SomeGuy12

magnemoe : you can add new software so long as you have remaining area on one of the FPGAs in your computer, or are willing to shuffle automatically. I don't see any technical reason that would make complex programs "impossible", just more expensive to create. "Yourself", what I meant by instant start is that the application would basically be "running" all the time because the computer system gives physical chip area to each installed application. So you aren't really "starting" the application, you are actually just making it active again. [COLOR="silver"][SIZE=1]- - - Updated - - -[/SIZE][/COLOR] [quote name='Yourself'] I'm working on an application right now at work that takes about 20 seconds to start up. We haven't really optimized it so we could probably cut that time down immensely, probably in the realm of 10-15 seconds. I don't imagine it'll get much faster than that, though, because there's stuff it just [b]must[/b] do before starting and that includes reading through about 1GB worth of data and processing it into appropriate searchable data structures and building geometric primitives for displaying it (on a map). I don't see how your solution can have enough of an impact on execution time or I/O to improve that necessary load time..[/QUOTE] You could in principle pause your application after starting up and copy the data in memory to disk directly. Startup would occur the opposite way. This would take 5-10 seconds for users on conventional hard drives if there is a gigabyte of memory in use (100 megs a second, sequential read) and possible 2-3 seconds for SSD users. I don't know of any applications that do this, although Windows does this.

So I have been working on several moderately complex software systems recently. (a control system, a game, stuff like that) I've noticed that there is a huuuuggggeee difference in reliability between a system where : 1. Some outsourced programmers slapped together a mess in a high level language that depends on a bunch of desktop libraries and interpreters 2. Somebody wrote a rigid, explicitly defined architecture with documentation (visio flowchart) for each module and a test script for each module The system in #2 is like 100 times faster and more responsive and rarely fails. I've been able to add features to it that worked the first time I clicked the build+run button. I've also started on a fault tolerant design where the client needs a piece of equipment that works at high temperatures. I've been using a CPLD. It's more work but not as bad as you'd expect... So this got me thinking. The basic microprocessor architecture is there's an ALU and a set of control registers, and a block of memory. Processor loads instructions, opcode selects which circuits get used to determine the output, output is stored in a register, memory controller saves it back to memory later. For the 1970s, 1980s, etc, this basic architecture is one of the most efficient ways to use limited numbers of transistors. You use magnetic tapes and platters so the amount of memory needed is minimized. Well, it doesn't have to be that way. My CPLD design, when the system is powered up, each module begins operating. At one end, SPI modules begin polling sensor ADCs for data. They hand the data to modules that act like dual ported memory, which pass the data to dedicated comparator modules that keep running integration counts of total signal magnitude, and then they pass the data to a module that implements a ring buffer in parallel ram. It's only like 5 times harder than doing the same thing in C. And it has occurred to me that you could design vastly more complex systems using this method. You would do it with "bottom up" design, implementing well tested building blocks that you hook together to build large and complex software systems. You could have network stacks, web browsers, email clients, the whole 9 yards. The difference is that all the running software on a computer would occupy actual chip regions of specific FPGAs in the computer system. There would be a set of low level interfaces that very strictly enforce who gets to access which parts of storage and the I/O. Why would you do this? 1. I think a rigid, careful design of the software in a computer system would result in stuff that is a lot more reliable. 2. Applications that are loaded into a chip would start up truly instantaneously, within the next video frame 3. It would be a lot more secure. It would literally be impossible to do most forms of computer hacking today. Data used internally by one application cannot be accessed by [I]anybody[/I] - not the OS, not other applications, nothing, because the internal data is literally not connected by LUT routing to anything else. (well, not directly - applications could still leak information due to faulty design but they get a chance to process the data before outputting it) TLDR, a megacorp with enough resources could make a family of computers that start instantly, work every time, are almost perfectly reliable, and hackers can rarely do anything with them. I think they might have a big enough advantage in the marketplace to overcome their drawbacks - the drawbacks being that you must have a large number of expensive FPGA chips in each computer, and they need to be specific models. Newer computers would need to keep inside them a whole circuit-board full of "legacy" chips in order to run older software. It would cost about 5 to 10 times as much money to develop software of the same complexity. But it's not just desktop pcs/tablets/laptops that would benefit. Automated cars basically have to be built this way. Maybe "have to" is a bit strong, but it's the correct solution. The microprocessor/microcontroller architectures take too long to restart and have a lot more failure modes. It would never have been possible for the recent round of hacks to be done had they used automotive CPLDs instead.

