by Shannon McConnell
The year is 1977. People stood in line for days waiting for a chance to meet Han Solo and Luke Skywalker in a Galaxy Far, Far Away. Atari released the first consumer marketed video game console. Apple released its first mass market computer. It was a time of great advancements in technology. While humans were experiencing these new technological achievements, engineers working in American’s Space Program were creating a similar revolution. In late summer, 2 spacecraft lifted off from the hot Florida coast on an adventure to explore our solar system. These 2 spacecraft were uniquely designed and built to travel far beyond our Sun’s influence. The twin Voyager spacecraft could operate in the darkest, coldest regions of space.
Launched September 5, 1977, Voyager 1 left the warm confines of Earth on a journey to Jupiter and Saturn. From there, the spacecraft headed across the Solar System. In a twist of cosmic fate caused by geometry, Voyager 2 launched 2 weeks before Voyager 1. On August 20, Voyager 2 set off to explore Jupiter, Saturn, and then continued on to encounter Uranus and Neptune.
Both spacecraft uncovered mysteries across the Solar System. Through these planetary encounters, the world learned that Jupiter’s moon Io was an active, violent landscape of volcanic eruptions. At Saturn, mysteries about what minerals are embedded in its expansive rings kept scientists on edge. Titan, the planet’s largest moon, was shrouded in think clouds, revealing almost nothing of its surface. At Uranus, scientists found a planet tipped on its side. And Neptune revealed a huge storm system. Each scientific discovery yielded hundreds of more questions.
Now, some 43 years later, the twin spacecraft are outside our solar system. They are the furthest human made objects from Earth. Despite their distance from Earth, both travelers still return back data from their adventures. But at over 125 times as far away from Earth as the Sun is, those communications are difficult at best.
Engineers at NASA’s Deep Space Network (DSN) communicate with the 2 travellers weekly. They compile command sequences using technology that was developed when music was still purchased on vinyl. They upload it over a communications link that takes nearly a full day to reach the spacecraft. And they eagerly await news from beyond our solar system. Communicating with spacecraft at that advanced distance from Earth is a waiting game. Like explorers before, engineers on Earth send data to the spacecraft and just wait. And wait. And Wait.
A command from Earth travels over 18 hours to reach Voyager 2. Double that for the return trip. Add in processing time onboard and the engineer will wait 2 full days to hear back. That’s a best-case scenario. The DSN maintains a global complex of radio astronomy antennas. NASA doesn’t have infinite space communications resources, so time has to be scheduled on the DSN antennas. DSN routinely tracks over 2 dozen spacecraft travelling throughout space and their communications requirements are as varied as their destinations.
Voyager has to vie for time on the DSN antennas with younger explorers whose missions have a higher priority to NASA. That’s not all. The Voyager Spacecraft are so far away their signals are barely more than a whisper. Setting up a communications link with Voyager takes time, using equipment born of 1970’s technology, kept operating with old school electronics processes.
The fleet of explorers at Mars are newer spacecraft with advanced communications technology. The one-way light time (the amount of time for a command to travel from Earth to the spacecraft) is a matter of minutes. Juno, orbiting Jupiter is further from Earth and thus returning data at a slower rate. Still these spacecraft are broadcasting a rock concert compared to Voyager. When Voyager send data back, it’s like listening to a bird chirp in a tree 5 miles away.
How do NASA engineers capture this faint signal whispering across billions of miles of space? While some think it’s magic, space communications with Voyager is a combination of solid radio engineering, large aperture antennas, some old-school hands on electronics that would make MacGyver envious, and 4 decades of practice.
The Voyager spacecraft are the 2 oldest members of NASA’s fleet of interplanetary explorers. They have been flying so long, an entire generation of engineers has come and gone sicne they launched. These spacecraft use an older communications strategy. It was cutting edge in the 1970’s. In today’s world, communicating with Voyager is akin to using the rotary dial phone attached to the wall of mission control while every other spacecraft boots up skype using a smart phone.
Voyager is far away. Space communications signals travel at the speed of light so they obey the same laws of physics as light waves and radio signals. As those signals travel, the intensity of the signal drops at the inverse proportion to the square of the distance. In other words, if your light beam travels 10 feet away, the intensity of the beam is 100 times less intense then where it started. It’s impossible for us to detect the intensity change from 10 feet, but at 11 billion miles it’s a huge change. This is known as the “Inverse Square Law.”
Voyager 1 and 2 communicates with Earth using a transmitter similar in signal strength to a refrigerator light bulb. At over 11 billion miles, the signal is so weak it is drowned out by the background noise from space when it arrives at the DSN. Ground engineers have to physically cool the signal down, slowing the electrons, and allowing the modulated signal from the spacecraft to be visible amidst the unmodulated noise. Then the signal can be reconstructed into the data necessary for the science and engineering teams to analyze.
How much longer will these intrepid explorers continue to whisper back to Earth? Flight engineers believe the transmitters on the spacecraft will fail sometime in the late 2020’s or early 2030’s. Someday that faint signal will not be found hiding in the background noise. Until then, DSN engineers will continue to lock onto the 2 travellers, collecting data and sending new information back across the solar system to Voyager. In return, the twins will continue to send postcards from Beyond our Solar System, giving humans a glimpse into a universe we have just begun to explore.
Shannon McConnell is United States Country Coordinator of One Giant Leap Australia and can be reached here. Shannon worked for NASA Jet Propulsion Laboratory and served as the Deep Space Network Public Engagement Manager. Shannon has been introducing students to the excitement of space exploration since 1998. She has led the Galileo Outreach Team, the Cassini Formal Education Team, and the Deep Space Network Education and Public Outreach Office. Before her work in outreach and education, Shannon worked mission planning and design for the Cassini Spacecraft, Sequence design and execution for the Galileo Mission, and Data Analysis for the Magellan Mission. Shannon also spent 1993-1994 working payload operations for 2 Space Shuttle Flights managed by JPL.
Shannon holds Bachelor’s and Master’s degrees in Astronomy and Environmental Engineering (University of Southern California) as well as being a Committee Chair for the Pasadena Tournament of Roses. Her professional affiliations include membership in the National Association of Interpretation, National Science Teachers Association, and National Council for the Teachers of Mathematics. Shannon is also a current member of the Board of Trustees for Don Bosco Technical Institute in Rosemead, California.
Shannon has travelled to 50 countries on all 7 continents and is always on the lookout for a new adventure. Shannon lives in Altadena, California.