Northstar1989

Also, what do you want to do about "Exit Area" and calculation of Atmospheric ISP? As I pointed out by PM, the 0.7657 m^2 approximation was *VERY* inaccurate (based on the performance of an SRB with a similar size/shape nozzle that, as it turned out, had performance with an inaccurate relationship to its actual nozzle model). The actual Timberwind had a nozzle-area of about 0.8 meters, so our scaled-down version should be about 0.2 m^2 for identical performance. However, if we relied on our physical model's nozzle area, and assumed a Nozzle Efficiency of 95% (typical values are 90-99%), we would get an Exit Area of 4.66 m^2 (which would lead to a *NEGATIVE* predicted Sea-Level Thrust...) So, we could basically go with any value we wanted between those two for our Exit Area. The larger our Exit Area, the higher we should set our Vacuum ISP and Vacuum Thrust, however... If we go with Fractal_UK's relationship between Vacuum ISP and Sea-Level ISP (which ignores Mass Flow Rate and just assumes 40% of Vacuum Thrust as sea-level for ALL possible Thermal Rocket combinations) we would need an Exit Area of about 1.25 m^2. I would advise that we still need to replace his "ispratio" term with a term to subtract (Exit Area * Background Pressure), though, or we will still get the ridiculous result that a multi-Gigawatt Microwave Thermal Rocket loses 60% of its Thrust at sea-level... Regards, Northstar

I was looking back over the math I used to calculate that, and I accidentally divided the expected Thrust in half (that is, I was balancing against 1/8th the Thrust of Timberwind 75 instead of 1/4th...) I must have been running the numbers a little too late at night, sorry... Timberwind 75 had a Thrust of 735.5 kN http://www.astronautix.com/engines/timind75.htm With a diameter of 2.03 meters, it was [(2.03)^3] / [(1.25)^2] = 4.28 times as large as the "Sethlans" reactor Which, I've been approximating as 4 times as large to make the math simpler... If I do the math a little more precisely though... (735.5) / (4.28) = 171.72 kN and then correcting for a Vacuum ISP of 1150 seconds from the nozzle (so a 15% increase to Thrust) 171.72 * 1.15 = 197.5 kN However, I thought we agreed to just go with a 1/4th approximation before (this is what the ThermalPower figures are based on, and the reactor *IS* a lot heavier for its size and likely built with more modern materials than we had in 1992), in which case it's: (735.5)/4 = 183.875 kN (183.875) * 1.15 = 211.5 kN That last bit is where the 211.5 kN number comes from. We could go with either number, but the ThermalPower production ratings are already based on a simple 1/4th approximation. I'm inclined to stick with Thrust ratings built on the 1:4 approximation so that we get a realistic Thrust/MW relationship. The level of ThermalPower production could reasonably be expected to be a bit higher since our reactor is almost 4x heavier for its volume (in fact 88% as heavy as the full-scale version despite its smaller size- and would be built with 20 years more advanced materials and engineering if it were a present-day design), but Thrust/MW is based on the physics of exhaust temperature and nozzle size... Sorry about futzing that calculation before. I thought I already listed the *correct* target Thrust (211.5 kN) in several other posts though... Regards, Northstar

A little adjustment of the configs, and... I'm getting there. I got these values by changing the ISP multiplier to 21, and the Thermal Rocket Thrust Multiplier to 2... The thrust is still a *tad* high (at this ISP, Thrust should be about 211.5 kN if we're basing performance on the Timberwind, as I said in my PM), but it's very close to accurate... Unfortunately, because KSP-I ties Thrust and ISP together, it's hard to tweak the values to *exactly* what I want them to be... Even when I do out the math, it's easy to make some minor rounding-errors and such... Anyways, if we fix this, make the Atmospheric ISP vary realistically with Mass Flow Rate (by subtracting Exit Area * Background Pressure in the Thrust calculation, which will tie Atmospheric ISP to Vacuum Thrust in such a way as to create the correct relationship with Mass Flow Rate...), fix the displayed ISP-multiplier in the VAB/SPH from 17 to whatever we adjust it to as the default value, and get some CO2-storage tanks rolling we'll be golden. OK, I know that's a LONG list- but it's good to keep the end in mind. Maybe I can write up a MM patch to allow LqdCO2 to be stored in RealFuels tanks to make all this easier on you... Thanks as always for the hard work FreeThinker! Regards, Northstar

OK, so I performed some quick testing (launching a NTR with Infinite Fuel to get it above the atmosphere) in vacuum conditions confirmed it is at least getting the right ISP and ThermalPower, and it matches up with your results. Now, we just need to fix the Thrust/MW... The CORRECT Thrust/MW is 2.127 times higher than it is currently set. REMEMBER, the additional Vacuum ISP beyond 1000 seconds (the Vacuum ISP of Timberwind) is *NOT* due to concentrating the ThermalPower in less exhaust mass, it is due to harvesting a larger % of the energy of the exhaust stream with a larger exhaust nozzle- and thus achieving higher Thrust for the same Mass Flow Rate and ThermalPower (indirectly increasing Vacuum ISP in the process) at the expense of increased atmospheric-compression... So, we need to multiply the Thrust/MW by an additional 212.7% (712.5% increase vs. before the 0.60 Extension Config). We also need to fix the calculation for Atmospheric ISP to be based on the formula I presented earlier (Atmospheric Thrust = Vacuum Thrust - Exit Area * Background Pressure). Right now the Thermal Rocket Nozzle is still only operating at an ISP of about 490 seconds at sea-level, instead of 803.5 seconds... This appears to be as it is still using the stock atmosphere curve (where sea-level ISP is set to 40% of vacuum ISP, regardless of throttling) originally provided by Fractal_UK... This means eliminating the "ispratio" term in Fractal_UK's equation for Thrust, and instead subtracting (Exit Area * Background Pressure) from the rest of the equation, where Background Pressure is in kPa. Regards, Northstar

That's good (105.9 kN Vac Thrust is better than before), but still not up to the target performance: Sethlans Target Performance: Vac Thrust: 225.25 kN Vac ISP: 1225 seconds Sea-Level Thrust: 147.66 kN Sea-Level ISP: 803.05 seconds Remember, it should have 1/4th the Thermal Power of the Timberwind 75 (which produced 735.5 kN Vac Thrust) and 22.5% higher Thrust/MW due to the larger nozzle yielding 22.5% higher Vac ISP... (735.5 kN / 4) * 1.225 = 225.25 kN Also, what did you do with the "Exit Area" value? With ISP multiplier currently set to reflect the larger nozzle size, the Exit Area should be left at 0.7657 m^2 for the 1.25 meter Thermal Rocket Nozzle, leading to the lower Sea-Level Performance than the Timberwind... In short, the nozzle on *OUR* NTR is designed more like an upper-stage nozzle than a launch-nozzle: which leads to a higher Vac ISP, but a lower Atmospheric ISP than the Timberwind designs... (which were designed as launch engines) Regards, Northstar

KSP-Interstellar normally uses LiquidFuel as a placeholder that gets overwritten by other fuels. However, in this case the MM patch to change LiquidFuel to Kerosene is preventing it from replacing LiquidFuel with "ChargedParticles"... Regards, Northstar

Velocity, experts DON'T always change their mind, even when confronted with mountains of evidence. In real life, I trained as a Stem Cell Biologist. And you'd be amazed how long it took to even convince people of the existence of Stem Cells (or now, to convince people they're not the magical cure-all for everything). The senior scientists, in particular, were hard-headed and ignored mountains of evidence for the new concept... Now, we're seeing something similar with the Cancer Stem Cell theory- which is far less developed than Stem Cell Theory, but still has LARGE amounts of evidence to support it... The fact is, skeptics are skeptics because of precisely what you warned against- they let their emotions get in the way of logical reasoning. Their egos, their pessimism, or their desire not to get hurt again after being disappointed by a potentially-exciting discovery in the past are usually what lead senior scientists and many such skeptics to refuse to acknowledge new discoveries... People, as a rule, are remarkably illogical. I'm currently residing in Illinois, and you would not *BELIEVE* how many people out here are evolution-deniers, or think that the Moon Landings were a hoax... Why do I mention all this? Because the comment you were responding to was right- there are some "skeptics" who will continue to call this a hoax even if it works out to the point we're sending interplanetary probes with this... Centuries of modern science have taught us one thing above all else: we know *NOTHING* compared to what there is to know... Regards, Northstar

