Starman4308

It's going to be difficult, and you aren't going to get much altitude. You've got to pay for your altitude with kinetic energy, so the absolute best you can get, off a 50 m/s boost from rover wheels, would be about 127 meters above your starting point. If you don't mind cheating on the "glider" definition a bit, you can either go for a Firespitter propeller, an ion engine, or perhaps a 0.625m jet engine from NecroBones's Modular Rocket Systems mod.

The typical conversion you see in RealFuels is that 1 unit of LF or oxidizer is about 5L of fuel, and 1 xenon seems to be about 0.1L. For mass, a tonne is a tonne. RealFuels does knock down the mass of fuel tanks a lot, but that is because KSP fuel tanks have unrealistically low fuel/dry mass ratios.

Oh, now that the thread's bumped a bit: Thanks for the source code. It really helped me with my WIP mod (which is, sadly, not progressing as fast as I want, and is requiring way more knowledge of Keplerian mechanics than I thought at first).

There is no reason why a maximally-efficient launch in FAR should be of 2.0 TWR. In FAR, ignoring aerodynamic stresses, it is the point where increasing engine mass (and thus TWR) to reduce gravity losses is cancelled out by the loss of dV caused by increased engine mass. 2.0 TWR is entirely an artifact of stock aerodynamics and terminal velocity. If engines were infinitely light, and we ignored aerodynamic stresses, ideal FAR TWR would be something crazy like 30.0, enough to once again hit terminal velocity. Ideal TWR is somewhere around 1.4 because of the parameters (typical engine TWR, Isp, surface gravity) which go into the calculations of efficiency. EDIT: In short, ideal ascents go like this: at launch, infinite thrust until you hit terminal velocity, followed by maintaining terminal velocity all the way up (and, as such, infinite TWR again in vacuum). This is the absolute minimum amount of dV loss to the sum of gravity and atmospheric drag. The only reason you do not see this is that engines have finite mass and finite thrust: that TWR costs you dV.

No. Terminal velocity is, was, and forever will be "the velocity at which this object, traveling in its current orientation, would experience a drag force equal to gravity". Yes, during the course of a launch, this changes. However, in stock, you have a curious situation where, for the first 10 km of ascent, terminal velocity is easy to reach, does not increase very rapidly, and is crucial in determining launch efficiency. In stock, you design for that first 10km of crawling at 100 m/s, whereas in FAR, you design on other factors, mostly independent of terminal velocity.

I seriously suggest you play FAR a bit before making such statements. Ascent path is determined by a different, only partially overlapping set of factors in FAR. Aerodynamics plays a huge role in ascent path. If it were "mostly determined by the planet", you'd never see the 1 km/s dV savings out of FAR that you do. Stock requires you to stay vertical for ~6-10 km because drag is so horrendous. In FAR, you're usually already several degrees off vertical before you ever crack 1000m, and your path from there to around 30 km is determined mostly by aerodynamics and TWR, because your rocket orientation is constrained to a narrow cone around prograde. This is contrasted with stock, where your pitch profile is determined solely by gravity, TWR, and atmospheric density, because aerodynamic stability/instability is just not a thing in stock. Your "advice" is shown false by the large number of people who have actually played FAR, and the fact that few real-world rockets have first-stage TWR above 1.6 (and those which do generally lose some SRBs in less than a minute). In stock, ideal TWR is very much a factor of terminal velocity, because you want to minimize losses in the 0-10 km zone, which means an efficient terminal-velocity ascent. In FAR, atmosphere drag is almost a negligible concern, and ascent path is more determined by other factors, such as aerodynamic stress, aerodynamic stability/instability, and balancing minimization of gravity losses against maximizing dV by minimizing engine mass.

Incorrect. Sure, you get less drag, but terminal velocity is also a lot higher. Unlike in stock, where you can get to terminal velocity relatively quickly, FAR would require an absolutely thunderous acceleration to get to terminal velocity*. *Keep in mind that, the farther up you go, the thinner atmosphere is, and the higher terminal velocity is. If you don't hit terminal velocity in the first 10km, you're unlikely to ever hit it.

