This gadget lover is a long way from home. The Voyager 1 spacecraft is currently about 18 billion kilometers (about 11.18 billion miles) away from earth, heading into interstellar space at a speed of 17,000 meters per second, or about 38,000 miles per hour. That makes the Voyager 1 spacecraft both the most distant and the fastest man-made object* in history. Launched in 1977, the craft has made a string of discoveries through encounters with all of the outer planets, taking breathtaking photos and scientific measurements at Jupiter and Saturn, before being catapulted by Saturn’s gravity out of the plane of the solar system towards interstellar space. Sister ship Voyager 2 also visited Uranus and Neptune**. After these encounters, both spacecraft are now heading out into the unknown, looking for the elusive point where the influence of the sun ends and interstellar space begins.
In 1990, Voyager 1 swung around to take one last set of photos, producing the the first ever composite photo of all of the planets of the solar system, including the Earth, which was described by Dr Carl Sagan as “a mote of dust, suspended in a sunbeam” This is the famous Pale Blue Dot photo. After it was taken, the craft was commanded to turn off the camera to conserve power.
The Voyager spacecraft are far from finished, though. Although the Radioisotope Thermal Generator (RTG) that powers them are running low, they are still still producing enough juice to keep some of the science instruments going, and mission planners expect that Voyager 1 will keep returning data until at least 2020. By that time, it should be clear into interstellar space, where it will drift for many thousands of years. In about 40,000 years, it will pass a star called AC+79 3888, although it won’t come any closer than 1.6 light years. After that, where the Voyager 1 spacecraft goes is anyone’s guess.Voyager 2 will pass the star Sirius in about 296,000 years, but only at a distance of 25 trillion miles.
But wherever these spacecraft end up, they will be taking a little piece of the Earth with it, in the form of a 12-inch gold-plated record, which contains images, music and sounds of earth, ranging from greetings in 55 different languages to the sounds of a baby crying. The music on the disc ranges from Beethoven to Blind Willy Johnstone, via a Navajo chant.
That’s not a bad list of achievements for devices run by three computers that can hold just 4096 instructions, and which stores data on an 8-track digital tape recorder that can hold about 536 megabits of data (about 68 KB, or about 0.06 GB).
Both Voyagers carried a large number of instruments, including two cameras, four magnetometers, cosmic ray sensors and plasma sensors. Together, these instruments allow the craft to sense the environment around it, looking for charged particles and magnetic fields, sniffing for the controlling influences of the space around it. Most of the instruments are located on the body of the craft, but the two low energy magnetometer are located on the end of a long extending boom (NASA calls it an astromast, PDF link, see page 51) that frees it from the influence of the spacecraft itself, allowing it to sample the magnetic field of its environment.
So, out of all of this scientific equipment, which gadget does a deep spacecraft love the most? We talked to Voyager 1, with the assistance of Jia-Rui Cook, the Media Rep for the Outer Planets at the Jet Propulsion Laboratory.
Richard Baguley: What is your favorite gadget?
Voyager 1: I have a suite of favorite gadgets that measure the charged particles and magnetic field in the environment. With this suite of instruments, I can tell whether I’ve made it into interstellar space, which is the space between stars. (People often ask me about my cameras, but space is so empty out here, 11 billion miles away from the sun, that we’ve turned off the cameras to have power for the charged-particle instruments.) In the last year or so, these instruments have told me that I’m now bathed in the particles ejected from the death of nearby stars and that particles from our sun have disappeared. But, I am still riding on the magnetic field lines of our sun, so I’m not in interstellar space yet. The magnetometer is the instrument that discerns the magnetic field and that hasn’t shown an abrupt change in direction. My scientists expect that interstellar space will have a different magnetic field orientation.
Richard Baguley: What do you love about this gadget?
Voyager 1: I love that they’re still working well after nearly 36 years of travel. We’ve gone through some pretty gnarly radiation environments (I.e., Jupiter and Saturn) and now we’re so far away from the sun that it’s very cold. We calibrate the instruments regularly and they continue to work just as designed so many years ago.
The instruments have exceeded their design lifetimes by a long shot. The LECP (Low Energy Charged Particle) instrument, for instance, has a stepper motor that was tested for 500,000 steps, enough to reach the orbit of Saturn. It’s now gone beyond 6 million steps. We do have some limitations, however. By about 2020, we expect that there will not be enough power to operate all the currently operating instruments and my team will have to start turning off instruments one by one. By 2025, my team expects all my science instruments to be turned off, though I can continue to send back some engineering data for a short while after 2025. I get power through the natural decay of plutonium and I carry only a finite supply.
Richard Baguley: What do you hate about this gadget?
Voyager 1 : We don’t really hate anything about these devices. But do we have a wish list? Of course. With the rigors having to endure a long journey and changing space environments, there are still things we have to do by hand here on the ground. Some of the data from my instruments is difficult to process. With the magnetometer, for instance, we have to calibrate the instrument by doing periodic roll maneuvers. We can only do those every few months. Then once we get the calibration data down, we have to check it against the raw data from the instrument. We have to subtract out the effect of the magnetic fields that our own instruments and power source may emit. It’s painstaking work to get the signal from the “noise.”
Richard Baguley: What one feature/ability do you wish that this device had?
Voyager 1: It would be great if my instruments had computers with lots of memory to store data and the power to send the data back more quickly. My sister Voyager 2 and I each only have 68 KB of memory, total. For comparison, an iPhone 5 has 1 GB of memory, so it has about 17,000x the memory of Voyager. For perspective, 1 GB would hold 19 months of all the data I send back. Also, I transmit at about 160 bits per second. Most wireless systems are working in MEGAbits per second. But in 1977 when I was launched, Apple was only coming out with its Apple II computer. So you can imagine that technology has come a long way since then.
Richard Baguley: If you were being launched again today, would you choose the same gadgets and instruments?
Voyager 1: It’s hard to argue with success. The instruments and subsystems I have were state-of-the-art at that time. No doubt a Voyager launched today would have better cameras (I can only dream of megapixels!), bigger processors, a faster “internet” connection. But the important thing is that my instruments all WORKED in the extreme environment of space through my prime mission at Saturn and Jupiter, and key instruments that will tell us about the charged particle and magnetic environment of interstellar space are still streaming back data no other spacecraft can send back. I just hope we’ll have enough power for them to be on whenever I break on through to the other side.
Richard Baguley: How does it feel to be the fastest and most distant man-made object, all the way out there in the depths of space?
Voyager 1: Well, where I am in space is very empty and quite cold. There are still reminders of where I came from: my team talks or listens to me practically every day. And there is still a slight, just-perceptible gravitational tug backward on me by our sun. Mostly I’m just excited to get to interstellar space so I can see what it’s like. I can’t get there fast enough.
Thanks to the Voyager 1 spacecraft (with assistance from Jia-Riu Cook of JPL) for answering our questions! You can read more about the ongoing mission of Voyager 1 & 2 to boldly go where no spacecraft has gone before at the Voyager Interstellar Mission Web site.
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*Some people maintain that a manhole blown away from a nuclear explosion may have travelled faster (an estimated 150,000 miles per hour), but I prefer to consider objects that have remained intact to tell the tale.
**Planetary purists will notice the lack of Pluto, which has recently been redefined as a minor planet. Whatever you call it, Voyager 1 & 2 did not visit this planet(ary body).