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Voyager program was designed to study the planets and outer solar system.
Voyager space program consists of a pair of unmanned scientific probes, Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s. Although they were officially designated to study just Jupiter and Saturn, the two probes were able to continue their mission into the outer solar system. They have since continued out and exited the solar system. These Voyager space program probes were built at JPL and were funded by NASA.
Both missions have gathered large amounts of data about the gas giants of the Solar System, of which little information was known. In addition, the spacecraft trajectories have been used to place limits on the existence of a hypothetical post-Plutonian Planet X.
History of the Voyager space program.
The Voyager probes were originally conceived as part of the Mariner program, called Mariner 11 and Mariner 12, respectively. It was originally named Mariner Jupiter-Saturn', but later retitled Voyager because it was more appealing and romantic. Voyager is a scaled-back version of the Grand Tour program of the late 1960s and early 1970s. The Grand Tour's plan was to send a pair of probes to fly by all the outer planets; it was scaled back because of budget cuts. However, in the end, Voyager fulfilled all the Grand Tour flyby objectives except for Pluto, which was then considered a planet.
In the 1990s, Voyager 1 overtook the slower travelling Pioneer 10 to become the most distant human made artifact in space. It will keep that record for at least several decades; even the fast (at launch) New Horizons probe will not catch up with it since its final speed will be less than Voyager 1's. Voyager 1 and Pioneer 10 are also the most widely-separated man made objects in the Universe because they are travelling in roughly opposite directions from the sun.
Periodic contact has been maintained with both probes to monitor conditions in the outer expanses of the solar system. The crafts' radioactive power sources are still producing electrical energy, fuelling hopes of locating the solar system's Heliopause. In late 2003, Voyager 1 began sending data that seemed to indicate it had crossed the Termination Shock, but interpretations of this data are in dispute. It is now believed that the termination shock was crossed in December 2004, with the heliopause an unknown distance ahead.
Due to budget shifts prompted by George W. Bush's Vision for Space Exploration, it was rumored that the probes were to be deactivated and abandoned as early as October 2005, before they would have observed the Heliopause. However, the program continues to be funded into 2006.
Voyager Spacecraft design.
The identical Voyager spacecraft are three-axis stabilized systems that use celestial or gyro referenced attitude control to maintain pointing of the high-gain antennas toward Earth. The prime mission science payload consisted of 10 instruments (11 investigations including radio science).
Only five investigator 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 8 filters in a commandable Filter Wheel mounted in front of the vidicons. One has a low resolution 200 mm wide-angle lens with an aperture of f/3 (Wide Angle Camera), while the other uses a higher resolution 1500 mm narrow-angle f/8.5 lens (Narrow Angle Camera).
Unlike the other onboard instruments, operation of the cameras is not autonomous, but is controlled by an imaging parameter table residing in one of the spacecraft computers, the Flight Data Subsystem (FDS).
The computer command subsystem (CCS) provides sequencing and control functions. The CCS contains fixed routines such as command decoding and fault detection and corrective routines, antenna pointing information, and spacecraft sequencing information.
The Attitude and Articulation Control Subsystem (AACS) controls the spacecraft orientation, maintains the pointing of the high-gain antenna towards Earth, controls attitude maneuvers, and positions the scan platform.
Uplink communications is via S band (16-bit/s command rate) while an X band transmitter provides downlink telemetry at 160 bit/s normally and 1.4 kbit/s for playback of high-rate plasma wave data. All data are transmitted from and received at the spacecraft via the 3.7-meter high-gain antenna (HGA).
Power for the Voyager spacecraft.
Electrical power is supplied by three radioisotope thermoelectric generators (RTGs). The radioisotope thermoelectric generators are powered by plutonium, and provided approximately 470 W of 30-volt dc when the spacecraft was launched. Plutonium-238 decays with a radioactive half-life of approximately 85 years, so RTGs using it lose a factor of of their power output per year, approximately 0.81%. 23 years after launch, such an RTG would produce only 470 W × 0.991923 ~= 390 W - or roughly 83% - of the initial power. However, the bi-metallic thermocouples used to convert thermal energy into electrical energy degrade as well; by the beginning of 2001, the power generated by Voyager 1 and Voyager 2 had dropped to 315 W and to 319 W respectively, about 80% of the power output at launch. Both of these power levels represent better performance than the pre-launch predictions, which included a conservative degradation model for the thermocouples. As of July 14, 2006, power levels are about 290 W for each spacecraft. As the electrical power decreases, power loads on the spacecraft must be deactivated in order to avoid exceeding its remaining power supply. As loads are turned off, some spacecraft capabilities are eliminated.
Powering down the Voyager spacecraft.
To date, the entire Voyager 2 and Voyager 1 scan platform, including all of the platform instruments, has been powered down. The ultraviolet spectrometer (UVS) on Voyager 1 was on until 2003, when it too was deactivated. Gyro operations will end in 2010 for Voyager 2 and 2011 for Voyager 1. Gyro operations are used to rotate the probe 360 degrees six times a 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 science data from a full complement of VIM science instruments. Both spacecraft also have adequate electrical power and attitude control propellant to continue operating until around 2020, when the available electrical power will no longer support science instrument operation. At this time, science data return and spacecraft operations will cease.
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 recovers either of the Voyager craft. The contents of this record were selected by a committee chaired by Carl Sagan.
Voyager space program in fiction and popular culture.
The Voyager launches occurred just before the dawn of the media-savvy 1980s, and the program's discoveries during the primary phase of its mission, including striking never-before-seen close up color photos of the major planets, were regularly documented by both print and electronic media outlets. As a result, the Voyager program, especially at the high points of its mission, has seen significant public limelight. As a result, there are a number of references to the Voyager program or to the particular probes themselves within popular culture.
The section Voyager 2 in fiction and popular culture in the Voyager 2 article contains specific references to Voyager 2 in pop culture.
Voyager space program spoiler warning: Plot and/or ending details about Star Trek: The Motion Picture follow.
Spoilers end here.
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