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Post by nivik on Oct 27, 2016 17:10:39 GMT
Just to be clear I am mostly talking about missiles after performing orbital maneuvers that engage enemy ships which have long range laser weapons. Not can this push the starting range of the engagement out to 250km but the missile in question will have already used at least a bit of its delta v for the orbital maneuvers. I believe it is safe to assume the player will be plotting and carrying out the maneuvers so no need to automate that part. End of the day this is the scenario: After expending some amount of delta v under manual guidance to intercept the missile enters combat with a ship with 250km range lasers. The lasers should be assumed to be effective but they could simply be dummy lasers to push out the starting engagment range. As such most missiles will have to do an initial burn to get close to the target and enter a cruise phase while still quite a distance out. During the cruise phase the enemy will be engaging with counter weapons either lasers or something else and maneuvering to avoid intercept. I didn't know that lasers went out to 250km. Hmm. Interesting. Yeah, you're correct that boost-coast-boost guidance algorithm would be useful. I'll start looking into the math for that; I think it's fairly straightforward.
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Post by captinjoehenry on Oct 27, 2016 17:19:13 GMT
Just to be clear I am mostly talking about missiles after performing orbital maneuvers that engage enemy ships which have long range laser weapons. Not can this push the starting range of the engagement out to 250km but the missile in question will have already used at least a bit of its delta v for the orbital maneuvers. I believe it is safe to assume the player will be plotting and carrying out the maneuvers so no need to automate that part. End of the day this is the scenario: After expending some amount of delta v under manual guidance to intercept the missile enters combat with a ship with 250km range lasers. The lasers should be assumed to be effective but they could simply be dummy lasers to push out the starting engagment range. As such most missiles will have to do an initial burn to get close to the target and enter a cruise phase while still quite a distance out. During the cruise phase the enemy will be engaging with counter weapons either lasers or something else and maneuvering to avoid intercept. I didn't know that lasers went out to 250km. Hmm. Interesting. Yeah, you're correct that boost-coast-boost guidance algorithm would be useful. I'll start looking into the math for that; I think it's fairly straightforward. Yeah lasers can be set to a max range of 250km no matter what their power is. So I personally would consider it always beneficial to have even a shitty laser on a space craft with its range set to 250km to force missiles and other things into combat at that range.
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Post by jonen on Oct 27, 2016 17:59:02 GMT
Yeah lasers can be set to a max range of 250km no matter what their power is. So I personally would consider it always beneficial to have even a shitty laser on a space craft with its range set to 250km to force missiles and other things into combat at that range. On my to do list is a small, cheapskate version of the drone laser to be mounted on all spacecraft for this purpose. Just waiting for the ability to name modules before doing it. I'm thinking "Dazzler" or "Target Marker" or "Laser pointer". (If you don't want to engage at 250km, disable the laser before intercept, and hope the enemy doesn't have one of their own.)
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Post by captinjoehenry on Oct 27, 2016 21:01:25 GMT
I am talking about coasting once combat is entered. Mostly dealing with the range lasers can engage at being far longer than the distance a missile can travel under power. I assume the player is dealing with the orbital manuvers 100 kilometers is the current maximum weapon range. Missiles can cover that distance under power and still be quite capable, particularly if their payload is relatively small. Not every missile can, but it's certainly both possible and practical. Here's my current counter-missile. Its powered range envelope is 98 km if it doesn't maneuver: It doesn't get really effective at interceptions until about 75km. However, once it's at that range, it can swat Strikers and Devastators in their coast phase pretty easily: However, that said, I think a power-coast-power algorithm can be done pretty easily. Given that you know how much delta-v you're going to store in reserve, you can calculate approximately what position the missile will be at burnout, what its target-relative velocity will be, and what range it'll have from the target. You'd then calculate what direction you want the missile to be going at that point in time by using the same target-leading algorithm you'd use for a ballistic weapon like a railgun. While in coast, the missile would continuously update its time to closest approach and compare it to its remaining burn time. When its time to closest approach becomes less than its remaining burn time, it then goes back under power for terminal guidance and from that point onwards acts like a normal missile. The only part of this that seems tricky to me is determining the missile's location when it goes into coast. That position and the target lead deflection angle for the ballistic part of the trajectory are very closely tied to one another; closely enough that the first powered phase may need to use simple trajectory projection/prediction as opposed to a PN variant (PN is an negative-feedback error minimization algorithm, and thus doesn't actually project or guarantee any particular flightpath). In my prior experience, target predictive guidance is most effective early in a missile's flight, while PN variants tend to be better later in flight, so this actually could work out quite nicely. Hmm I just realized I really like that counter missile of yours. Can you post all the bits that goes into it so I can mess around with the design myself?
