Noob gameplay questions [MKS/KSPI-NearFuture integration]

[MatterBeam]

Hi.

I have some questions about Modular Kolonisation systems and KSP Interstellar, rebalanced to Integrate Near Future technologies by Free Thinker.

1) I have unlocked nuclear propulsion and thermal rocket nozzle in the tech tree. They provide huge amounts of power, with great TWR and ISP. However, once I reach space, the power output drops to a fraction of the power output in the atmosphere... Why is that? I have more than enough waste heat removal.

2) Why is it that the nuclear reactor/thermal nozzle combo has much less thrust when using liquid hydrogen as propellant than Liquid Fuel or LFO? I can't see an increase in ISP to compensate.

3) I kinda guessed that there is a pruner program that removes all the thermal nozzle duplicates 0.625-1.25-2.5m...) to leave only one nozzle I have to use tweakscale to resize. However, the 2.5m nozzle has much more thrust and ISP than the 3.75m nozzle, and the 5m nozzle is worse than the smallest nozzles ?!

4) The Near Future nuclear reactors I have unlocked so far (MX-1, MX-4, MX-EXP) are much much worse than the KSPI reactors, and the KSPI reactors themselves are completely unbalanced between themselves. The MX series produces anemic levels of power (MX-1: 26MW thermal) with terrible TWR (11.5 tons) and extreme cost. The Large Molten Salt Reactor from KSPI has 15 tons weight... But costs much less, and produces 742MW thermal.

Even worse, I have no reason at all to use the Molten Salt Reactors. The Akula Particle Bed reactor produces a whopping 4.5GW, outclassing anything.

5) Uraninite. I can mine it, store it, but I don't know how to convert it into something like the UF4 the nuclear reactors use.

[Streetwind]

This sounds like something you might want to post in FreeThinker's mod thread, since pretty much all your questions are related to part balance and mod interaction in that very specific crossover case.

[RoverDude]

I can answer #5. Use an MKS science lab to convert Uraninite into EnrichedUranium for use in MKS/NFT reactors.

[impyre]

I can take a stab at numbers 1 and 2. These mods are most likely attempting to produce results that are more realistic. (More in line with what we expect based on generic physics ideas) There is a pretty significant deviation that KSP takes from the real world. In the real world, thrust decreases as the atmosphere decreases in density. Also, the ISP increases proportionally (mostly) to the decrease in thrust. This is because in thick atmosphere the exhaust gasses have something to "push against". The atmosphere soaks up the momentum and creates a high-pressure area beneath the rocket. The atmosphere pushes back, creating additional thrust. Of course, since ISP is related to exhaust velocity, it makes since that it would be lower where there's atmosphere in the way.

In KSP, the thrust (in stock anyhow) doesn't change with the presence or absence of atmosphere... so, to "simulate" this change they modify the fuel flow rate instead. They have talked about rectifying this soon: http://kerbaldevteam.tumblr.com/post/110666185425/devnote-tuesday-point-sharp-end-towards-space. My guess is that the mod makers decided to use their own solution long before Squad announced any plans to "fix" it... which would be why your engines are taking a hit to thrust once they get out of the atmosphere. Don't worry though, I doubt they'd short-change you... you're likely getting a nice steady, predictable fuel flow rate regardless of circumstance.

As to the second question, this is just a guess again, but I imagine the thermal engine is probably made to be as "realistic" as possible. In this case, it's a reflection of how thermal engines work. They essentially heat something up really quickly without actually exposing it to flame. The expansion results in the exhaust gasses used to propel the craft. Whether combustion occurs or not depends on the temperatures and propellants involved, but the idea of thermal nozzles is generally to avoid combustion (but I guess it isn't unimaginable). The short answer here is that the thrust provided by a thermal nozzle depends on several factors: the propellant's specific heat, density, heat of vaporization, molecular weight, etc. My guess is that they believe that hydrogen would be a far weaker propellant because of its extremely low density. You can think of the rocket equation as being similar to standing on a boat and throwing a rock... the resulting reactive motion of the boat is directly proportional to the momentum of the thrown rock. Throwing a bigger, heavier rock helps... depending on the maximum power you can put behind it. IE: bullets carry quite a bit of energy when fired from a gun... but if you're talking about the energy of a thrown object, a baseball is a far better option than a bullet because your arm simply doesn't move that fast. Likewise, there's a limit to how quickly thermal energy can spread (and it varies from one substance to another).