NASA Just Regained Contact With Voyager 2
For the last 45-plus years, the Voyager 2 spacecraft has been hurling through space further from Earth. At around 12.3 billion miles (20 billion kilometers) away, the spacecraft is in uncharted territory and an important asset to NASA and the space community. This is why many were concerned when communication with the probe was lost late last month in July.
This communication interruption had to do with a series of instructions sent by the agency that ended up altering the antenna placement. Thankfully, just days ago the agency was able to receive science and telemetry data from the spacecraft. However, they don’t expect a full fix until an automated maneuver meant to happen in October.
By now, Voyager 2 has completed its main objectives and has managed to survive much longer than originally thought. As it flies through interstellar space, who knows what discoveries it could make. Here I will go more in-depth into the communication dropout, how NASA was able to reestablish communication, the journey of this probe, and more.
Communication Blackout
NASA said in a statement that “A series of planned commands sent to NASA’s Voyager 2 spacecraft on July 21 inadvertently caused the antenna to point 2 degrees away from Earth. As a result, Voyager 2 is currently unable to receive commands or transmit data back to Earth.” This obviously was not good news and had some within the agency worried about the state and future of this spacecraft. Thankfully, a few days ago on the first, using multiple antennas, NASA’s Deep Space Network (DSN) was able to detect a carrier signal from Voyager 2.
A carrier signal is what the spacecraft uses to send data back to Earth. The signal is too faint for data to be extracted, but the detection confirmed that the spacecraft was still operating. At the time, the spacecraft also continued on its expected trajectory. NASA said that “Although the mission expects the spacecraft to point its antenna at Earth in mid-October, the team will attempt to command Voyager sooner, while its antenna is still pointed away from Earth. To do this, a DSN antenna will be used to “shout” the command to Voyager to turn its antenna. This intermediary attempt may not work, in which case the team will wait for the spacecraft to automatically reset its orientation in October” they said.”
This leads us to yesterday the fourth, when the agency’s Deep Space Network facility in Australia, sent the equivalent of an interstellar “shout” more than 12.3 billion miles (19.9 billion kilometers) to Voyager 2, instructing the spacecraft to reorient itself and turn its antenna back to Earth. To put in perspective the distance between Voyager 2 and Earth, with a one-way light time of 18.5 hours for the command to reach Voyager, it took 37 hours for mission controllers to learn whether the command worked. At 12:29 a.m. EDT on Aug. 4, the spacecraft began returning science and telemetry data, indicating it is operating normally and that it remains on its expected trajectory.
As far as the reset, this will still happen on October 15th. In the case that communication is lost again between now and then or an issue arises, this should reorient the spacecraft and ensure it’s pointing toward Earth. Right after this small scare, NASA had said that the mission team expects Voyager 2 to remain on its planned trajectory during the quiet period. In other words, they were confident that even though they weren’t able to make contract with the spacecraft, that it would continue on without issue until the October timeline.
In reality, the fact that Voyager 2 is still operating and the agency is still talking to it is a feat in itself. The primary mission goal was to flyby a few planets without our solar system and the ice giants in particular. Back in the early 70s, it was realized that a periodic alignment of the outer planets would occur in the late 1970s and enable a single probe to visit Jupiter, Saturn, Neptune, and a few others, by taking advantage of the then-new technique of gravity assists.
Voyager 2 included 16 hydrazine thrusters, three-axis stabilization, gyroscopes, and celestial referencing instruments to maintain pointing of the high-gain antenna toward Earth. Collectively these instruments are part of the Attitude and Articulation Control Subsystem (AACS) along with redundant units of most instruments and 8 backup thrusters. The spacecraft also included 11 scientific instruments to study celestial objects as it traveled through space. In order to keep the spacecraft alive NASA has altered some of its power sources and needs.
Interstellar Space
A few years ago in 2018, the spacecraft made history, when for the second time in history, a human-made object reached the space between the stars. NASA’s Voyager 2 probe had exited the heliosphere – the protective bubble of particles and magnetic fields created by the Sun. At the time, comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on Nov. 5. This boundary, called the heliopause, is where the hot solar wind meets the cold, dense interstellar medium. Its twin, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that provides first-of-its-kind observations of the nature of this gateway into interstellar space.
The most compelling evidence of Voyager 2’s exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause. Until this milestone, the space surrounding Voyager 2 was filled predominantly with plasma flowing out from our Sun. This outflow, called the solar wind, creates a bubble – the heliosphere – that envelopes the planets in our solar system. The PLS uses the electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on Nov. 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which made mission scientists confident the probe had left the heliosphere.
While impressive, these spacecraft and Voyager 2 in particular is not meant to last forever. The missions are slowly losing power from their nuclear radioisotope generators, but engineers have made several alterations to preserve their systems where possible. The heaters have been shut off, for example, and earlier this year, engineers disabled Voyager 2’s surge protector (or voltage regulator). All in an effort to keep the probe alive as long as possible.
“There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” said Ed Stone, Voyager project scientist based at Caltech in California. Together, the two Voyagers provide a detailed glimpse of how our heliosphere interacts with the constant interstellar wind flowing from beyond. Their observations complement data from NASA’s Interstellar Boundary Explorer, a mission that is remotely sensing that boundary.
“Voyager has a very special place for us in our heliophysics fleet,” said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. “Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun’s influence gives us an unprecedented glimpse of truly uncharted territory.”
While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won’t be leaving anytime soon. The boundary of the solar system is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun’s gravity. The width of the Oort Cloud is not known precisely, but it is estimated to begin at about 1,000 astronomical units (AU) from the Sun and to extend to about 100,000 AU. One AU is the distance from the Sun to Earth. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it.
The Voyager probes are powered using heat from the decay of radioactive material, contained in a device called a radioisotope thermal generator (RTG). The power output of the RTGs diminishes by about four watts per year, which means that various parts of the Voyagers, including the cameras on both spacecraft, have been turned off over time to manage power. By now, both spacecraft have traveled well beyond their original destinations. The spacecraft were built to last five years and conduct close-up studies of Jupiter and Saturn. As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left Earth. Their two-planet mission became a four-planet mission. Their five-year lifespans have stretched to 46 years, making Voyager 2 NASA’s longest running mission. An exciting fact that the agency hopes to keep going for the coming years and beyond.
Conclusion
Just yesterday NASA was able to reestablish communication with Voyager 2 after commands shifted the spacecraft’s antenna away from Earth. After around 37 hours of travel time, the message was sent to and received from the spacecraft. We will have to wait and see how it progresses and the impact it has on the space industry.
