Talk Is Cheap
Shockingly cheap!
I remember the first time my father called me when he was on an overseas business trip in the early 1970s. "Listen to the delay. That's our conversation traveling from your phone down the wires to the phone company, then up to a satellite, and from there to a satellite station here in Europe and then the whole rest of the trip to my hotel room." I'd learned about the delay lags watching the 1960s Apollo missions--2.5 seconds round trip to Moon. Mars is a major issue. It's between 8 and 48 minutes round trip for a signal depending on whether we're on the same side of the sun.
Our call had just enough delay to make it better if we each hesitated before starting the next sentence. The actual delay of the signal to travel to geosynchronous orbit and back should have been about 1/4 of a second (barely an echo), it was at least double that. Dad promised to explain signal latency when he got home and it would be cheaper to do so in person. Basically, a satellite is handling a lot of traffic, so it buffers signals in a temporary memory and then sends them in batches. Neat in one way, but really annoying in others when folks started trying to talk long distances with computers. Hence, one of the many reasons for these new, low-orbiting satellite networks by Space X, OneWeb, and others, very low distance lag and newer electronics to mitigate latency lag.
I found one reference that said that call from France to New York State cost about $7/minute in today's money compared with about $1/minute to call coast-to-coast or $0.35 to call the next town over. (Yes, we used to get charged for all that.)
Now, I grab a cellphone. My signal goes up to a tower, through the carrier into a fiber optic cable laid all the way under the ocean, and pops up wherever I want to talk to (except for a few obscure exceptions like Antarctica, which still need satellites). Delay? Near enough zero to not care. Cost? Using VOIP (Voice Over IP--Skype, etc.) it's often free, even when going trans-oceanic. As I said: Cheap!
However, ships and submarines, much like Antarctica, are not attached to a whole lot of fiber optic cables. So, the answer of how they communicate varies--a lot!
Talking to submarines
One the surface is easy. They put up a radio mast and can talk locally to another boat using the same range of frequencies you and I listen to on the car radio or with walkie-talkies. Easy-peasy. Nobody nearby? Bounce the call off a handy satellite and you're good to go.
But standard range radio waves don't exactly punch through water. If they don't want to surface, they have the option of a little antenna buoy that they can release to the surface on a wire and talk through that. But what if they're too deep for that?
Or don't want to risk even that little chance of being spotted?
Unlike short radio waves, longer sound waves travel relatively happily through water. Next time you're in a pool or hot tub, put one ear in the water and notice how much clearer the filter's motor noise is. Submarines can talk acoustically up to about thirty kilometers without exotic equipment.
Neat trick: The US and Russia have placed acoustic couplers on certain undersea cables along common submarine routes. When a sub passes near one, it can phone home with relative ease.
Talking To The Depths
But when a sub gets off the main routes? There are two solutions here: VLF and ULF (Very and Ultra-Low Frequency [which includes Extremely Low Frequency ELF]). This is where it gets really interesting.
Let's talk about these radio waves for just a second. The longer the wave, the farther it can penetrate into water or through the Earth itself. Most of what we know about the interior of our planet comes from using seismographs to "listen" to how earthquake shock waves bounce off the interior layers of the planet with enough power to shake the Earth's surface somewhere far away.
There are a couple of catches here.
- An ELF radio wave is big. Commonly around 3 Hz (Hertz) means that it is vibrating three times per second. One wave length is about the same length as the diameter of the Earth. And an antenna needs to be some reasonable amount of that size to generate the signal. China, India, Russia, and the US are the only players at this scale.
- Generating a big signal is much harder than hearing it. The world's largest ELF generator, China's (https://www.thedrive.com/the-war-zone/25728/chinas-new-york-city-sized-earthquake-warning-system-sounds-more-like-way-to-talk-to-subs), is roughly the size of New York City and requires an immense amount of power to generate an Earth spanning signal. It has to be strong enough to be heard everywhere around the globe. A submarine can use a much smaller antenna to hear it because the signal is already there.