This is a thread for discussion of Microwave Thermal Spaceplanes, as are *CURRENTLY* being developed by the company "Escape Dynamics". Read more about them here: http://escapedynamics.com/ After you've introduced yourself a little to the concept, I suggest doing some more reading about Microwave Beamed Power: http://en.wikipedia.org/wiki/Beam-powered_propulsion http://www.cnet.com/news/rocket-scientist-aims-to-relaunch-propulsion-technology/ Only AFTER you're sure you know what this is about, feel free to discuss... Regards, Northstar

Given that you've never heard of Escape Dynamics, which is trying to do a full-orbital spaceplane, I'd say you haven't heard of all the players in the marker either. An I *HAVE* heard of some of those (Stratolaunch in particular). ALL your criticisms are ones that can broadly be applied against orbital spaceplanes, suborbital spaceplanes, or even VTVL reusable rockets (Space-X style) for that matter. It's a defeatist altitude, and excessive cynicism- not a realistic view of the world. I shouldn't even bother addressing most of them, however... You also have the additional guidance systems, the cost of checking the engines for damage, etc. You're taking a very unrealistic view of Space-X just so as to make spaceplanes look worse... You can't say "nobody" expects them to make money if people are currently funding some of them (and funded others in the past), and people make their careers designing them. And your analysis is blatantly-unrealistic. VentureStar, for instance, would have been a MUCH cheaper alternative to the Shuttle according to most estimates. Not saying it would have been cost-competitive with the cheapest expendables, but those don't have any carry-back capacity to bring scientific experiments back to Earth... No, you're dead wrong. The wing are ONLY useful for the portion of the Delta-V where you DON'T need proper heat-shielding. The Lift/Drag ratio decreases the faster you go, and the wings become basically useless once you enter the ballistic phase of a spaceplane ascent. Which is why I suggest suborbital spaceplanes- as soon as you reach the point where the wings are just weighing you down, ditch them (and the rest of the plane) and just head the rest of the way to orbit on a rocket (which does NOT necessarily have to be single-stage or reusable, by the way). The spaceplane can make it back to the ground on its own residual fuel... Expendables don't beat ANYTHING right now. They cost $10,000/kg to orbit. ANY system that can offer cheaper launches than that can beat them out for market-share... I can name several- but you just hedged your bets by saying that "payloads are where the money's at". Which allows you to say you were right either way, based on two alternative definitions of payloads (payloads as the money you get paid for launching things to LEO, or payloads as in components for orbital spacecraft). As it so happens, the example I was citing was from a real component we were looking at for the KSP Cubesat project, as the crazy profit-margins are the worst in orbital components... I've also talked to numerous people in the know- space component manufacturers/subcontractors (and there are a *NUMBER* out there selling components at very high prices completely unrelated to operating their own launch vehicle- such as the manufacturers of the Space Shuttle SRB's, which didn't operate the Shuttle itself...) What do you think the $190 labor cost was for a component that took $10 to make? I was referring to MOST of that being in quality control and certification. There's absolutely no need to insult me here. Control yourself. As another player astutely pointed out, companies can just threaten to go to other countries closer to the Equator if local regulatory agencies give them a hard time (like OTRAG did in going to Sub-Saharan Africa, originally). There *ARE* ways around this... They're barely at break-even because their expenses are so high, bot because their revenues are low (in fact, they're MASSIVE). I do also have to point out "barely at break-even" is often an spoiled and overused term with these big companies- they usually have a *LOT* of fat they could afford to cut (like corporate jets and luxurious conferences at tropical resorts for their high-ranking executives). They'd just rather go bankrupt than do so (their executives will be fine if that happens, thanks to Golden Parachutes... It's only the little guys that get screwed when a big company fails...) If you can develop a system that gets payloads to orbit much more cheaply, you can make a MUCH bigger profit- assuming that you're the only game in town that can accomplish the cheaper launch-system, and you don't have any competition (which the LONG history of flat launch costs would seem to indicate would most likely be the case- if you can get a payload to orbit for $5000/kg, nobody else will be able to match it: you can then charge $9000/kg and still drive all the $10,000/kg companies out of business...) Regards, Northstar

Based on various cost-analyses that are already out there. The analysis could be wildly-inaccurate, of course (as is sometimes the case with aerospace). Space-X's mission architecture makes great sense for chemical rocketry. In fact, it's my go-to launch system for my current KSP 0.90 Career Game in RSS 64K (because at a realistic relationship between part-size and Delta-V requirements, true orbital spaceplanes just aren't feasible, and suborbital designs have an INCREDIBLY low payload-capacity... See my OP: that large spaceplane was used just to put a tiny Mun lander with an unpressurized cockpit and 4 km/s Delta-V into orbit, which used almost all its fuel getting there on a scale where it's only 8 km/s Delta-V to orbit... I would expect to only be able to get about 5-6 km/s Delta-V out of the spaceplane portion in real life, where it's 10-11 km/s to orbit...) But a Space-X architecture does NOT work well for Microwave Thermal Rocketry... (see below) Exactly. If we design a suborbital spaceplane that we get 30-40 years use out of (with slight retrofitting, like the Shuttle), the savings on repeated manufacturing costs become significant... My thoughts exactly. If governments aren't too welcoming to an unmanned suborbital spaceplane design, the company could/should just threaten to move to a country closer to the equator... (where it will of course take slightly less Delta-V to get to prograde orbit) Exactly. Space-X faces some of the same regulatory hurdles a suborbital spaceplane would- and most countries already have far more runways than launchpads... This is why we need Microwave Thermal Spaceplanes- to massively push up the ISP, so you need a much smaller plane for the same Delta-V... Indeed. A Microwave Thermal Spaceplane could theoretically be powered by wind and solar on the ground... (and from water-electrolysis plants for the relatively small amount of LH2 needed for propellant compared to a rocket) Look at the company Escape Dynamics. They're already working on a fully-orbital Microwave Thermal Spaceplane. I only suggested a *SUBORBITAL* version because it would require a smaller spaceplane (or offer a higher payload-capacity) and be easier to design... http://escapedynamics.com/ Regards, Northstar

This is *precisely* the kind of stuff I'm talking about... I'm aware of the costs of developing such a spaceplane. As I've repeatedly stated all around these forums, the solution is to go with Microwave Beamed Power. It synergizes well with spaceplanes because you can get a MUCH heavier plane off the runway with the same thrust than rocket off the Launchpad (as I've said, you can take off with a TWR of 0.2 easily...) and because with the high ISP (infinite with Thermal Tubojets, 1000 seconds when you switch to LH2 at high altitude- which can also be used as a cold sink for precooling the atmospheric intakes earlier in the flight...) you need much less plane to get a given payload suborbital... With a Microwave Thermal Spaceplane using Thermal Turbojets to get off the runway, you can get off the ground with maybe 1/32nd the beamed-power to get a rocket going upwards with a TWR of 1.6 using Thermal Rockets (you only need 1/8th the TWR on the runway, and Thermal Turbojets can produce easily 4 times the Thrust for the same amount of beamed-power). Since 95% of the costs are in the Microwave Transmitters with a Microwave Beamed Power launch scheme, this saves *MASSIVELY* on the total cost to a suborbital trajectory. Also, there seems to be some confusion here. You talked about the difficulties of releasing a payload at hypersonic speeds in-atmosphere. By its very definition, a suborbital trajectory goes ABOVE the atmosphere- so you just release the upper stage during the ballistic phase of your flight like you later suggested... Regards, Northstar

