Voyager program

File:Voyager probes with the outer worlds.jpg

A poster of the planets and moons visited during the Voyager program.

The Voyager program is an American scientific program that employs two interstellar probes, Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment to explore the two gas giants Jupiter and Saturn and potentially also the ice giants, Uranus and Neptune—to fly near them while collecting data for transmission back to Earth. After Voyager 1 successfully completed its flyby of Saturn and its moon Titan, it was decided to send Voyager 2 on flybys of Uranus and Neptune.<ref name="The Fantastic Voyage of Voyager">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

After the planetary flybys were complete, decisions were made to keep the probes in operation to explore interstellar space and the outer regions of the Solar System. On 25 August 2012, data from Voyager 1 indicated that it had entered interstellar space.<ref name="JPL.NASA" /> On 5 November 2019, data from Voyager 2 indicated that it also had entered interstellar space.<ref name="NASA-20181210" /> On 4 November 2019, scientists reported that on 5 November 2018, the Voyager 2 probe had officially reached the interstellar medium (ISM), a region of outer space beyond the influence of the solar wind, as did Voyager 1 in 2012.<ref name="EA-20191104">Template:Cite news</ref><ref name="NYT-20191104">Template:Cite news</ref><ref name="NASA-Solar-System">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In August 2018, NASA confirmed, based on results by the New Horizons spacecraft, the existence of a "hydrogen wall" at the outer edges of the Solar System that was first detected in 1992 by the two Voyager spacecraft.<ref name="GRL-20180807">Template:Cite journal</ref><ref name="LS-20180809">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Template:As of the Voyagers are still in operation beyond the outer boundary of the heliosphere in interstellar space. Voyager 1 is moving with a velocity of Template:Convert, or 17 km/s, (10.5 miles/second) relative to the Sun, and is Template:Convert from the Sun<ref name="JPL.Voyager1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> reaching a distance of Template:Convert from Earth as of May 25, 2024.<ref name="voyager">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Template:As of, Voyager 2 is moving with a velocity of Template:Convert, or 15 km/s, relative to the Sun, and is Template:Convert from the Sun<ref name="JPL.Voyager2">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> reaching a distance of Template:Convert from Earth as of May 25, 2024.<ref name="voyager" />

The two Voyagers are the only human-made objects to date that have passed into interstellar space — a record they will hold until at least the 2040s — and Voyager 1 is the farthest human-made object from Earth.<ref name=":0" />

History

Mariner Jupiter-Saturn

File:Voyager Path.svg

The trajectories that enabled the Voyager spacecraft to visit the outer planets and achieve velocity to escape the Solar System

File:Voyager 2 velocity vs distance from sun.svg

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Voyager did things no one predicted, found scenes no one expected, and promises to outlive its inventors. Like a great painting or an abiding institution, it has acquired an existence of its own, a destiny beyond the grasp of its handlers.{{#if:Stephen J. Pyne<ref name="The Fantastic Voyage of Voyager"/>|{{#if:|}}

— {{#if:|, in }}Template:Comma separated entries

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The two Voyager space probes were originally conceived as part of the Planetary Grand Tour planned during the late 1960s and early 70s that aimed to explore Jupiter, Saturn, Saturn's moon Titan, Uranus, Neptune, and Pluto. The mission originated from the Grand Tour program, conceptualized by Gary Flandro, an aerospace engineer at the Jet Propulsion Laboratory, in 1964, which leveraged a rare planetary alignment occurring once every 175 years.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> This alignment allowed a craft to reach all outer planets using gravitational assists. The mission was to send several pairs of probes and gained momentum in 1966 when it was endorsed by NASA's Jet Propulsion Laboratory. However, in December 1971, the Grand Tour mission was canceled when funding was redirected to the Space Shuttle program.<ref name="GTN">Template:Cite book</ref>

