火箭设计学

RuohongZhao

【此帖纯粹搬运+经验评论分享】作为Wiki百科一部分。参见 http://bbs.deeptimes.org/forum.php?mod=viewthread&tid=2123294 6楼。

一楼目录。

二楼：从官网上D下来的教程。正在翻译……

三楼开始：自己和大家分享心得吧。。。

RuohongZhao

Basic Rocket Design 初级火箭设计

Bare Essentials

Unless you are an expert at THE GAME, you will need to do this. For a beginner, I would recommend using the one-manned pod. It is smaller and you can fit the simpler parts to it. (If you are in the demo, don't worry about that.) On the top of your Command Pod, put a parachute. At the bottom, a decoupler. Did you catch that? That was important.

Symmetry 匀称

On the top left portion of your screen, you may see a circular gauge-like thing with a dot in the middle. If not, keep looking. That is the symmetry feature. If you click on it, you will see it change. This new pattern represents 2 things. Try placing down a part on the side of your ship. On the other side of your ship, there will be a duplicate of that piece! If you click it again, you can have 3 parts, 4, 6, and then 8. Your rocket MUST be perfectly symmetrical, or else it will explode in your face on the launchpad. In other words, the game is more fun without symmetry.
Liquids And Solids

There are two types of people in the world. Those who use liquid engines for most tasks, and those who are new to KSP. So, in short, Liquid fuel engines are your run-of-the-mill rockets, and Solid Rocket Boosters, or SRBs, are best for launching your rocket. Once an SRB has been fired, you cannot control it. This makes it best for your first, launching stage. Liquid Fuel Engines are, as stated earlier, your run-of-the-mill rockets, and can be controlled with the thrust gauge.

SAS 稳定装置（翻译有待讨论）

One of the most important aspects of KSP is the SAS. SAS is designed to help stabilize your ship. It is best to use one advanced SAS, and turn it on by pressing T. if that doesn't work, than add either a few normal SAS units, or replace one or two of your liquid engines With a thrust vectoring liquid engine. You can tell if an engine is thrust vectoring by mousing over it and looking at its menu.

RCS and Vectoring Engines 姿态火箭与矢量发动机

RCS and Vectoring Engines both do the same basic thing. They help you control your rocket. RCS is strange In that, as well as requiring its special mini fuel tanks, It can be placed anywhere. By that, I mean it doesn't need to be placed on the fuel tanks. To enable RCS, press R. It will now automatically activate to help you move your ship faster. Vectoring engines do the same, but require to be firing instead of a toggle.

Tips n' tricks 小技巧

Those couplers that let you split your rocket into three sections are couplers, not decouplers. You need to put a decoupler at the top of them. If you have the full game, pressing caps lock will change the controls a bit. Sometimes this can give you an advantage. Also requiring the full game is trimming. This is mostly for spaceplanes, but just for the record, if you hold ALT and steer your ship, the game will automatically continue to steer your ship that way. this is for a problem with spaceplanes, but you should know just in case. Also, moving back to the demo, Right clicking on the symmetry feature will lower the amount of things. Also in the demo, One thing you should never do, no matter what, is have your RCS and SAS on at the same time. Well, as long as that is an Advanced SAS, or ASAS.

EVAs! 出舱活动

It is version 16, and we have EVA's! If you mouse over one of your crew members, an "EVA" Option comes up. click that and you can walk around! You can move with WASD, and You can activate a jet pack by pressing R, and then Shift to go up and Ctrl to go down. You can also hold shift to run, But only on Kerbin. You also have limited fuel, which refills when you go into your command pod.


