Northstar1989

Good news! Rabada has sent me the latest version of the Nova Aerostrake-based Thermal Fin part he created, so that I can share it with you guys: https://www.dropbox.com/sh/aj8nch2v3fnx77p/AAAKTjGtm9fpHCds1_RVfnqUa?dl=0 This part should be a lot more aerodynamic replacement for the current boxy Thermal Fin. Additionally, Labhouse contacted me a while back about creating a replacement Thermal Fin model as well. So I might have another (possibly even better) model to post from him soon as well! (he won't be writing up a corresponding config though- so I'll have to do that for him before I can post it...) EDIT: The part Rabada shared with me was clearly overpowered in terms of heat dissipation for its mass and surface area, and he didn't correct the right fields to adjust its attachment strength in relation to its greater ratio of mass/drag to contact area with the surface attaches to (he tried to edit this parameter, but did so incorrectly). So I edited the part config to have the the same ratio of heat dissipation to mass as the existing Thermal Fin part (if it's more effective for its surface area, that's not necessarily a problem- some of the increased mass for the surface area could represent more powerful heat-exchange equipment creating a larger temperature difference with the inside of the fuel tank). I also fixed a few other odds and ends (such as reducing the Max Temperature to a more reasonable number for a thermal fin), and increased the strength of its attachment in correlation with its sturdier shape (it has significantly more contact area with the tank below it relative to its surface area compared with the existing Thermal Fin- so I increased BreakingTorque, for instance) Here is a link to the UPDATED folder in my Dropbox. I'd submit a pull request, but I don't know how. Please include this in the dev build (and the next release) of RealFuels if it looks good to you. https://www.dropbox.com/sh/7v29geiqf8x1d1m/AADewSgV7v0Zo7PLVq1H0SAJa?dl=0 Regards, Northstar

Awesome! That fixed everything! I feel bad wasting your guys' time with a set of bugs that turned out to be entirely due to a missing .DLL, but at least you guys were patient with me and helpful. I'll try to get the final version of the KSP-Interstellar integration config posted soon (there are only 4 odds/ends left to cover at this point), and then hopefully I'll be able to lay off bugging you guys for a while, except to express my appreciation for this awesome mod. Regards, Northstar

Besides the flaws in your mothership argument, which Fuzzy quite succinctly and effectively points out, you seem to be under some fundamental misconceptions about which type of vessel would require which type of propulsion... A "mothership" vessel, since it would be manned, would need to rely on "low ISP chemical propellant", so as to keep the acceleration and trip time to a reasonable length. A Cycler ship, on the other hand, can launch completely unmanned (it would pick up crew on its second cycle around Earth) and SLOWLY accelerate to its cycle trajectory. There is no limit to how low the TWR could be, except for human patience. You could use Nuclear Thermal (American NERVA, Timberwind, or the Russian-American BNTR cooperative project), Microwave Thermal, Nuclear Electric, Microwave Electric, or even solar sail propulsion (which requires ZERO propellant) if you were patient enough... Regards, Northstar

Not expensive propellant-wise compared to a Mars or Earth-transfer, which is the whole point... They have. Or rather, they're working on it now. Expect to see similar prototypes within the decade (a subscale demonstration is scheduled for 2018). The main obstacles to Microwave Thermal Rocketry are not scientific, engineering-related, or technological. Rather, they are political/bureaucratic and financial... First of all, there's getting government authorization to shoot the Microwaves through the air at a Thermal Receiver outside of a laboratory- people have unreasonable fears about that kind of thing- even though we already shoot loads of radio waves through the air- and Microwaves are less energetic than Visible Light or Infrared (which is why they pass through the air so much more efficiently, whereas lasers tend to diffract...) Second, Microwave Thermal Receivers and (especially) Microwave Transmitters (aka. gyrotrons) aren't cheap. The technology is inherently expensive, because it involves some of the same microlayer-coating techniques used to manufacture photovoltaic panels and circuit boards. Not more expensive than a space-grade rocket engine, mind you (such an engine is MUCH more expensive)- but rocket engines are actually an inherently cheap technology. You can build a low-quality rocket engine (definitely *NOT* up to standards for use in space) for a fraction of the cost of a Microwave Transmitter (a gyrotron), Microwave Thermal Receiver, or for that matter, a jet engine. A 1 MW gyrotron, by contrast, goes for $2 million a pop (Microwave Thermal Rocketry is cheap because you leave the gyrotrons on the ground, and can re-use them literally *thousands* of times before they eventually wear out...) The cost of researching Microwave Thermal Rocketry on even a small (1 Megawatt) scale means very few laboratories/universities can afford to do so in the current economic climate. ESPECIALLY when there isn't exactly a lot of government support for this kind of research (unlike, say, research on high-powered lasers...) We're lucky that NASA just recently shelled out $2 million to actually buy a Microwave Transmitter unit for use specifically in Microwave Thermal Rocketry research... Here, the lead NASA researcher on the project (at NASA's Ames Research Center) discusses the technology. Note that he mentions there are currently only 3 people on the project as of 2011, when the article was written (NASA hasn't *YET* made it a high funding-priority, which is why progress has been slow), but he also mentions that they're trying to recruit more researchers, and that they were slated to receive the $2 million 1 MW gyrotron in 2012 (later articles confirm that they did indeed receive the unit, and are working on a subscale demonstration for 2018 as planned and on-schedule...) http://nextbigfuture.com/2011/02/nasa-researcher-kevin-parkin-discusses.html There's also a small private company called Escape Dynamics working on the technology, by the way- for which the lead NASA researcher on the project is an adviser. They hold some patents related to the technology, and are working on designing working spaceplanes using the technology (the MUCH higher ISP than chemical rocketry makes spaceplanes actually feasible- and spaceplanes can lift off with a TWR less than 1, meaning you can lift a heavier vehicle with the same amount of beamed-power...) Regards, Northstar

