The Voyager program is an American scientific program that launched two unmanned space missions, the probes Voyager 1 and Voyager 2. These were launched in 1977 to take advantage of a favorable alignment of the planets during the late 1970s. Although they were designated officially to study just the planetary systems of Jupiter and Saturn, the space probes were able to continue on their mission.
On August 25, 2012 Voyager 1 became the first human-made object to enter the previously unexplored region of space known as interstellar space, traveling "further than anyone, or anything, in history". Voyager 2 is expected to enter interstellar space within a few years of 2016, and its plasma spectrometer should provide the first direct measurements of the density and temperature of the interstellar plasma.
As of 2013, Voyager 1 was moving with a relative velocity to the Sun of 17 kilometres per second (11 mi/s). The amount of power available to the probe has decreased over time, and will no longer be able to power any single instrument by 2025.
Both of the Voyager missions into outer space have gathered large amounts of data about the gas giants of the solar system, and their orbiting satellites, about which little had been previously known. In addition, the trajectories of the two spacecraft have been used to place limits on the existence of any hypothetical trans-Neptunian planets.
Data and photographs collected by the Voyagers’ cameras, magnetometers, and other instruments revealed previously unknown details about each of the giant planets and their moons. Close-up images from the spacecraft charted Jupiter’s complex cloud forms, winds, and storm systems and discovered volcanic activity on its moon Io. Saturn’s rings were found to have enigmatic braids, kinks, and spokes and to be accompanied by myriad of “ringlets.” At Uranus Voyager 2 discovered a substantial magnetic field around the planet and 10 additional moons. Its flyby of Neptune uncovered three complete rings and six hitherto unknown moons as well as a planetary magnetic field and complex, widely distributed auroras.
These two space probes were built at the Jet Propulsion Laboratory in Southern California, and they were paid for by the National Aeronautics and Space Administration (NASA), which also paid for their launchings from Cape Canaveral, Florida, their tracking, and everything else concerning the space probes.
The two Voyager space probes were originally conceived as part of the Mariner program, and they were thus named Mariner 11 and Mariner 12. They were then moved into a separate program named Mariner Jupiter-Saturn, later renamed the Voyager Program because it was thought that the design of the two space probes had progressed sufficiently beyond that of the Mariner family that they merited a separate name.
The Voyager Program is essentially a scaled-back version of the program "Grand Tour" of the Outer Planets planned during the late 1960s and early 70s. Gary Flandro, an aerospace engineer at the Jet Propulsion Laboratory on the study team, discovered that the alignment of the outer planets would make it possible to use gravitational assists from Jupiter to go to Saturn, and thence on to Uranus and Neptune. The plan of the "Grand Tour" was to send several pairs of probes to fly by all the outer planets, including Pluto, along various trajectories, including Jupiter-Saturn-Pluto and Jupiter-Uranus-Neptune.
The major plans for the "Grand Tour" were dramatically scaled back because of lack of money appropriated by Congress. In the end, the Voyager Program fulfilled many of the flyby objectives of the "Grand Tour" excepting any mission to Pluto, and dual missions to Uranus and Neptune.
Of the two space probes of the Voyager Program, Voyager 2 was launched first. Its trajectory was designed to take advantage of an unusual alignment of the planets (that occurs once every 175 years) that allowed one space probe to fly by Jupiter, Saturn, Uranus, and Neptune, if everything went well. Of course, in the event of a serious malfunction involving some, or all of the space probe's radio transmitters or receivers, then that would have been the end of the long mission (to four planets), since there was no backup space probe to fill the gap. This was the gamble that NASA and the JPL were forced to take.
Voyager 1 was launched after its sister probe, but along a shorter and faster trajectory that sent it to Jupiter and Saturn sooner— and which unfortunately ruled out visits to the outer planets. Voyager 1 also had the high-priority mission of making a close fly-by of the Saturnian moon Titan, which was known to be quite large and to possess a dense atmosphere very much worth studying.
During the 1990s, Voyager 1 overtook the slower deep-space probes Pioneer 10 and Pioneer 11 to become the most distant man-made object from Earth, a record that it will keep for the foreseeable future. Even the faster (at its launch) New Horizons space probe will not surpass it, since the final speed of New Horizons (after maneuvering within the solar system) will be less than the current speed of Voyager 1.
Voyager 1 and Pioneer 10 are the most widely separated man-made objects anywhere, since they are traveling in roughly opposite directions from the Solar System.
Periodic contact has been maintained with Voyager 1 and Voyager 2 to monitor conditions in the outer expanses of the Solar System. The radioactive power sources of both spacecraft were still producing significant amounts of electric power as of 2012, keeping them operational, and it is hoped that this will allow the heliopause of the Solar System to be located and investigated.
In late 2003 Voyager 1 began sending data that seemed to indicate it had crossed the termination shock, but interpretations of these data are in dispute, and it was later believed that the termination shock was crossed in December 2004. The heliopause remains an unknown distance ahead.
