wumpus

I'm convinced they had to. I suspect the engineers in the program knew this as well and also knew what it would do to the schedule (and budget) so it never happened. There's no point in understanding how to build it right after you've blown the budget (and schedule) and you can't build it afterwards anyway. All they could do was launch and hope the problems were small enough to fix on the fly (they weren't). They at least got to test all the other systems at once. I'm sure the engineers were also kicking themselves for not making the N-15 sufficiently similar to a non-slagging rocket that could act as a stand-in to test the control circuitry. The requirements for those controls are mind boggling (think 90s Cisco gear in the 60s) and needed testing much more than the engines themselves. In engineering, often the steps (which aren't often obvious) in between "off" and "working" are harder to get right than getting the working state to work right. In large projects, this means that each little step has to be possible (note that I have no idea if the Nova could have met the pre-1970 schedule had Gemini not proven that lunar rendezvous was a reasonable choice. This was merely an obvious individual step that needed to be done).

NASA has to answer to Congressmen from 50 states and 435 congressional districts, each one wanting special treatment. While the money may be spent on companies efficiently, often the "wrong" company is in the right location to get the job. I've heard that Thiokol's contract to build the shuttle boosters only made sense politically. I suppose it is slightly easier for an American company to build anywhere in America (see Blue Origin's Mobile, Alabama plant) for political reasons than an EU company to build anywhere in the EU (presumably because the EU hasn't been around long enough to make this happen). Is ESA directly funded by the EU? Last I heard it was funded by individual countries who thus had a lot more say in where the money was spent. If the funds came out of the EU general fund, I'd assume it could eventually look a lot more like NASA.

You hardly need a laser, an LED (or even some more efficient light) would work just as well (and the lower the wavelength the better). In the end you have the same basic claim of the em drive (electricity in, momentum out) but with wildly lower efficiency. Also, for any ultra-high Isp drive, don't be surprised if your heat sink produces significant thrust (possibly as much as your "main" thrust). Maximize the albedo of the thing, except for low albedo bits on the engine side and only for high frequencies (how you want all your heat emitted as energy).

I have a hard time believing you would get better telemetry from a launch than a test jig (at least for the stage the rocket was in when they canceled). Perhaps it worked when fixed in a test jig, but kept needing to be shut down as attached to a rocket? I have to admit that knowing this makes my impression of the decision to use these (specific engines) in the Antares rocket much less a good idea.

All rocket failures are human failures. Most fail due to errors in design. Challenger was a program management failure. Spaceship One was a combination design and pilot error. I'm curious why the rockets were so untestable. Presumably you had to test them vertically, keep them above anything that burns/melts when rocket flame present (i.e. everything), and restrain them with more force than the weight of an N-1 rocket. I have to get back to reading "Rockets and People", but while the US may have snatched up all the V-2 rocket scientists, the Soviets managed to grab any test rigs in sight (and were happy to get them). I'd assume that such test equipment would still have a high priority in building the N-1. I can only assume that such a rig was possible, but by the time the necessity of such was obvious it couldn't be built remotely before Apollo landed on the Moon. I'm guessing that the difficulty of strapping that many engines together wasn't obvious (I still can't imagine the control circuitry, it sounds like it is up there with the CDC6600*), and there may have been bureaucratic issues (see the "it wouldn't explode, since Glushko's engines were reliable and didn't fail" defense of the RD-270). * the CDC6600 was a super computer designed by Seymour Cray and shipped at the end of the 1960s. It lead to a famous memo by an IBM executive that their high profile "stretch" computer was beaten by "34 guys and a janitor" (which was certainly an exaggeration, but do you really think IBM would deal with a manager whose status report would read "[yearly status report: 1/6 way of building the world's fastest computer]"?). Even more to the point, one of the lead engineers (Throton) wrote a book on the design "Design of a Computer", and I think it is still available free as an e-book. http://ed-thelen.org/comp-hist/DesignOfAComputer_CDC6600.pdf

