Voyager 2 is a space probe launched by NASA on August 20, 1977, as part of the Voyager program. It was launched on a trajectory toward the gas giants Jupiter and Saturn and enabled further encounters with the ice giants Uranus and Neptune.
It remains the only spacecraft to have visited either of the ice giant planets, and was the third of five spacecraft to achieve Solar escape velocity, which allowed it to leave the Solar System. Launched 16 days before its twin Voyager 1, the primary mission of the spacecraft was to study the outer planets and its extended mission is to study interstellar space beyond the Sun’s heliosphere.
Voyager 2 was successful in the accomplishment of its main mission objectives. It has successfully visited the Jovian system in 1979, the Saturnian system in 1981, the Uranian system in 1986, and the Neptunian system in 1989. It is currently operating in the extended mission mode for the exploration of the interstellar medium. The distance between it and Earth, as of November 2024, is 138.27 AU (20.7 billion km; 12.9 billion mi).
It penetrated the interstellar medium on 5 November 2018 at a distance of 119.7 AU, or 11.1 billion miles (17.9 billion kilometers) from the Sun and traveling at 15.341 km/s or 34,320 mph relative to the Sun. Voyager 2 has entered the interstellar medium, moving through it, still inside the Solar System, like Voyager 1, which entered the interstellar medium in 2012. Voyager 2 has started giving the first direct measurements of the density and temperature of the interstellar plasma.
Voyager 2 remains in contact with Earth through the NASA Deep Space Network. Communications are the responsibility of Australia’s DSS 43 communication antenna, located near Canberra.
History
Background
With the dawn of the early space age, it was realized that an alignment of the outer planets would recur in the late 1970s that could allow a single probe to visit Jupiter, Saturn, Uranus and Neptune by exploiting the then-new gravity assists technique. NASA started work on a Grand Tour, which transformed into a highly ambitious undertaking where two sets of two probes, one to the Jupiter, Saturn, and Pluto and the other to the Jupiter, Uranus, and Neptune, were devised.
The whole spacecraft was supposed to be developed with redundant systems to ensure the survival of all through the complete tour. It was by 1972 when the mission got downsized, and instead two Mariner program-derived spacecraft became the Mariner Jupiter-Saturn probes. To keep apparent lifetime program costs low, the mission would include only flybys of Jupiter and Saturn, but keep the Grand Tour option open. As the program progressed, the name was changed to Voyager.
The primary goal of Voyager 1 was to study Jupiter, Saturn, and Saturn’s largest moon, Titan. Voyager 2 would also view Jupiter and Saturn on a course which would include an option of taking it out toward Uranus and Neptune-or have it switched over to take Titan as its secondary target on a trajectory sent ahead of, as a cover plan for, Voyager 1.
Once these were accomplished objectives by Voyager 1, NASA had agreed for an extension and then send that probe on Uranus and towards Neptune. Titan was selected because of the interest generated after the pictures taken by Pioneer 11 in the year 1979 revealed that the atmosphere of the moon was significant and complex. Therefore, the trajectory was planned for optimal Titan flyby.
Spacecraft design
Built by the Jet Propulsion Laboratory (JPL), Voyager 2 had 16 hydrazine thrusters, three-axis stabilization, gyroscopes and celestial referencing instruments (Sun sensor/Canopus Star Tracker) to maintain pointing of the high-gain antenna toward Earth. Collectively these instruments are part of the Attitude and Articulation Control Subsystem (AACS) along with redundant units of most instruments and 8 backup thrusters. The spacecraft itself carried 11 scientific instruments to examine the nature of celestial objects as it traveled through space.
Communications
This would almost sound like an SVG plot description of five interstellar probes whose heliocentric positions and related information such as launch dates, flyby dates, and some other celestial body positions are graphed along with markers on every fifth year to indicate their position on January 1st. The views vary by projection type and scale, and interactive features are added to explore the data in greater detail.
To be clear, this would be a dynamic, interactive SVG graphic where:
- Plot 1 shows the heliocentric positions from the north ecliptic pole, to scale.
