Where are you people getting all this force?

[Red Iron Crown]

If you watch Saturn V launch, it looks like it might not even get off the ground. It worked well enough for NASA. They are a lot smarter than I.

(also notice the turn before it even clears the tower)

That's actually a maneuver to ensure the rocket clears the tower safely, as I understand it the gravity turn was actually in another direction. You're right though that it started almost immediately.

[Alshain]

That's actually a maneuver to ensure the rocket clears the tower safely, as I understand it the gravity turn was actually in another direction. You're right though that it started almost immediately.

Ah, that's probably right. You know I wasn't even alive yet.

[EdFred]

You can't make a blanket statement of TWR needs to be 2, or it needs to be 1.00000000000000000001. I've found with my rocket designs, neither one of those are most efficient. For my designs, I aim for a TWR in the 1.6-1.7 range. This allows for full throttle without needing to throttle back to avoid hitting terminal velocity - with my designs. Lower than that, and I don't make it into orbit without tapping into the transfer stage.

[Superfluous J]

I too have found that 1.6 seems to be a sweet spot of TWR in stock atmosphere. Straight up to 9-10km then slowly bring the nose east. I aim to be at 45 degrees (halfway between straight up and sideways) when my apoapsis is at 20km, 30 degrees when my apoapsis is 30km, and sideways when my apoapsis is 50 km. I find that if I start with 1.6 I never have to throttle down but I get very close to (or go slightly over) atmospheric efficiency.

I get all these numbers from Kerbal Engineer Redux, but if you want to do it on your own shoot for 150m/s at 5km, 200m/s at 7km, and 260m/s at 10km when you start your turn. If you never have to throttle down to get these numbers just keep the engines burning from there on out. If you had to throttle down, keep it throttled down to about 15km and then punch the throttle to max until your apoapsis is where you want it.

All these things change in modified atmospheres such as those in FAR and NEAR, but I think that is outside this discussion and frankly I'm new to those and am still learning.

[Alshain]

The launch profile of stock is not that much different from FAR, only the fuel required and the aerodynamic construction of the craft (EDIT: Oh and the fact that you can't do the inefficient launch in FAR without the craft falling apart). The TWR is no different, because FAR doesn't change thrust or weight to my knowledge.

If your waiting to 10km to turn, your using more fuel than necessary, stock, near, far, or otherwise. But, it's your game, you paid for it. If that's what you like I can tell you it's less efficient, but I sure can't tell you that it's worse.

Edited August 20, 2014 by Alshain

[Superfluous J]

The launch profile of stock is not that much different from FAR, only the fuel required and the aerodynamic construction of the craft (EDIT: Oh and the fact that you can't do the inefficient launch in FAR without the craft falling apart). The TWR is no different. If your waiting to 10km to turn, your using more fuel than necessary, stock, near, far, or otherwise. But, it's your game, you paid for it. If that's what you like I can tell you it's less efficient, but I sure can't tell you that it's worse.

Weird, because in every single test I ran when I was crafting my standard ascent profile, if I started my turn earlier than about 8km the total dV of whatever craft I used was less once I reached orbit. I tried all kinds of profiles from turning right at the pad 45 degrees to turning right at the pad 5 degrees to turning at 4km 45 or 5 degrees to ... well you get the point. Lots and lots of launches.

If I turned before 8km I ALWAYS took a hit to the dV. And if I turned after 12km I ALWAYS took a hit to dV.

I would love to test one of your craft files in stock atmo, trying my method and yours, to see how they work. I'd love to learn something new about getting to orbit.

[EdFred]

I start my turn in the 6k range, but only going about 10-15 degrees, and slowly rolling over so that when I'm at 10k, I'm just about at 45. From there it varies slightly depending on the TWR, but my experience pretty much seems to be about the same as 5th.

[Moonfrog]

just a theory, but I think if you turn early you would need to make up for any normal loss by using wings to add lift. The lift would add an extra force upwards, which would help with delta V loss. If you don't use wings, you would be better of turning after you are through the thickest part of the atmosphere. Since I think the drag against your rocket if u started to turn in the thick atmosphere your force against gravity would decrease. at a 45 angle, it would be half as effective against gravity, meaning u would need a greater TWR to overcome gravity. If you used lift to counteract gravity, then all your force would be applied to making it to orbit. But I think it would be a preference. Not sure how much delta V were talking about if it would be worth it or not in the kerbal universe. Never seen a real life rocket with wings, I imagine they don't use them due to icing which would add drag and instability issues. Which don't exist in kerbal universe. Then again I think I may be wrong.

