Voyager I: Off to Interstellar Space
If there has ever been a Golden Age for scientists and engineers in the United States, you could make a good case that it was the 1960s. NASA was launching ever-more sophisticated devices into orbit and was gearing up to put a man on the moon. Engineers had key roles in hit TV shows including the NASA-based I Dream of Jeannie (1965-1970) and Star Trek (1966-1969), and no challenge seemed to be too difficult for the best and the brightest to tackle. Although less well-known than the moon launch, NASA spent considerable time and effort in the 1960s planning a series of missions for what it called the Grand Tour of the Planets. The most famous and arguably most successful of these missions was Voyager I, a mission which continues today and is about to reach a remarkable milestone.
Voyager I was launched on September 5, 1977 with its primary goal to survey Jupiter, Saturn, Uranus and Neptune. Its secondary mission was to survey the edge of the solar system and to boldly go where no man-made object had ever gone before, interstellar space.
A review of the technology of Voyager I helps to illuminate the vaunted status of rocket scientist among professions considered to require great intelligence. Voyager I is propelled by hydrazine thrusters (sounds like Star Trek eh?). Hydrazine is a liquid with the chemical formula N2H4. When you pass hydrazine over a metal catalyst, an extremely exothermic reaction occurs which produces high pressure nitrogen and hydrogen gas which can be vented to propel and steer a space probe. The beauty of this fuel stems from it being a single component that decomposes. If Voyager used a traditional sort of fuel that burned, it would need to have a heavy oxygen tank which would crowd out space for scientific instruments.
Voyager I has ten scientific instruments, cameras, particle detectors, energy spectrometers and the like, to take measurements and pictures which are transmitted back to earth by radio wave. To generate the electricity to run these instruments, Voyager I is equipped with a radioisotope thermoelectric generator (RTG). An RTG contains radioactive fuel which generates heat from the radioactive decay which can be converted to electricity through the thermoelectric effect. The instrumentation in Voyager I, all created before the personal computer or the cell phone, has been churning away for 36 years now on a journey of just about 12 billion miles.
Voyager I has now reached the outer limits of our solar system, a zone called the heliopause. When it exits this zone, likely later this year, it will allow us to directly investigate galactic cosmic rays and the magnetic fields of other stars for the first time. In case Voyager I runs into any intergalactic parties, it carries with it pictures of Earth and a gold plated record with sounds of the ocean and Chuck Berry’s Johnny B Goode. The RTG will continue to provide power to transmit data back to Earth until 2025, 48 years after launch. (Odd that our laptop computers only last a couple of years, but that is a subject for a different column.) These remaining 12 years of data transmissions will provide us with a treasure trove of new information about our universe. Even now, Voyager is teaching us that some of our assumptions about the edge of the solar system were incorrect.
Here in 2013 our enthusiasm for space travel has cooled a bit. While we talk about a possible mission to Mars, the space shuttle program has been cancelled. Having been born in 1966, I am a product of this golden age of engineers and grew up and made my career choices under its influence. Perhaps I am already becoming a nostalgic old man, but I have a sense of loss with the decline of NASA. Perhaps on the last leg of its journey Voyager I will discover something remarkable while it still has the power to phone home and reignite our passion for space exploration.
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