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Post by RA2lover on Oct 25, 2016 14:07:27 GMT
Not a coincidence. Your rocket will lose kinetic energy if it accelerates after being at a velocity over twice its exhaust velocity. Apply the rocket equation to it, and you get e² as the mass ratio needed to achieve that.
Personally i use a mass ratio about 5 instead, mostly because i don't accelerate my missiles that much.
EDIT: Interestingly, maximizing momentum leads to a mass ratio of e. What are we trying to optimize for anyways?
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Post by nivik on Oct 25, 2016 17:10:48 GMT
Not a coincidence. Your rocket will lose kinetic energy if it accelerates after being at a velocity over twice its exhaust velocity. Apply the rocket equation to it, and you get e² as the mass ratio needed to achieve that. Personally i use a mass ratio about 5 instead, mostly because i don't accelerate my missiles that much. EDIT: Interestingly, maximizing momentum leads to a mass ratio of e. What are we trying to optimize for anyways? I'm maximizing kinetic energy (E = 1/2 m * v 2), replacing the "v" term with the rocket equation (dV = v e ln[m 0/m f]). The difference between energy and momentum is really interesting, though. From what I can tell, momentum will be more useful in transferring motive power into the target (knocking the target into a spin or causing shear damage to armor) while pure kinetic energy is better for causing penetration and maximizing thermal effects. It makes sense. With the stock weapons, the lower velocity, high-mass coilgun rounds knock ships around pretty significantly, while high-speed, low-mass railgun rounds of similar energy tend to ricochet and not impart much motion on the target. Yet the higher velocity round has more penetration potential. Hmm. Momentum force over time, too, which indicates that if you want to maximize force on the target, momentum is what you want. Since material toughness is heavily related to strain, which is force divided by area, shots with a high momentum and low surface area (such as osmium long-rod penetrators) probably have the best shot of crashing through armor materials. It appears as though toughness (expressed as yield_strength2/(2*youngs_modulus)) is the measure of how much actual energy a material can absorb, according to Wikipedia. This implies that materials with a high yield strength and low Young's modulus are best against high-velocity rounds, but materials with a high ultimate tensile strength are best against heavier, low-velocity rounds. Need to test this to see if it's actually a design tip or just theory that doesn't pan out. Edit: here's a site that graphs materials based on strength vs toughness
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Post by captinjoehenry on Oct 25, 2016 17:30:26 GMT
Not a coincidence. Your rocket will lose kinetic energy if it accelerates after being at a velocity over twice its exhaust velocity. Apply the rocket equation to it, and you get e² as the mass ratio needed to achieve that. Personally i use a mass ratio about 5 instead, mostly because i don't accelerate my missiles that much. EDIT: Interestingly, maximizing momentum leads to a mass ratio of e. What are we trying to optimize for anyways? I'm maximizing kinetic energy (E = 1/2 m * v 2), replacing the "v" term with the rocket equation (dV = v e ln[m 0/m f]). The difference between energy and momentum is really interesting, though. From what I can tell, momentum will be more useful in transferring motive power into the target (knocking the target into a spin or causing shear damage to armor) while pure kinetic energy is better for causing penetration and maximizing thermal effects. It makes sense. With the stock weapons, the lower velocity, high-mass coilgun rounds knock ships around pretty significantly, while high-speed, low-mass railgun rounds of similar energy tend to ricochet and not impart much motion on the target. Yet the higher velocity round has more penetration potential. Hmm. Momentum force over time, too, which indicates that if you want to maximize force on the target, momentum is what you want. Since material toughness is heavily related to strain, which is force divided by area, shots with a high momentum and low surface area (such as osmium long-rod penetrators) probably have the best shot of crashing through armor materials. It appears as though toughness (expressed as yield_strength2/(2*youngs_modulus)) is the measure of how much actual energy a material can absorb, according to Wikipedia. This implies that materials with a high yield strength and low Young's modulus are best against high-velocity rounds, but materials with a high ultimate tensile strength are best against heavier, low-velocity rounds. Need to test this to see if it's actually a design tip or just theory that doesn't pan out. Edit: here's a site that graphs materials based on strength vs toughnessThis is really interesting but does it consider the behavior of hyper velocity impacts and the fact that if you have a suitable whipple shield the projectile will be made into plasma?