[Pecan]

You can't make a blanket statement of TWR needs to be 2, or it needs to be 1.00000000000000000001. I've found with my rocket designs, neither one of those are most efficient. For my designs, I aim for a TWR in the 1.6-1.7 range. This allows for full throttle without needing to throttle back to avoid hitting terminal velocity - with my designs. Lower than that, and I don't make it into orbit without tapping into the transfer stage.

This. Step back a moment guys; I might have found my brain again ...

The big thing no-ones talked about here is staging; how often and at what burn-times.

A launch TWR of 2.5 is quite reasonable with early-staged boosters that more or less just get you off the pad. (Second stage presumably being much lower).

A SSTO rocket with much more than 1.3 TWR at launch is probably going to have more than 5 by the time it reaches space.

Between those sorts of extremes there is a whole world - universe? - of compromise and experimentation.

And that's before you start considering the cost before or after recovery

Why else would it be fun?

:-)

[GoSlash27]

Honestly... I think we've wandered pretty far off the original topic.

Not sayin' you're wrong Pecan, but AFAICS staging has nothing to do with how people are pulling off missions with tiny rockets.

Intelligently designed staging, optimal flight paths, accurate piloting... yeah, all that stuff contributes to a successful mission and I'm not claiming otherwise.

*But* AFA how you get really far with a tiny rocket, the bulk of it is 1) understanding the rocket equation 2) using it to plan your mission and design your launch vehicle, and 3) ruthlessly eliminating dead weight. The rest of that stuff is part of the job also... but it's not part of *this* part of the job (if you catch my meaning).

Best and no feather-ruffling intended,

-Slashy

[Pecan]

Honestly... I think we've wandered pretty far off the original topic.

Not sayin' you're wrong Pecan, but AFAICS staging has nothing to do with how people are pulling off missions with tiny rockets.

Intelligently designed staging, optimal flight paths, accurate piloting... yeah, all that stuff contributes to a successful mission and I'm not claiming otherwise.

*But* AFA how you get really far with a tiny rocket, the bulk of it is 1) understanding the rocket equation 2) using it to plan your mission and design your launch vehicle, and 3) ruthlessly eliminating dead weight. The rest of that stuff is part of the job also... but it's not part of *this* part of the job (if you catch my meaning).

Best and no feather-ruffling intended,

-Slashy

Absolutely point 3.

Squad doesn't want us to know about point 1, ssshhh!

Therefore point 2 is moot. *wink*

But, yeah; decide your mission, no extra mass, calculate your rocket. See my tutorial if this isn't clear.

The rocket equation is nice but any programmer who wrote as cryptically and ambiguously as a mathematician would probably get fired after their first week.

In maths: dV = VeLN(m1/mo)

In computerese: Exhaust_Velocity = Isp * GRAVITY; Mass_Ratio = Total_Mass / (Total_Mass - Fuel_Mass); deltaV = Exhaust_Velocity * ln(Mass_Ratio);

In English: You can do more stuff if you use more economical engines or have more fuel. The trouble is the more fuel you add the more weight you have to lift in the first place so as you add more and more you get less and less extra from it, until you hit the limit for the engines.

Pfft; that's it - if I don't have visitors this weekend I'm doing "Basic Rocket Design - Explained Simply, With Pictures" (to complement the classic Aircraft one, of course) ^^

[GoSlash27]

Absolutely point 3.

Squad doesn't want us to know about point 1, ssshhh!

Therefore point 2 is moot. *wink*

But, yeah; decide your mission, no extra mass, calculate your rocket. See my tutorial if this isn't clear.

The rocket equation is nice but any programmer who wrote as cryptically and ambiguously as a mathematician would probably get fired after their first week.

In maths: dV = VeLN(m1/mo)

In computerese: Exhaust_Velocity = Isp * GRAVITY; Mass_Ratio = Total_Mass / (Total_Mass - Fuel_Mass); deltaV = Exhaust_Velocity * ln(Mass_Ratio);

In English: You can do more stuff if you use more economical engines or have more fuel. The trouble is the more fuel you add the more weight you have to lift in the first place so as you add more and more you get less and less extra from it, until you hit the limit for the engines.