I think pessimists such as yourself need to consider this quote: "We were born of risen apes, not fallen angels, and the apes were armed killers besides. And so what shall we wonder at? Our murders and massacres and missiles, and our irreconcilable regiments? Or our treaties whatever they may be worth; our symphonies however seldom they may be played; our peaceful acres, however frequently they may be converted to battlefields; our dreams however rarely they may be accomplished. The miracle of man is not how far he has sunk but how magnificently he has risen. We are known among the stars by our poems, not our corpses." - by Robert Ardery, American Anthropologist - Consider for a moment the powerful truths of that statement. We, humans, have risen from brutal, ignorant apes that made a regular practice of killing one another (despite what some ignorant fools may tell you, neither murder nor warfare is a uniquely human tradition, even among Earth's primates... Animals engage in... murder, slavery, forced coitus, and warfare just like humans have...) What is most impressive, most amazing, is not how often we kill one another- but how often we don't. What's most unique among humans is our art, our poetry and music, our desire to understand the universe, and our ambition. An ape may be content to sit eating bananas and masturbating (yes, animals do this too) all day in the jungle amidst its own filth when it's not killing other members of its species, but humans aspire to, and reach for, the stars... Regards, Northstar

I *just* saw your reply, so... Sorry for the slow response. I know and understand what's its like to be busy and have other things going on in real life. We're almost done with the config (as far as I can tell- I'm having some difficulties play-testing it with RF 8.2 due to trouble locating the updated DLL on Github...) If you're able to help push just a couple more odds-and ends through, we'll have a 100% complete config! Well, I can't pay you, but I can summarize all of the remaining things that need doing in one place, so you don't have to hunt for them. They are: (1) The KSP-Interstellar ISRU Refinery needs to produce Hydrazine instead of Monopropellant. AFAIK the resource proportions are only correct FOR THE CURRENT DENSITY OF AMMONIA (see goal #2), so this is a bit more than a simple name-change... (see goal #2) It might be worthwhile to make the name-change contingent on the presence of Module RCSFX, for both this and the plasma engines that already use Monoprop/Hydrazine... (and had their fuel name changed so they *always* require Hydrazine) (2) The density of the Ammonia resource changes when going from KSP-Interstellar "Ammonia" to RealFuels "LqdAmmonia". This means the rates of Ammonia-consumption need to be adjusted for the Monoprop/Hydrazine production reaction, as mentioned in goal #1, to ensure conservation-of-mass. The rates of resource-extraction should also be adjusted if possible (gathering 100 units of "Ammonia" a second IS NOT the same as gathering 100 units of "LqdAmmonia" a second...) (3) The dedicated KSP-Interstellar Ammonia Tank needs to have its fuel capacity switched from "Ammonia" to "LqdAmmonia". The capacity (in units) should ideally be altered to preserve the same fuel-fraction as before, although an argument can be made for leaving it as-is (and I posted code to do this before, without changing unit-capacity, back in the Request thread... I also re-posted the code earlier on this page, for your convenience.) That fuel tank should probably also be insulated- as the main place it gets used is on Eve- where it's hot enough to boil Ammonia. (4) The KSP-Interstellar ISRU Refinery needs to have insulated tanks for its integrated cryogenic fuel-storage. Namely, LqdOxygen, LqdAmmonia, and LqdHydrogen. Oh yeah, did I mention LqdHydrogen? I can't emphasize that one enough- otherwise all the Hydrogen from Water Electrolysis will boil-off before it even has a chance to be stored in another fuel tank- as electrolysis can proceed quite slowly if the power supply is limited... I hope having everything in one place helps. As you can see, there are only 4 things left to be done- and (part of) one of them I already did for you, if you consider my solution satisfactory... Regards, Northstar

Rendezvous with objects making an orbital flyby is perfectly possible. Try doing it with a few asteroids, and even craft already on transfer-trajectories to other planets that haven't yet left the Kerbin system before saying it's impossible (the latter is much more difficult, and I've done it). The only thing that changes in real-life is the amount of Delta-V necessary... And honestly, that Delta-V doesn't add up to a lot of fuel when you're just accelerating a tiny capsule. In fact, you need not even use a pressurized capsule- if the rendezvous will take less than 36 hours, I think it's perfectly reasonable to ask the ask the astronauts to sit in their space suits and space diapers, hooked up to oxygen tanks in an unpressurized capsule, to save literally hundreds of thousands of dollars on the mission cost... Regards, Northstar

Considering the correction-burns would be a few dozen m/s at most, and he was describing them as expensive in propellant, I *highly* doubt he has an accurate idea about how a Cycler ship works... Actually, working Microwave Thermal Rockets have already been built and fired in the laboratory (the technology scales perfectly well to larger sizes- unlike combustion engines- if you can build a 1 kN unit you can build a 10,000 kN unit...) The gyrotrons that would be used, on the other hand, already find various applications in heavy industry (especially metallurgy). So it's basically taking some off-the-shelf microwave heating-units from a foundry, and scaling up a thruster that already works in the laboratory, and you have a working thruster that can be scaled to any size. The engineering challenges are MUCH simpler than with combustion (which experiences all sorts of problems when you scale it up...) There's nothing far-future about it. Regards, Northstar

