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Post by ๐ญ๐๐๐๐๐๐๐๐๐ on Sept 30, 2017 10:18:58 GMT
This is the lightest practical engine I could come up with. In what scenario is that kind of thrust practical? When you fire a flak round out of a railgun where its already going like 50 kilometers per second. over the course of the 30 second travel time, the rocket engines could make adjustments to the course to keep it on target if the enemy is trying to get out of the way. assuming your flak weighs like 2 grams, which it would have to to get massave velocities out of a railgun.
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Post by Kerr on Sept 30, 2017 11:01:25 GMT
In what scenario is that kind of thrust practical? When you fire a flak round out of a railgun where its already going like 50 kilometers per second. over the course of the 30 second travel time, the rocket engines could make adjustments to the course to keep it on target if the enemy is trying to get out of the way. assuming your flak weighs like 2 grams, which it would have to to get massive velocities out of a railgun. How do you install processors and sensors in a sub hectogram railgun projectile? Wouldn't the G forces destroy the an 100ยตm thich engine bell made out of lithium? And isn't that engine a bit too massive compared to an small and compact flak?
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Post by Kerr on Sept 30, 2017 11:03:31 GMT
In what scenario is that kind of thrust practical? When you try to make a small cargo hover over an asteroid I guess Wouldn't an bottle of coke and a few mentos be enough to make an multi-kilogram cargo orbit an normal asteroid? Or do you mean asteroid on the scale of ceres?
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Post by The Astronomer on Sept 30, 2017 11:13:56 GMT
When you try to make a small cargo hover over an asteroid I guess Wouldn't an bottle of coke and a few mentos be enough to make an multi-kilogram cargo orbit an normal asteroid? Or do you mean asteroid on the scale of ceres? I think a bottle of soda plus a few mentos provides more thrust than that engine.
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Post by Kerr on Sept 30, 2017 11:32:13 GMT
Wouldn't an bottle of coke and a few mentos be enough to make an multi-kilogram cargo orbit an normal asteroid? Or do you mean asteroid on the scale of ceres? I think a bottle of soda plus a few mentos provides more thrust than that engine. Well, an 1m fountain requires 4m/s exit velocity. If 30% of an 1.25L Diet Coke has left the bottle after the reaction the created thrust must be 1.5N.
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Post by ๐ญ๐๐๐๐๐๐๐๐๐ on Sept 30, 2017 20:37:21 GMT
This is the lightest practical engine I could come up with. In what scenario is that kind of thrust practical? micro drones/micro missiles When you make really tiny stuff, you focus more on weight losing and less of the engine's efficeicy because weight is a bigger difference in the rocket equation. and that engine would be pulling like 20 gees without a fuel tank its funny because the reactants are Hydrogen and flourine going out of a lithium bell so any excess flourine would react with the lithium
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Post by ๐ญ๐๐๐๐๐๐๐๐๐ on Sept 30, 2017 20:38:26 GMT
When you try to make a small cargo hover over an asteroid I guess Wouldn't an bottle of coke and a few mentos be enough to make an multi-kilogram cargo orbit an normal asteroid? Or do you mean asteroid on the scale of ceres? a bottle of coke doesn't have an exit velocity of over 4 kilometers per second
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Post by boersgard on Aug 16, 2018 3:51:54 GMT
I'm looking for some advice on engine/fuel choice, working constraints:
1. Maximize acceleration 2. Maximize gimbal 3. 10-15m Diameter (smaller preferable) 4. Low mass fuel 5. High delta-v
From what I know, I should be looking at a hydrogen-deuteride NTR engine?
Ship rough specifications: ~170m length ~30m width ~3-8kt payload mass
I want a minimum of 1g acceleration and 12km/s delta-v without making a gigantic engine, but I need to know which type I should start fiddling with to work it out.
