Adding more engines doesn't get me any closer to orbit?!

[liquidhand]

I've managed to get into orbit with just a basic rocket, but I can't seem to scale it to get a larger payload up.

I want to get some science stuff up there with another rocket stage to get to the Mun, but I can't get it into orbit no matter what I do.

I've tried multiple stages using various different engines and boosters. I've tried to make the rocket have as little dead weight as possible.

One thing that bothers me is that I get no closer to orbit using six engines firing at the same time than I do with three.

I try to limit my speed to around 200 m/s below 10000 m and then start to throttle up.

I figured that with more engines firing that each individual engine wouldn't have to work as hard and that the fuel for each would last longer, but it seems that each engine can barely carry itself with some fuel and nothing else.

I've read all kinds of stuff on the wiki and here on the forums, but I just can't figure it out.

I'm in career mode so I don't have all techs unlocked.

Here's what's in my rocket:

What I want to get into orbit is - command module, science jr., service bay with some batteries and science stuff, FL-T200 & FL-T400 fuel cells, and a LV-909 engine.

I'm hoping I can get to the Mun with that.

Below the LV-909 I have a FL-T400 and a LV-T45 engine to use to adjust and finalize my orbit around kerbin..

For the main thrust stage I have in six sided symmetry - two FL-T400 tanks stacked above a LV-909 engine.

EDIT

Sorry, I miss typed. I'm using six LV-T45's for the main thrust stage, not the LV-909.

Like I said above, I've tried it with three in symmetry without success as well, and I've also tried it using the LV-T30 engine instead, but I would lose control at between 6000 - 10000 m.

Any help would be appreciated.

Edited May 12, 2015 by liquidhand
Miss-typed

[Ape_Descendant]

I would recommend using a mod like Kerbal Engineer Redux to be honest. Then at least you will get information of the total Delta-v produced by the rocket. As long as you can get it above 4000m/s then should reach orbit no problem. Its really tricky to work it out by "eyeballing" the rocket.

Adding MOAR! boosters doesnt always work as you are just adding more mass...and therefore need more thrust...so you add more boosters...which increases the mass...and so on.

[Kelderek]

For the main thrust stage I have in six sided symmetry - two FL-T400 tanks stacked above a LV-909 engine.

Definitely don't do this. The LV-909 is an upper stage or vaccuum-only engine, do not use it at the launch pad. Use the LV-T30 engines for your first stage and maybe use a single LV-T45 (if available) to provide some gimbal control. If you don't have that yet then use some fins near the bottom of your rocket to add control.

Also, you should be going full throttle all the way to orbit. Use a very gradual turn to the East starting very soon after liftoff. Turn slow enough that you get to about 45 degrees by the time you reach 10-12 km, then keep turning slowly until your apoapsis (you can see this from map view) reaches 60 km at which point you should be nearly horizontal. Keep burning until your apoapsis is 75-80 km. Shut off your engines and coast until you can circularize your orbit at the apoapsis (burn prograde until periapsis > 70 km).

The turn must be very slow in the sense that you never want to point more than a few degrees away from your prograde marker the entire way to space.

[Streetwind]

There's a big reason why "adding more stuff" doesn't make your rocket go farther:

The equation used to calculate delta-V, which is the measure of "how far can my rocket go", does not scale off of mass or size or anything like that. It scales off of what's called the "fuel mass fraction". In other words, how much of your rocket, percentage wise, is fuel.

The result is that a rocket weighing 10 tons, 8 of which is fuel, will go exactly as far as a rocket weighing 1000 tons, 800 of which is fuel.