No: the changes are more comprehensive than that. Drag in FAR is a function of parts, how they are arranged, and the orientation/speed of the vessel. You seem to be hung up on the nickname of "souposphere" and assume I mean to say FAR affects atmosphere. You also seem to be vastly downplaying the differences between FAR and stock: FAR plays a lot different.

You are misunderstanding a few things. FAR changes not only drag coefficient, but also cross-sectional area. Cd is now a function of rocket shape and Mach effects, while cross-sectional area is a function of rocket shape. In stock, Cd is 0.2 for most parts, while cross-sectional area is 0.008 * mass. As such, an object with 0.2 Cd in FAR (which is only true for a certain orientation) will only fall at the same rate if it's cross-sectional area happens to be 0.008 * mass. What this means in practice is that atmospheric drag almost disappears, because Cd * A will almost always be vastly less in FAR than stock, even if you're in the worst of the trans-sonic region. This means that TWR and launch profile are vastly changed, particularly because FAR can now model aerodynamic stability and instability: try to pull that 45 degree gravity turn at 10 km altitude, and your rocket will flip out and destroy itself. Really, just try it. There's a reason stock aerodynamics is called the "souposphere": when you move to a realistic aerodynamic model, atmospheric drag plummets radically, particularly for streamlined designs. EDIT: I may or may not slightly misunderstand the details of the FAR calculation (my experiences have had some wonkiness about how cross-sectional area and Cd are calculated), but from experience, I can tell you this: FAR is vastly removed from stock aerodynamics, FAR drag is vastly less than stock for any reasonable design, and FAR ascents have to be much different from stock.

It looks like a combination of a weird conics setting*, and Ike being Ike, where Ike is not so much a moon, as it is Murphy made manifest. I forget how to change your conics setting, and there's nothing to be done about Ike, unfortunately. *How your orbit is portrayed on the map. For example, a lunar flyby could be projected either from Kerbin's frame of reference or the Mun's frame of reference.

Dependent on the vehicle in question. A small, poorly designed rocket is going to have lower terminal velocity than a large, aerodynamic rocket*. In any event, the answer is "way more than is practical". About the only place I can think of where you might run into terminal velocity is an Eve/Venus ascent, because you've got a lot more atmosphere, and a lot more time lingering in high-density atmosphere. *Scale up a rocket by 5x, and while cross-sectional area goes up by 25x, mass (and therefore inertia) go up by 125x. It's probably the biggest reason why no orbital launch vehicle I know of has been less than ~10 tonnes.

I personally like Modular Rocket Systems and SpaceY.

Le Z-1k battery. Depends on how you define drag. Is it the sum of (part mass * Cd), or is it the weighted-average Cd? For purposes of launch, the first definition (an absolute value) is more useful, while for purposes like terminal velocity, the second definition (effectively mass-normalized) is more useful.

The short version is that in FAR, you aren't getting to terminal velocity, so you shouldn't bother trying. In stock, terminal velocity is crucial, because for the first 10 km of your ascent, you're basically fighting gravity every step of the way at a sluggish 100 m/s-ish pace. You are taking 9.8 m/s^2 of gravity drag every second for ~100 seconds for that first part of ascent. In FAR, that consideration is gone. You can heel over almost right off the pad, so the primary consideration is exactly where it is that adding more engine mass reduces delta-V faster than the increased TWR reduces gravity losses. There is also consideration for atmospheric stresses: a high-velocity rocket in low atmosphere is going to be under a lot of aerodynamic stress, something which affects a significant number of real-world rockets. As to the 2.0 TWR approximation: for that first 10km, terminal velocity requires only a tiny bit more than 2.0 TWR, and most rockets will get that tiny bit anyways from burning fuel. 2.0 is a good approximation, and conveys the point of "one gravity of acceleration to fight gravity, one gravity to fight atmosphere". When explaining it, I usually add "and a bit more for accelerating as terminal velocity goes up". EDIT: In short, rocket designers trade off almost horrific gravity losses in the first minute or so for improved performance during the rest of the ascent. Don't forget that body lift is a thing in FAR and the real-world: you can get away with a bit lower TWR than would otherwise be necessary because of that. Also, real-world fuel tanks and engines are much lighter than KSP, so there tends to be a bigger difference in TWR between the start and end of a stage.

