John Carlos BaezAug 6, 2023

I have so many questions about what just happened with Voyager 2. But let's review:

On August 20, 1977, Voyager 2 was launched from Earth.

In December 1977, it entered the asteroid belt.

In June 1978, its main radio receiver failed. Since then it's been using the backup receiver!

On July 9, 1979, it flew past many of Jupiter's moons, made its closest approach to Jupiter, and took tons of beautiful pictures.

On August 26, 1981 it shot past Saturn and took tons of beautiful pictures.

On August 25, 1989 it shot past Neptune and took tons of beautiful pictures.

On November 5, 2018 it crossed the heliopause and entered interstellar space, 120 times farther from the Sun than we are.

On July 18, 2023, it overtook Pioneer 10 and became the second farthest man-made object from the Sun.

3 days later, some idiot sent a command that pointed its high gain antenna 2 degrees away from Earth. HOW EXACTLY DID THIS HAPPEN?

On August 4, 2023, NASA used its most high-powered transmitter to successfully command Voyager 2 to reorient towards Earth, resuming communications. HOW WAS THAT POSSIBLE?

Voyager 2 is now 133 AU away. How can you "shout" across such a distance and attract the attention of someone who is not looking in your direction? That's very far. It takes light about 18 hours to travel that far.

Show threadtjhowseAug 6, 2023

@johncarlosbaez My guess:

The receive side of the Voyager's radio has a wider margin for error than the transmit side. A transmitter on earth has a MASSIVE power budget — many kilowatts — compared to Voyager's meagre 350 watts (roughly) total power budget.

Voyager must whisper, with its tiny power output, so its transmit antenna needs to be carefully pointed for us to hear it.

Earth can shout SUPER LOUD so it doesn't matter if Voyager's receive antenna is pointed slightly wrong.

Show threadJohn Carlos Baez
@tj - apparently Voyager's antenna can detect signals that are 2.3° off center, and the idiot(s) who turned the antenna the wrong way only turned it 2° off. So we are lucky.
Aug 6, 2023 at 1:11pmWeb
Show threadtjhowseAug 6, 2023

@johncarlosbaez Well there you go!

I'd also gently advise against calling the scientists and engineers working on the Voyager mission "idiots". Anyone can make a mistake. Should there be safeguards in place to prevent this? Sure. Is this system VERY old and probably hard to modify? Almost certainly. Was there a failsafe built into the system to re-orient back to earth in this failure mode? Yes.

Show threadJohn Carlos BaezAug 6, 2023
@tj - 'twas a joke. I bet everyone responsible *felt* like an idiot! But the problem is not with the intelligence of individuals but with the system of cross-checks used before sending a command like this.
Show threadRachel GreenhamAug 6, 2023
@johncarlosbaez @tj i'm sure there's some poor sod, who's generally very good at their job, who's been sweating it out the last few days. everyone will have been very kind and knows the process is what failed really, but still, they know that one day their name will leak and they will forever be known as the person that lost Voyager.
Show threadJohn Carlos BaezAug 6, 2023
@StrangeNoises @tj - heh, maybe. But actually any decision this big should be vetted by a team of people. So it'll be interesting when we finally find out what happened. Only by studying what happened can NASA improve their procedures.
Show threadjnbhlrAug 6, 2023
@johncarlosbaez @tj it's not like there is a limit where there is no reception at all. The antenna has a very strong directional preference, but basically if you shout loud enough from amy direction the antenna will pick it up. 2,3° might be the error margin of the transmitting power used. So I guess they shouted a bit louder than they needed to.