On December 10, 2007, instruments on board Voyager 2 sent data back to Earth indicating that the solar system is asymmetrical. It has also reached the termination shock, about 10 billion miles from where Voyager 1 first crossed it, and is traveling outward at roughly 3.3 AU per year.
In August 2009 Voyager 1 was over 16.5 terameters (16.5×1012 meters, or 16.5×109 km, 110.7 AU, or 10.2 billion miles) from the Sun, and thus had entered the heliosheath region between the solar wind's termination shock and the heliopause (the limit of the solar wind). Beyond the heliopause is the bow shock of the interstellar medium, beyond which the probes enter interstellar space and the Sun's gravitational influence on them is exceeded by that of the Milky Way galaxy in general. At the heliopause, light from the Sun takes over 16 hours to reach the probe.
By December 2010 Voyager 1 had reached a region of space where there was no net velocity of the solar wind. At this point, the wind from the Sun may be canceled out by the interstellar wind. It does not appear that the spacecraft has yet crossed the heliosheath into interstellar space.
On June 10, 2011, scientists studying the Voyager data noticed what may be giant magnetic bubbles located in the heliosphere, the region of our solar system that separates us from the violent solar winds of interstellar space. The bubbles, scientists theorize, form when the magnetic field of the Sun becomes warped at the edge of our Solar System.
The Voyager spacecraft weighs 773 kilograms. Of this, 105 kilograms are scientific instruments. 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 pointed towards their targets, sometimes with the help of a movable instrument platform for the smaller instruments and the electronic photography system.
The diagram at the right shows the high-gain antenna (HGA) with a 3.7 m 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 UVS; 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. 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. The data 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 200 millimeter wide-angle lens with an aperture of f/3 (the wide angle camera), while the other uses a higher resolution 1500 millimeter narrow-angle f/8.5 lens (the narrow angle camera).
Unlike the other onboard 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. 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.
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 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 based on RCA CD4000 radiation-hardened, silicon-on-sapphire (SOS) custom-made integrated circuit chips, combined with standard transistor-transistor logic (TTL) integrated circuits.
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 3.7-meter high-gain antennas.
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. 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 was increased from 64 m to 70 m, dramatically increasing their areas for gathering weak microwave signals.
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. This was done at Goldstone, California, Canberra, and Madrid 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. Using this new technology of antenna arrays helped to compensate for the immense radio distance from Neptune to the Earth.
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, 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, such an RTG would inherently produce 470 W × 2−(34/87.74) ≈ 359 W, about 76% of its initial power. Additionally, the thermocouples that convert heat into electricity also degrade, reducing available 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.
Voyager Interstellar Mission
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. 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."
As of the present date, the Voyager 2 and Voyager 1 scan platforms, including all of the platform instruments, have been powered down. The ultraviolet spectrometer (UVS) on Voyager 1 was active until 2003, when it too was deactivated. Gyro operations will end in 2015 for Voyager 2 and 2016 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.
The two Voyager spacecraft continue to operate, with some loss in subsystem redundancy, but retain the capability of returning 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 until around 2025, after which there may not be available electrical power to support science instrument operation. At that time, science data return and spacecraft operations will cease.
The telemetry comes to the telemetry modulation unit (TMU) separately as a "low-rate" 40-bit-per-second (bit/s) channel and a "high-rate" channel.
Low rate telemetry is routed through the TMU such that it can only be downlinked as uncoded bits (in other words there is no error correction). At high rate, one of a set of rates between 10 bit/s and 115.2 kbit/s is downlinked as coded symbols.
The TMU encodes the high rate data stream with a convolutional code having constraint length of 7 with a symbol rate equal to twice the bit rate (k=7, r=1/2)
Voyager telemetry operates at these transmission rates:
- 7200, 1400 bit/s tape recorder playbacks
- 600 bit/s real-time fields, particles, and waves; full UVS; engineering
- 160 bit/s real-time fields, particles, and waves; UVS subset; engineering
- 40 bit/s real-time engineering data, no science data.
Note: At 160 and 600 bit/s different data types are interleaved.
The Voyager crafts have three different telemetry formats:
- CR-5T (ISA 35395) Science , note that this can contain some engineering data.
- FD-12 higher accuracy (and time resolution) Engineering data, note that some science data may also be encoded.
- EL-40 Engineering , note that this format can contain some science data, but not all systems represented.
- This is an abbreviated format, with data truncation for some subsystems.
It is understood that there is substantial overlap of EL-40 and CR-5T (ISA 35395) telemetry, but the simpler EL-40 data does not have the resolution of the CR-5T telemetry. At least when it comes to representing available electricity to subsystems, EL-40 only transmits in integer increments—so similar behaviours are expected elsewhere.
Memory dumps are available in both engineering formats. These routine diagnostic procedures have detected and corrected intermittent memory bit flip problems, as well as detecting the permanent bit flip problem that caused a two-week data loss event mid-2010.
