> I am annoyed by the redundant "systemd/system" directory name
It's not redundant, you also have /etc/systemd/user (and /lib/systemd/user) where units that run in the user context (as opposed to system-wide context) are stored.
Second stages definitely are getting dropped elsewhere, commonly the southern Indian Ocean, as well. Point Nemo doesn't always or even often line up with the target orbit, and you can't keep second stages in space for extended periods of time, because the propellant needed to deorbit boils off.
It's not space debris, it's the deliberate disposal of the upper stage of the rocket precisely to prevent it from becoming space debris. The time and location of re-entry are planned and controlled. This is not going to crash into your neighborhood (except if you're neighborhood is in certain areas of China, where they they happily dump spent rocket stages on populated areas).
Not OP, but with supercapacitors you're talking about a wildly different amount of energy. A 5F/5V cap stores about 62 J, while a 2500mAh 1.2V AA battery stores 10 kJ. With three of them you can store almost 500x as much energy.
You don't need that much of energy to keep CMOS memory and RTC clock running. The battery will self-discharge way before it's exhausted by the load. IMHO.
> So about 2/3 of the latency is caused by relays and switching equipment.
Not really; the speed of light in fiber optic cable is only about two-thirds of that in a vacuum. That means it takes light about ~60ms to travel the 12,000km great arc distance.
thats a great point, I failed to consider c in the propagation medium. however, OP didn't specify that either, he just insinuated that we can perceive propagation delays by c. we are both wrong (in his specific case about telecom delays, we have absolutely contrived experiments to detect it)
Microseconds even! Light travels about 0.3 meter in a nanosecond, and the Eiffel tower has a height of ~300 meter, so it takes about a microsecond for light to get from the ground to the top.
New Horizons didn't nearly overtake Voyager. It's currently traveling about 4 km/s slower, and as it's still closer to the Sun, it's also decelerating more.
Yes, I wrote that short for brevity. If you must have the full thing spelled out: New Horizons nearly got enough velocity at Jupiter to eventually overtake Voyager. 4 km/s is "nearly" in astronomical terms. New Horizons wasn't really trying to optimize for speed at Jupiter (its closest approach was over 10m km), and a spacecraft that did could easily overtake Voyager using Jupiter alone and not need an alignment with Saturn or anything else.
> 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.
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.
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?
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.
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.
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
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.
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.
> […] 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?
It's not redundant, you also have /etc/systemd/user (and /lib/systemd/user) where units that run in the user context (as opposed to system-wide context) are stored.