Jump to content

How can I get this heavy rocket into Kerbin orbit?


Recommended Posts

I've been trying to get this heavy rocket into Kerbin orbit and see if it can get to the Mün as it has a considerably high ammount of fuel plus backup fuel, but whatever I do it seems that I can never increase my Apoapsis without burning most of my fuel due to it's weight.

I tried to use boosters to help my rocket get to outer space and use it's fuel reservatories for good, but it all boiled down to a pretty fireworks display for some reason. Also, once I change from boosters to normal thrusters, it's hard for my rocket not to lose momentum gained from the boosters and not fall back to Kerbin due to it's weight. Help? Currently insane ammounts of fuel are the only way I can use to get to the Mün, and that comes with the cost of extreme weight.

Here's how the rocket looks like:

jcpayFh.png

There are a few changes. There are now around eight boosters at the bottom, six more above it, and even more six at the middle. They are all used before the main thrusters.

Take note I'm using the demo version, so check the list of items in the demo version before you try suggesting me ion boosters or something like that.

Link to comment
Share on other sites

Posting a step-by-step of your flight profile might help us figure out what is wrong.

Are you doing a gravity turn? Those are important. When you get to a certain height (can't remember exactly what height), you should start to pitch over so that you have some horizontal velocity. When your apoapsis is high enough, cut engines and coast up above the atmosphere, then burn prograde to make your orbit a circle. If you're trying to do a direct burn towards the Mun without orbiting Kerbin first, you're usually doing it wrong.

Link to comment
Share on other sites

The best (and most sane) advice I can give you is to say that I see you have the knack for building obnoxiously large rockets and that the only solution would be to buy the game.

Otherwise use more stages and try to keep your TWR above one.

I have to ask what is your goal with this rocket? If it's only to get to the Mun you could probably design a much smaller and simpler rocket to the same job. Smaller requires less thrust and fuel to get to orbit and subsequently to the Mun.

Link to comment
Share on other sites

A few things that strike me right off the bat:

1. Your second stage (the one between the launcher and what I assume is meant to be the lander and return vehicle) is probably a good bit larger than it really needs to be. I'd dump the radial engines and tanks on that stage entirely, and maybe cut the core down to just one of the long tanks as well.

2. You've probably got a few more winglets than you really need as well. I'd keep a set of 4 on the bottom stage and ditch the rest, as once you get high enough in the atmosphere, they don't really help keep your rocket that stable because the atmosphere isn't nearly thick enough for them to be effective.

3. You could probably make do with just those four boosters in your picture if you make the other two changes. In fact, you may not even need any boosters at all, if you pilot it well.

Hope this helps :)

Link to comment
Share on other sites

Posting a step-by-step of your flight profile might help us figure out what is wrong.

Are you doing a gravity turn? Those are important. When you get to a certain height (can't remember exactly what height), you should start to pitch over so that you have some horizontal velocity. When your apoapsis is high enough, cut engines and coast up above the atmosphere, then burn prograde to make your orbit a circle. If you're trying to do a direct burn towards the Mun without orbiting Kerbin first, you're usually doing it wrong.

Going to post a log of what happens in the next launch.

And yes, I am doing gravity turns. Scott Manley says it's to do it at 10,000m, but the sheer scale of the rocket's weight makes it impossible to do that at 10,000m, so I do it at ~21,000m where it's easier. I know how to orbit it, before I got KSP I watched a walkthrough of it and learned that it's not as simple as firing a rocket towards the Moon straightly.

Problem is, my rockets always seem to run out of fuel/lose fuel for the rest of the trip whenever I make a circular orbit around Kerbin, it's like I'm cursed. Either that or Kerbin hates being alone and is trying to force me not to go to the Mün.

The best (and most sane) advice I can give you is to say that I see you have the knack for building obnoxiously large rockets and that the only solution would be to buy the game.

Otherwise use more stages and try to keep your TWR above one.

I have to ask what is your goal with this rocket? If it's only to get to the Mun you could probably design a much smaller and simpler rocket to the same job. Smaller requires less thrust and fuel to get to orbit and subsequently to the Mun.

I only build large rockets because smaller ones ALWAYS end with it running out of fuel. Someone gave me a basic layout of a rocket that could go to the Mün and back. It ran out of fuel before a full orbit around Kerbin could be made. Scott Manley's example for the Demo version ended with the craft running out of fuel by the time I was going to land on the Mün, resulting on me killing several Kerbalnauts.

And I use several stages alterady. I believe this alterady got ~nine stages.

