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peadar1987

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Everything posted by peadar1987

  1. If you want to be really clever you just put two turrets with a half-hemisphere field of fire back-to-back. Same coverage, far less complexity.
  2. Just a guess, but if it was formed from remnants of Theia and ejecta from earth, the individual pieces would all have been on either hyperbolic or suborbital trajectories, but when they smashed together, they would change each others' paths into something that didn't hit the surface or escape the system. Then once you have an elliptical orbit in a "dirty" region of space, it will tend to circularise, as the body is hitting things harder and more often at perigee when it is moving faster. As well as circularisation due to tidal effects.
  3. I was just going to say he's probably a lot further away than the looks due to foreshortening, but I like this idea better
  4. And what type of energy are you trying to deliver to it? Kinetic? Thermal? Potential? Does it matter if the object is destroyed in the process? What is its mass? What material is it made of? Are you working to a tight timescale, or have you got as long as you need?
  5. Hammer?! Although i you want to game the question, the easiest way would be to move it to somewhere warmer than it is now and leave it there for a while.
  6. Of course. But I'm not arguing that the Shuttle is terrible, or that it is better or worse than any other spacecraft, I'm just disagreeing with Yobobhi's claim that "the Commies were bad at engineering".
  7. Cost is a pretty big handicap. If I want to put a 1000kg payload in orbit, cost and reliability are the two things I'm going to use to decide which launcher is "best". Which is why the Soyuz is the "best" launcher for a lot of the applications we've had for the past 30 years, and is still flying whereas the Shuttle has been retired, in spite of its superior technical capabilities in certain areas. All engineers are given a budget. If you meet the design brief within the budget then you're a good engineer. Bigger budgets don't make better engineers.
  8. You're completely missing the point. The 747 is better than the Shuttle at what it was designed to do. The Shuttle is better than the 747 at what it was designed to do. Heck, my lawnmower is better than the shuttle at what it was designed to do. Just using total up-mass per launch as the be-all and end-all of launcher comparison is far too simplistic. The Apollo LEM descent stage could put a payload of 4,700kg on the Moon. The Shuttle could put zero payload on the moon. Does this mean that the LEM was categorically a better spacecraft, or simply that it was designed for a different purpose?
  9. May be useful to start an arms race and bankrupt your rivals?! Other than that, orbital weapons platforms don't give any particular advantage* *Unless we start developing unprecedentedly powerful and efficient laser weaponry, in which case the huge, unobstructed field of view from an orbital platform would be of some benefit.
  10. So just after a quick google: 4.5kWth, 42kg: http://www.aircon247.com/p/8849588/Toshiba-compressor-ACC-kw-btu-portable-air-conditioning-unit-.html?gclid=CMqnwYXdxtMCFVUz0wodIKIGoA 4.4kWth, 29kg: http://www.appliancesdirect.co.uk/p/p15hp/electriq-p15hp?refsource=Apadwords&gclid=CMPW8rzdxtMCFVEW0wodphoA1Q 2kWth, 22kg: http://www.appliancesdirect.co.uk/p/ac9000e/electriq-ac9000e-air-conditioner?refsource=Apadwords&gclid=CMGP4L7dxtMCFYoaGwod1o8A7g 4.1kWth, 35kg: https://www.toyotomiusa.com/factoryOutletStore/index.php?route=product/product&product_id=133 These are portable heat pumps so will be designed to be relatively lightweight, but mass won't have been the #1 optimisation criterion. Specific powers are about 100-150W/kg, so I'm guessing if mass was a major issue you could probably design one with a specific power of 200-250W/kg. Again, for your temperature question, it's not something that would really come up. The temperature is a design parameter, and there's no real reason to compare systems that produce a different temperature output, you will always just go with the one that produces the minimum temperature that satisfies the design brief.
  11. Ah right, no idea. Any thermodynamic systems I've worked on are firmly attached to the ground, so mass is right down the list of parameters I'd be optimising.
  12. Well giving Mars an atmosphere of ~6% the pressure of earth's would mean your blood wouldn't boil at atmospheric pressure, and you could breathe with an oxygen mask, and go outside wearing (extremely) warm clothes. Mars has a surface gravity of 0.38g, and a surface area 0.28 that of earth's, so an atmosphere 82% of the mass of earth's would give the same surface atmospheric pressure. An atmosphere 6% as thick as earth's would therefore have a mass of 2.5*1017kg. A decent sized comet (let's say Halley's comet) has a mass of about 1014 kg, so even if that's all ice and volatiles you'd need to smash 1,000 of them into the planet to give you that atmosphere. Your best bet would probably be to redirect an icy Jupiter or Saturn Trojan. However, that's currently far, far out of our technological reach. You'd need some sort of nuclear fusion torch drive. The other option is "building" an atmosphere from gases produced in-situ on the Martian surface. I don't know enough chemistry to say what the best candidate for that would be.