Oh phooey. You're right. The DLL is actually missing altogether. The only logical explanation for that is that my virus scanner (I recently switched antivirus programs) removed the .DLL without asking. I'll try disabling the antivirus and downloading it again (either the antivirus or 7-zip is somehow destroying the .DLL, and since I used 7-zip for my earlier installs that worked, I'm inclined to say it's probably the antivirus...) EDIT: Looks like it *wasn't* the antivirus' fault. There is currently NO DLL in the file you get by downloading the .ZIP folder directly from Github, period. I'm probably the only person experiencing this problem because (a) I'm using the dev build rather than the latest release, as I need to play-test the KSP-Interstellar integration config in the latest version rather than 8.1, and ( I'm using the "RealFuels" folder from the Master .ZIP folder you get from Github, without reconstructing/recompiling the folders directly from the source- which I assume is what the devs are doing when they work on updating the mod... Where can I find the *LATEST* .dll file? (NOT the one from 8.1, the latest stable one for 8.2) Once again, I need to perform some play-testing of the KSP-Interstellar integration configs with the upcoming 8.2 build, as they're not even included in 8.1, so that I can get Dreadicon news on whether it works (and maybe fix some bugs myself if I can figure out how...) now that he's finally come out of hibernation on the project... Regards, Northstar

Everything wears out. But if you manage a couple decades of use out of one of a Cycler Ship, you've more than got your money's worth- that's at least 12 cycles over a little more than 20 years' time (each cycle takes about 20 months- 5 one way, and 15 the other). DEFINITELY cheaper than 12 separate manned missions each with their own Mars departure and return vehicles (most plans actually call for 2 separate vehicles, so the return stage will already be at Mars before the first astronauts arrive). I also have to point out, nuclear reactors last a lot longer than 20 years- many reactors operational today are 30-40 years old... And an onboard nuclear reactor isn't strictly necessary- you could more than get by with solar panels or Microwave Beamed Power from Earth/LEO... Solar Sails essentially never wear out- except the electric motors used to rotate them and occasional micrometeorite impacts that would punch holes in them... In fact, micrometeroites would probably be the greatest hazard to Cycler Ships (or any other interplanetary vessel), and any Cycler Ship would probably best operate unpressurized when uncrewed (to avoid loss of atmosphere through small holes) and with repair materials onboard to repair leaks from small impacts... Regards, Northstar

I know I've been a little slow on posting updates lately, but I've been trying to troubleshoot my way through some MAJOR bugs with RealFuels (currently, using the latest dev version of RealFuels and the Stockalike config, the fuel tanks are stuck on LF/O, the engines on their default *realistic* fuel mix, and tech-levels are completely unavailable- making anything but an electric-propeller aircraft completely unusable right now...) Anyways, I've still got some backed-up progress I haven't reported here yet, so here it is... First of all, I made a suborbital hop after my last Mun landing, and collected a bit more Science before ascending to orbit: Then, I ascended back to orbit and rendezvoused with the Munar Waystation/ Munar Orbital Science Station- and the attached Command/Service Module (CSM) designed to take my Kerbals home... After cleaning out the experiments, prepping the Command/Service Module (CSM) a little, and transferring over the Science- my Kerbals were ready to return home: The return-burn went entirely smoothly: The CSM then made SEVERAL aerobrake passes, before safely returning to Kerbin's surface near the KSC: Following that, I was able to make some science/tech purchases over at R&D: Finally, last but not least, several (real-life and Kerbin) days later, the Minmus Fuel Tanker performed a plane-change maneuver to match planes with Minmus. Now it's just a matter of waiting until Minmus is in the correct orientation before it can complete its transfer there (Minmus is current roughly 180 degrees away from where I need it to be in its orbit) As always, I hope you guys enjoyed the update! Feel free to suggest new mission ideas over in the mission-proposal discussion thread (linked on the first page), or to comment on progress, etc. over here! Regards, Northstar

I know this is a cross-post, but... It's necessary as this bug affects both RealFuels (the fuel tanks) and Stockalike (the engines). Raptor seems to think the issue is actually with RealFuels, as the engine context menus don't open up (but the engine use the default realistic fuels just fine according to the debug console) Re-installed RealFuels (the latest dev build), Stockalike (2.06), and KSP-Interstellar (0.13) AGAIN, as well as updating ModuleManager to 2.5.3 and Tech Manager (mod used for custom tech trees such as the one for KSP-Interstellar) to 1.5, and it's still bugged: The fuel tanks are broken- they only hold LF/O. The engines won't tweak off their default fuel mode, and have no tech levels. And the worst part is, I have absolutely NO IDEA what's causing this... Clearly, it's an issue with the base RealFuels mod, at least in part, though- as the fuel tanks are also broken. I found the debug menu, but how do I export it? Regards, Northstar

Re-installed RealFuels (the latest dev build), Stockalike (2.06), and KSP-Interstellar (0.13) AGAIN, as well as updating ModuleManager to 2.5.3 and Tech Manager (mod used for custom tech trees such as the one for KSP-Interstellar) to 1.5, and it's still bugged: The fuel tanks are broken- they only hold LF/O. The engines won't tweak off their default fuel mode, and have no tech levels. And the worst part is, I have absolutely NO IDEA what's causing this... Clearly, it's an issue with the base RealFuels mod, at least in part, though- as the fuel tanks are also broken. I found the debug menu, but how do I export it? Regards, Northstar