A few things that strike me right off the bat:

1. Your second stage (the one between the launcher and what I assume is meant to be the lander and return vehicle) is probably a good bit larger than it really needs to be. I'd dump the radial engines and tanks on that stage entirely, and maybe cut the core down to just one of the long tanks as well.

2. You've probably got a few more winglets than you really need as well. I'd keep a set of 4 on the bottom stage and ditch the rest, as once you get high enough in the atmosphere, they don't really help keep your rocket that stable because the atmosphere isn't nearly thick enough for them to be effective.

3. You could probably make do with just those four boosters in your picture if you make the other two changes. In fact, you may not even need any boosters at all, if you pilot it well.

Hope this helps :)

1. Actually the radial engines are connected to a stage below the lander and return stage. If you look closely you can see a decoupler above the fuel tank that has the two radial tanks connected to it. And said radial tanks are mainly used as a backup fuel. If I don't need the fuel, I just ditch them. But it's quite unlikely as I am seemingly cursed to never be able to have enough fuel.

2. Just saying, there are three boosters instead of four, the demo doesn't has a quad-stacker, only a tri-stacker. So there's actually a set of three winglets. But I'm going to remove the others.

3. If I remove the boosters, the rocket will crumble under it's own weight. That's why I added a ton of boosters.

Edited by Commissioner Tadpole
Link to comment
Share on other sites

Scott Manley says it's to do it at 10,000m, but the sheer scale of the rocket's weight makes it impossible to do that at 10,000m, so I do it at ~21,000m where it's easier.

Do you think you could explain what you mean by that statement in a little more detail? I'm not quite sure I follow.

Link to comment
Share on other sites

I've only had the game for about a week and a half or so. I was running into similar problems, where I would build a ship, and run out of fuel, so i put on more fuel and usually more boosters. I ended up with giant rockets that wouldn't get into orbit. It really just turned out to be my Thrust to Weight ratio. All that extra fuel was dead weight during launch, and just made things worse (or the same if I added a rocket / booster).

Before proceeding, calculate this by determining your total mass (go to map view while on the launch pad, and click on the "i" on the right), multiply by 9.81 m/s^2 to get your total weight. Divide your total thrust (add up the active engines on take - off) by your weight. You want to be hitting between 1.7-2.2 Any slower and your wasting fuel on gravity drag, and faster and you're wasting fuel on wind resistance.

Ideally, you should be going at terminal velocity at each appropriate altitude. So at 10,000 meters when you start your gravity turn, you should be going around 260 m/s. If you're under that by a lot, your thrust to weight ratio is way too low, and that's whats causing the problem. You need to remove fuel / payload or add active rocket engines.

Also if you start your gravity turn too late, you will never get into orbit. I suspect you're going too slow, and that's why you can't do the gravity turn at 10,000 meters (does it "fall" to the side?).

Link to comment
Share on other sites

This is what happened when I removed all but three of the boosters in the lower part of the rocket and tried to perform a liftoff:

tA9jgXW.png

Do you think you could explain what you mean by that statement in a little more detail? I'm not quite sure I follow.

When the rocket is launching, it is solely relying on boosters. Afterwards, by the time it reaches ~7,000m, I'll have to try to make the rocket cope with the loss of thrust by shoving the thurst bar all the way to the top until the rocket stops falling. By the time I can stabilize the rocket's thrust, it is alterady around ~14,000m, and I still have to gradually decrease the thrust for me to be able to slowly move my rocket east and then jam it all the way.

I've only had the game for about a week and a half or so. I was running into similar problems, where I would build a ship, and run out of fuel, so i put on more fuel and usually more boosters. I ended up with giant rockets that wouldn't get into orbit. It really just turned out to be my Thrust to Weight ratio. All that extra fuel was dead weight during launch, and just made things worse (or the same if I added a rocket / booster).

Same problem here.

Before proceeding, calculate this by determining your total mass (go to map view while on the launch pad, and click on the "i" on the right), multiply by 9.81 m/s^2 to get your total weight. Divide your total thrust (add up the active engines on take - off) by your weight. You want to be hitting between 1.7-2.2 Any slower and your wasting fuel on gravity drag, and faster and you're wasting fuel on wind resistance.

There is no "i" button.

Ideally, you should be going at terminal velocity at each appropriate altitude. So at 10,000 meters when you start your gravity turn, you should be going around 260 m/s. If you're under that by a lot, your thrust to weight ratio is way too low, and that's whats causing the problem. You need to remove fuel / payload or add active rocket engines.

That's the problem, I'm around 88 m/s at MAXIMUM!

Also if you start your gravity turn too late, you will never get into orbit. I suspect you're going too slow, and that's why you can't do the gravity turn at 10,000 meters (does it "fall" to the side?).