That kind of thing isn't helping. In fact, it's just rude and disrespectful- which kind of proves my point. That was entirely accidental- I ahven't been *trying* to mangle your handle. But as you said yourself, you deliberately mangled mine... -SNIP- I do think that you need to introspect a little as to why you're acting this was Starwaster. Because I haven't done anything to deserve it. Regards, Northstar - - - Updated - - - My credibility was attacked directly. Repeatedly. It's only about time I stand up for myself. Because my ideas AREN'T that radical, and SHOULD NOT require a separate mod. They're what should be simple adjustments to a widely-popular mod, some of which NathanKell previously said were priorities anyways (like fixing atmospheric ISP so it doesn't bottom out at 1 atm pressure). They're only being shut down out of disrespect. And I ask you, what have I done to deserve it? DON'T fall into the common trap of justifying treatment of a victim by how they react to the criminal- you can't say I deserved to be treated with disrespect based on finally going ahead and making a list of all the times I've been ignored after MONTHS of this... Is there any need to be rude and abrasive? What have I done to you to deserve this? Treat others with respect- as you would wish to be treated. Honor them at all times. If you have a quarrel with your brother, state it frankly and provide evidence (which is what I've done here). These are simple moral imperatives (and might I add, very close paraphrases from how the Bible directs us to treat others- if you're a Christian). I think we can all live up to them- you and everyone else on these forums is better than to stoop to rude behavior. Regards, Northstar

We didn't touch the Fusion Reactors, so Thrust shouldn't be affected by the update. Now if you saw decreased Thrust with the FISSION reactors, it might have been that we increased the Reactor Temperature of the fission reactors to more realistic values. However we also up-rated the Thermal Power to realistic values, so I would *EXPECT* more ISP *AND* Thrust using the Fission reactors... Regards, Northstar - - - Updated - - - Good stuff. Awesome! I guess this only leaves me with one more concern about the fission reactors- do you think Fractal_UK will be willing to integrate the changes when he comes back, especially if they're in an outside-config rather than written into the main code itself? Also, I'm still hoping we can get Carbon Dioxide working as a storable propellant in RealFuels. You took a look at that code I pasted before for that (using adding LqdWater wherever there's Kerosene as an example), right? In fact, I think you could just directly copy that code, just replacing "Kerosene" with "LqdMethane" which is the RealFuels version of Methane, and "LqdWater" with "CarbonDioxide" which is the CRP version of CO2- and do something similar with a Liquid CO2 resource as well). Regards, Northstar

Interesting. It looks like Fractal_UK had some of the same thoughts we did, only 4 months ago... (we should still update the displayed calculation in R&D/SPH/VAB though...) That's GREAT. But I'm not sure if you're reading the formula format correctly. Here's how I read it, based on already knowing what it SHOULD look like: Engine Max Thrust = Math.Max [(* 2000 * thermal_power_received * heat_exchanger_thrust_divisor * ispratio * myAttachedEngine.currentThrottle, 0.01) / (MaxISP * g0)], thrust_limit Note that Engine Max Thrust is the functionally equivalent to "Vacuum Mas Thrust", as an engine always produces max thrust in vacuum at full-throttle... ISP * g0 = Exhaust Velocity, and Exhaust Velocity is normally found in the denominator of this type of Thrust calculation (Thrust = Thermal Power/ Exhaust Velocity), so that's why I assigned both terms (MaxISP and g0) to the denominator here... The equation, as a whole, is clearly derived from E = 1/2 m v^2, solving for m*v, which is Thrust (mv = 2 * E / v = Thrust). Exhaust Velocity = "v", and E is in terms of Megawatts (so you have to convert it to kW by multiplying by 1000, if you want Thrust in kN- hence "2000" instead of "2" in Fractal_UK's equation..) Now the question is, what do some of the other terms mean? I'm GUESSING: thrust_limit Is normally a Thrust value (in kN). Reflects the maximum thrust that a Thermal Rocket Nozzle can produce. Somehow, Fractal_UK has figured it into the equation such that this # cannot be exceeded, likely using the "Math.Max" function... (which is why I placed it OUTSIDE the parentheses) heat_exchanger_thrust_divisor Is probably normally a number between 0 and 1, representing the *fractional efficiency* of a heat exchanger (so 50% = multiply by 0.5) Or, alternatively, a number in the denominator you divide by to the same effect (i.e. 50% - divide by 2). This is a real factor in thermal rocket design (not all Thermal Power is transferred to the propellant stream), I just had no idea Fractal_UK had integrated it into KSP-Interstellar... I don't know if this corresponds to the "fuel_efficiency" value on reactor parts, or is found somewhere else... myAttachedEngine.currentThrottle Looks like the Throttle Setting to me (which would be a value between 1 and 0.01) I haven't included it in all my previous calculations, but I've always assumed it would fit into the final equation for Thrust... ispratio This small, mysterious term *S PROBABLY THE MOST IMPORTANT OF ALL* for getting the correct value. I'm guessing that it represents the effect of the nozzle on the Thrust, that is the ability of a nozzle to amplify Thrust beyond (Thrust = Power/ Exhaust Velocity) to [Thrust = (Power/Exhaust Velocity) + (Exit Area + Exhaust Pressure)]. In short, I'm guessing this value holds the key to understanding the precise way Fractal_UK is converting Thermal Power to Thrust, and why your predictions probably won't match up with actual results... (see borrom) I'm guessing "ispratio" is the whole-number ratio (so a value greater than 1) of vacuum Thrust based purely on (Mass Flow Rate * Throat Velocity) to actual Vacuum Thrust, which is (Mass Flow Rate * Exhaust Velocity). Note I use the term "Throat Velocity" to indicate the speed of the exhaust when it exits the rocket, and enters the nozzle; whereas "Exhaust Velocity" is the speed of the exhaust when it leaves the nozzle (which acts to accelerate the exhaust-stream by expanding it, at the expense of Exhaust Pressure and thus Atmospheric ISP...) That is, the ratio between the isp BEFORE the nozzle and AFTER the nozzle, which is exempt from the trade-off between ISP and Thrust normally seen with higher-temperature reactors vs. reactors with higher Thermal Power, as it serves to INCREASE Thrust *AND* ISP by the same factor... Alternatively, "ispratio" could just be the ratio of Vacuum to Atmospheric ISP, using the stock ISP curve... (in which case it's a number between 0 and 1, and the Thrust/MW will be hopelessly inaccurate...) Try these same calculations using known Thermal Power, Heat Exchanger Temperature, and ISP values taken from a screenshot of a NTR in-flight... See if the predicted Thrust (for that reactor, using this formula as you understand it to work) matches the observed Thrust. I suspect it won't, because we don't know the value of "ispratio" yet, and it figures into the equation somewhere... EDIT: Also, when everything is working correctly for the 1.25 meter "Sethlans" reactor, it should produce 225.25 kN Vacuum Thrust at 1225 seconds Vacuum ISP. That is because any additional ISP beyond 1000 seconds is due *PURELY* to the exhaust nozzle (which increases ISP by increasing Thrust for a given Mass Flow Rate, *NOT* reducing fuel-consumption...) and thus does not come at the expense of Vacuum Thrust, but rather to its benefit... SethlansTarget Performance: Vac Thrust 225.25 kN Vac ISP 1225 seconds Note that the high Vacuum ISP should come at a rather significant price in atmospheric ISP... The original Exit Area approximations for the Thermal Rocket Nozzles seem appropriate- although I still have no idea where to code in the formula I've been posting here (Atmospheric Thrust = Vacuum Thrust - Exit Area Factor * Background Pressure) Regards, Northstar