Nibb31, I don't say this to be mean or brash, but clearly you don't understand how a Cycler Ship works at all. I suggest you read the material I linked to in the OP (I'll try and add a better explanation later on what a Cycler actually is to avoid issues where people don't bother reading it) A Cycler Ship (such as an Aldrin Cycler) is set on an orbit that intercepts two planets (such as Earth and Mars) regularly. Virtually no velocity-change is required to adjust the orbit at either end. This is comparable to how a free-return trajectory to the Moon only requires a one-way burn, except instead of getting a free return from the Moon, you're getting a free return from Mars- and back again and again and again. This is for a "full-cycler". There are also "semi-cycler" designs which depart from LEO or Low Mars Orbit, and enter into a trajectory that will EVENTUALLY (slowly) take them back to Earth or Mars for free. In these designs, like with the full cycler, the crew only rides the cycler one way because the return-voyage is extremely slow. The advantage of a semi-cycler is that it's MUCH easier to intercept with an "interceptor" vessel as the velocity-difference is much smaller. With either version of cycler (full or semi), there are two possible variants of the orbit- one that travels from Earth to Mars quickly (5-6 months), but takes a long time (15+ months) to return, and one that travels from Mars to Earth quickly (5-6 months), but takes a long time to return to Mars (15+ months). Thus, with any manned round-trip mission, you would normally want at least two cyclers in operation- so the crew takes the short leg of a journey each way. Ultimately, with a Aldrin Cycler or other design of Cycler Ship, you only need to accelerate the Hab Module (which can include rotational/centrifugal "artificial gravity"), Life Support Systems (which can include heavy things like greenhouses), heavy radiation shielding, and solar panels or nuclear reactor to the cycle-trajectory ONCE. It costs less than twice as much Delta-V as sending these directly to Mars for a full-cycler, yet doesn't require any fuel for a return-voyage, and can be re-used an unlimited number of times. The components you re-use are some of the heaviest components for a Mars-Mission (especially the radiation shielding), and don't have to be accelerated quickly. In fact, if you were patient enough you could literally launch the cycler ship to LEO and accelerate it to the cycle-trajectory using ion engines or however many square kilometers of solar sail over the course of several YEARS (you would only launch crew to it later, on its next cycle around). These same ion engines/ solar sails could be re-used for the minor course corrections (only a few dozen m/s or so every couple years!) necessary to maintain the cycle orbit against the solar wind and repeated Mars/Earth gravity-assists (to minimize these, the taxi/lander would detach while the Cycler Ship was still a few days out from Earth/Mars, and move onto a closer approach trajectory- whereas the Cycler Ship would just skirt the edge of the Sphere of Influence), With solar sails, ZERO propellant would be required for course-corrections (all course-corrections would be made by constantly trimming the solar sails during the entire voyage). With ion engines, only a VERY small amount of propellant would have to be carried to Cycler Ship on each interceptor ship. And, of course, if you equipped the Cycler Ship with a heavy nuclear reactor and a laser or gyrotron to beam that power as microwaves, you could use that nuclear reactor to accelerate the Cycler to its cycle trajectory in the first place via nuclear-electric propulsion, and then re-use that same reactor an unlimited number of times to accelerate interceptor ships via Microwave Thermal Rocketry (the higher TWR of thermal rocketry vs. electric propulsion would be necessary for the interceptor ships) to meet up with the Cycler Ship, and landers/crew capsules to reach the surface of Earth/Mars... Microwave Thermal Rocketry has around a 1/4th efficiency at these large distances (1/3rd efficiency when beaming power *through the atmosphere* to a craft ascending to LEO)- meaning if you placed a 800 MW reactor on the Cycler Ship, the tiny interceptor-ship would have around 200 MW of beamed-power available, which would allow for a MASSIVE TWR (in fact, with a reactor this powerful, and a typically tiny interceptor ship, maybe you would want to use a high-powered microwave-electric propulsion scheme just so you didn't kill your crew with g-forces... Or, you could just use a much smaller nuclear reactor and take longer to accelerate the Cycler Ship in the first place...) Regards, Northstar

