Hacker News Reader

Comment by TriangleEdge | Hacker News Reader

From a quick search: Voyager 1 is 25B km from earth and runs on 240 watts of power.

I'm no physicist, but I don't understand how a signal is detectable from that far. Also, am very impressed that voyager can aim at earth from that far away too.

View on HN

The antenna has a beam width of 0.3°. So it only needs to aim that accurately in the general direction of earth. In general, antennas don't need to aim more or less accurately as they get closer or further away, it is only in function of their beam width.

I'm pretty sure, at that distance, it doesn't even matter anymore whether it is pointing at earth, the moon or the sun.

Can you provide some details on how we on earth are able to pick up such a signal amongst all the noise?

The transcript from this podcast has some answers:

https://www.nasa.gov/podcasts/invisible-network/bonus-dsn-yo...

According to https://gigazine.net/gsc_news/en/20240604-voyager-1-photons-... they have a really big 70m dish which collects about 60 RF photons per second per square meter.

How does it locate earth to .3 accuracy while they’re both moving ?

Voyager is so far away that from its perspective, earth isn't moving. There is also no force acting on voyager. So practically speaking, compared to the distance between them and the 0.3° beam width, both are hanging pretty still.

It does have an AACS system, which is tracking the sun and a bright star (Canopus) to orient itself earlier in the mission.

A quick search indicates it is still doing about 1 puff per hour to keep pointing the right way. The biggest problem seems to be that the lines for those puffs are clogging.

0.3 degrees is pretty narrow :) I would not consider that "in the general direction".

.3° at 25B km is still a pretty large distance. Some random calculator online says that would be 1.3090e+8 kilometers or 130,900,000km. The earth-moon distance is roughly 240,000km. 1AU ~= 149,597,900 So .3° is just under 1AU, and essentially to cosmological scales .3° = 1AU. And it's only getting bigger as it continues to get further away. So essentially, just point at the sun and it'll hit earth

Of course, the sun will amplify the radio waves!

What the huh? That's not even funny if I tilt my head sideways and squint at it.

You didn't watch the three body problem, I gather :)

I'm glad someone got it :)

The apparent size of the moon is 0.5 degrees. So 0.3 degrees is not _that_ narrow. You can point your finger at the moon.

Reply on news.ycombinator.com