Pfft; that's it - if I don't have visitors this weekend I'm doing "Basic Rocket Design - Explained Simply, With Pictures" (to complement the classic Aircraft one, of course) ^^

With you on pretty much all of this, but I disagree with the "cryptic and ambiguous" part. Math is not cryptic, it's just another language. And the beauty of it is that it is completely unambiguous in what it says.

In this case, every job you have in this game can be quantified in "delta-V" Getting into orbit requires such-and-such meters/sec. Going to the Mun requires such-and-such meters/sec. Etc.

The equation merely says that the DV a rocket can produce is directly proportional to it's specific impulse and the natural log of it's wet/dry ratio. Simplified, it's really just a matter of having an efficient engine and having enough of your rocket be fuel instead of not-fuel. That's really the entire trick to how we do what we're doing.

But math, being entirely logical and unambiguous, allows us to do a lot more than that. Algebra allows us to restate the sentence to answer other questions, such as "if I need to do this job (stated in m/sec of DV) and I'm using this engine to deliver that payload... how much fuel (and thus tanks) do I need". Or which engine/ fuel combo will accomplish this job with the least overall mass, etc.

The rocket equation isn't *everything*, but it's most of it.

Best,

-Slashy

[Wanderfound]

With you on pretty much all of this, but I disagree with the "cryptic and ambiguous" part. Math is not cryptic, it's just another language.

It's a language that I'm constitutionally incapable of being fluent in, unfortunately. English and Latin I can do, everything else: nope.

Quite happy that KSP allows reasonably effective design by eyeball without calculation.

[Pecan]

...I disagree with the "cryptic and ambiguous" part. Math is not cryptic, it's just another language. And the beauty of it is that it is completely unambiguous in what it says...

MODS! Tell me off for this if you need to but, yes, I was deliberately teasing and that could be called trolling.

Sorry Slashy but that's almost exactly what I expected you to say; to which my response is, "I said mathematicians write cryptically and ambiguously." You and I know "IspG" means the same as "ISP.G", "Isp * G" or "Engine specific impulse multiplied by local gravity" and obviously there are good and international reasons why the shorthand of mathematical notation is as it is. Nevertheless, as a programmer, conventions such as implied multiplication and operator precedence are anything but unambiguous. Unfortunately you've caught me getting irate with "Artificial Intelligence; A Modern Approach", the most benighted tome through whose obscurantist verbiage it has been my woe to have to work. (Apologies again, I'm trying to translate it so programmers can understand it).

When you are trying to explain something like the rocket equation there simply is no excuse for using single-letter terms rather than, as programmers are taught, meaningful variable names or using implied, rather than explicit, operator precedence.

[cantab]

If you think maths is cryptic, you should try Perl ;-)

But I'd contend that code along the lines of

dV = Isp * g * ln(m1/m0)

is using meaningful variable names. Terse, yes, but meaningful and instantly recognisable by anyone familiar with rocketry. And explainable in a few lines of comments for the benefit of anyone who's not come across it before. Coding the rocket equation as

output = in1 * const1 * ln(in2/in3)

would be using meaningless variable names.

[Pecan]

But I'd contend that code along the lines of

dV = Isp * g * ln(m1/m0)

is using meaningful variable names.

;-) As I said, I'm in a very crotchety mood from reading too much bad text by good mathematicians. Yet more apologies for expressing it here.

[Wanderfound]

If you think maths is cryptic, you should try Perl ;-)

But I'd contend that code along the lines of

dV = Isp * g * ln(m1/m0)

is using meaningful variable names. Terse, yes, but meaningful and instantly recognisable by anyone familiar with rocketry. And explainable in a few lines of comments for the benefit of anyone who's not come across it before. Coding the rocket equation as

output = in1 * const1 * ln(in2/in3)

would be using meaningless variable names.

dV is delta-vee, which is something to do with how much push your rocket has. Isp is specific impulse, which is something to do with how fuel efficient your rocket is. G is, I guess, probably something to do with gravity. Ln is probably one of those logarithm things that I've never been able to understand. Haven't the foggiest about in, or what the 2 and 3 relate to.