- Plots 2 to 4: third-angle projections on a 20% scale for various views.
- Hovering over a trajectory or orbit will highlight the corresponding probe’s path and the associated launch and flyby events.
If you want to know how to make or work with this SVG, I can generate code or describe specifics!
Power
Voyager 2 is equipped with three multihundred-watt radioisotope thermoelectric generators (MHW RTGs). Each RTG includes 24 pressed plutonium oxide spheres. At launch, each RTG provided enough heat to generate approximately 157 W of electrical power. Collectively, the RTGs supplied the spacecraft with 470 watts at launch (halving every 87.7 years).
They were predicted to allow operations to continue until at least 2020, and continued to provide power to five scientific instruments through the early part of 2023. In April 2023, JPL began using a reservoir of backup power intended for an onboard safety mechanism.
As a result, all five instruments had been expected to continue operation through 2026. In October 2024, NASA announced that the plasma science instrument had been turned off, preserving power for the remaining four instruments.
Attitude control and propulsion
Because of the energy needed for the Jupiter trajectory boost with the payload of 825 kilograms or 1,819 pounds, the spacecraft consisted of a 1,123 kilograms or 2,476-pound solid-rocket motor as well as eight hydrazine monopropellant rocket engines. Among those, four controlled pitch and yaw attitude and the other four provided roll attitude. The propulsion module was jettisoned only some minutes after the successful Jupiter burn.
Sixteen hydrazine Aerojet MR-103 thrusters on the mission module provide attitude control. Four are used to execute trajectory correction maneuvers; the others in two redundant six-thruster branches, to stabilize the spacecraft on its three axes. Only one branch of attitude-control thrusters is needed at any time.
Thrusters are supplied by a single 70-centimeter (28 in) diameter spherical titanium tank. It contained 100 kilograms (220 lb) of hydrazine at launch, providing enough fuel until 2034.
Scientific instruments
Images of the spacecraft
Mission profile
Images of trajectory
Voyager 2 Mission Timeline
| Date | Event |
|---|---|
| 1977-08-20 | Spacecraft launched at 14:29:00 UTC. |
| 1977-12-10 | Entered asteroid belt. |
| 1977-12-19 | Voyager 1 overtakes Voyager 2. (see diagram) |
| 1978-06 | Primary radio receiver fails. The remainder of the mission flown using backup. |
| 1978-10-21 | Exited asteroid belt |
| 1979-04-25 | Start Jupiter observation phase |
| 1979-07-08 | Encounter with Jovian system. |
| 1979-07-08 | Callisto flyby at 214,930 km. |
| 1979-07-08 | Ganymede flyby at 62,130 km. |
| 1979-07-08 | Europa flyby at 205,720 km. |
| 1979-07-08 | Amalthea flyby at 558,370 km. |
| 1979-07-08 | Jupiter closest approach at 721,670 km from the center of mass. |
| 1979-07-08 | Io flyby at 1,129,900 km. |
| 1979-08-05 | Phase Stop |
| 1981-06-05 | Start Saturn observation phase |
| 1981-08-22 | Encounter with Saturnian system. |
| 1981-08-25 | Iapetus flyby at 908,680 km. |
| 1981-08-25 | Hyperion flyby at 431,370 km |
| 1981-08-25 | Titan flyby at 666,190 km. |
| 1981-08-25 | Helene flyby at 314,090 km. |
| 1981-08-26 | Dione flyby at 502,310 km. |
| 1981-08-26 | Calypso flyby at 151,590 km. |
| 1981-08-26 | Mimas flyby at 309,930 km. |
| 1981-08-26 | Pandora flyby at 107,000 km. |
| 1981-08-26 | Saturn closest approach at 161,000 km from the center of mass. |
| 1981-08-26 | Atlas 287,000 km |
| 1981-08-26 | Enceladus flyby at 87,010 km. |
| 1981-08-26 | Janus at 223,000 km |
| 1981-08-26 | Epimetheus at 147,000 km. |