Starwaster, that's a jab at my credibility, and I really don't appreciate it. There's a reason I felt the need to post that long list of posts, showing how my ideas have been consistently brushed off on this thread *from the very beginning*, and your treatment of my ideas has been a BIG part of that. You can't justify brushing off every idea AFTER that bit with the cryogenic-liquids compression debate (which I've already admitted I was wrong about: several times), since you've been brushing off my ideas for literally MONTHS before that (the proof is right in this thread, if you're willing to play archivist like I was). You just don't want to lsiten to anything I have to say. Also, this equation has sources. It has LOADS of evidence behind it. You don't have to look any further than Wikipedia to find it (although that's NOT where I originally got it- I got the equation from a NASA document on rocket equations!) http://en.wikipedia.org/wiki/Rocket_engine_nozzle#Specific_Impulse When you substitute the definitions for the symbols, you get, right there on Wikipedia: Force = (Mass Flow Rate of Exhaust Gas) * (Exhaust Gas Velocity at Nozzle Exit) + (Exhaust Gas Pressure at Nozzle Exit - External Ambient Pressure) * (Cross-Sectional Area of Nozzle Exhaust Exit, m^2) Which is what I've been simplifying and posting here as either: Force = (Mass Flow Rate) * (Specific Impulse) * g + (Exhaust Pressure - Background Pressure) * (Exit Area) *OR* (note that the term "Background Pressure" is the more commonly used one on university and NASA websites, rather than "Ambient Pressure") Atmospheric Thrust = Vacuum Thrust - (Background Pressure) * (Exit Area Factor) Where (Exit Area Factor) is Exit Area with modification for Nozzle (In)Efficiency, and the following mathematical simplifications/generalizations are made: Force = Thrust Vacuum Thrust = Mass Flow Rate * Exhaust Velocity + Exhaust Pressure * Exit Area (Note that both Mass Flow Rate and Exhaust Pressure, and thus Vacuum Thrust, scale linearly with throttle setting- at least in theory...) Exhaust Velocity = Specific Impulse * g The fact that I can even make all these mathematical conversions/simplifications so easily/flawlessly should indicate to you that I have a firm grasp of the subject-matter, if you're *ALREADY* not convinced by my overall intellect (IQ in the genius-range, I'm sure it comes across in my writing) and repeatedly-stated very high level of education in real-life (I have a Bachelor's from an Ivy League school with good grades, and a Master's from a major research university...) I try not to brag, but if you're going to attack my credibility just because of one stupid mistake discussing a subject I didn't have much knowledge about... (cryogenic fuel storage in rockets) Regards, Northstar P.S. I'm aware of the need for a term to reflect "Nozzle Efficiency"- however these are *idealized* equations, simply re-posted to make a point. The version we include in RealFuels can and should include adjustments like a term for Nozzle (In)Efficiency, and anything else you may think is worth reflecting regarding how practice (which I don't know enough about) diverges from theory... (which I have a quite reasonable grasp of some aspects of)

