architeuthis

I recall reading on Centauri Dreams an essay suggesting we would need a 50 sq km phased array antenna to make sense of our own civilization's radio signals if they were hypothetically broadcast from Proxima Centauri only 4.4 ly away. This is a simple ramification of the inverse square law of radiation. It implies that our current SETI is based on the faith that other civilizations either use very high energy broadcasts, or are trying to actively signal us themselves. The silence of the galaxy is troubling. One explanation is that we are the first in our galaxy, however this seems improbable. There is too little information to accurately gauge the risk of broadcasting for all to hear our location to the galaxy. Inferences made about E.T. civilizations based on our own history and psychology is bound to be loaded with indefensible cultural assumptions, not to mention the mother of all sampling biases. So we may have everything to gain... or maybe we have everything to lose. IMO it is foolish to make existential bets when you don't know what the odds are.

For space applications, one advantage of using a molten salt coolant is that you can use it to drive a magneto-hydrodynamic generator directly, instead using a brayton or rankine cycle steam turbine. A MHD generator is less efficient, but as it has no moving parts it is much more mechanically reliable.

Nice. I've been wanting to go since they opened the Atlantis exhibit. Alas, Florida is a long way from Oregon:/

Positrons are relatively easy to produce; they are a natural product of beta decay from radioactive elements. They can also be produced by pair production with lasers or very strong magnetic fields. My very simplistic understanding is that if a particle's kinetic energy exceeds the energy equivalent of its inertial mass than it can produce an antiparticle when it collides with a target. In this way particle accelerators accelerate protons until their energy is on the order of 1 GeV (the energy equivalent of their rest mass E=mc^2), and collide them with a very dense target, made of tungsten or gold to produce anti-protons. The process is very energy intensive and capturing the particles thus produced is horribly inefficient (like .001% efficient). AFAIK the best we've done is capture a few hundred atoms at a time. And they don't store for very long, even when cooled to very low temperatures in a high vacuum. I have faith that we could someday produce large volumes of antimatter economically, but our current technology and engineering isn't optimized with industrial scale anti-proton production in mind. And efficient production technologies like gamma-ray lasers are probably still a very very long way off. Also even if the process was 100% efficient, we would still need tremendous amounts of power to produce large volumes of anti-matter; thousands and thousands of terawatts to produce maybe a few hundred kilograms of antihydrogen a year. We would need huge Dyson arrays, or similar megastructures closely orbiting the sun, to produce this much power. Still, assuming warp drive doesn't pan out then antimatter rockets, despite their many practical problems, are about the only half-way feasible way in which humans could travel to nearby stars in reasonable time spans. When antihydrogen is reacted with hydrogen it produces , among other things, charged pi-mesons that could be funneled out of a magnetic nozzle with exhaust velocities of up to .9 c. Put that in your Tsiolkovsky's rocket equation and smoke it! You could crank up to .5 c and make the crossing to Alpha Centauri in less than 15 years in a single stage rocket with a mass ratio of 3! FTW!!

For the love of science and a good challenge we can roleplay over KSP's little simplifications and thicken the game's veneer of realism. Considering the sandbox nature of the game these sorts of things can help keep the game fresh and add interesting layers of depth and nuance. I thought it would be neat to compile a list of roleplay techniques used by the community. Here is one to start off with: If you're using radiator systems in KSP Interstellar or Near Future Technologies you should consider not radially mounting your radiator panels such that they can "see" each other. Thermal radiation is just a form of light, it shines in all directions from an emissive source. Ultimately, the point of a radiator is to reject waste heat out into the depths of space so that it doesn't melt your spacecraft. However, if the radiators aren't mounted 180 degrees apart then they will be effectively radiating heat on to each other rather than away from the spacecraft. If your panels radiate on to each other then the total heat rejected by the system will be reduced by the view factor F, which is engineering parlance for the fraction of radiation leaving one surface that is intercepted by another surface. If you assume that the panels are of equal dimensions and have a roughly common edge (i.e. the radius of placement of these panels is small compared to their overall length) then the view factor is approximately F=1-sin(alpha/2) where alpha is the angle between them. and the total heat rejected by your radiators will be qnominal*(1-F)=qactual I often see screenshots where people mount their radiators at right angles to one another. This reduces their effectiveness by roughly 30%. Panels with smaller angles are even less effective. For applications in an atmosphere heat is usually removed more quickly by forced convection than by radiation so it is okay to mount panels more closely (in this case they would be called fins). Here surface area is the main thing you really need to care about. tl;dr point your radiators away from light sources (such as other radiators).