[quote name='Streetwind']A single stage to orbit rocket basically needs two things: - A TWR on the pad >1 - A combination of fuel/mass ratio and engine Isp that yields the necessary ~ 9km/s dV For example, an average Isp of 300 and a fuel mass fraction of 90%: dV = 9.807 * 300 * ln(100/10) = 6774,4 <--- not enough But make it ~400 average, like an RS-68 would have, and something like 92%: dV = 9.807 * 400 * ln(100/8) = 9907,9 <--- yep, that works! I would say that most rocket first stages today fulfil these requirements, especially those flying fully liquid fueled. So yeah, this bit of "news" is not really special nor particularly surprising. I would have been more surprised if the F9 first stage was [I]not[/I] SSTO capable.[/QUOTE] So...nothing in your equation mentions anything about the size of the rocket. Could someone build a small rocket (10 feet high or something?) that could reach orbit?

So, TLDR, to land a [I]real [/I] Moon lander you need computer engine control. You cannot throttle to 31% thrust so you are descending slowly and gracefully. So when Armstrong "went to manual", the computer must have still be in the loop to help him control the craft, he was just telling it to move laterally because the boulder field was a bad spot.

One issue is that space habitats are worth a lot more than buildings on earth. And it's a lot harder to sneak up on one. (let's just call it "ridiculously hard" so we don't have another endless "stealth in space" argument) The whole point of infantry is that if bad guys a holding a place, and you want to capture the place intact or capture some of the bad guys alive, or save some hostages, you send in infantry to shoot the bad guys individually. But if you don't care about the above, or there is no practical way to accomplish the mission, you might as well just fire at the space habitat with railgun rounds or lasers from maximum range until it's vapor. Point is, it's really hard to save hostages, or take a station intact, or capture anyone alive if the enemy team decides if they are going to die, they are going to make sure you can't get what you wanted. In space there's so many high energy mechanisms - ways to self destruct, vent the place, purposefully trash the place so you can't use it again, and guarantee the hostages can't be recovered via armed assault. James Corey books pointed this out. An assault force of space marines is trying to take over a real warship. But it's space, and in space every warship has fission bombs as kind of the lowest tier weapon onboard. So you just set off a nuke as a scuttling charge and the whole thing vanishes in a flash. So you really need to stop the bad guys from taking over in the first place. You ain't getting it back if they do.

So, ok. For keeping order inside a space station or spaceship, I think you'd want to use tasers - either the extending prong kind or the kind that shoot low velocity bullets that shock people from a greater distance. Well, what if the unruly populace make themselves anti-taser armor (basically a suit made of foil)? Then you'd have to use regular bullets. Thing is, I don't think the risk of a puncture is as bad as it sounds. The material that space habitats will be made of probably will handle getting shot fairly well. That is, there might be a hole, but it won't lead to a rip, just a slow leak through a small bullet hole. Well, so long as only one shot is fired. If you are talking about full scale military scuffles, both sides will be wearing pressure suits and the place they are fighting over will be evacuated of air one way or another (either by parties blowing holes in the side so they can board from an unexpected angle, or from the cumulative effect of firing thousands of rounds of ammunition that is designed to punch through space suits...and walls...and everything else) Another factor that would probably prove relevant are : 1. By the time there are enough people in space to even have a battle with, there will be various combat drones. In a low gravity habitat, flying drones is really easy to do, either using air fans or thrusters or both. Instead of sending space marines you are going to want to send drones, with the marines themselves controlling them safely from a distance. 2. Remember how Tracking Point introduced a guided firearm where the gun locks on to targets and helps you aim? That kind of thing would be on every space gun. [COLOR="silver"][SIZE=1]- - - Updated - - -[/SIZE][/COLOR] [quote name='Tada']Long stick with nail on one end - for making holes into pressure suits![/QUOTE] [I]That[/I] might not work so well...but isn't there some kind of anti-shark weapon that is a shotgun shell on a pole? You jab the shark and the pressure of contact triggers the shotgun shell? A very crude and dangerous weapon (to the people wielding it), but it sounds like it would work fine in space.

