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wumpus

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Everything posted by wumpus

  1. First, relativistic mass isn't considered a good idea anymore. It made a lot of sense when Einstein wrote special relativity, and I'm sure he included it in his descriptions of it, but I think it was quickly obsoleted after looking closely at general relativity. The obvious failure is that there exists some speed where anything would become a black hole if "relativistic mass" was a thing. If it then decelerated below that speed, it would no longer be a black hole. Also whether or not it was a black hole would depend on the speed of both the observer and the "black hole" in question. It really doesn't work like that (well that's what I've been told, I have zero tensor calculus) ma=dp/dt : still true after special relativity. p=vm(1+v^2/c^2) : true, but don't assume you can declare mass = mass(at rest)(1+v^2/c^2) Other notes: When you cross the event horizon your escape velocity is >=c (this gives you a quick and dirty way to calculate where it is. It is the "wrong" way to do it, but for simple black holes it should be right), not your actual velocity. Consider a beam of light crossing the path of a black hole: it will never change velocity, but it will change wavelength and bend towards the black hole (and if close enough will get trapped itself). Consider a sci-fi spaceship capable of arbitrary acceleration: it could conceivably sit just outside the event horizon at full thrust (a bad ideal. You'd have to push at "full thrust" for a long time (to beyond well over twice the even horizon's radius) before you could even think of escaping by some other means (presumably orbiting the black hole and spiraling out).
  2. Generally speaking, what you see with a minimal rocket (perhaps just a solid booster plus capsule) will have the same Squad-written overhead as a large and complex rocket. The extra physics and rendering of the complex rocket is done entirely in Unity. So it doesn't appear that making the non-Unity parts of KSP would really improve anything (unless they re-wrote the entire physics engine, presumably to use 64 bit floats). Unity calls are what slows down the machine, and the degree that unity can use the second (or more) processor determines how fast KSP will run.
  3. I'm curious what strategy you have for using solids for such landings. I'd assume a '"hoverslam" is right out, although it might be possible to blow the tops of the motors (presumably side mounted). Some sort of two step (burn to near hover, then descend on weaker engines) sounds far more possible, but replaces fine ignition timing with controls issues. My point above is that a ring rudder isn't reliably stable under 10m/s (that's probably well beyond where the fins stall, but fairly easy to check by launching off a rod with controlled acceleration (probably just using a weight and lever to launch)). You would either have to land with at least the rudder stall speed or put the rudder in the exhaust (or similar games with the exhaust). Personally, I'd probably stick to "proof of concept" where I retrorocketed to some predetermined height and parachute the rest of the way (not sure if you can get a parachute to open from a good height to measure. Possibly CO2-assissted parachutes are in order).
  4. First with python: you have sci-py downloaded (the replacement for numpy)? Not sure how well it works with pypy, for simple things it might make sense just to work with pypy. Also if you want your "loop fineness" remotely reasonable, make sure all floats are 64bit. Python should be 64 bit (I just checked mine, it is), but I've run into this issue with FFTs and such. Can you wrap FAR (I assume it is c#) into something you can call with Python (I'm not even sure about the license, you may have to talk to the author)? I'm guessing the aerodynamics are "good enough" (except that they are for far larger rockets, it might not scale down well to model rockets). You might be able to build your rockets in KSP and then scale them down and run FAR on them. Will you even get transonic? I'd assume that "beyond transonic" would be past the range of model rocketry (in all but large multistage rockets), but getting transonic might be a problem. And as far as retropropulsion in model rocketry: first, I'd recommend measuring your ignition delay on the groudn with whatever means you are using to ignite your retrorocket. Also model rockets are kept stable by fins. It is fairly easy to determine the required speed (about 10m/s assuming stability after a 5g launch off a 1m rod) for stability, so don't try to retro decelerate below 10m/s without fancy stability controls.
