Zeiss Ikon

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About Zeiss Ikon

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    Sr. Spacecraft Engineer
  1. We used to discuss nitrous/ethane for self-pressurized systems on the model rocket newgroup as far back as the early '90s (I'm sure they were examined by actual rocket scientists further back than that), and I recall reading that ethylene was thermodynamically similar but with higher energy due to the strain in the double bond. IMO, either one would be a preferred replacement for propane (in that there's no need to use oxidizer to pressurize the fuel). Those propellants weren't taken seriously in the '50s and '60s because of tank weight, but modern composite tanks can contain 800+ psi vapor pressure at reasonable weight, hence give useful mass ratios. As noted in the article, where this system shines is as a storable, self-igniting bipropellant system. Not technically hypergolic, but all that's needed is a little electric power (a couple hundred watts for a few seconds, seemingly) to heat the catalyst to get a start. The ability to use the oxidizer as a monopropellant saves stage weight, possibly enough to offset the required batteries. BTW, this article indicates nitrous-isopropanol is good for 233 s -- not top of the line for liquid bipropellant, but if self-pressurized and self-igniting, the system mass savings on pumps and igniters (not to mention cost savings on things you don't have to design or build) might make the whole-stage performance a win. Nitrous-ethylene might do better (ethylene has a near-zero energy of decomposition due to the double bond, so you get more energy per mole than any alcohol).
  2. I think those were to be the fuel, with LOX as the oxidizer. For amateurs, hydrogen and methane are impractical; they have to be too cold to keep them liquid (and pressurized gasses aren't practical due to tank weight). On an amateur basis, the best combination of safety and performance in liquid fuels is probably kerosene (or diesel fuel) or gasoline, with ethanol/methanol as an alternate for some situations, with either LOX or nitrous as oxidizer. FWIW, nitrous/alcohol has been used in high power model rockets (yes, Tripoli launches have included liquid bipropellant rockets, at least in the mid-1990s). The tanks and combustion chamber are one long tube. A sliding piston pushed by the nitrous pressurizes the alcohol, and a "pyrovalve" (a small chunk of solid propellant initially blocking the injectors) serves to both start propellant flow and ignite the motor. Yes, you can have a flight-weight liquid biprop motor as small as a couple inches diameter and a couple feet long, including tanks, fuel feed, and thrust chamber. Don't know if they sold enough of them to stay in production, but I'm pretty confident I could build one from scratch, given time and material resources.
  3. As noted above. High Test Peroxide is much harder to obtain than LOX, which is less practical in amateur quantities than nitrous oxide. Another oxidizer that was used a lot back in the 1950s and 1960s, largely because it's hypergolic with some fuels, is nitric acid. Liquid at ambient pressure/temperature, and in anhydrous form it's about 3/4 available oxygen by mass (and something like 10% denser than water). There are handling issues, but in general, I'd rather deal with fuming nictric acid on a flight line than 95% peroxide (I'd rather work with LOX than either one). You can use nitric acid as an oxidizer with almost any fuel, but the main reason to put up with its tendency to literally eat its way through tanks and pipes is that nearly any hydrazine derivative is hypergolic with some variant of nitric acid (white fuming, which is the anhydrous, pure HNO3, or red fuming, which is white fuming plus as much N2O4 as will dissolve). Modern rockets have almost entirely replaced nitric acid with pure N2O4 compressed to liquid, because it's hypergolic with some hydrazine derivatives (unsymmetrical dimethyl hydrazine and monomethyl hydrazine are most commonly used) it doesn't eat plumbing as badly and if you have a leak, while highly toxic, it will evaporate instantly instead of sitting on the tarmac waiting for enough energy to come along to ignite the asphalt. Nitric acid, N2O4, and peroxide are all considered "storable", because they don't boil off at room temperature. Nitrous oxide is sort of storable, too, since it won't go anywhere if you have a tank strong enough to keep it liquid. This is why liquid fueled ICBMs (including the Titan II that also launched Gemini) mostly used some variant of nitric acid and hydrazine, or nitric acid and kerosene (jet fuel, called paraffin in British usage) plus a "starting slug" of a hydrazine variant preloaded into the fuel line to get things started. BTW, liquid oxygen forms a high explosive mixture with anything that combines combustible and porous. Yes, that includes asphalt (a LOX spill on an airport tarmac is a bomb-squad emergency, though if you can keep it from going boom for a while the LOX evaporates off). The early attempts at motors for the A-4 (what everyone by Germany called the V-2) resulted in dropping high explosive alcohol/oxygen jelly on the launch pad several times, when ignition failed to ignite -- at least, once, it actually went off.
  4. Yes, but it won't produce a flight-weight engine/tank system. The weight of a compressed oxygen bottle, to hold anywhere from 150-330 bar, is too great relative to the mass of oxygen it contains to give reasonable system performance. Nitrous oxide compresses to a liquid at a mere 35-ish bar, so a smaller, thinner tank will hold more usable oxygen. High test peroxide is a liquid at ambient pressure and temperature, and decomposes exothermically, eliminating the need for an igniter. Otherwise, liquid oxygen is the way to go if oxygen is your choice -- it's reasonably dense, doesn't require a high tank pressure, and is an excellent oxidizer from an energy standpoint; plus, it's less hazardous to handle than high test peroxide, and not much more so than nitrous oxide.
  5. You could do the same with a larger aperture, as long as you keep the focal ratio similarly long -- in other words, as long as it's f/28, it doesn't matter if it's 4" or 12" (though it may be impractically long in the latter case). Should give some nice planetary views with that long focus, though.