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Post by nivik on Oct 25, 2016 18:36:34 GMT
This is really interesting but does it consider the behavior of hyper velocity impacts and the fact that if you have a suitable whipple shield the projectile will be made into plasma? Nope. Most of my interest here lies in objects that are sufficiently massive that a Whipple shield will have minimal effect on them. A Whipple shield will convert any sufficiently small projectile into a more-or-less pure thermal effect on the underlying armor layer. However, when you have a 100mm projectile and are trying to decide if you want it to travel at 3,000 m/s and weigh 3.68 kg at burnout or travel 6,000 m/s and weigh 1.35 kg at burnout, this stuff becomes relevant. If I maximize KE, I'll get 24 megajoules with a momentum of 8,110 kg * m/s. If I maximize momentum, I'll get 16 megajoules with a momentum of 11,040 kg * m/s. This means that with a high KE warhead, I'll produce 50% more heat and spalling (which translates into better damage against low melting point materials and excess energy to transfer into fragile internal components -- I think), but with a high momentum warhead, I'll produce 36% more stress/pressure against the armor on impact (which translates into better penetration of high-strength "citadel" type armor -- I think).
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Post by captinjoehenry on Oct 25, 2016 19:30:56 GMT
This is really interesting but does it consider the behavior of hyper velocity impacts and the fact that if you have a suitable whipple shield the projectile will be made into plasma? Nope. Most of my interest here lies in objects that are sufficiently massive that a Whipple shield will have minimal effect on them. A Whipple shield will convert any sufficiently small projectile into a more-or-less pure thermal effect on the underlying armor layer. However, when you have a 100mm projectile and are trying to decide if you want it to travel at 3,000 m/s and weigh 3.68 kg at burnout or travel 6,000 m/s and weigh 1.35 kg at burnout, this stuff becomes relevant. If I maximize KE, I'll get 24 megajoules with a momentum of 8,110 kg * m/s. If I maximize momentum, I'll get 16 megajoules with a momentum of 11,040 kg * m/s. This means that with a high KE warhead, I'll produce 50% more heat and spalling (which translates into better damage against low melting point materials and excess energy to transfer into fragile internal components -- I think), but with a high momentum warhead, I'll produce 36% more stress/pressure against the armor on impact (which translates into better penetration of high-strength "citadel" type armor -- I think). So you are more talking about energy transfer than penetration. Okay that makes sense. Also how big does a projectile need to be in order to be unaffected by a whipple shield? Do you have a quick and dirty way to estimate it?
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Post by nivik on Oct 25, 2016 21:02:47 GMT
Nope. Most of my interest here lies in objects that are sufficiently massive that a Whipple shield will have minimal effect on them. A Whipple shield will convert any sufficiently small projectile into a more-or-less pure thermal effect on the underlying armor layer. However, when you have a 100mm projectile and are trying to decide if you want it to travel at 3,000 m/s and weigh 3.68 kg at burnout or travel 6,000 m/s and weigh 1.35 kg at burnout, this stuff becomes relevant. If I maximize KE, I'll get 24 megajoules with a momentum of 8,110 kg * m/s. If I maximize momentum, I'll get 16 megajoules with a momentum of 11,040 kg * m/s. This means that with a high KE warhead, I'll produce 50% more heat and spalling (which translates into better damage against low melting point materials and excess energy to transfer into fragile internal components -- I think), but with a high momentum warhead, I'll produce 36% more stress/pressure against the armor on impact (which translates into better penetration of high-strength "citadel" type armor -- I think). So you are more talking about energy transfer than penetration. Okay that makes sense. Also how big does a projectile need to be in order to be unaffected by a whipple shield? Do you have a quick and dirty way to estimate it? Nothing that I can back up with proof, I'm afraid. Naively, I'd expect any projectile that has more total heat capacity before its melting point than the volume of the Whipple layer it's trying to penetrate to survive in some way, shape, or form: once the Whipple shield vaporizes from the energy transfer and escapes the vicinity as a gas, it no longer presents a medium in which the projectile can convert its kinetic energy to frictional heating. If there's still projectile left at that point, it'd carry on through the shield. But really, I mostly consider anything over 100 grams to be more-or-less Whipple-proof. That equates to an iron sphere between 13 and 14 mm in diameter. That isn't even remotely based in reality, though; I have no idea how effective Whipples actually are.
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Post by captinjoehenry on Oct 27, 2016 2:39:19 GMT
Fascinating thing I have discovered. If you have a decane fueled combat ship you can equip it with resistor jets that have better thrust velocity than the nuclear engines and still have a worth quite a good deal of thrust. So you can have some very high thrust nuclear rockets for combat maneuvers and a few nongimballed resistor jets for maneuvering around a planet. The power draw isn't going to be massive and you get so much more thrust than using an ion engine and you only need one type of propelent
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Post by nerd1000 on Oct 27, 2016 3:31:45 GMT
Fascinating thing I have discovered. If you have a decane fueled combat ship you can equip it with resistor jets that have better thrust velocity than the nuclear engines and still have a worth quite a good deal of thrust. So you can have some very high thrust nuclear rockets for combat maneuvers and a few nongimballed resistor jets for maneuvering around a planet. The power draw isn't going to be massive and you get so much more thrust than using an ion engine and you only need one type of propelent Indeed. Hafnium-Tantalum carbide (the highest melting point material available, it can withstand 4200K) is the best material for a resistor jet coil: With it you can easily build a Decane resistor jet that rivals Methane NTRs in exhaust velocity or a hydrogen resistor jet that beats the stock Xenon MPD! It's a touch expensive, but the coil can be very small and light even on a extremely powerful thruster so that's basically a non-issue. I'd love to have access to something like ATTILA for electric propulsion. I reckon MPDs would be essentially obsolete at that point.