  5. Back when KSP was released, there were still at least two versions of the demo. The original demo was on squad's site, while the "new" 1.0.0 based demo was on Steam. While 1.0.0 is in many ways a great improvement over the ancient free KSP, it certainly had a lot of bugs (some of the worst may have just been Steam issues not updating critical files). In any event you can't distribute the 1.0.0 demo You can distribute the early (before KSP went on sale) editions. Here's a link: https://drive.google.com/drive/folders/0B9S8km6a08YmcFNFdFRCajJkb3c 18.3 is the "old demo" and recommended for those interested in a demo. The others are more of historical interest. WARNING: Don't expect to take your mad 0.18.3 skills straight into 1.5.x, many of us had to completely relearn how to get into orbit now that stability is an issue and the souposphere is gone. The biggest change is that with 0.18.3, the typical way to get into orbit is to go up 10km, turn east about 45 degrees (towards the horizon) until your apossis (try looking at ["M"]ap view). Coast to apossis. Once there, fire your engines again prograde (the way you are heading) until your orbit is completely in space. Yes, that's the extremely condensed method to get into orbit, but it is mostly about the difference needed between 0.18.3 and modern KSP. You don't have to worry about aerodynamic stability (just that the force of the engines doesn't tear the thing apart), that comes with 1.5 (started with 1.0).
  6. I mentioned it in the Hubble thread: https://forum.kerbalspaceprogram.com/index.php?/topic/178825-the-hubble-space-telescope-is-fixed/&page=2&tab=comments#comment-3473903 Scott Manley mentioned it (and put it in the title): Soyuz, Hubble, Chandra & Kepler Updates (Recovering, Fixing, Fixed, Probably Dead) https://www.youtube.com/watch?v=fVAIsZwnMGw But the only reason I knew of it was a social media group member (that's been around since roughly web 2.0 was a new thing) was someone senior on the project.
  7. One Venus year = 224 Earth days. 7 Venus years = 1568 Earth days Time to Jupiter: 550-560 days. So 2/3rds the time for there and back again. But you get your Mercury transits much faster than every 224 days (not sure how *much* faster, but faster), and if you used a Jupiter injection it would be heading back to Jupiter (taking at least over 650 days) and with a much smaller time within Mercury (but probably still long enough for steady state temperature soak). It only works if you are willing to fire your engine near Mercury to lower apposis to within Venus or so. And even then, I suspect that the last few Venus flybys are within an orbit much faster than 224 days, so the time might be closer than that.
  8. The issue is that you are taking the problem that doomed Fukushima (cooling water sufficient for normal operation stopped flowing at all) and putting it a vacuum. While I couldn't find the mass of the ISS's heatsink, it does have about 2 tons of ammonia just to pump around the heat. And 5-7% of NASA's NERVA would take about 3 orders of magnitude more cooling capacity of the ISS. You'd need something like heat pumps to drive the radiators to their melting point, and then it would still be massive. I still think you would "just" stage your reactor rods. I'd expect that what's left would be pretty radioactive, but not bubbling away at anything like 5-7%.
  9. I'd be impressed if KSP could outperform a 1960's wind tunnel and various other physical modeling systems. Just because they didn't have computers, doesn't mean they couldn't design rockets. There did exist one computer in Germany while the V-2 was in use (the Zuse machine), but that was more an "art project" and presumably the officials would confiscate it as a "waste of valuable materials" if they ever found it. I've been reading "Rockets and People" off and on (volume 2 started with mostly descriptions of political offices, and got rather dull), and computers didn't seem to be critical to early Russian rocketry. NASA might have been able to simulate flow inside of a rocket nozzle, but from what I've heard they simply constructed the models and kept blowing them up until they could build a single nozzle for an F-1 engine. KSP hardly cares about that, all it has to bother with is working "LEGO" pieces. And nothing about KSP rocket designs are all that realistic (except maybe the balance of fuel, thrust, and mass. Certainly not any structural issues). Mission simulation might be pretty good, but still I'm not aware of popular "reliability issue" mods where things tend to go wrong (gyro failure!) and you have to diagnose things with limited diagnostics and hour-long pings. I've heard detailed reports of NASA teams dealing with issues from Chandler, and it sounds nothing at all like a game of KSP. That said, while KSP isn't good enough for NASA (cue "four words you can't say at NASA"). Good enough for theplayingdead's class/classmates? I'd certainly hope so. I can't imagine the class in rocket science that couldn't be improved with KSP.
