Hacker News Reader

Comment by rexreed | Hacker News Reader

And yet, MH370 is still missing. Yes I know satellites can't see under water but the earth can still hide mysteries.

Reading about the two nacro subs captured in the last year it's pretty clear you don't even need to go deep.

For a long time I was under the impression that diesel subs stand out like a sore thumb on sat photos and nation states watch them all like hawks, but apparently not and drug cartels can just roll around as they please in them.

It's probably less about hiding and more about a needle in a haystack. Narco subs are small.

Diesel subs at 30 meters become nearly invisible. They're hell to find. And if they stop, they're really, truly silent. The best way to find one is don't lose it in the first place. Track it from base it's entire trip.

Pardon my layman ignorance on this, but they still need to surface pretty often right? And the diesel engines leave a distinct signature when they surface to recharge the batteries?

Watched countries argue a bit over diesel vs nuclear submarines and this is where I've been imprinted with the idea that nuclear subs are the only actual true stealth subs you can build. I may be wrong here, but the evidence seems overwhelming based on usage. Diesel subs are for homeland defense purposes and don't worry about the enemy knowing their whereabouts, nuclear subs go silent for months and everyone is completely clueless as to where they actually are.

True. But they're stealth enough, can operate with a snorkel without completely surfacing and modern li-ion battery tech allows them to operate underwater for weeks.

may be wrong here, but the evidence seems overwhelming based on usage. Diesel subs are for homeland defense purpose

AIP technology means non-nuclear subs still have lots of uses. They can get closer in shore to gather signals intelligence or drop off/pick up SF.

Yes, diesels have to surface and recharge. Nukes can't be completely silent because of the coolant systems. Each has it's strengths and weaknesses.

Nation states may just not be interested in exposing information about their military capabilities for law enforcement purposes.

Small ones. Additionally, the military intelligence agencies with access to spy satellites probably don't care about blowing their cover or capabilities discovering makeshift drug running submarines.

In many ways its harder to see something through water than it is to see it through rock. Ground-penetrating microwave radar can get through tens of meters of quartz but centimeters of water. VLF and ULF penetrate 10-100x farther through the ground than through seawater. The frequencies that can penetrate more than a few hundred meters of water are around the same as the ones powering your lights. Antennas at those frequencies are miles long. You need special, non-conductive soils and bedrock to make them work. In short it's a real pain in the butt.

After 200 meters the ocean is practically opaque. Objects much deeper than that are reflecting a handful of photons. Below 500-1000 meters you're talking about photons per second at the surface.

Water is one of a quite small number of general radiation absorbers. To block alpha/beta/gamma radiation you need pure density- more mass per volume to slow down high energy particles. You can use heavy atoms like lead or uranium, or very densely packed lighter atoms. Neutron radiation is different- the actual number of atoms per volume is critical to maximizing the number of scattering events. That means you use things like polymers- hydrocarbons, so you have as many small atoms (hydrogen) in a volume as possible. Water is one of the denser liquids, while still being 11% hydrogen by mass, vs 14% for pure polyethylene. That makes it quite good.

Even sound isn't great underwater, relatively speaking- being a fluid in motion, there's a constantly-changing distortion on everything. The thermal conductivity also means thermal signatures spread out quickly.

Water is a poor medium for photons, but a great one for sound. That's why the US and other countries surveil the seas with linked arrays of underwater microphones, i.e. the Integrated Undersea Surveillance System (IUSS).

https://fas.org/irp/program/collect/iuss.htm

Judging from this anecdote it seems diesels subs can be stealthier than nuclear ones[0].

[0] https://www.popularmechanics.com/military/navy-ships/a197847...

This assumes, of course, that nation states would want to stop the submarines of drug cartels.

But they do have a good idea as to the area it's in. It's just very difficult to search such a wide area.

Yes, that's sad. But on the other side it's strange, because I did read, from at least one private company, they would have every 20 Minutes pictures from the whole earth. And there are several of such companys and many government agency who make pictures nonstop. So I think there should be a pic from MH370 somewhere.

There may very well be, but intelligence agencies don't want to expose their capabilities.

Disclaimer: My opinion.

I am fairly sure, no one is taking pictures of the whole earth, in 20 minutes intervals in a sufficiently high resolution to pick out an airplane. Specially one, flying over water.

For reference, ISS at its height ~400km, can see roughly 3% of the Earth's surface. This is without any kind of lens.

If someone has any kind of evidence, showing it otherwise, it would be great to see.

Theoretically, if Starlink satellites had cameras of that sort of caliber on-board, pointed down with wide enough lenses, they could capture the entire planet continuously and feed that data back down at close to real-time.

In a few years Blacksky should have a capability close to what you're describing

Nobody is going to offer evidence otherwise. Here’s a quick estimate for what you’re talking about: the Earth is about 500 trillion square meters of surface area. An image where each pixel was a meter would be a 500 TP (terapixel) image. Even with impressive compression the downlink requirements alone are insane, even ignoring all the other issues that would have to be worked out. Edit: just for fun, I estimated the file size- likely between 50 and 100 terabytes per image. We’ll get there one day, but no satellite constellation is downlinking that much data just yet. https://toolstud.io/photo/megapixel.php?compare=video&calcul...

The bottom line is that nobody is imaging the entire surface of the Earth at any useful resolution daily (aside from low resolution meteorological satellites, but they can’t find a plane). If you want to track a plane you have to start with other means to point a camera and take an image.

There is a huge difference between a company that has enough satellites in orbit to be able to take an image of any requested area within 20 minutes, and a company that can take an image of all areas on Earth every 20 minutes. MH370 is very unlikely to be captured in an image by coincidence. If there is imagery of it during its last flight then it would be because someone knew in advance that something was going to happen (it seems unlikely that anyone would have known).

Who would take a picture of the entire earth as a single image at one time?

Take that 500 Trillion Square Meters and divide it up by 1000 satellites (or whatever Starlink plans) and take images sequentially rather than all at once and it becomes rapidly much more manageable.

You don't need a single mult-terapixel image. You just need lots of much smaller images covering more territory on a continuous basis.

if you wanted pictures of the entire earth every 20 minutes, you'd need to figure out how many satellites would give you that coverage, the amount of resolution per image, and the bandwidth requirements transportation of those images in parallel.

Realistically, to get whole-earth coverage every 20 minutes would require a very large constellation of satellites. It's much more reasonable to get some less-than-100% coverage of the earth on a less-than-every-20-minute schedule and scale up from there.

Oh sure, there caves and forests

Reply on news.ycombinator.com