In order to make the rocket go farther, you must either improve the fuel mass fraction (have 9 out of 10 tons be fuel, instead of 8 out of 10 tons), or you must use more fuel efficient engines. The measure of engine fuel efficiency is specific impulse (Isp). The higher, the better. But be careful: because the atmospheric pressure is fighting the rocket engine's ability to push out its exhaust, engine efficiency is dependant on atmospheric pressure. All engines only reach their full potential once in a vacuum. And some engines, especially those that are really vacuum-optimized and have the best stats, perform really really badly inside an atmosphere, or have low thrust... or both. So you need to carefully select the right engine for each stage. The highest tech level one is not always the best choice!

Edited May 12, 2015 by Streetwind

[Prepper-Jack]

Yes - if anything, you should throw some LV-909's on the pod headed to the moon. They have very poor performance in the atmosphere, but can really shine in getting to, and landing on, Mun and Minmus. Their low profile make them good choices for landing with the basic landing legs, and they're quite light as well. Going nuclear (although there's a mission to use the experimental engine on the Mun) is not one of the best options for early landers. They are heavy, slow, and with super small crafts they can't dissipate heat very quickly. I came way too close to exploding just trying to land on Mun with the bloody thing.

Otherwise - try to minimize weight and drag in the pod. Not sure which command module you are using, but if it's the one that houses 3 Kerbals, know that it's really heavy.

In lower stages, you might want to work on some asparagus staging with some Reliants and/or Swivels. Dropping a couple empty fuel tanks per stage as you ascend makes for a pretty large gain in both efficiency and speed. For basic early landers, like the one you are referring to, I tend to use 6 Reliants and 1 Swivel, with a couple FL-T800's per engine. That will generally get me into orbit, with a few LV-909's getting me to Munar orbit.

[adinfinitum]

Okay, so first thing, you definitely want each engine working as hard as possible. Sometimes its unavoidable that you can't run them at full throttle because you want to keep your speed down, but any engine that isn't full throttle is weight you can do without.

If you find you're running out of fuel, add more fuel, and add engines only as you need them. Like others said, you want the first, and sometimes second, stages to have the highest atmosphere Isp. This means LV-T30s, '45s and solid boosters.

To fix the problem of losing control, stick some find on the bottom of the rocket. Controllable ones work best, but if you don't have those any fin will move your center of drag down and keep your rocket pointing up.

[Aethon]

Welcome to the forums.

If I understand your design correctly, your problem is the LV-909's in the first stage. If you right click on the LV-909 in the VAB parts list you can see that it's ISP at sea level (ASL) is 85, and it's thrust is only 14.873, but in a vacuum ISP is 345 and its' thrust is 60, so the LV-909 should only be used in space.

Here's my early Mun Sci flyby ship. It will easily do a free return trajectory science flyby of the Mun.

After The swivel burns out (about 35,000m) the the LV-909 kicks in. The entire upper stage returns from Mun (heat shield unnecessary) for recovery. The fins on the command pod allow me to turn off SAS at about 50,000 m for a hands free reentry.

Hope this helps.

It will probably do a flyby of Minmus as well. I shot it out to 70,000,000 m to test reentry. With a 30 km periapse, and all that burned off was the MK 16 'chute on the top.

Edited May 12, 2015 by Aethon

[Lukaszenko]

As others have mentioned, albeit perhaps not as clearly as I am about to, DO NOT ADD MORE ENGINES. The less engines you have the better. Just make sure you have enough thrust to get off the pad and go up (more than 1.0 TWR in the atmosphere).

As has been mentioned, it's all about how much fuel you have moving how much mass. Engines are NOT fuel, they are mass. Therefore they decrease the Delta-V of your rocket. They are of course necessary to get moving, but use as few and as light engines as possible.

[rcp27]

Here's what's in my rocket:

What I want to get into orbit is - command module, science jr., service bay with some batteries and science stuff, FL-T200 & FL-T400 fuel cells, and a LV-909 engine.

I'm hoping I can get to the Mun with that.

That seems reasonable to me so far

Below the LV-909 I have a FL-T400 and a LV-T45 engine to use to adjust and finalize my orbit around kerbin..

