[0.90] KSP Interstellar port maintance thread

[crystalkalem]

i dont think this works with newer mod manager version. idk.

[Drew Kerman]

So although this mod adds radiation it doesn't actually do anything right? Watching the new K-radiation mod and wondering if anything will conflict

[FreeThinker]

i dont think this works with newer mod manager version. idk.

Why not? what is needed? does it need to be standalone?

- - - Updated - - -

So although this mod adds radiation it doesn't actually do anything right? Watching the new K-radiation mod and wondering if anything will conflict

Probably not, the Radiation in Interstellar does nothing but count some numbers based on your location in space. But they could interact with eachother, like adding some interface to ORS to readout the current radiation levels of nearby radioactive reactors, that way, a Kerbal on EVA should properly burn to a crisp if a reactor starts to spray its deadly radiation. Could also be used as a weapon, to kill the crew of nearby crewed vessels, just point your aft at nearby ship and they will all die in a matter of minutes.

Edited February 8, 2015 by FreeThinker

[Northstar1989]

Yes but it now seems the Thermal nozzle connected to a Fusion reactor get's screwed by its of high ISP (3398), causing low trust (389.4 kN) which is barely sufficient to overcome atmospheric pressure @ Kerbin surface. At least for thermal noozles there might be some justification to partially convert a ISP into trust and then apply our atmospheric presume effects.

Wait, the Fusion Thermal Rocket's Vacuum ISP is over 3000? Hold on there a minute...

With Fractal_UK's changes, ISP was supposed to cap at 3000 seconds for Hydrogen (and less in inverse-proportion with the square root of (Molecular Mass of propellent/ Molecular Mass of H2) for other propellents) and the remaining Thermal Power *WAS* supposed to get converted into Thrust. If this change hasn't already been implemented, I *STRONGLY* suggest you go and do it. The 2.5 Fusion Reactors *SHOULD* have a Mass Flow Rate that is:

(Old ISP/New ISP)^2 = New Mass Flow Rate (this is as E = 1/2 m v^2, with m representing Mass Flow Rate, and E remains unchanged as the Thermal Energy is the same)

(3398/3000)^2 = 1.2829 times higher than what it would be at 3000 seconds

Then, if you multiply the new Mass Flow Rate by the 3000 second ISP (as Thrust = Mass Flow Rate * Specific Impulse), you get the following new Thrust-rating at 3000 s:

389.4 kN * (3000/3398) * (3398/3000)^2 = 389.4 kN * (3398/3000) = 440.7206 kN

The extra heat that can't be poured into a higher Exhaust Velocity doesn't simply disappear- it gets converted into extra thrust instead... So, the new Thrust for any Thermal Rocket when changing the ISP and keeping the same total Thermal Energy (and propellent), becomes:

Old Thrust * (Old ISP/ new ISP) = New Thrust

Note that the value of (Old ISP/ New ISP) is *ALWAYS* greater than 1 when *reducing* the ISP (as the extra Thermal Energy doesn't have to simply disappear- it goes into a higher maximum possible Mass Flow Rate), and *ALWAYS* less than 1 when *increasing the ISP (heating less mass up to a higher temperature)...

Also, the maximum ISP of other propellents should be lower than of Hydrogen (as the ISP will be lower at the same temperature). The Molecular Mass of Methane is 16.04 and of H2 is 2.01588, so the maximum ISP with a Thermal Rocket Nozzle should be:

3000 / [(16.04 / 2.01588)^(0.5)] = 1063.5 seconds

Whereas it was previously:

3398 / [(16.04 / 2.01588) ^(0.5)] = 1204.6 seconds

Remember that this is just the equation for changing the ISP when switching between two different propellents at the same temperature [ New ISP = Old ISP / sqrt (New Molecular Mass / Old Molecular Mass) ] as the per-particle energy (E = 1/2 m v^2) is the same between the two...

As with Hydrogen, the remaining thermal energy gets dumped into increasing mass-flow rate (and Thrust) so the Thrust of a 2.5 meter fusion using Methane (or any different propellent) at the new temperature should be:

(New ISP/ Old ISP) * New Mass Flow Rate = (New ISP/Old ISP) * (Old ISP/ New ISP)^2 * Old Thrust = Old Thrust * (Old ISP / New ISP) = New Thrust

Remember that (Old ISP / New ISP) ^2 is the PROPORTIONAL increase in mass-flow rate (so if = 1.2, Mass Flow Rate is 20% higher), which is why you multiply in the Old Thrust... Anyways, for Methane the New Thrust becomes:

(1063.5 / 1204.6) * (3398 / 3000)^2 = 1.1327 times what it was before (13% higher)

And as the Old Thrust was 1098.44 kN, the New Thrust for Methane is:

1244.2 kN

This may *SEEM* a little high, but notice that the new Mass Flow Rate is 28.3% higher what it was before, and the ISP is only 11.7% lower...