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Post by Pttg on Oct 28, 2016 5:06:18 GMT
Using very small missiles, it is possible to build a 1kw launcher with 33 mm/s launch velocity and 20ms reload rate.
DO NOT DO THAT.
The missiles -- and this is a technical term here -- bunch up in space and explode each other.
Incidentally, even after I punched up the initial velocity and increased the reload speed to 500ms, I still had the problem of rapidly deploying over a thousand missiles and turning my computer into slag. I bet it would do great against laser defenses, though!
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Post by jonen on Oct 28, 2016 12:47:11 GMT
Using very small missiles, it is possible to build a 1kw launcher with 33 mm/s launch velocity and 20ms reload rate. DO NOT DO THAT. The missiles -- and this is a technical term here -- bunch up in space and explode each other. Incidentally, even after I punched up the initial velocity and increased the reload speed to 500ms, I still had the problem of rapidly deploying over a thousand missiles and turning my computer into slag. I bet it would do great against laser defenses, though! Basics of launcher design: You want to launch objects at sufficient velocity to allow them to clear the launcher before the next object is launched. Advanced launcher design: If you launch things fast enough and at sufficient velocity that your launcher could potentially be used for corrective orbital burns, you probably want to refrain from using "launch all", and set very restrictive ranges for automated launching.
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Post by nivik on Oct 28, 2016 15:58:20 GMT
Using very small missiles, it is possible to build a 1kw launcher with 33 mm/s launch velocity and 20ms reload rate. DO NOT DO THAT. The missiles -- and this is a technical term here -- bunch up in space and explode each other. Incidentally, even after I punched up the initial velocity and increased the reload speed to 500ms, I still had the problem of rapidly deploying over a thousand missiles and turning my computer into slag. I bet it would do great against laser defenses, though! Basics of launcher design: You want to launch objects at sufficient velocity to allow them to clear the launcher before the next object is launched. Advanced launcher design: If you launch things fast enough and at sufficient velocity that your launcher could potentially be used for corrective orbital burns, you probably want to refrain from using "launch all", and set very restrictive ranges for automated launching. I usually set my launchers for a 2 to 3 second reload time and use multiple launchers to salvo if I feel it's necessary. I'm a huge proponent of high dV missiles, though; the faster the missile is going, the less time it spends in point-defense range.
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Post by Rocket Witch on Oct 31, 2016 21:26:49 GMT
Here's a fun one: missile launchers on the fronts of ships still launch the missiles facing the ship's front despite taking up horizontal space across the nose. In direct combat, this immediately adds to the velocity of the launcher to each missile. If one launcher is used, this also has the effect of meaning they can be launched at a high rate and won't flounder around trying (and failing) to avoid collisions; they just thrust forward straight to the target. Issues include a limit on the length of the missiles used for a given ship width, and inability to taper the ship's nose completely. Ultimately one is better off using a gun for this niche application, but I couldn't get a gun to actually shoot its guided ammunition when I tried making one, and I ended up with this.
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Post by Durandal on Oct 31, 2016 21:29:55 GMT
Here's a fun one: missile launchers on the fronts of ships still launch the missiles facing the ship's front despite taking up horizontal space across the nose. In direct combat, this immediately adds to the velocity of the launcher to each missile. If one launcher is used, this also has the effect of meaning they can be launched at a high rate and won't flounder around trying (and failing) to avoid collisions; they just thrust forward straight to the target. Issues include a limit on the length of the missiles used for a given ship width, and inability to taper the ship's nose completely. Ultimately one is better off using a gun for this niche application, but I couldn't get a gun to actually shoot its guided ammunition when I tried making one, and I ended up with this. Try using separate ammo storage from the launcher.
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Post by Rocket Witch on Oct 31, 2016 21:54:44 GMT
Try using separate ammo storage from the launcher. ;) This ship already does. A big plastic tub of 1000 5kt nukes. There's also a gun turret within the small gap at the centre of the launchers.
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Post by ross128 on Oct 31, 2016 22:02:03 GMT
I use separate ammo for all my ammo-based weapons. Putting the ammo in-line with the rest of the components generally adds less total volume (which in turn keeps cross-section and armor area down), and once the first ammo bin is placed I can keep adding to the cluster until it hits the cap of 20 or reaches the same radius as its neighboring components, which allows me to pack a lot of ammo into as little space as possible. For ammo that is an explosion hazard, there's the added benefit that all of the ammo can be gathered into one heavily-armored section.
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