Here's a running record of the changes I've suggested so far, numbered by their chronological order... I skip posts unrelated to changing/improving RealFuels Post #1 - I suggested fixing the "Radial Engine Body" part (the stack-mounted part that acts as both an intake and fuel tank, changed to hold fuel in 0.24) to hold fuel, and the radial RCS tanks to hold RealFuels RCS propellents. Post #2 - I clarified what the radial engine bodies were. Another player interjected that the models had been around since C7, and only recently got fuel. Only then was it stated that they would be fixed (although as of this release, 5 months later, only 1 of the 2 parts of this type *have* been fixed- one of the radial engine body type parts still only holds LiquidFuel in RealFuels 8.3...) Post #3 - I suggest adding a KSP-I/Realfuels Integration config for the first time ever. I was answered that the existing config was dated, but no response was made to my suggestion of adding/fixing it. Post #4 - I suggest working the new KSP-I/RF config off the old/dated config, and try to recruit Regex to help create it (as I don't have the expertise). Post #5 - I also try and recruit undercoveryankee to work on the KSP-I/RealFuels config. Regex responds shortly after with a brusque and slightly rude refusal to help (even though I've done nothing that should have given him reason to take offense), NathanKell politely refuses, and undercoveryankee apparently ignores me altogether. Post #6 - Noticing that my requests for an experienced hand are being ignored, I start work on fixing some of the issues with KSP-I/RF integration not already covered by the existing integration-config. I post a link to my progress so far, kept on another thread... Post #7 - I point out for the first time the Square-Cube Law is not being applied to tank boil-off rates in RealFuels: large fuel tanks are suffering far too high a rate of boil-off/ heat leakage as a result. NathanKell shortly thereafter responds that it is a "good point" I brought up, and seems to be considering the merits of changing boil-off rate to the (2/3rd) power of volume, which he presents as an *alternative* to scaling boil-off rate at the ratio of Surface Area: Volume despite the fact that this is precisely the mathematical relationship that describes the ratio of surface area: volume (essentially he politely says "No, you're wrong- this is what it should look like" and then goes on to describe *exactly* what I just suggested in his own words...) Post #8 - After doing some additional background reading (including a NASA document on cryogenic liquids boil-off), I come to the realization that boil-off should actually scale with approximately the (4/9) power of volume instead of the (2/3) power- and refine my suggestion accordingly. NathanKell responds shortly thanking me for the NASA doc, but showing no indication he will fix the boil-off rate to scale anything other than linearly with volume... (to my knowledge, boil-off *STILL* scales linearly in "Realfuels"- where's the realism there?) Post #9 - I remind NathanKell that, if boil-off rate is not fixed, the behavior of RealFuels will still be unrealistic. I also discuss (on an entirely unrelated note) that I would like help adding water-storage to RealFuels tanks to players using KSP-Interstellar can store their HydroLox as water and only electrolyze it shortly before it is needed on long voyages. Finally, I ask about the code I've already written up for KSP-I/RealFuels integration (more progress since the last post I mentioned it) getting integrated into RealFuels... Post #10 - I point out that the KSP-Interstellar Meth/LOX engine performs very poorly compared to real life designs. Regex shortly thereafter politely reminds me that such issues should be brought up in one of the engine config threads... Post #11 - I raise the concern that there might already be a MM patch to change the resources the KSP-I Meth/LOX engine consumes, and that having multiple MM patches aimed at the same part might cause issues... Post #12 - I confirm that there is indeed an existing MM patch to the engine I want to fix. I also point out that there is a duplicate-entry in the existing KSP-I/RealFuels config (the one that is outdated) and suggest some additional lines of code to add to the integration-config in the meantime while Dreadicon (who at this point I have begun collaborating with) works on a more complete integration-config starting with the work I've already done... Post #13 - I realize that the name of Liquid Oxygen has been changed in the latest RealFuels update, overnight. I post a new set of lines of code that correct for the name-change. The changes are in *exactly* the same style as changes already in the existing (outdated) KSP-I/RealFuels integration-config at this point, yet Regex rudely berates me for "3 walls of text" (though most of my posts are code, not text) and for wanting to "edit an Engine" through RealFuels- completely ignoring that the vast majority of my 3 posts are about adding new fuel-modes for the KSP-I NTR's in *exactly* the same way as existing MM patches do in the existing config. A player (diomedea) posts shortly thereafter citing a CTD caused when trying to load KSP, with one of the responsible files being *precisely* the file I was trying to fix to use the new resource-names before Regex rudely shut me down... Post #14 - I am suffering some confusion about how to add water-storage to RealFuels tanks (an issue I have still not received much help with), and as to precisely what Regex means by "tank types" in RealFuels. I also point out a series of NovaPunch2 fuel tanks (the "K1 Tanks") that are still stuck holding LF/O... (eventually fixed, I believe, but not 100% sure as I ended up deleting all cylindrical fuel tanks to be replaced by Procedural Parts tanks at a later date...) NathanKell announces a bit later that he has *completely pulled* the existing KSP-I/Realfuels config from the current version of RealFuels, and will not allow any more discussion of the integration-config on the RealFuels thread (which still seems quite dictatorial to me- and I doubt would have been done had it been anyone else working on the integration-config...) He does promise a fix to boil-off rates in RealFuels 8.2, though- although to my knowledge this promised fix *still* hasn't been included as of RealFuels 8.3 or the next approaching version... Post #15 - I acknowledge NathanKell's orders, and as *one last thing* I need to say on the topic, ask that no MM patches that apply to the KSP-I engines be included in future KSP-I/RealFuels integration-configs (when they are added back in) that go with the main RealFuels mod, but instead be kicked over to the individual engine-configs so there will only be one MM pass on each engine... (to avoid potential bugs/issues) I also wish Regex well, as he says he is sick. Dreadicon announced the KSP-I/RealFuels integration-config is almost ready a bit later, without any repercussion from NathanKell (confirming my suspicion that either NathanKell is only saying this to shut me up, or is enforcing the rules unevenly- although I am/was happy Dreadicon got in no trouble as I was collaborating with him on said config...) Post #16 - I point out another NovaPunch2 tank that only holds LF/O. AFAIK, this tank still hasn't been fixed as of today, despite being pointed out *nearly 5 months ago*... (confirming my point- my suggestions are largely being ignored unless someone else being treated with more respect jumps on the bandwagon as well...) I also ask if somebody could do a round-up of other parts in NovaPunch2 that need fixing, as I am trying to learn ModuleManager (as most of Regex's help has amounted to telling me to learn ModuleManager). Regex then immediately jumps in and basically (tacitly) tells me to go do the roundup (make the list) myself... Post #17 - Despite my stated intent to spend my time trying to learn ModuleManager, I agree to do the round-up anyways (I never do end up learning ModuleManager, partly as a result...) Regex says a bit later he's fixed the Novapunch2 tanks- and some of them do end up getting fixed, although at least one of the tanks I suggest never appears to get fixed... (or perhaps the fix was just bugged) Post #18 - In as few words as possible (due to NathanKell's restriction on discussing the KSP-I/RealFuels integration-config) I explain that I haven't updated yet, as I am waiting on said integration-config (which is finished, for the time being- and as it turns out for all time ever, as Dreadicon never ends up helping finish up the remaining loose ends...), and point out a couple Firespitter tanks that still hold LiquidFuel or Oxidizer (they are one-resource tanks, and *to this day* still have not been fixed for Realfuels- despite this post being 5 months ago...) A while later, a player named Kolago talks about wanting to store water in RealFuels tanks and electroylze it- precisely what I was trying to do before, but received no help with... Nobody is able to point out he can already do this with RealFuels, as the KSP-I/RealFuels integration-config makes this possible, due to NathanKell's ban on discussing the config... Post #19 - I remind NathanKell about his promised fix to tank boil-off rates, and refine my explanation of the expected behavior a little further (not only does boil-off scale at the 4/9th power for a tank with a given outer wall thickness, larger tanks tend to have thicker walls and thus experience less heat-leakage...) I ask him how the boil-off fix is coming along. NathanKell never responds to my question. Post #20 - I explain that some crew capsules are only carrying Monopropellant instead of Hydrazine or a RealFuels RCS tank of some sort- an issue which is *very* slowly responded to, and *still* has not been fixed for many mod crew capsules as I understand it (I've been so into unmanned rockets and manned service modules coupled with probes lately that I haven't used a crew capsule in a month or two- but I pointed out the issue 5 months ago, and 2-3 months back it was *still* a major issue...) Post #21 - I respond to another player's question about how to figure out if RealFuels resource prices are accurate, and comment that the SolidFuel prices are way out-of-wack (*MUCH* too high) in RealFuels: implying that they should be fixed. The other player later jumps on this bandwagon as well, and IIRC the issue *was* eventually fixed, much later. I also remind NathanKell about the crew capsule issue, as nobody had responded to my last post about the issue... NathanKell later responds about SolidFuel costs (acknowledges they are too high- although a fix doesn't materialize for a long time thereafter), the crew capsule issue (says Regex fixed it- although as it later turned out he did an incomplete job...), and basically declares that he is not going to fix boil-off rate after all as it would make small tanks boil-off too quickly (although making small tanks less desirable for cryogenics and large tanks better was the *WHOLE POINT* of implementing the Square-Cube Law in this aspect...) Post #22 - I argue a little for still fixing boil-off rates to correspond to the Square-Cube Law, and NathanKell appears to change his mind about not fixing it (briefly). Post #23 - I argue for more aerodynamic thermal fins, as the current parts in RealFuels at this time are extremely un-aerodynamic (short+boxy). Eventually this will lead to the creation of a deployable Thermal Readiator part, based on the same ZZZ model as is used in KSP-Interstellar: but not until a considerable number of posts where I am constantly told it is unnecessary... A thermal fin with an actual aerodynamic shape (so that it can operate during launch, rather than having to fold up inside a fairing) is a dream of mine that is never realized, however- I eventually try to create such a part myself, and even get it (briefly) integrated into RealFuels, but it doesn't work right- and nobody ever helps me to fix it despite multiple requests for help... This list of posts has gone on long enough. What would come next is a long group of posts where I debate the merits of adding an aerodynamics thermal fin (which is never added- but a deployable version is instead based on somebody else's idea...) and a debate over compression of cryogenic liquids (about which I was completely wrong, as I got some numbers a couple orders-of-magnitude off, and though LH2 compressed over 60% when it only compresses about 0.6% at high pressures, and most other cryogenics not at all...), as well as my latest posts advocating fixing the Thrust/ISP relationship to be even more realistic in-atmosphere (by switching to a method of ISP calculation that takes into account changes in exhaust pressure based on throttling, and doesn't floor at 1 atmosphere of pressure...) A pattern has emerged, though. I try and suggest something, and Regex, Starwaster, or somebody else is rude/confrontational about it any brushes off my idea no matter how good/bad it is. Sometimes, they insult me for no reason (like calling me "Northrats" instead of "Northstar", or berating me for a "wall of text" when it was literally just lines of code and a few short paragraphs of text...) NathanKell then sometimes comes in, and acts as a peacemaker- but makes promises to add features that are never included (a fix to boil-off, for instance), gives orders not to discuss certain subjects, etc. I don't mean this list to irritate or annoy anybody. I don't do it to build up my own ego, or tear anyone else down. I just do it to show that, from literally some of the very first suggestions I made on this thread, I have been treated with a lack of respect becomes most obvious when compared to how I am treated across most of the rest of this forum, and on other mod threads I have suggested changes to... Meanwhile, NathanKell is a moderator on these forums, and has felt it appropriate to warn me for things like bugging Dreadicon too much (I won't go into more details, since I don't believe we're supposed to publicly discuss Infractions), but has done absolutely nothing when Regex is just brusquely rude (although I'm aware he treats a lot of people that way, it's still not right/acceptable) or even spoken up a little when Starwaster simply ears my ideas apart with little mercy... (even when they are quite valid, and ought not to be torn apart) Regards, Northstar

The explanation of Nuclear rockets is also blatantly wrong- modern NTR designs can achieve TWR's of around 10 when designed for vacuum use (as in the SNTP Program) and around 30 when designed as launch-engines (as in Project Timberwind- which honestly was just ludicrous from a safety/environment standpoint...) http://en.wikipedia.org/wiki/Project_Timberwind Oh well, you can't always have it all... - - - Updated - - - Actually, there *IS* a coded formula. Haven't you ever looked at the entry labeled "Atmosphere Curve" in a KSP engine config? It's expressed as a set of numbers that basically feed into a formula for a curve coded elsewhere in KSP (much like Module Engines references code elsewhere in the game). There *IS* code that is used to generate the current atmospheric performance of engines, it's just not code that is accurate to real life... (Fuel Flow varying rather than Thrust with ISP, for instance...) How so? Many people could have said *PRECISELY* the same thing about coding the Thrust/ISP fix that RealFuels includes, yet we went ahead and did it. Why should making atmospheric ISP vary with throttle-level (or not floor out at 1 atmosphere of pressure) be any different? I'm getting the sense that you're resisting the idea just because it's *MY* idea, and you would have eagerly supported it if it had been made by anybody else. I've gotten very little attention given to *any* of my suggestions made for this mod from you (or to a lesser degree, NathanKell), and the vast majority of them (even simple changes so that parts hold RealFuels tanks instead of LiquidFuel) were simply never implemented at all with no good reason given... I'm only trying to help this mod be all it can be. I'd appreciate it if you cooperated and worked with me towards that more- we're both after the same goals here, and I know you're capable of much better behavior than simply ignoring me... Regards, Northstar

