sgt_flyer

Oakridge MSRE only used uranium based salts (U-233 and U-235) - and was pretty safe, as the primary loop was kept at all time inside the reactor confinment. They used uranium bred from thorium, but never directly used thorium in it. And it never had in situ reprocessing directly integrated with the primary loop - so that's one key part of today's design that was never tested

Using sodium for primary or secondary loop comes with it's own problems though - in case of sodium leakage, hot sodiul m would catch fire immediately at ambient atmospheric pressure (and good luck extinguishing a mass spill of sodium - and to keep it away from water ) @someguy The windfarms/solar farms with underground storage have special requirement though - you need to have such geologic structures avaible on hand for pressurised air (and imagine the amount of land you'll need to cover to match a nuclear or classic power plant) Solar panels have a terrible w/m2 performance (especially if you are in less sunny countries) and you need to keep wind turbines apart from each other. (Else the resulting wind vortices would lower the other wind turbines efficacity - and those turbines have a huge concrete feet to hold them upright) If we want to limit our dependancy on nuclear power / classic power plants, maybe we can try to lower the needed baseload at first ? (which means to try to waste less electricity all around the year ) - more efficient house insulation, more efficient industrial machinery, etc - would allow to both lower the overall energetic mix load needs - less power plants needed

Well, this launcher is meant to make use of AR's Pyrios booster, using their F-1B engine (basically a Saturn-V F-1 engine built with today's lower cost techniques and materials knowledge) (they already tested the gas generator recently) If the pyrios booster is not selected in the first place for SLS, it will lose quite some appeal (and ATK's booster seems to have better traction) Besides, Orion is meant for beyond LEO operations, where you need the full SLS to send it. (For LEO operations, they will be able to call upon Boeing's CST-100 or spaceX dragon V2 anyway) So, a bit redundant for now (though, the engine itself might still potentially spark some interest - if they manage to build it for reasonable costs)

The thorium needed for MSRs is basically natural thorium - much more abundant than natural uranium - and it doesn't need heavy fuel processing (centrifuges and such) to be transformed into usable fuel. thorium MSR (Molten Salt Reactor) don't use fuel rods - it basically uses fuel in liquid form at operating temperatures. The fuel directly becomes the primary loop which is pumped in and out of the reactor. After the primary loop heat exchangers, the still liquid fuel is cleaned of decay products (much easier to reprocess liquids than solid fuel rods) before being reinjected in the reactor core. (The fuel is cannot go critical in itself - the initial reaction needs to be kickstarted (one of those kickstart means being weapon's grade uranium, and is sustained thanks to the breeding and the moderators in the reactor) One of the problems with solid fuel rods, is that once the transmutation of the fuel rod into it's decay products goes over a certain treshold (and even only a few % of transmuted material is enough) the reaction cannot sustain itself (because the neutrons have more chance to hit non fissile byproducts) - so the fuel rod has to be taken out and either reprocessed - or discarded, which creates a lot of waste. With molten salt constant reprocessing, they want to extract only the byproducts, which would allow to create less waste. Some proposed highlights of the MSR design : if the fission rate starts to accelerate, the liquid would expand naturally from thermodynamic laws, and the resulting additional space between fissile atoms would mean that more neutrons are lost - so the reaction is supposed to be able of a certain amount of self regulation. The molten salts can run at much higher temperatures (as much as 850°C) (as they don't have risks of damaging the fuel rods) - would give higher temperatures for the secondary loop, enabling the use of more efficient steam turbines. The molten salts also operate at low pressure, simplifying the reactor's design. Security measures : the reactor can be emptied from it's fuel through gravity - in case of failure, there is basically supposed to be an actively cooled cap in the primary loop - if the power fails / primary loop pumps stop, the cap is not cooled anymore and melts - the fuel then flows thanks to gravity directly inside a containment under it. Downsides : molten salts at these temperatures are very corrosive, so you need to build out of materials able to withstand that (and some of those can embrittle...) Each reactor would need it's own small reprocessing fuel plant to extract the byproducts. Also, Current production of the weapon grade uranium needed to initiate the reaction is nowhere near enough to sustain a country wide thorium MSR power plants. You could also use reactor grade plutonium to initiate the reaction, but it would end up generating much more byproducts to be cleaned out of the fuel afterwards.

One thing comes to mind though with all this talk - Power density is also of importance and has to be taken into account (especially on islands like japan, were space comes at a premium - unless you build your renewable energy over water, which will increase maintenance costs (storms, corrosion) and might cause fishing problems (notably for japan which is extremely dependant on fishing) Found an article describing the power densities problems (and remember that people also need to eat - so you need farmland) : http://www.theenergycollective.com/robertwilson190/257481/why-power-density-matters And one interesting point of this article, is to see how much energy / people is required (notably for occidental lifestyle countries) So - wouldn't trying to make everything more and more energy efficient be also a good way to limit pollution ?

