Northstar1989

So... Should we add a MM patch to the KSPI_RF config file such as to allow the RealFuels radiators to double as KSP-I radiators when both KSP-I and RealFuels are installed? It would be a relatively simple process, and myself and FreeThinker (if I haven't worn him out as well with all the tweaks that have been required with adding Propulsive Fluid Accumulators and Nitrogen/CO2 electric/thermal propulsion to KSP-Interstellar) would probably be more than happy to help come up with a MM patch for this... Also, nice catch on how to utilize (exploit?) the Launch Clamp pumps there, lurkoholic! It didn't occur to me that I could do that. As I am consistently running up against problems with my mass-limit on the Level 2 Launchpad (I am also using RealFuels 64K, so I need some really big rockets- and RSS 64K doesn't touch the mass-limits at all), I'll have to give this a try... Regards, Northstar

Do you mean the radial Hexcan for D/T? Which part *exactly* is missing? Speaking of Cryostats, though, FreeThinker, you're going to have to do a MAJOR revision on the Nitrogen cryostat costs: A Nitrogen Cryostat should *NOT* be this expensive! (> 5 million Funds) The Deuterium/Tritium Cryostats are extremely expensive, but *ONLY* with an initial full loadout of Deuterium and Tritium (both very expensive resources, *especially* the Tritium) is added to the cost. An *EMPTY* Deuterium/Tritium Cryostat costs LESS THAN 5,000 Funds! (4958 Funds to be precise) However because Liquid Nitrogen is a fairly cheap resource by comparison to Tritium, an empty Nitrogen Croystat still costs well over 5,000,000 Funds! A (empty) Nitrogen Cryostat should *NOT* cost 1000x what a (empty) Deuterium/Tritium Cryostat costs! Besides that, as I already explained here, the Nitrogen Cryostats need their power consumption adjusted... Re-Cap: - A 1.25 meter Nitrogen Cryostat should only require about 3.9185 kW of electrical power to run (I suggest rounding up to 4 kW), as its contents don't need to be kept nearly as cold as Deuterium/Tritium (-249.84 for D/T vs -195.79 degrees for N2, 78.37% the difference from 0 Celsius). There is already precedent for different cryostats requiring different amounts of electricity based on the temperature they need to keep their contents at: a Helium Cryostat requires 8 kW of power whereas a Deuterium/Tritium Cryostat only requires 5 kW! - A 2.5 meter Nitrogen Cryostat requires even less power for its volume, as it has 8 times the volume (I incorrectly thought you had set the volume to only be 4x instead of 8x before, based on a PM you sent me... Turns out the volume was increased 8-fold as it should be, and is correct...) but only 4 time the surface area. As a fuel tank in space this means two things: the heat load on the cooling equipment is less due to having fewer square meters of surface area per liter of volume, and the heat load is also reduced due to the tank having walls twice as thick (a fuel tank in space is a pressure-vessel, and has a linear relationship between volume and tank mass *despite* the Square-Cube Law- this is as a larger vessel has relatively greater stresses on its tank walls, which must thus be proportionally thicker...) - When you combine these three factors (thicker walls, relatively less surface area, and a higher operating temperature), you find that a 2.5 meter Nitrogen cryostat has approximately 3 times the power requirements (by conservative estimates- the actual requirements are even less) of a 1.25 meter D/T Cryostat (which requires 5 kW). Thus, a 2.5 meter Nitrogen Cryostat should only require approximately 15 kW to operate (this is a *little* less than 4 times a 1.25 meter Nitrogen Cryostat, due to thicker tank walls and the fact that we rounded up from the 1.25 meter Nitrogen Cryostat's calculated power-consumption of 3.9185 kW...) If you intend to maintain the *SAME* relationship between cost and volume as with a Deuterium/Tritium Cryostat (which costs exactly 4958 Funds when empty), then a 1.25 meter Nitrogen Cryostat should cost 4958 Funds (the Liquid Nitrogen is so cheap as to be negligible in cost- a full 1.25 meter cryostat's worth only costs around 1 Fund...) and a 2.5 meter Nitrogen Cryostat should cost 39,664 Funds. Although, frankly, I think given the significantly higher operating temperature of a Nitrogen Cryostat, the fact that Liquid Nitrogen Cryostats are a common sight here on Earth (as a biologist, we used LN2 all the time in some of the labs I was in...) and the fact that it doesn't need to deal with Hydrogen-embrittlement (like a D/T Cryostat does), the Nitrogen Cryostat's cost should be *significantly* lower than that... (maybe 24,000 Funds and 3,000 Funds respectively, for some nice even numbers...) Regards, Northstar

Glad to have you onboard fellow Kerbonaut! Space is something that hopefully everybody can get behind. It is, after all, humanity's future. I think sometimes of all the stories of astronauts seeing Earth from the Moon and their perspective changing dramatically, and I really don't think that would be a bad thing for *ANY* country right now. Perhaps a flight to the Moon would even get some of the crazier Iranian (and American!) politicians to stop wanting to kill each other and their "enemies" all the time! Never forget the Cold War- there was a time when half the world had nukes pointed at the other half, and the fate of humanity balanced on a razor's edge! I *do* believe the Apollo Program helped put an end to such madness! By the way, I *really do* hope Iran doesn't just follow the path of basically every other developing space program and re-create what's already been done. What I would *REALLY* like to see is for some of the newer space programs to invest more in more creative launch-systems, like Microwave Thermal Rocketry, Spaceplanes (Microwave Thermal Rocketry, in particular, makes this possible) Mas Drivers, Momentum Exchange Tethers, etc... Some of these systems could very well lead to more international cooperation- the most efficient way to do Microwave Thermal Rocketry, for instance, would be to have the entire world collaborate on a series of Microwave transmitter stations around the globe, and a handful of Microwave Relays in orbit, such as to provide beamed-power coverage to the entire planet... Microwave Beamed Power isn't just useful for rocker launches and spaceplanes- it can also be utilized for high-powered electric propulsion in orbit, communications platforms mounted on long-endurance high-altitude aircraft (a cheaper alternative than communications satellites in many cases), to run Propulsive Fluid Accumulator satellites and Mass Drivers in orbit (the latter can be utilized to de-orbit debris and capsules returning to the surface, so as to recycle their momentum), and potentially to someday even beam power back DOWN to the Earth's surface from solar power collectors in orbit- utilizing the Microwave relays to help get the power to where it's needed on the planet (and where people are willing to pay for it- although the whole system requires MUCH cheaper launch costs to Low Earth Orbit to be effective... Luckily Microwave Beamed Power makes spaceplanes with high payload fractions possible that could help actualize such low launch costs...) Regards, Northstar

Greetings Binker! Glad to have you aboard! Bring the glories of Kerbal Space Program to Canada for us, will you?! Regards, Northstar