| 1981-08-26 | Telesto at 270,000 km. |
| 1981-08-26 | Tethys flyby at 93,010 km. |
| 1981-08-26 | Rhea flyby at 645,260 km. |
| 1981-09-04 | Phoebe flyby at 2,075,640 km. |
| 1981-09-25 | Phase Stop |
| 1987-08-20 | 10 years of continuous flight and operation at 14:29:00 UTC. |
| 1989-06-05 | Start Neptune observation phase |
| 1989-08-25 | Encounter with Neptunian system. |
| 1989-08-25 | Neptune closest approach at 4,950 km. |
| 1989-08-25 | Galatea flyby at 18,360 km. |
| 1989-08-25 | Larissa flyby at 60,180 km. |
| 1989-08-25 | Proteus flyby at 97,860 km. |
| 1989-08-25 | Triton flyby at 39,800 km. |
| 1989-10-02 | Phase Stop |
| 1989-10-02 | Begin Voyager Interstellar Mission. |
| 1997-08-20 | 20 years of continuous flight and operation at 14:29:00 UTC. |
| 1998-11-13 | Terminate scan platform and UV observations. |
| 2007-08-20 | 30 years of continuous flight and operation at 14:29:00 UTC. |
| 2007-09-06 | Terminate data tape recorder operations. |
| 2008-02-22 | Terminate planetary radio astronomy experiment operations. |
| 2011-11-07 | Switch to backup thrusters to conserve power. |
| 2017-08-20 | 40 years of continuous flight and operation at 14:29:00 UTC. |
| 2018-11-05 | Crossed the heliopause and entered interstellar space. |
| 2023-07-18 | Voyager 2 overtook Pioneer 10 as the second farthest spacecraft from the Sun. |
Launch and trajectory
The Voyager 2 probe was launched by NASA on August 20, 1977, from the Space Launch Complex 41 located at Cape Canaveral, Florida, using a Titan IIIE/Centaur launch vehicle. Two weeks later, on September 5, 1977, its twin, Voyager 1 probe, was launched. However, Voyager 1 reached both Jupiter and Saturn sooner as Voyager 2 had been launched into a longer, more circular trajectory.
Voyager 1’s initial orbit had an aphelion of only 8.9 AU (830 million mi; 1.33 billion km), less than one AU short of Saturn’s at 9.5 AU (880 million mi; 1.42 billion km). Voyager 2, by contrast had an aphelion of 6.2 AU (580 million mi; 930 million km), far short of Saturn’s orbit.
In April 1978, for a short period of time, no commands were sent to Voyager 2. The spacecraft switched from its primary radio receiver to its backup receiver. The primary receiver later failed completely. The backup receiver was operational but suffered from a dead capacitor within the receiver that made it capable of receiving transmissions only at one particular frequency. This frequency was affected by the Earth’s rotation (due to the Doppler effect) and the onboard receiver’s temperature, among other factors.
Encounter with Jupiter
Voyager 2’s closest approach to Jupiter occurred at 22:29 UT on July 9, 1979. It came within 570,000 km (350,000 mi) of the cloud tops of the planet. The Great Red Spot was characterized as a complex storm moving in a counterclockwise direction. Various smaller storms and eddies were seen within the banded clouds.
Voyager 2 · Jupiter · Io · Europa · Ganymede · Callisto
Voyager 2 sent back pictures of Jupiter and its moons Amalthea, Io, Callisto, Ganymede, and Europa. It was during a 10-hour “volcano watch” that it confirmed Voyager 1’s findings on active volcanism on the moon Io and revealed how the moon’s surface had changed in the four months since the previous visit. Together, the Voyagers saw the eruption of nine volcanoes on Io, and there is evidence that other eruptions took place between the two Voyager flybys.
Europa, one of Jupiter’s moons, showed a large number of intersecting linear features in the low-resolution photos taken by Voyager 1. Scientists initially thought that the features might be deep cracks, caused by crustal rifting or tectonic processes.