Minmus is a lot bigger than any comets that have been observed in our solar system, also as many have noted its albedo is much too high. It's possible that, due to some series of fortuitous orbital encounters, Minmus avoided any low perihelion orbits of Kerbol before being captured by Kerbin and thus sublimating off its volatiles to gradually reveal a darker sub-surface. The thing is, even though Minmus orbit is inclined, it has zero eccentricity which would be really odd for a recently captured body.

There can be only one conclusion: Kerbals don't use radiation shadow shields:) The Kerbal 'propellium' liquid fuel may very well be a hydrogen analog, after all there is an obvious parallel between the Kerbal S3 KS-25x4 Engine Cluster and the SLS core stage with its 4 RS-25 engines which are cryogenic. Also a NERVA type NTR wouldn't get anything like 800 s by using kerosene as reaction mass. Then again if the Kerbal LFB KR-1x2 is supposed to be the Dynetics Advanced Liquid Fueled Booster with 2 F-1 engines, which seems patently obvious to me, then both the cryogenic and rp-1 analogs are both running on the same liquid fuel. I agree, the current LV-N balance is fine. I don't think they need a special fuel, but it would be nice if they didn't need an oxidizer.

So... DL? Soon I hope?

I don't think the size of the turbopumps is the problem. Propellant crossfeed isn't pumping from tank to tank, just engine feedline to feedline. Its problems are not dissimilar to those of the SM-65 Atlas stage an a half approach. There may be weird shutdown transients associated with jettisoning the side boosters for one thing. While propellant crossfeed is technically feasible (the principle was demonstrated on the Space Shuttle for instance), the main problem is just the surprisingly high amount of development and cost risk associated with making the feed and separation systems doubly or triply redundant with very high reliability. Unfortunately this is not trivial and we should recognize that Space X is taking a risk here. Obviously KSP handwaves away all the engineering difficulty that goes into this. It will be really cool if propellant cross feed pans out for the falcon heavy.

These are the main advantages of bimodal NTR IMO, but KSP doesn't simulate reactor warmup times, coolant dynamics or thermal cycling so the point is lost somewhat. On a mass basis, at least for Mars missions solar panels make more sense than bimodal NTR. Bimodal NTR uses very low efficiency thermoelectric conversion cells, and requires heavy radiator mechanisms. In reality radiators are prone to breaking down (as we have seen on the ISS), but manual repairs in the immediate vicinity of a nuclear reactor are completely out of the questions for safety reasons. Solid state radiators are even less efficient on a per mass basis than the ammonia cooled ones. For these reasons, among others, the most recent NASA Mars design reference mission uses nuclear thermal for propulsion, and solar to generate electricity. TLDR; Keep the LV-N like NERVA unless there is a waste heat management dynamic added to the game. Seconded!

It is a silly urban legend that NASA lost the Saturn V blueprints (wake up sheeple! lol). On the contrary NASA put in a pretty unprecedented amount of effort to document everything when they shut down the Saturn V production line (at the time NASA administrator Thomas Paine assumed the shutdown would be temporary and wanted to retain the ability to reproduce the factory tooling as rapidly as possible). They still have all of that stuff. Blueprints are only a piece of the manufacturing puzzle at any rate. The thing is the engineering has progressed since the 1970's and SLS will have roughly Saturn V like performance, but at a fraction of the cost. The difference between now and then is during the Space Race NASA's budget was proportionally 10 times higher than it is now (literally). Nobody wants to build the old F-1s, as impressive as they were, we can do alot better these days in terms of performance and cost. Also, why are you worried about hydrogen? Cryogenic upper stages are common in many launch vehicles. The Saturn V's second and third stages were cryogenic for instance, as is the upper stage of the Atlas 5 and of the Delta 4, as well as the core stages of the Space Shuttle and the Ariane 5. Frankly I'd be alot more concerned about the nitrogen tetraoxide/UDMH/red fuming nitric acid used by Russian launch vehicles.