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Post by bigbombr on Aug 16, 2018 9:16:16 GMT
I'm looking for some advice on engine/fuel choice, working constraints: 1. Maximize acceleration 2. Maximize gimbal 3. 10-15m Diameter (smaller preferable) 4. Low mass fuel 5. High delta-v From what I know, I should be looking at a hydrogen-deuteride NTR engine? Ship rough specifications: ~170m length ~30m width ~3-8kt payload mass I want a minimum of 1g acceleration and 12km/s delta-v without making a gigantic engine, but I need to know which type I should start fiddling with to work it out. Fuel is probably best U-233 dioxide unless you have mods. As for propellant, hydrogen deuteride has the highest exhaust velocity, but a very low density. Methane has a pretty high exhaust velocity, but a higher density. Larger hydrocarbons have a lower exhaust velocity yet a higher density. Which propellant is ideal depends on delta-v and armor.
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Post by boersgard on Aug 16, 2018 22:13:44 GMT
Well, I went with my hunch on Hydrogen Deuteride and it worked out - managed 10kt mass, 1g, 12km/s delta-v
This with an off-the-shelf engine from apophys but I'm wondering if I can trade more length on the engine for higher performance or smaller diameter
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ghgh
Full Member
Still trying to make kinetics work.
Posts: 136
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Post by ghgh on Aug 16, 2018 23:05:23 GMT
Add more rocket attachments, they increase the thrust without taking from the DV (though this might be a bug). It definitely increases the mass and cost by way of momentum wheel and turret frame, but the amount of thrust you get more then pays you back. Also, Hydrogen Deuterium rockets tend to be long due to the low density of the propellant. You should have plenty of distance for your crew compartment to be rad protected.
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Post by boersgard on Aug 17, 2018 6:19:39 GMT
I want longer rocket engines because given the choice between a short and fat engine and a long skinny one, the long skinny one is easier to pack into a rocket that's shaped like a cigar without ballooning the surface area.
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ghgh
Full Member
Still trying to make kinetics work.
Posts: 136
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Post by ghgh on Aug 17, 2018 12:46:03 GMT
Longer rockets are more efficient but harder to gimbal. The rocket attachments are reliant on the gimbal turret and increasing the length also increases the mass of the rocket so you are going to hit a brick wall as far as efficiency goes.
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Post by boersgard on Aug 17, 2018 13:46:44 GMT
I'm moving towards dropping the gimbal entirely, but playing around with some Hydrogen Deuteride engine designs it looks like it's actually impossible to make an engine that's 10-20m in diameter like I want. I guess I'm stuck with packing a bunch of small engines together
Edit: Whew this engine design stuff is finnicky as heck.
Can I get some advice on maximal materials? It looks like the control rod HAS to be Titanium Diboride - absolutely nothing else will work(?), and the chamber wall HAS to be diamond likewise (unless I go with a cooler engine, which as I understand means guaranteed lower exhaust velocity).
And the absolute maximum exhaust velocity I can possibly get out of this engine is 9.55km/s because it's a function of the temperature and any higher is impossible with default materials?
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Post by AdmiralObvious on Aug 18, 2018 6:43:45 GMT
I'm moving towards dropping the gimbal entirely, but playing around with some Hydrogen Deuteride engine designs it looks like it's actually impossible to make an engine that's 10-20m in diameter like I want. I guess I'm stuck with packing a bunch of small engines together
Edit: Whew this engine design stuff is finnicky as heck.
Can I get some advice on maximal materials? It looks like the control rod HAS to be Titanium Diboride - absolutely nothing else will work(?), and the chamber wall HAS to be diamond likewise (unless I go with a cooler engine, which as I understand means guaranteed lower exhaust velocity).
And the absolute maximum exhaust velocity I can possibly get out of this engine is 9.55km/s because it's a function of the temperature and any higher is impossible with default materials?
My go-to control rod is Boron Carbide. You don't need much to actually create a sub/super critical range. I'm guessing the thing you're trying to do is get the hottest possible engine? It's not necessarily efficient depending on how fast you have the injector going. What I generally look for is high Acceleration, and high DeltaV. Exhaust velocity is just a useful byproduct stat for me. Especially since I like to use unconventional fuels, like Mercury, or with mods, heavy metals like lead.
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