The 3.75 meter "Akula" is actually 1.5 * 1.5 * 1.5 = 3.375 times larger than the "Sethlans 2". Remember, parts grow in all 3 dimensions. That is why I've repeatedly stated that the "Sethlans" reactor only has about 1/4th (23.3%, to be precise) the volume of the Timberwind 75, despite having 62% (1.25/2.03 m) the diameter and 38% (1.5625/4.1209 m^2) the cross-sectional area... Thus, the Akula sees a *MUCH SMALLER* bonus for its scaling: 5.3% (6400/6075) vs. a 20% bonus for the "Setlhans 2" (1800/1500) compared to what you would expect simply from the relative-size compared to the next-smallest reactor. This reflects diminishing-returns from scaling up reactors. The "Akula" is actually the *LIGHTEST* of the Pebble Bed Reactors on a ton-per-cubic-meter basis... That's nice to know. Would it be hard for your to fix that so it's accurate again? I'll soon be checking vs. the actual numbers, though, as I plan to vacuum-test a Sethlans and a SAFE-1500 or KIWI today... Well I already gave you numbers to implement for the new Thermal Power ratings, and if the ISP constant was already changed to 22 in the Boris version (is this new to his version or from the vanilla Interstellar version- and where did you find out what the actual # being used in the calculation is?) then it doesn't need to be up-rated to 21 (I thought about suggesting 22 instead of 21, as the actual most realistic coefficient would be about 21.6, but decided to round down to stay conservative...) Could you get the Thermal Power #'s I gave you implemented into the base code/ part configs? Meanwhile, I'll be working on some #'s for the adjustments to the Thrust/MW based on actual measured Thrust in vacuum (*especially* if the ISP-coefficient was already increased, this needs to be raised: otherwise you will be getting VERY low Thrust/MW compared to real life...) I would like to see the Thrust/MW values I come up with to match real life predictions added to the Extension Config defaults (or the base code) rather than being my own personal settings, obviously... Also, please look into making the info in the R&D/VAB/SPH show up accurately. Players need accurate numbers in order to plan their missions correctly. If a player launches a rocket with a NTR upper-stage (like was proposed in real life for the Saturn V-N), only to discover his ISP is twice what the SPH predicted and his Thrust only half the prediction, he probably isn't going to make it into space that day... (he'll fall back into the atmosphere before he circularizes) If I were testing anything that had been updated since 0.4.1, I would have been sure to have had the latest version. I've been going by the changelog to see when I need to update (which is also why I encourage you to keep the changelog complete+accurate, it doesn't even mention CO2 as a new Thermal/Electric resource, for instance...) Because I use Active Texture Management, any time I update KSP's mods the game takes a *LOT* longer to start the first time after, so I tend to delay it as long as possible... Also, we still need a RealFuels and a Procedural Parts MM patch to allow CO2-storage. Can I suggest you implement a solution something like the following code Dreadicon used to add the option to hold KSP-I LqdWater to any RealFuels tank type that can already hold Kerosene? //Add water tank using KSPI water. (TO-DO: integration with TACLS water without trampling KSPI or TACLS) @TANK_DEFINITION[*]:HAS[@TANK[Kerosene]&!TANK[LqdWater]]:NEEDS[WarpPlugin]:FOR[RealFuels] { +TANK[Kerosene] { @name = LqdWater } } PLEASE NOTE: The "&" symbol is no longer a valid coding character in ModuleManager, and should not be used in any fix you create. It still needs to be replaced with a "," (comma) symbol, which will have the same intended function, in the release-version of RealFuels... Just use the existing RealFuels "LqdMethane" (which replaces the KSP-Interstellar Methane when RealFuels is installed) as a reference for what can hold CO2- since any tank type that can hold liquid Methane should reasonably be able to hold liquid CO2 with a little modification... After you come up with such a fix, submit a pull-request on the RealFuels "KSPI_RF" file that adds the changes, and that way RealFuels compatibility with the new KSP-I resource will be added from the RealFuels end... Such a fix would also work for Procedural Parts when RealFuels is installed. To get it working without would require submitting a pull-request with a similar fix to the base (rather than RealFuels) version of the Procedural Parts mod though... Regards, Northstar

It doesn't matter if the virtual particle promptly vanishes. As long as it was there to be acted on in the first place. Exhaust doesn't have to actually leave a reaction-engine to have generated its thrust- the moment it acted on the appropriate reaction-harvesting surface (such as the engine nozzle of a chemical rocket) its force has been transferred, and it could promptly disappear into nothingness for all anybody cared and the engine would be no worse off for it... Regards, Northstar

You can *EASILY* set the Exit Area to reflect the same Vacuum and Sea-Level ISP as in real life. The shape of the curve will automatically be the same as now in-between as a result (assuming you haven't made any changes to the way it is calculated at intermediate atmospheric pressures for a particular engine). Let's say that with the actual Exit Area, as measured by the nozzle-size of the Poodle engine, we get a Sea-Level ISP of 80 seconds. Yet we know that the real Poodle gets a Sea-Level ISP of 120 seconds. Just reduce the Exit Area used in the calculation accordingly (or add a Nozzle Efficiency term to the equation to implement the necessary adjustment) to a value where Sea-Level ISP = 120 seconds, and all the other performance parameters should match how they are in RealFuels now. Without fixing the formula, we don't have a realistic relationship between Atmospheric ISP and throttle-level, and the Atmospheric ISP bottoms out at 101.325 kPa, and never dips lower. Considering that we already know how to implement the formula such that it perfectly matches *measured* real-world performance (either change the Exit Area to a non-physical value, or add a Nozzle Efficiency term for each engine), why are you so reluctant to change the code for the better? Regards, Northstar

No, I have not taken a look at the SNTP report. The SNTP program never got nearly as far along as the Timberwind program, and as such their data is much less trustworthy. I guess that means the current mass and TWR figures are more reasonable than expected, but the lower ISP than Timberwind can only mean they had a lower operating-temperature (especially since they probably also had a larger rocket nozzle). If there's any uncertainty I'm strongly inclined to err on the side of Timberwind, since once again, their program made it much further along. It's also reasonable to assume that if KSP-I reflects current or slightly-futuristic technology, the reactor core temperatures possible would have at least stayed the same since Timberwind- which is all that is needed for the 1150 second Vacuum ISP with the vacuum nozzle (and the changes to the ISP code). @FreeThinker I got the 17 * SqRt (Exhaust Temp) number from the R&D screen view of the Thermal Rocket Nozzle in my current game. I'm running a slightly older version of the Extension Config (0.4.1) in this save, as I haven't gotten around to updating it yet (and am waiting for the addition of CarbonDioxide to the list of storable resources in RealFuels/Procedural Parts tanks before I do... I asked you about that some time ago- how are we doing on that? A universal tank is nice, but players using RealFuels and/or Procedural Parts are still going to want to be able to store CO2 in the respective tank types... Also, CO2 isn't listed as a Thermal/Electric propellant in the KSP-I Extension Config changelog yet, though I gave you the ISP/Thrust figures you need for that a while back as well...) Did you change the ISP calculation in KSP-I+Extension Config (I don't have anything to do with NearFuture except for the solar panels) since 0.4.1? If not, are you sure that you really changed the formula before? I'm more inclined to go with the formula I see in-game than any changes you attempted to code in before, as the code changes might not have taken hold... I just unlocked NTR's in my current Career save (the one I've been testing in). I'll be testing them in extra-atmospheric conditions some time soon, and will be able to report on what the current Thrust/MW rating is for Thermal Rockets, and what it needs to be to accurately reflect real life with a rocket nozzle this size... (note that the changes also affect Microwave Thermal Rockets- which apparently also produce too little Thrust/MW, as the current relationship is wrong universally for all Thermal Rockets) Regards, Northstar