Hey all, I just wanted to make sure everybody reading this thread is aware there is a currently a KSP-Interstellar 0.90 port, maintained by Boris-Barboris: http://forum.kerbalspaceprogram.com/threads/104943-0-90-KSP-Interstellar-port-maintance-thread Also, myself and FreeThinker (he does the coding, I do the research) have been working on a KSP-Interstellar "Extension Config" to fix a few lingering bugs with the game, give players more settings they can configure in the mod's settings (the default settings remaining the same), and expand the In-Situ Resource Utilization system to allow the Atmospheric Scoop parts to also act as Propulsive Fluid Accumulators: by being able to work *just* outside the official edge of the atmosphere (so the scooping can occur in time-warp thanks to some code borrowed from Karbonite) to simulate scooping above the Karman Line in the Thermosphere (which is where Propulsive Fluid Accumulators are designed to work), and by allowing players to scoop Nitrogen and eventually Carbon Dioxide (the latter hasn't been implemented *yet*) as potential Thermal Rocket/ Plasma Thruster propellants (both N2 and CO2 have been validated as potential plasma thruster propellants in real life, and CO2 has been extensively studied for use in a small RTG-powered thermal rocket "hopper" exploration craft on Mars...) Here is the link to the post presenting the latest version of the Extension Config: http://forum.kerbalspaceprogram.com/threads/104943-0-90-KSP-Interstellar-port-maintance-thread?p=1703194&viewfull=1#post1703194 Regards, Northstar

FreeThinker, A little more background on why Carbon Dioxide should DEFINITELY be usable as a plasma thruster propellant, as well as a thermal propellant. Both possibilities are very well-studied in real life. Consider the following quote from the Wikipedia INTRODUCTION on plasma thrusters, for instance... (emphasis added to the phase "Carbon Dioxide") "This fact, combined with the absence of hollow cathodes (which are very sensitive to all but the few noble gases) allows the intriguing possibility of being able to use this type of thruster on a huge range of propellants, from Argon, to *CARBON DIOXIDE*, Air mixtures to astronaut urine." NASA is even looking at utilizing a CO2-electric thruster for a Mars atmosphere-skimming satellite in the future, although the thruster is designed to optimize maximum thrust production using a Hall Thruster (due to the very anemic power budget- the plan calls for solar panels as the electricity source! Somebody should suggest to these people they use a nuclear reactor or deploy a solar collector in a higher orbit and beam power down to the satellite!) rather than for high ISP with a plasma thruster: http://www.nasa.gov/pdf/716067main_Hohman_2011_PhI_Atmospheric_Electric_Thruster.pdf As for CO2-thermal thrusters, a European Space Agency team is currently working on a CO2-thermal "hopper" craft powered using an RTG as its heat source to do *precisely* that: http://www.hngn.com/articles/13172/20130924/mars-hopper-leap-over-obstacles-using-liquified-co2.htm - - - Updated - - - This is an issue, clearly. Boris, FreeThinker, anybody want to take a look at trying to fix this bug? Regards, Northstar

It's meant to include some bugfixes, and features that Fractal_UK himself expressed an interest in adding to the mod (but didn't have time/ had other priorities). The extension config seeks to extend the functionality in a way that would be palatable to Fractal_UK himself, and to Boris, so that it can first be integrated into the 0.90 port, and then submitted as a pull request to Fractal_UK so he can implement it into the main KSP-Interstellar mod when he returns from his current hiatus. It's true, we're taking a bit of a risk by going out and continuing Fractal_UK's work without his explicit imput that the way in which we implement the feature of Nitrogen (and eventually CO2) as harvestable, usable resources might not turn out to be to his liking- but since we're closely modeling the implementation on his existing work (even going so far as to use the same formulae he used to determine the other thermal rocket and plasma thruster propellants' efficiency/ISP, for instance), hopefully he will be grateful for our effort and work them into the main mod with little or no modification of the additions necessary... Also, FreeThinker, I know I've been throwing a lot at you at once lately (tweaking Nitrogen Cryostat performance, fixing Nitrogen efficiency/ISP, and even requesting assistance with my Mass Driver mod), but how are you coming along in adding Carbon Dioxide as a harvestable/storable resource? Like N2, CO2 should be usable as both a thermal rocket propellant (although with an ABYSMALLY low ISP- even lower than Nitrogen, but VERY high Thrust to compensate...) and an electric propellant. More importantly, it should be usable to perform the Sabatier Reaction outside of an atmosphere- allowing one to keep the ISRU refinery in orbit of the planet/moon (Duna in particular, obviously) and simply launch the CO2 into orbit to be reacted with LH2 stored there (possibly harvested from local water/ice, or shipped from Kerbin for mass-leveraging...) CO2 is trivial to liquify (boiling point -57 degrees Celcius) and even to store as a solid (melting point -78 Celcius, that's what "Dry Ice" is!) Its boil-off is nearly insignificant in the -40 degree ambient temperatures of Low Earth Orbit, and it may actually require some *HEATING* to prevent in from freezing in interplanetary space (which can easily dip below -100 degrees Celcius). So I can think of no reason it should NOT be a harvestable/storable propellant, in fact in real life, it's the easiest resource to harvest and store of all the resources utilized in KSP-Interstellar so far! By the way, CO2 should have the the following efficiency, ISP, and Thrust values compared to Nitrogen: Thermal ISP: 79.78% of Nitrogen (actual ISP and Thrust values vary by Reactor Core Temperature) Electric ISP: 2465.56 s (based on molecular mass, once again 79.78% of Nitrogen) Plasma Thruster Efficiency: 82% (*EXTREMELY LOW* dielectric constant at low pressures and temperatures) Regards, Northstar

Hi MichaelHester, As I've tried to notify you of several times now, I forked the Mass Drivers from the mod (as the CDDL-1 license allows it, as long as I credit you), and re-released them as a separate mod... http://forum.kerbalspaceprogram.com/threads/103511-Pre-Release-0-90-FIXED-Netherdyne-Mass-Driver-Mod I seem to be experiencing a problem with the Mass Accelerators, however. Instead of simulating recoil (Newton's Third Law: for every action there is an equal and opposite reaction) as I would expect, and indeed initially thought was the case, the Mass Accelerators seem to in many cases being accelerating themselves in the *SAME* (rather than opposite) direction as the payload- despite the fact that this breaks all the laws of physics... I could use some help figuring this out. And if I was wrong, and the Mass Accelerators do NOT simulate recoil (and the existing acceleration is just due to friction with the loading-rails on horizontal designs), I would ask that you release a new version of the .DLL that causes the Mass Accelerators to now simulate recoil (and would allow me to use it in my fork by still using the CDDL-1 license, allowing me to replace the earlier .DLL with the newer one...) Thanks again for your awesome work! I hope you'll address my issue relatively soon! Regards, Northstar