Voyager Golden Record
Voyager 1 and 2 both carry with them a golden record that contains pictures and sounds of Earth, along with symbolic directions for playing the record and data detailing the location of Earth. The record is intended as a combination time capsule and interstellar message to any civilization, alien or far-future human, that may recover either of the Voyager craft. The contents of this record were selected by a committee that included Timothy Ferris and was chaired by Carl Sagan.
Pale blue dot
The Voyager program's discoveries during the primary phase of its mission, including never-before-seen close-up color photos of the major planets, were regularly documented by both 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 popularised by Carl Sagan with the quote:
"Consider again that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam".
- Timeline of Solar System exploration
- Pioneer program
- Planetary Grand Tour
- Family Portrait
- Tom Krimigis, PI for the LECP
- Jpl.Nasa.Gov. "Voyager Enters Interstellar Space - NASA Jet Propulsion Laboratory". Jpl.nasa.gov. Retrieved 2013-09-14.
- Cook, Jia-Rui C.; Agle, D. C.; Brown, Dwayne (12 September 2013). "NASA Spacecraft Embarks on Historic Journey Into Interstellar Space".
- Barnes, Brooks (September 12, 2013). "In a Breathtaking First, NASA Craft Exits the Solar System".
- Morin, Monte (September 12, 2013). "NASA confirms Voyager 1 has left the solar system". Los Angeles Times.
- "Voyager 1 has entered a new region of space, sudden changes in cosmic rays indicate". Retrieved 20 March 2013.
- "Report: Humanity Leaves the Solar System — Or Maybe Not". Time News Magazine. 2013-03-20. Retrieved 20 March 2013.
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- "Voyager Mission Operations Status Report # 2013-05-31, Week Ending May 31, 2013". JPL. Retrieved 19 August 2013.
- Chapter 11 "Voyager: The Grand Tour of Big Science" (sec. 268.), by Andrew,J. Butrica, found in From Engineering Science To Big Science ISBN 978-0-16-049640-0 edited by Pamela E. Mack, NASA, 1998
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- Chapter 11 "Voyager: The Grand Tour of Big Science" (sec. 269.), by Andrew,J. Butrica, found in From Engineering Science To Big Science ISBN 978-0-16-049640-0 edited by Pamela E. Mack, NASA, 1998
- Brown, Dwayne; Cook, Jia-Rui; Buckley, M. (December 14, 2010). "Nearing Interstellar Space, NASA Probe Sees Solar Wind Decline". Applied Physics Lab, Johns Hopkins University. Retrieved 2011-01-28.
- Smith, Catharine (2011-06-10). "WATCH: NASA Discovers 'Bubbles' At Solar System's Edge". Huffington Post.
- Amos, Jonathan (15 June 2012). "Particles point way for Nasa's Voyager". BBC News. Retrieved 15 June 2012.
- Ferris, Timothy (May 2012). "Timothy Ferris on Voyagers' Never-Ending Journey".
- Morin, Monte (September 12, 2013). "NASA confirms Voyager 1 has left the solar system". Los Angeles Times.
- "Report: Humanity Leaves the Solar System — Or Maybe Not". Time News Magazine. 2013-03-20. Retrieved 20 March 2013.
- Haynes, Robert. "How We Get Pictures from Space, Revised Edition". NASA facts. NTRS.
- Voyager - Spacecraft Nasa website
- "Voyager 1 Narrow Angle Camera Description". NASA / PDS. 2003-08-26. Retrieved 2011-01-17.
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- The Actinide Research Quarterly: Summer 1997
- "Interstellar Mission". NASA.
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- NASA - Transitional Regions at the Heliosphere's Outer Limits
- "Voyager – Spacecraft Lifetime NASA website". Retrieved 2011-09-13.
- NASA Voyager website – Main source of information.
- Voyager Mission state (more often than not at least 3 months out of date)
- Voyager Spacecraft Lifetime
- Space Exploration – Robotic Missions
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- Voyager 1 and 2 atlas of six Saturnian satellites (PDF format) 1984
- JPL Voyager Telecom Manual
NASA instrument information pages:
- "Voyager instrument overview".
- "CRS – COSMIC RAY SUBSYSTEM".
- "ISS NA – IMAGING SCIENCE SUBSYSTEM – NARROW ANGLE".
- "ISS WA – IMAGING SCIENCE SUBSYSTEM – WIDE ANGLE".
- "IRIS – INFRARED INTERFEROMETER SPECTROMETER AND RADIOMETER".
- "LECP – LOW ENERGY CHARGED PARTICLE".
- "MAG – TRIAXIAL FLUXGATE MAGNETOMETER".
- "PLS – PLASMA SCIENCE EXPERIMENT".
- "PPS – PHOTOPOLARIMETER SUBSYSTEM".
- "PRA – PLANETARY RADIO ASTRONOMY RECEIVER".
- "PWS – PLASMA WAVE RECEIVER".
- "RSS – RADIO SCIENCE SUBSYSTEM".
- "UVS – ULTRAVIOLET SPECTROMETER".
- 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
- Gray, Meghan. "Voyager and Interstellar Space". Deep Space Videos.