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Post by jakjakman on Oct 27, 2016 21:29:19 GMT
Hmm I just realized I really like that counter missile of yours. Can you post all the bits that goes into it so I can mess around with the design myself? I'm interested also! I'd like to try them out against my main workhorse missiles.
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Post by nivik on Oct 27, 2016 23:31:42 GMT
Hmm I just realized I really like that counter missile of yours. Can you post all the bits that goes into it so I can mess around with the design myself? Hmm I just realized I really like that counter missile of yours. Can you post all the bits that goes into it so I can mess around with the design myself? I'm interested also! I'd like to try them out against my main workhorse missiles. Sure thing! I'm pretty proud of the engine in particular. I realized that running an oxidizer-rich mixture would bring my engine temperatures down and increase my average fuel density -- fluorine has a density of 1.5 tons per cubic meter -- so I'm running a 40% surplus on fluorine in a H2F2 rocket. Exhaust velocity is still over 4km/s, and TWR is over 600. I'm using magnesium for the injector purely for flavor reasons: a lithium injector would burn hot enough that the hydrogen would be completely redundant. If we ever get hybrid rocket motors, lithium/fluorine is gonna be a great fuel mix. Edit: I use graphite aerogel as the gimbal "armor" because it's extremely light, extremely cheap, and if anything hits the engine the missile's out of commission anyway. The warhead is a pretty standard pocket nuke. I'm certain there's room for improvement, but the main advantages are that A) it weighs half a kilo, and B) it can still do nuke-related activities. For a counter missile, keeping mass down is pretty important. The fuel tanks are pretty standard UHMWPE tanks. The oxidizer tank is split into two pieces so I could get the precise amount of oxidizer I wanted. Other than that, just make sure the radius is under 5 cm. I don't think they're worth a screenshot. The launcher takes minimal power, requires very little radiator area, and fires once every three seconds. This seems to work out just fine against salvos of between 10 and 30 missiles. I'm using a 200 round attached magazine for a total mass of under three tons and a total cost of 13.0 kilocredits. Considering as Strikers cost 9.83 kc each, I'm pretty happy with the system. Edit: The thing isn't armored, because the missiles are non-explosive and once you're in gun range, counter-missiles are redundant. I believe I selected boron nitride as the casing material due to its high specific heat capacity and high melting point; those properties appear to help harden the module against any stray nukes.
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Post by captinjoehenry on Oct 28, 2016 0:03:44 GMT
Thanks!
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Post by nerd1000 on Oct 28, 2016 0:10:27 GMT
Hmm I just realized I really like that counter missile of yours. Can you post all the bits that goes into it so I can mess around with the design myself? I'm interested also! I'd like to try them out against my main workhorse missiles. Sure thing! I'm pretty proud of the engine in particular. I realized that running an oxidizer-rich mixture would bring my engine temperatures down and increase my average fuel density -- fluorine has a density of 1.5 tons per cubic meter -- so I'm running a 40% surplus on fluorine in a H2F2 rocket. Exhaust velocity is still over 4km/s, and TWR is over 600. I'm using magnesium for the injector purely for flavor reasons: a lithium injector would burn hot enough that the hydrogen would be completely redundant. If we ever get hybrid rocket motors, lithium/fluorine is gonna be a great fuel mix. Edit: I use graphite aerogel as the gimbal "armor" because it's extremely light, extremely cheap, and if anything hits the engine the missile's out of commission anyway. The warhead is a pretty standard pocket nuke. I'm certain there's room for improvement, but the main advantages are that A) it weighs half a kilo, and B) it can still do nuke-related activities. For a counter missile, keeping mass down is pretty important. The fuel tanks are pretty standard UHMWPE tanks. The oxidizer tank is split into two pieces so I could get the precise amount of oxidizer I wanted. Other than that, just make sure the radius is under 5 cm. I don't think they're worth a screenshot. The launcher takes minimal power, requires very little radiator area, and fires once every three seconds. This seems to work out just fine against salvos of between 10 and 30 missiles. I'm using a 200 round attached magazine for a total mass of under three tons and a total cost of 13.0 kilocredits. Considering as Strikers cost 9.83 kc each, I'm pretty happy with the system. Edit: The thing isn't armored, because the missiles are non-explosive and once you're in gun range, counter-missiles are redundant. I believe I selected boron nitride as the casing material due to its high specific heat capacity and high melting point; those properties appear to help harden the module against any stray nukes. If you're going for flavour on that engine, you should be aware that (to paraphrase Derek Lowe) at 700 degrees C fluorine starts to dissociate into monatomic radicals, thereby losing its gentle and forgiving nature. I doubt there's a nozzle material in the universe that would stand up to contact with a mixture of monatomic fluorine and hydrogen fluoride at 6000K... So for roleplay I suggest switching to fluorine/methane and running fuel rich like the stock stinger drone thruster. You'll lose a bit of performance of course...