In 1972, a scaled-down (four planets, two identical spacecraft) mission was proposed, utilizing a spacecraft derived from the Mariner series, initially intended to be Mariner 11 and Mariner 12. The gravity-assist technique, successfully demonstrated by Mariner 10, would be used to achieve significant velocity changes by maneuvering through an intermediate planet's gravitational field to minimize time towards Saturn.<ref name="HMSmurmeier1974">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The spacecrafts were then moved into a separate program named Mariner Jupiter-Saturn (also Mariner Jupiter-Saturn-Uranus,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> MJS, or MJSU), part of the Mariner program, later renamed because it was thought that the design of the two space probes had progressed sufficiently beyond that of the Mariner family to merit a separate name.<ref> Chapter 11 "Voyager: The Grand Tour of Big Science" Template:Webarchive (sec. 268.), by Andrew,J. Butrica, found in From Engineering Science To Big Science Template:ISBN edited by Pamela E. Mack, NASA, 1998</ref>

Voyager probes

File:Voyager Probe.stl

Interactive 3D model of the Voyager spacecraft .

On March 4, 1977, NASA announced a competition to rename the mission, believing the existing name was not appropriate as the mission had differed significantly from previous Mariner missions. Voyager was chosen as the new name, referencing an earlier suggestion by William Pickering, who had proposed the name Navigator. Due to the name change occurring close to launch, the probes were still occasionally referred to as Mariner 11 and Mariner 12, or even Voyager 11 and Voyager 12.<ref name="GTN" />

Two mission trajectories were established: JST aimed at Jupiter, Saturn, and enhancing a Titan flyby, while JSX served as a contingency plan. JST focused on a Titan flyby, while JSX provided a flexible mission plan. If JST succeeded, JSX could proceed with the Grand Tour, but in case of failure, JSX could be redirected for a separate Titan flyby, forfeiting the Grand Tour opportunity.<ref name="HMSmurmeier1974" /> The second probe, now Voyager 2, followed the JSX trajectory, granting it the option to continue on to Uranus and Neptune. Upon Voyager 1 completing its main objectives at Saturn, Voyager 2 received a mission extension, enabling it to proceed to Uranus and Neptune. This allowed Voyager 2 to diverge from the originally planned JST trajectory.<ref name="GTN" />

The probes would be launched in August or September 1977, with their main objective being to compare the characteristics of Jupiter and Saturn, such as their atmospheres, magnetic fields, particle environments, ring systems, and moons. They would fly by planets and moons in either a JST or JSX trajectory. After completing their flybys, the probes would communicate with Earth, relaying vital data using their magnetometers, spectrometers, and other instruments to detect interstellar, solar, and cosmic radiation. Their radioisotope thermoelectric generators (RTGs) would limit the maximum communication time with the probes to roughly a decade. Following their primary missions, the probes would continue to drift into interstellar space.<ref name="HMSmurmeier1974" />

Voyager 2 was the first to be launched. Its trajectory was designed to allow flybys of Jupiter, Saturn, Uranus, and Neptune. Voyager 1 was launched after Voyager 2, but along a shorter and faster trajectory that was designed to provide an optimal flyby of Saturn's moon Titan,<ref name="Swift1997">Template:Cite book</ref> which was known to be quite large and to possess a dense atmosphere. This encounter sent Voyager 1 out of the plane of the ecliptic, ending its planetary science mission.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Had Voyager 1 been unable to perform the Titan flyby, the trajectory of Voyager 2 could have been altered to explore Titan, forgoing any visit to Uranus and Neptune.<ref name="Bell2015">Template:Cite book</ref> Voyager 1 was not launched on a trajectory that would have allowed it to continue to Uranus and Neptune, but could have continued from Saturn to Pluto without exploring Titan.<ref name="Stern">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

During the 1990s, Voyager 1 overtook the slower deep-space probes Pioneer 10 and Pioneer 11 to become the most distant human-made object from Earth, a record that it will keep for the foreseeable future. The New Horizons probe, which had a higher launch velocity than Voyager 1, is travelling more slowly due to the extra speed Voyager 1 gained from its flybys of Jupiter and Saturn. Voyager 1 and Pioneer 10 are the most widely separated human-made objects anywhere since they are travelling in roughly opposite directions from the Solar System.