OK, if it helps any, I can get you a new value for the Thrust/MW as well, just so long as I have a couple values at known Specific Impulses, Thermal Powers, and Exhaust Temperatures... What was the Exhaust Temperature (found by right-clicking on the reactor, or maybe nozzle, as "Heat Exchanger Temperature") at the precise moment you got that Thrust value before? The best way for me to figure this out would be to launch a suborbital rocket (for ease, you don't need to circularize, just make it above the atmosphere...) and fire off any 1 of the unupgraded gen fission reactors with two different fuel types (say LiquidFuel/Hydrogen, and Methane) and take a screenshot wit the context menu for the reactor or nozzle visible in each situation so I can get precise value for the Exhaust Temperature and Thrust at an exact moment in time... It might also be helpful to have data for one each of the Molten Salt Reactors and Pebble Bed Reactors (isntead of 2 different fuel types, but launching such a rocket is a little bit harder), to confirm Thrust/MW is (as I suspect) coded as a function of the Thermal Rocket Nozzle and not somehow of the reactor type... Regards, Northstar

The "Timberwind 75" produced 735.5 kN of Vacuum Thrust, not 647.25 kN. That value is what we would need to aim for in order to get the same TWR (30). However, see my post above- I think it would make a lot more sense to decrease the reactor mass to more reasonable levels for its size (currently it weighs 88% as much as the Timberwind 75 despite only being 1/4th the size) and up-rate the Thermal Power by a smaller amount in order to maintain greater realism and not break the game balance by as much (a heavier reactor with the same TWR can lift a taller stack and has a better Ballistic Coefficient in atmospheric flight- overall it's too good/useful...) That won't actually be a large enough increase in Thermal Power to get a TWR of 30 if you also up-rate the reactor temperature to something closer to the real-world value (3000 K) so that the Vacuum ISP will be closer to the real-world values as well. Currently the Vacuum ISP at full-throttle using Hydrogen is only 582.3 seconds instead of more than 1000 (the Timberwind 75 design had 1000 seconds, but our version has a relatively larger nozzle and should have a better vacuum ISP as a result...) None of those Thermal Power ratings will be high enough with an increase in the reactor temperature either... Why? I rather like the idea of having a nozzle that is large enough for vacuum-usage. If we just give the ISP-calculation a little nudge in the right direction we can make the Vacuum ISP reflect the current nozzle size... (see my post above: we should change the coefficient from 17 to 21 to get a 15% increase in Vacuum ISP) Currently the calculation actually gives *too low* a Vacuum ISP for given reactor temperature- for instance a 3000 K Timberwind reactor had a Vacuum ISP of 1000 seconds, but the same temperature reactor only gives about 931 seconds in KSP-Interstellar... Having a better Vacuum ISP coefficient will not only reflect the actual larger size of the nozzle in-game (and make the NTR's more useful- they're better vacuum stages than launch stages after all- Timberwind was crazy to try and build an NTR launch vehicle, which is where their small nozzle comes from), it will also IMPROVE the sea-level ISP of Thermal Rockets with VERY high sea-level Thrust (such that a larger nozzle would be required to optimally expand the exhaust-stream...) such as high-powered Microwave Thermal rockets... Once you correct the reactor temperatures (which is necessary to correct the ISP, unless you want the ISP calculation's coefficient to grow to some wacky number completely out-of-wack with nozzle size...) the Thrusts won't be right anymore. To get the right performance, you need to fix all 3 calculations (Thermal Power, Vacuum ISP, and Thrust/MW) in one go... Regards, Northstar