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Post by nivik on Oct 28, 2016 0:53:03 GMT
If you're going for flavour on that engine, you should be aware that (to paraphrase Derek Lowe) at 700 degrees C fluorine starts to dissociate into monatomic radicals, thereby losing its gentle and forgiving nature. I doubt there's a nozzle material in the universe that would stand up to contact with a mixture of monatomic fluorine and hydrogen fluoride at 6000K... So for roleplay I suggest switching to fluorine/methane and running fuel rich like the stock stinger drone thruster. You'll lose a bit of performance of course... Ah, Things I Won't Work With. How I love thee. I'll consider other, more fuel-rich options, definitely. I hate fluromethane, though, just 'cause it's "the thing" and I hate doing "the thing".
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Post by captinjoehenry on Oct 28, 2016 1:03:32 GMT
Honestly I will say that fluorine hydrogen is a really good fuel in really all ways compared to fluorine methane. I assume it is non explosive?
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Post by ross128 on Oct 28, 2016 1:11:13 GMT
LO2-LH2 is a pretty okay alternative to F-LH2, especially if you don't like the idea of toting fluorine around in a plastic bottle. A little less punchy, and ends up being a tiny bit less cost-effective just because you're bringing more total fuel, but overall it's pretty okay and 300% more OSHA-compliant.
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Post by captinjoehenry on Oct 28, 2016 1:17:11 GMT
LO2-LH2 is a pretty okay alternative to F-LH2, especially if you don't like the idea of toting fluorine around in a plastic bottle. A little less punchy, and ends up being a tiny bit less cost-effective just because you're bringing more total fuel, but overall it's pretty okay and 300% more OSHA-compliant. Well it is also a LOT more massive. The reason fluorine hydrogen is so good is that it is about 20 fluorine per hydrogen which saves a huge amount of volum compared to the 4.7 to 1 hydrogen which results in huge hydrogen fuel tanks which is really inconvenient for small missiles.
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Post by cuddlefish on Oct 28, 2016 2:57:15 GMT
I've been using LO2-LH2 at a very oxygen heavy mix to maximize fuel density (and thus mass ratio) at the expense of velocity - 19:1 fraction gets my missiles 5km/s with 10.7 mass ratios.
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Post by nivik on Oct 28, 2016 3:01:00 GMT
Honestly I will say that fluorine hydrogen is a really good fuel in really all ways compared to fluorine methane. I assume it is non explosive? LO2-LH2 is a pretty okay alternative to F-LH2, especially if you don't like the idea of toting fluorine around in a plastic bottle. A little less punchy, and ends up being a tiny bit less cost-effective just because you're bringing more total fuel, but overall it's pretty okay and 300% more OSHA-compliant. Well it is also a LOT more massive. The reason fluorine hydrogen is so good is that it is about 20 fluorine per hydrogen which saves a huge amount of volum compared to the 4.7 to 1 hydrogen which results in huge hydrogen fuel tanks which is really inconvenient for small missiles. My main consideration with missiles, to be honest, is volume. Missiles -- particularly countermissiles -- are so lightweight compared to the mass of a ship that I don't care too much about the missile's mass. For a 1.5 to 4.0 kiloton vessel, gaining or losing three tons of ammunition isn't a big deal to me. However, the larger the missiles are, the larger their launcher is. Which means the forcer and stator are larger, the missile magazine is larger, the added volume in the ship's hull is larger (with the added armor load that implies), the hole cut into the armor to fit the missile launcher is larger...it gets out of hand really quickly. Fluorine is much more dense than LOX: 1.7 tons per cubic meter, as opposed to 1.1.' I'm looking at the database, and the highest density oxidizers after that are hydrogen peroxide (explosive), nitrogen dioxide (which I don't think has any reactions listed for it), nitrous oxide (1.23, can only be used as a monopropellant or burned with RP-1, neither of which is a great solution) and then LOX. If I didn't care about explosiveness, I'd probably use hydrogen peroxide and nitromethane. H2O2 has a density of 1.45 and nitromethane has a density of 1.13. Even with a crap exhaust velocity, missile volume would be pretty low. Oxygen is the densest flexible nonexplosive oxidizer aside from fluorine, and the densest nonexplosive fuel is probably decane at 0.73 (compared to methane's 0.42). Most of my shipkillers already use the decalox reaction for that exact reason. I believe the absolute densest nonexplosive bipropellant mix is fluorine/ammonia (1.7 and 0.68, respectively). Edit: Damn. H2O2/nitromethane isn't a valid reaction.
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Post by illectro on Oct 28, 2016 18:25:42 GMT
If you really want to look at high efficieny propellants, and OSHA isn't a concern, the highest specific impulse ever achieved from a chemical rocket was a Lithium-Fluorine-Hydrogen tripropellant system. Apparently the exhaust is so ionized that it would interfere with communications.
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