|Exploring The Planets
The Voyager Spacecraft
Diagram of Voyager Spacecraft
|Voyager is a Mariner spacecraft much like those
that have explored Mercury, Venus, and Mars. Because they traveled nearer
the Sun than Voyager, these earlier Mariners could be powered by solar
electric panels. Too little sunlight reaches the outer solar system
for the Voyagers to use this power source. Instead, they are equipped
with Radioisotope Thermoelectric Generators (RTG's) that convert
heat (generated by radioactive decay of plutonium) into electricity.
The Voyagers were designed with large antennae 3.7 meters (12 feet) in diameter to transmit data over great distances. Voyager 1 has transmitted data from more than 15 billion kilometers (9 billion miles) away.
Voyager Components and Instrumentation
- High Gain Antenna
- Voyager's antenna is a 3.7 meter (12 foot) diameter parabolic reflector. Data transmission can be as rapid as 115,200 bits (binary digits) per second (bps). In comparison, Mariner 4 transmitted pictures from Mars at the agonizingly slow rate of 8 1/3 bits per second in 1965.
The communication system is also used to probe planetary atmospheres by monitoring the strength of the signal as the spacecraft passes behind a planet.
- Sun Sensor
- The sensor views the Sun through a hole in the antenna. Similar instruments on the side of the spacecraft sense the star Canopus. By maneuvering the Voyager to keep the Sun and Canopus in sight of these sensors, the orientation of the spacecraft is fixed and the antenna points toward Earth.
- The bus or body of the spacecraft contains compartments for electronic circuits, such as the radio transmitter and computer.
- Distributed around the Voyager are 16 thrusters or small rockets powered by the decomposition of hydrazine. The thrusters are fired to change either the spacecraft's orientation or its velocity.
- Imaging System
- The imaging system is a pair of television cameras attached to telescopes with focal lenths of 200 millimeters (8 inches) for wide angle coverage and 1500 millimeters (59 inches) for high resolution. The cameras also have various filters so color pictures may be taken.
- Infrared Interferometer Spectrometer (IRIS)
- This instrument measures infrared radiation emitted or reflected by the planets. The data indicate the composition and temperature of the planets' atmospheres.
- The photopolarimeter measures the amount of light scattered or reflected from the planets at different wavelengths and angles. The data from this instrument provide information about the nature of planetary surfaces and particles in the atmosphere.
- Ultraviolet Spectrometer
- This spectrometer measures ultraviolet radiation emitted from the planets to determine the composition and structure of their atmospheres.
- Cosmic Ray Detectors
- This instrument records the number and energy of cosmic ray particles near the spacecraft. Cosmic rays are charged particles that travel through space at speeds nearly as great as that of light.
- Low-energy Charged Particle Detectors
- These detectors measure low-energy charged particles that are trapped in the radiation belts of planets.
- Plasma Detector
- Plasma is a gas composed of charged particles with very low energies. Whereas the other particle detectors count particles, the plasma detector measures the properties of the gas such as its density and pressure.
- These instruments measure the patterns of planetary magnetic fields. The detectors are mounted on a boom 13 meters (43 feet) long to minimize interference from magnetic fields generated by electronic instruments on the spacecraft.
- Planetary Radio Astronomy Antennae
- The radio astronomy receiver measures radio emissions from the planets. The same antennae are also used to measure the motion of particles in the plasma. The Voyager antennae are 10 meters (33 feet) long.
- Radioisotope Thermoelectric Generators (RTG's)
- Three RTG's provide electric power to Voyager. The generators produce about 1800 watts of heat by the radioactive decay of plutonium. The heat is then converted to about 400 watts of electric power by thermocouplers. The RTG's are mounted on a boom to protect the scientific instruments from excess heat and radioactivity.
- Calibration Plate
- Scientific instruments on the scan platform are calibrated by pointing them at the calibration plate whose reflectivity is known.
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|| Uranus || Neptune || Our Solar System
Exploring The Planets
©2002 National Air and Space Museum