Voyager 2 - WikiHQ

Voyager 2 is a space probe launched by NASA on August 20, 1977, as a part of the Voyager program. It was launched on a trajectory towards the gas giants (Jupiter and Saturn) and enabled further encounters with the ice giants (Uranus and Neptune). The only spacecraft to have visited either of the ice giant planets, it 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 successfully fulfilled its primary mission of visiting the Jovian system in 1979, the Saturnian system in 1981, Uranian system in 1986, and the Neptunian system in 1989. The spacecraft is currently in its extended mission of studying the interstellar medium. It is at a distance of from Earth .

The probe entered the interstellar medium on November 5, 2018, at a distance of from the Sun and moving at a velocity of Voyager 2 has begun to provide the first direct measurements of the density and temperature of the interstellar plasma.

Voyager 2 is in contact with Earth through the NASA Deep Space Network. Communications are the responsibility of Australia's DSS 43 communication antenna, near Canberra.

History

Background

In the early space age, it was realized that a periodic alignment of the outer planets would occur in the late 1970s and enable a single probe to visit Jupiter, Saturn, Uranus, and Neptune by taking advantage of the then-new technique of gravity assists. NASA began work on a Grand Tour, which evolved into a massive project involving two groups of two probes each, with one group visiting Jupiter, Saturn, and Pluto and the other Jupiter, Uranus, and Neptune. The spacecraft would be designed with redundant systems to ensure survival throughout the entire tour. By 1972 the mission was scaled back and replaced with two Mariner program-derived spacecraft, 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.

The primary mission of Voyager 1 was to explore Jupiter, Saturn, and Saturn's largest moon, Titan. Voyager 2 was also to explore Jupiter and Saturn, but on a trajectory that would have the option of continuing on to Uranus and Neptune, or being redirected to Titan as a backup for Voyager 1. Upon successful completion of Voyager 1s objectives, Voyager 2 would get a mission extension to send the probe on towards Uranus and Neptune. Titan was selected due to the interest developed after the images taken by Pioneer 11 in 1979, which had indicated the atmosphere of the moon was substantial and complex. Hence the trajectory was designed for optimum Titan flyby.

Spacecraft design

Constructed by the Jet Propulsion Laboratory (JPL), Voyager 2, whose bus is shaped like a decagonal prism, included 16 hydrazine thrusters, three-axis stabilization, gyroscopes and celestial referencing instruments (a Sun sensor, and a 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 also included 11 scientific instruments to study celestial objects as it traveled through space.

Communications

Built with the intent for eventual interstellar travel, Voyager 2 included a large, parabolic, high-gain antenna (see diagram) to transceive data via the Deep Space Network on Earth. Communications are conducted over the S-band (about 13 cm wavelength) and X-band (about 3.6 cm wavelength), providing data rates of up to 115.2 kilobits per second at the distance of Jupiter; this rates decreases according to inverse-square law as it travels farther away from Earth. When the spacecraft is out of line-of-sight and unable to communicate, a digital tape recorder (DTR) can record about 64 megabytes of data for transmission at another time.

Power

thumb|upright=1.2|Voyager RTG unit|left

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 required to achieve a Jupiter trajectory boost with an payload, the spacecraft included a propulsion module made of a solid-rocket motor and eight hydrazine monopropellant rocket engines, four providing pitch and yaw attitude control, and four for roll control. The propulsion module was jettisoned shortly 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 diameter spherical titanium tank. It contained of hydrazine at launch, providing enough fuel to last until 2034.

Scientific instruments

{| class="wikitable" style="text-align:center;"

! scope="col" style="width:135px;"| Instrument name

! scope="col" style="width:50px;"| Abr.

! Description

| (ISS)

| style="text-align:left;" | A two-camera system (narrow-angle/wide-angle) provides imagery of the outer planets and other objects along the trajectory.

{| class="wikitable collapsible"

! colspan="2" | Filters

{| style="text-align:center"

! colspan="4" scope="col" style="width:320px;"| Narrow Angle Camera Filters

! scope="col" style="background:#e5e5e5; width:60px;"| Name

! style="background: #e5e5e5" | Wavelength

! style="background: #e5e5e5" | Spectrum

! style="background: #e5e5e5" | Sensitivity

| Clear

| 280–640 nm; 460 nm center

| 50px|center

| style="background:#fff;"|

| UV

| 280–370 nm; 325 nm center

| 50px|center

| style="background: #1d0036" |

| Violet

| 350–450 nm; 400 nm center

| 50px|center

| style="background: #8300b5" |

| Blue

| 430–530 nm; 480 nm center

| 50px|center

| style="background: #00d5ff" |

| '

| '

| 50px|center

| '

| Green

| 530–640 nm; 585 nm center

| 50px|center

| style="background: #ffef00" |

| '

| '

| 50px|center

| '

| Orange

| 590–640 nm; 615 nm center

| 50px|center

| style="background: #ff8900" |

| '

| '

| 50px|center

| '

{| style="text-align:center"

