Retro Tech in Space: 45 years of the Voyagers
In 1977, scientists at NASA launched the Voyager mission to study the outer Solar System planets. Stacked with 15 different scientific instruments, the probes fulfilled their mission… and then some. It provided us the only pictures we have of Uranus and Neptune, discovered Io’s volcanic activity, and became the first man-made objects to reach interstellar space. In an unprecedented feat, 45 years later, the Voyagers are still alive and studying the space beyond the heliosphere and providing us with invaluable information. The mere survival of these probes, along with the still working outdated technology, is a miracle all on its own and a surprise to the engineers who built them. So, what technology is aboard the voyager? How has it survived this long? And how does it reach the modern technology back on Earth?
The Voyager mission—first called the Mariner mission— was approved on 1972. The mission had many changes before the two probes finally saw space in 1977. Voyager 2 launched on August 20 and Voyager 1, on Sept 5. When launched, the technology on board was top of the line for the 70s. Today, that technology is but a fraction of what we have on our daily basis and pales in comparison with many household items.
The computers aboard the Voyagers have a memory of 69.63kb, which is much less than the average computer and is closer to the size of a single JPEG photo. They are capable of executing 81,000 instructions per second and, while that sound like a lot, your smartphone is 7,500 times faster. On top of that, their circuitry has an astounding 65,000 parts. An average color TV nowadays requires a lot less; in fact, the number of parts on the Voyagers is equal to about 2,000 color TVs. These computers require 400 watts, ¼ of what an average residential home in the US operates with.
To make the Voyagers even more outdates, all the data is recorded into a data tape recorder (DTR), which is a belt driven recorder with magnetic tapes aka an 8-track… like your grandpa used to have. The DTR on the Voyagers doesn’t have a counterpart on Earth (not even in museums), but we do have some information on them. Their recording speed is between 115.2kbps to 7.2kbps and playback clocks in at 57.6kbps. Obviously, the tapes limited capacity was maxed a long time ago, but new information is rewritten constantly. Unfortunately, due to problems experienced, the DTR on Voyager 2 was turned off back in 2007.
Several other instruments have been turned off on both Voyagers in order to conserve energy. One of these was the camera, which powered off shortly after taking the famous Pale Blue Dot picture that shows the Earth as a small dot in the vast blackness of space. In theory, scientists could bring the camera back online, but NASA computers no longer have the software necessary to analyze them.
Originally, the Voyagers relayed their data back to Earth at 21kbps. Nowadays, with Voyager 2 being 11 billion miles away and Voyager 1, 13 billion miles, the relay speed is of 160 bits per second. For comparison, old slow dial up was 20,000 bits per second. At the speed the Voyagers relay information, it would take you eight years to watch a 5Gb movie on Netflix.
Nevertheless, even as slow and old as the probes are, the most important thing is that they are still working!
After 45 years, they are further than anything has ever been from the Earth and they communicate home, giving us a view of what lies beyond our neighborhood. They’ve sent us more than 10 trillion bits of scientific information. And, while their technology is that of a bygone era, ours continues to improve; therefore, it makes it possible to continue communicating with them.
In order to receive the Voyager’s data, scientists use the Deep Space Network (DSN), three deep tracking antennas located in Madrid, California, and Australia. These antennas need to pick up a signal with the wattage of a fridge lightbulb. An easy way to bring into perspective the Voyagers’ distance and their small signal is to compare them with other closer missions. A communication to any Moon probe or telescope takes about 2 to 3 seconds. Communication with the Mars Rovers took 10 to 20 minutes. Communicating with the Voyager probes takes 35 hours.
Scientists believe the reason why the Voyagers have survived this long is thanks to the redundant autonomous systems. Basically, there are two of everything and if anything fails, the Voyager switches to the back up systems without the need for human intervention. Thankfully, there has never been a double failure and all systems have been able to function as necessary. The plutonium dioxide radioisotope thermoelectric generator (RTG) that powers the probes still has energy left to provide, only losing 4 watts per year…
But nothing lasts forever.
NASA will now begin to slowly power off the instruments aboard the Voyagers and by 2030 they will all be offline in order to reroute all the remaining power to the communication antennas, which will continue struggling to send a message back home. While these measures will help prolong contact with Earth, eventually, and long before the power goes out, we will lose contact with the Voyager.
The Voyagers will continue to drift in interstellar space carrying a golden disk with the map to our planet, music and greetings in different languages. There is little risk for something to collide with them as they continue their journey beyond. So maybe in the distant future some intelligent life form will discover the two interstellar travelers and have them signal back home one last time.
Jet Propulsion Lab
NASA Technical Report Server
Institution Mechanical Enfineering
University of Iowa