Gorgeous Jool texture! Easily the best anyone's done so far IMO. How is it installed?

Is your criticism based only on aesthetics? They may be goofy looking, but my understanding is these new suits are a major functional improvement over the current EMU design NASA uses. EMU is only good for space walks, not planetary surfaces for one thing, but these new suits should also be lighter and offer substantially improved mobility and range of motion as well. Also astronauts will not have to prebreathe at lower atmospheric pressure for hours before starting an EVA.

As far as I know there is no way to completely eliminate waste. But we could pretty dramatically reduce the the volume, and mitigate the environmental impacts, of high-level waste though transitioning commercial power to low-waste generation and a combination of geological repositories, reprocessing, and integral fast neutron reactors.

American atheists often presume a privileged credibility for Christianity that they don't for other religions. This is difficult to justify on philosophical grounds. Could Zeus convince fervent Christans, or Hindus for that matter?

Radiation? Yes. Lord yes. Radioactivity? Unless the fuel elements are leaking, or neutron activated stuff is ablating in the exhaust stream, then no. Kerbals? Safety features? The NERVA integral shadow shield (not including the external shield) is a thick disk of beryllium and tungsten. Its got a planar density of around 3500kg/m^2, and the the Kerbal LV-N is about 1 meter in diameter. The LV-N only weighs 2.25 tons, which means it is %122 shielding by mass:) Lets face it, the only thing between those poor kerbonauts and the atomic gorgon is the propellant tanks... you've got propellant tanks between the kerbals and the reactor right? Space radiation consists mostly of protons from the solar wind, solar storm protons, x-rays and cosmic rays. NASA expects astronauts on a 360 day round trip to Mars to accumulate close 1 Sievert of absorbed radiation. As a chronic dose this is associated with a 3% increased risk of cancer. For sure, space is radioactive. If however, you are unfortunate enough to be EVA'ing about 1.5 meters from the immediate vicinity of an operating NERVA type engine you would be raking in over 200 billion Sieverts per second! At this rate of abosorbed radiation you would get an acute fatal dose in roughly 0.375 trillionths of a second. Simply put, space radiation doesn't compare with this (unless you are orbiting a neutron star or something). I'm not at all against NERVA, they are probably quite safe (and obviously incredibly useful) when used correctly. (Frankly I'm impressed NASA even bothered doing the analysis for the operating absorbed radiation environment at that resolution, who would be stupid enough to bear hug an operating nuclear reactor core? Kerbals I guess?) As soon as the fission reaction is stopped, neutron and gamma flux decay exponentially, to roughly safe levels within 4-10 hours (depending on the length of the burn). The gradual build up nasty fission products in LV-N will also put out residual gamma depending on the reactor's operational history (e.g. how many times it has lit for a burn), at a roughly constant rate irregardless of how recently the reactor was in operation. If you want to roleplay the LV-N these I think make good rules of thumb: don't run the LV-N within 50-100km of a space station or an EVA'd kerbal (use RCS for docking maneuvers). If you want to get fancy, always keep the LV-N pointed away from your docking targets as you approach them. Never put a Kerbal within a clear line of sight of the reactor. And for the sweet love of god don't use them for landing stages. People get worked up about this, but ironically this probably the safest time for a nuclear reactor. As brotero already mentioned earlier in the thread, nuclear reactors emit lots of gamma and neutron radiation when they are actively running because of the fission reaction. If they are not running they are just a lump of uranium, and uranium is not particularly radioactive. A launch failure with an inert reactor wouldn't be a "space Chernobyl", it would probably be less environmentally devastating than the unfortunately routine chemical spills which happen hundreds of times a year all over the Earth. The Kosmos satellite was more dangerous because it was an uncontrolled reentry of an old reactor. Old reactors will have built up fission byproducts which are much more highly radioactive.

