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Everything posted by peadar1987

  1. 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".
  2. 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.
  3. 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?
  4. 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.
  5. So just after a quick google: 4.5kWth, 42kg: 4.4kWth, 29kg: 2kWth, 22kg: 4.1kWth, 35kg: 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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)
  11. 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.
  12. You rest your case that the N-1 program failed because Commies are inherently worse at engineering?
  13. 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.
  14. 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.
  15. 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.
  16. 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.
  17. 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.
  18. Except they made Buran, and never developed it further because Soyuz was a cheaper way of putting humans and cargo in space.
  19. 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.
  20. Well this is going to end well...
  21. While eating loads of sugar almost certainly isn't great for you, I'd always advise caution on blaming it for the increase in "western diseases". Often, these diseases, heart disease, cancer, dementia, are paradoxically symptoms of a healthy population. As in, if you live long enough to get cancer, it means you haven't already been killed by an infectious disease, or malnutrition, or any of the million and one other preventable things that still kill people on a daily basis in the developing world.
  22. This started off as me imagining how different countries and societies might have developed on Kerbin. It eventually developed into a semi fleshed-out world, and it seemed like a waste not to set some stories in it. I've tried to avoid just creating analogues for real-world nations, although some influences and parallels are going to be pretty obvious. This is my first attempt at writing fiction since I left school over a decade ago, so any feedback is very welcome and useful! Here's the map I came up with, with the main players highlighted: We have: -The Atlavandian Empire Formerly the dominant military power on Kerbin, with an empire spanning half a hemisphere. Atlavand was torn apart a generation ago in a succession war between brother and sister, and many of their colonies around the Atlav Ocean took advantage of this to declare their independence. Now an uneasy peace exists between the Emperor of West Atlavand and the Empress of East Atlavand, with both halves isolated, paranoid, and not on the best of terms with any of their neighbours -The Eslen Alliance The largest economic force in the southern hemisphere, the Alliance is more of a trading bloc than a unified country. Think modern day European Union more than USA. It grew up around a collection of small seafaring merchant republics around the Eslen Sea. They are prosperous, liberal and forward-looking, but tend to lack direction and strong leadership -Shaland An isolationist nation that has developed along the Great Lakes. These provide a natural highway making the nation very easy to defend against enemies, but the trackless badlands and highlands further from the lakes are harder to hold, so the Shalanders long ago gave up trying. Traditionally, the warlord who controls the Narrows between the two lakes controls the country. -Tespen Confederation Another group of separate countries that have become rich from a trading network around an inland sea. The Tespen Confederation is a collection of deeply conservative monarchies who club together to snuff out change if it starts to crop up in any one country, protecting the power of the monarchs and nobility. They tend to view anyone from outside the Confederation as savages. -Yeflana A totalitarian desert nation, which claims to be a benevolent dictatorship. The economy is mostly communistic, although slightly less brutal and rigid than the Soviet system. Has a history of friction with the Tespen Confederation. In the past the strength of the Confederation and the harsh climate of Yeflana have kept the border from moving too far from its current location -Zeswurg The island of Zeswurg was famous for its pirates and raiders for many years, heavy seagoing ships making easy pickings of the lighter vessels from the sheltered Eslen Sea. More recently they have developed a reputation for uncomplicated yet reliable engineering, building on a culture that necessarily placed rather a high value on not sinking without a trace. The political system is a council that developed from individual pirate kings I'll follow up the background info with the first installment of the story over the next few days.
  23. Wow, where did that six weeks go?! I haven't had a spare minute to write, but figured I probably deserve a bit of a break from the thesis, so here goes. Arbus Military Cemetery, Tokana, the Tespen Confederation. It was a cliché that it always rained at funerals. Partially because of a string of writers taking dramatic license with the weather, and partly because the Arbus military cemetery was located on a particularly wet promontory adjoining the naval base of the same name. Today, a stiff breeze drove white-capped waves against the base of the cliffs and over the bow of a Tokanan submarine steaming out to probe Yeflanan defences in the Straits of Neb. It churned slate-grey clouds as they rolled overhead, and it bit into the group of mourners assembled for the interment of the nine non-noble victims of what had become known as the Javelin Catastrophe. The noble victims had been flown back to their family estates, to be placed in crypts or mausoleums, underneath elaborate marble headstones with family crests. The rest would be laid to rest under simple wooden memorial plaques on a headland with countless others who had fallen in the line of duty. Less than half of them had any relatives there, time off for agricultural workers during harvest season was nearly impossible to come by, and lords didn't want to set a precedent of allowing Kerbals to stop work just because a loved one had been killed. However, the embryonic space program had captured the public's imagination to such a degree that millions were said to be listening to the broadcast all over the Federation. After the speeches had concluded, Jadra