ALL of these calculations come from manipulating E = 1/2 m * v^2, as the amount of thermal energy per-particle and in the total exhaust-stream is fixed for a given temperature (which is what actually defines the 3000 seconds ISP-cap for a Thermal Rocket- the highest exhaust temperature the components can handle without melting...)

Another problem might be that KSPI Thermal Noozles produce too little thrust in General. Just take a basic small nuclear reactor (1.25m) for example which combined with a thermal noozle produces much less power (8.75 kN) that an equivalently sized stock nuclear thruster (60 kN). In my own KSP Interstellar Near Future Integration I correct this by making the conversion from heat into trust much more efficient. But I kept wondered if there is any basis for this large difference in perforce in the real world.

There are two decent reasons the NERVA engines have so much better TWR in stock KSP.

First of all, the masses are COMPLETELY WRONG in Stock. Like the ion engine, it was probably changes as such for gameplay reasons. However, a NERVA with 60 kN of thrust should weigh CLOSE TO 6 TONS (and in fact it does so with RealFuels + Stockalike installed), making the engine's TWR barely more than 1! NERVA was *not* the peak of real-world nuclear thermal rocket designs, despite what some people think. For that, you need to look to Project Timberwind, which developed Nuclear Thermal Rocket designs with a TWR of up to 30 using Particle Bed Reactors (that would equate to a 60 kN rocket only weighing 200 kg- but Timberwind reactors were designed to *MUCH* higher thrust-levels than 60 kN...)

The second reason, besides the stock KSP NERVA's being less than a fourth the mass of their real-world analogs for the thrust they produce (although not out of the range of what is achievable with real NTR's- a KSP NERVA has a TWR of only a little over 4, compared to Timberwind's 30... MOST engines in KSP have very low TWR's compared to real life, though...) is that the NERVA reactors were designed for only very limited operating life. Most were'nt designed to operate more than an hour or two at full-throttle with just a handful of ignitions, tops, and carried a very small amount of nuclear fuel (which is heavy) and were built to VERY slim engineering margins as a result. So, this tended to lead to lighter NTR's as well than the ones in KSP-I (which can potentially operate for HUNDREDS of hours at full-power with the fuel loads they carry...)

I will agree that the TWR values are *EXTREMELY* low in KSP-Interstellar, though.

The Akula-series reactors (which are supposed to be direct analogs of the Timberwind reactors) do *NOT* get a TWR of 30 when coupled with a Thermal Rocket Nozzle. It's not that their ISP is too high (it's *NOT*- in fact the Timberwind 75 would have achieved a Vacuum ISP of 1000s and a sea-level ISP of 890 seconds due to its VERY high Exhaust Velocity *AND* Mass Flow Rate), it's that their Thermal Power production (and resultant Mass Flow Rate) is *MUCH TOO LOW* for a Particle Bed Fission Reactor...

I can understand that Fractal_UK didn't want to make the KSP-I NTR's too powerful relative to stock, but in doing so he created a reactor with a MUCH lower power-density than in the real world... A Timberwind 75 (the *SMALLEST* of the Timberwind designs- 2.03 meters in diameter) could produce 735.5 kN of Thrust (at an ISP of 1000s) using Hydrogen- which is MORE Thrust than a fusion-reactor currently does in KSP-Interstellar!

It's always nice when the real world is so much more awesome than our own attempts to imitate it- kind of like when in the movie "Armageddon" they tried *so hard* to scare the audience when they talked about the force of the impact of the dinosaur-killing asteroid, and actually ended up under-stating the explosive force by something like 10,000 fold...

No it won't give any "performance" advantages, it just another simple multiplication, part of a much more complex calculation which is something a PC is really good at (it can use both L1 cache and pipelining). Also it's trivial for code complexity, it actually makes the code clearer since it now uses real world quantity (m2) which everybody can understand instead of a slight more convenient (kN/atm). Besides, I already have released several versions, it would cause backward incompatibility issues if I switched back.

That's good to know. If the performance advantage is insignificant, maybe you *DO* want to keep Exit Area in terms of m^2 and atmospheric pressure in kPa like I suggested before reversing my own opinion...

Regards,

Northstar

P.S. Note that the figures for the NERVA TWR come from that of the Saturn V third-stage designed to work on NERVA engines... The Thrust of the entire stages was 333.6 kN, whereas the mass was 34.019 metric tons. However, this included some (relatively light) fuel tank mass and (relatively heavy) radiation-shielding. The NERVA-2 design, which was just nearing completion at the end of the NERVA program, would have produced 867 kN for the same exact weight, so clearly a TWR of just over 1 (for NERVA-1) was far from the limits of the NERVA design-type...

Edited February 8, 2015 by Northstar1989

[FreeThinker]

ALL of these calculations come from manipulating E = 1/2 m * v^2, as the amount of thermal energy per-particle and in the total exhaust-stream is fixed for a given temperature (which is what actually defines the 3000 seconds ISP-cap for a Thermal Rocket- the highest exhaust temperature the components can handle without melting...)

