RainDreamer Posted September 19, 2015 Share Posted September 19, 2015 Can you see a rocket launch from the moon with naked eyes in perfect condition (fullmoon/newmoon - not sure which is better, weather is clear, high visibility, etc)? Quote Link to comment Share on other sites More sharing options...
SargeRho Posted September 19, 2015 Share Posted September 19, 2015 No, but an IR telescope, possibly even a regular IR camera, might be able to if you're up on a mountain. While a rocket is very bright, it's not bright enough to be visible by the naked eye from 380,000km. Quote Link to comment Share on other sites More sharing options...
insert_name Posted September 23, 2015 Share Posted September 23, 2015 (edited) how do asteroids such as demios and phobos get captured in orbits around planets Edited September 23, 2015 by insert_name Quote Link to comment Share on other sites More sharing options...
ChrisSpace Posted October 9, 2015 Share Posted October 9, 2015 What is the gravitational binding energy of Deimos? In other words, how powerful a nuke would a need to get rid of it? Quote Link to comment Share on other sites More sharing options...
K^2 Posted October 9, 2015 Share Posted October 9, 2015 Just use the formula for spherical body of constant density (E = 3GM²/(5R)) using Deimos' mass and mean radius. It's not going to be exactly right, but correct answer requires a complicated integral that you couldn't probably even find all the input data for. Quote Link to comment Share on other sites More sharing options...
ChrisSpace Posted October 9, 2015 Share Posted October 9, 2015 Just use the formula for spherical body of constant density (E = 3GM²/(5R)) using Deimos' mass and mean radius.How do I do that? Quote Link to comment Share on other sites More sharing options...
K^2 Posted October 9, 2015 Share Posted October 9, 2015 Plug in numbers for M, G, and R into formula? I'm not sure what the question is at this point. Quote Link to comment Share on other sites More sharing options...
PB666 Posted October 9, 2015 Share Posted October 9, 2015 (edited) Plug in numbers for M, G, and R into formula? I'm not sure what the question is at this point.ROFL, He wants an explosion so large at the core of diemos that is blows everything far enough away that it will not recoalesce. I beleive its an acedemic question. We have a nunber of people in the group with a sudden fascination for either blowing up each other, others ships, stars and now it appears moons. Rather annoying trend. Don't forget, small bodies have solid cores that are fused, while these cores have lower tensile strength, they still contribute. because of things like nuclear decay and cooling these bodies will have fracture zones making explosions non-ideal. More than half the energy would be wasted. IOW i think he wants to know how big a bomb it would take to blow diemos into choatic cloud of space dust. Its not going to happen, anyway. There will be significantly size space boulders unless the device used is several magnitudes more energetic than the minimum required. Edited October 9, 2015 by PB666 Quote Link to comment Share on other sites More sharing options...
ChrisSpace Posted October 10, 2015 Share Posted October 10, 2015 Plug in numbers for M, G, and R into formula?Okay, I have my answer now! For those wondering it's 1.392x10^16 Joules, or the energy of a 3.328 Megaton thermonuclear explosion. Since it obviously wouldn't be 100% efficient the bomb would actually have to be a bit more powerful. Quote Link to comment Share on other sites More sharing options...
K^2 Posted October 10, 2015 Share Posted October 10, 2015 I would err on the side of, "A lot more powerful". Even if you drill the hole to the center, I wouldn't expect this to work without at least 100x the minimum energy. But that's still a surprisingly feasible amount... 400MT, while tricky, is something we can build with existing tech. Drilling ~6km into the rock to place the device is also doable.I don't know why you'd want to, but yeah, it sounds like we could totally blow the crap out of Deimos. Quote Link to comment Share on other sites More sharing options...
ChrisSpace Posted October 10, 2015 Share Posted October 10, 2015 I don't know why you'd want to, but yeah, it sounds like we could totally blow the crap out of Deimos.I just wanted to know because I read this on Atomic Rockets:So Terra has told Cape Dread "Here's the deal: you don't mine any phosphorus and we don't nuke Deimos into blue glowing gravel"And I just wanted to know if that could have been taken literally. Quote Link to comment Share on other sites More sharing options...
RainDreamer Posted October 11, 2015 Share Posted October 11, 2015 Which cost more energy: heating something cold, or cooling something hot? Quote Link to comment Share on other sites More sharing options...
K^2 Posted October 11, 2015 Share Posted October 11, 2015 Which cost more energy: heating something cold, or cooling something hot?Depends entirely on the environment. It's always cheaper to bring heat from another object than create it, and destroying heat is impossible, so you have to extract it out of an object to make it colder. In both cases, differences in temperature between object and environment will determine efficiency. Quote Link to comment Share on other sites More sharing options...
shynung Posted October 11, 2015 Share Posted October 11, 2015 How could the brakes on a car generate much higher acceleration than the engine, despite being much smaller and lighter? Quote Link to comment Share on other sites More sharing options...
K^2 Posted October 11, 2015 Share Posted October 11, 2015 (edited) How could the brakes on a car generate much higher acceleration than the engine, despite being much smaller and lighter?Because converting thermal energy to kinetic is much easier harder than kinetic to thermal.Edit: Sorry about that silly mistake. Edited October 14, 2015 by K^2 Quote Link to comment Share on other sites More sharing options...