  10. Near as I can tell, NASA was basically using patched conics for all ~20th century simulations. Certainly they did for the Voyager flights, which certainly made gravity assists known to the public. I think the "weird ways to abuse gravity" (https://en.wikipedia.org/wiki/Interplanetary_Transport_Network) weren't pushed until the 1990s. As far as the computational power that NASA had, the absolute most powerful computer of the Apollo era was the CDC6600, and that wasn't available until September 1964 (no idea if NASA had one. Only 50 were made and sold at over $2,000,000 a pop). The thing had a *most* a megabyte of space (all hand crafted core memory, I really don't think NASA or the contractors used anything else) and could run (with extremely carefully assembler, and expect *everything* run on a CDC6600 to be hand crafted assembler) 2 MIPS (that *might* be 2 MFLOPS, but I'm not willing to bet it). So I really don't think NASA could run FAR even if they had the code. They didn't have computers capable of it. I'd also assume that all the software knowledge to be found in the source code to be abstract theoretical use only: they couldn't run it on their computers and most of it was for relatively theoretical interest only (networks were small enough to be trivial). Fun fact: the error-correcting code used in SSDs and I think at least one TV specification (and probably a *lot* of wireless use) is called LDPC. It was invented by one Robert Gallager and used for his doctoral thesis (1960) as a possible means of achieving Shannon's theoreticly perfect error correction code (Shannon showed that it could exist by randomly generating enough codes until it magically appeared. A system that obviously scales poorly). Gallager later went on to "write the book" on error correcting codes, where he didn't even bother to include his own code because no conceivable computer could use it. Much later (1990s) somebody invented the "turbo codes": these were codes that could essentially achieve Shannon levels of correction and simply changed everything (the jump in performance was so high plenty of guys in the field insisted it was a hoax). Since they were patented, there was a certain reason to try to find other methods of achieving the same thing (since it was clearly possible). Eventually somebody dug up Gallager's LPDC codes that were now possible to run. So even if you dumped a ton of 21st century software tech on Apollo era computer scientists, it might make more than a few deep level changes in fundamental assumptions but in practical aspects there would be a great likelyhood that everything would be forgotten before it could be put to use.
  11. Two notes: I'd suggest reading Einstein's own description. It helps to think of c as "the speed of casuality (or time)". The other thing that I got wrong (for decades) was the idea of "relativistic mass". It works fine for special relativity, but really shouldn't be used (it doesn't work at all once general relativity is considered). Momentum is still conserved, but forcing it to equal mass*velocity causes problems since such "relativistic mass" doesn't create gravity quite the same way. An easy thought experiment to prove this would be to imagine a spacecraft accelerating to the point it turns into a black hole to an outside observer, and returns to "space" after decelerating (also consider how observers in multiple coordinate systems would view it), this is absurd and not how gravity works at all (although I have to take the word of other people who claim to be able to solve the equations. I have zero tensor calculus). I think all of Einstein's pre-general relativity work includes it, so the concept comes up a lot (and should be taken with a grain of salt when reading Einstein's own work (later explanations have the benefit of hindsight into Einstein's truly great work)).
  12. If you want to wait for 1% of normal operation (which seems wildly excessive, I'm sure that during the burn it radiates at least 1% into the rest of the spacecraft) you are likely waiting (and dumping 1% of your hydrogen from a normal burn) for an entire hour. Cut it to 2% and you are dealing with dumping hydrogen (at twice the rate?) for 10 minutes. You need to eat 4% if you want the shutoff to be in (10-60) seconds. 4% (or even 2%) of a slow burn for a Hohmann transfer is one thing, but it is another thing when you need sufficient thrust to leave a launch pad. It even is a wildly huge problem for a Hohmann transfer. From a little googling: https://www.quora.com/How-long-does-it-take-to-shut-down-a-nuclear-reactor According to wiki: The ISS has heatsinks that can handle 70kW of power, so they can handle %4 of 1.75MW reactor. While I'd expect the reactor cooling fluid to be hotter than the ISS's (and thus more efficient over mass) you can begin to see the problem. Either you build a ship with orders of magnitude larger heatsinks than the ISS, or you have to deal with cooldowns in terms of hours (leaking fuel the whole time), probably both. For a simple comparison, the ISS heatsinks are about 1/10th the size (don't know the mass off the top of my head) the size of the solar panels. There's a reason I suggest slagging and ejecting the entire reactor core after each burn, although I don't expect there is any way to make it "the cheap part" of a nuclear rocket engine.