Can they do it? I mean, so you come up with a flyable design that is streamlined enough according to your CAD software. You buy engines...somewhere....that can handle this kind of intake speed. You put together the wing box, wings, etc, using materials that can take the aerodynamic load. If you don't have all the overhead of lockheed or boeing and you have more of a startup mentality and you have 1.2 billion bucks to work with. It sounds possible. SpaceX did it, making a brand new rocket with new engines that can reach space for less money than these guys took. It flew. You have all the modern tools like software, rapidly prototyping shops, off the shelf parts and alloys that can handle the stress. Hundreds of supersonic aircraft have been built and flown before, and you can find senior engineers who did the design for them willing to work as consultants. You know it's possible - you can absolutely make an aircraft shaped object about this size with jet engines exceed the speed of sound, dozens of military aircraft have been designed and built around this size. Now, whether or not the company makes a [I]safe [/I]product, or gets enough sales to stay in business is a totally different story. I think it's entirely possible whatever they come up with will be unsafe, crash prone, and too expensive to keep flying.

[quote name='More Boosters']Yeah if you want to kill poor miners from 10 kilometers away, why not go for a recoilless gun?[/QUOTE] That's just a hole in the back of the gun that lets gas escape the other direction, right? And those "poor" miners are adequately compensated and our internal investigation reveals their conditions meet minimal UN requirements for humans. They are showing a flagrant disregard for the law and must be dealt with.

Solid propellant has low ISP. These are like tiny millimeter sized pits in the bullet capable of tiny course corrections, making up for irregularities in the gun barrel and the enemies jumping out of the way.

[I]Edit : I meant liquid hydrogen/oxygen, not straight oxygen. Please don't respond with "pure liquid oxygen isn't reactive by itself..."[/I] So you need a Space Gun to holster in your Space Holster while you wear your Space Stetson hat and try to bring order to those scummy asteroid miners. I am aware that conventional gunpowder works fine in space, because the oxidizer is part of the package. But, suppose the Space Bean Counters are trying to shave every gram. Heck, they want you to 3d print your space gun after you arrive at the asteroid belt, instead of hauling it in your luggage. Your Space Sheriff badge unlocks the 3d printer so it can print this restricted item using metal mined from the asteroids. So, could you make a gun, used while wearing a spacesuit in low gravity (so the mass and bulk of the cryogenic tanks isn't a big deal - also it might draw from the same tanks that your RCS pack runs on), that mixes liquid hydrogen and oxygen together behind the bullet and ignites it when the trigger is pulled? A preliminary glance at the requirements seems to suggest this could work - liquid oxygen + fuel is an explosive in it's own right, and burning hydrogen has a rapid explosion velocity. The space gun would be a revolver, naturally, with a mixing chamber behind each bullet, so you can rapid fire. Each bullet would of course have onboard solid propellant thrusters and be "smart", obeying encoded instructions from the firing gun, so you can pick off those pesky asteroid miner outlaws from 10 kilometers away.

I'm also going to say the spent fuel rod idea is the best one I've seen. If you only have fusion power, but it's the style that produces neutrons (deuterium/tritium, etc), you can irradiate cobalt rods to make cobalt-60, a standard way to produce a whole bunch of deadly gamma rays. Radiation sterilization via gamma rays is also one of the best ways to sterilize anything, and as nuclearnut points out, the gamma rays should leave most of the affected sectors of the ship still usable. For bonus drama, the intense radiation could cause the robot that moves the rod around to fail...

If it's multi-axis spin, is it even possible, or are you out of luck? I guess my "tangential tip velocity matching" proposal would work. You would "just" need a more sophisticated computer model to predict where the desired capture point will be in an hour or so. You set up a velocity matching burn and fly on an intercept course, such that you reach the desired capture point at the right moment in time, reaching closest approach at that moment. The capture point has to be an object that is far from the spacecraft - the end of a boom or something. No hub docking possible, generally. And this is not possible at all if the tumbling spacecraft is continuing to leak gas (probable way it got this way) and thus the numbers are changing.