I don't think you understand what exactly we're talking about here with regards to space-access technologies. By their very nature, these technologies are MUCH CHEAPER than conventional rocketry. That's why they're worth building/developing. They're *not* a more expensive investment, as you insinuate- rather, they're actually a cheaper option for demand here an today. Let's take the example of Microwave Beamed Power, for instance. If you can launch 100 missions a year with it, Microwave Thermal Rocketry becomes a MUCH cheaper alternative to chemical rockets. That may sound like a lot of launches- but if the system is scaled to launch 1 ton of payload on each rocket or spaceplane, then that's in the range of support costs for the ISS, which required 60-100 tons of supplies a year before the installation of a Sabatier Reactor to reduce life support costs... (food, water, oxygen, station-keeping fuel, etc.) I think it's down to around 40-50 tons of supplies a year now- which is still nothing to sneeze at... Microwave Beamed Power cost-scaling is at least linear or better- meaning a rocket with twice the payload capacity will be no more than twice as expensive (including cost of ground facilities and the rocket itself) with the same number of launches per year. Probably less so, as larger rockets have batter fuel-fractions and ballistic coefficients, both of which tend to bring down the cost-per-ton to orbit... Since the thermal engines are technically very simple (there is only one propellant, no combustion, and very few moving parts), it's extremely easy to scale them up to higher thrust levels without any of the engineering difficulties that drive conventional rockets to use engine-clusters instead of larger monolithic engines... None of these technologies require MASSIVE investments to carry out on a scale usable for unmanned missions and satellites. A Microwave Beamed Power system capable of launching 1-2 ton payloads is QUITE cheap- much cheaper than existing conventional launch infrastructure, even after you include the research/development costs... A Microwave Beamed Power system using disposable rockets could pay for its own R&D costs, and facilities costs, within 5-10 years of completion if all it did was supply the ISS and launch a handful of small GEO satellites each year- which is quite impressive compared to any cutting-edge conventional systems (that's one reason we've been using some of the same launch vehicles for over 30 years...) I haven't even scratched the surface when it comes to the cost-savings from reusable launch vehicles. A Two Stage to Orbit Microwave Thermal Rocket that re-uses its launch stage Space-X style, or better yet a 100% reusable spaceplane (with ISP over 800 seconds, and potentially *infinite* ISP in the lower atmosphere using Microwave Thermal Turbojets, Microwave Thermal Rocketry places spaceplanes squarely within the realm of possibility...) would reduce costs even further. Did I mention that, besides being highly reusable, a spaceplane can carry more payload to orbit than a rocket with the same amount of available beamed-power, due to the fact that spaceplanes can lift off and reach orbit with a TWR of much less than 1? NONE of the technologies I mentioned are geared solely towards high-energy manned missions. In fact ALL of them, including Skylon, Microwave Beamed Power, and magnetic launch-assist systems work BETTER with smaller payloads and more frequent launches. It's much easier to build a spaceplane that can carry 2 metric tons to LEO in a single launch than it is one that can carry 12 or 20, and requires less beamed-power if you're utilizing Microwave Thermal Rocektry... If you're using a magnetic launch-assist system, the launch tube can only provide a set amount of energy, and only to a rocket of a set size. For instance, Star Tram's first-generation design would be limited to 2.5 meter rockets massing no more than 40 tons on the ground (which amounts to getting 5-8 tons of payload to LEO thanks to the greater payload-fraction a magnetic launch-assist at multiple km/s enables...) Of course, as I've pointed out several times before, the most expensive Delta-V is the first few hundred m/s, with each m/s becoming cheaper as the rocket becomes lighter, due to the Rocket Equation. Comparing a system than can provide 1800 m/s to a rocket out the top of a mountain and one that can "only" provide 900 m/s, the less powerful variant is going to cost less than twice as much, while providing more than half the fuel and cost-savings... (BEFORE you even consider the thermal-management and aerodynamic-stability issues 1800 m/s in the lower atmosphere entails: which are manageable, as hypersonic aircraft already demonstrate, but add to cost and mass...) Also, as I've pointed out several times, some of these systems can be combined for even greater cost-savings (such as Microwave Beamed Power and spaceplanes- as the company Escape Dynamics is attempting; or ISRU and Microwave Beamed Power, if you power the ISRU reactor with beamed-power, or with a nuclear reactor equipped with a gyrotron to beam power at the return-voyage...) None of these systems are unable to be utilized for resupplying the ISS and launching GEO comm satellites,but all of them can be scaled-up for cheaper manned missions to Mars ... Regards, Northstar

This is a thread to discuss Cycler Ships- particularly the "Aldrin Cycler" envisioned by Buzz Aldrin to carry humans between Mars and back, and other Mars cyclers. Although, discussing cycler trajectories to other planetary systems besides Mars is perfectly welcome as well... http://en.wikipedia.org/wiki/Mars_cycler http://buzzaldrin.com/space-vision/rocket_science/aldrin-mars-cycler/ I'm particularly interested in how this technology could be combined with things like Microwave Beamed Power (what if the Cycler Ship carried a heavy nuclear reactor and a gyrotron that it kept disabled for most of the journey, but activated when in close proximity to Earth or Mars to power the "interceptor" or "taxi" ships as they caught up to the Cycler Ship, for instance? The mass of the reactor and radiation-shielding for crew would be a lot less of an issue on a Cycler Ship since it would only have to be accelerated to a Mars-intercepting orbit once...) or solar sails (free course-corrections, anyone?), or basically any other advanced technology intended to save mass/cost that could be implemented with today's scientific understanding. But discussion of the basic idea is of course more important and just as welcome... I'll try to improve this explanation in the future- I'm tired, and it's *very* late here... Regards, Northstar

Answers about life beyond Earth. Our place in the universe. The future of mankind and our ability to eventually settle other planets in our solar system. All of these things are IMMENSELY important goals- and humans can answer most of them MUCH more effectively than robots (whatever you may think, we're not nearly to the point of humanoid robots than can operate without remote-control yet... And even if we were, one of the goals is to discover if HUMANS can survive on other planets...) Plus, humans have some nifty abilities robots will always lack for the foreseeable future- like the ability to repair themselves of minor injuries with nothing but food and rest, and the ability to maintain an entirely sealed-off, constant environment separate from the outside world (we call this process homeostasis in biology- and robots lack it. Even something as seemingly minor as Martian dust can cause problems with robots...) We're also much more nimble- which helps with things like repairing broken equipment (there's a reason we send humans and not robots to repair Hubble), and constructing a semi-permanent base. That's not to say humans are cheaper, or that robots CAN'T do these things- only that humans can do many of them better. Ultimately, humans will attract more public attention, and are the more desirable option. We just need a way to get them there for a fraction of the total mission cost we currently can- which is where things like Microwave Beamed Power, magnetic launch-assist systems to get off Earth, Propulsive Fluid Accumulator Satellites, In Situ Resource Utilization, and Cycler Ships (look those up if you don't know what I mean- specifically I'm thinking of an Aldrin Cycler) come into play... Regards, Northstar