OK, it took me a bit of tweaking and testing of my own to figure out what was going on with you, as I've definitely experienced downward recoil when firing straight up before... (at least I *THINK* it was downward recoil- it would slam the Mass Accelerators into the launchpad, and struts/clamps seemed to fix it...) Turns out that what was going on is that the payload was getting a little bit caught on the loading rails (probably clipping slightly into them) and the Mass Accelerator was thus trying to accelerate the ENTIRE firing platform forward instead of just the payload to a degree. I was just building ultra-lightweight horizontal launch platforms of my own- often the payload would get a tiny bit stuck on one of the loading rails (I used Firespitter helicopter landing pads as rails, for what it was worth), and the Mass Driver would thus pull the ENTIRE platform forward- never mind the fact that, physically, it shouldn't be able to accelerate itself... (its kind of like the Kerbals-on-ladders physics bug: it's a result of how KSP calculates physics rather than of the source of force itself...) I don't know how to fix this, but I do know this- recoil is currently unlikely to be simulated correctly, as there seems to be a tendency of the Mass Driver to pull themselves along with the payload they are firing. The most reductive way I could imagine if finding if recoil is still currently being simulated correctly is if one were to build a spacecraft that approaches a single Mass Accelerator ring in-orbit (with some radial batteries and a command pod attached around the ring's rim), and the Mass Accelerator were to accelerate that spacecraft... It's also possible that I wrong about recoil entirely, or that the mass accelerators were pulling themselves apart during vertical launches because they were actually trying to fire themselves UPWARDS, instead of recoiling down... Regards, Northstar

AWESOME. I didn't know it was possible to get a payload going that fast that low in the atmosphere with FAR installed (you *DID* have FAR installed, right?) without dynamic pressure crushing it like a tin can or causing it to rip itself apart... As for the recoil, I'm not sure. It's definitely there (you can measure this with an unsecured Mass Driver built sideways on the runway), but perhaps it wasn't enough to overcome the static friction of those tank treads on the runway? Just how heavy WAS your firing station? If it was more than a few hundred tons, it might not have been enough to move it (alternatively, maybe everything occurred too fast for physics to simulate recoil correctly- I've never launched anything that light at that high a power-level before...) Consider that each Mass Driver produces a force of 11760 kN/s at 100% power, and your firing tube was pointed at an angle above the horizon (meaning that much of the force was directed DOWNWARDS- further increasing static friction with the Runway). If nothing else, maybe there was some kind of a bug with the force not being transmitted throughout the craft based on the way the Mass Drivers were attached... EDIT: On more careful inspection of the video, it does look like the firing unit lurches *very slightly* back, although it may just be my imagination... The heavier the firing station, the less the velocity-change it would experience, even without ground friction to hold it in place... Try utilizing a much LIGHTER firing station pointed purely horizontally if you want to see if the recoil is still working, or perhaps bugged for you for some reason... Regards, Northstar

Awesome FreeThinker! As always, I'm HIGHLY grateful for your amazing work to extend KSP-Interstellar! Did you see/make the adjustments to Nitrogen Cryostat volume (the 2.5 meter Nitrogen Cryostat previously have only 4 times instead of 8 times the volume of the 1.25 meter cryostats, even though it was double the length) and electricity consumption? Regards, Northstar

Hey Freethinker, I must apologize- it turns out I was wrong about the efficiency and ISP of Nitrogen in a plasma thruster. Both should be *significantly* higher than I initially guessed. I went back and applied hard mathematics to figure out the correct values... Unlike with a Thermal Rocket, where they're relative, (and ISP should be 75.675% and thrust 132.14% that of the next-heaviest thermal propellant Methane for any given reactor temperature...), it's possible to come up with a single concrete value for the plasma thruster, since a plasma thruster operates effectively the same at all reactor temperatures... CORRECT Nitrogen efficiency/ISP: 78% efficient, ISP = 3090.34 s Please see this post for more details: http://forum.kerbalspaceprogram.com/threads/104943-0-90-KSP-Interstellar-port-maintance-thread?p=1702243&viewfull=1#post1702243 Also, I noticed something else that is off before- you assumed that the new 2.5 meter Nitrogen cryostat you added to KSP-Interstellar should have 4 times the surface area of the 1.25 meter Deuterium/Tritium cryostat, and thus require 4 times the power top operate. At the time, that comment effectively slipped through the cracks because I had so much else I was thinking about. But unfortunately, that assumption is also wrong for two very important reasons... First, due to the Square-Cube Law a larger fuel tank (or cryostat) actually has LESS surface area relative to its volume. So, while a 2.5 meter cryostat may hold 4 times the volume per meter of length (if you simply up-scaled the 1.25 meter cryostat, the length also doubled as well though- and it should hold EIGHT times the volume...) it actually has only twice the surface area per unit of length- meaning it has half the lateral surface area per unit of volume. This is looking only at the lateral surface area- the part that will be exposed to the outside environment. The cross-sectional area is indeed 4 times as great (and in many ways this actually dominates the power-usage of the cryostat, as conduction from the rest of the rocket will be the main way heat flows into the cryostat), but the cryostat is also twice as long- meaning it has half the end-plate surface per unit of volume. So, in summary, the 2.5 meter cryostats should hold exactly EIGHT times the volume of the 1.25 meter cryostats, but require 4 times the power usage IF HOLDING THE SAME PROPELLANT (more about that is a second). You were right about how the power-usage increases with size, but wrong about its relation to volume- which increases even more (by contrast, a cryostat with a 3.75 meter cross-section and triple the length of the 1.25 meter cryostat would hold 27 times the volume, but only require 9 times the power consumption... Square-Cube Law again for ya'...) The second error was assuming that a Deuterium-Cryostat would require the same amount of power to operate as a Nitrogen Cryostat (of the same size). That absolutely couldn't be further from the truth... A Deuterium-Tritium Cryostat has to maintain its contents at an EXTREMELY cold temperature: at -249.84 degrees Celcius or colder (as this is its boiling-point of Deuterium, the lighter and therefore more easily boiled of the two Hydrogen isotopes). This requires a LOT of energy. (a Helium Cryostat should require even more power- it has to maintain its contents at -268.9 degrees Celcius or colder, *just* above absolute-zero...) A Nitrogen Cryostat, on the other hand, only has to maintain its contents at a "modest" -195.79 degrees Celcius or colder. This requires A LOT LESS power. If one makes the simplifying assumption that one only has to expend an amount of power proportional to the difference between these propellant's boiling points and 0 degrees Celcius, then a Nitrogen Cryostat should only require 78.37% of the power of a Deuterium-Tritium cryostat of the same dimensions. Add all this up, and a 2.5 meter Nitrogen Cryostat only requires 3.13 times the power of a 1.25 meter Deuterium-Tritium Cyrostat, despite holding 8 times the volume! However we're not done yet! There is still one more minor factor that must be taken into account... Any fuel tank in a vacuum is a pressure-vessel. Meaning that the mass of the container increases linearly with the volume, despite the Square-Cube Law. This is as larger pressure-vessels require thicker tank walls (the change in ratio in volume: surface area increases the stresses on each square meter of tank wall proportionally). However, thicker tanks walls are better insulators- meaning that even if no additional insulation is added on, the larger Cryostat will have to contend with slightly less heat leaking inside the fuel container! If we assume this relatively minor effect only decreases heat-leakage by 5% (this is probably under-estimating the effect of nearly DOUBLING the tank wall thickness), and then round-up to stay on the conservative side, then we get the following nice, clean number which I suggest you use: A 2.5 meter Nitrogen Cryostat should contain 8 times the volume of a 1.25 meter Deuterium-Tritium Cryostat, but only require 3 times the power (15 kW vs. 5 kW) to operate. Regards, Northstar