My serious suggestion is "Effects of nosecones in stock aerodynamics". I'm in no rush to re-title it though. The less-serious one is "Particularly minute minutiae of nosecones in stock aerodynamics".

Muuuch lower TWR in FAR/NEAR: the sweet spot is usually 1.2-1.6, probably optimal around 1.4. While increased TWR reduces atmo drag, you also need engine mass to get that TWR, and that engine mass will reduce your available dV. Reduced atmo drag also means that, to some extent, you can get away with it: there's not so much pressure to get out of the super-duper-drag zone (roughly 0-10km) as quickly. There's also a consideration vis-a-vis pulling off your gravity turn: if your TWR is too high, you generally wind off shooting up to space and lose too much to gravity, whereas a lower TWR helps you manage a good, tight gravity turn. I make too many 1.6-ish TWR boosters, and I curse and struggle and scream trying to bring the rocket's pitch down. You can also look at real-world boosters, which tend to be in the 1.2-1.6 TWR range. Saturn V came in at around 1.17-ish, while Proton-K came in around 1.55. I've heard of some with around 2.0-ish, but that is only on account of SRBs which last maybe 30 seconds before being discarded. EDIT: I think the reason you see so much "2.0 to terminal velocity" is that, for the crucial first stage of ascent in stock aero, 2.0 TWR is a very good approximation of hitting terminal velocity, and it's roughly the upper bound of what you should be aiming for (particularly in asparagus-staged designs).

Stock aero. FAR has never entered this conversation, because we all know nosecones are a good idea with FAR. With stock, the empty truck and the truck full of generic rocket parts go the exact same distance, because both of them have the same inertia/drag ratio. However, the truck full of nosecones goes farther, because nosecones only have drag proportional to 0.1*mass, instead of 0.2*mass: thus, the truck has an overall lesser drag coefficient, and thus has more inertia/drag.

It's not a contradiction. Let's take an illustrative example with a similar property: ascent from an airless planet with variable Isp. Assume for a moment that we have two mostly-identical rockets. Rocket A has a 400s engine, while Rocket B has a hole in a fuel line, and only gets 200s Isp. At the moment of launch, both perform identically, except with Rocket B using twice as much fuel. As time goes on, however, Rocket B uses up more of its fuel, and can go horizontal more quickly, because it no longer has to spend as much thrust fighting gravity. Rocket A, burdened by unspent fuel, falls increasingly behind, and must use more acceleration fighting gravity. When you add things up in the end, Rocket B spent less delta-V fighting gravity. However, Rocket A has used less fuel, because it had the more efficient engine. If you define "gravity drag" as being in delta-V terms, Rocket B is the winner, but if you care about the overall result, Rocket A spent much less fuel. This is what is going on with stock nosecones. You lose less delta-V to atmospheric drag, because your average Cd was lower and terminal velocity was higher. However, by having the nosecone, you reduced the overall delta-V and TWR available, and as such, you get to orbit with less fuel and less delta-V. EDIT: In short, your gut instinct is correct: stock nosecones are a bad thing. They only seem to be a good thing because of a giant loophole in how atmospheric drag is defined, as a loss of velocity. It'd be a bit like minimizing gravity drag by going with a 4.0 TWR rocket: it's not actually helping the overall problem (getting to space with the most payload), it's just making one component of the problem look less bad.

