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Voyager program

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"Voyager spacecraft" redirects here. For the fictional starship from the television show Star Trek: Voyager, 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)
For all other uses see Voyager.
The trajectories that enabled Voyager spacecraft to visit the outer planets and achieve velocity to escape our solar system



Spacecraft design

Voyager 2 passing Saturn (Image generated with Celestia)

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.[1] 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 Voyager spacecraft have three RCA 1802 CPUs running at 6.4 MHz. These CPUs sent to space were operating at full military specification temperatures (-55 to +125 °C).

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 is transmitted from and received at the spacecraft via the 3.7-meter high-gain antenna.

Power

Radioisotope thermoelectric generators for the Voyager program.

Electrical power is supplied by three 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, [2] so RTGs using Pu-238 will lose a factor of of their power output per year. In 2006, 29 years after launch, such an RTG would produce only 470 W × 2-(29/87.74) ~= 373 W — or about 79.5% — of its initial power. However, the bi-metallic thermocouples that convert heat into electricity also degrade, so the actual power will be even lower. As of August 11 2006, the power generated by Voyager 1 and Voyager 2 had dropped to 290 W and 291 W respectively, about 60% of the power at launch. This is better than the pre-launch predictions based on a conservative thermocouple degradation model. As the electrical power decreases, spacecraft loads must be turned off, eliminating some spacecraft capabilities.

Powering down

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)[3] on Voyager 1 was active 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 scientific 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 that time, science data return and spacecraft operations will cease.

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.

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.

  • 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.
  • John Carpenter's 1984 movie Starman opens with the Voyager 1 probe being intercepted by an alien spacecraft, whose occupants play the golden record.
  • In the Beast Wars transformers cartoon, Megatron steals the Voyager golden records from Cybertron and tries to use them in a conquest of prehistoric Earth. He uses their images to find and change human prehistory.

Notes and references

  1. ^ -Nasa Website Voyager
  2. ^ The Actinide Research Quarterly: Summer 1997
  3. ^ "Ultraviolet Spectrometer". Voyager: The Interstellar Mission. NASA JPL. Retrieved 2006-06-11.

See also


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