The boiling point of Nitrogen is -195.9 degrees Celcius. The boil-off rate should be somewhere intermediate between Liquid Hydrogen and Liquid Oxygen (like its boiling point), though *MUCH*, *MUCH* closer to LOX than LH2 due to its higher molecular mass- it takes more heat to raise its temperature by a degree or turn a Liter of it into a gas at the boiling point... (heats of vaporization: LOX 6.82 kJ/mol, LN2 5.56 kJ/mol, LH2 0.904 kJ/mol). Its boiling point is also much closer to LOX than LH2... (-183 for LOX vs -252.9 for LH2, and -195.9 for LN2) - - - Updated - - - Also, FreeThinker, I was COMPLETELY wrong about the efficiency and ISP of Nitrogen in a plasma thruster... Some further investigation reveals that the efficiency of a plasma thruster is related to the dielectric constant of the propellant- with lower numbers being better... The dielectric constant of Liquid Nitrogen (dielectric constants are typically measured in liquid form, but are also applicable in gas/plasma states inside a plasma thruster) is 1.43 By contrast, the dielectric constants of the other propellants that can be used in the plasma thruster part are much higher (with the sole notable exception of Lithium- which is *highly* conductive, and becomes a superconductor at extremely low temperatures or high pressures... Its efficiency in KSP-I is the highest, at 86%) Xenon: 1.874 (69% efficient in KSP-I) Argon: 1.504 (76% efficient in KSP-I) Ammonia: 16.5 (54% efficient in KSP-I) Lithium: variable, can act as a superconducter near temperatures of absolute-zero (86% efficient in KSP-I) Hydrazine: 51-52 (dependent on temperature; 52% efficient in KSP-I) Liquid Hydrogen: 1.01-1.26 (dependent on density; 72% efficient in KSP-I) As you can see, with the sole exception of LH2 (which has wonky behavior in electrical thrusters as in many other systems), the efficiency of the different propellants is closely related to the dielectric constant. Liquid Nitrogen has a better dielectric constant than all the other fuels but LH2 and Lithium (and LH2 doesn't really count for, reasons...) So, Nitrogen should actually be one of the MOST efficient fuels for a plasma thruster- I'd estimate an appropriate efficiency of around 78% Efficiency determines waste heat production (VERY low for Nitrogen). As for the ISP- well that should be very low as well- but NOT lower than Hydrazine (which is N2H4, and thus slightly *heavier* than N2). It turns out the factors that limit its ISP in real life were specific to the Helicon Double Layer plasma thruster- and wouldn't apply to other types of plasma thrusters. Hydrazine has an ISP of 2803.25 with a KSP-I plasma thruster, so Nitrogen should have an ISP of 3090.34 (110.24% higher due to its lower molecular mass). This is squarely in the middle of the plasma thruster propellants (some of which have significantly higher molecular mass- Xenon and Argon in particular... ) Liquid Hydrogen: 11213.00 s Lithium: 6469.90 s Ammonia: 3812.42 s Hydrazine: 2803.25 s Argon: 2491.75 s Xenon: 1383.68 Please fix the ISP and efficiency settings as soon as possible. I apologize for giving you the wrong data- I should have looked at the way KSP-Interstellar calculated ISP and efficiency for the existing propellants, and inferred Nitrogen's likely behavior from there, rather than looking at a specific design of plasma thruster that apparently operates on very different principles... Nitrogen is definitely fair game for this class of plasma thruster though- in fact its low dielectric constant makes it BETTER than most of the other propellants already in use in KSP-I's plasma thrusters... Regards, Northstar

That's a very KERBAL way of building a launch-assist system, though that's not really so much a Mass Driver as it is a Space Gun... Either way, whatever works for you- this way shouldn't consume any fuel for the initial boost though... If by mess relays, you mean orbital mass driver systems, though- it's already possible with this mod. Just stick a stack of Mass Accelerators on top of a REALLY BIG ROCKET, and you can launch them to orbit (or, alternatively, just build them in orbit using the Extraplanetary Launchpads mod- Mass Drivers are little more than a coil of aluminum wire, and it's one of the few things I would say is *legitimate* to build in orbit if you only consider Kerbals to have modern-day technology...) The Mass Accelerators work perfectly fine in orbit (in fact better, as there's no ground for the recoil to drive them into and cause them to explode...) and you can utilize the recoil force in clever ways to actually GAIN orbital velocity for the mass driver from de-orbiting debris, returning capsules and such- and then transfer this orbital velocity to a spacecraft bound for a higher orbit (or the Mun, or another planet) by boosting it in the prograde direction when at periapsis of the resulting elliptical orbit... Regards, Northstar

You don't need terraforming to live on another planet. Most likely, the early Mars colonists (and perhaps all inhabitants of that planet ever) will live in pressurized domes and hab modules... They will spend their time expanding those habitats, prospecting/mining resources, manufacturing things, providing goods and services to the colonial population, building+working greenhouse modules, and researching exciting new scientific discoveries- just like on Earth... They won't be lacking for things to do... Life expectancies might be significantly shorter (due to higher radiation levels and greatly increased risks of cancer), but that will just provide more incentive for scientists on Mars to collaborate with teams on Earth in working on a cure for cancer- a discovery that would have ENORMOUS economic benefits hear on Earth as well! The main economic benefit of off-world colonies to Earth will NEVER be resources or manufactured goods (excluding, possibly, spacecraft like Cycler Ships, fuel tankers, and orbital tugs...) It will be intellectual property (books, movies, scientific discoveries) and corresponding tax-revenue to the Earth countries those colonies remain loyal to (as long as that lasts- or better yet colonies could be a United Nations project that splits the revenues equitably and makes sure to provide representation and government services to the colonies it return...) and in the benefits of that intellectual property (especially scientific/technological discoveries) to populations here on Earth... A self-sufficient colony provides this intellectual property at ZERO continuing costs to nations here on Earth- aside from any government services they elect to provide on Mars in exchange for the tax revenue... Regards, Northstar P.S. I'm trained as a biologist in real life, and I can assure you we *WILL* cure cancer someday- one of the greatest obstacles is just understanding how the disease works in the first place. See, for instance, the Cancer Stem Cell theory, which as a biologist in the field who studied cancer and stem cells extensively, I can assure you is one of the *MAJOR* breakthroughs that is going to change how we treat/cure cancer... (It's nice that the Wikipedia article on the subject finally has a decent introduction- for the longest time it was a very low-quality article that didn't do the subject justice...)