Incorrect. Adding a part with a lower Cd than the average will reduce the average Cd, which, in stock, means a higher terminal velocity. This is, as mentioned, because terminal velocity is inversely proportional to average Cd, and is independent of actual mass. Gravitational force goes up proportional to mass, while drag force is proportional to (average Cd * mass), so if you reduce average Cd, you have less drag at any given velocity. You can test it out yourself. I took an OKTO2, and added either a 0.1t nosecone, or two 0.05t batteries. The one with the nosecone reached about 20 m/s faster peak velocity when dropped from 5 km (using Hyperedit). Now, this doesn't mean you should slap a nosecone on stuff in stock: I'm still not convinced you will ever find a scenario where a rocket can lift off more efficiently, because while a nosecone increases terminal velocity, it also increases mass and absolute drag. This means less dV available to your rocket, and I strongly suspect it won't do you much good for net atmo/gravity drag losses.

On that one, you're incorrect. Nosecones will increase the absolute amount of force, but terminal velocity in stock aero is a function of drag force normalized to mass. Since a nosecone will reduce the drag/mass ratio by having Cd < 0.2, a nosecone will increase terminal velocity. If you need convincing: build a small 1.25m rocket, and build a big rocket with multiple 3.75m stacks. Same terminal velocity, because they both have about the same weighted-average Cd (0.2). You did see the thing I posted about what happens when you add thrust to the analysis, right? Your acceleration to drag is less, but your acceleration to thrust is also less for the added mass (which reflects less dV due to more mass).

I do see one way in which nosecones could maybe reduce drag losses. Nosecones will increase terminal velocity, thus decreasing time spent in low atmosphere. Whether it is possible for this effect to outweigh the increased mass/drag of a nosecone, I am uncertain, and I suspect the answer is "never". I just haven't got a mathematical proof of that yet.

Err... the first post I had (vis-a-vis FAR ascents) seemed to be fairly relevant, as a poor ascent profile could explain wobbly rockets. Should I repost that section here? One possible explanation I have is that his rocket lacks fins, which would cause a lot of wobbling in FAR, something I'd addressed in that post.

That's true under the assumption of zero thrust. Under the assumption of "actually trying to get to space", increased total drag force will mean more overall force resisting your rocket at a given speed. In addition, the added mass means your thrust counts for less. So, under thrust (let's assume 200 kN) With nose cone: a = (200 - 7.84k) / 39.4 = 5.076 - 0.199k Without nose cone: a = (200 - 7.8k) / 39 = 5.128 - 0.2k At k = 0 (stationary), no nose cone is better. The crossover point is at k = 51.282. Now let's see what k means: Fd = 0.5 p*v^2*Cd*A = 0.5*p*v^2*0.008*Cd. Since I had Fd = k*Cd, k = Fd/Cd = 0.5*p*v^2*0.008 = 0.004 * p * v^2 This means that the crossover for acceleration occurs when p*v^2 = 51.282 / 0.004 = 12820.5. At p = 1 atm, that would require a velocity of 113.23 m/s. I haven't quite worked out the math yet, but I suspect that terminal velocity (most efficient velocity of ascent) will always lag behind the k-crossover. It just doesn't make sense to me that a rocket would ascend with greater efficiency when it has more drag and gravity force working against it.

No, it's always worse. Nosecones always add mass, they always add drag. Therefore, unless you use FAR/NEAR, nosecones are always bad unless you are looking for aesthetics. You can thank stock "aerodynamics" for this conclusion. EDIT: Unless you're looking to, for some reason, have a ballistic collision with terrain at the highest possible velocity. Nosecones will reduce drag/mass ratio, so they'd be good for that. I have no idea why you would want to do this, but it would be a use for nosecones.

Well, as long as we're coming up with silly ways to move Pallas: A mere 53,000 Harrington-verse missiles should do the trick. The Lorentz factor for 0.8c is 1.67, so the inertia of a single 100-ton missile is 4*10^13 kg*m/s. We need to shift Pallas by about 0.01 m/s, so we need 2.11*10^18 kg*m/s of inertia, which comes out to about 53,000 missiles. I think I remember missile swarms of about that size in major fleet engagements, so that's reasonable. One might be able to get away with even fewer if the missiles have a top speed faster than the 0.8c limit of the ships, and in a pinch, a suicidal superdreadnought should do the trick. It says something about the Harrington universe, that moving Pallas is feasible for them.