In December 2004, Voyager 1 crossed the termination shock, where the solar wind is slowed to subsonic speed, and entered the heliosheath, where the solar wind is compressed and made turbulent due to interactions with the interstellar medium. On 10 December 2007, Voyager 2 also reached the termination shock, about Template:Convert closer to the Sun than from where Voyager 1 first crossed it, indicating that the Solar System is asymmetrical.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In 2010 Voyager 1 reported that the outward velocity of the solar wind had dropped to zero, and scientists predicted it was nearing interstellar space.<ref>Template:Cite news</ref> In 2011, data from the Voyagers determined that the heliosheath is not smooth, but filled with giant magnetic bubbles, theorized to form when the magnetic field of the Sun becomes warped at the edge of the Solar System.<ref>Template:Cite news</ref>

In June 2012, Scientists at NASA reported that Voyager 1 was very close to entering interstellar space, indicated by a sharp rise in high-energy particles from outside the Solar System.<ref name="BBC-20120615">Template:Cite news</ref><ref name="Ferris-201205">Template:Cite magazine</ref> In September 2013, NASA announced that Voyager 1 had crossed the heliopause on 25 August 2012, making it the first spacecraft to enter interstellar space.<ref name="NASA-20130912">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="agu">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="NASA">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In December 2018, NASA announced that Voyager 2 had crossed the heliopause on 5 November 2018, making it the second spacecraft to enter interstellar space.<ref name="NASA-20181210"/>

Template:As of Voyager 1 and Voyager 2 continue to monitor conditions in the outer expanses of the Solar System.<ref name="NYT-20170905">Template:Cite news</ref> The Voyager spacecraft are expected to be able to operate science instruments through 2020, when limited power will require instruments to be deactivated one by one. Sometime around 2025, there will no longer be sufficient power to operate any science instruments.

In July 2019, a revised power management plan was implemented to better manage the two probes' dwindling power supply.<ref name="NASA-20190712">Template:Cite news</ref>

Spacecraft design

File:Voyager Program - spacecraft diagram.png

Voyager spacecraft diagram

The Voyager spacecraft each weighed Template:Convert at launch, but after fuel usage are now about Template:Convert.<ref name="FAQ"/> Of this weight, each spacecraft carries Template:Convert of scientific instruments.<ref>Template:Cite journal</ref> The identical Voyager spacecraft use three-axis-stabilized guidance systems that use gyroscopic and accelerometer inputs to their attitude control computers to point their high-gain antennas towards the Earth and their scientific instruments towards their targets, sometimes with the help of a movable instrument platform for the smaller instruments and the electronic photography system.

The diagram shows the high-gain antenna (HGA) with a Template:Convert diameter dish attached to the hollow decagonal electronics container. There is also a spherical tank that contains the hydrazine monopropellant fuel.

The Voyager Golden Record is attached to one of the bus sides. The angled square panel to the right is the optical calibration target and excess heat radiator. The three radioisotope thermoelectric generators (RTGs) are mounted end-to-end on the lower boom.

The scan platform comprises: the Infrared Interferometer Spectrometer (IRIS) (largest camera at top right); the Ultraviolet Spectrometer (UVS) just above the IRIS; the two Imaging Science Subsystem (ISS) vidicon cameras to the left of the UVS; and the Photopolarimeter System (PPS) under the ISS.

Only five investigation teams are still supported, though data is collected for two additional instruments.<ref>Voyager - Spacecraft Template:Webarchive Nasa website</ref> The Flight Data Subsystem (FDS) and a single eight-track digital tape recorder (DTR) provide the data handling functions.