  13. The previous poster's description of onion staging "firing all engines during lift off" was how early rockets were staged at all and still used in Soyuz. Of course, nobody has yet built a kerbal "magic fuel line", so no fuel is transferred from drop tanks to the sustainer engine, but real life fuel tanks are far more mass efficient than anything designed by kerbals. Note that if you can get bamboo staging to work (in orbit or otherwise outside an atmosphere), then that is going to be optimal in KSP (you might have to use "Pe kicking" to get anywhere, because it works best with low-TWR engines). Again most of the reason it makes so much sense is thanks to the inefficiency of kerbal fuel tanks so don't expect to see it much IRL (the lack of "magic fuel lines" is a bigger problem). If you want the engine to start and stop repeatedly (which of course you will for any mission that can justify nuclear propulsion), then lowering the thrust makes the whole start/stop cycle wildly easier. Nuclear engines have a relatively long cool down between adding control rods and the (secondary) nuclear reactions stopping. Presumably some of this would be included in the delta-v of the burn, but you will still need to feed cooling hydrogen through the reactor while it cools down, leaving the end of the burn rather inefficient.
  14. Mary Roach has written a number of great books including (I hope) "Packing for Mars". Although this isn't a [science] fictional account of life on Mars, Mary Roach is a great science writer and I'd expect a great deal of accuracy in what you should expect on Mars and what you should bring. Just got it out of the library, so will read it shortly.
  15. I forgot the context of the fictional work I was referencing. If you are teraforming a planet, you will have an unlimited supply of newts. If you have a small Mars base or space station, your newt supply is limited. I didn't think the newts were all that limited in the reference work. I'm guessing that they did feed a few "premium" animals, but the locals still got the bulk of their calories from newts. Any guesses on the amount of calories of corn consumed by Americans? I guess most of it goes to animal feed or high fructose corn syrup, because you see plenty of corn farms but only eat a small portion of it is directly eaten (on the cob or canned). I guess we got sick of corn as well.
  16. If you have enough newts, you can feed them to something you want to eat. The obvious first choice would be chickens, but I'm not all that sure if chickens would eat newt either (you might get them to eat algae as well). Some sort of alligator might be better, presumably the growth/food of reptiles should be better than birds or mammal livestock, at least after enough breeding generations to match modern domestic animals. Then again, I'm not sure the people of Bujold's worlds (outside of Jackson's Whole and Baryar) are all that approving of carnivorous diets.
  17. Considering how SLS is turning out, I'd expect that SAS (SApolloS) would have as many issues and would probably have to be entirely redesigned with similar engines. Each stage had to be fairly modular, they typically were all built by separate contractors, but there's no reason to believe that paper rockets can ever be built as smoothly as they claim. I'd still expect it to work better than how the shuttle did, but I'm also absolutely certain it would never get 135 manned missions before being cut.
  18. It looks like a monolithic design would require 4 SRBs, and wind up looking a lot more like Buran (I'm not sure there is room for them plus the main tank. Especially if you want them to stage at different times. I suspect that "kerbal design" would go right out for real life safety). I'm sure there were tons of "I told you so" from the monolithic people after the Challenger disaster, but somewhat muted since doubling the number of SRBs isn't exactly improving safety. I'm sure it wouldn't help that Aerojet's monolithic building facility (had to be) not only in Florida, but close enough to KSC to certainly be in the same Congressional district.
  19. This only makes sense if you are sufficiently picky about which orbit (mainly inclination) your smallsat/cubesat gets. Otherwise you can hitch a ride with the big boys or simply group enough sats in one big launch. Certainly it would cheaper/less risky to charter a falcon and fill it with a "group launch buy" than to build your own rocket.