Intermediate Rocket Design 进阶火箭设计

Center of gravity, point of action and how they demand symmetry in your rocket. 火箭的质量中心，反推作用点和怎么保持火箭的平衡

The center of gravity is the point in your rocket where it would be in total balance. It's the point where, if the rocket was resting on that point, you could give it a nudge and it would freely follow that nudge without gravity having a say, because left and right, up and down, front and back, they're all equally heavy and perfectly balanced on this single point. That is always one single point in space, and unless you have a very oddly shaped rocket, that point is somewhere inside your rocket. Sadly, this point is usually not the point of action, i.e. the point where your engines create thrust. If it was, that would be sweet, since we could push the rocket wherever and however we want (ignoring air resistance, of course). So the next best thing we can do is to put that point of action "behind" the center of gravity and point its action vector towards the center of gravity. Or, simpler put, put the engine behind the mass and thrust in the other direction. What sounds obvious at first has some implications. First, your point of action, actually the vector sum of your thrust vectors, for you nitpickers, HAS to be lined up with your center of gravity. In other words, your rocket has to be symmetrical to be stable. You can try that for yourself. Get a broom. Put the endpoint of the handle on your hand, with the brush up, and you will notice that you can balance it. You will also notice two things: First, it's easy to balance it as long as you work hard on it, and it can very easily tilt to one side, and if it does it falls FAST. And second, it's surprisingly more easy to balance the broom with the brush up towards the ceiling rather than having it resing on your hand. If you would now put a lot of pressure on that handle, you could thrust that broom upwards without it falling to the side (trust me, it would work). That's basically how our rocket works. Now attach something to the side of the broom and see how this works out for you. If you try to balance the broom the same way, it will fall to the side where you tacked something onto it. Unless you hold it at an angle to the side... looks stupid if it were a rocket, doesn't it? If you would thrust that broom upwards, it would not only fall to that one side, it would actually start to spin around the x-axis and do "loops"... or crash, which is more likely since gravity is playing in this game as well. So the first thing to keep in mind is to keep your rocket symmetrical, at least to the point where the center of gravity is always above the combined point of action (if you have more than one engine, you have more than one point of action, which can be summed up to a total point of action and an action vector). In physical terms, that point of action has to be lined up with the center of gravity, with its vector aligned with the hypothetical axis that exists between the cog and the poa. In simpler terms, the point where your rocket would be in balance has to be behind the point where the combined force of the engines pushes, and the engines have to push towards that center of gravity, i.e. their thrust exhaust has to point away from it. That also means that "inwards" thrust stabilizes the rocket, as long as the thrust is equal from all sides. It forces the rocket to stay in its current direction, but it also means that you are wasting fuel since you have engines thrusting "against" each other. Think of it as the toe-in of your cars steering wheels.

Mass vs. weight 质量与重量

As long as you're on Kerbin, they're interchangeable. Your mass is directly related to your weight. It's a bit different in space. Weight is the result of mass being accelerated, either by gravity or by movement. And while you're weightless in space (well, your outwards acceleration from your speed matches the inwards acceleration from gravity), you're not without mass. To cut the theoretical crap short, the more mass you have, the more energy you have to expend to change its speed and direction. The heavier your rocket is, the more fuel you have to spend to make it faster (or slower!), provided you do not have gravity to work for you. Usually, in this game as well as when you're overweight, gravity works against you. This also means, that a mass gets "heavier" if you accelerate it faster. It doesn't increase its mass (unless you're approaching light speed, let's ignore that for now), but the stress weight puts on the mass increases. That's called g-forces. On Kerbin, you experience 1g. Which is equal to an acceleration equal to Kerbin's gravity at surface level. How does this affect your rocket? Well, it affects it twofold. First, the more mass you have, the more fuel you have to spend to get that mass up into orbit. Hence "bigger" isn't always "better". We'll get to that in detail later. The other factor is that the faster you accelerate your rocket, the more stress you put on its parts. Some parts are able to sustain that stress. Some are not. It is, in general, easier to build a slowly climbing rocket than one that jumps into orbit at 9g or more, not only because our passengers don't really like having a truck sitting on their chest (which isn't as much an issue so far), mostly the problem now is that the acceleration you put into the rocket stresses the parts that keep it together past their breaking limit. Which means you have to add struts, which add to the mass, which cost you fuel.