The FDS configures each instrument and controls instrument operations. It also collects engineering and science data and formats the data for transmission. The DTR is used to record high-rate Plasma Wave Subsystem (PWS) data, which is played back every six months.

The Imaging Science Subsystem made up of a wide-angle and a narrow-angle camera is a modified version of the slow scan vidicon camera designs that were used in the earlier Mariner flights. The Imaging Science Subsystem consists of two television-type cameras, each with eight filters in a commandable filter wheel mounted in front of the vidicons. One has a low resolution Template:Convert focal length wide-angle lens with an aperture of f/3 (the wide-angle camera), while the other uses a higher resolution Template:Cvt narrow-angle f/8.5 lens (the narrow-angle camera).

Three spacecraft were built, Voyager 1 (VGR 77-1), Voyager 2 (VGR 77-3), and test spare model (VGR 77-2).Template:Sfn<ref name=":0">Template:Cite journal</ref>

Scientific instruments

Template:Nowrap

Instrument name	Abbreviation	Description
check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	Used a two-camera system (narrow-angle/wide-angle) to provide imagery of Jupiter, Saturn and other objects along the trajectory. Filters Narrow-angle camera<ref name="NACam3">{{#invoke:citation/CS1|citation CitationClass=web }}</ref> Name Wavelength Spectrum Sensitivity 0 – Clear 280–640 nm File:Voyager - Filters - Clear.png 4 – Clear 280–640 nm File:Voyager - Filters - Clear.png 7 – UV 280–370 nm File:Voyager - Filters - UV.png 1 – Violet 350–450 nm File:Voyager - Filters - Violet.png 2 – Blue 430–530 nm File:Voyager - Filters - Blue.png 5 – Green 530–640 nm File:Voyager - Filters - Green.png 6 – Green 530–640 nm File:Voyager - Filters - Green.png 3 – Orange 590–640 nm File:Voyager - Filters - Orange.png Wide-angle camera<ref name="WACam3">{{#invoke:citation/CS1|citation CitationClass=web }}</ref> Name Wavelength Spectrum Sensitivity 2 – Clear 280–640 nm File:Voyager - Filters - Clear.png 3 – Violet 350–450 nm File:Voyager - Filters - Violet.png 1 – Blue 430–530 nm File:Voyager - Filters - Blue.png 6 – CH4-U 536–546 nm File:Voyager - Filters - CH4U.png 5 – Green 530–640 nm File:Voyager - Filters - Green.png 4 – Na-D 588–590 nm File:Voyager - Filters - NaD.png 7 – Orange 590–640 nm File:Voyager - Filters - Orange.png 0 – CH4-JST 614–624 nm File:Voyager - Filters - CH4JST.png Principal investigator: Bradford A. Smith / University of Arizona Data: PDS/PDI data catalog, PDS/PRN data catalog
check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	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 the Saturn rings and the ring dimensions. Principal investigator: G. Tyler / Stanford University Data: PDS/PPI data catalog , PDS/PRN data catalog (VG_2803), NSSDC data archive
Infrared interferometer spectrometer and radiometer {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	Investigated both global and local energy balance and atmospheric composition. Vertical temperature profiles were also obtained from the planets and satellites, as well as the composition, thermal properties, and size of particles in Saturn's rings. Principal investigator: Rudolf Hanel / NASA Goddard Space Flight Center Data: PDS/PRN data catalog, PDS/PRN expanded data catalog (VGIRIS_0001, VGIRIS_002), NSSDC Jupiter data archive
Ultraviolet Spectrometer {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	Designed to measure atmospheric properties, and to measure radiation. Principal investigator: A. Broadfoot / University of Southern California Data: PDS/PRN data catalog
Triaxial Fluxgate Magnetometer {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }} File:Deployed magnetometer boom of one of NASA's Voyager PIA21738.jpg	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	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. Principal investigator: Norman F. Ness / NASA Goddard Space Flight Center Data: PDS/PPI data catalog , NSSDC data archive
Plasma Spectrometer {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }} File:PIA22922~orig.jpg	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	Investigated the macroscopic properties of the plasma ions and measures electrons in the energy range from 5 eV to 1 keV. Principal investigator: John Richardson / MIT Data: PDS/PPI data catalog , NSSDC data archive
Low Energy Charged Particle Instrument {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }} File:Voyager Low Energy Charged Particle Instrument.jpg	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	Measures the differential in energy fluxes and angular distributions of ions, electrons and the differential in energy ion composition. Principal investigator: Stamatios Krimigis / JHU/APL / University of Maryland Data: UMD data plotting, PDS/PPI data catalog , NSSDC data archive
Cosmic Ray System {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	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. Principal investigator: Edward Stone / Caltech / NASA Goddard Space Flight Center Data: PDS/PPI data catalog , NSSDC data archive
Planetary Radio Astronomy Investigation {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	Used a sweep-frequency radio receiver to study the radio-emission signals from Jupiter and Saturn. Principal investigator: James Warwick / University of Colorado Data: PDS/PPI data catalog, NSSDC data archive
Photopolarimeter System {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	Used a 6-inch f/1.4 Dahl-Kirkham-type Cassegrain telescope with an analyzer wheel containing five analyzers of 0,60,120,45 and 135 degrees and filter wheel with eight spectral bands covering 2350 to 7500A to gather information on surface texture and composition of Jupiter, Saturn, Uranus and Neptune and information on atmospheric scattering properties and density for these planets. Data: PDS/PRN data catalog and PDS Atmospheric Node
Plasma Wave Subsystem {{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}	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. Principal investigator: Donald Gurnett / University of Iowa Data: PDS/PPI data catalog