  20. In other news, Chandra is also back up and running after a scare into safemode (yes, a balky gyro) last week.
  21. It gets that high to justify the cost of a "simplified" expendable SSME costing more than twice the original. The plan is to run out of available SSMEs, but it doesn't look likely to happen (I can't imagine SLS trying to launch often once either BFR or New Glenn exist). If you want to launch a shuttle, your best bet is a dream chaser (which I suspect FH or F9 could manage if they had to. Especially if you could wrap a fairing around it). You'd probably have as good of a chance launching a Buran (isn't there an engine in production that is basically half an Energia?) as a STS Shuttle, basically zero. I always thought that "returning a spy satellite" was from unclassified Congressional debate, and a real thing. Certainly Hubble was basically an inverted spy satellite (except that the mirror didn't require adaptive optics). In fact, I've assumed that was roughly the point when the US spy agencies stopped pretending that the existence of adaptive optics was a big secret: the US was obviously using spy satellites with mirrors greater than ~30cm diameter and they were useless without some highly specialized technology. While the Shuttle eventually returned 52 "space items" (which might include bits from ISS) totaling over 100 tons, it never launched from Vandenburg, thus never launched into a polar orbit. I doubt any of them were spy satellites. I'd maintain that the internal cargo hold was source of most of the Shuttle's woes (an external fairing would have made infinitely more sense). While BFS's re-entry and landing profile might be the wave of the future, there's no way it could have been done with 1970s tech: they were stuck with wings for re-use (and certainly far too many spaceplane fanboys have tried to make winged spacecraft regardless of how silly it is IRL). That's odd. I thought the AJ-260 was monolithic and certainly tested. It did have the issue of blowing off the first nozzle applied to it, but that might have had to do with its extreme-thrust design (it was far more powerful than the shuttle boosters). No idea if trying to extend the burn length would have been an issue.
  22. Pretty much. And there wasn't enough money to keep spacex in business with the Falcon 1. Considering how many smallsats can piggy back on the big boys, I'm not remotely sure how they will survive now. It doesn't help that Rocket Labs already has a successful flight. Not to mention that the big boys might well be interested in using the Rutherford engine as a throttleable landing engine (at least it looks like one to me). Pegasus has very few flights these days. Falcon 1 is outright canceled. Companies that have competed in this space are abandoning it, making me question just what it is that they are chasing (well I get the rocket scientists, it is who is funding them that doesn't make any sense).
  23. First mission, I had to google that you had to hit the spacebar to launch the probe. Then I had to learn that you needed either a probe core or capsule (with kerbals), I think it let you put a rocket on the launch pad without them. I'm pretty sure orbit wasn't easy (unless you wimped out and used an orange tank + mainsail just for orbit because this was well before career mode [now called "science mode"]). Without "career mode" we had unofficial "campaigns" like these: https://wiki.kerbalspaceprogram.com/wiki/Campaigns I know I skipped that whole "hit another continent with a suborbital rocket" (I could see that KSP controls weren't designed for that) and skipped docking to go straight to the Mun, but in general the campaign ideas were a good thing to follow (and allowed you to skip bad missions without grief). I then got overzealous about "rocket simplicity" and how much I could do on low tech (primarily RT-10 SRBs), and stuck around landing on the Mun almost entirely on RT-10s (expect 4 layer "wedding cake" to do it with pre-release KSP).
  24. 21 Shuttle flights was enough to construct the entire fleet and hang the sunk costs and existing jobs around the neck of Congress. By then it was too late to cancel the Shuttle, and they are even today insisting on paying for those same jobs via the SLS (which has far less justification than the Shuttle). There's no way you would get 135 crewed flights of an expendable rocket, Congress would have shut it down in a few years. Sure, they might plan a follow up, but US astronauts have been limited to Soyuz for 7 years and counting. And if we were relying on Congress and SLS, we'd still have to use Soyuz between rare SLS flights. While politics might be a forbidden topic, no bucks - no Buck Rogers. Managing Congress and finding ways that will get them to pay not only today but for decades is what makes NASA administrators successful. No idea what that does to the irreplaceable bits that NASA does (we have a bunch of billionaires deciding to turn manned flight into the next sportsteam competition, but not so much science and air R&D), although the ESA is certainly doing plenty of science now.
  25. With a smaller payload capacity, two options are available: you can either add a fairing to the shuttle (with no return capacity) or you can have an array of expendable launchers for everything else. If the shuttle can't lift the external payload, you are out of luck. Also DoD backing was deemed necessary, and that enlarged cargo area was needed to bring home a keyhole if necessary (did they even launch at Vandenburg? I don't think they launched anything into polar orbit from a shuttle)... If you allow competing expendable rockets, you give Congress that much more power to cancel the shuttle. I don't think it could survive the competition. Granted, such things were routine after the Challenger disaster, and you could plan on the Challenger disaster simply by checking the expected safety of the Shuttle, but don't expect congressmen to do math (you'd think their staff could do that, but they are mostly wannabe congressmen). Congress wasn't at all interested in Apollo-level budgets for NASA, thus the need to exaggerate cost savings at every opportunity. They weren't approving the shuttle, they were approving the dream of what the shuttle could be. They already canceled the 3 other programs that worked together for a modern space plan, leaving the Shuttle a 'bus to nowhere'.
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