For the main thrust stage I have in six sided symmetry - two FL-T400 tanks stacked above a LV-909 engine.

These stages seem to be the main problem. The LV-909 is a "vacuum" engine rather than an "atmospheric" engine.

I've just had a go and managed to get a free-return flyby of Mün with the following:

from the top down:

Top stage:

Mk 16 Parachute, Mk1 command pod, 1.25 m heat shield, TR18-A decoupler

Next stage:

Science Jr, service bay (containing 2 each of the Z-100 batteries and goo pods), FL-T400, LV-909, TR18-A decoupler

Bottom stage:

4x FL-T400, LV-T45 and four AV-T1 winglets

Radially attached: 4x

TT-38K radial decoupler, RT10 SRBs each with an aerodynamic nose cone. I set the trust on each of the SRBs to 75% in the VAB.

All of those are available with the Start, Basic Rocketry, Stability, General Rocketry, Advanced Rocketry and Basic Science nodes unlocked.

My flight plan was turn on SAS on the pad, launch with the LV-T45 on but throttled right back, instantly roll over to about 5 degrees. When the SRBs run out, run the LV-T45 up to about 75% thrust and turn off SAS. It hits about 45 degrees over at somewhere between 15,000 and 20,000 m, where I run the engine up to 100% thrust. Keep going (if you are rolling over too fast, put SAS on for a bit to prevent the nose falling) until the Ap is about 85,000 m, kill the engine. At this point, I had a little bit of fuel left in the main launch stage. Circularise at Ap, the bottom stage runs out and is staged off just at the beginning of the circularisation burn. From there, I set a manoeuvre node to give a free return fly-by of Mün, with a Münar Ap of about 250 km and a return Kerbin Pe of about 35 km. There was a fair amount of fuel left, it might be possible to use this design to actually orbit Mün and get back. That gets science in space high above Mün. after the flyby, go on EVA and take all the science out of the science gear so that when you dump that stage, the science is safely in the capsule.

[EtherDragon]

Hi liquid hand! You had some good ideas, and are seeing results that aren't (yet) making sense. Your hypothesis, "add more Rocket Motors should give me more Altitude!" was a good one to try, but the experimental result was - it didn't. That's excellent and exactly the kind of Science I love this game for! Now you know something you didn't know before - more rocket motors does not necessarily mean more altitude. Here's why:

More rocket motors produces more thrust.

More rocket motors adds more mass.

More rocket motors consumes more fuel (per second).

If you look at the statements above, and think for a bit, you'll probably come to the same conclusion I do: "If I have three rocket motors, I use three times as much fuel - which means it lasts 1/3 as long, but I go 3 times as fast... hmmm..."

Essentially (an oversimplification) you end up going just as far, but getting there in less time. Think of it like a car...

At best your car can go so many miles before needing to fill up gas. If you go faster, you can get where you're going faster, but you still only have so much total range. Now, if you pile on a bunch of engines, so you can go really fast, you're still limited on how far you can go based on the gas you carry. This applies to rockets, too!

What you need to do to scale up to larger carrying capacity is find a way to add more fuel along with more rocket motors. More motors for power, more fuel for distance.

Good luck!

Edited May 12, 2015 by EtherDragon

[Empiro]

Your initial intuition is exactly correct: don't carry dead weight around.

However (and it's not immediately obvious), don't forget that engines that aren't being fired at 100% are also dead weight. If you're throttling less than 100%, then consider taking some engines away and firing at 100%. That's less mass for the same thrust.

In addition, half-empty fuel tanks are also dead weight. When you added more boosters, you're also hauling them for the same amount of time (or even longer if you throttled down). This is why asparagus staging is considered efficient: you drain just 2 tanks at a time, and ditch them (and the engines attached to them) as soon as they drain.

[liquidhand]

First thank you everyone for your responses, you're all giving me a lot of good info.

It looks like I've got some changes to make. I think I might also need to make some adjustments to my ascent and some more practice.