• Voyager instruments boom.jpg

  A view of some of Voyager's instruments from below. Left: the cameras, ultraviolet and infrared spectrometers (far left), plasma detector (black box lower right), particle and radiation detectors (far right). On the boom, center and right, are plasma, particle, and cosmic ray detectors.

• Voyager’s 13-meter-long magnetometer boom.jpg

  Voyager's fully extended 13-meter-long magnetometer boom

Computers and data processing

There are three different computer types on the Voyager spacecraft, two of each kind, sometimes used for redundancy. They are proprietary, custom-built computers built from CMOS and TTL medium-scale CMOS integrated circuits and discrete components, mostly from the 7400 series of Texas Instruments.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Total number of words among the six computers is about 32K. Voyager 1 and Voyager 2 have identical computer systems.<ref name="FAQ">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The Computer Command System (CCS), the central controller of the spacecraft, has two 18-bit word, interrupt-type processors with 4096 words each of non-volatile plated-wire memory. During most of the Voyager mission the two CCS computers on each spacecraft were used non-redundantly to increase the command and processing capability of the spacecraft. The CCS is nearly identical to the system flown on the Viking spacecraft.<ref name="Tomayko">Template:Cite book</ref>

The Flight Data System (FDS) is two 16-bit word machines with modular memories and 8198 words each.

The Attitude and Articulation Control System (AACS) is two 18-bit word machines with 4096 words each.

Unlike the other on-board instruments, the operation of the cameras for visible light is not autonomous, but rather it is controlled by an imaging parameter table contained in one of the on-board digital computers, the Flight Data Subsystem (FDS). More recent space probes, since about 1990, usually have completely autonomous cameras.

The computer command subsystem (CCS) controls the cameras. The CCS contains fixed computer programs such as command decoding, fault detection, and correction routines, antenna-pointing routines, and spacecraft sequencing routines. This computer is an improved version of the one that was used in the Viking orbiter.<ref name="Tomayko"/> The hardware in both custom-built CCS subsystems in the Voyagers is identical. There is only a minor software modification for one of them that has a scientific subsystem that the other lacks.

