Voyager program

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"Voyager spacecraft" redirects here. For the fictional starship from the Star Trek universe, see USS Voyager (Star Trek)

This article is about the deep-space probes. For the planned series of missions to Mars by the same name, see Voyager program (Mars)

The trajectories that enabled Voyager spacecraft to tour the four gas giant planets and achieve velocity to escape our solar system

The Voyager 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 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.

1 History
2 Spacecraft design
- 2.1 Power
- 2.2 Powering down
3 Voyager Golden Record
4 Fiction and popular culture
5 Notes and references
6 See also
7 External links

[edit] History

Location of the Pioneer and Voyager spacecraft with respect to Saturn, Uranus, Neptune, & Pluto as of October, 2006 Using the solar system simulator on the JPL web site

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.

Voyager 1 is thought to have penetrated the termination shock in late 2004

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 ^[1] as early as October 2005, before they would have observed the heliopause. However, the program continues to be funded into 2006.

[edit] Spacecraft design

Artist's concept of Voyager in flight

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).

[edit] Power

Radioisotope thermoelectric generators for the Voyager program.

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 Pu-238 will lose a factor of $1 - \sqrt[85]{0.5}$ of their power output per year. In 2006, 29 years after launch, such an RTG would produce only 470 W × 0.9919²⁹ ~= 371 W — or roughly 79% — of its initial power. However, since the bi-metallic thermocouples used to convert thermal energy into electrical energy degrade as well, the actual power generated will be lower. As of August 11th, 2006, the power generated by Voyager 1 and Voyager 2 had dropped to 290 W and 291 W respectively, about 60% 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 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.

[edit] Powering down

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)^[2] 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.

[edit] Voyager Golden Record

Main article: 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.

[edit] 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.

Spoiler warning: Plot and/or ending details about Star Trek: The Motion Picture follow.

Star Trek: The Motion Picture has as its premise an alien intelligence, V'ger which turns out to be the fictional Voyager 6. It is able to show the character Spock its history through holographic recordings, analogous to the Voyager Golden Disk, and is on a journey back to earth to bond with its creator.

In the television series Star Trek: Voyager the starship the crew travels on is named after the Voyager space probes. In the "Life Line" episode of that series, Dr. Lewis Zimmerman wrongfully mentions Voyager as Pioneer. This is an attempt at humor since both the Pioneer 10 and Pioneer 11 space probes shared the same fate as the Voyager 1 and Voyager 2 space probes. The Pathfinder project in the same episode probably references NASA's Pathfinder project.

In the animated television series Beast Wars: Transformers, the Predacon leader Megatron travels back in time and uses data encoded on Voyager 1's golden disk as a guide to altering Earth's history. "Code of Hero", "The Agenda: Part 2"

Stephen Baxter's novel Titan (1997) describes what will happen to the Voyager probes billions of years in the future as the metal from which they are constructed gradually disintegrates.

In L. Ron Hubbard's novel Battlefield Earth, aliens who stumble on Voyager and its golden contents proceed to find and conquer Earth.

In the X-Files episode "Little Green Men" in Season 2, Special Agent Fox Mulder (David Duchovny) hears part of the golden record played back to him in an extraterrestrial transmission received at Arecibo Observatory. The selection played is the Brandenburg Concerto part II by Bach.

John Carpenter's 1984 movie "Starman" opens with the Voyager 1 probe being intercepted by an alien spacecraft, whose occupants play the golden record. Accepting its invitation of friendship, the aliens send an emissary to visit Earth. Upon arrival, the emissary is shot down by US Fighter planes. The alien then assumes the form of a widow's deceased husband (Jeff Bridges) to make the hazardous journey to rendezvous with his mother-ship at Meteor Crater, Arizona. During the journey, the alien frequently sings or quotes excerpts from the soundtrack of Voyager's golden record.