Speaking of the zzz radiators, have they been coded to also double as KSP-Interstellar radiators as well? Logically, it would only make sense for the heat systems to all be integrated. In real life, it makes no difference to a fuel tank whether the heat comes from thermal leakage into the spacecraft, or waste heat from an onboard nuclear reactor (which might actually be a real life difficulty factor with nuclear rockets- the cryogenic fuel they rely upon does not like being stored at high temperatures, but nuclear reactors produce a lot of excess heat... Oh well, one more reason to use Microwave Thermal rockets- which only produce heat when power is being actively beamed at the spacecraft- I guess...) Regards, Northstar

The Hybrid Thermal Turbojets are indeed a separate part that can act as both a Thermal Turbojet and a Thermal Rocket Nozzle. If they're not showing up in your save, then it might very well be a bug that needs to be fixed by Boris, FreeThinker, or some other talented coder... First, I suggest you make sure you have access to the parts- by trying to find them in a Sandbox game. If they're usable in Sandbox, but don't show up in Career/Science games, then it's probably an issue with the tech tree unlock... Also, FreeThinker, do you think you could create a ModuleManager patch to allow Liquid Nitrogen to be used as a fuels with Procedural Parts? It should be a cryogenic fuel much like LOX or LH2, and should be storable in any tank that can hold other cryogenic fuels... The advantage of putting Liquid Nitrogen is Procedural Parts tanks is that I can then design the tanks to any size/shape I want- including conical fuel tanks, etc... It also provides more flexibility with my storage solutions- i.e. do I want to store it in an un-insulated/un-cooled tank, an insulated but not cooled tank, a cooled but not insulated tank, or a tank this is both insulated and cooled. Optimal solutions depend on the availability of electricity, the difficulty/expense in launching additional fuel tank mass to that location (insulation and cooling equipment are both expensive), and how long-term the storage needs to be. For instance, I might want to use an unisulated fuel tanker to ferry Liquid Nitrogen between an insulated/cooled fuel depot in a low Kerbin orbit, and one in a much higher orbit, or a Kerbin-Duna Cycler Ship with insulation and cooling onboard... (there's no point weighing down the tanker with insulation and active-cooling equipment if it's only going to be storing the Liquid Nitrogen for a very short time) Regards, Northstar

Oh, but we COULD colonize *MARS* well before the end of the century. See my threads on the following subjects to lean more about some of the technologies and strategies that could make it affordable, and don't require ANY major scientific breakthroughs (though that's not to say it will be EASY...) Next-Generation Launch Technologies (because getting to orbit is currently the most expensive part of getting anywhere from Earth...) Cycler Ships (Buzz Aldrin first came up with the idea, for crying out loud! It's nothing but a ship in a special orbit- no new rocketry technology required- although I do point out some rather magnificent ways it could synergize with other new technologies...) Propulsive Fluid Accumulators (Because when you have unlimited reaction-mass in orbit, your imagination's the limit. Keep in mind you still need to launch empty fuel tanks, and if you choose to scoop Nitrogen, rather than Oxygen, you need a way to use it as propellant- either thermal rocketry, or electric propulsion... Which, in practicality, means nuclear rockets or Microwave Beamed Power...) Big Dumb Boosters (Thread of the Month back in July. This is a real-life strategy for rocket-design, rather than a technology. The concept is to build bigger, cheaper reliable rockets with lower payload-fractions or, alternatively, cheaper rockets with high failure-rates for use launching the cheaper payloads such as fuel and life-support consumables...) Regards, Northstar

