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Comment by Denvercoder9 | Hacker News Reader

> If amateurs can detect the signal from the Voyager probes with a small dish antenna

They can't, at least not for any reasonable definition of small. As I'm writing this, NASA is listening to Voyager using the DSS-14 antenna of the Deep Space Network, a dish with a 70 meter diameter, and the signal it receives is 10^-19 Watt. That's only 15000 photons per second. Coincidentally the area of that 70 meter dish is also roughly 15000 m^2, so a small dish of 1 m^2 will catch roughly 1 photon per second. Given that the datarate is 40 bits/second, it's physically plain impossible to receive the signal with a small dish.

Voyager's security is that it's really far away and you need a big, expensive dish to talk with it.

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https://news.ycombinator.com/item?id=34227604

DonHopkins on Jan 3, 2023 | root | parent | next [–]

John McCarthy trolled me once!

When I met him, we were chatting about Stanford, and I mentioned that I really admired that huge radio telescope that you could see around 280 and Page Mill Road in the hills above Stanford.

He looked puzzled and confused, and asked "Which huge radio telescope?"

I was flustered and explained how you couldn't miss it, right by 280 and Page Mill Road, it's out there in a field, its huge, it's enormous, gigantic I tell you, there's no way you can miss it, bla bla bla...

He let me go on and on, describing it, and acted like he had absolutely no idea what I was talking about, like I was crazy for hallucinating a gigantic radio telescope that both of us must have passed zillions of times.

Finally he let on and said, "Oh, you mean that SMALL radio telescope???"

inamberclad on Jan 3, 2023 | root | parent | next [–]

It's just called The Dish, and I mean, it's only medium sized (46 meters) compared to the main antenna at a DSN site (70 meters).

There is fundamental limit (Shannon limit) on decoding a signal Eb/No = -1.6dB [0]

where Eb is energy received per bit of information and No is noise spectral density.

This makes it paramount to collect as much energy per bit (Eb) as possible which in turn requires large antennas for far away objects such as Voyager probe.

[0] https://en.wikipedia.org/wiki/Eb/N0#Shannon_limit

But you dont need to hear voyager in order to hack it. It just needs to hear you. Nasa needs the big dish to hear voyager's tiny transmitters. Someone wanting to send a disruptive message to voyager could use a massive transmitter and a relatively smaller dish.

But you dont even need that. You need just enough outbound signal to jam the legitimate uplink, enough that voyager can no longer tell you from the real signal. That is likely much less than the power needed to send a command.

Or you could jam the nasa ground stations. A one-watt transmitter on a carefully positioned cubesat in low orbit would be enough to nullify voyager's real signal. (Setup the orbit to be over the deep space network stations every day as voyager comes into view.)

Even then you need a fairly large transmitter. It is quite easy to detect EM transmissions even when they are low energy. This would be incredibly easy to detect. There are plenty of regulations already by FCC, ITU and equivalent on what is allowed on what wavelength which most nations are signatories too.

Violating these is already solved by law enforcement, even if a rogue nation state is protecting you it will be handled with big gun diplomacy, America after all has the biggest guns.

As xkcd put it, $5 wrench is all it takes no matter how strong your encryption, that works both ways, if a government can find a malicious actor all it takes is $5 wrench to stop you. There is limited value for nation state to protect you from hacking voyager, there is no military or strategic value in it. Dormant satellites in LEO or GEO can be used as kinetic weapons so are lot more valuable.

There are also tech solutions like active jamming that could easily be deployed to counteract you that civilized world can use first even if they don't/can't blow you up without risking retaliation from your state sponsor.

> Violating these is already solved by law enforcement, even if a rogue nation state is protecting you it will be handled with big gun diplomacy, America after all has the biggest guns.

No one is going to war over ITU regulations or Voyager.

ITU regulations or more precisely spectrum they regulate is one of the most valuable and scarce resources today . Nations would will go to war if they are threatened .

Voyager itself is not economically valuable, but it a cultural symbol of American achievement like say Eiffel Tower in itself does not have value economically (apart from tourism ) but it is very big part of their identity so yeah plausible it would start a war .

> ITU regulations or more precisely spectrum they regulate is one of the most valuable and scarce resources today . Nations would will go to war if they are threatened.

They'd go to war if they're threatened, but a violation is ITU regulations isn't a sufficient threat. I mean, North Korea and South Korea occasionally shell each other (much worse, https://en.wikipedia.org/wiki/2010_Yeonpyeong_bombardment), and no hot war has resulted.