OK, so I had a major realization just now, that really needs to be acted upon: The reactor temperatures are HOPELESSLY far off from their real-world counterparts in KSP-Interstellar (and need to be fixed). Previously, I had been assuming the reactor core temperatures were correct, and it was just the nozzle shape/size that led to the Thrust/MW and Vacuum ISP needing to be adjusted. However, some actual reading and checking of the current values reveals that is NOT the case... To start with, here are some real-world temperatures: NERVA "KIWI" Exhaust Temperature: 2683 K (source) NERVA "Phoebus" Exhaust Temperature: 2370 K (source) Timberwind Exhaust Temperature: 3000 K (source) OK, now a little background. There are two types of first-generation fission reactors in KSP. The first are Molten Salt Reactors. The second are Pebble Bed Reactor. The PBR's are capable of higher-temperature performance at the expense of Thermal Power production, and have a higher Thermal Power output but lower operating temperature when fully-cooled (such as when running as a Nuclear Thermal Rocket at full-throttle in-atmosphere). Anyways, NEITHER type of reactor operates in as high a temperature-range as the real-life versions: "KIWI/Aegletes" Molten Salt Reactors Exhaust Temperature: 1674 K "Sethlans/Akula" Pebble Bed Reactors Exhaust Temperature: 1173 K - 2700 K (note that the reactor produces NO POWER at 2700 K) So, the hottest of the gen-1 reactors in KSP-Interstellar (a Sethlans/Akula running at 2700 K) is still 300 degrees colder than the Timberwind reactors, and produces absolutely no ThermalPower power at this temperature... Now, what about the ISP? The Thermal Rocket Nozzle currently uses the function: ISP = 17 * SqRt (Exhaust Temperature) for Hydrogen, with corresponding (and accurately-balanced) decreases in the Specific Impulse (but increases in the Thrust production) with higher Molecular Weight fuels. So, using the above formula for a fission reactor operating on Hydrogen (called "LiquidFuel" in Stock, but re-named as "Liquid Hydrogen" in RealFuels) the ISP is... "KIWI/Aegletes" Molten Salt Reactors: 695.5 seconds (not very impressive- the NERVA-2 based off the NERVA "KIWI" design had 825 seconds Vacuum ISP) "Sethlans/Akula" Pebble Bed Reactors: 582.3 - 883 seconds So, basically, neither reactor operates at even 70% of the Vacuum ISP of the Timberwind reactor (Vac ISP 1000 s) at full-throttle despite having a 2.4 times larger nozzle, and the Pebble Bed Reactor (which is EXACTLY the same type as the Timberwind reactors- and Fractal_UK even stated was based on them) are only capable of VERY small amounts of thrust (high temperatures can be maintained by operating at low throttle) at less than 80% the ISP (and no more than 90% the temperature) of the Timberwind reactors; performance at full-throttle. Several changes are in order: First of all, we need to increase the Thermal Power Production. The names of the Tibmerwind design designations ("Timberwind 45, Timberwind 75, and Timberwind 250") as far as I can tell seem to correspond to the power-production, with one caveat: each produces 10 MW times the number (so 450 MW, 750 MW, and 2500 MW), which lines up well with the power-to-thrust ratio of the earlier NERVA (which had approximately 1/10th the thrust of the Timberwind 75 for 75-85 MW of Thermal Power). So, the new Thermal Power production should be as follows for the "Sethlans" to match the power-density of the "Timberwind 75" reactor design (750 MW for a 2.03 meter diameter) "Sethlans" 1.25m Particle Bed Reactor- 187.5 MW (currently 85 MW) "Sethlans 2" 2.5m Particle Bed Reactor- 1800 MW (currently 770 MW) "Akula" 3.75m Particle Bed Reactor - 6400 MW (currently 4500 MW) I didn't have many numbers to go by for the Molten Salt Reactors, but I did find that the Aircraft Nuclear Propulsion "ARE" reactor was 2.5 MW (it was the *FIRST* Molten Salt Reactor *EVER* built, and looks to have been around the size of the SAFE-1500, but only operated at a temperature of 950 K) in keeping with Fractal_UK's convention of their having lower power-density, I decided on the following: "SAFE-1500" 0.625 meter Molten Salt Reactor- 15 MW (currently 1.5 MW, worse than the "ARE" despite a *MUCH* higher operating-temperature...) "KIWI" 1.25 meter Molten Salt Reactor- 128 MW (currently 40 MW) "Aegletes" 2.5 meter Molten Salt Reactor- 1200 MW (currently 500 MW) "Aegletes 2" 3.75 meter Molten Salt Reactor- 4200 MW (currently 3000 MW) You'll notice that I continued with Fractal_UK's convention of the larger reactors producing proportionally more power for their volume (and also mass). This is out of respect for Fractal_UK's great work, but also because he was onto something- in real reactor designs, it becomes easier to achieve higher power-densities the larger the reactor design. This is part of why it's very difficult to build an efficient and high-performance reactor that could fit in a truckbed, but much easier to build one that fits in a large power plant, for instance... Second, the operating temperature needs to be increased.... "Sethlans/Akula" Proposed Heat Exchanger Temperature Range- 3000 - 3600 K (base temperature selected to match the Timberwind reactor exhaust-temperatures) "SAFE/KIWI/Aegletes" Proposed Heat Exchanger Temperature- 3200 K I kept with Fractal_UK's convention of allowing the Molten Salt Reactors to operate at higher temperatures than the Pebble Bed Reactors at full-throttle, but allowing the Pebble Bed Reactors to operate at potentially higher temperatures at lower throttle. I narrowed the range of temperatures quite a bit, though, as the new temperatures are pushing up against the limits of what is possible with current materials-science (aircraft ceramics can be made that are safe up to 4000 K, but some components are much more heat-sensitive than this...) Alright, so with the new operating-temperatures and Thermal Power levels, what are we up to for performance? Let's take a look at the "Sethlans" Reactor again (since we have the best model for it- it appears to be a 1/4th scale of the Timberwind 75) Hydrogen ISP = 17 * Sqrt (3000) = 931.1 seconds (Vacuum ISP) That's a little low... The Timberwind reactors had 1000 seconds of Vacuum ISP with the same exhaust temperature, but their nozzles were relatively smaller. Ours are optimized for vacuum at this power-level (the same nozzle would work well at sea-level at much higher power-levels), and so should have better ISP than Timberwind, not worse... I suggest changing the Thermal Rocket Nozzle ISP-calculations (which all take the form M * 17 * SqRt (Exhaust Temp), where "M" is the correction-factor for the fuel's Molecular Mass) to the following: Vacuum ISP = M * 21 * SqRt (Exhaust Temp) This should correct the Vacuum ISP to about 1150 seconds, which represents a 15% improvement in the Vacuum ISP vs. a rocket with a Timberwind-sized nozzle (a little conservative, but reasonable for a rocket with 2.4 times the nozzle area and an inefficient/short shape...) Anyways, how are we doing for Vacuum Thrust? Vacuum Thrust = 2 * (Thermal Power / Exhaust Velocity) + (Exit Area)(Exhaust Pressure) = 2 * (187500 kW / 9131.2498 m/s) = 41.07 kN + (Exit Area)(Exhaust Pressure) Err, not great... We're expecting 91.9375 kN of thrust just to match the Timberwind performance, so we're at about 44.7% of the expected value just using the ISP of 931 seconds (and even worse with 1150 seconds). However, we still have additional Thrust from the nozzle to account for- which the Timberwind reactor also benefited from... With our relatively larger nozzle, we're hoping for about 105.728 kN of Vacuum Thrust assuming a 15% increase in Vacuum ISP from the larger nozzle... Here's where some actual in-game testing will be necessary- by what factor (if any) does KSP-Interstellar multiply (2 * Thermal Power / ISP * 9.80665) to obtain the Thrust for a given engine? Most likely, the Thrust will be lower-than-expected even before we increase the ISP to account for the larger rocket nozzle. And because KSP-Interstellar is using a model that ties Specific Impulse and Thrust together, so after we fix the ISP-calculation the Thrust will dip even lower before we also institute a correction-factor there so that the Thrust also reaches expected values (once again, 105.728 Vacuum Thrust for this reactor/fuel combination using a 1.25 meter Thermal Rocket Nozzle...) We will need to fix this for ALL the Thermal Rocket Nozzle parts... Sorry for the long post... Here's a quick summary of what needs to be done... Summary: - Increase the Thermal Power ratings to the numbers provided - Reduce all reactor masses by 75% (to 1/4th their current values). Reduce Thermal Rocket Nozzle masses by 75% as well (will still lead to a slightly heavier reactor+nozzle pair than in real life.) - Increase the ISP-calculation to M * 21 * SqRt (Exhaust Temp) for all Thermal Rocket Nozzles (the ISP calculation is NOT found in a part file- is in Interstellar.dll) - Increase the Thrust/MW calculation to generate expected performance (like the actual code for Thermal Rocket Nozzle ISP, it is not found in the part files- but in the Interstellar.dll) Regards, Northstar

I mean the following: (1) ALL reactors produce too little Thermal Power for their mass and volume. Even if we reduced the mass to levels that would be more appropriate for their size (the Sethlans Particle Bed Reactor- the 1.25 meter version of the Akula line I've been focusing on lately- weighs 2.2 tons with its nozzle in KSP-I, whereas the Timberwind 75 it is based on weighs 2.5 tons but has 4 times the volume...) their Thermal Power production (and thus TWR as Thermal Rockets) is still much too low for their size. I suggest reducing mass AND increasing Thermal Power until a Sethlans weighs 0.625 tons without its nozzle and produces 1/4th the Thermal Power of the Timberwind 75, for instance. (2) It turns out, upon close inspection of the relative sizes of the nozzles, that they are more than 2.4 times the size of the ones used on Timberwind relative to the reactor size. This means that the Vacuum Specific Impulse (and Vacuum Thrust- which is related by Vacuum Thrust = Vacuum ISP * Mass Flow Rate) is considerably less than it should be. We have two options- we can either ignore the actual size of the nozzles, and pretend they are the same relative-size as the nozzles on Timberwind (which doesn't make a lot of sense- the Timberwind engines had nozzles designed for use in a rocket first-stage, whereas the Thermal Rocket Nozzles are clearly designed for vacuum at the Mass Flow Rates of a fission reactor), or we can adjust the Vacuum ISP and Thrust/MW upwards. I suggested approximately 20% (so that basically the Vacuum ISP drives a 20% increase in the Vacuum Thrust...) before, but actually the re-balancing needs to be more drastic than that... (see part #2 of this post) The more I think about it, the more I prefer the latter solution of adjusting the Vacuum ISP and Thrust/MW, because the values are just so far off (20% was a HUGE under-estimate as it turns out.... See below) You can basically forget the second comment of mine you quoted- that was from AFTER I had confirmed that the relationship between Thrust and Thermal Power was accurate for a Timberwind or NERVA Reactor, but *BEFORE* I realized the nozzle size was relatively larger for the reactor-size than what was used on either system (the NERVA had a relative smaller nozzle because its total Mass Flow Rate was much lower, the Timberwind because it was designed for atmospheric use...) It's worth double-checking the actual operating ISP of a Sethlans Reactor in vacuum before taking anything I say about the Vacuum ISP as the word of God (in fact, I already have KSP open- I think I'm going to go and do it now). It's possible that Fractal_UK already adjusted the ISP of the Sethlans/Akula Reactor series to match the predicted vacuum performance of a reactor as hot as the Timberwind, but with a nozzle designed for vacuum (the target ISP should be about 1200). The Thermal Power production and Vacuum Thrust/MW *definitely* need to be up-rated though... That's because I consider Antimatter Reactors so far beyond the realm of current scientific knowledge that I don't even bother trying to understand/explain them. For all we know, by the time the Kerbals have Antimatter Reactors maybe they have some mystical material that absorbs all that gamma-radiation and such and converts it directly into heat. I just don't feel qualified to theorize about Antimatter Reactors in any way, shape, or form. Personally, I never use them. Fission Reactors, on the other hand, we have extensive experience with in the real world (even ones designed for use in rocketry), and I use in KSP-Interstellar all the time... Regards, Northstar