Ok, so that where the magic number 3000 comes from. The method of limiting ISP to 3000 and convert to trust is already implemented, I just changed this constant into a configurable setting called MaxThermalNozzleIsp, which I put at 5000 to allow AntiMatter reactors to reach higher ISP scores. Players were complaining that antimatter reactors do not give sufficient edge when it comes to thermal engines. I will change the setting back to 3000 but the antimatter reactor seems incorrectly implemented. Right now, antimatter reactor are implemented as simple heat producing machine, like nuclear reactors are. This seem not accurate because from my understanding a large part of antimatter annihilation is released in radiation and charged particles.

Antiproton annihilation reactions produce charged and uncharged pions, in addition to neutrinos and gamma rays. The charged pions can be channelled by a magnetic nozzle, producing thrust. This type of antimatter rocket is a pion rocket or beamed core configuration. It is not perfectly efficient; energy is lost as the rest mass of the charged (22.3%) and uncharged pions (14.38%), lost as the kinetic energy of the uncharged pions (which can't be deflected for thrust), and lost as neutrinos and gamma rays

Edited February 8, 2015 by FreeThinker

[FreeThinker]

I can understand that Fractal_UK didn't want to make the KSP-I NTR's too powerful relative to stock, but in doing so he created a reactor with a MUCH lower power-density than in the real world... A Timberwind 75 (the *SMALLEST* of the Timberwind designs- 2.03 meters in diameter) could produce 735.5 kN of Thrust (at an ISP of 1000s) using Hydrogen- which is MORE Thrust than a fusion-reactor currently does in KSP-Interstellar!

At least we agree on something, but how can we fix this inbalance, or at least give the player an option to experience an more realistic performance without overpowering.

For example, what performance would you expect of a 1.25 Nuclear Reactor coupled with a thermal noozle? 20, 40, 60, 80, more?

Edited February 8, 2015 by FreeThinker

[Northstar1989]

At least we agree on something, but how can we fix this inbalance, or at least give the player an option to experience an more realistic performance without overpowering.

For example, what performance would you expect of a 1.25 Nuclear Reactor coupled with a thermal noozle? 20, 40, 60, 80, more?

I would expect a TWR of about 30 for an Akula-style Particle Bed Reactor coupled with a Thermal Rocket Nozzle (as it is modeled after Project Timberwind reactors) in the 1.25 meter size-range (a Kerbal-scale analog of the 2.03 meter Timberwind 75).

The reactor weighs 1.8 metric tons, and the 1.25 meter Thermal Rocket Nozzle weighs 0.4 metric tons. So I would expect the combination to produce 647.24 kN of Thrust in Vacuum at a Vacuum Specific Impulse of 1000 seconds:

2.2 * 9.80665 * 30 = 647.25 kN

Which means, using the measured/known sea-level ISP of 890 seconds:

647.25 * 0.89 = 576.04 kN at sea-level

It's worth running the numbers with out current Exit Area for the 1.25 meter Thermal Rocket Nozzle to see how our prediction compares to the actual sea-level ISP of a Timberwind 75:

Thrust = Vacuum Thrust - Exit Area * Background Pressure

Thrust = 647.25 kN - 0.7657 (m^2) * 101.325 (kPa) = 569.7 kN

Only 7 kN less than the known value. Not bad considering out current Exit Area is only a first-guess...

For comparison, the Timberwind 75 produces 735.5 kN vacuum, 654.6 kN sea-level: our 1.25 meter reactor produces 88% the power despite only having 39% the cross-sectional area and 23% the absolute size. So maybe a reduction of the absolute mass of the reactor+nozzle (to 583.690 kg for BOTH parts combined) and the Thrust (to 171.7 kN vacuum, 152.8 kN sea-level) are in order. In which case a large reduction of our Exit Area (to 0.1867 square-meters to generate matching performance) is also in order...

Regards,

Northstar

P.S. Obviously you can't do both of these things. Pick one. I suggest the first choice (increasing the Thermal Power of the reactor), because it doesn't involve reducing the mass of the reactor, nozzle, and Exit Area to much smaller values... I can get you the new Thermal Power value to use soon- or you can calculate it yourself based on the current, existing, and CORRECT relationship between Thermal Power and Thrust-production in KSP-Interstellar (DON'T change that- it's based on real world physical laws!)

Edited February 8, 2015 by Northstar1989

[FreeThinker]

It's worth running the numbers with out current Exit Area for the 1.25 meter Thermal Rocket Nozzle to see how our prediction compares to the actual sea-level ISP of a Timberwind 75:

Thrust = Vacuum Thrust - Exit Area * Background Pressure

Thrust = 647.25 kN - 0.7657 (m^2) * 101.325 (kPa) = 569.7 kN

Only 7 kN less than the known value. Not bad considering out current Exit Area is only a first-guess...

