Today, Voyager 2 Turns 45

That's right; August 20, 1977 Voyager 2 started its four year mission to the outer solar system.  In a "it doesn't have to make sense" moment, Voyager 2 launched 16 days ahead of Voyager 1, on September 5, 1977.   Soon enough, both will be in the 45th year of their four year missions.  

I've done many columns on the Voyagers; in my view of the History of the world, a strong candidate for the title of "Greatest Achievement of Mankind" is the two Grand Tour satellites of Voyager 1 and 2.  A pair of missions that almost didn't happen. 

In the late 1960s, a doctoral student named Gary Flandro was working at the Jet Propulsion Lab in Pasadena.  He was the guy who plotted the positions of all of the outer planets for the coming 20 years, (with pencil and paper) and realized that a trajectory was possible where a probe could use each planet in series as a gravitational slingshot to the next.  A complete tour of Jupiter, Saturn, Uranus and Neptune could be done in 10 or 12 years rather than the decades such a tour might require otherwise. The mission launch window would open for a matter of months in the late 1970s, and then the geometry would be gone - not appearing for another 175 years.  

NASA pretty much didn't sell the grand tour mission to Congress for the funding it would require, but was funded for four year missions to Jupiter and Saturn.  Voyager 1 completed its tour at Saturn in November of 1980 and headed for interplanetary space, but Voyager 2 took the tour, arriving at Saturn in August of '21, then visiting Uranus in January '86 and Neptune in August '89 before it, too, headed into interplanetary space - in a different direction than its sister probe. 

Voyager mission summary graphic from the Voyager mission website at JPL. 

The Voyagers have not been without problems, but clever people on the ground found ways around them.  Not even a year after launch, April of '78,  Voyager 2 had a major failure.  A capacitor failed in a frequency synthesizer.  It was the receiver's tracking loop, used to tune the receiver to remove Doppler shift effects from the relative motion of the earth rotating and the satellite receding.  The fix was to calculate what the frequency shift would be at the satellite, and then adjust the transmit signal frequency during transmissions to it.  Tune out the Doppler on the ground instead of in the satellite.  Voyager has been flying handicapped by not having that circuit since 1978.

Reality is that the Voyagers don't have much time left.  Both probes are powered by Radioisotope Thermal Generators (RTGs) and those are expected to keep the few instruments that need to run alive until 2025, but that could change with the random failure of any one of thousands of components.  The RTGs might operate longer than 2025 although probably not much longer.  Either way, eventually the RTGs will no long be able to power enough of the instruments to get data and transmit it back.  Eventually, first one Voyager then the sister spacecraft will go silent.  Even though they won't generate enough heat to run the RTG, they might keep the Voyagers a little warmer, but eventually they'll cool to almost absolute zero.   

As I said a full decade ago, if we're lucky some day a ship from Earth may find one and bring her back to whatever serves as the equivalent of the Smithsonian in those days.  In all probability, they will simply follow the Newtonian laws of motion, cool to a couple of degrees Kelvin and glide away forever, all alone in the night.