The logic doesn't make sense: dropping tanks reduces mass, which means the engines are going to be more efficient. Granted, the stated engines were mammoths, which are fine for launch but not always ideal after all the drop tanks are gone. One other favorite trick of mine is to place a small/medium tank below the capsule/probe and a larger tank above it (you might need a lander for stability). Use the top engine first, jettison it, and keep going with the bottom one. Granted, this normally only makes sense with terriers and poodles which are cheap and light, but you still get the efficiency of "bamboo staging" in something that works. Without the souposphere, drop tanks generally replace asparagus staging (although twinboar asparagus likely has advantages). Often aerodynamic concerns outweigh the advantages of drop tanks, although combining them with SRBs make more sense. Note that for small rockets, it often makes more sense to stage a cluster of hammers with a single decoupler. The thrust from a hammer is high enough that an extra hammer is cheaper than an extra decoupler, and two hammers likely out thrust the main rocket (and don't ask about the cost of at least two fuel tanks and lines).

I'd be curious how often the serial numbers were changed specifically to meddle with such intelligence. I've heard of it being done often enough in the commercial world, where a higher serial number* might feel safer for customers. There have been a few software releases that started as "2.0" for similar reasons. * When Seymour Cray was making supercomputers, plenty of his customers would fight/pay for "serial #1" of the next new computer. Often new models were introduced to sell as many "serial #1s" as possible (or claim "first to DoD", first to Government", "first to the private sector").

If they really cared about that, why are they using hypergolics? Ignition can't be *that* hard for the first stage.

Generally speaking, sports and horse betting are supposed to use the odds to balance the betting so that any outcome leaves the house with the "House rake". You are effectively betting against other players. - I think there was a panic in Las Vegas over the chance that the Golden Knights would win the Stanley Cup (they took way to many "local sucker" bets on the expansion hockey team). No idea if you can get decent odds on the Capitols (who have a severe advantage right now) to cover the bookies' fear of a Vegas victory. Bettors aren't rational, and you can't always balance the books by giving the "right" odds. - as far as I know, the odds on a horse race keep changing as long as they take bets (which probably doesn't stop until they start loading the horses). Whatever they are when the race starts, that is what is paid out. What they were when you made your bet is irrelevant (although a huge swing implies blatant mob action).

Hard to say. A reusable rocket program might actually be more expensive, and if they can be in position to have the only orbital station after the ISS is retired they want one. Long term you want both, but the orbital station may have more time constraints. Some financial analyst ran the numbers and insists that the Falcon 9 reusability program doesn't save anything. On any US government contract (other than R&D specifically for reusability), this would be considered a failure. For any long term planning organization (like Spacex or the Chinese space program), this would be considered "learning how to land rockets for free" and a wild success. Still, delaying reuse until the kinks are worked out of disposable rockets is probably a good idea (spacex presumably hired enough people who understood disposable rockets).

