Can someone help me and tell me how to combine engines of different types? I would like to have like an inner and an outer ring on the bottom of my ship. Is that at all possible? With ultra heavy lasers you have a lot of spare power. And while most MPDs are not viable as main engine, it would be a shame to let all that power go to waste. So I would like to add some MPD to an otherwise NTR or Resistojet propelled spacecraft. How can this be done nicely? And by nicely I mean not have a single mpd sticking out at the side of the ship (ugh).
A megawatt of radiation ? The robot needs to move to be able to work.
5mm Li6 blocks all the neutron flux. Design your electronics with redundancy/checking ala modern spacecraft electronics for the rest.
The problem with thin Li-6 shielding is that it will convert to Li-7. Li-6 absorbs neutrons (and does so with relatively few emissions); Li-7 largely does not. This gives the shielding a poor service life. If we were actually engineering some of these things in real-life, we'd probably use a small thickness of Li-6 against neutron radiation...but as a failsafe for the primary radshield. When you're sinking a decade of Africa's GDP into a spacecraft, you use failsafes
Other concerns not modelled are secondary radiation and of course heating. A megawatt of power is a megawatt of power and even the most efficient radshield is not going to sink all the incoming power into changes to its atoms. In real life, when volume and mass matter more than price we use graded-Z shields that gradually power down the radiation as it moves through layers of materials from high to low atomic numbers (when price matters, most radiation is just stopped by using a lot of lead—it works and it's dirt cheap). The modern spacecraft tend to have radshields of different kinds, depending on what the payload is, before the radiation even gets to the redundant electronics.
Of course, don't get me wrong, the game poses fun optimisation problems that are rooted in real world physics. But when we build optimised ingame stuff, some of the RL design parameters are being solved for us with handwavium. I think that's what dwwolf is pointing out. It's a game
I've been trying to get every last micro-gee of performance I can out of this engine, but I've been fiddling with all of the settings for around three hours and I've been able to get precisely no improvement. I think that my main limiter is the dimensions of the missile I'm planning on mounting it on
which constrains me to a max radius of around 10 cm for all the components, not including the gimbal. To be frank, given those constraints I think that I might've hit a theoretical wall, but I'd appreciate it if someone more experienced and versed in the theory could either prove me wrong or confirm.
caiaphas sorry i'm late, saw your post last night but didn't have the chance to respond.
Okay, so since you need to keep the engine compact I have left the average neutron flux low, and not changed the dimensions of the injector; This makes the engine less efficient than it could be, but this considers your package requirements.
List of changes:
16.5g of U233 for control rods; The reactor can be better controlled through dimension changes, so less control rod mass is needed.
Chamber material to UHMWPE; This is lighter than boron, and keeping regenerative cooling high and neutron flux low allows its use.
Massively reduced throat radius to 5.9mm; It's critical to get the throat size right since it effects the overall dimensions of the nozzle.
Increased chamber contraction ratio to 10; This is to compensate for the control rod mass, but it also gives a tiny bit more performance for less mass.
Nozzle expansion ratio to 79 & expansion angle to 10°; With this the engine should have an exhaust velocity of 5.37km/s, going higher will yield diminishing returns very quickly making the engine very heavy. However, since the suggestions here make the engine alot lighter, you would be fine increasing the expansion angle until you reach the same mass as the original rocket.
Injector material to lithium; Lithium is far lighter and perfectly capable of withstanding the forces since the injector is small.
Gimbal armour to graphite aerogel; This is simply to save mass.
Momentum wheel material to potassium @18krpm; Again simply to save mass
All these changes should leave you with savings of 125g mass, 74c cost and gains in all other departments. Feel free to tweak this until you're completely satisfied; Just remember that two engine with identical exhaust velocity, the lighter of the two will yield better delta-v.
In case I missed anything, what I am suggesting can be seen in full here.
I've been messing around with some mini-combustion rockets (as I am sure most people have been) for interceptor missiles to attempt to create a viable CIWS addition to a laser drone to defend against mini-missile swarms. I figured I would post what I have come up with as the rockets themselves seem to work fairly well.
You can lower the thrust and mass by reducing the injector RPM but I am pretty happy with the performance at 80 grams.
jasonvance unfortunately there isnt a whole lot, if anything, that can be done to improve an engine like this; if you want to keep the package requirements that is.
I see you're using 3 of these engines? If that is the case, I would suggest using a single larger engine that is much better placed to take advantage of the lower limits of the engine designer; Since one engine at this scale can not only produce more thrust, but also more exhaust velocity and weigh less than three smaller engines.
Assuming these are for simple interceptor missiles, having two engines to facilitate rolling isn't really necessary. But that's upto you.
Anyone up for designing a small 60kN ish decane NTR for 700kg class missiles ?
Without any other spec requirements to go off of this should work... If you need it re-optimized to be shrunk radius wise, mass wise, or cost wise let me know. I didn't know what was important for the design so I just threw something together.
Last Edit: Jan 6, 2017 11:53:58 GMT by jasonvance: Derped on the first design fixed now