For all of this, whenever it's being discussed I have to pause a second to mentally translate each variable into English, which slows down my thinking enough that I can't follow the discussion. And my doctorate and academic publication record suggest that it's not because I'm a stupid person.

Mathematics is awesome and important, and I'm very glad that other people can do it. But if I was dictator of the world, every university and technical business would have a stats/calculus department in the same way as they have an IT support department. "Here's the data from my experiment, crunch the numbers for me please".

The greatest failing of mathematicians is that they fail to comprehend just how incomprehensible their language is for non-mathematicians. I've never seen teaching more incompetently done than what I experienced from the math faculty at university.

[Liowen]

I might have the more unpopular answer than getting mod X to help solve your issues, to me a mod might show you part of the problem the other has to be learned through trail and error. When I was learning I stayed away from the large parts, the orange tanks at that time were the big ones, and focused my time on the smaller part to get into orbit and come home again. Then I looked at what others have used to go to Mun, although Minmus is by far easier I set my goal for something hard because I wanted a challenge. After seeing what other used I built something using ques I took from their design and did more trail and error, all without mods telling how much dV or TWR my craft had as I had enough on my plate without trying to perfect the "numbers (this is just me as I would most likely not fly anything if the numbers were just right).

While my crafts might not be the end all of efficiency they do the job well enough to get me to where I wanted to go. Using mods you do not fully understand right off the bat will end up being more harmful than helpful, IMHO. I have yet to use Kerbal Engineer since I started playing in October and I have been to other planets and returned from most, but I have learned something from every mission I have launched. I may get it soon to see what I can change to make things work out better, but for now I am happy where I am.

Rambling thoughts when tired

[SRV Ron]

The mods can certainly be helpful, but they cannot replace the learning experience of the Kerbal School of Hard Knocks. (Build something, test it, and see if it works or not. Then rebuild it to see if it will work better.)

An example. This orange fuel can lifter either had too much power using all Mainsails which wasted fuel, or not enough power with all skippers which also wasted fuel. Using Skippers with a pair of Mainsails on the last pair of the asparagus gave vastly improved performance to the design by giving the design the right amount of power over weight for the most fuel efficient flight.

[GoSlash27]

;-) As I said, I'm in a very crotchety mood from reading too much bad text by good mathematicians. Yet more apologies for expressing it here.

No harm, no foul. I missed what you were actually referring to, and yes... it's frustrating. Scientists and engineers tend to do that too. It's because they're trying to convey a very specific concept using a very imprecise language.

Best,

-Slashy

[rkman]

My gut feeling says the latter is more inefficient because while you are throttling back you're still "lifting" excess fuel.

It is inefficient not because of the fuel but because the engines are not fully utilized. You still have to lift all the mass of the engine but use only part of its max thrust, making it in effect a low twr engine. Does not make a big difference as long as you throttle back only a little for a short amount of time.

My launch twr is usually around 1.7, resulting in max thrust up to ~5km, then throttle back to ~85% between 5km and ~12km, then max throttle again.

[eataTREE]

Well, I'm a noob (playing for about two months), and in that time I've gone from "completely hopeless" to "sorta okay" at building and flying rockets, so I thought I would contribute my two cents.

1) As many others have said, bigger is not better. It is easy to get into this sort of tail-chasing design mode where you are building a bigger rocket because you built a big rocket and now you need a bigger rocket to lift your big rocket; adding weight, cost, and complexity to your design without actually increasing the payload mass or the delta-V all that much. When adding to the design is no longer improving the situation, try taking away instead.

2) Use a mod that shows you your delta-V during construction, like Kerbal Engineer or MechJeb. Yes, you can design perfectly fine rockets by eyeball, but do you want to do ten test flights or one before you get it right? A little automatic number crunching can let you spend your gaming time flying Jeb through space instead of watching him crash and burn repeatedly.

3) There is no rocket so well-designed that it can withstand lousy piloting. Learn how to perform the "gravity turn" maneuver for efficient ascent, and how not to waste all your fuel landing (MechJeb's autopilot can actually make you a better manual pilot: watch how it flies ascents and landings, and then do what it does!)

4) Patience and perseverance. My first successful Mun landing was my twenty-third attempt, but now I'm a decent journeyman rocket jock (if I do say so myself). Hang in there, and enjoy this wonderful game.