Just a rather odd thought to add to this discussion- what if theoretically you built a small onboard Mass Driver into the Cycler Ship? What I'm thinking is something like this- at the point where the interceptor ship departs the Cycler Ship again to meet up with any cargo or landers in orbit of the planet it is heading to (which would have been sent unmanned ahead of time on a slower transfer orbit, which would be more fuel-efficient for cargo), it would normally have to perform a burn to place itself on a closer approach to the planet/moon than the Cycler Ship (which skirts by the planet at a large distance to minimize the need for course-corrections due to gravitational perturbations of its orbit by the planet). What if the Cycler Ship had a small Mass Driver onboard (an electromagnetic accelerator similar to a rail-gun), and used that to place the ship on the closer approach instead? That way, the Cycler Ship could be on a trajectory that heads more directly towards the planet until that point, and use that impulse to place itself on an orbit that passes at a greater distance from the planet. Meanwhile, the interceptor-ship doesn't have to perform any burn at all, which reduces the opportunities for a potential mission-critical engine-failure, and saves on fuel mass that has to be launched for the mission... The Cycler Ship may have to perform some course-corrections as a result of this, of course (although, as stated, it may be possible to design the impulse to create desirable changes in trajectory for *both* vessels), but it has the luxury of a lot more time to make these than the interceptor-ship, which means it can make these corrections with higher-ISP, lower-thrust engines (or even with Solar Sails) that it would have onboard for regular course-corrections anyways... - - - Updated - - - Heh, I'm starting to imagine an entire mission-architecture here that creates regular shuttle flights between Earth and Mars at EXTREMELY low marginal cost... (that is, with a high set-up cost, but that can be re-used until parts wear out virtually for free...) (1) A computer/remote-controlled Microwave Thermal Rocket spaceplane shuttles crew members to Low Earth Orbit onboard a small interceptor-ship to be used later in the mission (the Earth-based Microwave Beamed Power will be needed for other mission-components anyways...) The extremely high ISP and TWR rating of Microwave Thermal Rockets (850-1000s and 2-3x comparable chemical rocket engines, respectively), as well as the ability to use Microwave Beamed Power for Thermal Turbojets (which use the atmosphere as their only propellant), makes spaceplanes possible... (2) Once in orbit, the spaceplane docks with a fuel depot containing Liquid Nitrogen gathered from Earth's Thermosphere using a microwave-powered Propulsive Fluid Accumulator... (the Propulsive Fluid Accumulator carries a rectenna and uses the electrical power to cool/compress scooped Nitrogen, and to run a Nitrogen-electric plasma thruster such as a Helicon Double Layer Thruster for orbital station-keeping and maneuvering back to the fuel depot in a higher orbit...) The spaceplane then refuels with a small quantity of Liquid Nitrogen (which can also be utilized in Microwave Thermal Rocket thrusters, which are *extremely* fuel-flexible, and require no retro-fitting...) and uses it to perform a powered/controlled re-entry, while the crew continue on with the mission in the interceptor-ship... (3) The interceptor-ship docks with the fuel depot. The interceptor-ship is launched with empty fuel tanks, which are meant for holding cryogenic liquids for short periods of time (and are only lightly insulated). It is equipped with a Microwave Thermal Thruster, and is a small, lightweight, possibly *unpressurized* capsule (the emphasis is on low mass so that it can be carried to orbit by a relatively small spaceplane, and high TWR so that it can perform its purpose effectively... Think a thin metal can with walls designed to do nothing more than stop loose objects from floating off into space, astronauts sit in EVA suits inside... Guidance is remote-controlled like a probe...) The fuel depot is equipped with a pressurized living-quarters that the crew transfer over to while awaiting the arrival of the outbound Cycler Ship... (4) When the outbound Cycler Ship (in an Aldrin Cycler Orbit with the "short" 5-month leg of its cycle going from Earth to Mars) is nearing closest-approach to Earth, the crew suits up and transfers over to the interceptor-ship: which fuels up on Liquid Nitrogen stored in the depot just before the arrival of the Cycler Ship. Using Microwave Beamed Power transmitted from Earth's surface, the interceptor-ship "burns" to intercept the Cycler Ship when the Earth's rotation is such as to allow the ground-based transmitters to focus on the interceptor-ship... (alternatively, orbital Microwave Relays are scientifically/technologically possible- which can reflect and re-focus a microwave beam around the curvature of the Earth...) (5) The interceptor-ship performs small course-correction "burns" (with a thermal rocket, no actual combustion occurs- thermal expansion of superheated propellants drives the entire thrust effect) and matches velocity at closest approach to the Cycler Ship, then proceeding to initiate a hard-dock (the interceptor will remain docked with the Cycler Ship for the next 5 months) and transfer over crew (via airlock if the interceptor was unpressurized), life-support consumables, and any scientific experiments designed to be performed in deep-space rather than in orbit of Mars... (6) The interceptor-ship also transfers over surplus Liquid Nitrogen for storage/use on the Cycler Ship (the interceptor-ship should carry MUCH more than is needed for rendezvous: the Nitrogen has a variety of uses on the Cycler Ship including being used in course-corrections with Nitrogen-electric thrusters, to dilute Oxygen in the Cycler Ship's breathable atmosphere, and in jets of compressed Nitrogen for Reaction Control Thrusters... The massive surplus of Nitrogen also gives the interceptor-ship abort capabilities if it is necessary to turn around and return to Earth instead of rendezvous with the Cycler Ship...) The Cycler Ship should have been accelerated to its cycler-trajectory using microwave-powered Nitrogen-electric propulsion in the first place, and thus be equipped with significant Liquid Nitrogen storage-tanks. These tanks should be actively-cooled and/or heavily-insulated to allow for long-term storage without extensive boil-off (although Nitrogen gas can also be removed from the tanks and put to use diluting the otherwise Oxygen-rich atmosphere of the Cycler Ship...) unlike the lightly-insulated tanks of the interceptor ship only designed for short-term storage... (7) Equipment on board the Cycler Ship allows for a largely regenerative life-support system, thus reducing the need for consumables shipped onboard the interceptor-ship. The crews spends most of the next 5 months onboard the Cycler Ship enjoying the spacious (for a spaceship) centrifugal living accommodations (to prevent bone-loss and other health effects of zero-gravity), greenhouses (part of the regenerative life-support system), abundant electrical power from Microwave Beamed Power (from Earth) and solar panels or a nuclear reactor, and possibly even a well-equipped science laboratory. The Cycler Ship is also equipped with a small mass-driver that will provide the interceptor ship with the tiny course-correction it needs to depart on its Mars-intercept near closest-approach (and doubles as a system to eject useless non-recyclable garbage as reaction-mass for course-corrections...) (8) Shortly before closest approach to Mars, the interceptor ship is launched on a Mars intercept-trajectory by the Cycler Ship's mass driver. The Cycler Ship is equipped with small Nitrogen-electric thrusters (TWR is a lot less of an issue with regards to how long it took to reach the cycler-orbit in the first place, as there were no crew onboard at that time...) and possibly solar sails to reduce propellant usage, and performs any necessary course-corrections to adjust after ejecting the incerceptor ship with the luxury of time... (9) The interceptor ship captures into Mars orbit using a combination of aerobraking and propulsive capture (the atmosphere is too thin for a pure aerocapture). The propellant for the capture-burn is Liquid Nitrogen (originally scooped from Earth using a Propulsive Fluid Accumulator) stored aboard the outbound Cycler Ship during the 5-month voyage. The power-source is Microwave Beamed Power from a large nuclear reactor either onboard the Cycler Ship, or sent in a cargo module to Mars orbit (via minimal-energy Hohman Trajectory) ahead of the crew, as Mars will be too far away from Earth art this point for large amounts of concentrated Microwave Beamed Power to reach the interceptor-ship (due to the problems of microwave beam-diffusion over long distances: although one option is to convert the microwaves to a tight-beam laser in Earth-orbit, send the energy to Mars orbit, and convert it back to microwaves with a satellite orbiting there...) Either way, the nuclear reactor would have been be a lot more than deadweight up until this point- it could have also been utilized to power a Nuclear Thermal Rocket or Nuclear Electric Propulsion system onboard the spacecraft that brought it out to the vicinity of Mars... (10) The crew rendezvous with any (preferably reusable) landers, pressurized orbital habitats, laboratories, fuel tankers, etc. as necessary in Mars orbit, and carry out the mission there. Ideally, Nitrogen for the interceptor-ship to rendezvous with the return-trip Cycler Ship (a separate Cycler Ship from the outbound ship, also in an Aldrin Cycler Orbit, with the "short" 5-month leg of its journey headed from Mars to Earth rather than the other way around) should have been sent ahead of time to Mars on a small fuel-tanker (possibly simply as fuel tanks attached to a larger vessel) on a slower, minimal-energy Hohman transfer-orbit... (as this takes less energy than accelerating to a cycler orbit and than capturing at Mars from there...) The cargo sent ahead of the crew could have all been accelerated to Mars and captured into orbit there via Nitrogen-electric propulsion (utilizing Microwave Beamed Power from Earth on the outbound burn, and from the local nuclear reactor on the capture-burn: with arrival times at Mars staggered such as to allow each to capture before the next begins its capture-burn, thus allowing each to receive the full load of microwave-power available at any given time...) (11) When the mission is complete, the crew transfer to the interceptor-ship and utilize Microwave Thermal propulsion (using either cryogenic Nitrogen from Earth, or cryogenic Methane produced on Mars by Sabatier Reaction) to rendezvous with it and transfer back over as before (however any life-support consumables stored onboard *this* Cycler Ship would have been transferred to the Cycler Ship by an unmanned tanker when it last swung by Earth, and stored for the past 15+ months of the "long" leg of the journey, as it would cost *MUCH* more energy to send the consumables to Mars orbit and then to a Mars-Earth cycler-orbit than just to send it to the Mars-Earth cycler-orbit in the first place...) (12) When the return-journey Cycler Ship nears Earth, the interceptor-ship is ejected via Mass Driver (which also does double-duty ejecting garbage as reaction-mass) onto an Earth-intercept trajectory, and captures into Earth orbit using a combination of aerobraking (limited by heat-management and dynamic-pressure concerns rather than rthe atmosphere being too thin) and propulsive-capture via Microwave Thermal propulsion (using either Nitrogen sent to the Cycler Ship via unmanned tanker with the life-support consumables, or Methane manufactured on Mars using the Sabatier Reaction and locally-extracted Hydrogen from water-ice... Methane has a higher ISP, and a lower fuel-density then Nitrogen, and can be combined with Oxygen for an afterburning-effect following the thermal expansion of the Methane: to add thrust but reduce ISP further... In either case, the power-source is Microwave Beamed Power from Earth...) The interceptor-ship then docks back with the fuel depot, transfers over the crew to the larger/pressurized crew quarters onboard, and awaits the launch of a spaceplane identical to the one in (1) to take the crew down to the surface, and the interceptor-ship for inspection and refusrbishing... (since the interceptor-ship was designed to be carried to orbit by the spaceplane in the first place, it only makes sense that the spaceplane should be able to carry it back to the surface for inspection/refurbishing... Of all the ships utilized, the interceptor-ship would be the most likely to sustain fatigue/damage due to its ultra-lightweight design and repeated long burns: most other ships in this mission profile, except the Mars lander, only perform one or two major burns and then remain in Mars orbit, cycler orbit, etc. for the remainder of the mission...) Now THAT was a long and detailed mission architecture. But I'm glad I took the time to draw it out. ALL of these steps are actually reproducible in KSP (with the right mods). Maybe somebody will even try this mission out some day... (I think my computer would *DIE* with this many sophisticated craft in a single save, but I'll probably give it a try... Setting up a ship in a cycler-orbit in KSP will be the most challenging aspect- but it's possible, and I might skip out on the life-support and centrifugal habitats because I'm already reaching my memory-limit...) Regards, Northstar

