Where are you people getting all this force?

[Catthedragon]

I've been playing KSP for a couple weeks now, and I've been on youtube looking at people doing things in this game. There was one video where someone made it to Gilly *and* Minmus with only 5 parts in their craft. My question is: How? It takes me 6 solid fuel tanks and 2 orange tank mainsails just to make it into orbit, let alone to one of Kerbin's satellites. I'm trying to figure out how to get to more distant bodies, and it just baffles me how people do it so effortlessly with a tenth of the parts I already have. How do you do it?

[dryer_lint]

Probably with either nuclear or ion engines. Those things are crazy efficient, but they have very low thrust.

[Specialist290]

First, welcome to the forums!

The real trick to getting the most efficient use out of your launchers, which is basically what your question boils down to, is that ultimately, it's less about the absolute size and more about the relative proportion of the mass of the bit of your craft that makes it to orbit versus the total mass of the entire vehicle on the launchpad. The ratio of your rocket's fully-laden mass to its mass when the rocket runs out of fuel is also known as its mass ratio, and this ratio (along with a measure of engine efficiency known as exhaust velocity, which in-game can be gotten by multiplying the specific impulse by the standard value of acceleration due to gravity (9.8 m/s^2)) is vitally important to calculating the total potential change in velocity (often abbreviated to delta-v) that your vehicle can achieve.

For further reference, you may want to take a look at MyKSPCareer.com, which goes into detail about the basics that I've mentioned above and how you can use them to figure out what your rocket can (theoretically) do before it even leaves the launchpad. You may also want to take a look at these four web pages over at Atomic Rockets as well, which discusses the same principles as applied to non-KSP-specific general rocketry.

Hope this helps!

[SRV Ron]

Probably with either nuclear or ion engines. Those things are crazy efficient, but they have very low thrust.

There was a challenge called how far can you go with the fewest parts. With a five part rocket and some fuel flow and engine disabling commands, a rocket consisting of a capsule, Ftl-800 fuel can, LV-N engine, Orange fuel can and Skipper engine, made a one way trip to Laythe and beyond. So, how do you stage it? When the orange fuel can is empty, you disable the Skipper, activate the fuel in the FTL-800, Fire the LV-N and it stages by blowing up the orange fuel can.

So, yes, one way trips to Eve, Duna, Jool and its moons are possible with a five part design and careful power management.

This 10 part is no different other then it has two decouplers, parachute, and two solar panels.

[GoSlash27]

Small payloads.

-Slashy

[SRV Ron]

Small payloads.

-Slashy

Bare minimum to orbit.

Small Payloads;

Edited August 20, 2014 by SRV Ron

[Superfluous J]

The trick is these people are FREAKISHLY GOOD at the game. The guy you're talking about is probably Scott Manley. He knows his stuff.

If you're really interested in building very efficient rockets I suggest you install the Kerbal Engineer Redux mod. It will tell you while building your rocket how much dV your rocket has. You may be surprised when you find that doubling your rocket's size does NOT double your dV. However doing a couple things (like shedding excess mass when you can) can triple, quadruple, and more your total dV.

And if you don't know, dV is like mileage in cars. Your car holds far less fuel than a mack truck but you can probably drive farther. Likewise, Scott Manley's ships hold far less fuel but can go farther than your behemoths because he built them for efficiency, not raw size.

(dV is a complex topic just know that more is better. You need about 4500-5000 to reach Kerbin Oribt, and another 1000 or so to escape Kerbin orbit to Sun orbit. If your rocket has about 5500 dV you should be able to get out of Kerbin's SOI but not much further, no matter what size your ship)

[GoSlash27]

^ I pretty much fully agree with 5thHorseman, with one point of contention: delta-vee is not all that complex a topic, and is the key to making all of this work.

Pretty much everything in this game is a matter of changes in velocity (DV in m/sec) and acceleration rates (m/sec^2). If you can sort out the math, then you can accomplish just about anything. And the math isn't all that hard once you get the hang of it. The little that remains is just planning, organization, and piloting.

The important thing (at least the way that I do it) is to design your missions backwards with a careful eye towards doing each step the job with as little mass as possible.

Good luck!

-Slashy

[Superfluous J]

Actually I added that so the next 10 pages of this thread wouldn't be people pointing out that I'm wrong and that delta-V isn't in fact perfectly analogous to gas mileage, when all I wanted was to give a solid real-life example to show how "amount of fuel" doesn't equal "amount of stuff you can do with your vehicle."

[Wanderfound]

I've been playing KSP for a couple weeks now, and I've been on youtube looking at people doing things in this game. There was one video where someone made it to Gilly *and* Minmus with only 5 parts in their craft. My question is: How? It takes me 6 solid fuel tanks and 2 orange tank mainsails just to make it into orbit, let alone to one of Kerbin's satellites. I'm trying to figure out how to get to more distant bodies, and it just baffles me how people do it so effortlessly with a tenth of the parts I already have. How do you do it?

