Since the two Voyager spacecraft transitioned into interstellar space it’s been fairly quiet around those two extreme long-distance travelers. Launched in 1977 it’s a technological miracle that they are still working, and the fact that we can still communicate with them is nothing short of amazing.
The twin spacecraft were launched a few weeks apart, taking full advantage of orbital mechanics to reach the outer solar system and explore the mysterious gas giants Jupiter, Saturn, Uranus and Neptune. Much of the follow-up science concerning those planets hinged on the discoveries the Voyagers made. Voyager 1 took a close look at Jupiter and Saturn, while Voyager 2 used different gravity-assist maneuvers to also visit Uranus and Neptune. During its Neptune flyby, Voyager 2 also snapped pictures of the giant moon Triton.
It was this very encounter that flung Voyager 2 out of the general orbital plane of our solar system, and towards the south, or beneath it. By now it has traveled so far that only one station in the Deep Space Network (DSN) can access it — the giant radio dishes outside of Canberra, Australia. The other two stations, located near Madrid, Spain and in the Mojave Desert at Goldstone, California, are too far north for a direct line of sight for Voyager 2’s trajectory.
At a distance of about 11.7 billion miles (yes, that’s billion with a “b”) it takes a radio signal from Earth almost 17.5 hours to reach Voyager 2, and the same amount of time to send a reply, so as you can imagine, even a short conversation with Voyager takes a long time (and it’s even worse with Voyager 1 — at a distance of 14.1 billion miles it’s 42 hours for a radio signal roundtrip!).
While the transmitter aboard the spacecraft runs at 23 watts (about three old-fashioned night light bulbs combined), what arrives here on Earth is less than a billionth of a billionth of a watt, or an attowatt. That’s a nearly incomprehensibly minuscule amount of power, but there are a few factors that come into play when we consider the mindboggling technology sensitive enough to pick up an energy signature this faint.
First off — the radio dishes at the DSN are BIG. As in truly gigantic — the biggest one is about 230 feet across, and each DSN station has one of those, plus an assortment of smaller ones. The secret lies in the very special shape of those dishes, as they can concentrate and thus amplify the incredibly weak signals coming from the Voyagers. By the same token, they can also send incredibly strong signals back out – in the order of tens of kilowatts, to ensure the signal reaches the spacecraft.
Since these radio dishes are in near-constant use their regular meticulous maintenance is of the essence. And in March of this year, the giant dish at the Canberra station was taken offline for major repairs and upgrades – from the pedestal to the receiver. This meant of course an extended period of radio silence for Voyager 2, as the other DSN stations couldn’t just take over. Last week a major portion of the repairs was completed, and the antenna was tested by making contact with Voyager 2. And just like clockwork, Voyager 2 responded, confirming the receipt of the message and sending back a status report and science data!
Whew. What a relief!
Have you ever seen photos of what computers looked like in the early 1970s? Big, unwieldy monsters of wire and spinning tape disks that worked painfully slowly compared to even the simplest cell phone today. That’s the kind of technology that’s on board the Voyagers. But those spacecraft were built to last, and so far they have performed extremely well. Their nuclear power sources are constantly fading, however, and in about five years they will no longer be able to produce enough electricity to power the transmitters aboard. Until then, though, we will get regular data downloads, and they take a long time for even small amounts of data.
But those giant dishes are patient, and so are the engineers that capture those faint whispers from outer space, and the scientists who interpret the data.
Eventually, both Voyagers will fall silent, but they will continue their journey through the great beyond. And one day in the distant future, they will arrive in another solar system as messengers from an ancient civilization long since extinguished, and perhaps someone will find them and study them and catch a glimpse of human ingenuity and maybe inspire them to reach out into the unknown as well.
Read up on Voyager 2’s long-distance calls home via the DSN at Canberra at https://www.cdscc.nasa.gov/
Beate Czogalla is the Professor of Theater Design in the Department of Theatre and Dance at Georgia College & State University. She has had a lifelong interest in space exploration and has been a Solar System Ambassador for the Jet Propulsion Laboratory/ NASA for many years. She can be reached at email@example.com