February 08, 2018 at 03:38AM

Today I Learned: 1) A couple of data facts for you, brought you to in part by Andy Halleran. Current total data of the human race is estimated at around 10^24 bytes. That's a trillion terabytes, or a yottabyte. I know some pretty big metric prefixes, but I had to look that one up. The estimated total data size of all (unique) genomes on the planet is 10^36 bytes. That's... a truly ludicrus amount of data. But we're catching up. For a (three-year-old) overview of some of our biggest data generators, see this (open-access!) review article: http://ift.tt/1HcOjIi. A few highlights: a) The Australian Square Kilometre Array Pathfinder project acquires 7.5 terabytes *every second*. b) Twitter's data storage needs are estimated at around 500 terabytes per year. Not massive by big data standards, but it does put into perspective why Twitter doesn't, in general, make their Tweets algorithmically searchable*, and makes it all the more impressive that they can serve up selected data as quickly as they do. c) We're predicting to store somewhere on the order of 2 to 40 *exabytes* (~8.5 billion terabytes) of human genome sequences alone. * You can collect random tweets from a couple of Twitter APIs, known as the twitter firehoses, and you're welcome to make your own mini-database. 2) A couple of rocket facts for you today, courtesy of Andrey Shur. Liquid-fuel rocket engines use (effectively) a turbojet to pressurize their fuel just before it's burned. To rocket good, you have to make really, really high-pressure air. One way to pressurize air really efficiently is to burn it; that's why explosions are useful in rockets. Another way to pressurize air is to use a pump; that's why turbojets are useful in rockets. The "turbojet" in a rocket is actually called a "turbopump", and its job is to pressurize incoming liquid fuel (as it's aerosolized coming out of the fuel tanks, I gather) so it can be exploded really efficiently. Now, pumping fuel requires a lot of energy. You *can* run turbopumps electrically, if you want, but a much more common strategy is to *pre*burn a bit of your fuel and use *that* explosion to spin up the turbopump. It is not intuitive to me that this should be efficient, but apparently it is. I guess pressurizing fuel before burning it must give you a disproportionate boost in thrust post-burn. There are (at least) two main kinds of turbopumps. An "axial flow" turbopump looks pretty much like a turbojet, which is the big spinning engine on the wing of a commercial plane. Basically, it's a bunch of high-density propellors that force air through a narrowing chamber, compressing them. The "centrifugal" turbopump is more common in rockets, and it's the one that makes me giggle -- it works by spinning really fast and *flinging fluid to the outside* where it's collected at high speed. So now you know -- these things (https://www.youtube.com/watch?v=PfHu-UJaK0Q) are, when you get right down to it, centrifugal squirrel pumps. Not quite a fact, but here's a gem from the Wikipedia page on rocket engines, on the topic of the dangers of liquid propellants: "With liquid propellants (but not gaseous), failure to ignite within milliseconds usually causes too much liquid propellant to be inside the chamber, and if/when ignition occurs the amount of hot gas created can exceed the maximum design pressure of the chamber, causing a catastrophic failure of the pressure vessel. This is sometimes called a hard start or a rapid unscheduled disassembly (RUD)." 3) You know how you're not supposed to daisy-chain together power strips? If you don't already know this, you're not supposed to plug power strips into other power strips. Ever wonder why? Like, why would that be dangerous? I've been told these terrible stories of daisy-chained power strips sparking and causing fires, but nobody ever gave me a reason that they would do that. Well, today I got fed up and googled the answer. It turns out that daisy-chained power strips are dangerous mostly because they make it much, much easier to accidentally draw too much total power at once. Power strips (and, for that matter, house circuits) are only rated for so much current draw, and if you exceed it, you risk overheating or shorting the strip. Practically speaking, most power strips have fuses and will commit suicide before they do any real damage, but it's still a hazard. The upshot -- you should be safe daisy-chaining power strips *if* you are quite sure you're not going to exceed the max draw for your power strips (say, if you fill every plug with cell phone chargers).