According to Guinness Book of Records, CCS holds record of "longest period of continual operation for a computer". It has been running continuously since 20 August 1977.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The Attitude and Articulation Control Subsystem (AACS) controls the spacecraft orientation (its attitude). It keeps the high-gain antenna pointing towards the Earth, controls attitude changes, and points the scan platform. The custom-built AACS systems on both craft are identical.

It has been erroneously reported<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> on the Internet that the Voyager space probes were controlled by a version of the RCA 1802 (RCA CDP1802 "COSMAC" microprocessor), but such claims are not supported by the primary design documents. The CDP1802 microprocessor was used later in the Galileo space probe, which was designed and built years later. The digital control electronics of the Voyagers were not based on a microprocessor integrated-circuit chip.

Communications

The uplink communications are executed via S-band microwave communications. The downlink communications are carried out by an X-band microwave transmitter on board the spacecraft, with an S-band transmitter as a back-up. All long-range communications to and from the two Voyagers have been carried out using their Template:Convert high-gain antennas. The high-gain antenna has a beamwidth of 0.5° for X-band, and 2.3° for S-band.<ref name=Ludwig2002/>Template:Rp (The low-gain antenna has a 7 dB gain and 60° beamwidth.)<ref name=Ludwig2002/>Template:Rp

Because of the inverse-square law in radio communications, the digital data rates used in the downlinks from the Voyagers have been continually decreasing the farther that they get from the Earth. For example, the data rate used from Jupiter was about 115,000 bits per second. That was halved at the distance of Saturn, and it has gone down continually since then.<ref name=Ludwig2002>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Some measures were taken on the ground along the way to reduce the effects of the inverse-square law. In between 1982 and 1985, the diameters of the three main parabolic dish antennas of the Deep Space Network were increased from Template:Convert<ref name=Ludwig2002/>Template:Rp dramatically increasing their areas for gathering weak microwave signals.

Whilst the craft were between Saturn and Uranus the onboard software was upgraded to do a degree of image compression and to use a more efficient Reed-Solomon error-correcting encoding.<ref name=Ludwig2002/>Template:Rp

Then between 1986 and 1989, new techniques were brought into play to combine the signals from multiple antennas on the ground into one, more powerful signal, in a kind of an antenna array.<ref name=Ludwig2002/>Template:Rp This was done at Goldstone, California, Canberra (Australia), and Madrid (Spain) using the additional dish antennas available there. Also, in Australia, the Parkes Radio Telescope was brought into the array in time for the fly-by of Neptune in 1989. In the United States, the Very Large Array in New Mexico was brought into temporary use along with the antennas of the Deep Space Network at Goldstone.<ref name=Ludwig2002/>Template:Rp Using this new technology of antenna arrays helped to compensate for the immense radio distance from Neptune to the Earth.

Power

File:MHW-RTGs.gif

RTGs for the Voyager program

Electrical power is supplied by three MHW-RTG radioisotope thermoelectric generators (RTGs). They are powered by plutonium-238 (distinct from the Pu-239 isotope used in nuclear weapons) and provided approximately 470 W at 30 volts DC when the spacecraft was launched. Plutonium-238 decays with a half-life of 87.74 years,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> so RTGs using Pu-238 will lose a factor of 1−0.5^(1/87.74) = 0.79% of their power output per year.

In 2011, 34 years after launch, the thermal power generated by such an RTG would be reduced to (1/2)^(34/87.74) ≈ 76% of its initial power. The RTG thermocouples, which convert thermal power into electricity, also degrade over time reducing available electric power below this calculated level.

