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Post by Durandal on Jan 18, 2017 23:13:36 GMT
But honestly ship maneuvering is mostly irrelevant you are never going to achieve more thrust than an intercepting missile or some other high acceleration design. Unless you have higher acceleration than what you are trying to dodge you will never dodge it (all it has to do is mirror your burns). So the difference between a 10mG spaceship and a 10G spaceship (which would kill its crew for prolonged thrust) is irrelevant when compared to a 11G missile. If the industry standard is 20G maneuvering ships the industry standard intercepting missiles will be 25G you can't win that battle and there is actually a hard limit on how fast you can accelerate with squishy humans in your ship. While I agree about not being able to outmanuenver a missile, strong acceleration isn't something I'd write off. Orbital maneuvers have their place. Say that you have a PD system that can kill said 25g missile; then what? You need to be able to thrust into range to kill the target (assuming you or the target either don't have high energy lasers/they've been disabled). *edit* Also, as dorkius said out thrusting incoming KE weaponry is *always* an application for high(er) g acceleration.
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Post by Enderminion on Jan 19, 2017 5:27:41 GMT
As I like to say, incoming fire has right of way, moving on if you wanna go fast with reasonable TWR and resistojets and Nuclear Thermal Rockets are the way to go, NTRs have the benefit of that they don't take (Edit)power to work
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Post by apophys on Jan 19, 2017 8:07:57 GMT
For hybrid MPD + NTR, I recommend hydrogen deuteride, methane, or ethane.
For hybrid MPD + resistojet, decane produces the best thrust by far. Other hydrocarbons are fine, too, but less so. Most propellants in general can be used, but not really effectively. Resistojets are limited by the percentage of your power generation that you decide to spend on weapons, so the thrust obtained is low if you don't use decane.
You can do without a high-thrust option. Pure neon MPD works, and I like it.
I don't see a need to do all three thrust systems on one ship.
The cost and mass of your high-thrust engine choice, whether NTR or resistojet, is not high compared to the cost and mass of the ship. So use either.
I'm personally drifting toward hydrogen deuteride MPD + NTR. Since you currently use hydrogen, switching to HD is easy (and mostly a straight upgrade).
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Post by argonbalt on Jan 19, 2017 8:26:36 GMT
Yes ive been running some tests, neon is heavier sure, but damn cheap compared to pure Hydrogen and the density pays off in the thrust department, i will make another version with Hdeuteride and see. Besides a cheaper and better Exhaust velocity, how is the thrust on Hdeuteride MPD + NTR combos?
Also correct me if im wrong here, but high thrust is useful for moving your ass someplace new quickly, where as high exhaust velocity is better for the longer cruising stages, giving it a better overall specific impulse but over a longer period right?
I know Hdeuteride is better over all to base Hydrogen, but doesn't it still suffer from density problems?
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Post by apophys on Jan 19, 2017 8:45:11 GMT
From the Stinger drone replacement thread, page 3: This is running on a 100MW reactor. MPD: 40.0 km/s, 21.6 mg 0, 1d 18h burn time NTR: 4.31 km/s, 3.17 g 0, 1m 51s burn time
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Post by darthroach on Jan 19, 2017 9:36:52 GMT
okay general question here, is there any advantage to very high exhaust velocity? Depends on what you mean by "really high" and what the mission profile is. Ve is inversely correlated with thrust and therefore acceleration, because given some constant amount of energy, choosing to accelerate the remass to a higher velocity massively reduces the mass flow rate. Same kinetic energy but diminishing change in momentum (Wk = mv^2 ; p = mv ; forgive eastern european notation). Chemical rockets have an overabundance of thrust but have very low dela v, so higher Isp is always welcome. But once you reach certain levels - enough to do partial brachistochrone trajectories, for example - it becomes a tradeoff. You can accelerate for longer, but you also take much longer to accelerate. Not only does this mean you will take months or years to get anywhere, it also makes maneuvers like orbital insertions difficult. So rule of thumb: the further you want to go, the more Isp you want. You don't want too much.
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Post by newageofpower on Jan 19, 2017 15:27:04 GMT
That huge increase in cross section though... Literally attackable from more than twice the range.