- It's dog slow. An ELF transmission at 3 Hz can send about 4 characters per minute (and not fancy ones, we're talking about the alphabet, numbers, and not much more). Not a fast way to talk. The most common transmission code? "Get close enough to the surface that we can talk to you with VLF." And actually, the US has so enhanced their VLF technology that they've shut down their biggest ELF transmitters even as China is just starting to bring theirs on line.
However, ELF is very useful if you need to send a code to everyone in your submarine fleet at once, or make sure you reach a specific boat even if you have no idea where in the world it may be at the time. (A missile submarine's job is to go out and get well and thoroughly lost so that no one can find it.)
It still ain't easy.
Now Do It From A Plane
The US "Doomsday" planes mentioned in the previous NerdGuy Friday (and the latest Miranda Chase novel, Nightwatch) have a rather unique solution to this problem. In the aft of the plane, an 8-kilometer-long antenna is spooled up on a drum. On demand, they can unroll this antenna, kept relatively straight by a small drogue cone at the back until it trails its full length behind the airplane. They can then directly communicate to any submarine as needed, from this fortress in the air.
Again, this is far trickier than it sounds. Of course there's the challenge of generating enough power to send a signal on that scale. This plane has a lot of power dedicated to running all the extra on-board electronics.
But also imagine being at 50,000 feet, trailing a 5-mile long piece of copper wire. And it gets hit by a lightning bolt. Or even worse, the electro-magnetic pulse of a near-miss nuclear weapon. The last thing you want is the giant antenna, designed to send and gather radio signals, to gather in a huge shock that disables the aircraft. Some very tricky engineers up there.
Doing It On Nightwatch
All of that, plus much more, boiled down to make this short excerpt (with mild spoilers).
He was in it now and there was no backing out unless he wanted to be reported for breaking his security clearance—which would lead to a whole world of hurt. He had to do what they asked, but…how?
He realized that he didn’t need to convince anyone to deploy the eight-kilometer-long ultra-low-frequency antenna to talk to the aggressor sub. He didn’t know the details about that system and didn’t care, but he knew that only four countries maintained the capability to converse with the deepest-sailing subs via ULF. They needed antennas that were miles long, China’s latest was bigger than New York City, driven by obscene amounts of power.
And ULF was so damn slow, allowing only four eight-bit characters per minute. The most common message sent via ULF was to order a particular sub to surface so that command could talk to it at a reasonable rate via satellite uplink.
Any country other than the big four: US, Russia, China, and India—and he hadn’t asked for an ID from his new benefactor—wouldn’t even have ULF equipment aboard. A standard VLF could punch through forty meters of ocean. If they were deeper than that, then, well, he’d have to tell his newest clients to go to hell.
Well, maybe not tell them that, but he could at least say he’d tried. Also, a very-low-frequency radio was standard gear on an E-4B Nightwatch, and he knew exactly who to ask.
Lately he’d been chatting up one of the comm techs. Suzy was a lowly airman first class, overwhelmed to be noticed by someone as grand as a tech sergeant with over ten years of service compared to her sixteen months. He’d found a way in by playing stupid and asking her about her job and her comm gear. They all had top secret or better clearance aboard the Nightwatch, so she was most forthcoming.
At least about the comm ops. She wasn’t hot the way Tamisha was, but she was plenty cute with her tangle of curly red hair and tight little body despite being almost pancake flat. And he’d been careful to be nice and funny; she always smiled easily at his approach. But that’s where it ended.
Anyway, he had bigger, more financially important concerns at the moment. He drifted back along the central aisle, passing the mostly unattended pairs of desks until he reached the comm shack that separated battle-staff operations from crew recreation…mostly meaning chairs that tilted back and the freedom to read or play a video game.
Jackpot!
Suzy was alone at her station.
And there was that smile that gave him an odd buzz.
“Hey Suzy. I was just sitting there, bored out of my skull, and reviewing all the cool shit you taught me. I can’t remember how the VLF transmitter works. Could you show me again?”