Thrust-weight ratio 推重比

Basically, it's the result of dividing your thrust (in Newtons) by your weight (in kilograms times acceleration, i.e. kg*m/s², so... well, also in Newtons). Thrust is what gets you up, weight is what keeps you down. And if thrust>weight, i.e. if your thrust-weight ratio is more than 1, you go up. If thrust<weight, you can put your engines into overdrive and you won't move an inch. For the record, the Saturn V first stage rocket engine had a TWR of 94.1. In other words, it could have lifted itself over 94 times. Beat that! What does that mean for our space vehicle? Basically, it means that whatever we put as rockets behind our craft, it has to overcome the total weight of the craft. Which also means that, if you have multiple stages, the upper stages are just dead weight at start. Yes, yes, there are rockets in there and they might have a lot of punch, but they do not add to the thrust at start. Thrust is always only the thrust you ACTUALLY apply, not the thrust your rocket can eventually do in total. Note that every rocket engine has a TWR of more than one. By definition. Engines below a TWR of 1 need some kind of aerodynamics on the craft to get it off the ground. The question is, though, whether the dead weight sitting on top of it STILL keeps that equation above 1. The F1's 94.1 TWR doesn't mean that the Apollo craft got shot into orbit at 100g. It means that there was a friggin' HUGE rocket sitting on top of that engine and hence it could barely get the whole behemoth up into an orbit! My guess is that Kerbin has a gravity of about 10m/s² (much like earth), meaning that a rocket engine rated at 200 max thrust (like the non-gimballed stock engine) can lift 20 units of mass (or 8 stock liquid fuel tanks). Given that a rocket of 1 stock command center, 7 fuel tanks and 1 engine (totalling a mass of 20.5, 7*2.5+2+1) can't get off the ground but with 6 fuel tanks it can, I'd say that should be about right. So when building your rocket, always add up the weight of the parts you assembled, multiply by 10, then divide by the thrust of the engines, but ONLY the engines that actually thrust. The more you get out of that, the faster your rocket will climb. Considering that engines seem to overheat more readily if they're operated at the TWR limit, try to get to a TWR of at least 1.7 in your first stage. My Mun rocket has a first stage TWR of 2.2, which is plenty but not overdoing it to the point where the g-forces become unmanageable. Also, keep in mind that you will use up fuel as you climb. Your fuel tanks will get emptier with every second your engine fires, making them lighter, meaning, less weight has to be lifted. Plus, gravity decreases with distance squared, which also makes the pull of Kerbin less and less with every inch you climb. Not as much as one would wish, though.

Staging, and when to do it 多级火箭的分级与分离时间

Staging usually means tossing dead weight. You jettison spent rocket parts to make your craft lighter. Less mass means less energy required to move the rest of the mass. The obvious choice would now be to stage as much as possible, to carry around as little dead weight as possible. This is not the best strategy, though. Staging also means that you have to carry around the weight for the staging equipment and, in case of a liquid fuel set, another liquid engine. A spent stock booster weighs 0.36. The equipment to jettison it weighs 0.4. A spent liquid tank weighs 0.3. The additional engine and the staging equipment to toss it weighs 2.8. A compromise has to be found. There is no hard limit to tell when to stage and when not to, what matters is how long you'd have to haul around the dead weight (if it's just a few seconds between the booster's end of life and until the other engine of this stage burns out, just keep the booster attached, it's not worth the extra weight for another set of staging couplers. If it's for the rest of the flight, tossing it pays off easily), whether the spent stage prevents you from firing the next (a lower stage burned up covering an upper stage has to be jettisoned, of course) and what the stage is used for (an upper stage is usually in use longer than a stage to reach orbit that is burning at max power constantly, i.e. a fuel tank in upper stages lasts much, much longer). I find the sweet spot for liquid tanks to be around 4-5 for lower stages and about 2 for upper stages.

