments on the spacecraft.

The other science instruments still collecting data include the planetary radio astronomy receiver and the ultraviolet spectrometer.

Spacecraft electrical power is supplied by radioisotope thermoelectric generators (RTGs) that produced some 470 watts of power at launch. Due to the natural radioactive decay of the plutonium fuel source, the electrical energy output continually declines.

By 1997, the power generated by Voyager 1 had dropped to 334 watts and Voyager 2 to 336 watts. However, those levels were better than had been predicted before launch.

There might have been four

NASA patch commemorates Voyager 1 and Voyager 2 NASA originally planned a Grand Tour of the outer planets, including two launches to Jupiter, Saturn and Pluto in 1976-77 and two launches to Jupiter, Uranus and Neptune in 1979. There would have been four Voyagers.

However, space exploration financing was not much different then from now. NASA was not allocated sufficient funds to carry out the complete plan.

The Grand Tour project underwent a dramatic revision down to two spacecraft, each of which would travel only to Jupiter and Saturn.

The name of the mission was changed to Mariner Jupiter/Saturn, or MJS. Later, six months prior to launch, it was renamed Voyager. The downsized mission was estimated to cost only a third of what the Grand Tour design would have cost.

Where will they end up?

NASA says both Voyagers are headed towards the outer boundary of the Solar System in search of the heliopause — the region where the Sun's influence wanes and the beginning of interstellar space can be sensed. Sometime in the next 10 years, the two spacecraft will cross an area known as the termination shock where the million-mile-per-hour solar wind slows to about 250,000 miles per hour.

After reaching the termination shock, the Voyagers will continue on to cross the heliopause in another 10 to 20 years.

One Astronomical Unit (AU) is equal to the distance from the Earth to the Sun – about 93 million miles (150 million kilometers).
The heliopause is somewhere between 5 and 14 billion miles from the Sun. It never has been reached by any spacecraft from Earth, so the Voyager twins will be the first human-built spacecraft from Earth to pass through that region.

The Voyagers have enough electrical power and thruster fuel to operate at least until 2020. By that time, Voyager 1 will be 12.4 billion miles from the Sun and Voyager 2 will be 10.5 billion miles from the Sun.

Eventually, the Voyagers will pass other stars: Voyager 1 and Voyager 2 are destined to wander through our Milky Way galaxy eternally — unless they crash into something we can't yet calculate.

Project management. Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology, manages the Voyager Interstellar Mission for NASA's Office of Space Science, Washington, DC.

Learn more about the Voyagers:
Learn more about the Solar System . . .
Star: The Sun  
Inner Planets: Mercury Venus Earth Mars  
Outer Planets: Jupiter Saturn Uranus Neptune Pluto
Other Bodies: Moons Asteroids Comets  
Beyond: Pioneers Voyagers