Yes, the rocket goes incredibly slow. And the rocket indeed fall to the side.

Replies in bold.

Edited by Commissioner Tadpole
Link to comment
Share on other sites

It is definitely possible to get very very large rockets into orbit in the demo (though it's much easier in the full game since you have larger components at your disposal.) As part of a challenge I managed to get to the surface of Eve and back (the hardest single destination return mission in the game) using only demo parts, but that required a ridiculous number of parts and was impractical for anyone with any kind of sense.

From what I'm seeing it looks like you should have more than enough delta-v to reach orbit with the design you've got (in the OP, not the exploding monster.) I would be surprised if it couldn't get to Munar orbit, if not the surface, with good flying.

One thing that I see is that your upper pair of boosters should be connected to the central rocket via fuel lines. You would activate all three engines at the same time and jettison the boosters when they are out of fuel.

A second thing involves the pair of RCS tanks at the top. What are they for, and do you really need two of them? It's not much mass, but every bit you put at the top requires fuel to lift, and that fuel requires further fuel to lift, and so on. Cutting even a very small amount of mass from your uppermost stage can cut the total mass of the rocket dramatically (or extend your fuel significantly.)

If you post your .craft file I would be happy to check it out to see if there is something obviously messed up or if there are easy things you could correct.

Other than mechanical issues, it seems likely that it's your ascent profile that is the problem. Perhaps the ship is unwieldy, but starting a gravity turn at 21km means that you're spending far too long burning upward against gravity. Getting into space is far less about getting high above the surface and far more about getting going fast enough that you're able to fall around the planet instead of crashing back into it. Even a slight turn that begins earlier will save you fuel.

Link to comment
Share on other sites

One thing that I see is that your upper pair of boosters should be connected to the central rocket via fuel lines. You would activate all three engines at the same time and jettison the boosters when they are out of fuel.

I don't think the demo has fuel lines available, so this might not be possible.

EDIT: Nevermind. Apparently they are, judging by the reply below.

Edited by Specialist290
Link to comment
Share on other sites

Adding a reaction wheel between the tri-adapter and decoupler may help with handling... it's pretty close to the COM where it'll be most effective. Alternatively you can add three reaction wheels on top of each of the first stage stacks which will put them all very near the COM as well.

Ditch the winglets on the upper stage and the upper set on the first stage, they're mostly dead weight and just add drag.

On the wiki there's a table of terminal velocities. Adjusting your throttle to keep your ship near those velocities at those altitudes will help improve efficiency as your engines won't have to work as hard fighting the air resistance. In fact you can probably keep your first stage engines off entirely until those boosters burn out (hard to tell but you might already be doing that based on the staging I can see)

=Smidge=

Link to comment
Share on other sites

It is definitely possible to get very very large rockets into orbit in the demo (though it's much easier in the full game since you have larger components at your disposal.) As part of a challenge I managed to get to the surface of Eve and back (the hardest single destination return mission in the game) using only demo parts, but that required a ridiculous number of parts and was impractical for anyone with any kind of sense.

From what I'm seeing it looks like you should have more than enough delta-v to reach orbit with the design you've got (in the OP, not the exploding monster.) I would be surprised if it couldn't get to Munar orbit, if not the surface, with good flying.

One thing that I see is that your upper pair of boosters should be connected to the central rocket via fuel lines. You would activate all three engines at the same time and jettison the boosters when they are out of fuel.

Should the fuel lines start at the boosters and connect towards the central rocket, or vice-versa?

A second thing involves the pair of RCS tanks at the top. What are they for, and do you really need two of them? It's not much mass, but every bit you put at the top requires fuel to lift, and that fuel requires further fuel to lift, and so on. Cutting even a very small amount of mass from your uppermost stage can cut the total mass of the rocket dramatically (or extend your fuel significantly.)

For when I need to use a ton of RCS to steer a massive heavyweight rocket that weights 1T whenever I'm in the outer atmosphere of Kerbin. I used one tank before for a similarly big rocket and it ran out of fuel in seconds.

If you post your .craft file I would be happy to check it out to see if there is something obviously messed up or if there are easy things you could correct.

I'm going to upload it soon.

Other than mechanical issues, it seems likely that it's your ascent profile that is the problem. Perhaps the ship is unwieldy, but starting a gravity turn at 21km means that you're spending far too long burning upward against gravity. Getting into space is far less about getting high above the surface and far more about getting going fast enough that you're able to fall around the planet instead of crashing back into it. Even a slight turn that begins earlier will save you fuel.

Makes sense. I was suspecting of that.

Replies again in bold.

