Yet another Hacker News

What is a light-day? The milestone Voyager 1 is closing in on

46 points geox 2 hours ago 18 comments

polalavik 1 hour ago | parent

Free space pathloss for rf signals is proportional to 1/r^2, absolutely bonkers we can get anything from voyager.

freedomben 1 hour ago | parent

And with 50 year old tech! I do wonder if humanity will get to a point where we can retrieve the spacecraft at some point in the future (cue Star Trek fantasies)

bonzini 1 hour ago | parent

Technically, the receivers need not use 50 years old tech. I am saying that not to be annoying but because I wonder how much that matters.

cryptonector 6 minutes ago | parent

Indeed, it could have been obsolete tech as of launch. That's typically how it goes.

deadnomore 1 hour ago | parent

I would prefer they just maintain it as long as possible and maybe deploy a proxy for earth that trails behind it indefinitely once it’s finally out of range. Let’s set an unbreakable record.

rnhmjoj 1 hour ago | parent

1/r² is for an isotropic radiator, but Voyager 1 mounts (thankfully) a high gain directional antenna. The gains seem to be 36dBi or 48dBi, depending on the frequency [1]. This means that when pointed towards Earth, the signal power is actually between 4000 to 63000 times stronger than what that formula would give you. It's still tiny, but not as bad as that would suggest.

[1]: https://space.stackexchange.com/questions/65801/what-are-the...

robotresearcher 1 hour ago | parent

For clarity, it’s still proportional to 1/r², but with a much larger multiplier than one.

soniman 1 hour ago | parent

So it is traveling 1/18250 the speed of light. That is pretty fast.

zomtorg 1 hour ago | parent

And the closest known galaxy to the Milky Way, Canis Major Dwarf Galaxy, is just 25,000 light-years away - it's almost incomprehensible how vast the universe is!

seydor 24 minutes ago | parent

Yeah the only space tech worth pursuing is Wormholes

cryptonector 6 minutes ago | parent

I have bad news about that...

robotresearcher 1 hour ago | parent

> the spacecraft, in flight since 1977, is cruising at nearly 38,000 mph (61,000 kph) through the vacuum of space,

The page takes great pains to explain things, but omits a frame of reference for this speed. I’m guessing it’s sun-relative, but it could be relative to its take-off on Earth. Does anyone know?

zimpenfish 41 minutes ago | parent

Checked my bot's post from earlier today (taken from NASA's data[0]) and it says "Velocity relative to the Earth is about 34 km/sec (~77,173 mph); to the Sun about 16 km/sec (~37,763 mph.)"

[0] https://eyes.nasa.gov/assets/dynamic/dynamo/sc_voyager_1/now...

robotresearcher 32 minutes ago | parent

Thanks! And probably the earth relative velocity depends on the time of year :)

mek6800d2 10 minutes ago | parent

The Voyager Mission Status page has real-time updating distances, speeds (relative to the Sun), and light times for both Voyagers:

https://science.nasa.gov/mission/voyager/where-are-voyager-1...

You're right that Earth is catching up to the Voyagers during part of its orbit for several months in the early part of the year (and you'll see that reflected on the Mission Status page). Consequently I used to wonder if Voyager 1 would reach 1 light day from Earth 3 times - the first time, then a second time when the Earth distance decreased, and then a third time when distance increased again!

If you scroll down on this TheSkyLive page, you can see a graph of Voyager 1's distance from Earth over time and it's an up-sloping ripple instead of a straight line. You can play with the markers to zoom in and see that the catch-up phase happens in the early part of the year:

https://theskylive.com/voyager1-info

https://theskylive.com/voyager2-info

decoydave 39 minutes ago | parent

So glad voyager has real stuff on it for aliens to see rather than the crap that’s put out today by those with an agenda