For comparison, the Timberwind 75 produces 735.5 kN vacuum, 654.6 kN sea-level.

Regards,

Northstar

So basically we can conclude that trust reduction based on ExitArea works very well for real world nuclear Thermal Nozzle performance. But that also means that applying the same trust reducing mechanism to KSPI current thermal engines makes no sense at all without the corresponding performance !

Now we need to somehow Kerbalize this power to levels that fit in a Kerbal universe. You mentioned earlier that all trusters have less performance than their real world equivalent version. Perhaps we can use this to Kerbalize real world thermal power to more acceptable levels, would 1/4 work (size of Kerbal compaired to Human)?, or 1/10 (Size of Kerbin compaired to Earth)

Edited February 8, 2015 by FreeThinker

[Drew Kerman]

Probably not, the Radiation in Interstellar does nothing but count some numbers based on your location in space. But they could interact with eachother...

Ok that's what I thought. Yea, I'm hoping you and the K-rad guy can get some inter-op going. I like where his discussion is headed in regards to making the radiation component something that can be easily referenced by other mods.

[Olympic1]

I updated my CTT config for KSPI (again ). Thank you FreeThinker for the requests.

Download

Changes:

Command:

* Moved the Science Laboratory from "Advanced Science Tech" to "Scientific Outposts".

Electrical:

* Moved the Antimatter Initiated Reactor from "High Energy Science" to "Exotic Reactions".

* Moved the Flat Radiator from "Advanced Electrics" to "Nuclear Power".

* Moved the circradiatorKT from "Advanced Electrics" to "Nuclear Power".

* Moved the circradiatorKT2 from "Advanced Electrics" to "Large Scale Nuclear Power".

* Moved the circradiatorKT3 from "Advanced Electrics" to "Large Scale Nuclear Power".

* Moved the Large Flat Radiator from "Advanced Electrics" to "Large Scale Nuclear Power".

* Moved the Radial Heat Radiators from "Advanced Electrics" to "Large Scale Nuclear Power".

* Moved the Heat Radiators from "Large Electrics" to "High Energy Nuclear Power".

Engines:

* Moved all the Magnetic Nozzles from "Advanced Plasma Propulsion" to "High Efficiency Nuclear Propulsion".

* Moved the Thermal Rocket Nozzles from "High Efficiency Nuclear Propulsion" to "Improved Nuclear Propulsion".

Science:

* Moved the IR Telescope from "Experimental Science" to "Extended Duration Science Tech".

Utility:

* Moved the Gas Chromatograph Mass Spectrometer from "Advanced Science Tech" to "Specialized Science Tech".

* Moved the Liquid Chromatograph Mass Spectrometer from "Advanced Science Tech" to "Specialized Science Tech".

[Northstar1989]

So basically we can conclude that trust reduction based on ExitArea works very well for real world nuclear Thermal Nozzle performance. But that also means that applying the same trust reducing mechanism to KSPI current thermal engines makes no sense at all without the corresponding performance !

Now we need to somehow Kerbalize this power to levels that fit in a Kerbal universe. You mentioned earlier that all trusters have less performance than their real world equivalent version. Perhaps we can use this to Kerbalize real world thermal power to more acceptable levels, would 1/4 work (size of Kerbal compaired to Human)?, or 1/10 (Size of Kerbin compaired to Earth)

Increasing the Thermal Power to 1/4th the Thermal Power of the Timberwind 75 would make sense (like I suggested in my 2nd paragraph before) as the reactor is only approximately 1/4th (23% to be precise) the volume of the Timberwind 75.

Increasing the Thermal Power to roughly 1/4th the Timberwind 75 for the 1.25 meter Akula-line reactor ("Sethlans") as well as reducing the mass of the reactor to about 625 kg (this is a good bit more than 1/4th the mass of the Timberwind 75- which was 2.5 tons *WITH THE NOZZLE*) makes sense to me... The nozzle currently weighs 400 kg, and should have its mass reduced as well- the current mass is just unreasonable for the size of the nozzle, and is out-of-proportion with the new reactor mass...

However the nozzle Fractal_UK designed for the Thermal Rockets are rather large for their diameter- in fact they are 95% the size of Timberwind (we can back-calculate the nozzle area from the atmospheric performance, using the equations above) for only 39% the cross-sectional area. They CLEARLY aren't designed for sea-level performance.

The Timberwind 75 had an effective Exit Area of only .798 square-meters (for a 2.03 meter diameter rocket!), based on its atmospheric performance. The current 1.25 meter Thermal Rocket Nozzle has an effective Exit Area of 0.7657 square-meters: based on using the NovaPunch2 3-Segment Advanced SRB (which has a nearly identical nozzle shape and size relative to its diameter, and is in turn closely based on the performance of the Ares V solid rocket designs) as a model for the 2.5 meter Thermal Rocket Nozzle, and scaling-down. Notice I use the term "effective" as the SRB it is based on has some Nozzle Inefficiency (and the Thermal Rocket Nozzle can be expected to as well...)

