Once a year we get closer to NASA’s Voyagers – here’s why

NASA’s two Voyager spacecraft are on a one-way trip in interstellar space on their way out of the solar system.

The groundbreaking missions launched in 1977 to send two probes into the outer solar system, which would jointly view Jupiter, Saturn, Uranus and Neptune. Voyager 1 successfully completed a Saturn flight in 1980 and soared high above the plane of the solar system, while Voyager 2 took advantage of a rare alignment to see Uranus and Neptune up close, the only spacecraft to do so to date – although scientists push for a deeper dive into Uranus.

The spacecraft, which still happens to be operational, continues to send data back. But every year comes an orbital quirk. Although the Voyagers are quickly leaving our solar system, there is a period when the spacecraft is a little closer to us once a year for a few months.

Distance data from NASA’s Jet Propulsion Laboratory, for example, shows that Voyager 2 was 130,05518 astronomical units (Sun-Earth distance) from our planet on February 20. Still, on June 2, the spacecraft will be at 129,72179 astronomical units (distance Sun-Earth) earlier. pull away again.

The reason is Earth’s motion rather than the spacecraft: “If Earth is on the same side of the sun as the Voyagers, she’s closer,” said Candice Hansen-Koharcheck, senior scientist at the nonprofit Planetary Science Institute. . inverse† “When it [Earth] is on the other side of the sun than the Voyagers, then they are further.”

Hansen-Koharcheck said the best way to understand it is to take a piece of paper and draw a dot in the center representing the sun. Then draw a line from the sun to the edge of the paper; that’s one of the Voyagers headed for interstellar space.

Then draw a circle around the sun. That circle represents the Earth’s orbit. As the circle shows, there are times in our planet’s 365-day journey around the sun when we’re on the other side of the departing Voyagers, producing a greater distance.

Both Voyagers wander off to points outside the Solar System in different directions. NASA

How long do the Voyager probes last?

Both Hansen-Koharcheck and a representative from NASA’s Jet Propulsion Laboratory noted that the temporarily increased distance between the spacecraft and our planet does not affect communications or the mission. The Deep Space Network, a series of antennas around the Earth, monitors communications from the nuclear-powered Voyagers.

“It doesn’t matter much to the Deep Space Network, because Earth is so far away from Voyagers now,” says Hansen-Koharcheck. Although there would be a slight difference in signal strength, both Voyagers have enough power to continue transmitting for now.

The two spacecraft are celebrating 45 years of space operations this summer. This is two to four times the lifespan of a typical solar-powered spacecraft. But this situation will not last forever, the JPL representative said.

“Both spacecraft face dwindling power supplies as their onboard RTGs [radioisotope generators] continue to deteriorate, reducing their power by about 4 watts per year,” the rep tells me inverse in an email.

“In recent years, the team has turned off heaters and other subsystems that are not essential to the operation of the spacecraft or its scientific instruments,” they say. “That included a few scientific instrument heaters, but amazingly, the instruments continue to work. The engineering team has done a really incredible job keeping these two spacecraft going.”

NASA edited this composite to show the view exiting the Triton area. NASA / JPL-Caltech

Will NASA ever send a probe to Neptune?

Hansen-Koharcheck and Heidi Hammel, now vice president of science at the Association of Universities for Research in Astronomy (AURA), were both on the Neptune imaging team when Voyager 2 made its historic flight in 1989. (Hammel was unavailable for an interview before the deadline of this article.)

“They [Heidi] was the person who knew the most about Neptune as seen through a telescope,” said Hansen-Koharcheck, who was at JPL at the time, about Hammel’s contribution. “So Brad Smith, the head of the imaging team, invited her over.”

Hansen-Koharcheck’s job was to provide Voyager 2’s slow-scan color television camera to take images of the planets, and to program the spacecraft’s imaging observations. She recalled that the spacecraft’s view of Neptune began to improve relative to ground observations about six or eight months before the spacecraft reached its closest point on August 25, 1989, marking several intense months of work for the imaging team.

“Every afternoon Heidi and I had this little meeting, so to speak, where she would walk from her office. She and I went to what was essentially a broom closet, but it was actually a place where you didn’t have a window. You can look at the screen and pull out the images,” says Hansen-Koharcheck.

“We were supposed to get the data for the day. Heidi kept all the notes and I operated the computer. The two of us were the first to see things like the Great Dark Spot [storm] and start measuring the rotational speed of the images… and looking at the different circulation of the different latitudes of the atmosphere,” she adds.

Hansen-Koharcheck says the meeting with Neptune and the team work of the camera crew has resulted in “great times” and says she is hopeful that the community’s decades-long lobbying will contribute to a new mission to Neptune.

But so far, the deep blue planet has not yet been honored with another attempt. A close shave took place in 2021 with Trident, a proposed NASA Discovery-class mission that would have flown past Neptune and its largest moon, Triton, by 2038. DAVINCI+ and VERITAS.

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