Sevio

Hi Fractal_UK: Thanks for all your hard work with the new update, I can't wait to play with the new reactors and all the other things! Unfortunately I seem to have hit upon a rather severe bug. It's easy to reproduce, create a vessel with probe brain, FL-T800 fuel tank, 2 small deployable radiators and strap 4x symmetry generator/Omega fusion reactor/thermal rocket to the fuel tank. When on the launchpad, after running the engines for a bit and the thermalpower of the reactors has run out, one of the 4 engines drastically loses thrust, creating an uncontrollable spin effect due to the asymmetric thrust. Or it would, if the test ship had enough TWR to lift off. Which brings me to a question, I've noticed the Omega and GEKKO fusion reactors have had their mass significantly increased (from 1.5t to 2t for the Omega), why is that? I don't think that was needed, their TWR even with LFO fuel was nothing to write home about.

I have been hammering at the nuclear-powered SSTO challenge myself, as Fractal said it's been quite the engineering challenge to even design one that can get into orbit. However today I seem to have finally hit a sweet spot. I present to you the Seraph Surface-to-orbit Shuttle: The Seraph without cargo weighs 21.075 tons, can operate in any atmosphere due to being purely fusion-powered and for its test flight carried a cargo of 10.8375 tons into LKO, consisting of a large metal can plus 2.4 tons of useless oxidizer. Other mods used: B9, Modular Fuel Tanks, Extraplanetary Launchpads (heavy metal cargo can), Mechjeb (only for statistics) I used some part clipping to make the thing look somewhat aesthetic. Key elements are: Works in any atmosphere! 4 upgraded fusion reactors with 1.25m direct conversion generators. The middle ones are clipped into their generators to keep engine section from sticking out too far behind. Sabre M intake + 3 supersonic inlets on each side. Although the Sabre Ms are technically attached to the precoolers (the adapter behind it is just there for show), the supersonic inlets mounted radially on the precooler don't seem to benefit from its effect and thus the engines will still show some overheating. Take care not to activate your engines in airbreathing mode when reentering at high speed! Plasma Thruster in the middle to squeeze more thrust out of the fusion reactors after switching away from airbreathing mode mode for the burn to orbit. Both Xenon and Argon are suitable for this stage, go for Xenon if you are worried you won't have enough thrust to get out of the atmosphere quickly. Modular Fuel Tanks: Thanks to MFT, the twin engine mount at the back can contain some monopropellant for docking, plus the LFO needed for the burn to orbit and rendez-vous maneuvers. The middle LFO tank contains either 54 Argon or 4480 Xenon for the plasma thruster, and 480 units of (cargo) oxidizer but could also be used to transport kethane or other fuels. Small 2m cargo bay: It's not very useful for actually deploying space probes due to its small size and the wing above blocking part of the bay. However it has 2 internal attachment points that can be used to attach cargo containers in line with the Center of Mass such as metal cans. The 8t metal can clipping through the craft hasn't been a problem on my multiple test flights. This makes it useful for transporting various resources between surface and orbit. Secondary cockpit has room for 2 passengers Ascent strategy: Climb up to 10 km on the Thermal Turbojets, begin leveling out once engine thrust starts to rise more slowly. At around 12-13 km their thrust will be optimal, so try to squeeze as much speed as possible out of this stage while climbing very slowly to 950-1000 m/s at 20km. Once there thrust will start dropping sharply, so pitch up to about 30 degrees, switch 2 of your engines over to LFO mode and activate the plasma thruster, while the other 2 turbojets continue to squeeze more thrust out of their now doubled intakeatm. Once the remaining airbreathing turbojets' thrust drops below that of your LFO thrusters (you should be at 30 km now), switch them over as well, turn off your intakes and pitch up to 45 degrees for the burn to orbit. Once you break 50 km altitude you can lean down and simply point prograde until you reach your desired Ap. Depending on execution, there should be around 600 - 1200 delta-V left after circularizing at 80km. Some notes on construction: If you're not using Modular Fueltanks, you will probably have to get creative to avoid bringing too much dead weight with you. You'll have to use Xenon for the plasma thruster (the only argon container is far too big and heavy for a spaceplane), or alternatively you can leave out the plasma thruster entirely, replace the 1.25m generators with 62.5 cm ones and add some more LFO, but this will have slightly lower total thrust at the critical burn to orbit stage. If someone would like the .craft file to give it a try, let me know and I'll put it up somewhere for download. I hope this writeup helps some of you out with your interstellar spaceplane efforts! Happy flying!