While all of the answers above me are correct and contain good advice, you can still get where you want to go even if you suck at designing efficient rockets.

Put a docking port on the biggest fuel tank you can lift (as unburnt cargo, not using its fuel). Fling that into orbit. Then, build your interplanetary vehicle, making sure that it also has a docking port, empty most of the fuel out of it (this will hugely reduce its mass), and fling that into orbit as well. Dock the two vehicles together, use the first tank to fill the vehicle from the second launch, ditch the first tank and head off. Even when you're only sending out one vehicle, you don't have to launch it all at once.

[MarvinKitFox]

Small payloads.

-Slashy

Big truth there.

Double your payload, and you need to double **everything** else too.

Slightly more than double, actually, as a bigger assemblage of bits n pieces will need more decouples, struts, fins, flappits and whatnots.

Reduce the payload to the absolute minimum, and you can *go* *places*..

[cantab]

What's your ascent profile like? If you're going full throttle all the way and your rocket doesn't lift off very slowly then you're probably going too fast and wasting energy on drag. If you see white shockwaves or red flames on ascent you're *definitely* making that mistake. As you've seen, small rockets can make orbit - if they're flown well.

[GoSlash27]

Actually I added that so the next 10 pages of this thread wouldn't be people pointing out that I'm wrong and that delta-V isn't in fact perfectly analogous to gas mileage, when all I wanted was to give a solid real-life example to show how "amount of fuel" doesn't equal "amount of stuff you can do with your vehicle."

Yeah, not nit-picking your response. It's all good information. I'm just pointing out that the DV equation isn'y all that difficult to understand and work with and it's worth anyone's time to become adept at using it if they want to be successful.

Best,

-Slashy

[UmbralRaptor]

Where are you people getting all this force?

(emphasis added)

Other posters are giving good information, but I want to clear up this misconception. Thrust is not that important, and depending on a given craft's configuration, adding more can be counterproductive. Raw thrust is of especially little value, and even TWR (thrust to weight ratio) does little good above a certain point (typically around 2.5x the local gravity).

[1of6Billion]

There are some mods around that will show the TWR (trust-to-weight-ratio) and dV of your rocket in the VAB (the rocket build place).

I know Mechjeb does that. And I believe also Kerbal Engineer Redux.

Keep your payload as light as possible. Aim for a TWR of ± 2 and a dV of at least 4500m/s for your ascent stage.

Happy launching!

[Alshain]

There are some mods around that will show the TWR (trust-to-weight-ratio) and dV of your rocket in the VAB (the rocket build place).

I know Mechjeb does that. And I believe also Kerbal Engineer Redux.

Keep your payload as light as possible. Aim for a TWR of ± 2 and a dV of at least 4500m/s for your ascent stage.

Happy launching!

TWR of 2 is wasteful in my opinion. You can get to orbit with TWR of 1, though 1.25 to 1.5 is probably a little less boring. Remember TWR increases the higher you go so even if you start at 1.25, it will be 2 before long and even then you will be wanting to throttle back to prevent wasting fuel.

[DeepSpaceDutch]

TWR of 2 is wasteful in my opinion. You can get to orbit with TWR of 1, though 1.25 to 1.5 is probably a little less boring. Remember TWR increases the higher you go so even if you start at 1.25, it will be 2 before long and even then you will be wanting to throttle back to prevent wasting fuel.

This brings up a question I sometimes ask myself when launching; when launching really heavy payloads I often do not have throttle back to stay below 150m/s below 7km altitude, other times when launching lighter payloads I do have to throttle back because the TWR is higher. In those cases I have the impression you "save" fuel (especially when using solid boosters) that is used higher up during the ascent. My gut feeling says the latter is more inefficient because while you are throttling back you're still "lifting" excess fuel. So I try to design my rockets that the TWR stays lower at lower altitudes, but is this really more efficient? Or is the difference negligible?

[Pecan]

...How do you do it?

The tutorial in my signature tells you ;-0

[Red Iron Crown]

This brings up a question I sometimes ask myself when launching; when launching really heavy payloads I often do not have throttle back to stay below 150m/s below 7km altitude, other times when launching lighter payloads I do have to throttle back because the TWR is higher. In those cases I have the impression you "save" fuel (especially when using solid boosters) that is used higher up during the ascent. My gut feeling says the latter is more inefficient because while you are throttling back you're still "lifting" excess fuel. So I try to design my rockets that the TWR stays lower at lower altitudes, but is this really more efficient? Or is the difference negligible?

It's more efficient in the sense that you're not carrying excess mass in the form of unused engines. I've found my best payload fraction designs have an initial TWR of 1.2-1.3. Higher TWR designs will use less dV but more fuel (seems like a contradiction but it isn't).

Edited August 20, 2014 by Red Iron Crown
Changed awkward phrasing.