Hydroelectric dams are better to be considered more as a battery than an energy source. Their very fast response time to peak demands is great (only need to open the valves) - though, as you empty your dam, you'll need to use overproduction from the rest of the power grid to refill the dam. (precipitations alone are generally not enough to keep up with the demands) - Swiss actually plays on that a lot - they buy electricity to europeans when they are overproducting (this electricity still need to be somehow spent - so swiss get that cheap) and use it to refill their dams - once european face peak demands, they sell back electricity from their dams at a higher price (as the rest of the europe still need additional energy to meet the peak demands) - the only 'renewable' versions of hydro dams are the ones that use sea / river currents or tides (those tidal dams need specific geographic conditions, but their output is totally predictable - you only need to pick your tide tables, and you'll know your output a long time in advance) Afterwards, dams are still a costly infrastructure to create - especially if you want to minimize environmental damage - as you need to remove all the trees from were the water will be stored - if you let those trees there when filling the dam - you'll end up with a lot of roting biomass creating notably methane gas in huge quantities. (Can't really say that dams are 'green' in this regard...)

Oh they did made test bench versions of those rocket engines Chloride trifluoride + hydrazine nontheless http://naca.central.cranfield.ac.uk/reports/1949/naca-rm-e9f01.pdf But as with the tripropellant, the problems still far outweight the benefits (not the least that the oxyded layer must remain intact within the fuel tank )

I think he meant about what randall wrote in his what if article that if you wanted to try to get inside the pool for a swim you'll die long before reaching it - from severe lead poisoning gunshot wounds - though, it was still a fun comment (guess randall's way of mixing a bit of humor with facts is what made these series so appreciated ) Guess that'll depend in which country you try something like that, but you'll still be intercepted (and most likely a bit roughed up by the security teams - unless you try to continue at all costs) long before entering any critical buildings, before being put into police custody. (Not taking into account the various security doors etc in your way - with keycards, guardposts controlling an airlock etc)

You'll find all kind of answers here https://en.m.wikipedia.org/wiki/Life_support_system but basically, short duration mercury / gemini / apollo missions used pure oxygen at reduced pressure, and EVA suits also use partial pressure +pure oxygen (lighter life support + less reduced mobility from pressure stiffening for the suits. Russians spacecrafts always used sea level air pressure with air like mix.

Well, they wanted to see what was the best ISP they could achieve with only chemical reactions of 'classic' atoms / molecules (stuff like metallic hydrogen are a bit outside classic chemical reactions ) - though here, the downsides far exceeds the upsides (imagine the enormous costs to build and maintain a facility capable of safely fueling (yeah with moving fluoride and hot lithium through fuel pipes ^^) and launching such a thing... Yup, LH2-Lox seems far safer (and cheaper) in comparison

Guess what was tested back then in 1967 has the edge in dangerosity... (Though, hopefully, this combination is so difficult to do outside of test benches that it's not really adaptable) https://www.flightglobal.com/pdfarchive/view/1967/1967%20-%200069.html Tripropellant Lithium - fluoride - hydrogen rocket engine tested in the 60s... - 542 ISP ! But uses : liquid hydrogen (to be kept below 23°K) liquid lithium (to be kept above 453K - speak about insulation problems in a rocket ) and liquid fluoride... Imagine the care needed with liquid lithium... (AKA absolutely 0 humidity nor contact with oxygen allowed) Plus fluoride to be safely kept

well - randall wrote a what-if once about spent nuclear fuel pools https://what-if.xkcd.com/29/ So, even swimming on the surface of this kind of pool would be quite safe (at least from the radiations - from the security teams, that would be another story )

Orbital assembly using astronauts would be terribly exhausting for the crew if they have to put on EVA suits (even MCP suits) and not very efficient, because of the severely affected hand mobility. (Not counting the time spent donning the suits and prebreathing.) You would need a pressurisable hangar for manual orbital assembly, so the astronauts could work in 'normal' work clothes. (So they'll have their full strength & dexterity at their disposal) Now imagine having to use a lot of tools in a microgravity environment - they'll have to ensure safety at all points to prevent their work from damaging the hangar. (Plus, arrays of anchor points / beams for the astronauts to grab on - imagine if an astronaut get into a space were he as nothing to grab on - besides, they'll need such supports if they ever need to have any meaningful leverage strength.

Well, ESA did get some useful infos on how to pull off this kind of mission from the rosetta mission. (Afterall, the lander will have some of the same jobs philae had - CONSERT like tandem instruments, etc. And now that ESA knows roughly what didn't work on philae's landing systems (notably the harpoon nitrocellulose charges), they'll be able to refine their landers.

