On August 30, 1977 Voyager II was launched from Cape Canaveral aboard an Titan/Centaur. Its companion spacecraft Voyager I was launched sixteen days later on September 5, 1977. Ultimately their goal was to enable us to better understand the solar system. More specifically they were designed to perform flybys of both Jupiter and Saturn. During theses flybys they would take "pictures" of these two planets and their moons in a broad range of wavelengths. They would also investigate the planet's magnetic fields and several other characteristics of the planets.
The original design for Voyager was to produce one spacecraft that would visit all of the outer planets. As is true for many missions, funding was a major constraint. After extensive study it was determined that this design would be to costly. The existing mission, two satellites visiting only Jupiter and Saturn, flew as a budget compromise. The second largest constraint was the time frame for the launch. Only once in every 176 years is the geometry of the outer planets such that a space craft could visit all of them without major boosters and fuel.
The two space crafts were nearly identical with only a few minor differences. They consisted of two major units: the Control and Communications Subsystems and the Instrument Subsystems. The Control and Communications Subsystems consisted of the following elements: The Attitude and Articulation Control Subsystem, the High Gain Antenna, the Computer Command Subsystem, the Flight Data Subsystem, and the Radioisotope Thermoelectric Generators. The eleven Instrument Subsystems will be described in greater detail in the following paragraphs.
The Imaging Science Subsystem (ISS) consisted of two cameras, one wide angle and one narrow angle. Utilizing eight filters they would produce 800x800 pixel pictures of the target body in wavelengths from slightly ultraviolet through the visible spectrum.
The Infrared Interferometer Spectrometer and Radiometer (IRIS) worked in the ultraviolet, visible and infrared ranges and among other uses it could determine the presence of different molecules from their absorption spectrums.
The Ultraviolet Spectrometer (UVS) was also used to determine the presence of different molecules form their absorption spectrums.
The Photopolarimeter Subsystem (PPS) was the most sensitive sensor on Voyager to visible light. Two of its scientific uses were to infer the texture and composition of solid surfaces and to determine the density, particle size, and composition of the rings.
The Planetary Radio Astronomy (PRA) subsystem used a pair of ten meter antenna to listen to radio signals produced by the sun and the planets.
The Plasma Wave Subsystem (PWS) was essentially a radio receiver and amplifier. It would listen to frequencies that the human ear could hear.
The Radio Science Subsystem (RSS) was mainly used to communicate scientific and engineering data back to the earth. It was also used to perform many experiments including but not limited to: probing planetary/satellite atmospheres to determine temperature, pressure, density and composition; determining the mass of objects passing close to voyager through the imposed Doppler shifts; and the testing of general relativity through the measuring of the slowing of the signals as they pass massive objects.
The Magnetometer (MAG) subsystem measures changes in the sunŐs magnetic field with distance and time to determine if each outer planet has a magnetic field and how moons and rings interact with the field.
The Plasma Subsystem (PLS) captured small, low energy, charged particles examining their speed and direction.
The Low-Energy Charged Particle (LECP) and Cosmic Ray subsystem (CRS) examined particles with higher energies than the PLS. Both of these instruments had a limited ability to determine the energy of the particle, its direction, and it composition.
To store all the information that these instruments gather while the space craft cannot transmit to earth the Voyager has a 61 MB tape that can record at two speeds of 115.2 Kbps and 7.2 Kbps. Playback can be achieved at two speeds of 21.6 Kbps and 7.2 Kbps.
The space crafts were launched on August 30 and September 5, 1977. At the end of their boost phase they had achieved a velocity of approximately 14.4 km/sec. On their eighteen month journey to Jupiter they spent over nine months crossing the asteroid belt. Voyager I started its observation phase of Jupiter in January of 1979. During its closest approach to the planet, 277,400 km, on March 5 the PPS failed rendering it completely inoperative. While in the Jovian system Voyager's trajectory sent it within 22,000 km of Io, and it also made detailed observations of Eruropa, Ganymede, and Callisto. Voyager I also used Jupiter's emnse gravity to assist it on to Saturn at an additional 16 km/sec. Then in mid-April Voyager I ended its observations of Jupiter having returned over 18,800 images of the planet and its moons.
Voyager II suffered many problems even before it encountered Jupiter. On September 23, 1977 a major problem degraded the telemetry system. Almost seven months later command receiver #1 failed and command receiver #2 was damaged. Then finally in April of 1979 Voyager II began observing Jupiter. To safeguard the space craft it traveled a much more cautious route through the Jovian system. Voyager II would only come within 650,180 km of Jupiter, and make detailed observations of Eroupa, Ganymede, and Callisto. This cautious approach was made able by the great success of Voyager I's encounter of the system. Like its companion Voyager II also used Jupiter's gravity to propel it on to Saturn at an additional 10 km/sec. When Voyager II turned its cameras away from the system it had taken over 14,900 images.
The two main highlights of Voyager's encounter with the Jovian system were the discovery of Jupiter's narrow dusty rings and the discovery of nine active volcanoes on Io.
Voyager I made its closest approach of Saturn, 123,910 km, on November 12, 1980. Along with many observations of Saturn itself it made detailed observations of Titan, Rhea, Dione, and Mimas. By the time Voyager I left the system it had returned over 13,550 images to earth. This encounter with Saturn changed its trajectory by 45 deg and set its departure speed from the solar system at 16.7 km/sec.
Voyager II made its closes approach of Saturn, 100,830 km, on July 25, 1981. This encounter sent it on a trajectory for Uranus with an additional speed of 5 km/sec. While in the system Voyager II made detailed observations of Enceladus, Tethys, Hyperion, Iapetus, and Phobe. By the time Voyager II completed its observations it had returned over 11,850 images of the system.
The major highlights of Voyager's encounter with Saturn are the discovery of 1000+ mph winds on Saturn, detailing its elaborate, varied structure of rings, and the discovery that Titan's atmosphere is 90% nitrogen.
Voyager II continued on to Uranus and it came within 81,440 km of the planets surface on January 24, 1986. While in the system it investigated Uranus itself and also Miranda, Titania, Ariel, Umbriel, and Oberon. Apon completion of its observations of the system Voyager II would return over 5,800 images. Using Uranus' gravity to direct it on to Neptune Voyager II gained about 3 km/sec.
The major highlights of Voyager's encounter with Uranus were the discovery of its tilted, off-center magnetic field and the discovery of ten new moons and two new rings.
On August 25, 1989 Voyager II made its closest approach to Neptune of 29,183 km. This is only about 4,800 km from the cloud tops. While in the system Voyager also made detailed observations of Triton. Unlike Voyager II's encounter with Jupiter, Saturn, and Uranus its trajectory through the Neptonian system will slow the space craft down by about 4 km/sec giving it a final departure speed from the solar system of approximately 16 km/sec.
The Voyager project was much more successful than planed. The success of Voyager I's encounters with Jupiter and Saturn enabled the engineers to "save" Voyager II during its encounters with these planets and then redirect it on towards Uranus and Neptune. The project returned a vast amount of data, the images from Uranus alone amount to over 4.5 GB, that is still being processed and reprocessed. One major aspect of the mission that enabled them to be so successful was that all of the Command and Control subsystems had redundant backups. If the redundants were not used Voyager II would have been lost before it had even reached Jupiter. The greatest strength of the project was the creativeness of the engineers during the mission. They were able to fix several major problems with the spacecraft during its mission and they also developed and implemented new methods of communicating with the space craft at these massive distances. As stated before many things went wrong during the mission but over all it has been a tremendous success.
Sunday, 01-Aug-2004 00:36:47 CDT
CSR/TSGC Team Web
