The Voyager 1 and 2 probes are icons of Solar System exploration during the last quarter of the 20th century. In the following century, Voyager 1 in particular became a probe of the interstellar medium, adding to our knowledge. However, since November 2023, the probe had only been transmitting an incoherent message to Earth, raising fears that its mission may have become impossible. But since the beginning of March 2024, hope has been rekindled.
Most members of Generation X have surely been marked by the Voyagers, which began their grand tour of the Solar System almost 50 years ago. Voyager 2 left first towards Jupiter on August 20, 1977, and then on September 5, 1977, it was Voyager 1’s turn to set out towards the planets of the Solar System.
Voyager 1 and Voyager 2 revealed to us the volcanoes of Io, the ice caps of Europa, and the turbulent atmospheres of Jupiter and Saturn, as well as some glimpses of Titan. While Voyager 1 then headed towards the boundaries of the Solar System, Voyager 2 was the first visitor of the noosphere to fly over Uranus and Neptune.
A video for the 40th anniversary of the Voyager mission. For a fairly accurate translation into French, click on the white rectangle in the lower right corner. The English subtitles should then appear. Click on the gear icon to the right of the rectangle, then on “Subtitles” and finally on “Translate Automatically”. Choose “French”. © NASA Jet Propulsion Laboratory
Among the members of the Voyager missions were the late André Brahic, whom the French discovered in the 1980s, as well as Carl Sagan who, with Frank Drake, was behind the famous Voyager Golden Record titled “The Sounds of Earth,” two versions of which are on board each probe. Containing images and sounds representative of Earth and its noosphere, they serve as an “interstellar message in a bottle” intended for potential extraterrestrial civilizations capable of detecting and recovering such messages.
From Interplanetary Probe to Interstellar Probe
In the 2010s, Voyager 1 became an interstellar probe by crossing the heliopause at 17 km/s, venturing beyond the bubble of solar wind that envelops the Sun.
It is worth noting that the heliopause is defined as the boundary where the pressure of the solar wind balances that of the interstellar plasma. At least for many, as some prefer to consider the edge of the Solar System as the Oort cloud, roughly the limits of the Sun’s gravitational influence compared to other stars.
The energy that enables Voyager 1 to make observations and communicate with Earth so far from the Sun, rendering solar panels inoperable, is provided by three radioisotope thermoelectric generators (RTGs) based on the radioactive decay of plutonium-238 producing heat converted into electricity. The probe was supposed to still function until 2025, but concerns arose last year that the Voyager 1 mission might already be over.
We can gauge NASA’s concern at thisAt that moment, with the statement by Suzanne Dodd (seen in the video above), project manager of the Voyager mission, as reported by Frank Drake’s daughter, Nadia Drake, in the article by Scientific American dedicated to the event: “This is the most serious problem we have encountered since I became project manager, and it’s scary because you lose communication with the spacecraft.”
Resolving this issue is complicated due to the fact that it takes a radio signal 22.5 hours to reach Voyager 1 at 24 billion kilometers from Earth. Therefore, the engineering team must wait 45 hours to receive a response from Voyager 1 and determine if a command had the expected result. Moreover, the engineers who worked on this mission and are familiar with the technology of that time are becoming scarce, yet they are most likely to solve the problem. As explained in a NASA statement, this often means that “modern engineers must consult original documents written decades ago by engineers who did not anticipate today’s problems. The team needs time to understand how a new command will affect the spacecraft operations to avoid unforeseen consequences.”
The problem began manifesting in November 2023 when instead of receiving a complex series of binary coded information from Voyager 1, there was only a meaningless repetition of 0s and 1s.
Engineers concluded that the issue lies within one of the three onboard computers of Voyager 1, called the Flight Data System (FDS). It is not communicating properly with one of the probe’s subsystems responsible for sending scientific or technical data on the probe’s health and status towards Earth.
On March 1, 2024, NASA attempted to send an instruction to the probe, and on March 3, they received a message that was no longer repetitive but still incomprehensible until an engineer from the Deep Space Network, which operates the radio antennas communicating with Voyager and other spacecraft traveling to the Moon and beyond, decoded it.
It turned out that the sent message involved a full readout of the FDS memory containing its code, instructions on what to do, as well as variables or values used in the code that may change based on commands or the spacecraft’s state. The electronic memory of Voyager 1 may have been affected in some way by an energetic cosmic ray beyond the heliopause, modifying one or more bits of information, causing a bug.
To investigate further, NASA engineers will compare the memory content before and after this bug, a process that will take time, with hopes of finding a solution to the problem before 2025.