Cant seem to find the fuel\weight balance

[OptiSTR]

Hello

So, i managed to get into orbit, and back, with some science done all went well.

Now i want to go to the Mun, ive tried several designs, light and heavy (with what the early game provides me with), both with and without solid fuel rockets.

The conclusion was like this:

Light rocket, enough fuel to reach the Mun, and land on the Mun, but no enough fuel to get into Mun orbit or to fly back home.

tried it with both 1\2 and 1\2+1\4 tanks, pretty much the same result.

Heavy rocket, 3 of 1/2 fuel tanks in the middle + 2 of 1/2 fuel tanks X 4 on the sides > kept loosing control during take off (rocket barely reacts to any maneuvers).

So i watched a clip on youtube with someone going to the Mun and made a copy of his rocket, and still ran out of fuel.

I came to think that my main problem located at the point where i break loos of Kerbin gravity pool, it looks like i spend too much fuel, while orbiting at 100k

all my attempts ended up with same result, i menage to get into orbit, but by the time i make final orbit corrections, i end up spending fuel from my final stage

Can someone please point me to what can i possible do wrong?

[Taki117]

ARe you using Asparagus staging? Also, pics of your rocket (And mission) would be helpful.

[capi3101]

Okay...so you want to fly to the Mun and do science, huh?

Short answer: you need roughly 5410 m/s of delta-V for a Munar flyby and free-return, 6,480 to go into Munar orbit and later return, or 7,760 for a Munar landing and return.

Your payload is going to need to be somewhere between 4-16% the total mass of your rocket depending on how you have things staged (4% for SSTO, 16% for asparagus)

Your piloting during launch also matters. Go straight up to 10,000m, then turn along course 090 at 45 degrees elevation and hold that until you're between 20-25k (about 30-45 seconds to apoapsis). Turn and follow the navball at that point, and burn along the horizon once your altitude is about 45k. Keep burning until your apoapsis is where you want it. Circularize once you're up there.

Too much is dependent on the mass of your payload, your intended mission and your current progress along the tech tree (assuming a career game), so we do need some details. What exactly are you trying to do?

[OptiSTR]

Okay...so you want to fly to the Mun and do science, huh?

Short answer: you need roughly 5410 m/s of delta-V for a Munar flyby and free-return, 6,480 to go into Munar orbit and later return, or 7,760 for a Munar landing and return.

Your payload is going to need to be somewhere between 4-16% the total mass of your rocket depending on how you have things staged (4% for SSTO, 16% for asparagus)

Your piloting during launch also matters. Go straight up to 10,000m, then turn along course 090 at 45 degrees elevation and hold that until you're between 20-25k (about 30-45 seconds to apoapsis). Turn and follow the navball at that point, and burn along the horizon once your altitude is about 45k. Keep burning until your apoapsis is where you want it. Circularize once you're up there.

Too much is dependent on the mass of your payload, your intended mission and your current progress along the tech tree (assuming a career game), so we do need some details. What exactly are you trying to do?

How do I calculate my Delta V? (And i cant do asparagus staging yet, dont have the tech)

Now about my payload, its just the capsule with one kerbal in it and 3\4 goo capsules for science

[Alistone]

It seems like a pretty light payload; it should have more than enough to reach mun with fuel to spare. I suspect your ascent may be loosing a lot of energy.

If possible you should try to reach 100m/s as quickly as possible after launch. Then slowly accelerate from 100m/s up to 200m/s as you climb up to about 10,000 meters. Use "terminal velocity" in the chart below to tell you what your most efficient velocity is at any given elevation.

http://wiki.kerbalspaceprogram.com/wiki/Kerbin#Atmosphere

Now after looking at that you get to have some fun. If you can't get up to speed MOAR engines! If you are going too fast MOAR FUEL! And then try to balance that with staging to jettison empty tanks and any unneeded rockets as soon as possible.

EDIT: You'll probably notice that after you get to 100m/s at the start you don't need a very high T/W ratio, but toward the end of your ascent you benefit from a higher T/W ratio. To achieve this people try to keep more thrust in their "center stack" so that it doesn't get jettisoned. I also have a tendancy to use some small solid rocket boosters on larger vessels to get them up to 100m/s as quickly as possible after launch.

The other experiment I always run is to see if my boosters can lift themselves. I see how much fuel I can add before they can't push themselves up. Then I subtact 1 so that I know they are always contributing to lifting the core rather than dragging it down. If you don't know what the limit is then it is too easy to accidentally add more fuel and suddenly you're just dragging your whole ship down.

After 12,000 meters, don't pitch over to more than a 45 degree angle until you are mostly out of the atmosphere. It is important to continue climbing quickly to get out of the atmosphere. If you don't have a lot of thrust to spare you can "stall" your climb and lose a lot of energy trying to accellerate horizontally while still in atmosphere.