hurried through the uniformed remnants of the Tespen astronaut corps until she came to General Billgren. He hadn't been on the aircraft when it went down, but he could scarcely have looked worse if he had. "General Billgren, can I have a word?" "Of course, Private Jadra" said the general, pulling his jacket tight against the wind. "General, I've been thinking a lot since the crash. About what happened, and what I could have done. Virenna and Lorcan tried to guide the plane down. Dunfrey spent the entire descent stabilising the injured. What did I do? I got scared, pulled up some floorboards and lost my spanner. I'm not cut out for this. I'd like to offer my resignation from the astronaut corps." "Resignation not accepted" replied the general. "With resp..." "Private Jadra, can you guess why I selected you, above any of the thousands of other candidates, to take part in this programme?" "Because I was the Kerbal of the moment in the media? Because I am about as common as you can get, and it would look good to send up a peasant? Because I'm expendable?!" "No. That's why I was allowed to pick you. And you have repaid my faith in you. You might think all you did was get scared and lose your spanner. Do you know what I have heard about the accident? I heard two pilots tried for ten minutes to fly an aircraft with obviously severed control lines because they couldn't think of anything else to do. I heard about a medic who treated burst eardrums and minor lacerations on Kerbals who were about to hit the ground at 300 knots. And I heard about a combat mechanic who, in spite of being terrified, did not for one second stop thinking of creative solutions, and who nearly saved the aircraft and everyone on board. Our Kerbals are going further, higher and faster than any Kerbal has ever gone before. Things are going to go wrong. Unexpected events are going to happen. Things we can't train for, could never train for. And the only Kerbal on this entire program I've seen show a hint of being able to swallow their fear and fix a problem like that is you." Jadra stood with her mouth open, unable to think of anything to say. The general continued. "I'm being replaced as head of the space program. Heads have to roll after a foul-up like this, and apparently mine is one of them. But before I go, I'm arranging for you be put to the front of the rotation for the first Kerballed spaceflight" With that, he turned on his heel and walked, solitary, through the dwindling crowd and out of the cemetery. Jadra stayed rooted to the spot, a thousand emotions competing for space in her head. ------------------------------------------------------------------ Nammard, Yeflana Tombart and Matrick sat at a café at the side of a small courtyard in one of the oldest districts of Nammard, sheltered from the sun by a dense carpet of shadevines creeping along a network of wires strung across the courtyard for that very purpose. The vines needed minimal water, produced delicious berries, and could grow in the thinnest of soils, and seemingly every street in the city was protected by a canopy of their waxy leaves. Their five-pointed, star-shaped flowers had become the symbol of Yeflana, stylised to the star on the hats of the PEB agents sitting at the table next to Tombart and Matrick. Tombart couldn't tell if they were being monitored specifically, or if the PEB were simply everywhere in Yeflana to make sure nobody misbehaved or read the wrong sort of newspapers. "So the accident enquiry could have gone worse" said Tombart, trying to make conversation. "Main engine turbopump casing failure, leading to combustion chamber damage. Escaping gas causing a torque on the vehicle for which the control system was unable to compensate", rattled off Matrick from memory. The enquiry had lasted several days, and a seemingly endless series of twisted and blackened metal had passed across the desk of the committee of which Matrick and Tombart were both a part. Indeed, they had spent more time explaining to the PEB appointee how rocket engines worked than they had trying to decipher why this particular one had failed. "So now how do we stop it from happening again?" "It's hard to say. The problem is the scaling. I've only ever worked on lab-scale rocket engines before. I can get them working with 99% reliability, and good specific impulse, but you just can't get something capable of lifting a Kerbal into orbit into a lab and fire it. This is all virgin territory, and every time we try one of the bigger turbopumps the entire thing flies apart." "So we don't scale them" suggested Matrick. "You said we've got the specific impulse to make orbit, just not the thrust. How about we use your smaller designs, and just cluster them together? Ten or fifteen of them should be able to get our first stage off the ground, no?" "Good idea, and we already looked into it" said Tombart, sipping a shadeberry cordial. It was punishingly hot, even under the shadevines. "the problem is vibration. One turbopump running at a time, we can predict what that's going to do and damp things properly. Fifteen turbopumps? The test rig and half the engines shook themselves to pieces within half a minute. The vibrational modes interact with each other in ways we can't even begin to predict. It will make a nice PhD thesis in ten years time, but we're not going to the Mun any time soon with any more than five clustered engines." Matrick stared down into his empty coffee cup and debated ordering another. The coffee at the space centre was terrible, and he didn't know when he would next pass through Nammard. Although if they couldn't solve the thrust problem, it wouldn't be long before the next enquiry. -------------------------------------- And meanwhile, deep underneath a mountain towards the northern reaches of West Atlavand, the First Air Lord inspected a welding crew putting the finishing touches to the steel wall of a wide vertical tube that ran all the way to the surface, almost 10km above. Even if the blast doors at the mouth of the shaft had been open, there was no way any light from outside could have filtered down to here. He smiled to himself. West Atlavand weren't going to the Mun just yet, but at least with what they had developed down here in a disused copper mine, they could spring a few nasty surprises on the upstarts to the west.
  24. Convergent evolution
  25. Well technically anything in freefall you're experiencing zero g. Hit a bump hard enough in a car and you'll experience zero g for a second.