By 7 October 2011 the power generated by Voyager 1 and Voyager 2 had dropped to 267.9 W and 269.2 W respectively, about 57% of the power at launch. The level of power output was better than pre-launch predictions based on a conservative thermocouple degradation model. As the electrical power decreases, spacecraft loads must be turned off, eliminating some capabilities. There may be insufficient power for communications by 2032.<ref>Template:Cite news</ref>

Voyager Interstellar Mission

File:PIA22835-VoyagerProgram&Heliosphere-Chart-20181210.png

Voyager 1 crossed the heliopause, or the edge of the heliosphere, in August 2012.
Voyager 2 crossed the heliosheath in November 2018.<ref name="NASA-20181210">Template:Cite news</ref><ref name="NASA-20181005">Template:Cite news</ref>

The Voyager primary mission was completed in 1989, with the close flyby of Neptune by Voyager 2. The Voyager Interstellar Mission (VIM) is a mission extension, which began when the two spacecraft had already been in flight for over 12 years.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The Heliophysics Division of the NASA Science Mission Directorate conducted a Heliophysics Senior Review in 2008. The panel found that the VIM "is a mission that is absolutely imperative to continue" and that VIM "funding near the optimal level and increased DSN (Deep Space Network) support is warranted."<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The main objective of the VIM was to extend the exploration of the Solar System beyond the outer planets to the heliopause (the farthest extent at which the Sun's radiation predominates over interstellar winds) and if possible even beyond. Voyager 1 crossed the heliopause boundary in 2012, followed by Voyager 2 in 2018. Passing through the heliopause boundary has allowed both spacecraft to make measurements of the interstellar fields, particles and waves unaffected by the solar wind. Two significant findings so far have been the discovery of a region of magnetic bubbles<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and no indication of an expected shift in the Solar magnetic field.<ref>Template:Cite journal</ref>

The entire Voyager 2 scan platform, including all of the platform instruments, was switched off in 1998. All platform instruments on Voyager 1, except for the ultraviolet spectrometer (UVS)<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> have also been switched off.

The Voyager 1 scan platform was scheduled to go off-line in late 2000 but has been left on to investigate UV emission from the upwind direction. UVS data are still captured but scans are no longer possible.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Gyro operations ended in 2016 for Voyager 2 and in 2017 for Voyager 1. Gyro operations are used to rotate the probe 360 degrees six times per year to measure the magnetic field of the spacecraft, which is then subtracted from the magnetometer science data.

On 14 November 2023, Voyager 1 stopped sending all telemetry and data, though the signal was still present. After months of experiments, made considerably more difficult by the 45 hour round trip time, the cause was traced to a bad memory chip. New software was written to avoid the bad memory block, and engineering data resumed on 20 April 2024.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Science data from two instruments resumed in May 2024,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and full recovery (of all science instruments that were still powered up) was in June 2024.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> For more details of this intricate operation, see Voyager 1.

The two spacecraft continue to operate, with some loss in subsystem redundancy but retain the capability to return scientific data from a full complement of Voyager Interstellar Mission (VIM) science instruments.

Both spacecraft also have adequate electrical power and attitude control propellant to continue operating and collecting science data through at least 2026.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Though additional science instruments may need to be turned off, the spacecraft are expected to be able to communicate until 2036, in the absence of additional failures.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Mission details

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By the start of VIM, Voyager 1 was at a distance of 40 AU from the Earth, while Voyager 2 was at 31 AU. VIM is in three phases: termination shock, heliosheath exploration, and interstellar exploration phase. The spacecraft began VIM in an environment controlled by the Sun's magnetic field, with the plasma particles being dominated by those contained in the expanding supersonic solar wind. This is the characteristic environment of the termination shock phase. At some distance from the Sun, the supersonic solar wind will be held back from further expansion by the interstellar wind. The first feature encountered by a spacecraft as a result of this interaction – between interstellar wind and solar wind – was the termination shock, where the solar wind slows to subsonic speed, and large changes in plasma flow direction and magnetic field orientation occur. Voyager 1 completed the phase of termination shock in December 2004 at a distance of 94 AU, while Voyager 2 completed it in August 2007 at a distance of 84 AU. After entering into the heliosheath, the spacecraft were in an area that is dominated by the Sun's magnetic field and solar wind particles. After passing through the heliosheath, the two Voyagers began the phase of interstellar exploration. The outer boundary of the heliosheath is called the heliopause. This is the region where the Sun's influence begins to decrease and interstellar space can be detected.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Voyager 1 is escaping the Solar System at the speed of 3.6 AU per year 35° north of the ecliptic in the general direction of the solar apex in Hercules, while Voyager 2Template:'s speed is about 3.3 AU per year, heading 48° south of the ecliptic. The Voyager spacecraft will eventually go on to the stars. In about 40,000 years, Voyager 1 will be within 1.6 light years (ly) of AC+79 3888, also known as Gliese 445, which is approaching the Sun. In 40,000 years Voyager 2 will be within 1.7 ly of Ross 248 (another star which is approaching the Sun), and in 296,000 years it will pass within 4.6 ly of Sirius, which is the brightest star in the night-sky.<ref name="JPL.NASA">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The spacecraft are not expected to collide with a star for 1 sextillion (10²⁰) years.<ref name=lavender>Template:Cite journal</ref>