Having a large nozzle isn't purely a drawback, though. As I discussed before, rocket nozzles exist for the sole purpose of increasing the Exhaust Velocity of the rocket (which is directly related to the Vacuum ISP). This both helps (through raising the Vacuum ISP) and hurts (through raising the Exit Area) the atmospheric ISP. For any given atmospheric pressure, there is an ideal size of exhaust nozzle at which you obtain the highest atmospheric ISP- beyond which the larger Exit Area outweighs the higher Vacuum ISP in the equation:

Thrust = Vacuum ISP * Mass Flow Rate * g - Exit Area * Background Pressure

Usually rockets nozzles are designed for lower atmospheric pressures than where they begin operation- a launch stage might be optimized for atmospheric pressure at a 10-15 km altitude, for instance, as it will spend part of its time at a lower altitude and part of its time at a higher altitude than this...

Nevertheless, the size of the Thermal Rocket Nozzle in KSP-Interstellar is best-suited for operation in vacuum at the very low Mass Flow Rates of a fission Nuclear Thermal Rocket (keep in mind the higher your Mass Flow Rate, the larger your optimal rocket nozzle should be- which is why the same Thermal Rocket Nozzle works perfectly well for a Microwave Thermal Rocket at high power-levels at sea-level...)

You were onto something in your NearFuture-Interstellar config, FreeThinker. The Thermal Rocket Nozzle currently produces too little Thrust/MW. This is due to the rocket nozzle being large enough to significantly increase the Exhaust Velocity...

To account for the benefits of the very large (and HEAVY- a 1.25 meter nozzle weighs 400 kg) nozzle for the Thermal Rockets we need to increase *BOTH* the Thrust/MW and the Vacuum ISP of the Thermal Rockets by approximately 56.8% (as the current nozzle is 146% larger for the cross-sectional area than the Timberwind 75, and thus I assume has a 146% higher Expansion Ratio... Don't make me delve into the math of how this affects total Vacuum Thrust/ISP- because I barely understand it myself, and got lucky in running the numbers here...)

Fractal_UK's current numbers for Vacuum Thrust and ISP currently assume a nozzle with the same size-relationship to its Mass Flow Rate as the Timberwind- but the current nozzles are 2.46 times as large (146% larger) for the rocket cross-sectional area (which is 39% that of the Timberwind 75...) A larger nozzle means you increase Vacuum ISP and Vacuum Thrust values with the same reactor, at the expense of Exit Area and thus sea-level ISP...

A 56.8% increase in the Vacuum ISP and Thrust with the current Exit Area will still lead to a much lower sea-level ISP than the real rockets (as you are putting 39.2% the Thrust through 95% the Exit Area) but will lead to better vacuum-performance than the real Timberwind designs. Which is fine by me- the Timberwind NTR's were *DESIGNED* as launch engines, to operate best at sea-level. If the Timberwind reactors/nozzles had been designed for vacuum-use, they would have had larger nozzles and even higher vacuum ISP than 1000 seconds (but lower sea-level ISP than 890 seconds) as a result...

Maybe none of this is what you meant by "Kerbalizing" the performance- but this is how you make the performance REALISTIC. The current reactors are far too heavy for their size, produce too little Thermal Power for their mass, and have too low of a Vacuum ISP and Thrust/MW for having such large nozzles...

EDIT: Further reading indicates that short nozzles like the one used in the Thermal Rocket Nozzle are maybe only half as efficient at increasing thrust as longer ones with a smaller angle... So, Vacuum Thrust/ISP should only be increased maybe 20-25% to reflect the larger nozzle- I'd go with 20% to stay conservative (for a target vacuum ISP of 1200 seconds using Hydrogen with the Sethlans reactor at maximum Thermal Power... Note that the reactor loses Thermal Power but gains temperature and ISP if WasteHeat is allowed to accumulate...)

Regards,

Northstar

Edited February 9, 2015 by Northstar1989

[not-a-cylon]

I'm not sure if this is a bug, or if it's just me not doing stuff right...

Using the Omega Fusion Reactor with a thermal turbojet in atmospheric mode shows a higher TWR in the VAB than when in actual use both in Mechjeb and KER. Why is the maximum TWR lower in flight?

Edited February 9, 2015 by not-a-cylon

[Northstar1989]

I'm not sure if this is a bug, or if it's just me not doing stuff right...

Using the Omega Fusion Reactor with a thermal turbojet in atmospheric mode shows a higher TWR in the VAB than when in actual use both in Mechjeb and KER. Why is the maximum TWR lower in flight?