And... I realized I forgot to answer the actual question. When do I think humans will land on Mars? In 2040+, after either Congress has forgotten about how much SLS cost to design in the first place (if we're smart, we'll maintain manufacturing capabilities for SLS until at least 2050, if we're wise enough to design the final version to have loose enough engineering margins to have a lower per-ton payload-to-orbit cost than existing launch vehicles...) and is willing to shell out the big bucks for a flag-and-footprints exercise, or after NASA has finally finished (slowly) embracing the philosophy of In Situ Resource Utilization and is now designing all future Mars missions to make use of it (either should take at least 25 years). Sooner if we actually have the common sense to invest in a lower-cost method of launching things to orbit than SLS: like Big Dumb Boosters (I highly doubt SLS will ever go *that* far towards cost on the inefficiency/cost spectrum determined by engineering margins- especially since the project already has a lot of momentum towards becoming an expensive "Smart Booster"...), Microwave Beamed Power Thermal Rocketry (which also places spaceplanes squarely within the the realm of feasibility, like Escape Dynamics is working on- leading to even greater cost-savings), or magnetic launch-assist systems (which, carried to an extreme, could give rockets enough velocity to escape the atmosphere with a large horizontal component, as with Star Tram; but would actually yield the greatest Return-on-Investment by simply giving a rocket a few hundred m/s of velocity right off the ground, as the first few hundred m/s are the most expensive due to the Rocket Equation...) NASA could also reduce the fuel mass needed for a Mars injection in the first place by making use of Microwave Beamed Power for the propulsion when leaving LEO (allowing ISP of over 800s when using Liquid Hydrogen in a Microwave Thermal Rocket Engine- or even better ISP if using the microwaves to power a VASIMR or high-powered magnetohydrodynamic engine via a rectenna, i.e. Microwave-Electric Propulsion), possibly solar sails for minute course-corrections en-route to Mars, and aerobraking to reduce the fuel needed for capture. That's not to mention the potential benefits of manufacturing Methane for the return-voyage via ISRU... If NASA got *REALLY* ambitious, they could collect the propellant needed for the outbound-journey (possibly the return-voyage as well: launching empty fuel tanks to be filled in LEO and sent to Mars-orbit ahead of the crew might be cheaper than launching the equipment necessary for ISRU) with Propulsive Fluid Accumulator satellites skimming the edge of Earth's atmosphere. Since Microwave Beamed Power is one solution to powering these satellites' proposed nitrogen-electric thrusters (solar panels produce too much drag for their power output- the other option besides beamed power is an onboard nuclear reactor), and Microwave Thermal Rocketry isn't particularly picky about the gasses you use for reaction mass (meaning the Propulsive Fluid Accumulator satellites could usefully collect *all* the gasses they passed through, not just the Oxygen fraction), you could easily just use Earth's upper atmosphere in its natural proportions for reaction mass on the Mars Mission (although you might want to filter out the Ozone due to its corrosive properties), so Microwave Beamed Power Thermal Rocketry has *GREAT* synergy with Propulsive Fluid Accumulator systems (both sharing the same beamed-power sources, and providing a use for almost 100% of the gasses available to the atmospheric scoops...) Did I mention Methane (which can easily be manufactured on Mars from the atmosphere and small amounts of water-ice in the soil using the Sabatier Reaction) also works for Beamed Power Thermal Rocketry? (or Nuclear Thermal Rocketry as well) Though at that distance you're going to need to convert the Microwaves into a visible light Laser first so as to reduce transmission-losses all the way to Mars... (and you definitely won't have enough power available to run an electric engine off beamed power at those distances). You might even be better off packing a high-powered nuclear reactor to run the Sabatier Reactor on the surface, and equipping it with a gyrotron so it can beam its power output to the return-vessel to get back to Earth, when the mission comes to an end and the electricity is no longer needed for fuel-production or life support... Even so, accelerating back towards Earth would probably take a bit over a month using Microwave Thermal Rocketry either way, due to transmission-losses over such vast distances, and the resultant very limited power-supply available from beamed power out by Mars... (if you packed a nuclear reactor equipped with a gyrotron, subsequent missions could also re-use that reactor if you packed a small satellite to orbit Mars and relay the power to the next landing site... If you also packed a new reactor with each mission, you could have a steadily increasing power-supply for ISRU and beamed-power rocketry on the return-voyage...) Did I mention all of this is possible with TODAY'S science? Microwave Thermal Rockets, gyrotrons, Microwave relays, Sabatier Reactors- all of these things have been tested and demonstrated on a small scale on Earth. The difficulty is in engineers/researchers obtaining the funding to build scaled-up, high-performance versions for use in space... If we used some of the more advanced mission-design concepts I mentioned here (like re-using a nuclear reactor packed for ISRU fuel-production for beamed-power propulsion on your return-voyage), we could easily have a man on Mars mission lifting off by 2038- which is probably about how long it would take to fully mature Microwave Beamed-Power and high-powered (multi-megawatt) electric engines to use that power if NASA got serious about both of them tomorrow... Regards, Northstar

Might the fact that Liquid Hydrogen is extremely difficult to store, and embrittles many metals (including steel!) have something to do with it? Building engines and fuel tanks that can handle LH2/LOX is a MAJOR engineering challenge compared to ones that burn/hold Kero/LOX... Ahh, but you can build a larger (higher-volume) launch stage because it's lighter. Hydro/LOX allows you to get more Delta-V for the same launch-engine if you increase the tank volume enough- but it comes at the duel costs of higher boil-off and more expensive fuel (LH2 is much more expensive than Kerosene- although in RealFuels, like in real life, fuel costs are basically negligible anyways...) The larger tanks are also more expensive- although whether Kero/LOX or Hydro/LOX is cheaper for the same payload largely depends on the relative cost of fuel tanks vs. engines. If tanks are cheap and engines expensive, then Hydro/LOX is cheaper. If it's the other way around (like in stock KSP- where an empty fuel tank can cost almost as much as engine under it) then Kero/LOX is cheaper. Personally, I play with Procedural Parts- which makes fuel tanks EXTREMELY cheap (I'm not sure it's balanced or realistic, but I play with what I've got...) so I've switched to Hydro/LOX for most of my launch stages... (which is one reason having all my engines in the VAB of my existing save suddenly stuck on hypergolics or Kero/LOX is so annoying- though at least existing craft seem unaffected...) Regards, Northstar