As much thrust as possible to the bottom 最合适的起飞重量

Also easy to see, the more thrust you apply right from the start, the less dead weight you carry around. It's usually quite pointless to have a lot of thrust further up if you cannot get off the launch pad. On the other hand, as mentioned above, the more thrust you put behind your crate, the more g-force it has to endure and the more you stress your parts. Not to mention the air resistance which is of course worst lower in the atmosphere.

draaaaaaag 该死的阻力神马的

While we're at it, drag. I hope I got that one right, it's kinda hard to tell how that part really works. Basically, every part you add has air resistance. Doesn't matter once you're in orbit (and hence satellites rarely look streamlined), but it's a big issue until you hit that magical 70,000 meters. I still have very limited data on how drag really works and what affects what, so far all I can say is that it's there and that you should probably take it into account, i.e. creating insanely wide rockets to cram in a lot of boosters to fire at the same time might be a drag. Literally. Especially if you try to fly such a rocket at high speeds. Funny enough, though, those wings seem to work in orbit as well. Don't ask me why.

Where do you need the most power? 什么时候需要功率全开？

That's a simple one again: From ground to orbit. You will NEVER in your flight have to spend as much energy as in that part of your flight. Getting from orbit to the Mun, landing on the Mun, getting back off the moon, flying back to Kerbin and landing there? Easily done with about 1/6th of the fuel spent to get into orbit. I am NOT kidding or exaggerating here. Remember that Saturn V rocket that sent Apollo to the moon? Remember how friggin' huge that thing was? And what a tiny little bit of it actually went to the moon, with the rest being tossed somewhere along the way? And how that little service module that got them basically from orbit to moon also got them back? It's the same here. You will spend a good 80% of fuel and dump about as much of your rocket before you reach the Mun.

Long or wide? 火箭胖一点还是高一点？


Preferably neither. Making your rocket longer is about as bad as making it wider. For various reasons. Wide rockets tend to be bottom-heavy (because, usually, they are wide at the bottom, to maximize thrust at liftoff), making them harder to control because they sway easily, and they are prone to out of control rolling if the thrusters on the outer edges are not PERFECTLY aligned (which they are, well, never), due to leverage. Also, I'd expect them to be very susceptible to drag, meaning a lot of power is lost due to air resistance. Wide rockets usually need quite a bit of SAS to keep from spinning out of control. And they are prone to "flipping", i.e. uncontrollably going upside down because they are easy to tilt and bank. Think of the broom example at the beginning. Long rockets are very hard to tilt and bank, making them hard to steer and very sluggish. They also usually suffer from top-heaviness, especially after a good deal of their lower stage fuel is spent, which can result in rockets that are very hard to control and to keep from going "keel-up", i.e. nose-down without a lot of RCS thrust. Long rockets usually need quite a few wings to keep them manageable and responsive. And even then they are very slow to react and need foresightful piloting. They usually keep their direction pretty well as long as they are balanced and there's a lot of thrust applied, but once you bank and tilt them, they can very easily oversteer, especially in horizontal flight with a center of mass that's very close to the top (as it is usually just before your ascent stage is burned up, with a lot of empty and near empty fuel tanks hanging on your tail). Still, I prefer long over wide rockets.