[quote name='Armchair Rocket Scientist']Docking with the rim of a rotating station would be incredibly easy. Just make the rim significantly wider than the spokes, or build it without a hub. Then put maglev rails on the inner rim. The docking spacecraft maneuvers up to the rails as slowly and carefully as it wants, then clamps onto the rails and a braking system on the station automatically slows it down, at which point it is switched off the main rails to a docking bay. For undocking, the process occurs in reverse, with the spacecraft being catapulted backwards until its "true" velocity is zero, then unclamp from the rails and fly off with RCS. Heck, you could even build an actual runway on a station and land a spaceplane on it, although taking off would still need a catapult.[/QUOTE] Yeah that's an enormously better idea. A continuous ring of maglev track is enormously easier to couple to than a moving point on the station ring. As a practical solution it's so much better the method I proposed isn't even worth considering, since it also eliminates the jerk of a sudden grab of a heavy spacecraft. Also you could do the docking purely manually. Ironically, it would possibly be easier to pull off than doing docking in KSP right now.

If you wanted to dock to a rotating station along the rim, cuz you're crazy...can it be done? Let's see...if you draw an imaginary line out in space representing a tangent coming off the rim, and then position your spacecraft along that line, I think it would become an intercept problem. Suppose there's a particular docking port that passes a point on the tangent line with every revolution. You want to match velocities with the rim speed, and then arrive at the intersect point between the tangent line, the station, and the docking port at exactly the right instant. Assuming constant station velocity and a known distance, this is a pretty simple intercept problem. So you just jet on over, matching velocity during the initial burn, then at the very instance your docking apparatus (something that can grab really fast, like big honking electromagnets I guess) achieves closest approach to the station, at that exact same instance, the docking port revolves underneath it. A gigantic surge of current and the magnet sticks you to the station. The problem is you go from 0 acceleration (just coasting through space headed for the rendevouz) to 1 G instantly. A huge jerk. It seems like this might also be bad for the structure of your spacecraft and the station. Maybe shock absorbers could smooth it out? On the bright side, the actual rendevouz is easy. You can trivially monitor the relative position of the station wheel as you approach on computer control, via optically checking against markings on the wheel. Radars give your exact velocity of approach. You can easily fine tune your approach as you get closer, and if something happens to where the rendevouz will be missed, you just need a puff of RCS to push you away from the station so the closest approach is more than 10 meters separation. The timing is only difficult if humans have to do it. The hard part is the mechanical coupling and the whiplash.

TLDR, the heliums come hurtling out of the plasma in the middle of the reaction. As Nuke points you, you can add an electron back from a wire mesh grid energized to high voltages outside of the reaction core. Once it's neutral, the big honking magnets in the reactor no longer affect it, and it will just float around randomly outside the core. You have a vacuum pump always on, sucking gas out of the core, and it will get sucked out from that. The gas you have sucked out of the reaction probably then has to be cooled and condensed, and the helium separated, and then you can make party balloons or use it to cool your superconducting magnets or just vent it because you don't care.

But if you also get tired of running out of fuel and you want some kind of vehicle that can stay airborne for weeks if not years (weeks is more realistic because of maintenance requirements), you could in principle do it with a nuclear energy source that is lightweight and provides electricity and electric fans. Obviously, you could also use a basically open fission reactor core, where you suck air directly through pipes in the reactor core, and use variable geometry scramjet intake. The problem with this is you'd probably leak highly radioactive particles in your exhaust stream (with fusion, you can line the reactor with materials chosen to minimize neutron activation and use aneutronic fusion so that less than 1% of the reaction produces neutrons), and landing is hard because you have an engine that requires this constant flow of air or the reactor overheats, and you can't throttle down smoothly. With the fusion method, you would land using batteries.

[quote name='fredinno']"Hydrogen"- "Inert" :D[/QUOTE] There has to be oxygen or it is inert. Yeah, during flight in the lower atmosphere, it's super bad.

[quote name='Rakaydos']I'm going to put this here: [url]https://en.wikipedia.org/wiki/Beam-powered_propulsion[/url][/QUOTE] Yeah. Those 2 heat exchanger systems mentioned are what I'm talking about. I hadn't seen this wiki article, but this is what I meant.