Closer high-resolution photos from Voyager 2, however, were puzzling: the features lacked topographic relief, and one scientist said they “might have been painted on with a felt marker.” Europa is internally active due to tidal heating at a level about one-tenth that of Io. Europa is assumed to have an ice crust a few tens of kilometers thick; probably less than 30 km (19 mi). It may just float on top of a 50 km (31 mi)-deep ocean.
Two new, small satellites, Adrastea and Metis, were found orbiting just outside the ring. A third new satellite, Thebe, was discovered between the orbits of Amalthea and Io.
Encounter with Saturn
The closest approach was made on 26 August 1981 at 03:24:05 UT. During this encounter, as Voyager 2 went behind Saturn as seen from Earth, it utilized its radio link to investigate the upper atmosphere of Saturn and gather temperature and pressure data. At pressures in the high atmospheric regions, the temperature, at 1.0 psi (70 mbar), was reported to be 82 K or −191.2 °C; −312.1 °F by Voyager 2.
Further into the atmosphere, at 1,200 mbar (17 psi) pressure, the temperature was 143 K (−130 °C; −202 °F). The spacecraft measured that the north pole was about 10 °C (18 °F) colder at 100 mbar (1.5 psi) compared to mid-latitudes, a variation possibly due to seasonal changes.
After the Saturn flyby, Voyager 2’s scan platform suffered an anomaly that caused its azimuth actuator to seize. This caused some data loss and made it difficult for the spacecraft to continue its mission. The anomaly was traced back to a combination of issues: a design flaw in the actuator shaft bearing and gear lubrication system, corrosion, and debris build-up.
While overuse and depleted lubricant were factors, other elements, such as dissimilar metal reactions and a lack of relief ports, compounded the problem. Engineers on the ground were able to issue a series of commands, rectifying the issue to a degree that allowed the scan platform to resume its function.
Voyager 2 had been intended for a Titan flyby in the event that Voyager 1 could not make it because of the technical failure, thus it did not pass near the Titan and eventually continued on the mission to go around the system of Uranus.
Encounter with Uranus
The closest approach to Uranus was on January 24, 1986, when Voyager 2 approached the cloudtops of the planet to a distance of 81,500 km (50,600 mi). Voyager 2 also discovered 11 previously unknown moons: Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck, and Perdita.
The mission also studied the unique atmosphere of the planet, caused by its axial tilt of 97.8°, and examined the Uranian ring system. A day on Uranus as determined by Voyager 2 lasted for 17 hours and 14 minutes.
Voyager 2 showed Uranus to possess a magnetic field, misaligned from the axis of rotation and all the previously visited planets, with a helix-shaped tail magnetic structure 10 million kilometers or 6 million miles in distance away from the Sun.
The most important cloud features on Voyager 2 were shrouded when it visited Uranus by a veil of haze; but images enhanced in contrast and in false colors reveal rings of concentric clouds around the south pole. In addition, it was observed that this area also emits an extremely large quantity of ultraviolet radiation, sometimes known as “dayglow.” The mean temperature of the atmosphere is approximately 60 K (-351.7 °F; -213.2 °C). The illuminated and dark poles, and most of the planet, show nearly the same temperatures at the cloud tops.
The Voyager 2 Planetary Radio Astronomy (PRA) experiment recorded 140 lightning flashes, or Uranian electrostatic discharges, at frequencies of 0.9-40 MHz. The UEDs were detected from 600,000 km of Uranus over 24 hours, most of which were not visible.
However, microphysical modeling suggests that Uranian lightning occurs in convective storms in deep troposphere water clouds. If this should be so, then lightning would not be seen because there are thick cloud layers above the troposphere. The power of Uranian lightning is approximately 10^8 W, emits 1×10^7 J – 2×10^7 J of energy, and lasts for an average of 120 ms.
Detailed images from Voyager 2’s flyby of the Uranian moon Miranda showed huge canyons formed from geological faults. One hypothesis suggests that Miranda might consist of a reaggregation of material following an earlier event when Miranda was shattered into pieces by a violent impact.