[Alshain]

I agree with Red Iron Crown. throttling back to say 50% of a mainsail is 50% of a mainsail your not using but still dragging along, why not use a Skipper? Design with a TWR close to 1 (because that's what you need to get off the ground) and then throttle back as you ascend rather than starting with a TWR of 2 and throttling back immediately. Even more important now that we have money, mainsails are expensive and very rarely do you really even need them.

[DeepSpaceDutch]

I agree with Red Iron Crown. throttling back to say 50% of a mainsail is 50% of a mainsail your not using but still dragging along, why not use a Skipper? Design with a TWR close to 1 (because that's what you need to get off the ground) and then throttle back as you ascend rather than starting with a TWR of 2 and throttling back immediately. Even more important now that we have money, mainsails are expensive and very rarely do you really even need them.

Your example with the Mainsail does sounds very logical, but doesn't an initial TWR that is slightly above 1 cause you to linger longer in the lower atmosphere? I always had the impression that you need to get out of that part of the atmosphere as soon as possible.

EDIT: also my experience is throttling back say 10% to 20% where using a Skipper would give you a TWR of just above 1.

[Pecan]

I agree with Red Iron Crown. throttling back to say 50% of a mainsail is 50% of a mainsail your not using but still dragging along, why not use a Skipper? Design with a TWR close to 1 (because that's what you need to get off the ground) and then throttle back as you ascend rather than starting with a TWR of 2 and throttling back immediately. Even more important now that we have money, mainsails are expensive and very rarely do you really even need them.

That's the second time you've said that - You need more than a TWR of 1 to get off the ground - true, 1-and-a-slight-breeze is enough but burning huge amounts of fuel at full throttle to not go anywhere very much is not a winning forumla! That said, I agree that a launch TWR of 2 is overpowered - the consensus of advice and experience I've found aims for an average stage TWR of 2(ish). In other words, start low and finish high as the fuel burns.

More interestingly (to me anyway) is your assertion that mainsails are no good. I've always thought so prior to 0.24, but now they've had a buff they seem more cost-effective than skippers (which I'd also never use by choice before) for any payload over 10t. IF, that is, you are recovering them and getting most of the money back. My investigations on this and the other engines continues ...

[Alshain]

That's the second time you've said that - You need more than a TWR of 1 to get off the ground - true, 1-and-a-slight-breeze is enough but burning huge amounts of fuel at full throttle to not go anywhere very much is not a winning forumla! That said, I agree that a launch TWR of 2 is overpowered - the consensus of advice and experience I've found aims for an average stage TWR of 2(ish). In other words, start low and finish high as the fuel burns.

More interestingly (to me anyway) is your assertion that mainsails are no good. I've always thought so prior to 0.24, but now they've had a buff they seem more cost-effective than skippers (which I'd also never use by choice before) for any payload over 10t. IF, that is, you are recovering them and getting most of the money back. My investigations on this and the other engines continues ...

1. I believe I said close to 1 not AT 1. Earlier I suggested 1.25 to 1.5.

2. I never asserted mainsails are no good, just that people overuse them for loads that don't need them. If your load is heavy enough, absolutely use them, but beginners have a tendency to use nothing but mainsails (I'm guilty too, but I learned).

3. You seem to be twisting my words. I'm hoping that is unintentional.

Your example with the Mainsail does sounds very logical, but doesn't an initial TWR that is slightly above 1 cause you to linger longer in the lower atmosphere? I always had the impression that you need to get out of that part of the atmosphere as soon as possible.

EDIT: also my experience is throttling back say 10% to 20% where using a Skipper would give you a TWR of just above 1.

A little yes, but if your doing a good gravity turn (gradual right off the launch pad, rather than 11km) then that horizontal speed is yours to keep forever. Vertical speed on the other hand is eaten away by gravity so that is not preferred. The problem is it's hard to turn... or turn on time... going too fast in low atmosphere. This is true in stock but even more true if you use an atmosphere mod.

At really fast speeds you end up at your target apoapsis before you've extended your periapsis and so you have to burn for minutes instead of seconds to circularize your orbit, which eats a lot more fuel than the atmosphere does. Furthermore, using FAR, your craft just plain falls apart. So yes, lingering in the low atmosphere is less fuel efficient, but a better gravity turn is massively more fuel efficient.

Edited August 20, 2014 by Alshain

[Pecan]

...3. You seem to be twisting my words. I'm hoping that is unintentional.

8~0 I said what I intended but may well have misread what you wrote. I also think my mainsail figures are wrong. Apologies; I'm doing three things badly at the same time instead of getting any one of them right. Ignore me while I fail to make sense ...

[Alshain]

8~0 I said what I intended but may well have misread what you wrote. I also think my mainsail figures are wrong. Apologies; I'm doing three things badly at the same time instead of getting any one of them right. Ignore me while I fail to make sense ...

No problem man, I kinda figured you just misread.

One other final note, the Saturn V had a launch TWR of approximately 1.1 (depending on payload) and the STS Shuttle had a TWR of approx 1.5.

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)