The mun and Minmus both have over 6 biomes. Also, it is not just six sets of experiments your're bringing along but also all of the extra delta-v you need to land and return that stuff from a planetary surface (e.g. six separate landers, or a single lander with 6 sets of experiments). Also when Jool's moons get biomes, you might be quite happy to set up a small science station and transmit rather than having to spend a few years Hohmann transferring all that science back to Kerbin, though this would mean you would have to revisit any given biome several times to maximize your science return (but what is wrong with that?). As it is now I found it useful in the case of Minmus or the Mun, you can reuse a super minimalist lander to hit all the biomes, clean out the experiments at the lab after each surface sortie, EVA a kerbal to pack all of the science into a capsule, and then return the capsule back to Kerbin for a huge science payoff!

This is a really good point, I personally find the ARM SLS components to be overkill for most of the missions I tend to take on, but if we want to compare the new rockets to their assumed real life analogs it is easy to see a pattern that the KSP rocket engines tend to have slightly lower isp on average and a lot less thrust. Also propellant tanks tend to have lower mass fractions than in reality. So even if Kerbal rocket performance is worse the RL, they may not have been scaled down enough to compensate for the reduced delta-v requirements. But the point of KSP isn't to be as hard as real life! Assuming the Kerbodyne KR-2L is supposed to represent the Aerojet Rocketdyne J-2X that may potentially be used for a future cryogenic upper stage of the SLS, the Kerbodyne KS-25 is the same as the Rocketdyne RS-25 which powered the Space Shuttle as well as the the SLS core stage, and the KR-1 is the same as the Dynetics "Pyrios" advanced liquid booster (powered by two Rocketdyne F-1 engines!) which may be used for the 3rd SLS flight and forwards; and dividing by the number of engines per core, then we can make these comparisons: [table=width: 500] [tr] [td]Scale factor[/td] [td]thrust[/td] [td]Isp vac[/td] [td]Isp atm[/td] [/tr] [tr] [td]LVN/NERVA[/td] [td]0.18[/td] [td]0.94[/td] [td]0.58[/td] [/tr] [tr] [td]KR-2L/J-2X[/td] [td]1.91[/td] [td]0.85[/td] [td][/td] [/tr] [tr] [td]KS-25x4/RS-25[/td] [td]0.43[/td] [td]0.80[/td] [td]0.87[/td] [/tr] [tr] [td]KR-1x2/F-1[/td] [td]0.15[/td] [td]1.22[/td] [td][/td] [/tr] [tr] [td]S1 SRB-KD25/Shuttle SRB[/td] [td]0.06[/td] [td]0.93[/td] [td]0.97[/td] [/tr] [/table] My conclusions from this are that the KR-2L is probably intended to be an upper stage engine, given its high (by KSP standards) isp, but it otherwise bucks the trend of lower thrust for KSP engines compared to their RL analogs. The KR-2L has better vacuum isp than the KS-25 even though the RL RS-25 has slightly better isp than the J-2X. Both the KR-1 and S1 SRB boosters have massively less thrust than their RL analogs, though the KR-1 has substantially better vacuum isp than the mighty F-1. Interestingly the model used for the KR-1 is smaller than the one used for the KS-25 (though the RL F-1 easily dwarfs the RS-25s used on the Space Shuttle), and they have the same isp, but the KR-1 has slightly higher thrust (per engine). I agree completely.

It's ok, we're all a little crazy sometimes: witness a late 80's NASA plan to use a resistojet with electrolyzed waste water propellant for orbit keeping and attitude control for the future Space Station Freedom of the 1990's. Really low thrust, but the isp isn't half bad:)

The Drawing Boards in the tutorial forum has an extremely helpful series of links. You don't even to have to use the forum search! Here are several pertinent ones I found there: Kerbin Landing Chart: Land at KSC consistently from your stations. Atmospheric Landing Charts: Pinpoint landings! [NEW UPDATE: No Protractor Required!] Or use FAR. Blunt bodies can produce small amounts of lift.