Two words for you: velocity curve

The Thermal Turbojets, like all jets in KSP, currently lose Thrust as the velocity of your spacecraft in-atmosphere increases. In real life, this is a result of either the intake air superheating due to compression-heating, or attempting to perform combustion at supersonic speeds. If I'm not mistaken, using Precoolers on your intakes somewhat reduces the effect of the velocity curve in KSP-Interstellar (I know precoolers have that effect in real-life: it's the reason SABRE can operate at up to Mach 5 with a turbojet- a type of jet design that would normally only work well up to about Mach 2.5 without precooling...) Or, maybe I'm thinking of Advanced Jet Engines or FAR... Anyways, if this effect of precoolers isn't in KSP-Interstellar, it should be...

http://en.wikipedia.org/wiki/Precooled_jet_engine

Edited February 9, 2015 by Northstar1989

[not-a-cylon]

Two words for you: velocity curve

The Thermal Turbojets, like all jets in KSP, currently lose Thrust as the velocity of your spacecraft in-atmosphere increases. In real life, this is a result of either the intake air superheating due to compression-heating, or attempting to perform combustion at supersonic speeds. If I'm not mistaken, using Precoolers on your intakes somewhat reduces the effect of the velocity curve in KSP-Interstellar (I know precoolers have that effect in real-life: it's the reason SABRE can operate at up to Mach 5 with a type of jet design that would normally only work up to about Mach 2.5 without precooling...) Or, maybe I'm thinking of the Advanced Jet Engines mod...

Even right after takeoff, my MJ/KER TWR is shown lower than the projected one in the VAB.

[smart013]

Guys, although i understand and appreciate the great effort made to keep KSP interstellar up and running against all odds (and there seem to be a lot of these) i am really confused about all the modifications and forks and all the "little" changes that got incorporated since Fractal is afk.

So simple question: what version of interstellar is right now the one nearest to fractals original conception, including incorporated flaws by himself, that works in .90? What gives me the purest fractal experience, without including foreign concepts, ideas or changes?

Again, great to have the choice. But there is a saying in germany about "too many cooks mess up the pie". It seems that its simply irresistible for many to not only maintain interstellar in its pure form, but to use its weak moments to include own concepts and ideas, and while thats great its not why i want to play fractals mod.

Besides, great work, hope you get my vibe and take no offense.

[Atrius129]

Two words for you: velocity curve

The Thermal Turbojets, like all jets in KSP, currently lose Thrust as the velocity of your spacecraft in-atmosphere increases. In real life, this is a result of either the intake air superheating due to compression-heating, or attempting to perform combustion at supersonic speeds. If I'm not mistaken, using Precoolers on your intakes somewhat reduces the effect of the velocity curve in KSP-Interstellar (I know precoolers have that effect in real-life: it's the reason SABRE can operate at up to Mach 5 with a turbojet- a type of jet design that would normally only work well up to about Mach 2.5 without precooling...) Or, maybe I'm thinking of Advanced Jet Engines or FAR... Anyways, if this effect of precoolers isn't in KSP-Interstellar, it should be...

http://en.wikipedia.org/wiki/Precooled_jet_engine

Already done. From KSPi OP:

KSP Interstellar

Magnetic Nozzles, ISRU Revamp, Improved Stock Science Integration - Version 0.13

-Snip-

Version 0.9
-Snip
-New [B]precooler[/B] module, replaces the stock radial engine  body (which doesn't do anything) - atmospheric engines overheat at very  high velocities unless [B]precoolers[/B] are directly attached to intakes
-Atmospheric performance of engines vastly improved
-Snip-

Edited February 9, 2015 by Atrius129

[not-a-cylon]

example:

in SPH TWR 3.26

in flight TWR 2ish (MJ and KER disagree)

TWR doesn't change after launch clamps are released and craft is moving.

ninja edit:

it looks like the the TWR is somehow affected by altitude, which makes me think that ISP directly affects TWR in some way- the displayed TWR looks pretty close to what the projected one would be.

Is this all intentional? If so, how can I figure out my atmospheric TWR from a standstill before I launch my craft? I need to be able to have accurate numbers to make my physics correct sci-fi atmospheric to warp vtol spaceplanes

Edited February 9, 2015 by not-a-cylon
clarity

[FreeThinker]

So simple question: what version of interstellar is right now the one nearest to fractals original conception, including incorporated flaws by himself, that works in .90? What gives me the purest fractal experience, without including foreign concepts, ideas or changes?

Well I can understand your confusion, I'm a bit confused as well since I expected Boris to return a few weeks after he went AWOL like Fractal. He told me he was busy with school and would return after he had the time. But to answer your question, Right now Boris KSPI 0.90 Maintenance + KSPI 0.90 Extended is still 99% to Fractals experience, at least that's what I aim for.

To stop the confusion, perhaps I should start a new fresh Post offering a single download with proper CTT and CKAN support. What do you think?