Thanks for your response Fractal_UK. My previous post was in response to forsaken1111, although part of it leads nicely into what I'd like to say next. I'm OK with reactors scaling to be better with size, and the generator efficiency being where it is right now, since it can power the research lab. Looking at the 3 different available deployable radiator sizes and matching them up to the 3 largest nuclear reactors, there seems to be a large discrepancy at Tier 1 right now though, as it took 4 of the second-tier radiators to shed the heat of the KIWI reactor. Is it intended that it takes 3.2 tons of radiator to shed the heat of a 2.5 ton reactor for running a research lab?

They cap at 24%, which means the pictured science lab (which has radiators weighing more than the reactor itself), is running at only half of the efficiency it could have. It just seems rather poor for having 3.2 tons of radiator to 2.5 tons of reactor.

I started a new career save with 0.23, including this beautiful mod. I've just managed to unlock the first tier of nuclear reactors and decided to make a science lab and fly it to minmus to get some research going. To my surprise the waste heat started building up rather quickly, due to the change to radiators that I read up about in this thread. I've had to revert and launch several revised versions, each time with more radiator capacity. Each one suffered from waste heat buildup causing a drop in the generator's efficiency, forcing the reactor to run at higher capacity to keep the science lab running and making the problem worse. Eventually, the electric generator's efficiency drops so low that it can no longer supply the lab with power. Conceptually I like the way the radiators work now, building up heat until they reach equilibrium, and encouraging you to supply enough radiators to keep everything cool. However I'm starting to feel that the balance is off, at least when working with Tier 1 equipment. Here's the final version of my Minmus Science Lab that will stabilize just barely below 100% reactor throttle to keep the lab supplied with 5 MW: It's not quite visible from this angle but it took 4 of the medium sized radiators to just barely keep the 1.25m KIWI reactor cooled at ~97-98% throttle while supplying a permanent 5 MW of power for the lab, at an efficiency of just 12.9%. To put things in perspective, that's 3.2 tons of radiator for the second-smallest size 2.5 ton reactor. Is tier 1 equipment really intended to struggle this badly to power electrical things? With the research lab being the cheapest activity power-wise that I know of in the mod, I don't even want to think of what it would take to cool the Aegletes or even Aegletes 2 if you wanted to do anything with the refinery. All this radiator mass also puts a big toll on the TWR of thermal rockets, even in LFO mode. I launched a minimalistic combination of Stayputnik probe core, Science Lab, 1.25m Nuclear Reactor, Generator, Thermal Rocket, 4 medium radiators and FL-T400 fuel tank (180 LF/ 220 Ox) shows the following specs with MechJeb dev build 139, once in space: Max Acceleration: 2.084 m/s (Fuel mode: LFO) Max thrust: 24 kN Vessel mass: 11.4 t TWR: 0.21 Delta-V: 1298 For comparison, if I take out the thermal rocket nozzle and replace it with a stock LV-N nuclear engine, I see: Max Acceleration: 4.528 m/s Max thrust: 60 kN Vessel mass: 13.25 t TWR: 0.46 Delta-V: 1284 Much more usable thrust and delta-V only slightly lower, even though it's pushing more mass around due to having an "extra" nuclear reactor on board. Sorry for the wall of text, but to summarize: For the engineering and extra mass it takes to bring a KSPI nuclear reactor and assorted equipment into space, Tier 1 feels a little bit underpowered when compared with stock technology. A couple of suggestions: Rebalance T1 radiators to make T1 reactors a bit easier to cool Adjust the tooltips on the radiators to make it easier to determine at a glance how much radiator capacity is needed for effective long-term operation of a nuclear reactor. My test lab from above required ~7.5 times the reactor's capacity in radiator capacity to reach equilibrium at near 100% throttle. Possibly: Rebalance T1 reactors and thermal rockets to better match up against the stock LV-N Regardless of what you decide to do with my suggestions, thank you for one of the best mods the KSP community has to offer and keep up the good work!