Edited October 30, 2013 by Alistone

[capi3101]

The capsule (presumably with a small parachute) and four goo canisters weighs 1.5 tonnes. Since you've got goo, I know you're at least at Tier 1 (i.e. you've unlocked Basic Rocketry), which means you've also got access to the TR-18A Stack Decoupler. So serial staging it is.

Delta-V can be calculated by hand using the Tsiolkovsky Rocket Equation:

dV = ln(M/M_d)*9.81*Isp, where dV is delta-V, ln is the natural logarithm function (look for it on a scientific calculator or just use =LN() in Excel), M is the full mass of a stage, Md is the dry mass of a stage (i.e. once it's out of gas), and Isp is the specific impulse (efficiency) of the engines you're using.

Okay...so do you have access to the LV-T45 yet? How about the LV-909? I know you don't have Fuel Systems yet (because you need that for asparagus at a minimum), so what techs have you unlocked?

I'm trying to help you with a design but I need to know what parts you have available to you.

[SRV Ron]

I found this design most efficient for a Mun or Minmus orbit and return. With careful management of power usage and direct return to aerobraking, you will have both fuel and power to spare. This assumes that you have the LV-909.

If you don't have radical decouplers, this pancake design will also do the mission.

Once you get solar panels and probes, go for a landing. This one works well.

And, with fuel lines, you can head for Duna and Eve landing with this.

It is just a matter of trial and error to find out what combos work best and are most efficient.

Edited October 30, 2013 by SRV Ron

[Vanamonde]

Rather than make the whole rocket light or the whole rocket heavy, build light at the top and heavier as you go down. Make the final stage as small as it can be, then build a stage under that which is just strong enough to lift itself and the stage above, repeat as necessary until the rocket can get where you want it to go.

If you would like an example rocket you can download, the third one in this thread can make 1-kerbal moon surface round trips, and is built using parts only up to tier-3: http://forum.kerbalspaceprogram.com/threads/55636-Career-mode-starter-ships

[Moonfrog]

Possibly some information that I can give that may be useful. When breaking out of the atmosphere, you will expend lots of fuel just to get past the first 10,000m and beyond into orbit. To try to put what i'm saying is, take off is the most inefficient part of your launch. It is also the one part of your launch where you can over engineer as much as you want, still not really get much further.

I saw that someone told you u need so much Delta V to get into orbit. Although that is great for making very efficient craft and such, might be better to simply try and build stuff that works before getting everything down to a fine detail and complicating matters.

I tend to use this approach. If I build something big and powerful it gets me to go to the Mun, with tons of fuel left over then I just know to make it smaller. But at least I make it to Mun. If I build too small, I always end up failing to get to the mun, then struggle to know how much more I need to add to get it just right. I've stopped playing that way in trying ot ge things just right as u can't do it, without knowing exact Delta V measurements.

So I do things Kerbal way, Bigger is always better. Better to overshoot the Mun and end up on minmus then to fall short.

Just go crazy with your building. Keep your payload, your actually ship small on top. The lander or the probe. Then underneath just build big, without realising it you may end up with what happened to me. With a booster than actually used the central engine as a transfer stage, which I never originally designed, it just worked out that way. Because I always used to design things as on top, so I would build lander then underneath a transfer stage then underneath a launch booster etc. I don't build like that anymore. Now I just build big and whatever happens, happens.

I wanted to launch a probe to minmus in one of my missions, ended up going to Duna getting me more science instead. Aim big and dont' worry if your over shoot. That's the Kerbal way.

This was my career Mun Lander ship. Its very over engineered.

It uses 6 radial LT -200 engines as its main engine for take off. Those are supported by 12 SR boosters, 2 attached to each radial LT-200 engine. Think it has 3 of those half fuel tanks. Nose cones keep it steady. The central engine does not fire until it decouplers the 6 main engines. The solid boosters are detached at around 10,000m. Central engine acts as pushing itinto orbit as well as transferring to the mun.

The lander has two stages, first half is all landing fuel, has way too much. second stage is ascent module, it decouples and launches it self goes back home. Then just slows down in atmosphere and parachutes to safety.

Try not to be perfect, if u build something that can get to duna and its only going to the mun, then for your mission to duna your ship is already built

Edited October 31, 2013 by Moonfrog

[OptiSTR]

lol... thanks for the help guys.

but now i have a new problem, i cant control heavy rockets! and they are also no THAT heavy, just enough dV to get to the Mun and back

at 10.000 kilometers im trying to turn towards 70 angle and its as if my WSAD not responding

I built a new rocket, went to the Mun, without landing, and back, had just enough fuel, would of failed if landed on the Mun, and this rocket was BIG, barely could control it

[Sirrobert]

Watch this:

[capi3101]

Winglets (the AV-R8 in particular) and gimballing engines are what I'll recommend. If you're not using at least one LV-T45 in the center, you should be; its a gimballing engine that gives you steering authority; it works very well in concert with LV-T30s for raw thrust. That's assuming you haven't got access to the Skipper (with Heavier Rocketry).