- - - Updated - - -

Is this all intentional? If so, how can I figure out my atmospheric TWR from a standstill before I launch my craft? I need to be able to have accurate numbers to make my physics correct sci-fi atmospheric to warp vtol spaceplanes

Well from the looking at the code I know that the Athmospheric curve only get's updated outside the editor. Tools like Kerbal Engeneer Redux cannot work because they recieve the wrong numbers. As NorthStart correctly pointed out, the velocity curve (and ISP curve) is constantly beeing updated during flight, therefore trying to predict the thrust in the editor is imposible unless some special facilities (API) are exposed which can be interogated by those tools.

Edited February 9, 2015 by FreeThinker

[FreeThinker]

EDIT: Further reading indicates that short nozzles like the one used in the Thermal Rocket Nozzle are maybe only half as efficient at increasing thrust as longer ones with a smaller angle... So, Vacuum Thrust/ISP should only be increased maybe 20-25% to reflect the larger nozzle- I'd go with 20% to stay conservative (for a target vacuum ISP of 1200 seconds using Hydrogen with the Sethlans reactor at maximum Thermal Power... Note that the reactor loses Thermal Power but gains temperature and ISP if WasteHeat is allowed to accumulate...)

Note that the relationship between Thermal Power of the reactors and Thrust production *IS CORRECT* and should not be changed. What is inaccurate is that the reactors produce far too little Thermal Power for their mass...

I'm confused, should we increase vacuum trust/ISP by 20% overal and increase Reactor Thermal Power? Do you mean the thermal power of the smaller reactors (0.65m & 1.25m) which seem to disproportionately produce much less heat compared to the larger reactors (2.5m & 3.75) for their weight.

Btw, you have not responded regarding the charged particles production of antimatter reactors...

Edited February 9, 2015 by FreeThinker

[Northstar1989]

I'm confused, should we increase vacuum trust/ISP by 20% overal and increase Reactor Thermal Power? Do you mean the thermal power of the smaller reactors (0.65m & 1.25m) which seem to disproportionately produce much less heat compared to the larger reactors (2.5m & 3.75) for their weight.

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...

Btw, you have not responded regarding the charged particles production of antimatter reactors...

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

[FreeThinker]

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.

Ok let's make some estimations of the required thermal power and resulting trust in all engine sizes:

Sethan (1.25) old thrust 22.59 kN : new trust: 647.25/4=161,8125 kN (7.16 times stronger => requires about 7 more Thermal heat )

old thermal power output Sethan (1.25m) = 85 => new thermal power Sethan (1.25m) = about 600 MW

Thrust Sethlans (0.625m) =Seathan (1.25) / 8 => 75 MW => about 20 kN trust in Vacuum

Thrust Sethan (1.25) => =Seathan (1.25) x 1 = 600 MW => about 160 kN trust in Vacuum

Thrust Sethlans (2.5m) = Seathan (1.25) x 8 => 4800 MW => about 1280 kN trust in Vacuum

Thrust Sethlans (3.75m) =Seathan (2.5) x 2 => 9600 MW => about 2560 kN trust in Vacuum

For a fair calculation of Thrust in the atmosphere we should also only use 1/4 of surface area

Max trust Thrust Sethlans (0.625m) @ Kerbin surface = 20 kN - 0.25 * 0.191425 * 101.325 = about 15 kN (without 0.25 it would have been 0)

Max trust Thrust Sethlans (1.25m) @ Kerbin surface = 160 kN - 0.25 * 0.7657 * 101.325 = about 140 kN

Max trust Thrust Sethlans (2.5m) @ Kerbin surface = 1280 kN - 0.25 * 3.06 * 101.325 = about 1200 kN

Max trust Thrust Sethlans (3.5m) @ Kerbin surface = 2560 kN - 0.25 * 6.891 * 101.325 = about 2385 kN

Edited February 9, 2015 by FreeThinker

[Northstar1989]

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

Edited February 9, 2015 by Northstar1989

[FreeThinker]

I updated my CTT config for KSPI (again ). Thank you FreeThinker for the requests.

Changes:

Command:

* Moved the Science Laboratory from "Advanced Science Tech" to "Scientific Outposts".

Electrical:

* Moved the Antimatter Initiated Reactor from "High Energy Science" to "Exotic Reactions".

* Moved the Flat Radiator from "Advanced Electrics" to "Nuclear Power".

* Moved the circradiatorKT from "Advanced Electrics" to "Nuclear Power".

* Moved the circradiatorKT2 from "Advanced Electrics" to "Large Scale Nuclear Power".

* Moved the circradiatorKT3 from "Advanced Electrics" to "Large Scale Nuclear Power".

* Moved the Large Flat Radiator from "Advanced Electrics" to "Large Scale Nuclear Power".

* Moved the Radial Heat Radiators from "Advanced Electrics" to "Large Scale Nuclear Power".