Voyager 2 revealed two previously undiscovered Uranian rings. The measurements indicated that the Uranian rings are quite distinct from those of Jupiter and Saturn. The Uranian ring system may be relatively young, and it did not form at the same time as Uranus. The particles which make up the rings could be the remains of a moon which was broken up by either a high-velocity impact or torn up by tidal effects.
After a reevaluation of the old data captured during the flyby, NASA astronomers announced in March 2020 that they detected a large atmospheric magnetic bubble known as a plasmoid being released into outer space from the planet Uranus.
Encounter with Neptune
After a course correction in 1987, the closest approach of Voyager 2 to Neptune was on August 25, 1989. Prior to the event, flight controllers computed the best trajectory for Voyager 2 through the Neptunian system via repeated computerized test simulations.
Since the plane of the orbit of Triton is tilted considerably relative to the plane of the ecliptic, Voyager 2 was steered into a minor orbit about 4,950 km (3,080 mi) above the north pole of Neptune through course corrections. Five hours after Voyager 2 came closest to Neptune, it flew by Neptunes largest moon, Triton, at a distance of about 40,000 km (25,000 mi).
In 1989, the Voyager 2 PRA experiment detected approximately 60 lightning flashes, or Neptunian electrostatic discharges, that emitted energies higher than 7×10^8 J. A plasma wave system (PWS) detected 16 electromagnetic wave events that occurred in the range of 50 Hz-12 kHz in magnetic latitudes of 7˚-33˚.
These plasma wave detections could have been initiated by lightning greater than 20 minutes above the clouds of ammonia in the magnetosphere. At Neptune’s closest approach by Voyager 2, the PWS instrument provided the first plasma wave detections over Neptune at a sample rate of 28,800 samples per second. Measured plasma densities were between 10–3 and 10–1 cm–3.
Voyager 2 discovered previously unknown Neptunian rings and confirmed six new moons: Despina, Galatea, Larissa, Proteus, Naiad, and Thalassa. During its passage through the neighborhood of Neptune, Voyager 2 discovered the “Great Dark Spot,” which has since disappeared, according to observations by the Hubble Space Telescope. The Great Dark Spot was later hypothesized to be a region of clear gas, forming a window in the planet’s high-altitude methane cloud deck.
Future of the probe
The probe is expected to continue sending weak radio signals until at least the mid-2020s, more than 48 years after it was launched. NASA says that “The Voyagers are destined—perhaps eternally—to wander the Milky Way.”
Voyager 2 is not going to any specific star. The closest star is 4.2 light-years away, and at 15.341 km/s, the spacecraft travels one light-year in about 19,541 years—during which time the nearby stars will also move considerably. In approximately 42,000 years, Voyager 2 will pass the star Ross 248 (10.30 light-years away from Earth) at a distance of 1.7 light-years. If left unimpeded for 296,000 years, Voyager 2 would fly by the star Sirius at a distance of 4.3 light-years from Earth (8.6 light-years from our planet).
Golden record
Both Voyager space probes carry a gold-plated audio-visual disc, a compilation intended to represent the diversity of life and culture on Earth, should either spacecraft ever be discovered by any extraterrestrial discoverer.
The record, photographed under the auspices of a team led by Carl Sagan and Timothy Ferris, depicts images of Earth and its organisms, a compendium of scientific data, audio messages of welcome from many world leaders and officials, such as the UN Secretary-General, the US President, and “Sounds of Earth,” which mixes whale calls and a crying infant with waves rolling onto a shoreline and a patchwork of music representative of various continents and centuries; it includes works from Wolfgang Amadeus Mozart and Blind Willie Johnson to Chuck Berry and Valya Balkanska.
Other Eastern and Western classics are represented, as well as performances of indigenous music from all over the world. The record also features greetings in 55 different languages. The project aimed to depict the richness of life on Earth and stand as a testament to human creativity and the desire to connect with the cosmos.