  6. Nothing useless there. All you have to do is shim up the tool so it's more or less level on the front. Grinding technique will govern how the shape is generated; a little off level won't cause trouble. If you're feeling OCD about it, you could grind the back of the tool on a sidewalk or other rough-but-even concrete to take out most of the wedge. Save the plaster you ordered for the next one.
  7. D'oh!
  8. I'm not sure what GoG means in this context -- I keep seeing it as Guild of Greeters from URU: Myst Online, from 2003 (closed down, reopened, closed down again, and last I heard, running with static content as Myst Online: URU Live, for free). I bought KSP directly from this web site (kerbalspaceprogram.com) -- got it on special last fall, for around 1/3 the current retail price. Most fun I've had out of a commercial game for the price. And I've just verified that, yes, I seem to be able to download 1.3 without additional payment if I want/need to. I haven't seen any significant reason to upgrade, so far -- I don't need languages other than English, and was under the impression there is little if any update in the software itself compared to 1.2.2. My computer doesn't handle a bunch of extra stuff well (Core2Quad, with lower per-core performance than a current i3 iteration), so I don't run a bunch of mods. Edit to add: I quit using Windows on my own computer while I was trying to decide whether to upgrade to Vista or wait for 7 -- and got FBI Moneypak twice in six months, after almost 25 years without a malware infection. Both times, I was able to defeat it on my own, but that prompted me to actually start using the Linux I'd had set up for dual boot for a while. That was when MEPIS 11 was fresh. When it failed to upgrade for a long time (project fizzled, apparently), I switched to Kubuntu (I was used to KDE by then). I haven't booted XP on my desktop machine since 2011, and it's no longer bootable (not sure what's broken, don't really care). My laptop still has Win7 dual booted with Kubuntu 14.04, but I haven't booted it into Windows in almost two years (I bought it just over two years ago). My next machine will hopefully be preinstalled with Ubuntu, though I may replace the default version with Xubuntu or Kubuntu because I don't like the default GUI. I'm still on 14.04 because 16.04 went to KDE 5, which killed a lot of my visual pleasure in using Kubuntu (a lot of the eye candy was removed, and/or the developers of the eye candy couldn't be bothered to update their stuff in time for the release). I'm thinking of replacing my 16.04 Kubuntu with Xubuntu 16.04 to see if the underlying system has any significant improvements.
  9. I'm running Kubuntu 14.04.5 LTS (which includes KDE 4). Sometimes, when I feel like improving performance a little, I'll switch to XFCE desktop, which is quite a bit easier on system resources than KDE. This is necessary because I'm running a Core2Quad 2.7 GHz, instead of a modern processor with higher per-core performance (lack of many hundreds of dollars to upgrade the motherboard/CPU/RAM is responsible here). If it matters, I have the Linux native direct download (not Steam) version of KSP 1.2.2, only mods are Better Burn Time and just-installed Scatterer (quality has to be turned down a good bit to get decent frame rate and physics rate).
  10. Space is (still) a dangerous place. We are not naturally equipped to survive there. That does not mean we shouldn't go there. I'll be too old to go to Mars with SpaceX -- but that doesn't mean I'd turn down a trip it were offered.
  11. I'll make a prediction on that, similar to one Arthur C. Clarke made about life extension. He said (quite a few years ago, now): "There are probably people alive today who will never die." I'm going to approach it this way: There are probably people alive today who will travel to another star -- and return alive to report to the same people who launched them. To clarify, I think it's more likely we'll find a way to exploit the Alcubierre loophole (i.e. space warp) than that we'll ever launch generation ships or sleeper ships.
  12. A drill press isn't absolutely required. I've seen (photos of) trepanning machines built from pillow bearings, steel pipe, and plywood, powered with a sewing machine motor. Or, if you have a heavy-ish hand held power drill, you could improvise a stand to keep it steady and perpendicular to the mirror and let it move up and down, or just buy a drill press stand for it (Harbor Freight has them cheaply, last I looked).
  13. Better recheck. If your secondary is going to refocus and form a second real image without aberrations, it has to have two foci, which is part of the definition of an ellipse. A second paraboloid would be correct if you're collimating a parallel beam to a larger or smaller diameter, but that's not what a Gregorian needs to do. Trepanning the primary isn't too hard. After you finish the medium grits (say, 600) and have a reasonable sphere, make a bit by mounting a piece of copper pipe concentric with a shaft that fits your drill press chuck (you can use epoxy for this, no need to solder), and use 80-120 grit applied under the edge of the pipe, with water, to drill the glass from the back side. Stop just before you come through (1/16" remaining is about right), to finish after polishing and figuring, or if you go through, cement the plug back in with plaster of paris, to be softened by soaking after you finish polishing and figuring. Do make sure your drill press is plugged into a GFCI for this operation -- an ordinary grounding plug won't protect, but a GFCI will.
  14. I've wanted to make a Gregorian for literally decades. I think making the secondary to diffraction-limited accuracy is likely to be a significant challenge, since the secondary for a 10" Gregorian would be only around 2" diameter, and it needs to be ellipsoidal, rather than paraboloidal (complicates testing a bit, in some ways). One way to meet the challenge is to make the primary bigger, of course -- if you have a 16" primary, you could make the secondary with a standard 4" blank. Of course, then you have to trepan, grind, polish, and figure the 16" primary...
  15. The focus shortens quite a bit during polishing and figuring -- far more than it seems like it should. My 8" f/6.8 went from 70+ inches to 64 inches in those stages. I think it's because of removing the oblateness, which makes the affected portion much flatter than the average.