[Excl]

A couple simple things that I've found that helped ...

- Make sure you strut as much as possible! Tie the top and bottom of everything down to whatever is next to it. The parts seem to rattle really easily, and it will throw your control way out of whack during a launch. I think there should be a more sturdy general connection between parts, but that's another conversation. Just try to get everything tied down. If you notice your ship flexing a lot during launch (like you have your SAS locked, but the ship direction still wobbles back and forth), then it's probably because you need to tie your parts down more

- Make sure you've balanced the items on top of your ship, because the drag will kill you! If you find your ship pulling hard to one side during launch, it's probably because of the drag. I used to have several ladder pieces that ran down the one side of my lander. The weight is nothing, but the drag on even small parts is .2 ... and that adds up quick! Especially at the top of your ship. I started putting mirrored ladders on the other side of the ship, even if they led up to nowhere, and it balanced the ship much better during launch. On a recent launch I had with a huge staging system. I had one light and a few instruments on one side of the top capsule, and it pulled hard to the side during launch. I threw up a second light on the other side, and moved one of the instruments over, and the ship flew up straight as an arrow the next time.

- You shouldn't need to do anything complicated like asparagus staging to get to the Mun, but do make sure you're shedding stages as you go up. You should be able to land on the Mun with nothing more than a single engine and standard tank with some struts and instruments. That should also be enough to get off the Mun and back, as you really don't need a whole lot to get back into Kerbin gravity.

- Also make sure you have enough wing fins on your early stages, and RCS on your upper stages. The wings won't do much once you get out of the atmosphere, but they're going to provide you a lot of control during those early, hectic stages.

[Moonfrog]

I'm guessing you don't have inline reaction wheel yet. But u should have the 200 thrust liquid engines. As one guy has said they have a gimball, which basically means it can move the engine so u can steer it. Early on it is great for making stable rocket designs. number of things that allow u to turn ships. Ill list them.

Sas of the command pod.

Gimball of an engine while it is active.

Winglets, these can move to provide turning motion in atmosphere. don't work in space.

Reaction wheels, like the inline reaction wheel that u may or may not have yet in career mode.

RCS u may not have this yet in career mode.

One other thing, this was a mistake I made when I first played. I don't mean it to be offending or insulting, when u turned your ship, did u turn S.A.S off while u turned it? then turn it back on when u finish turning. If it is still on, then it will fight you while u try to turn. Something I didn't really notice at first myself. Many people here seem to work for N.A.S.A or something and talk in rocket language and miss the simple things.

[OptiSTR]

k guys so i managed to land on Minimus, made quite a bit of science and got some useful new techs.

a little problem i didnt found a solution for (even though i did googled it) > is there a guide to how to do science properly?

for example, i EVAd on my way back from Minimus, and tried to collect data and i had this message that i cant collect more data... and i had to trash it

[Alistone]

k guys so i managed to land on Minimus, made quite a bit of science and got some useful new techs.

a little problem i didnt found a solution for (even though i did googled it) > is there a guide to how to do science properly?

for example, i EVAd on my way back from Minimus, and tried to collect data and i had this message that i cant collect more data... and i had to trash it

The command pod can only store 1 EVA report (and 1 material sample). If you try to re-enter (which automatically stores their report / sample) with a second kerbal before transmitting or deleting the report (or sample) it would "overwrite" the previously stored report ( or sample).

They way around this is to transmit the reports. This is done by right clicking on the command pod and selecting "review data". Then the normal "science" pop-up will appear and you can transmit them.

[capi3101]

Of course, to transmit the reports, you need to include an antenna in your design. Fortunately, you've got the Communotron 16 in your arsenal from the get-go and it weighs almost nothing; its one of those parts you can place on your ship without balancing out the other side and still expect your ship to fly straight.

[OptiSTR]

K guys a little problem, check out my latest design, what is wring with it?

It appears that I run out of most of my fuel while just getting into Kerbin Orbit

[Kasuha]

Looks like Kerbal-X offspring. The problem I see is that after dropping SRBs you're carrying a lot of empty tanks with you until you drop the whole lifting part. You could drop the three engine stacks when they become empty, too, and finish the lift using just the middle column. Feeding fuel from the three stacks to the middle and putting an engine (preferably Skipper) below the middle column might improve the performance.