@kryten actually, nasa sucessfuly did some subscale tests of inflatable heatshields (even at 7600mph of speeds) as part of the ongoing HIAD research. http://www.nasa.gov/home/hqnews/2012/jul/HQ_12-250_IRVE-3_Launch.html

Welllll - the best answer will be - it depends hypergolic rocket engines obviously don't need an ignition system. (Proton rocket, the old Ariane 4 rocket) Non hypergolic systems use various means, but the origin of the ignition is always within the combustion chamber, because rocket engines need a stable combustion (SSMEs have a sparkplug like system in the middle of the injectors http://blogs.nasa.gov/J2X/tag/ignition/ ) Other engines can use a liquid that is hypergolic with either the fuel or the oxidizer - they inject a small amount of it within the combustion chamber, reacting with either the oxidizer or the fuel, then the combustion reaction is sustained. One example, boron based compounds (green flame at ignition ! - SpaceX falcon 9 use this stuff -saturn V F-1 engines also used it) https://en.m.wikipedia.org/wiki/Triethylborane There's also the possibility of using pyrotechnics to trigger the ignition (though obviously, it's generally for non restartable engines:p) Some companies work on laser ignitors too Soo - there's a lot of options, depending on the fuels used, the kind of work the engine will have to do (restartable / non restartable / air started / ground started)

Yup, but you lose in efficiency (mass fraction / 'real' ISP) in the process. However, given copenhagen suborbitals objectives and fundings, they are building nice experience with a cheap simple design well suited to accomplish their objective. The day they'll need a more efficient design, they'll be able to draw from the knowledge they acquired to devellop it

Welll - here's a breakdown of the composition of what created the kerbals https://en.m.wikipedia.org/wiki/Composition_of_the_human_body And indeed, the full complete thing proved that it can be quite deadly. But i doubt it can be simpky considered as a 'dangerous chemical'

Guess it's because it allows them to limit the complexity / needed materials a lot for the turbine (much less temperature to manage, so they don't need to use pricy specific materials for the turbine, and don't have to face thermal deformation. Besides, V2 rocket and the Redstone rocket / jupiter missile also used peroxyde + catalyst to drive their turbopumps

You need to think about the orbital mechanics at play here the debris is in orbit around earth fire at it from the earth surface, and the resulting ablative thrust will effectively be directed towards earth - however, this thrust will result in a radial / antiradial type of orbital manoeuver, the whole orbit will 'rotate' around the spacecraft. At one point, the orbit would intersect with the planet - ok the apoapsis will be farther from earth - but at the same time, if the periapsis has become low enough to go through the atmosphere, when the debris enter the atmo it will start to slow down (if it only pass through the high layers of atmosphere at first) and will end up being delrbited due to drag and will burn during atmospheric reentry.) edit : here's what doing radial/antiradial manoeuver looks like in KSP (i only tugged at the blue manoeuver node outwards) i have precise node and KER opened so you can check the orbital parameters (ok, 'besides, it works in KSP' is a corny line, but in this case, it would do the same in real life )

Yup but water covers 70% of the Earth surface much easier to go into water than taking a dip in a dangerous chemical container (which are most likely closed anyway / or have protection barriers to prevent you from doing so) It would be really worrying if any really toxic chemical which we only have in small quantities on Earth(compared to water, it's insignificant) could account for more deaths than water accidents water drowning is not a result of the water directly killing you - it's merely preventing you from getting enough dioxygen to sustain the body.

Peadar i think we are now well aware of the dangers of DHMO, (Dyhydrogen Monoxyde, AKA H2O ) Of course it can do all that. But given the number of posts on it already in this thread, i don't think it's useful to continue peole interested will check on the DHMO website Granted, the peculiar (and almost unique) reactions water undergo when solidyfying are damn dangerous, due to the cristallisation. But imagine the effects other more chemicals could have when their temperature change past their boiling point ? Example, mercury boils at 356°C - imagine the disastrous combined effects of mercury vapors on a human between the burn and the mercury poisoning.

Well demineralised water (basically pure H2O) can still be dangerous for health if you only drink that over time (even in reasonable amounts) - not replacing the minerals in your body is not really healthy Now, the DHMO trend started as a social experiment meant to prove that if information is presented a certain way, you can influence people (here, it was for signing a ban against DHMO ) As of today, there are still people who fall into it

Nah - you can shoot them from below too - the laser heating on the bottom of the part will result in ablation ejecting thrust towards the planet (the same as if you made tried to make a burn in KSP to get directly 'away' from the surface. making Radial and antiradial manoeuvers end up rotating the whole orbit with the debris as the center of rotation. (Instead of changing the orbit's opposite point altitude like in retrograde / prograde manoeuvers) Normal spacecrafts have generally no use for this kind of manoeuver because it's extremely costly in delta-V - but that's not a problem when using lasers on debris. If you picture your orbit rotating with your spacecraft as the center of rotation, (not talking about plane change here) the orbit will either end up intersecting the planet (or if you can target satellites in geostationnary orbit, potentially getting it into an escape trajectory before the orbit intersects with the planet) - think of the radial / antiradial manoeuvers as something akind to the spacecraft playing hula hoop with it's orbit firing from above or from below only change the direction of rotation. Once the orbit intersects, it does not matter the direction you rotated the orbit anymore If you want to test, just create a manoeuver node on an orbit in KSP and play with the radial / antiradial controls

antimatter alone will not do better than matter If you mix an antimatter chemical with the equivalent chemical (or simply come into contact with classic matter), you'll simply end up with a matter - antimatter annihilation anyway (total conversion into energy from the annihilation)