Great! Does it work with the KSP-Interstellar "Atmosphere Intakes" as well as the stock air intakes? I'd suggest looking at how Atmospheric Trajectories works. I suspect the mod's creator has already found a way to call on the Ballistic Coefficient of the vessel in FAR (the mod actually is designed to work best in FAR), since that would be the main relevant number for determining re-entry profiles... Also, a slight error on my part- I forgot to mention before that you want the INVERSE of the Ballistic Coefficient when determining fuel consumption. With Ballistic Coeffcient, like ISP, a high number (indicating a streamlined design) is a good thing for a Propulsive Fluid Accumulator. You still need to multiply by mass though- you're interested in the total drag force on the craft (in Netwons/kN), not the rate at which it slows down... So the PROPER formula would be proportional to: (1/ISP) * (1/Ballistic Coefficient) * Mass * Thermosphere/Atmosphere Density Alternatively, it might be possible to do something with the Terminal Velocity of the vessel- which already combines Ballistic Coefficient and Atmospheric Density into a single number (keep in mind both BC and Terminal Velocity *are for a particular Angle of Attack*, but you can assume a Propulsive Fluid Accumulator is always heading directly along the surface prograde vector to minimize drag and maximize intake...) The problem is, FAR doesn't calculate Terminal Velocity for any vessel above the Karman Line... (as, when KSP assumes no atmosphere, this number is effectively infinite) Regards, Northstar

Most likely you just need to add additional struts and Launch Clamps to the mass-driver. Pictures would help me figure out your problem, though. Regards, Northstar