I'm curious how you would ever compute pi so accurately, and leave behind records of such. In the Middle Ages, monks routinely scraped books clean to copy more valuable books, I'm sure random lists of numbers would be first on the list for scraping. Ancient texts are fairly common from Egypt (papyrus) and Mesopotamia (pottery shards). I think we have far more Mesopotamian texts than anybody can translate: often you have to complete a jigsaw (which requires understanding of the text to put it together) before finally translating it. This might be an amazing opportunity for AI researchers to show massive possibilities for their routines. Basically, if you want text to survive it needs to be more or less buried in the desert. Some temples might have survived, but often pillaged and any "sacred texts" over written by rival priests (I can't imagine the Inquisition was willing to allow Aztec temple writing remain). So expect to bury a *lot* of text if you want your texts to be found when somebody can read it. As far as complicated calculations of pi, of all the techs to "beeline" to, I can't see building a computer before the (electric) telegraph was ready for use (you might wind up building the telegraph, but don't expect a lot of help until the railroads really want some help in avoiding crashes. You'll need: Electricity (starting with battery cells) Highly ductile wire (and the temperatures to make them ductile metals that can withstand temperatures while other metals are drawn through them permenent which in turn require a great chain of the above magnetizing more magnets, but start with some fairly strong lodestones Once you have that you need a *ton* of cheap wire, magnets, and either generators or batteries. Don't plan on building a computer or telegraph on batteries. You really can't build a computer without building half the infrastructure of the Victorian era (or later). That said, if you were in the 1940s or so, once you understood how to make all the basic gates out of vacuum tubes and could make magnetic core memory, you could pretty much beeline to a CDC6600 (the supercomputer of the Apollo era, although presumably with tubes instead of transistors so it wouldn't be *quite* as fast). In the Victorian era, you *might* be able to get a full blown packetswitching telegraph system going, allowing you to scale up computers as you wish. Before that, you'd be pretty much like Babbage: toiling away a fortune trying to build something on the edge of technological feasibility with little to show for it (Babbage could at least influence an infrastructure on the verge of making use of it, a Roman Babbage would see his device suffer the fate of the Antikythera mechanism. The Romans had some massive watermills, but they had equally massive sunk costs and it was easier to just buy individual slaves (kind of like nuclear plants vs. natural gas turbines). The economics became far worse after Rome fell, and England wouldn't see watermills until around 1000 (most of the data comes from the Domesday book). Watermills nearly died out again before the fourteenth century, but the black plague gave the forests a chance to regrow. By the time the forests were in danger, the technology was ready to extract enough coal from the ground. So your sterling engines would have to have a greater work/cost output than watermills to even get built, then they would have to consume wood (charcoal, whatever) at a rate slower than the equal watermill. I suspect that if you managed to get a culture using Sterling engines, you could possibly choke off the whole industrial revolution and simply have the tech crash back to "medieval normal". The key word here is that the Syrians were casting iron/steel in the Middle Ages. Europe might have waited until the 18th century, but not everyone else did. This assumes you can simply give commands and 20,000 people will obey you. I'm not sure how many craftsmen it took to produce the Antikythera mechanism, but it seems more available to our forum time travelers. Of course, if you introduced gunpowder/greek fire at a time when it could obviously tip the balance, maybe you could have 20,000 people at your command. But I still suspect it wouldn't be as simple as that (and you would be more concerned with assassination attempts (sword of Damocles was from a similar era)) than "leaving a legacy that people of "your" time could decode". Organizing 20,000 people doesn't seem to be something that requires modern thinking anyway. I'd rather do it with modern (or even late medieval) accounting, but plenty of cultures managed with rudimentary math. Don't forget survivor bias in these ancient monuments. Medieval cathedrals all appear to be well designed which requires strong understanding of engineering. In reality, plenty of them simply collapsed and the ones that remain have the good designs. Oddly enough, they had quite a few similarities to government rocket programs. They were typically jobs programs first (which benefited *this* generation, the cathedral would benefit your great-grandchildren) and cathedrals second. The secondary point, glorifying God was also largely in theory (similar to "advancing science") while the real secondary goal was "to show up all the other local cities by having a Cathedral (and presumably the Archbishop that comes with it, who presumably could even tax/demand tithes from nearby areas [I'm less certain of the last bit, having just realized that the title requirements would likely change the local politics]).

It's way older than that. Unfortunately google finds a bunch of definition of "steam engine time" (when somebody, fairly quickly, will develop a steam engine), and an interview with William Gibson on said subject. Unfortunately, Gibson has written a book (The Difference Engine) that manages to get basic math wrong in a way even Micheal Crichton avoids. basic steam engine chronology: One Captain Savery invents both the steam engine and vaporware by describing his "wonderous" miner's friend. In practice, you would have to build it to the absolute highest precision possible at the time to pump any water before it blew up. - difference engines suddenly fail if someone attempts to execute a universal compressor. Math doesn't need angels rushing around to protect it, like angles rushing around to slay the good survivors and slay the weak to prevent evolution from happening. Math just is, and it would be like having spacecraft eaten by the Kraken to avoid exceeding C (instead of simply increasing their momentum more by mass than velocity). Of course, both "Going Postal" and "Making Money" by Terry Pratchet are highly recommended.