* Moved the Heat Radiators from "Large Electrics" to "High Energy Nuclear Power".

Engines:

* Moved all the Magnetic Nozzles from "Advanced Plasma Propulsion" to "High Efficiency Nuclear Propulsion".

* Moved the Thermal Rocket Nozzles from "High Efficiency Nuclear Propulsion" to "Improved Nuclear Propulsion".

Science:

* Moved the IR Telescope from "Experimental Science" to "Extended Duration Science Tech".

Utility:

* Moved the Gas Chromatograph Mass Spectrometer from "Advanced Science Tech" to "Specialized Science Tech".

* Moved the Liquid Chromatograph Mass Spectrometer from "Advanced Science Tech" to "Specialized Science Tech".

Alright, I have KSPI CTT config included it in my current version of KSPI Extended 0.5.7 which can now be downloaded from KerbalStuff.

Features

• Made ISP/Trust performance of Plasma Thruster in atmosphere depend on exitArea and atmospheric pressure
  
• Added support for other Techtrees
  
• Added ability of Atmospheric Scoop to function as Propulsive fluid accumulator which can be achieved by placing a vessel in a circular orbit at the edge of space with access to KSPI plasma engines and enough power.
  
• Electric engines power usage is limited by available power (optional)
  
• Added support for Community Tech Tree (CTT KSPI Config made by Olympic1)
  
• Added many new configuration settings including MaxThermalNozzleIsp, RadiationMechanicsDisabled
  
• Added Liquid Nitrogen en (RealFuels) Nitrogen as a resource which can be used for Thermal/Magnetic/Electric Rockets
  
• Added Cryotank which stores Liquid Nitrogen at low temperature, requiring electric power to maintain
  
• Added Integrated Nitrogen Radiator which stores Nitrogen gas and can perform Active cooling with Liquid Nitrogen
  
• Nitrogen can be scooped from the atmosphere with Atmospheric Scoop
  
• Improved Science Lab research : Profession & Skill now matter (+/- 50%) , effect of stupidity reduced (+/- 10%)
  
• Improved Science Lab feedback, it will at real time show how much science is already collected
  

Fixes

• Fixes KSPI Legacy issue where Computer Core would only give 1/4 of the research it should when unfocused
  
• Fixes KSPI Legacy issue where Reactors Retrofit(upgrade) button would not function
  
• Fixed KSPI Legacy issue where stupid Kerbals would actually improve research output in the Lab
  
• Fixes KSPI Legacy issue where Athmospheric scoop would not reset flow to 0 when flying out of atmosphere
  
• Fixes KSPI Legacy issue where Double Pivoted Solar Power generators could not be converted to Microwave power
  

Installation

• First remove any existing KSPI installation (GameData\WarpPlugin folder)
  
• Second install KSPI 0.90
  
• Third extract the patch into Your GameData folder.
  

WarpPluginSettings

• RadiationMechanicsDisabled (True by default) : Disables the calculation of accumulated radiation levels, when disabled, it fixes compability issies with external Planet Packs
  

Edited February 9, 2015 by FreeThinker

[Northstar1989]

Ok let's make some estimations of the required thermal power and resulting trust in all engine sizes:

Sethan (1.25) old thrust 22.59 kN : new trust: 647.25/4=161,8125 kN (7.16 times stronger => requires about 7 more Thermal heat )

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...)

old thermal power output Sethan (1.25m) = 85 => new thermal power Sethan (1.25m) = about 600 MW

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...)

Thrust Sethlans (0.625m) =Seathan (1.25) / 8 => 75 MW => about 20 kN trust in Vacuum

Thrust Sethan (1.25) => =Seathan (1.25) x 1 = 600 MW => about 160 kN trust in Vacuum

Thrust Sethlans (2.5m) = Seathan (1.25) x 8 => 4800 MW => about 1280 kN trust in Vacuum

Thrust Sethlans (3.75m) =Seathan (2.5) x 2 => 9600 MW => about 2560 kN trust in Vacuum

None of those Thermal Power ratings will be high enough with an increase in the reactor temperature either...

For a fair calculation of Thrust in the atmosphere we should also only use 1/4 of surface area

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...

Max trust Thrust Sethlans (0.625m) @ Kerbin surface = 20 kN - 0.25 * 0.191425 * 101.325 = about 15 kN (without 0.25 it would have been 0)

Max trust Thrust Sethlans (1.25m) @ Kerbin surface = 160 kN - 0.25 * 0.7657 * 101.325 = about 140 kN

Max trust Thrust Sethlans (2.5m) @ Kerbin surface = 1280 kN - 0.25 * 3.06 * 101.325 = about 1200 kN

Max trust Thrust Sethlans (3.5m) @ Kerbin surface = 2560 kN - 0.25 * 6.891 * 101.325 = about 2385 kN

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

[FreeThinker]

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

This will take me some time to realize, but I have had enough practice