Stargate525 Posted October 11, 2015 Share Posted October 11, 2015 Because converting thermal energy to kinetic is much easier than kinetic to thermal.Isn't that the other way around? Quote Link to comment Share on other sites More sharing options...
magnemoe Posted October 11, 2015 Share Posted October 11, 2015 Isn't that the other way around?Yes, also brakes works with almost 100% efficiency. simply converting your kinetic energy heat, the limit on how hard you can de-accelerate depend on the friction of the tires. Brakes are very simple compared to the engines for an reason and most of the complexity come so you can brake controlled.Heating and cooling it much of the same, heating is far simpler and more efficient than cooling.heating something can be done with close to 100% efficiency in an water heater. Cooling require refrigeration who if pretty inefficient. Quote Link to comment Share on other sites More sharing options...
SuperFastJellyfish Posted October 14, 2015 Share Posted October 14, 2015 I was reading about Hawking radiation on wikipedia, and it said this:Hawking radiation reduces the mass and energy of black holes and is therefore also known as black hole evaporation. Because of this, black holes that lose more mass than they gain through other means are expected to shrink and ultimately vanish. Vanish? Is that because it's been turned into a singularity, and it can never grow volumetrically again? Why wouldn't it turn back into a star, or some other lump of detectable matter after it evaporated beyond a certain mass? Quote Link to comment Share on other sites More sharing options...
ZetaX Posted October 14, 2015 Share Posted October 14, 2015 Because the only way for it to vanish would be to loose all its mass first. So no star or anything left then (all turned into Hawking radiation). But I am not sure what actually happens at the very end of a black hole, i.e. when the singularity would cease to exist. Quote Link to comment Share on other sites More sharing options...
SuperFastJellyfish Posted October 14, 2015 Share Posted October 14, 2015 Because the only way for it to vanish would be to loose all its mass first. So no star or anything left then (all turned into Hawking radiation). But I am not sure what actually happens at the very end of a black hole, i.e. when the singularity would cease to exist.I would think that during the evaporation process, there should be a point where there isn't enough mass to keep a singularity compressed into a singularity via gravity, and its mass would be able to expand from a 1D thingamajig back into regular 3D matter. Wouldn't this allow the mass to expand beyond the Schwarzschild radius and cause the event horizon to go away before it lost all its mass and just vanished? Or is there no coming back from being an event-horizon-shrouded singularity no matter how much mass has radiated away? Quote Link to comment Share on other sites More sharing options...
K^2 Posted October 14, 2015 Share Posted October 14, 2015 Isn't that the other way around?The three most common mistakes of a theoretical physicist are missing pi, factor of 1/2, or wrong sign.Yes, it's the other way around. Sorry about any confusion. Quote Link to comment Share on other sites More sharing options...
RainDreamer Posted October 14, 2015 Share Posted October 14, 2015 Is it possible to completely ignite the atmosphere of a planet similar to earth? (atmostphere full of burnable things like O2 and stuff)I thought of that after seeing these bombs from the Homeworld universe: http://homeworld.wikia.com/wiki/Low_Orbit_Atmosphere_Deprivation_WeaponAfter a few salvo of these the planet will be literally on fire. Quote Link to comment Share on other sites More sharing options...
Hary R Posted October 14, 2015 Share Posted October 14, 2015 (edited) Is it possible to completely ignite the atmosphere of a planet similar to earth? (atmostphere full of burnable things like O2 and stuff)I thought of that after seeing these bombs from the Homeworld universe: http://homeworld.wikia.com/wiki/Low_Orbit_Atmosphere_Deprivation_WeaponAfter a few salvo of these the planet will be literally on fire.The real life equivalent of this weapon is the fuel air bomb (thermobaric weapon), it use the surrounding O2 to ignite the fuel it carry. A large number of this weapon can surly burn a large portion of the O2 in a precise area (making the air unbreathable). But an entire atmosphere, I don't know! with enough number may be.... I guess.edit: yeah! Like what NuclearNut says below, the number of fuel air bomb required will be the equivalent of the mass of the atmosphere. That's not a few salvo. Edited October 14, 2015 by Hary R Quote Link to comment Share on other sites More sharing options...
NuclearNut Posted October 14, 2015 Share Posted October 14, 2015 (edited) Is it possible to completely ignite the atmosphere of a planet similar to earth? (atmostphere full of burnable things like O2 and stuff)I thought of that after seeing these bombs from the Homeworld universe: http://homeworld.wikia.com/wiki/Low_Orbit_Atmosphere_Deprivation_WeaponAfter a few salvo of these the planet will be literally on fire.Do you mean ignition, or do you mean ignition?From what I understand for the first, you would need a far more oxygenated atmosphere or far more burnable things to get such a large firestorm going, which at that point means you have to move around the mass of the atmosphere of the target planet with you. It would be much easier just to disperse some deadly poison or pandemic on the planet, or to simply introduce it to several salted nuclear weapons targeting their main cities, resulting in the death of millions due to radiation sickness.If you mean the second, I believe that thermal losses into space and the fusion of iron (among other things) in the crust would result in the reaction not being self sustaining and thus dying out quite rapidly, not adding much at all to the yield of any hypothetical nuclear weapon. Edited October 14, 2015 by NuclearNut Quote Link to comment Share on other sites More sharing options...
shynung Posted October 28, 2015 Share Posted October 28, 2015 As far as I know, nuclear reactors always have their energy extracted by boiling water into steam, turning a turbine generator somewhere. Nuclear reactors generate heat, so is it possible to use it to directly apply the heat to an industrial process - say, seawater desalination, or a blast furnace? Quote Link to comment Share on other sites More sharing options...
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