! colspan="4" scope="col" style="width:320px;"| Wide Angle Camera Filters

! scope="col" style="background:#e5e5e5; width:60px;"| Name

! style="background: #e5e5e5" | Wavelength

! style="background: #e5e5e5" | Spectrum

! style="background: #e5e5e5" | Sensitivity

| Clear

| 280–640 nm; 460 nm center

| 50px|center

| style="background:#fff;"|

| '

| '

| 50px|center

| '

| Violet

| 350–450 nm; 400 nm center

| 50px|center

| style="background: #8300b5" |

| Blue

| 430–530 nm; 480 nm center

| 50px|center

| style="background: #00d5ff" |

| CH4-U

| 536–546 nm; 514 nm center

| 50px|center

| style="background: #81ff00" |

| Green

| 530–640 nm; 585 nm center

| 50px|center

| style="background: #ffef00" |

| Na-D

| 588–590 nm; 589 nm center

| 50px|center

| style="background: #ffe200" |

| Orange

| 590–640 nm; 615 nm center

| 50px|center

| style="background: #ff8900" |

| CH4-JST

| 614–624 nm; 619 nm center

| 50px|center

| style="background: #ff7b00" |

| (RSS)

| style="text-align:left;" | Used the telecommunications system of the Voyager spacecraft to determine the physical properties of planets and satellites (ionospheres, atmospheres, masses, gravity fields, densities) and the amount and size distribution of material in Saturn's rings and the ring dimensions.

| (IRIS)

| style="text-align:left;" | Investigates both global and local energy balance and atmospheric composition. Vertical temperature profiles are also obtained from the planets and satellites as well as the composition, thermal properties, and size of particles in Saturn's rings.

| (UVS)

| style="text-align:left;" | Designed to measure atmospheric properties, and to measure radiation.

| (MAG)

| style="text-align:left;" | Designed to investigate the magnetic fields of Jupiter and Saturn, the solar-wind interaction with the magnetospheres of these planets, and the interplanetary magnetic field out to the solar wind boundary with the interstellar magnetic field and beyond, if crossed.

| (PLS)

| style="text-align:left;" | Investigates the macroscopic properties of the plasma ions and measures electrons in the energy range from 5 eV to 1 keV.

| (LECP)

| style="text-align:left;" | Measures the differential in energy fluxes and angular distributions of ions, electrons and the differential in energy ion composition.

| (CRS)

| style="text-align:left;" | Determines the origin and acceleration process, life history, and dynamic contribution of interstellar cosmic rays, the nucleosynthesis of elements in cosmic-ray sources, the behavior of cosmic rays in the interplanetary medium, and the trapped planetary energetic-particle environment.

| (PRA)

| style="text-align:left;" | Uses a sweep-frequency radio receiver to study the radio-emission signals from Jupiter and Saturn.

| (PPS)

| style="text-align:left;" | Used a telescope with a polarizer to gather information on surface texture and composition of Jupiter and Saturn and information on atmospheric scattering properties and density for both planets.

| style="text-align:center" |(PWS)

| style="text-align:left;" | Provides continuous, sheath-independent measurements of the electron-density profiles at Jupiter and Saturn as well as basic information on local wave-particle interaction, useful in studying the magnetospheres.

</div>

Mission profile

{| class="wikitable collapsible"

! colspan="2" | Timeline of travel

! scope="col" style="width:120px;"| Date

! scope="col" style="width:440px;"| 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.

| style="vertical-align:top;" | 1979-04-25

| Start Jupiter observation phase.

{| class="wikitable collapsible collapsed"

! scope="col" style="width:90px;" | Time

! scope="col" style="width:350px;"| Event

| 1979-07-08

| Encounter with Jovian system.

| 12:21

| Callisto flyby at 214,930 km.

| 1979-07-09

| 07:14

| Ganymede flyby at 62,130 km.

| 17:53

| Europa flyby at 205,720 km.

| 20:01

| Amalthea flyby at 558,370 km.

| 22:29

| Jupiter closest approach at 721,670 km from the center of mass.

| 23:17

| Io flyby at 1,129,900 km.

| 1979-08-05

| Phase Stop

| style="vertical-align:top;" | 1981-06-05

| Start Saturn observation phase.

{| class="wikitable collapsible collapsed"

! scope="col" style="width:90px;"| Time

! scope="col" style="width:350px;"| Event

| 1981-08-22

| Encounter with Saturnian system.

| 01:26:57

| Iapetus flyby at 908,680 km.

| 1981-08-25

| 01:25:26

| Hyperion flyby at 431,370 km.

| 09:37:46

| Titan flyby at 666,190 km.

| 22:57:33

| Helene flyby at 314,090 km.

| 1981-08-26

| 01:04:32

| Dione flyby at 502,310 km.

| 02:22:17

| Calypso flyby at 151,590 km.

| 02:24:26

| Mimas flyby at 309,930 km.

| 03:19:18

| Pandora flyby at 107,000 km.

| 03:24:05

| Saturn closest approach at 161,000 km from the center of mass.

| 03:33:02

| Atlas 287,000 km.

| 03:45:16

| Enceladus flyby at 87,010 km.

| 03:50:04

| Janus at 223,000 km.

| 04:05:56

| Epimetheus at 147,000 km.

| 06:02:47

| Telesto at 270,000 km.

| 06:12:30

| Tethys flyby at 93,010 km.

| 06:28:48

| Rhea flyby at 645,260 km.

| 1981-09-04

| 01:22:34

| Phoebe flyby at 2,075,640 km.

| 1981-09-25

| Phase Stop

| style="vertical-align:top;" | 1985-11-04

| Start Uranus observation phase.

