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> A radio signal takes more than 22 hours to reach Voyager 1 Voyager has a 23 watt radio and a 14 foot parabolic dish antenna, pointed directly at Earth which

> A radio signal takes more than 22 hours to reach Voyager 1 Voyager has a 23 watt radio and a 14 foot parabolic dish antenna, pointed directly at Earth which is presently 15 billion miles away. The corresponding earth ground station has a 100 foot dish and transmits at thousands of watts. It's astonishing to me that Voyager knows where Earth is at all. I imagine it uses Sol as a reference? Or maybe the high powered control signal carrier? Amazing stuff.

_joel 2y ago
https://space.stackexchange.com/questions/3093/how-does-the-star-tracker-in-voyager-1-lock-onto-a-specific-star https://space.stackexchange.com/questions/3093/how-does-the-... :)
Intralexical 2y ago
> It's astonishing to me that Voyager knows where Earth is at all. Wikipedia says that the high-gain antenna has a beamwidth of 0.5° for X-band, and 2.3° for S-band. You have: tan(0.5deg/2)*2*164astronomicalunit You want: astronomicalunit * 1.4311791 So it's so far that you could almost point it straight at the sun, and have the entire orbit of the Earth in the beam. 23 watts, spread out in a cone the size of a planetary orbit. https://en.wikipedia.org/wiki/Voyager_program#Communications https://en.wikipedia.org/wiki/Voyager_program#Communications
- quesera 2y ago
  Which correspondingly means that the received signal strength here on Earth is very low. Internet says approximately -160.48 dBm, which is one thousandth of the minimum strength that the most sensitive commercial FM radio receivers can discriminate. Hence the huge receiving dishes, and apparently one 100 foot dish alone does not collect enough energy to reconstruct the signal, so multiple are required at each Deep Space Network receiving station. And due to the rotation of the Earth, we need three DSN stations to maintain constant communication with Voyager.
  - HPsquared 2y ago
    I wonder if they could build a very large dish in Earth orbit. Probably cost prohibitive though. Also there's the power and cooling aspect when transporting... Would there be any advantage to a space based station?
    - bruce511 2y ago
      I'm no space expert, but I'm not sure this would be say better. It would certainly be epically more expensive. Two obvious issues spring to mind; The orbit would need to be polar to avoid being blocked by the earth (assuming the craft is in the solar plane). Whatever orbit was chosen at least some planes some of the time would be obscured by the earth. And orientation fuel becomes an issue. Outside of refueling it becomes a hard end-of-life factor. Contrasted to land-based stations. Which are happily operating 50 years and can be maintained etc. Frankly I'm not sure there would be any advantage to a space receiver- and it's several orders of magnitude more expensive.
      - Intralexical 2y ago
        > It would certainly be epically more expensive. Actually, microgravity means you could have a 50-meter dish unfold neatly from a backpack-sized wad of Mylar.
    - Intralexical 2y ago
      You could build a planet-sized interferometric array without having to obtain land in different countries. If the orbit's much bigger than the planet, you can have most of the antennae always be usable instead of half on the wrong side. You can pick up wavelengths blocked by the atmosphere. You can build multi-kilometer single dishes out of mylar or steel cable, without gravity and air currents bending them. You can use it to focus sunlight onto surface locations, but probably shouldn't.
  - Intralexical 2y ago
    > Hence the huge receiving dishes, and apparently one 100 foot dish alone does not collect enough energy to reconstruct the signal Around 30k photons a second. You have: ((23W/(pi*astronomicalunit^2)) * (pi(50ft)^2)) / (6.626e-34J/Hz * 10GHz) You want: Definition: 36024.297 / s …I don't know if that's a lot, or where the noise floor is.
Rinzler89 2y ago
>It's astonishing to me that Voyager knows where Earth is at all It's not that astonishing when you realize astral navigation is what sailors hundreds of years ago did to navigate the seas. Just look at the stars with a sextant and with some basic trigonometry you'll know where you are exactly. The Apollo space crew had to do that by hand and eyes using a sextant too when the astral navigation computer failed.
- dcl 2y ago
  Knowing your longitude is very difficult without a clock... Can't do it with just stars iirc.
  - rbanffy 2y ago
    I think you can, with the Moon and where it is in relation to the Sun.
  - fourgreen 2y ago
    You can determine your longitude without a clock, but achieving precision with this method is challenging. First, you need to observe the Moon's position relative to fixed stars, which gives you the UTC time. Then, observe the Sun's position relative to the horizon to determine the local time. By comparing the two, you can calculate your longitude.
    - monkeyfun 2y ago
      How are you going to usefully use this information if you wouldn't have an obvious way to know precisely how long it's been between whenever you lost track of the moon and stars and whenever the sun is clearly visible over the horizon?
  - quesera 2y ago
    This is true and there's a fascinating history for Earth-bound (little v) voyagers! But Voyager does not have this particular problem. :)
- 2y ago
exe34 2y ago
I know trident uses the stars to avoid gps jammers, so presumably voyager can do something similar.
deleted 2y ago
[deleted]