So, with all that, what IS now the best design? 那么到目前为止，什么才是最佳设计呢？

From these tidbits we can puzzle together a few cornerstones that give us a good idea what a GOOD design would be, and what would be a BAD one. It's a GOOD idea to put every engine that CAN actually thrust at launch to work right at launch. Else it's dead weight we first have to haul upwards. If that gives you too much thrust and your rocket starts to fall apart due to excessive G forces, slap on another can of gas for that liquid fuel rocket, or take off some boosters (yeah, right...). It MAY be a good idea to not run that liquid engine at full power if you get so fast that your friction is killing most of the power you put behind it. Actually, I usually take off with full throttle, only to ease off a little as I climb to keep the speed from going overboard and being burned in friction. But if you have a big rocket, it CAN be a very good idea to make the first stage(s) only of solid boosters, they're very light for their push and even with a coupler on them they have a better TWR than liquid engines. Their main drawback, the inability to control their thrust output, doesn't matter for the first 20,000 Meters since you actually just want to get the hell up there. Do not expect too much from that, a full complement of two solid-only stages underneath every single engine of my actual first stage only got me about half a fuel tank. Yes, half a stock fuel tank is all you get for slapping two rows of solid stages under your rocket. The diminishing returns are stunning! With bigger rockets, you'll run into the need to add SAS to keep them manageable. Only one ASAS module gives you any benefits, so put only one of them into your rocket. The key difference between SAS and ASAS is, as the description says, that ASAS is more like an autopilot, SAS is more like a gyroscope. In other words, ASAS only works as well as YOU could, or, in other terms, if the rocket is uncontrollable, ASAS cannot control it either. If you have wings (and, IMO, you should have some at least as long as you're hauling a big ass rocket about), you might even be able to forgo the normal SAS modules. My Mun rocket only has one ASAS module and no SAS modules. Your rocket should get thinner as it progresses upwards. From afar, it should look like a very steep pyramide. At least IMO. Top-heavy rockets are usually very hard to control, since their center of gravity is far from the point of action. The further away, the bigger the lever, the more wings and other control tidbits you need to keep it upright. You need most of your fuel on your way up. Once you're in orbit, even the trans-lunar shot is peanuts compared to the expense to get into an orbit. It's quite ok to create an unwieldy, but powerful lower stage and create a very manageable and precisely controlable stage for upper orbit that has rather little fuel compared to it. Try different designs here, it's all right to have zero control (aside of "keep it upright by ASAS") over the rocket for the first 20,000 or even 40,000 Meters of its trip.

Advanced Rocket Design 终极火箭设计！！！往下面看你会发现这已经不太像一个游戏了，更像大学物理系教授给同学们布置的小作业～

Introduction:
Getting to learn basic rocket science for a space game like Kerbal Space program can be very important to the success of building rockets that can perform a desired job. In this guide, we will be covering things like calculating the full Delta-V of your ship, explaining how to perform transfer maneuvers, getting Thrust to Weight Ratio, calculating the Peak G-force experienced during a particular burn, also calculating Delta-V needed for a full-Hohmann transfer and much more.

Delta-V 注意速度的变化

(change in velocity) is the bread and butter of rocket science. It is probably the most important thing to know about your rocket because it determines what your rocket is capable of achieving. Among the several things we will explain in this basic tutorial,   is most likely the most useful thing you will apply to Kerbal Space Program while building a rocket. To find the  of your rocket -- each stage at a time -- we have to sum up the part masses of every single part of the stage. When summing up fuel tank masses, it may be easier to write them like this on your paper:
Full Mass: x
Dry Mass: x
The reason for this is that it will be easier to calculate full mass and empty mass. So, simply sum up your entire stage mass.
The next important part of this set of calculations is to find your engine's specific impulse . Specific impulse is a measure of how fuel efficient an engine is (the greater the Specific Impulse, the more fuel efficient it is). For example, the non-vectoring stock engine has a vacuum specific impulse of 370 s. So here, we must apply the Tsiolkovsky Rocket Equation. More informally known as "The Rocket Equation".
It states:
kg1 = total mass of the stage (including subsequent stages),  kg2 = dry mass of the stage
So go ahead and sum up your stage's full mass with fuel. Then, go ahead and sum up the mass minus the fuels (this can be done by just adding up the 'dry mass' where given). Input these into the equation in the place of  and .

Note: To calculate the Isp for multiple engines with different Isp values, you need to take the weighted average of the specific impulses relative to thrust. The equation looks like this:

This will give you the correct  to use for your  calculation.

Calculating transfer maneuvers

The next very basic part of this tutorial is how to perform a transfer maneuver itself. This kind of action is called a Hohmann Transfer and it requires two burns at opposite points in an orbit. Adding velocity will boost our apoapsis higher. We would then simply wait until we hit our newly established Apoapsis and then add more velocity to boost our Periapsis to circularize. Or, we could drop our orbit by subtracting velocity by burning retro-grade.
We can also apply some  calculations to find out how much thrust we will need to perform this maneuver. We will break this burn up into impulses. For example purposes, we will start at a 100Km orbit and then boost into a 200Km orbit. Both circularized. The formula for the first burn is the following:

This is the formula for the final burn in the transfer:

Where:
u= Gravitational Parameter of Parent Body. (3530.461 km³/s² for Kerbin).
r1= The Radius of our first orbit. (100 km in this case).
r2= The Radius of our second orbit. (200 km in this case).
This formula will give us our velocity for the burn in km/s (multiply by 1000 to convert it into m/s). It's important to make sure that you will have the  in the stage to make this burn. Again, you can do that by using the calculations above.