In October 2020, astronomers reported a significant unexpected increase in density in the space beyond the Solar System, as detected by the Voyager space probes. According to the researchers, this implies that "the density gradient is a large-scale feature of the VLISM (very local interstellar medium) in the general direction of the heliospheric nose".<ref name="SA-20201019">Template:Cite news</ref><ref name="AJL-20200825">Template:Cite journal</ref>

Voyager Golden Record

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The cover of the Voyager Golden Record

Both spacecraft carry a Template:Convert golden phonograph record that contains pictures and sounds of Earth, symbolic directions on the cover for playing the record, and data detailing the location of Earth.<ref name="NYT-20170905" /><ref name="Ferris-201205" /> The record is intended as a combination time capsule and an interstellar message to any civilization, alien or far-future human, that may recover either of the Voyagers. The contents of this record were selected by a committee that included Timothy Ferris and was chaired by Carl Sagan.<ref name="Ferris-201205" />

Pale Blue Dot

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File:Pale Blue Dot.png

Seen from Template:Convert, Earth appears as a "pale blue dot" (the blueish-white speck approximately halfway down the light band to the right).

Pale Blue Dot is a photograph of Earth taken on February 14, 1990, by the Voyager 1 space probe from a distance of approximately Template:Nowrap kilometers (Template:Nowrap miles, 40.5 AU), as part of that day's Family Portrait series of images of the Solar System.<ref name="NASA-20200212">Template:Cite news</ref> The Voyager program's discoveries during the primary phase of its mission, including new close-up color photos of the major planets, were regularly documented by print and electronic media outlets. Among the best-known of these is an image of the Earth as a Pale Blue Dot, taken in 1990 by Voyager 1, and popularized by Carl Sagan,<ref>Template:Cite book</ref>

Consider again that dot. That's here. That's home. That's us....The Earth is a very small stage in a vast cosmic arena.... To my mind, there is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly and compassionately with one another and to preserve and cherish that pale blue dot, the only home we've ever known.{{#if:|{{#if:|}}

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See also

• Family Portrait
• The Farthest, a 2017 documentary on the program.
• Interstellar Express, a pair of Chinese probes inspired in part by the Voyagers.
• Interstellar probe
• Pioneer program
• Planetary Grand Tour
• Timeline of Solar System exploration

Further reading

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External links

Template:Sister project NASA sites

• NASA Voyager website
• Voyager Mission status (updated in real time)
• Voyager Spacecraft Lifetime
• NASA Facts – Voyager Mission to the Outer Planets
• Voyager 1 and 2 atlas of six Saturnian satellites, 1984
• JPL Voyager Telecom Manual

NASA instrument information pages:

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• Spacecraft Escaping the Solar System – current positions and diagrams
• NPR: Science Friday 8/24/07 Interviews for 30th anniversary of Voyager spacecraft
• Illustrated technical paper by RL Heacock, the project engineer
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• PBS featured documentary The Farthest-Voyager in Space
• Voyager image album by Kevin M. Gill