I'm less sure about the whole process, but I'm pretty sure that Damascus steel (wootz steel, not the fancy acid etchings now sold as "Damascus Steel") involved melting steel or iron. Similar things were done in Southeast Asia. I'm guessing the forges needed to survive the temperatures were pretty rare, but at least some of the steel they made is reasonably sure to come from such processes. https://en.wikipedia.org/wiki/Crucible_steel Not sure if they used charcoal or real coal (or even coke). I suspect a lot of bellows were used, and access to the right type of stone to make a forge. - note: you never cast a blade, but you might melt enough pig iron to pour the stuff you start with, then hammer away (at least one claim to the "secret" of Damascus Steel is that the alloy included vandium, and vandium plus enough hammering made a blade like nothing else you could make with medieval tech). - Anyone want to claim that the Antikythera mechanism is "proof" of time travelers/aliens/Atlantis? Granted, I don't think that any *one* technology or scientific understanding of the solar system was needed to make this device, but it would seem pretty unlikely that we just happened to find the absolute highest example of Roman technology out in the middle of the Mediterranean (see Carter fallacy thread, this would be a good application for that math). Isn't the "schwartzschild radius of Earth" 1cm, or did I make a mistake on the back of my envelope?

As far as I know, trebuchets were never used in pitched battles (although grapeshot might have changed things). Grenadiers were a thing (throwing them by hand), and I imagine grenadiers could achieve archery range (which is close enough to destroy a formation). I still think compound bows would be easier to teach people to make, and cheaper than handing grapeshot to your enemy (how many man-hours does it take to make shot in a medieval economy? Then again, arrow manufacture was a real pain). If you really want to defeat an enemy on the battlefield, maps and a compass will probably help more than any other tech. Part of the reason Hannibal was so effective was he did a lot of his own scouting. This allowed him to pick ideal battlefields. Prior to the telegraph, wars often involved armies groping around for each other until they finally collided. Get the maps first, then go to war. And yes, map generation will be hugely expensive. Might be justified if you have a merchant operation (you know double-entry accounting? that's a huge step up against anyone before 1000CE or so. Pen, paper [or clay and stylus], and money are the only infrastructure you need). I'm also drawing a blank on the means to a rise to power. Most of these skills are pretty obscure, requiring fairly old kerbanauts to have picked up enough. But your ideal time traveler is pre-teen, in order to learn the language. However you learn the language, I'd recommend trying to become a brewer if you can find the means to build a still (also knowing about yeast and sanitation should give you a huge leg up, but your competition has done it all their lives, and learned from guys who did it all their lives...). Becoming a drug lord has always been a great means to power, and if you're the only one who can distill alcohol [and again, infrastructure is everything: distilled alcohol is only great if you have the means to grow more food than you can easily transport as food/beer]. Maybe living just outside a big city (modern people can't expect to get used to the smell of a large ancient city).