I'm rather unclear why it needs to be this complicated. You have a velocity and a sum of acceleration vectors. You can trivially approximate this using various numerical integration methods - the simplest one being euler's method. They get a little more complex but you can use a library and you build your programming code in layers - define the function that computes the derivative as a separation function that gets called by the function doing the numerical integration. At every moment in time, you make the vector component for engine thrust caused acceleration (the other component is for gravity from the planet) the same direction as your vector for velocity. (prograde like you say) Just break the problem into tiny, logical pieces instead of that horrific mess you have above. Adding changing thrust becomes trivial - call a function to compute the actual thrust magnitude, and in a separation function, subtract fuel burned, recompute vehicle mass, and calculate the new effective acceleration. Drag is similarly easy, assuming you already have drag coefficients. You don't even need calculus...(well, the numerical integration is technically calculus but Euler's method is braindead simple. The more complex 2nd order + methods are more complex, but in programming terms are still simple)

I can confirm that Edmunds lists the base model Camry sedans as the most reliable vehicle in that category (medium cost small sedans). I considered purchasing a recent model used one myself recently (stuck with my old Honda for now)

[quote name='PB666']Refocusing laser is the least of you problems, its a red herring inyour argument. Its like saying you can fix fusion energy using a better water filter on the cantinas kitchen refridgerator. Glass and quartz start melting around 800, they would never survive the heat of explosion. Your idea is far fetched and implausible.[/QUOTE] I think you mistyped "[URL="https://en.wikipedia.org/wiki/Fused_quartz"]1700[/URL]" celsius. Well, if no substance can both take the heat and pressure of a rocket engine and also is transparent to visible light, you could use something transparent to IR or microwaves... Or don't have a window at all. Heat up a mess of tubes, exposed to the outside, and those tubes have the propellant flowing through. I just don't know how to evenly heat a cylinder of tubes when the laser only shines from one side. (presumably with really clever optical design, you'd make the tubes have all kinds of internal mirrors or something to evenly distribute light)

PB666, what are you talking about? Lasers do need to be "lensed" (lens and mirrors are 2 alternate ways to do the same thing). In fact, they obey the same laws as any other light source. What do you think [URL="https://en.wikipedia.org/wiki/Laser_Weapon_System"]that [/URL]is? Inside the laser turret, that shiny thing you see is a mirror. Longer range needs a bigger mirror, and you need a range of around 100 kilometers for an orbital launch. The lasers shine through a window onto a heat exchanger. The (ceramic, metal, whatever) plates in the heat exchanger get hot from absorbing laser light. The propellant flowing over the plates in turn heats up. Rocket roar comes out the bottom. It's the same principle as NERVA, except minus the nuclear reactor.

It's a heat exchanger. There's a gigantic array of lasers on the ground with mirrors that can keep the spot size small enough to keep the heat exchanger illuminated during ascent. This is for reaching orbit. The payload of the spacecraft contains stuff for maneuvering in space. You leave the spacecraft power source on the ground...

If you wanted an SSTO with non embarrassing mass fractions, you need higher ISP. You can't do much better than 500 with the most exotic chemical propellants. Nuclear has the problems of the reactor itself being heavy, the shielding, if there is any, being heavy, and the reactor has to be constructed very carefully and there is always a risk of it crashing and leaving a radioactive mess that is difficult to clean up. So why not construct an enclosed chamber. Quartz or other transparent material is used as a window along one side. There's a stack of plates with holes in them. The plates closer to the window have larger holes, and around each hole there is a ring of material with a surface that absorbs the frequency of laser light you are using (so it probably appears black). The plates also have heat radiator fins on the back side, opposite where the laser light comes in. Essentially, you use this apparatus to super-heat hydrogen flowing through the chamber and you send it out the bottom. The plates are made of the same material they make NERVA reactor tubes, so you should be able to reach temperatures that can produce 1000 ISP. You might have an air-breathing phase of flight where ram air intakes are opened to send ordinary air through the chamber instead of hydrogen, so that you don't have to consume onboard propellant.

Basically, I'm talking about a streamlined aircraft shape propelled by ducted fan engines like [URL="http://aviationweek.com/blog/econcept-eadss-hybrid-electric-airliner"]these[/URL]. The energy to run them would come from onboard [URL="https://en.wikipedia.org/wiki/Aneutronic_fusion"]aneutronic fusion[/URL] - yeah, yeah, a century away - that would produce electricity directly from the escaping helium ions. (by capturing the energy of the moving charged particles) Anyways, basically, it's a weight in the tail (radiation shield is a shadow shield to protect from side reactions) With this kind of 100% bypass, jet fan, can you even exceed the speed of sound? About how fast could you fly before the drag from the turbine blades limit your speed?