_joel 2y ago

https://space.stackexchange.com/questions/3093/how-does-the-star-tracker-in-voyager-1-lock-onto-a-specific-star https://space.stackexchange.com/questions/3093/how-does-the-... :)

Intralexical 2y ago

> It's astonishing to me that Voyager knows where Earth is at all. Wikipedia says that the high-gain antenna has a beamwidth of 0.5° for X-band, and 2.3° for S-band. You have: tan(0.5deg/2)*2*164astronomicalunit You want: astronomicalunit * 1.4311791 So it's so far that you could almost point it straight at the sun, and have the entire orbit of the Earth in the beam. 23 watts, spread out in a cone the size of a planetary orbit. https://en.wikipedia.org/wiki/Voyager_program#Communications https://en.wikipedia.org/wiki/Voyager_program#Communications

quesera 2y ago
Which correspondingly means that the received signal strength here on Earth is very low. Internet says approximately -160.48 dBm, which is one thousandth of the minimum strength that the most sensitive commercial FM radio receivers can discriminate. Hence the huge receiving dishes, and apparently one 100 foot dish alone does not collect enough energy to reconstruct the signal, so multiple are required at each Deep Space Network receiving station. And due to the rotation of the Earth, we need three DSN stations to maintain constant communication with Voyager.
- HPsquared 2y ago
  I wonder if they could build a very large dish in Earth orbit. Probably cost prohibitive though. Also there's the power and cooling aspect when transporting... Would there be any advantage to a space based station?
  - bruce511 2y ago
    I'm no space expert, but I'm not sure this would be say better. It would certainly be epically more expensive. Two obvious issues spring to mind; The orbit would need to be polar to avoid being blocked by the earth (assuming the craft is in the solar plane). Whatever orbit was chosen at least some planes some of the time would be obscured by the earth. And orientation fuel becomes an issue. Outside of refueling it becomes a hard end-of-life factor. Contrasted to land-based stations. Which are happily operating 50 years and can be maintained etc. Frankly I'm not sure there would be any advantage to a space receiver- and it's several orders of magnitude more expensive.
    - Intralexical 2y ago
      > It would certainly be epically more expensive. Actually, microgravity means you could have a 50-meter dish unfold neatly from a backpack-sized wad of Mylar.
  - Intralexical 2y ago
    You could build a planet-sized interferometric array without having to obtain land in different countries. If the orbit's much bigger than the planet, you can have most of the antennae always be usable instead of half on the wrong side. You can pick up wavelengths blocked by the atmosphere. You can build multi-kilometer single dishes out of mylar or steel cable, without gravity and air currents bending them. You can use it to focus sunlight onto surface locations, but probably shouldn't.
- Intralexical 2y ago
  > Hence the huge receiving dishes, and apparently one 100 foot dish alone does not collect enough energy to reconstruct the signal Around 30k photons a second. You have: ((23W/(pi*astronomicalunit^2)) * (pi(50ft)^2)) / (6.626e-34J/Hz * 10GHz) You want: Definition: 36024.297 / s …I don't know if that's a lot, or where the noise floor is.

Rinzler89 2y ago

>It's astonishing to me that Voyager knows where Earth is at all It's not that astonishing when you realize astral navigation is what sailors hundreds of years ago did to navigate the seas. Just look at the stars with a sextant and with some basic trigonometry you'll know where you are exactly. The Apollo space crew had to do that by hand and eyes using a sextant too when the astral navigation computer failed.

dcl 2y ago
Knowing your longitude is very difficult without a clock... Can't do it with just stars iirc.
- rbanffy 2y ago
  I think you can, with the Moon and where it is in relation to the Sun.
- fourgreen 2y ago
  You can determine your longitude without a clock, but achieving precision with this method is challenging. First, you need to observe the Moon's position relative to fixed stars, which gives you the UTC time. Then, observe the Sun's position relative to the horizon to determine the local time. By comparing the two, you can calculate your longitude.
  - monkeyfun 2y ago
    How are you going to usefully use this information if you wouldn't have an obvious way to know precisely how long it's been between whenever you lost track of the moon and stars and whenever the sun is clearly visible over the horizon?
- quesera 2y ago
  This is true and there's a fascinating history for Earth-bound (little v) voyagers! But Voyager does not have this particular problem. :)
2y ago

exe34 2y ago

I know trident uses the stars to avoid gps jammers, so presumably voyager can do something similar.

deleted 2y ago

[deleted]