Terry Pratchett had an interesting take on this type of thing. He had a group of teens (maybe slightly younger) travel back and forth in time (to WWII). During one of the stops, one is left behind. Back in their own time, the much older boy meets up with them. They assume he built computers or such, but he asks them to describe (using only 1940s tech) how to build a computer. Or even how to make a plastic spoon. None have any idea. What thy boy did was come up with something he *did* understand (and could work out his misconceptions): a hamburger stand. Of course once he had a nest egg, he had a huge advantage in investing. I'd be curious how many of us have skills that could be used in the bronze age (or before) to rise to power? Presumably you have to first prove yourself as an individual, and be able to build your technology base as your followers increased. I think you'd be surprised how adapted each time period's technology would be to its infrastructure. Building a superior infrastructure for you barely more advanced technology will be a Herculean task. I'm guessing a blacksmith would go a long way. I've studied history and technology (as an enthusiast, not at all an academic aside from an undergraduate class long ago) for a long time and as far as I can tell: technology *is* infrastructure. You aren't going anywhere until you build that infrastructure. Some "inventions" - the horse collar is the biggest "why didn't they think of that". Requires a lot more leather than an ox collar, but allows you to get a full horsepower out of each horse (without this you basically strangle the horse. Yes, chariot races were a lot slower than you'd think, largely because they were strangling the horses. - mouldboard plough would be the next: you need iron and probably the horse collar (you could do it with oxen, but get the horse collar first). - building hotter and hotter forges would be an amazing trick. Start with producing iron, and work your way up to steel, pig iron, and hopefully even crucible steel. Hope you know where historical iron and coal deposits are! - remember that while the katana was an amazing performer made out of questionable ore (lots of swords were far better, but almost certainly used better ore), samurai were far more likely to fight with spears on the battlefield. Forging something like a katana might get the attention of kings (for good or ill), but don't expect to change the course of a battle with them. - could you make a compound bow? Sounds hard, and I'd hate to imagine all the technology needed for it (maybe you could lathe hard wood/iron roller bearings instead of ball bearings), but it would probably become the "super weapon" of anything before gunpowder (you need hardened steel plates to even think of stopping it). And even if you can make gunpowder, can you make the steel barrel needed to contain the explosive (sure, you could probably use it to sack walled cities, but that doesn't sound like a long-term thinking that goes into leaving a legacy). Again, infrastructure is key. - there is likely a huge difference between a horse riding nomadic band and the same band with stirrups as cavalry. Expect amazing pushback from the tribe who learned to stay on a horse the hard way and insist that anyone who can't isn't part of their tribe. Don't be too surprised if the local cavalry have weird systems that work almost as well (the Romans had some weird circular stablizer). Finally: on writing systems: We all know that finding the Rosetta Stone meant that someone merely looked at the Greek text and was able to transcribe the Egyptian pictograms into Greek. Except it didn't happen that way at all. Certainly papers were written at the time that said as much, but it took another 20 years before Champollion finally got around to doing the hard work of matching up the text. Champollion was one of the few westerners (and probably few people altogether) who was fluent in Coptic. He was able to show that hieroglyphics were essentially Coptic, typically with stylized pictures to replace Coptic sounds (note that classical hieroglypics were often meant to be visually impressive to illiterates on temples and tombs and even if you could read them were often propaganda, so accuracy wasn't a big thing. Scribes had a separate simplified writing system for keeping records). A similar method was used with Linear B, and that had to be done without the aid of a Rosetta Stone: Alice Kober was able to show that it was an archaic form of Greek, using an ancient syllabary (each symbol meant an entire syllable, not just a sound). You'll need a lot of copies of a complete explanation of your language and writing system, and even then they don't have a great chance of being decoded. So far, unknown writing systems have relied on knowing the underlying language, but there is always hope. Recently, there may have been advances in decoding the Incan knot system, but the actual advances are far less than the clickbait titles may indicate.

Plenty of riverboat casinos in the US have realized this and can often go an hour between reaching port and letting people off. I really don't recommend these places. More likely the "riverboat" has a permanent foundation to a sand barge, but I've seen a few that you could get stuck on. I tried it once, and ran out of "mad money" much faster than expected and never returned (and carefully avoided the "cruising variety" after reading the fine print.

The X-15 was designed more for high speed tests (and flew many more flat tests than "parabolic space shots"), so all that shielding the X-15 had was necessary. SpaceShipOne has no speed requirements (outside of delta-v) and doesn't require the shielding for direct mission requirements. The shuttlecock shape allows it to reenter and still not worry about said shielding. The planes had different design goals and were designed differently. Imagine that!

I strongly suspect they speed up as much as legally allowed as play continues. Go fast enough and the player will hit "new game" and clear out a win...

Wasn't one of the goals of Arane 1 to be reusable? I thought they were pitching it to compete with the Shuttle (and lack all that extra mass to orbit). I'd assume they dropped the idea when it was obviously too hard (I can't seen Spacex pulling hoverslams off with 80s tech) and the Shuttle's refurbishment was too expensive anyway. My googling can't confirm this.

Redundancy is great until you realize you are accelerating redundant systems by 16,800m/s. Obviously, all kinds of sneaky ways should be used to create redundancy where it might not be so obvious. Like sending all the ascent vehicles before the first human, so even if the first n fail there is still another. But I suspect there will still be way too many ways for an ISRU system to fail that will either have all systems fail (typically a design error) or have a choke point that was unavoidable. Expect at least some human required repairs. Just think how hard it is to make sure that ground based docking lines up in KSP: you can test them on the runway, but that doesn't mean their suspensions will line up on Minmus. Now imagine doing it in real life.

