Voyager 2
Published on Jul 17, 2007 at 11:54 pm.
2 Comments.
Filed under space exploration, wonders.
My fifth choice in my list of 7 wonders of space exploration is Voyager 2. Really, this could be both Voyagers, but to keep it similar to the other entries in my list, I picked a single craft.
The planets of the Solar System all move around. In the 1970s, they were positioned such that a spacecraft could visit each of the outer planets. The spacecraft could be sent to Jupiter, and Jupiter’s gravity would hurl the spacecraft onward to Saturn in a maneuver called a gravity assist or slingshot maneuver. Saturn, then, could hurl the spacecraft onward to Uranus, which would hurl the spacecraft past Neptune. Such an alignment would not happen again in the near future, so NASA wanted to send an ambitious and advanced spacecraft called the Grand Tour. However, budget constraints cut back the size and cost of the spacecraft. Instead, two advanced Mariner class probes would be sent. In fact, these probes were initially designated Mariner 11 and Mariner 12. However, as they were the only Mariner probes to be sent on trajectories leaving the Solar System, they were renamed Voyager 1 and Voyager 2.
Unlike the other Mariner spacecraft, the Voyagers were going too far from the Sun for solar panels to provide sufficient electrical power to operate the spacecraft’s equipment. So, the Voyagers were powered with radiothermal generators (RTGs), which produced electricity from the heat of the radioactive decay of plutonium. When the spacecraft were launched in 1977, the RTGs provided 470W of power. However, the radioactive decay of the plutonium that provides the power also reduces the amount of plutonium available, so the RTGs are constantly losing the ability to produce electricity. Now, 30 years later, the RTGs are providing less than 290W of power. Already the most power hungry instruments have been turned off. By 2016, the RTGs would have decayed enough that there would be very little power left, and only one or two instruments at a time will be able to be powered. By 2020, it will be difficult for the RTGs to power even a single instrument. Once the power level drops below that needed to power any instruments, then the Voyager mission will be over.
Both Voyagers carry phonograph records with sounds of Earth: rivers, rain, thunder, birds, whales, cats, etc. as well as greetings in dozens of languages and music. The records were included primarily as a sort of public relations campaign. The idea was that just in case any aliens in the distant future were to find one of the Voyagers, then there would be a way for them to hear Earth. Of course, in reality, the Voyagers are going nowhere near any other star system for tens of thousands of years, and if they were, they’d still be just a tiny speck of metal, too hard to spot. And, even if they were found, then the tens of thousands, or more, years of exposure to the radiation of space, micrometeoroids, etc, would likely have degraded the phonograph records to the point of uselessness. A protective cover over the record attempts to show how to play the record, along with distances to several pulsars (a sort of map locating the Solar System).
But, the Voyagers were not the first spacecraft sent out of the Solar System. They were preceded on their trip by Pioneer 10 and Pioneer 11. However, the Voyagers were far more capable and returned far more data. The Pioneers were launched first to pave the way before the more expensive and important Voyagers were launched. No one knew what environment the spacecraft would be experiencing until the Pioneers went first.
Both Voyagers were launched in 1977. Voyager 2 was actually launched first, on August 20, 1977, and followed a couple weeks later by Voyager 1 on September 5, 1977. Though Voyager 1 got off to a later start, it was on a faster trajectory, so it arrived at Jupiter first, passing that planet in March, 1979. Voyager 2 did not arrive at Jupiter until July, 1979. Voyager 1 passed Saturn in November, 1980. A decision was made to risk the spacecraft crossing the ring plane (which may have resulted in an impact that would have destroyed the space probe). Voyager 1 then was hurled out of the plane of the ecliptic, so it could not pass by any other planets. It did receive a significant gravity boost, though, and wound up being the fastest spacecraft ever to leave the Solar System. It will keep that record, too. The New Horizons spacecraft launched from Earth faster, but it did not get the same gravity boost, so it will have slowed to the point of being slower than Voyager 1 by the time it reaches the outermost planets. Voyager 1 is now 103 AU from the Sun. It is expected that Voyager 1 will pass into interstellar space within the next 7 or 8 years. So, I could very well have listed Voyager 1 as one of the 7 Wonders of Space Exploration.
Voyager 2, though, was hurled by Saturn onwards to meet Uranus and Neptune. So, that is why I picked Voyager 2 as representing the Voyager program and as an entry into my 7 Wonders of Space Exploration list. It actually did the Grand Tour that had originally been proposed. Voyager 2 is now 83 AU from the Sun. At that distance, the Sun shines only as bright as the Full Moon, and it takes almost 11.5 hours for light to travel one way between Earth and the spacecraft.
Both Voyager spacecraft saw Jupiter and Saturn, and they were the first to discover the rings of Jupiter and volcanoes on Io. In fact, they provided the first clear views of the Galilean satellites of Jupiter. Voyager 2’s images of Europa provided the first inkling that there might be liquid water under the surface of that moon. And, the Voyagers showed features in the rings of Saturn that had not been anticipated. They discovered the shepherd moons that keep the rings together. But, Voyager 2 was the only spacecraft ever to visit Uranus and Neptune, discovering that Neptune was stormy and active, complete with a giant storm that was dubbed the Great Dark Spot. It also studied the moons of these worlds, seeing evidence of nitrogen geysers on Triton, and providing images suggesting that the moon Miranda had actually been blown apart and reassembled.
So, that is my pick for the number 5 spot on the list.
-Astroprof
Images courtesy of NASA
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