The Further Adventures of Voyager

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Pioneer 11: First to Saturn, 1979

The first spacecraft to visit Saturn was actually Pioneer 11,

Pioneer 11 discovered a narrow ring, the F ring, just outside the A ring, and imaged one new satellite. It discovered a second satellite the hard way by almost colliding with it. It did not take a picture of the satellite but passed close enough behind it to sense its disturbance of Saturn's magnetic field.

Some of the hot-dogger types at NASA wanted to fly Pioneer 11 through the Cassini Division, but cooler heads prevailed, pointing out that there might be a lot of orbiting debris in the gap. This turned out to be true; images of the shaded side of Saturn's rings showed the gap brilliantly lit by sunlight reflected off fine particles. Flying through the Cassini Division would have been the equivalent of emptying buckshot into the spacecraft - a spectacular end to the mission, to be sure, but not a good use of a spacecraft.

Voyager 1 at Saturn

Voyager 1 passed closer to Jupiter and got a greater gravitational boost than Voyager 2, so it arrived at Saturn nine months earlier. In addition to imaging Saturn and the shaded side of its rings, it got good images of the satellites Mimas, Dione and Rhea. It also passed close by Titan; unfortunately, this maneuver put Voyager 1 on a path steeply inclined to the plane of the Solar System so that it could not make any further planetary encounters.

Voyager 2 at Saturn

Voyager 2 viewed the sunlit side of Saturn's rings and got closeups of the satellites Iapetus, Hyperion, Enceladus and Tethys, and very crude distant images of the distant outermost moon Phoebe. A lubrication problem in the scan platform caused some of the best pictures to be lost but the problem was resolved in time to permit successful flybys of Uranus and Neptune.

Voyager 2 at Uranus, 1986

Between Voyager's visit to Saturn and its arrival at Uranus in 1986, Voyager 2 was essentially re-engineered. Its computer was almost completely reprogrammed from Earth. Particular problems to be solved included compensating for the mechanical limitations of the partially-disabled camera boom, devising better data transmission and storage routines to compensate for the longer signal time to and from Earth, and providing for longer exposure times to compensate for the low light levels in the outer Solar System. To take some of its photos, Voyager would have to roll at a carefully-controlled rate to compensate for its own motion during the long exposure.

Voyager successfully imaged Uranus and its rings and the five large moons of Uranus. It also discovered numerous new small moons, including shepherd moons for some of the rings.

Voyager 2 at Neptune, 1989

Voyager succesfully imaged Neptune and its rings. The rings, previously thought to be incomplete ring arcs, were shown to be complete but uneven. Voyager obtained good closeups of part of Neptune's large moon Triton. The other previously known moon Nereid was only imaged from a great distance. In addition, Voyager discovered a number of new moons, one of which is larger than Nereid.

Beyond the Solar System

Four spacecraft have now left the Solar System: Pioneer 10 and 11, and Voyager 1 and 2. On February 14, 1990, Voyager 1 turned on its cameras one last time and took a photograph of the entire solar system. Actually, only six planets were imaged; Mercury and Mars were too close to the Sun from Voyager's vantage point to see and were lost in the solar glare, and Pluto is too faint. The picture is not widely published because there's not much to see: 60 mostly blank frames with the planets as tiny dots in a few of them.

On February 17, 1998, Voyager 1's greater speed finally overcame Pioneer 10's long head start and Voyager 1 became the most distant human object. Both spacecraft were 10.4 billion kilometers from the Sun. Voyager 1 is receding from the Solar System at 17.4 km/second (almost 40,000 miles an hour). Voyager 1 is moving in roughly the same direction as the Solar System, and its last major mission is to explore the heliopause; the shock wave that occurs when particles flowing outward from the Sun impact the gases of interstellar space. Voyager 1 is expected to encounter the heliopause sometime in the next few years.

Carrying on a tradition begun by the Pioneers, the Voyagers carried a record of human culture on a phonograph record.

Essential Points

Note: you will need to visit the planetary sites for some of this information.

Additional Information on the Outer Solar System

References

Pioneer 11 Saturn Encounter.
Special issue of Science, vol. 207, No. 4429, January 25, 1980.
Voyager 1 Saturn Encounter.
Special issue of Science, vol. 212, No. 4491, April 10, 1981.
Voyager 2 Saturn Encounter.
Special issue of Science, vol. 215, No. 4532, January 29, 1982.
Voyager 2 Uranus Encounter.
Special issue of Science, vol. 233, July 4 , 1986.
Voyager 2 Neptune Encounter.
Special issue of Science, vol. 246, No. 4936, December 15, 1989.
Voyager 2 Findings on Triton.
Special issue of Science, vol. 250, December 15, 1989.
Voyager Portrait of the Solar System:
Planetary Report, July-August 1990, pp. 12-17.

NASA Publications:

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Created 18 March 1998, Last Update 9 April 1998

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