I'll try to get that to you soon, though I've never used the cheat menu (for *anything*), so I have no idea how to obtain that finalized config... any advice/help on how to do this would be appreciated. Also, I have more to add to my bug report, that I noticed after I posted before: Not only are none of the engines with multiple possible fuel modes are tweakable, tech levels also do not show/ are not adjustable when right-clicking on engines for me. For instance, this engine I showed before from NovaPunch2 is supposed to work with both HydroLox and hypergolics- but is currently stuck on hypergolics, and has no visible tech level I can tweak when I right-click on it when added to a rocket in the VAB/SPH... I don't know if this additional information is at all helpful, but I wanted to put it out there. Maybe knowing that the tech level interface is also broken somehow helps you figure out what might be the problem? I wish bugs like this weren't so difficult to figure out. Regards, Northstar

One more bit to add to my bug report: None of the engines with multiple possible fuel modes are tweakable, and tech levels do not show/ are not adjustable when right-clicking on engines for me. For instance, this engine from NovaPunch2 is supposed to work with both HydroLox and hypergolics- but is currently stuck on hypergolics, and has no visible tech level I can tweak... I'm not sure how much of the source of this problem might lie in code that's in the base RealFuels mod, and how much might be part of the "Stockalike" config, which is why I'm posting it in both threads... The problems with the engines would point at Stockalike, but the problems with the fuel tanks would point at the base mod... Arghh, why do these things always have to be so frustrating. Regards, Northstar

I just wanted to thank all you guys for all the love this thread has received! (tons of Rep points given, etc.) It's been my pleasure to help you guys learn more about the value and logistics of off-Kerbin refueling! Regards, Northstar

Not to necro this thread, but this is still an interesting topic worth discussing... Oh, and that's not right at all. Aquarius benefits from economies of scale by having incredibly low payload-capacity (only 1 metric ton per launch). Thus, even with the limited portion of demand it is restricted to (payloads with low intrinsic value- such as ISS consumables and fuel for missions beyond LEO), it still can be mass-produced (it would take 60-100 launches a year just for ISS consumables). Of course, it's not the only game in town for low-cost launches relying on mass-production and low payload-capacities. There is also the Microwave Beamed Power approach being developed by Escape Dynamics, for instance, which can easily be scaled-up for manned missions: http://nextbigfuture.com/2014/02/escape-dynamics-and-microwave-power.html Ultimately, only one low-cost launch system can succeed. Big Dumb Boosters. Microwave Beamed Power spaceplanes (the much higher ISP makes spaceplanes much more feasible). Conventional spaceplanes. StarTram-style mangetic launch-assist. I just hope ONE of them makes it to operation in the next 20-30 years... Regards, Northstar

Here's the thing about SLS- once it's designed, and the facilities have been upgraded, it's not actually that expensive for its payload capacity. The vast, vast majority of costs related to SLS are development and facilities-upgrade costs. Once that money has already been spent, those become sunk costs http://en.wikipedia.org/wiki/Sunk_costs Pleas, please take the time to read a little bit of that Wikipedia article on sunk costs. So many people (*especially* politicians) fail to understand this simple concept, and so make completely irrational decisions as a result. What is rational to consider is only the prospective costs of SLS once it has been fully-developed. That is, the cost of building and launching an SLS, completely independent from any earlier development costs, once the SLS is in active production and fully-developed. When you look at it from that perspective, SLS isn't actually all that expensive. In fact, it becomes quite competitive with any other launch vehicle on the market. Ignoring the fat/waste from overpaying government contractors to build SLS (that money technically recycles into the economy and creates high-paying jobs), it's technically a more efficient rocket than many existing launch vehicles thanks to its large size...Why are larger rockets more efficient? (1) Larger rockets can have proportionally less massive flight and guidance systems (a flight computer that can guide a Falcon 9 or Arianne 5 should work equally well for something the size of SLS). Alternatively, they can have the same mass-fraction of flight computers and greater redundancy of critical flight systems- which lowers insurance costs (and the likelihood of failure) for the rocket. (2) Larger rockets have better ballistic coefficients due to the Square-Cube Law. This means they experience proportionally less atmospheric drag in relation to their size/payload, and it takes them slightly less Delta-V to reach orbit. And we all know what that means. (3) Larger rockets require proportionally less payload fairing, assuming the payload is correctly-shaped. This is because you can enclose a larger space with proportionally less surface area, per the Square-Cube Law. The Square-Cube Law also applies to interstage fairings (equating to mass-savings if the engine nozzles aren't any taller, or the fuel tanks are designed to fit around the nozzles to minimize fairing mass...) (4) Larger rockets experience proportionally less boil-off of cryogenic fuels (such as Liquid Hydrogen). This is as fuel-tanks are pressure-vessels influenced by the Square-Cube Law. The fact that they are pressure vessels means that tank mass scales linearly with volume- for instance a tank with four times the volume requires four times the tank mass. However the Square-Cube Law dictates that larger tanks have less surface area- so larger fuel tanks end up with thicker walls instead (so that tank mass still scales linearly). This means that a tank with 4x the volume might only have 2x the surface area, but twice as thick walls. However Thermal Leakage (what drives boil-off of any cryogenic fuel) is proportional to tank surface area, and inversely related to tank wall thickness and number of layers of insulation. For instance, the 4x sized fuel tank would have LESS than 2x the boil-off of a 1x sized tank as its surface area is only doubled, and its walls are thicker. If, say, the tank had 4 layers of insulation, this would weigh the same as 2 layers of insulation on a 1x sized tank- but reduce boil-off a lot more. If there were 2 layers of insulation coated onto the tank, you still get greater insulation of the fuel (the tank walls are thicker, and thus better insulators, to start with) for proportionally less mass. Thus, with larger rockets you have a choice between reducing boil-off (directly reducing the mass of fuel you need, as you don't have to replace as much that boils off), or reducing tank mass proportional to volume (improving the fuel-fraction of the rocket and thus indirectly reducing the mass of fuel you need). With either option, you get a better payload-fraction. There are other benefits as well- for instance you can trade off some of the improved ballistic-coefficient of a larger rocket for side-mounted boosters (like the SLS uses) or drop-tanks, or you can take advantage of the higher terminal-velocity which an improved ballistic-coefficient confers and launch with a higher TWR (thus reducing time-to-orbit and the Delta-V expended fighting gravity) thus trading off some of the savings in atmospheric-drag for even greater savings in gravity-drag... Basically, larger rockets are more cost-effective (assuming you can't launch enough small rockets instead to reach the point of reaping benefits from mass-production), if you have a way to make use of their entire payload-capacity... Although it may seem like a waste to design an entire heavy-lifter just to resupply the ISS, the SLS can even do that job more efficiently than existing rocket designs. Yes, that's not worth the development/facilities costs on its own- but if we go ahead and design SLS and then don't come up with any other uses for it, those are still sunk costs that cannot be recovered. Per-ton of payload, heavier rockets have the capability to be more cost-effective. Of course, all this hinges on the engineering margins being equally tight. If you design the larger rocker to looser engineering standards (so, for instance, you don't need to know the mass or size of an individual part to within .001% accuracy- but instead only to w/in 0.1% accuracy), your payload capacity decreases, but the per-ton cost of getting the payload to orbit decreases as well- due to the exponential relationship between engineering standards and cost. What worries me most is the concern that NASA/Lockheed Martin might be designing SLS to super-high engineering margins, and contracting out construction tasks in a very non-competitive manner: thus throwing away all the cost benefits of using a larger rocket, and actually leading to a MORE expensive rocket per-ton (even before you include development/facilities costs...) Regards, Northstar P.S. If you take the pattern of building larger rockets with looser engineering margins to save costs to an extreme, what you end up with is a Big Dumb Booster similar to the Sea Dragon. Note that BDB's in the style of a Sea Dragon are actually MORE reliable than those built to tighter engineering margins (as a small mistake in construction is less likely to lead to mission failure), *unlike* those designed Aquarius-style (Aquarius is a BDB that is actually very small, and loosens engineering standards without increasing margins- thus trading off reliability for cost-savings and mass-production...)