I had my engines throttled back because I had read that it's inefficient to go more than 200 m/s below 10000 or so meters, but I thought that I also needed the extra thrust when I got higher than that.

I'll try out some of the ideas posted.

[Kelderek]

I had my engines throttled back because I had read that it's inefficient to go more than 200 m/s below 10000 or so meters, but I thought that I also needed the extra thrust when I got higher than that.

That may have been pre-1.0 info. In general, you don't want to go faster than terminal velocity as you ascend or else you will lose fuel efficiency by fighting against atmospheric drag. That 200m/s below 10km thing you read was probably true in the past, but the values for terminal velocity have changed, so you can go much faster now at lower altitudes. I would draw the line closer to 800-900 m/s below 10km.

As others have said, if you need to throttle down at all, then you are bringing too much engine for your current stage. The idea is to plan it so that you have enough thrust, but not too much, so that you can be full throttle the entire way to space.

Do you have the KER mod installed? If not, then I STRONGLY recommend you get that ASAP as it will give you lots of detailed info including your Delta-V and TWR. Your TWR must be > 1.0 for all of your stages if you want to get to orbit, and ideally you would be in the 1.5-1.7 range at the start of each stage. The TWR will naturally go up as you burn off fuel. Your final stage can be a bit lower but still over 1.0.

[Torquemadus]

Below the LV-909 I have a FL-T400 and a LV-T45 engine to use to adjust and finalize my orbit around kerbin..

For the main thrust stage I have in six sided symmetry - two FL-T400 tanks stacked above an LV-T45 engine.

I would suggest examining the weight of an LVT-30 or LV-T45 compared to the weight of an FL-T400 fuel tank. These engines are powerful, but they are also quite heavy. They burn through fuel quickly, but they can also lift a lot of fuel.

If you have too many engines lifting too little fuel, then you'll get fantastic acceleration, but not very much range. Try varying the ratio of fuel tanks to engines to see what works best!

[Venusgate]

I don't understand why the deltaV calculator in Kerbal Engineering Redux isnt stock yet. There's enough trial and error trying to make rockets not flip over that we really don't need to try to make efficient stages based on "intuition" or buckets of hand-written calculations, so yeah, I would say get that first.

Second, once you're out of the soup, upper stages don't really need more than a 1:1 TWR. If you have power to give you more than 1.5 TWR with full tanks in that stage, you're really just hurting yourself with the extra weight of the engines.

Bonus tip: if you're using KER mod, and trying to deliver a fuel payload to LKO, check either or both of the green arrows on the fuel tank fuel meters in the editor. This will make it so KER does not calculate your deltaV USING your payload fuel to get it up there

[Fishslap]

Although engines not being used are dead weight as said above, they do weigh much less than the fuel. Depending on the engine, the difference in weight between one engine with two tanks and two engines, two tanks and a decoupler isn`t too great. And you save having to haul the empty fuel container up to the next stage which is a plus. Early on I prefer a single central engine 30 with one fuel container, along with whatever boosters I need to get up to 10 000 at something like 350-400 m/s. Then a second stage 45 with a single engine with two fuel tanks and a 1-2 tank third stage for circularizing or going to a moon and back depending on the available tech. The flat engines, like the Terrier, are more efficient in vacuum so the third engine should be one of those I think. You can even land on them if you place the struts as low as they`ll go.

[liquidhand]

For those asking, no I don't have any mods installed. I've always been hesitant to use them for some reason.

I think I'm starting to get the hang of things. I've read some more and I know how to calculate delta v now. Hopefully that will help some.

I seem to be making some progress, although, with this game it seems that whenever I think I've got things figured out something else happens to flip me on my head.

Thanks everyone for your help

[Anglave]

First thank you everyone for your responses, you're all giving me a lot of good info.

It looks like I've got some changes to make. I think I might also need to make some adjustments to my ascent and some more practice.