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Post by apophys on Jan 19, 2017 20:27:57 GMT
I find that 20 mg 0 is the low end of acceleration that I'm comfortable with for orbital maneuvers, so I shoot for that with MPDs. It's not too hard to get. That huge increase in cross section though... Literally attackable from more than twice the range. That's partly because of the 100MW reactor, which takes up 1/4 of the internal space (whereas the original is almost totally full of propellant). And partly because I wanted really high dV. Bringing the cross-section to 10.1 m 2 by removing 2/3 of the propellant results in 16 km/s dV instead of 40 km/s. Also, the Biter will start shooting at the Stinger from 100 km away, while the Stinger will only start shooting the Biter from 6 km away (because of the Biter's crazy guns, fed by the aforementioned 100MW reactor.)
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Post by argonbalt on Jan 19, 2017 20:37:25 GMT
And partly because I wanted really high dV. Bringing the cross-section to 10.1 m 2 by removing 2/3 of the propellant results in 16 km/s dV instead of 40 km/s. Also, the Biter will start shooting at the Stinger from 100 km away, while the Stinger will only start shooting the Biter from 6 km away (because of the Biter's crazy guns, fed by the aforementioned 100MW reactor.) Yeah but what kinda idjiet sends Gun dronesVGun drones? Especially when the obvious counter is like one 20MW laser drone? Unless you are inter mixing with a missile crapper to clog the target area. Otherwise it would work well as a finisher to execute any surviving but crippled ships.
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Post by Enderminion on Jan 19, 2017 20:52:07 GMT
Drones need to have the acceleration to catch Capital ships (like 2g is the minimum), I think of them as missiles with guns
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Post by David367th on Jan 19, 2017 21:55:34 GMT
Drones need to have the acceleration to catch Capital ships (like 2g is the minimum), I think of them as missiles with guns Or ships without people. You could technically make them broadside and fight like normal ships.
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Post by argonbalt on Jan 19, 2017 22:22:37 GMT
Drones need to have the acceleration to catch Capital ships (like 2g is the minimum), I think of them as missiles with guns Or ships without people. You could technically make them broadside and fight like normal ships. If only we did not need to build ludicrous huge launchers and "ammo tanks" and could just side mount them with some explosive bolts or magnets.
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Post by tukuro on Jan 19, 2017 22:36:38 GMT
okay general question here, is there any advantage to very high exhaust velocity? If you want to launch an invasion it's pretty much mandatory. If you want to stay orbital however you don't really need 100-200 km/s exhaust velocities. The latter will get you from Earth to Saturn in about 6 months. However going hybrid is easy if you already have like 1> GW to spare. Hydrogen deuteride and methane both make for excellent NTR, Restiojet and MPD fuels. And once you go hybrid you might as well pick all 3. NTR for tactical propulsion, MPDs for invasions and resistojets as your directional thrusters. It's also possible to get decane thrust levels with both without sacrificing too much of your thrust-weight ratios.
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Post by newageofpower on Jan 20, 2017 0:41:51 GMT
Drones need to have the acceleration to catch Capital ships (like 2g is the minimum), I think of them as missiles with guns Part of me want's to "haha" and keep my silence/let you retain your innocence... but I'll explain. My MPD drones will eventually catch your caps when they run out of fuel, as long as I have more dV. if your caps have 20 km/s dV and 2G accel, while my drones have 50km/s dV and 0.1 g accel, you'll be able to outrun me while your fuel holds out... which won't matter, because I'll still have 60%+ of my fuel just to match velocity with you when you hit 0% fuel. Thrust is important, but more so from breaking free of low orbit/dodging stuff. Raw dV efficiency will beat thrusty craft at sufficient dV advantage.
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Post by theholyinquisition on Jan 20, 2017 1:20:27 GMT
Drones need to have the acceleration to catch Capital ships (like 2g is the minimum), I think of them as missiles with guns Part of me want's to "haha" and keep my silence/let you retain your innocence... but I'll explain. My MPD drones will eventually catch your caps when they run out of fuel, as long as I have more dV. if your caps have 20 km/s dV and 2G accel, while my drones have 50km/s dV and 0.1 g accel, you'll be able to outrun me while your fuel holds out... which won't matter, because I'll still have 60%+ of my fuel just to match velocity with you when you hit 0% fuel. Thrust is important, but more so from breaking free of low orbit/dodging stuff. Raw dV efficiency will beat thrusty craft at sufficient dV advantage. But is that fun?
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