[OptiSTR]

Looks like Kerbal-X offspring. The problem I see is that after dropping SRBs you're carrying a lot of empty tanks with you until you drop the whole lifting part. You could drop the three engine stacks when they become empty, too, and finish the lift using just the middle column. Feeding fuel from the three stacks to the middle and putting an engine (preferably Skipper) below the middle column might improve the performance.

I dont have a large engine powerful enough to lift this, at about 12K I start loosing speed really fast, and end up falling back to Kerbin

P.S

what is kerbal-x ?

[Moonfrog]

looking at the design I see your using 3 engines with the tri coupler attached too 3 fuel cells. That is the equal to using 1 engine too 1 fuel cell in terms of raw delta V. Your burning your fuel 3 times as fast so your sacrificing speed for distance. Either use less engines, or triple your fuel cells.

[Taki117]

what is kerbal-x ?

Kerbal-X is the name of the stock craft provided in Sandbox mode (It has Stock at the end of it) it is used to demonstrate asparagus staging.

[capi3101]

Kerbal X is a stock asparagus craft (not a particularly good one, but the idea is to demo asparagus). You can make a Münar landing and return with it if you fly it well (read: stick a KER flight chip on it).

Lessee....your payload looks like it's roughly 10.5 tonnes; you've got 6 X200-8s in the center and 9 FL-T800s on the sides being lifted by 9 LV-T30s in the booster stage, right?

That's 10.5 tonnes payload, 68 tonnes of fuel, 11.25 tonnes of engine, and 0.45 tonnes of tri-couper. 90.2 tonnes of rocket and 1935 kN of thrust (ignoring the SRBs)...TWR is 2.18, so you should have the thrust to handle your payload. Not much in terms of steering authority though. For that you want LV-T45s.

So let's look at delta-V. That booster is going to be 29.7 tonnes dry, Isp is 320, plug in the numbers......3487.28 m/s. You don't have enough delta-V on the booster to make orbit.

That said, you should also have enough fuel and thrust to be getting well past 12k. My recommendation is to check your fuel lines; make sure they are running from the bottom of the central stack to the outboard tanks and not the other way around. Check your piloting too...straight up to 10k, 45 degrees elevation on 090 until you're 35 seconds from the apoapsis, then follow the navball. Go horizontal when you're no closer than 45 seconds from apoapsis and burn until the ap is at the desired altitude.

Engine not powerful enough, huh? So no Skippers? I can work with that...

EDIT: Time out - those are -16s in the center, not -8s (always getting those mized up)

So you've got 94.5 tonnes of fuel...and 118.95 tonnes of rocket. Even with LV-T45s, your TWR should still be around 1.5.

10.5 tonnes dry...delta-V is 3844.84 m/s. Still not enough delta-V, still should be getting past 12k.

Edited November 1, 2013 by capi3101

[capi3101]

Actually, Temstar's Zenith II should be capable of lifting a 10.5 tonne payload; trouble is you don't have the tech levels to actually use his design, so here's how you replicate a substitute: below your payload, stick two of the X200-16 tanks. Put two Modular Girders on the bottom of the bottom tank by the narrow end, and attach two LV-T45s to the end of those; the girders allow fuel flow, but add fuel lines if it makes you feel better. You then want to add six TT-70 radial decouplers, each with two FL-T800 tanks attached and an LV-T30 on the bottom of those. Set up asparagus staging with these outboard stacks. Finally, add some AV-R8 winglets to the bottommost tanks.

Actually, you're running a fifteen tonne payload, aren't you? Well, a Zenith II replica should still handle that, but if it doesn't work, you could always try to replicate the Zenith III; that's two -16s and an -8 in the center with three LV-T45s, along with eight outboard asparagus stacks with two FL-T800s, an FL-T400 and an LV-T30 on the bottom. That should be good for payloads up to 25 tonnes or so.

If you need help with asparagus, we can delve into that too.

[OptiSTR]

Hey guys thanks for all the help

so, it appears that im getting better with my rocket construction, i built a nice light rocket with asparagus system, and made it to the Mun with a full light lander (one 1/2 tank)

im sure getting better at this, even though im still heaving problems with heavy rockets.

Now im still heaving issue with returning back to Kerbin from the Mun, what I noticed so far is that im using way too much fuel during Munar descend.

Usually I get into Munar orbit at about 600ms, I maneuver towards shallow landing, and at about 10k altitude I start braking,

I found out that I used about 65% of my fuel just to land the damn thing, then while lifting off, following an escape from Munar gravity, I end up using my entire fule and still fail to get into Kerbal deep space orbit.

its all pretty weird as i saw many videos where one small lander made it both landing on the Mun and then going back to Kerbin

Also Im having a big issue with large payloads, even though i have enough dV and boost, I end up loosing control

tried to use wings, lots of them, ended up with the same result