I feel the need to point this out: Once Orion/SLS is developed, it's a sunk cost. Meaning, you can't get back the development money you already put into it. And those (and the cost of upgrading launch facilities to handle a rocket of that size) are the vast majority of the costs related to Orion/SLS. The actual costs of building and launching an Orion/SLS rocket are MUCH, MUCH less than the costs of getting to the point where we can build and launch one. So even if political support starts to dry up, there's little reason to think we would turn around and abandon Orion/SLS... Saturn V was abandoned, but it was a different story- the technologies behind it were becoming increasingly outdated, and Saturn V was replaced with smaller, *more modern* launch vehicles. SLS is a different story- it's very much an apex technology- meaning there's not much room to refine it further unless we move to entirely new technologies like Full Flow Staged Combustion (the only current designs for which are the Space-X Raptor engine), reusable rockets (once again, Space-X), or actual viable spaceplanes (like the "Skylon" spaceplane for which SABRE engines were developed...) So, basically, we'll end up with either Orion/SLS or something even better. It sets a floor to be surpassed. We won't just drop the rocket we sunk all the expensive money into developing if there's no economic incentive to do so... Orion/SLS *can* be used to re-supply the ISS. It's not a cost-effective option when you include development costs- but once again, once that money is spent, those costs become sunk-costs. It's actually an easier and more efficient option (fewer launches, docking maneuvers, and rockets to build) if you completely ignore the development and facilities costs that can't be recovered... Remember, larger rockets are capable of higher payload-fractions. Thanks to the Square-Cube Law they have better ballistic coefficients- and experience proportionally less atmospheric drag. They can also have relatively less mass invested in flight computers (a flight computer that can guide an Ariannne 5 works equally well for something the size of SLS), fairings (once again, the Square-Cube Law in action- assuming the larger rocket carries a single, proportionally bulkier payload than a smaller rocket- such as a jumbo-sized resupply cargo for the ISS), and insulation for cryogenic fuels (due to the Square-Cube Law, and the fact that fuel tanks are pressure-vessels and thus have thicker walls with larger tanks, larger rockets have much less Thermal Leakage into the rocket proportional to their fuel volume...) Regards, Northstar P.S. A note on fuel tanks and Thermal Leakage/ the Square-Cube Law. Fuel tanks are pressure vessels, meaning their mass scales linearly with volume, and their walls become thicker in accordance with the Square-Cube Law. Thus, a tank with 4 times the volume might have twice the surface area and twice as thick tank walls (exact scaling of surface area vs. wall thickness depends on shape- but mass will always increase linearly). Thermal Leakage (what drives boil-off of cryogenic fuels such as Liquid Hydrogen) is directly proportional to surface area, and inversely related to tank insulation and the thickness of fuel tank walls. Thus, larger fuel tanks experience much less boil-off even without insulation, and can either have fewer layers of insulation for the same proportional boil-off (i.e. twice the boil-off for twice the fuel volume), or the same number of layers of insulation for greatly-reduced boil-off proportional to their volume. Both options lead to superior rocket performance (especially the option to use less insulation- which saves mass).