> Voyager itself is not economically valuable but it a cultural symbol of American achievement...it is very big part of their identity so yeah plausible it would start a war.

I'm sorry, if you think that, you're in a bubble. Voyager is not a "very big part of [American] identity," it's a nearly-kaput space probe that science and science-adjacent geeks (a tiny minority) occasionally get enthusiastic about.

The absolute worst that would happen if a nation state sabotaged it at this point, is the American government would send a strongly worded letter, and the saboteur's ambassador would be summoned for a tongue lashing.

No one's would start a war over the sabotage, and if they did such a war would go down as one of the stupidest casus belli ever. FFS, no one would even have died.

And no one's signing up to die in a war to avenge it. Would you volunteer to be sent to something like the meat-grinder of Eastern Ukraine, because a Voyager became incommunicado a few years early?

A satellite could jam the signal for a minute or two every ninety minutes, which isn't a lot, although it might be enough to be annoying.

Not if put into an eccentric orbit designed to have it hover in place. A tundra orbit could keep it in the way for many hours each day. Three sats could probably manage 24/7 coverage.

It's an air gapped system effectively

More like heliopause gapped !

There is some air in the gap, I suppose.

Thank you. Indeed, it's more accurate to say it is space gapped

pic of the dish for those curious https://www.planetary.org/space-images/the-70-meter-dss-14-a...

Also as seen from Google maps satellite view https://www.google.co.uk/maps/search/+goldstone+dss-14+/@35....

If 70 m is the diameter, not radius, that area is a factor of 4 too high. Should be more like ~3850 m^2. Still physically impossible at that size but it does make the required size a bit more tenable.

For those using freedom units that is about 200ft diameter, or about 31,000 square feet.

This works out to roughly 0.7 acres.

Funny enough the foot was restandardized to .3048m in 1959. So it is a metric-derived unit. Before that it was a feifdom unit, set by kings.

Was a tongue-in-check turn-of-phrase. This place is wound tight apparently.

Your tangential remark is ok but anyone else's is wound up too tight. OK.

I was trying to frame the numbers for people who don’t have an engineering background. My mistake.

And they provided an interesting tidbit of information about some of the units mentioned. I didn’t read it as anything negative towards your comment at all. Both your’s and their’s added to the conversation.

Oh, now you're just trolling the Apostrophe Nazis! ;)

And it made sense for you to then call it “freedom units“ why, of all possibilities?

Eh, it's a pretty common tongue-in-cheek way to refer to America's love of a slightly old fashioned system. I wouldn't read much into it.

Words matter.

At least half of the world has been violently invaded by this so-called “freedom“ and will take offense by this framing. Rightly so. Freedom by force is simply violence, with the additional violence of deliberate newspeak. Anyone repeating this joins the perpetrators, consciously or out of ignorance, and anyone not speaking out against it supports them by inaction and avoidance of their own responsibility and power.

Hey just having fun. Transatlantic banter and fun facts.

I had to look it up to check: my mental model was that a foot is some king's foot but there is more of a storied history.

Usually this joke flies but apparently, after the last election, people seem to take it seriously.

        Antennas at Goldstone Deep Space Communications Complex 
        Name                       Diameter  Description
        DSS 12: "Echo"             34m       Decommissioned in 2012.
        DSS 13: "Venus"            34m       Beam waveguide antenna (BWG) on altazimuth mount, located in Venus, California. ~910 m2 aperture.
    ->  DSS 14: "Mars"             70m       Cassegrain reflector on Alt/Az mount. ~3850 m2 aperture.
        DSS 15: "Uranus"           34m       "High Efficiency" reflector on Alt/Az mount
        DSS 24, 25, 26: "Apollo"   34 m      BWG reflector on Alt/Az mount
        DSS 27, 28: "Gemini"       34 m      BWG reflector on "High Speed" Alt/Az mount

https://en.wikipedia.org/wiki/Goldstone_Deep_Space_Communica...

To be clear, the heading of that column is Diameter.

https://www.jpl.nasa.gov/news/nasas-deep-space-network-looks...

As a sanity check, the video says the area of the dish is approximately one acre which would be ~4,046m2 and a 35m radius disk is ~3,850 m^2.

At the current rate of progress, when will it become physically impossibe to receive signals from it?

> […] a small dish of 1 m^2 will catch roughly 1 photon per second. Given that the datarate is 40 bits/second, it's physically plain impossible to receive the signal with a small dish.

Do you just mean plain impossible with the specific type of system used with Voyager, or are making a general argument that all systems that have a 1 photon/second rate cannot carry 40 bits/second of data?

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