Robots are great for specialized exploration, but the *REAL* value of putting humans into space (and indeed, on other planets/moons) is to learn more about what will be required when we eventually attempt to colonize these celestial bodies... Which, just so you know, *WILL* happen someday. Space-X is already talking about selling $500,000 one-way tickets to Mars onboard their Mars Colonial Transported within 30-40 years (not actually an unrealistic goal, if they succeed in their development of reusables and Full Flow Staged Combustion engines), which is a price many people would be willing to pay. Heck, even if the cost tripled or quadruples, I think many people would be willing to pay $1,500,000 or $2,000,000 for the chance to become one of the first settlers of Mars... And Space-X and reusables/Full Flow Staged Combustion is *NOT* the best we can do with today's technology... - A United Kingdom firm is working on SKYLON- a spaceplane which would be powered by the SABRE engine and be capable of reaching orbit for a fraction of the cost of even a Space-X reusable launch (estimated costs are $500/kg, as compared to current launch costs of $10,000/kg). The engine concept/design has already been validated, the pre-cooler (the most difficult part of the design) successfully built and tested... I can see no reason SKYLON should fail to actualize if the British continue to fund it... - The company Escape Dynamics is working on a Microwave Beamed Power spaceplane. The high ISP of Microwave Thermal Rockets (850-1000s when using LH2 as propellant) without any of the heavy reactors, safety risks, or measly thrust (Microwave Thermal Thrusters are capable of TWR's 2-3 times greater than that of any current chemical rocket engine when supplied with enough beamed-power, in fact) of Nuclear Thermal Rockets means that spaceplanes suddenly become a very real possibility. Spaceplanes are the *preferred* way to reach orbit with Microwave Thermal Rocketry, as aircraft can lift off the runway with a TWR less than 1 (and climb to higher altitudes, where the Microwave Thermal Thruster is subject to less atmospheric-compression of the exhaust stream and Thrust increases...) and can coat their ENTIRE underbellies with Silicon Carbide, which is highly-absorbant to microwaves (when built to the right thicknesses relative to the wavelength- similar technology to with solar panels) and heats up as a result when microwaves are pointed at it- allowing the thermal thrusters to operate... This means the microwave beam doesn't have to be as focused, as it has a larger target... Additionally, the Microwave Beamed Power can also be used to run Thermal Turbojets (relying on a Microwave Thermal Receiver instead of a nuclear reactor for the heat-source) for the initial part of the spaceplane's ascent- and the same Microwave-powered Thermal Turbojet technology has potential military and civilian applications for high-endurance aircraft... (super high-endurance aircraft may make for cheaper communications platforms than communications satellites, at current launch costs, according to some studies...) The Microwave Beamed Power has ANOTHER application still in Microwave-electric propulsion: that is beaming power to spacecraft in orbit to allow them to run electric thrusters at VERY high power-levels (and thus thrust levels) without any heavy nuclear reactor or massive solar panels to weigh them down (substantial radiator mass is still required to dissipate the excess heat from thruster-inefficiency, however...) making manned Mars travel using electric propulsion feasible... - The "Star Tram" proposal and similarly-named company (Star Tram Inc.) developed a proposal for an electromagnetic mass-driver for spacecraft assisted-launches, utilizing exactly the same basic technology as is used in Maglev trains (only scaled up in power-levels). There are some substantial engineering challenges that have to be overcome first for the versions with suborbital exit-velocities from the mass driver to become feasible, but there is *absolutely no reason* a scaled-down version couldn't be used to give rockets a few hundred m/s extra Delta-V right out of the launch tube... (the technology should actually be easier/cheaper per m/s at lower exit velocities, and less of it will get eaten up by aerodynamic drag in the lower atmosphere...) Due to the Rocket Equation, the most expensive 100 m/s is the FIRST 100 m/s (both in terms of fuel and thrust), and the second 100 m/s is a bit cheaper, and so-on and so-forth. Thus, anything that can give a rocket a free boost off the ground can bring down the cost orbit substantially... Among the benefits: your rocket not only has to meet a slightly smaller Delta-V budget to reach orbit, it can also start off with a TWR < 1, so long as the TWR climbs to 1 (from fuel-consumption and decreasing atmospheric pressure- in real life Thrust climbs with rising ISP due to decreasing atmospheric pressure, rather than fuel consumption falling with rising ISP like in Kerbal Space Program... The mod RealFuels already simulates this effect in KSP, though...) before all of the vertical velocity imparted by the mass driver has been eaten away by drag and gravity... In fact, I've already used mass drivers for *precisely* this reason in KSP (a slight Delta-V benefit, and a reduction in the liftoff TWR required) with my recently pre-released Mass Driver mod, which you can find a link to here and in my signature... Demonstration pictures of using the Mass Driver for a small (300-400 m/s) vertical boost are on the first post (the TWR of the night-launched rocket barely exceeded 1, and I've used TWR's of less than 1 at sea-level before as well...) Mass Drivers also mix *very* well with Microwave Thermal Rockets and Space-X style reusables (and ideally, both in one design). Because a Microwave Thermal Rocket (assuming it's not initially powered by a Thermal Turbojet) still has to lift all its propellant mass it needs to get to orbit, it is still subject to the Rocket Equation, and still benefits from the Delta-V savings. More importantly, the propellant of choice for a Microwave Thermal Rocket- Liquid Hydrogen (because of its very high ISP) is also subject to very high atmospheric-compressibility: meaning you lose a LOT of thrust in the densest part of the atmosphere, and need a lot more beamed-power just to get a rocket of the same mass off the launch pad than if the atmosphere were thinner... With a Mass Driver, you can boost the Microwave Thermal Rocket up above the thickest part of the atmosphere, and by the time its TWR needs to reach/exceed 1 in order to continue to climb, the air should be a good bit thinner- and you will need less beamed-power to do it... (with Microwave Thermal Rockets, the amount of beamed-power required, rather than the thruster itself- which is *VERY* cheap, working models have been built for less than a hundred dollars- is the main cost-driver...) Regards, Northstar

I'm trying to get FreeThinker to do precisely that... We'll see if he bites... - - - Updated - - - The problem with Solid Rocket Motors is that their ISP is already so low that they don't really allow for much wider engineering margins and less precise construction without losing their usefulness (beyond as strap-on boosters) altogether. A low-precision, high engineering-margin Kero/LOX Big Dumb Booster stage still has *MUCH* better ISP than a high-precision Solid Rocket Motor (and is cheaper, since the manufacturing can be much less precise). Not to mention, Solid Rocket Fuel isn't actually cheap- what makes SRB's cheap is that no work needs to go into designing separate engines or turbopumps or such- it's just "light and pray". The casing, control, and thurst-gimballing components still need to be built to *VERY* precise engineering margins in order to get much useful Delta-V out of them when using them as anything but strap-on-boosters... In Summary: A SRB built to Big Dumb Booster standards would have very low ISP *AND* terrible mass-fraction. Not exactly a recipe for lots of Delta-V. And you would see less in the way of cost-savings than with a Big Dumb Booster liquid stage, as less of the cost of a SRB is invested in the dry mass components anyways- and more of it is invested in the relatively much more expensive fuel... SRB's built to low precision and engineering standards could have exactly *ONE* use, and one use only- as strap-on boosters for the launch stage (where they are adding to Delta-V as long as their TWR exceeds the rest of the rocket...) And mant strap-on SRB's actually already are built to Big Dumb Booster standards anyways- many use corrugated steel with wide engineering margins for their casings due to its cheapness to machine (even though it's much heavier than aluminum)- and thus ALREADY qualify as Big Dumb Boosters... But due to the cost of the propellant itself, an SRB built like a Big Dumb Booster will never be as cheap as a liquid rocket built like a Big Dumb Booster... Regards, Northstar P.S. Those of you suggesting that Space-X style reusables will be more cost-effective than Big Dumb Boosters for the launch stage might very well be right- especially if Space-X succeeds in developing Full Flow Staged Combustion engines- but what about the upper stages? Space-X may have *plans* to re-use their upper stages, but I *highly* doubt this is going to turn out to be nearly as economical as they hope... Don't get me wrong- I'm sure they can do it (in fact, I regularly build Space-X style launch systems with reusable launch *and* upper stages with Real Solar System 64K, FAR, and Deadly Re-Entry installed all the time, and I'm not a professional engineer... Admittedly, my upper stages usually lack landing legs, and often make a soft-landing but then lose parts after falling over...) But, I suspect the cost of replacing all the thermal tiling and such between launches will be much higher than just building a cheap (Big Dumb Booster cheap, NOT high-precision engineering cheap) expendable upper stage and de-orbiting it (or boosting it to a graveyard orbit) after the payload is in place... Either way you're going to need to lift extra mass to orbit (either for having a Big Dumb Booster upper stage, or for all the heat-shielding and control systems necessary for a recoverable upper stage), but your cost-savings from cheap construction/manufacturing may be greater than your cost-savings from re-usability, when it comes to upper stages...

It's led to my realizing why space exploration is so expensive, and that our #1 priority for space has to be to make getting to it cheaper. Has it changed the public view about space exploration? Probably not yet. It certainly has influenced *some* people, but for it to make a real impact, those people have to go out and talk to other people, and those people talk to other people. Ideas, kind of like religions, spread by intentionally getting out the word... I.e. if you want to see altitudes on space exploration change, go talk to somebody who doesn't know much about it, but who you will have a number of opportunities to talk to. Teach them all you can (in short conversations- not all at once), and maybe even try and convince them to try KSP (once they pop for the game, they just won't stop...), then try and get them to spread the word likewise. Regards, Northstar

A Space-X style landing of a fuel tanker launch stage, right onto the Runway in Career Mode: A working Mass Driver: Regards, Northstar