Voyager 2 Battery Still Going Strong

Voyager 2 spacecraft

Photo by NASA used with permission: Voyager 1 and Voyager 2 launched from NASA’s Kennedy Space Center and traveled to explore the outer planets. Telemetry from the spacecraft was received on both the S- and X-bands at 2,560 bits per second. By the time they had reached Mars, a single signal had taken about 10 minutes to reach Earth. Due to both Voyagers’ successful encounters with Jupiter and Saturn, the mission was extended to include Neptune and Uranus in the mid 1980’s. After their encounters with the outer most planets, both Voyagers moved towards the edge of our solar system. Voyager 1 is further from the Earth than its counterpart at about 18 billion kilometers away; a signal from Voyager 1 takes over 34 hours round trip. Voyager 1 became the first man made object to exit the solar system in August 2012 and is still supported by the Deep Space Network today.

By Scott Hamilton

The last two weeks I wrote about batteries and some of the issues we face when it comes to battery technology. I would like to shift gears a little this week and talk about an amazing battery developed for NASA that has been in full operation for 46 years. NASA’s Voyager spacecraft are humanity’s longest-running spacecraft. Voyager 1 and 2 have been in flight since 1977 and have reached unfathomable distances from our sun, which is one of their primary sources of power.

It was not until the last ten years that NASA began noticing the power fading on the two craft as they reached distances too great for solar power to be effective. It was then that the on-board radioisotope thermoelectric generators (RTGs) took over the task of powering the craft. RTGs are basically a nuclear battery that converts the heat from decaying plutonium-238 into electrical energy.

The Voyagers don’t have to consume any energy to continue moving through space, the law of inertia is on their side here. If you don’t know, inertia means that a moving object will continue moving unless it is acted on by an outside force. In the deep regions of space there are very few forces at work to stop the Voyagers, but the instruments that send information back to earth require power.

In 2019 NASA began looking at ways they could conserve power on the craft; they noticed that the batteries were losing power at about four watts per year. In the first attempt to conserve the remaining power of the batteries, NASA turned off the heat. They expected some of the measurement equipment to fail in the harsh environment without heat, but thought it was worth the risk. Everyone was pleasantly surprised that none of the instruments failed, even though they were operating at temperatures 122 degrees Fahrenheit lower than had ever been tested. However, this still was not enough to squeeze out of the system if they wanted to reach even greater distances in space.

At the end of March, a team at NASA reprogrammed Voyager 2 and dipped into some of the reserve power meant to protect the craft from voltage spikes. This is kind of like removing your power strip/surge protector, from your computer or TV. It will not provide the protection if it is not there, but it will save a very small amount on your power bill. In the case of Voyager these circuits consume more power. NASA does not feel that the probes are at risk of electrical power surges as in the 46-years of operation, only a few have been encountered, and none have been encountered on Voyager since the craft left the heliosphere. The heliosphere is a protective bubble of particles and magnetic fields generated by the sun. Voyager 1 left the heliosphere in 2012 and Voyager 2 left in 2018.

The Voyagers are traveling at a rate of 35,000 miles per hour into the unknown, and as of May 2023, Voyager 1 had reached a distance of 159 astronomical units (AU) from home and Voyager 2 is at 133 AU, traveling in a different direction. (One AU is the distance between the earth and the sun, about 93 million miles.) Last year Voyager 1 experienced a slight problem with navigation controls, which is not surprising considering that at a distance of 159 AU, it takes 22 hours for a control signal to reach the craft. The design of control systems with a delay of nearly a full day is an amazing accomplishment. Could you imagine driving a car that turned even a minute after you turned the steering wheel? Let’s just say that there is not much real control over the Voyager crafts today. It also takes just as long for us to receive data from the crafts. It’s like clicking a link on a website and being told to come back in two days.

If the energy savings plans laid out by the team of NASA engineers are successful, the Voyagers could easily reach and possibly surpass the age of 50, and the team has high hopes of reaching 200 AU distances around the year 2035. They may only have a few instruments operational at that distance, as a part of the plan is to slowly turn off instruments as the battery level drops, to allow communication with the probes for as long as possible. These two craft tell the story of long lasting batteries for low power systems, unfortunately such a battery would not be safe for operation in an electric car because of the radiation exposure risks. Reading about the efforts to conserve power on Voyager made me wonder how much further into space we could have reached if NASA had skipped the heaters on the instruments from the very beginning, and if they will carry this knowledge forward to their new probes. The longevity of the Voyager probes also points to the importance of good documentation to pass knowledge on, as these craft could easily outlive the engineers who designed them. Until next week, stay safe and learn something new.

Scott Hamilton is an Expert in Emerging Technologies at ATOS and can be reached with questions and comments via email to sh*******@te**********.org or through his website at https://www.techshepherd.org.

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