I had my engines throttled back because I had read that it's inefficient to go more than 200 m/s below 10000 or so meters, but I thought that I also needed the extra thrust when I got higher than that.

I'll try out some of the ideas posted.

Let me join the others in recommending Kerbal Engineer Redux. It's really indispensable for any serious rocket designer. The most important things to pay attention to are each stage's TWR (Thrust to Weight Ratio) and ÃŽâ€v (delta-vee or 'change in velocity').

A good rocket design will have around 1.3 to 1.8 TWR in its lower stages. Any TWR above 1 is enough to push you up away from Kerbin. More than 1.5 to 2 TWR for a rocket probably means you'll be throttling your engines back to prevent going too fast low in the atmosphere.

The ÃŽâ€v number shows you how much "change in speed" your rocket will produce. It helps to know that reaching LKO (Low Kerbin Orbit) requires ~4000 ÃŽâ€v, and from LKO to Mun takes about 1200. This chart is old (the bodies with atmospheres are out of date as of game version 1.x and later), but still quite useful for mission planning.

As your rocket lifts, its TWR (within a given stage) will increase, for two reasons. First, you're lifting less and less mass as you burn fuel, so the Thrust is pushing against less Weight. Second (as of game version 1.x and later), as you rise through the atmosphere your engines will actually produce more thrust as the relative pressure of the atmosphere decreases.

For these reasons, it's normal to throttle back as each stage burns. But ideally your design starts each stage at full throttle. Lifting engines that aren't firing (or aren't firing at 100%) is inefficient (you could just use fewer engines pushing harder).

You mention that you thought you might need more engines higher in your orbital trajectory. The opposite is actually true. As your rocket's mass decreases, and as your distance from Kerbin climbs, you need less thrust to continue your ascent. Generally speaking your engines will grow more efficient, produce more thrust, Kerbin's gravity will exert less pull on you, and you'll experience less atmospheric drag.

You want the most thrust right at the launch pad, when you're lifting the full weight of your craft against the full pull of Kerbin's gravity, through the densest part of the atmosphere. And you still don't want a TWR of over about 1.8.

You mentioned some control problems higher in your flight. This might be for several reasons:

• You could be going too fast for the altitude you're at, increasing aerodynamic instability.
  
• Your rocket's Center of Mass might be shifting backward toward the engines as you burn fuel, increasing your aerodynamic instability. This is hard to avoid, it just means you need more vectoring or some fins at the rear.
  
• You might have a lack of control authority if you're relying on aerodynamic control surfaces over about 20km altitude, because the atmosphere thins out (so fins and things don't work so well). Make sure you're using vectored engines at the point where you're encountering difficulty.
  
• You might be trying to turn too radically too low in the atmosphere. Try to keep a straight line until over 20km.
  

You're right about keeping your speed low in the densest part of the atmosphere, trying to go too fast is just burning fuel to create more atmospheric drag, basically throwing the thrust away.

My plan is to not turn at all (go straight up) until about 20km altitude, and then execute my 45° turn to the East. Above 20km the atmosphere is thin enough that you can turn without too much trouble. Then push East until your apoapsis rises over 75km (mouseover it in map mode and watch it rise). Then coast to near apoapsis and burn facing prograde (directly east along the horizon) to circularize.

A slightly more efficient trajectory might turn 5° or so to the east directly off the launch pad, and hold that heading until over 20km altitude.

Mostly though, it seems like you're having trouble with early-game rocket efficiency, which is normal.

Let's pretend we have one of the tall thin FL-T800 fuel drums and the basic T45 vectored engine. It's going to go straight up quite quickly (probably too fast) until it burns out, but not nearly reach orbit. If we put, in radial symmetry, three radial decouplers and three more FL-T800 fuel tanks, each with their own engine, around it, and have all the engines fire at once, all of the engines are going to burn for the same duration and run out of fuel at the same time. They'll produce even more too-much thrust, but we're not going to get significantly higher. It's true we can run them at a lower throttle, but pushing the rocket at 1/4 throttle with 4x as many engines isn't going to gain us much.