  13. Are you talking about mass flow rate of the working fluid, or mass flow rate of thermal fluid (water for a water source, air for an air source, not really relevant for a ground source)? Normally you just talk about J/kg, which gives the amount of power per kg/s of flow rate (whichever one you prefer, although the thermal fluid is the more usual one). The output temperature is normally fixed for a given operation, so you don't need to take it into account as a variable when comparing systems for the same application. If you were concerned about comparing cycles with different outlet temperatures, you could compare them based on Second Law Efficiency. This has a few different definitions, but the most simple is just the Coefficient of Performance of the cycle divided by the Carnot Coefficient of Performance, which is given by COPCarnot=Tcold/Thot-Tcold. This will just be a percentage, and standard values are roughly 50%, as far as I have seen.
  14. Nope, the Russians didn't see a need for a spacecraft with the capabilities of the Shuttle, and therefore weren't working on it until the Shuttle program was revealed and the military demanded something with the same capabilities. Buran started development 3 years after the Shuttle, and first flew 7 years after the Shuttle. That's not the hallmark of a bad engineer. Also worth noting is that the Soviet Space Program received considerably less funding than the US equivalent. This source (from the CIA) estimates that the US program was receiving roughly 40% more funding. The Soviets weren't great at economics, but they absolutely, categorically were not bad engineers. As for the Dragon, it is not better or worse than the Shuttle. It was designed for a completely different job, namely delivering cargo and crew to space cheaply, and it does it far better than the Shuttle ever could. You might as well say that a 747 is "better" than the Shuttle because it carries more payload. It's true, but irrelevant.
  15. Rotational kinetic energy of the earth = 2.138×1029 J Orbital kinetic energy of the earth = 9*1031 J Chicxulub impactor = 4.2*1023 J (all from wiki) World nuclear arsenal = 6400Megatons = 2.7*1019 J (from here. Not sure of the accuracy of the source, but it gives an idea of magnitude)
  16. Obligatory post in every Mars terraforming thread. -The magnetic field has very little effect on radiation dose rates at the surface of earth (or a terraformed Mars). The vast majority of the shielding comes from the mass of the atmosphere itself. -While the magnetic field does protect the atmosphere from being stripped by the solar wind, atmospheric loss happens over the timescale of millions of years, so if we have the capability to give Mars an atmosphere, we have the capability to top it up or retain it. If magnetic field was a deal breaker, then Venus would be out as well, because not only does it also not have a magnetic field, it experiences far higher solar radiation than Mars.
  17. You rest your case that the N-1 program failed because Commies are inherently worse at engineering?
  18. So outboard motors tend to vent their exhaust below the water, close to the prop (apparently to reduce noise). This seems to be the cause of most of the bubbles I've seen in the wake when driving powerboats. From seeing large prop-driven ships moving at low speed, I don't seem to remember the wake being too frothy, mainly just turbulent water. Most of the froth, if there is any, seems to be cause by air being entrained by the bow slamming down after going over a wave.
  19. I've driven a RIB pretty close behind a fast ferry (This ugly brute) Not close enough to get hit by the jets from the impellers, but close enough that the water was still fizzing. There was no real noticeable drop in the buoyancy of the RIB, or the power from the prop when we entered the frothy water.
  20. Much of the ISS was designed for the STS to put in orbit, mainly because STS was there, not because STS was inherently a better way of putting them up. Most sections could have been redesigned for Proton without any loss in functionality. The only thing I can think of that only the STS could have done was the Hubble repair. And this is coming from a massive, posters-on-the-wall fan of the STS.
  21. Not really, cavitation causes parasitic drag if it happens on the hull, or reduces the efficiency of the prop if it happens there. Most ships will be designed to avoid it if possible.
  22. Having spent most of my youth in and around small boats, both sailing and powered, I think it's unlikely you'd be dragged into the prop. I've never seen it happen. The harbour where I learned to sail (Dún Laoghaire) was a pretty busy ferry port. There was always a lot of rubbish and debris in the harbour, and none of it seemed to get chewed up by the props of the ferries passing through, or the impeller on the fast catamaran that replaced them. Obviously this is a slightly different situation to stuff falling off the ship, but stuff already in the water generally tends to get pushed aside by the bow wave before it gets anywhere near the spinning death at the stern. One thing I have noticed is that at low speeds the boat can "tow" along quite a lot of stuff behind it. On my small sailing boat, below about 2 knots of speed, two eddies form at the corners of the stern, and small pieces of debris will sit in these vortices and follow me along.
  23. Except they made Buran, and never developed it further because Soyuz was a cheaper way of putting humans and cargo in space.
  24. Well that depends on the tank size. Hoop stress is given by P*r/2t, where P is the internal pressure, r is the tank radius, and t is the wall thickness. If you set the hoop stress to the tensile strength of you material you can work out a relationship beteen the radius and the thickness for a given internal pressure.
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