Sub-assemblies only seem to have a single designated attachment node. It would be useful to either be able to have more than one attaching node, or be able to designate the specific one you want when dropping in in the sub-assembly menu.

Say at some point we launch a seedship towards Tau Ceti which accelerates up to .1 c in a brachistochrone trajectory. It will take roughly 240 years (in Earth's reference frame) to get there. Then say 25 years after the seedship launches a technological breakthrough allows us build ships capable of accelerating up to .5 c. A seedship launched with the new technology now takes only 50 years or so to get to Tau Ceti so it will pass the older ship enroute and by the time the original seedship arrives it will find a 165 year old colony instead of the virgin territory they were expecting. This example has many simplifying assumptions but you get the idea: this is the basic problem with generation ships, and it only gets more and more extreme the farther away the destination is. Now if we are using a sufficiently powerful drive system, even if warp drive is miraculously invented, the people who leave early might only be a few decades rather than a few centuries late to the party. What's my point? It is not likely that anyone is ever going invest the resources to build interstellar generation ships. Fission fragment, Orion, or even proton-proton fusion interstellar rockets would need totally absurd mass ratios to reach and decelerate from relativistic velocities, therefore they are effectively generation ships. And if you're fine with generation ships, why not just go with oort cloud osmosis and save having to strip mine the whole solar system to build one single phobos sized rocket that can still only manage a 100 ton payload? The long and short is that Tsiolkovsky's rocket equation says there are only two ways to increase delta-v: increase your mass ratio, or increase your exhaust velocity. Untill we master the subtle art of building super star destroyers the latter option is where we have the most room to improve. Based on what we know now the magic eight ball of the future seems to be pointing towards "beam core antimatter or go home" ...(or don't bother with rockets).

I agree with your main point, global warming may not drive our species to utter extinction, but the comparison to the Eocene is not apples-to-apples. We've already thoroughly degraded much of world's ecosystems, and the climate transition will be grossly more abrupt. Ecosystems, like most complex systems, have limited abilities to adapt over the very short term. A 2-6 C global mean temperature increase over less than 100 years will result in a mass extinction event... pretty godddamn apocalyptic if you ask me, but it doesn't have to go down this way. We've still got the power to fix things.

Thanks for the information!

Why ever would you put in in LEO? They would have to be enormous there. Build them at the Earth-Sun L1 point. No drag to contend with either. Wouldn't be cheap, but it is essentially doable with our current level of technology. The established long term trend since the 70's has been declining world average rates of population growth. Birthrates have fallen around most of the world due to increases in education, increased standards of living and longevity, and improving access to healthcare. Human populations are growing, but by lower and lower rates each year. The U.N. projects a worse case scenario of the world population peaking in the 2050's at around 10 billion people, and declining gradually afterwards as the world average growth rate becomes negative (as it already is in most of the developed world). Other estimates suggest the peak will come sooner at 8-9 billion. The current world population is over 7.2 billion. The Malthusian problem has been avoided for decades because of huge improvements in agricultural productivity. This trend doesn't seem to be changing, though water resources will likely grow more scarce in the relatively near future. In the historical context war, disease and pestilence seem to be at record lows as well. So much for the horsemen. Fossil fuels, and biodiversity loss are the big problem for humanity right now. Part of the solution seems pretty straightforward: switch to renewables and nuclear. Land use habits may be more difficult to change.... Also, we might still need the sunshade to deal with the damage already done. But no death camps are necessary. Seriously, it depresses me to hear this typically anarcho-primitivist type fire and brimstone (unfortunately not uncommon among some of my fellow environmentalists). It reminds me of the people who pray for the apocalypse and they day when they can be raptured up to heaven and watch the unrighteous burn on Earth.