If we made it 6x radial, using the same design, all of our engines would still burn out at the same time, we wouldn't get much higher, and this craft almost certainly can't make orbit. At this point we're lifting insanely too much engine to do the job.

Let's build the same rocket, a central "core" tank and engine, then 3x radial tanks with engines, and then a second set of 3x radial tanks and engines. Then set the staging such that the first set of radial "boosters" fires first (lifting the whole craft on 3 engines). Then decouple the first set of 3 boosters and fire the second set. (still lifting the craft on 3 engines). Then decouple the remaining boosters and light the central "core" engine.

This still isn't a particularly efficient design, but it's going to get much farther with exactly the same parts as our example above, because it allows us to generate thrust for a longer duration.

Which gives us one of the secrets. Keep producing thrust for longer. Keep our engines burning continuously for as long as they're useful.

My strong recommendation would be to install KER and play around with some simple designs like this. Watch the TWR of each stage, and watch the total ÃŽâ€v of your rocket change.

I'm working on assembling a "basic KSP Knowledge base". Anyone interested in further reading or general gameplay tips, please take a look.

Last thing, once you're comfortable with the basic concepts I mentioned above, you should check out Asparagus Staging. I'm sure there are threads explaining it on the forums, and some of my craft design notes (linked above) utilize it. In Asparagus, you light all of the engines at once, but use fuel lines to pull the fuel from the outer stages to the inner stages, such that the outermost boosters get discarded when empty, leaving the inner stages full of fuel for as long as possible. This stretches out burn time of the core stages, and lets you discard spent fuel tanks and engines as they're no longer useful.

To asparagus-ify our example above, we'd put all the engines in the bottom stage (so all 7 fire off the pad), and we'd run fuel lines from the "first" set of 3 boosters to the second set, and from the second set to the core. So the first 3 fuel tanks are fueling all 7 engines (and will be depleted very quickly). Then we stage them away, getting rid of the empty fuel tanks and the engines that were lifting them, leaving us with less mass and fewer engines (a more balanced TWR), and all our remaining fuel tanks are all full. Next the remaining 3 booster tanks are fueling 4 engines, and finally we have 1 full tank with 1 engine as our core stage.

Using all 7 engines off the pad is going to give us a massive TWR for the example craft. Add more fuel tanks (make each stack taller) to bring the TWR down to a reasonable level. And presto, this thing goes to orbit easily.

This Mun Lander uses Asparagus staging to put a Kerbal on the surface of Mun and return him to Kerbin using only stock 1-meter parts.

Edited May 13, 2015 by Anglave

[davidpsummers]

I would recommend using a mod like Kerbal Engineer Redux to be honest. Then at least you will get information of the total Delta-v produced by the rocket. As long as you can get it above 4000m/s then should reach orbit no problem. Its really tricky to work it out by "eyeballing" the rocket.

Adding MOAR! boosters doesnt always work as you are just adding more mass...and therefore need more thrust...so you add more boosters...which increases the mass...and so on.

I will echo the others that you main problem may be you choice of rocket engine. The LV-909 won't produce much thrust and waste in the atmosphere (look at the ISP number listed).

At some point you will need to be able to calculate delta-v's. I liked playing around on getting to orbit by feel. If you goto the moons, it will become more important to know the delta-v's. And for planetary missions, it becomes very important.

I like to do this by hand (very instructional, I don't where the link to how to do this is, maybe someone else does) before going to the Kerbal Engineer Redux add-on.

[Beowolf]

The entire upper stage returns from Mun (heat shield unnecessary) for recovery. The fins on the command pod allow me to turn off SAS at about 50,000 m for a hands free reentry

I've never run into fins placed like that before, Aethon. Thanks for sharing.