Calculating fuel flow

Next, we will explain how to calculate fuel flow in mass to see how much fuel a burn uses up in a specific amount of time.
If we know the  needed for the burn and the total mass of the rocket before the burn, we can calculate how much fuel is required to complete the burn.
First, we calculate the mass of the rocket after the burn is complete. To do this, we use the Tsiolkovsky Rocket Equation, inputting the initial mass and  of the burn. We can then solve the equation for the final mass after the burn. The difference between these two masses will be used to determine the length of time that is needed to complete the burn.
The equation for mass flow rate of fuel, given Isp and thrust, is:

where m is the mass flow rate of fuel consumed (in seconds)
Dividing the difference between initial mass and final mass for the burn by the mass flow rate of fuel, we arrive at how many seconds are required.
Note: The mass flow rate of fuel can be converted into the consumption rate of the fuel units used in KSP (Liters, I presume). The conversion ratio is 1 mass unit per 200l of fuel.

RuohongZhao

a775914859

LZ开坑无数....

RuohongZhao

a775914859 发表于 2013-1-11 01:11
LZ开坑无数....

因为寂寞啊啊啊啊

wwppyicn21

好多坑...233

flyfire2002

二楼我帮你翻译一些吧。之前在wiki上看了两遍了

RuohongZhao

flyfire2002 发表于 2013-1-11 08:54
二楼我帮你翻译一些吧。之前在wiki上看了两遍了

好的，谢谢

回转先生

好帖啊LZ大好人

HoneyFox

最后那段我包了。。。这里顺便占楼。

EDIT1: 施工ing...

简介：
在KSP这样一个太空游戏里学会基本的火箭相关知识是很重要的，这样你才可以设计出能够达到你预期的火箭。在这一章节，我们将介绍全箭速度增量的计算，介绍如何进行变轨机动，了解推重比，计算在一个特定转弯中所受到的过载极值；以及如何计算一个霍尔曼转移过程中所需要的速度增量等。

速度增量
速度增量（或者说速度的改变量）是火箭知识中非常重要的一部分。想要知道你的火箭所具备的能力，这大概就是最重要的指标。在这个基础教学中所提及的东西中，它可能是最有用的。要得到你的火箭的速度增量，更准确的说是在某一个时刻，某一级火箭状态下的速度增量，我们要把该级火箭零件的质量之和累加起来。在累加的时候，最好在纸上写下：
全重（含燃料质量）： x
空重：y
之所以要这样列出，是为了之后计算的方便。
接下来一个重要的步骤：找到你火箭发动机的比冲。比冲是一种衡量发动机利用燃料效率高度的指标。（比冲越高，效率越高）例如：原版的不带矢量推力能力的发动机在真空的比冲为370s。现在我们要利用齐奥科夫斯基公式。也被称为“火箭公式”。
该公式如下：
kg1 = 该级时的全重（包括该级以上的后续级），kg2 = 该级的空重（该级以上的后续级的油箱还是应该以满油计算，除非你在该级会消耗上面级的油箱）
现在把这个全重累加出来，接着把该级空重也计算出来。
然后将两个数值套入下列公式。

注意：要计算多引擎的平均比冲，你需要计算以推力大小为权重的各发动机比冲的加权平均数。公式如下：


计算转移变轨
接下来一个基础概念是，如何计算某个转移变轨所需的速度增量。这种变轨被称为霍尔曼转移，它需要在轨道两个相对的位置分别开动发动机。增加速度将会提高轨道远点的高度，我们于是加速一直等到轨道远点抵达我们想要的高度，关闭发动机并在抵达远点后再次加速以提高轨道近点的高度来圆化轨道。当然也可以通过减速来降低轨道。
我们可以通过一些计算来得出这样一组变轨需要多少速度增量。