{| class="wikitable collapsible collapsed"

! scope="col" style="width:90px;"| Time

! scope="col" style="width:350px;"| Event

| 1986-01-24

| Encounter with Uranian system.

| 16:50

| Miranda flyby at 29,000 km.

| 17:25

| Ariel flyby at 127,000 km.

| 17:25

| Umbriel flyby at 325,000 km.

| 17:25

| Titania flyby at 365,200 km.

| 17:25

| Oberon flyby at 470,600 km.

| 17:59:47

| Uranus closest approach at 107,000 km from the center of mass.

| 1986-02-25

| Phase Stop

| style="vertical-align:top;" | 1989-06-05

| Start Neptune observation phase.

{| class="wikitable collapsible collapsed"

! scope="col" style="width:90px;"| Time

! scope="col" style="width:350px;"| Event

| 1989-08-25

| Encounter with Neptunian system.

| 03:56:36

| Neptune closest approach at 4,950 km.

| 04:41

| Galatea flyby at 18,360 km.

| 04:51

| Larissa flyby at 60,180 km.

| 05:29

| Proteus flyby at 97,860 km.

| 09:23

| Triton flyby at 39,800 km.

| 1989-10-02

| Phase Stop

| 1989-10-02

| Begin Voyager Interstellar Mission.

! colspan="2" scope="col" | Interstellar phase

| 1998-11-13

| Terminate scan platform and UV observations.

| 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.

| 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.

| 2024-10-01

| Turned off the plasma science instrument.

| 2025-03-24

| Turned off the low-energy charged particle instrument.

Launch and trajectory

The Voyager 2 probe was launched on August 20, 1977, by NASA from Space Launch Complex 41 at Cape Canaveral, Florida, aboard a Titan IIIE/Centaur launch vehicle. Two weeks later, the twin Voyager 1 probe was launched on September 5, 1977. However, Voyager 1 reached both Jupiter and Saturn sooner, as Voyager 2 had been launched into a longer, more circular trajectory.

Voyager 1s initial orbit had an aphelion of , just a little short of Saturn's orbit of . Whereas, Voyager 2s initial orbit had an aphelion of , well short of Saturn's orbit.

In April 1978, no commands were transmitted to Voyager 2 for a period of time, causing the spacecraft to switch from its primary radio receiver to its backup receiver. Sometime afterwards, the primary receiver failed altogether. The backup receiver was functional, but a failed capacitor in the receiver meant that it could only receive transmissions that were sent at a precise frequency, and this frequency would be affected by the Earth's rotation (due to the Doppler effect) and the onboard receiver's temperature, among other things.

File:Titan 3E Centaur launches Voyager 2.jpg|Voyager 2 launch on August 20, 1977, with a Titan IIIE/Centaur

File:Animation of Voyager 2 trajectory.gif|Animation of Voyager 2 trajectory from August 20, 1977, to December 30, 2000

File:Voyager 2 path.svg|Trajectory of Voyager 2 primary mission

File:Voyager 2 velocity vs distance from sun.svg|Plot of Voyager 2 distance from, and velocity with respect to, the Sun, illustrating the use of gravity assists to accelerate the spacecraft by Jupiter, Saturn and Uranus.

</gallery>

Encounter with Jupiter

thumb|Animation of Voyager 2s trajectory around Jupiter

thumb|The trajectory of Voyager 2 through the Jovian system

Voyager 2s closest approach to Jupiter occurred at 22:29 UT on July 9, 1979.

Jupiter's Great Red Spot was revealed as a complex storm moving in a counterclockwise direction. Other smaller storms and eddies were found throughout the banded clouds.

Voyager 2 returned images of Jupiter, as well as its moons Amalthea, Io, Callisto, Ganymede, and Europa. When Voyager 2 passed behind Saturn, viewed from Earth, it uses its radio link to investigate Saturn's upper atmosphere, gathering data on both temperature and pressure. In the highest regions of the atmosphere, where the pressure was measured at , Voyager 2 recorded a temperature of . Deeper within the atmosphere, where the pressure was recorded to be , the temperature rose to . Voyager 2, which would have been diverted to perform the Titan flyby if Voyager 1 had been unable to, did not pass near Titan due to the malfunction, and subsequently, proceeded with its mission to explore the Uranian system.

Encounter with Uranus

The closest approach to Uranus occurred on January 24, 1986, when Voyager 2 came within of the planet's cloudtops. Voyager 2 also discovered 11 previously unknown moons: Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck and Perdita.