Don't leave out Blake's Seven, it was Firefly at least a decade before Firefly. There has been a movement to rename SF "speculative fiction", and it is probably a good idea. Blake's Seven has basically no science whatsoever but simply posits an overwhelming galactic empire and explores the means required to control and the the means available to rebel, so great speculation and freedom to craft a story. Link to probably the origin of *Science* fiction snobbery: https://www.youtube.com/watch?v=Ctpvd2VvukQ Probably the most extreme case of SF snobbery was Niven's first published work. It relied on Mercury being tidally locked, but Niven wasn't aware that was already known to be false. When he learned of this, he offered to withdraw the work (it wasn't accepted).

First, the engine is designed primarily for open cycle mode. When the hydrogen runs out, your power drops considerably. My claim: You can't exceed 60MW per ISS heat sink radiator size ISS power (max) 90kW @ 382 m**2 radiators or .090MW per ISS heat sink radiator size your link: 16kW @ 50mm*2 radiator size or .122MW per ISS heat sink radiator size What don't I get? I certainly get that space is in vacuum, and heatsinks are a hard limit. I don't see a 35% improvement of a paper design over an existing (in space) design from 30 years back as a huge shock. It certainly doesn't hit my outlandish temperatures (used to generate the outlandish power limits), but then it doesn't hit any outlandish power outputs either. My point was that the laws of physics would have limits on even "Star Trek" level technology, and this paper hardly seems to hit that.

The original series was as close as it came. I'm pretty sure Harlan Ellison's Star Trek episode was just as sci-fi as his other works (New Wave had low standards). TNG was more like "space soap opera" with added "tech the tech" lingo. Producers quickly got the message that real sci-fi leads to cancellation. Star Wars is classic space opera. As far as movie or TV "real" sci-fi there's what? The Martian. Maybe 2001. Maybe Blade Runner. I haven't seen any of "The Expanse", maybe it. A few "Twilight Zone" episodes, but certainly the minority. I strongly doubt that Ellison was aware that since warp drive worked, the Trekverse was inherently non-causal and could justify his plot as hard sci-fi (they have to stop Bones from saving the woman that prevents US involvement in WWII). But I'm glad that Trek gets that one thing right (if almost nothing else). You can pretty much put "Hollywood itself" in the bad science fiction Hall of Fame. The exceptions are few and far between.

The problem isn't the difficulty itself. It is the difficulty, the issue of testing under actual conditions (.2g) , and the failure conditions (dead astronauts). Failure conditions often matter a lot more than actual difficulty in engineering. If you have to use the backup the first 10 times (and it is there and works), and then you finally get the ISRU going isn't a problem. If you get it going the second time but you didn't have a backup ascent vehicle the first time, that is a huge problem. Engineering tricks are one thing, but *reliable* engineering tricks almost always involve redundancy, and that means mass. Ascent vehicles require a total of 16,800 m/s delta-v (typically carried on other vehicles for all but the ascent, but it adds up), so there is a strong desire to keep said extra mass to a minimum (and yes, this includes spare ascent vehicles).

That looks like one mind boggling difficult engineering trick after another, with everybody on board dying on a single failure. You have the delivery of fuel or ISRU to the Moon (landing. High mass landing gets tricky, although you can try again without people dying. On this one only). You then get to load the fuel into a rover. The rover moves the fuel to the land. The lander refuels (likely compressing the fuel). The lander ignites and uses the fuel to return to Lunar orbit. This isn't a bad plan if you have another 'gassed up and ready to go' old-school pressure fed hypergolic lifter nearby to be used if one of those steps fail. In fact, the first thing I'd leave as cargo on the Moon would be a backup ascent stage. Of all the ways NASA feared Apollo astronauts dying, a failed ascent stage topped the list (more delta-v had to be budgeted to that stage than any other, so mass was kept to a minimum, and possibly below that).