I don't think the demo has fuel lines available, so this might not be possible.

It has. I never used it, though.

Link to comment
Share on other sites

Have you tried shortening the first stage and instead have a single FL-t800 2-high with another 2x4 FL-t800's in symmetry around it, then you could knock out one FL-t800 from the middle and still maintain your upper stage configuration.

It just looks very lanky and there's a lot of pressure in the middle.

Link to comment
Share on other sites

I agree with How2FoldSoup. What you are doing might make sense if you were designing a refueler and if you were trying to get into orbit with a bunch of extra fuel. But that rocket is way too big for going to the Mun. It looks to me like your entire second stage is probably unnecessary.

Here are my suggestions:

1) Eliminate the second stage. Your tri-adapter first stage with those three extra boosters is plenty to get you into a circular orbit around Kerbin if you aren't trying to lift that heavy second stage. I can't really tell from the picture, but I'm guessing you used LT-V30s for your first stage. That's what you want.

2) Lose all of the winglets except for the three at the very bottom. Neither your boosters or the LT-V30 are have thrust vectoring, so you will need those bottom winglets to keep you going straight during takeoff. However, just those bottom three are enough.

3) Lose all of the struts except for just one set of struts at the very bottom of the craft that connect your three main fuel tanks together. A lot of people say you can't have too many struts, but they weigh 0.05 each. That can add up fast if you have a lot of them. Add struts only to correct a seen problem. If your rocket doesn't wobble on the launch pad, you probably don't need any more struts.

4) Lose the RCS system. It's heavy and you don't really need it for a Mun landing mission. They are mainly valuable for docking. This modified version of your rocket is small enough that you don't even need any reaction wheels. The command module itself has enough torque to maneuver your craft in space, and the winglets can keep it under control during ascent.

Here's what your rocket looks like after making these modifications:

2vbr7sl.jpg

I was able to fly this to the Mun and back, so I know it works. Good luck.

Jeff

Link to comment
Share on other sites

Have you tried shortening the first stage and instead have a single FL-t800 2-high with another 2x4 FL-t800's in symmetry around it, then you could knock out one FL-t800 from the middle and still maintain your upper stage configuration.

It just looks very lanky and there's a lot of pressure in the middle.

Huh? By first stage you mean first stage starting from the bottom or from the top? I need some more information.

(Sorry, sometimes I have difficulty in understanding things)

I agree with How2FoldSoup. What you are doing might make sense if you were designing a refueler and if you were trying to get into orbit with a bunch of extra fuel. But that rocket is way too big for going to the Mun. It looks to me like your entire second stage is probably unnecessary.

Here are my suggestions:

1) Eliminate the second stage. Your tri-adapter first stage with those three extra boosters is plenty to get you into a circular orbit around Kerbin if you aren't trying to lift that heavy second stage. I can't really tell from the picture, but I'm guessing you used LT-V30s for your first stage. That's what you want.

2) Lose all of the winglets except for the three at the very bottom. Neither your boosters or the LT-V30 are have thrust vectoring, so you will need those bottom winglets to keep you going straight during takeoff. However, just those bottom three are enough.

3) Lose all of the struts except for just one set of struts at the very bottom of the craft that connect your three main fuel tanks together. A lot of people say you can't have too many struts, but they weigh 0.05 each. That can add up fast if you have a lot of them. Add struts only to correct a seen problem. If your rocket doesn't wobble on the launch pad, you probably don't need any more struts.

4) Lose the RCS system. It's heavy and you don't really need it for a Mun landing mission. They are mainly valuable for docking. This modified version of your rocket is small enough that you don't even need any reaction wheels. The command module itself has enough torque to maneuver your craft in space, and the winglets can keep it under control during ascent.

Here's what your rocket looks like after making these modifications:

2vbr7sl.jpg

I was able to fly this to the Mun and back, so I know it works. Good luck.

Jeff

Thanks. I'll see if it works.

Edited by Commissioner Tadpole
Link to comment
Share on other sites

Replies again in bold.

It has. I never used it, though.

The fuel lines would start at the boosters and run toward the center. The idea is to drain the boosters' fuel while also making use of the central rocket engine's power. The boosters will run out slightly sooner, but the net effect is a significant increase in delta-v.

Link to comment
Share on other sites

Huh? By first stage you mean first stage starting from the bottom or from the top? I need some more information.

(Sorry, sometimes I have difficulty in understanding things)

Oh yeah sorry, I mean like the set of engines that fire first, in this case the bottom of your rocket. Perhaps I am using the wrong terminology.

What I meant was to shorten your rocket by taking one FL-T800 out of the middle and reducing the base (first stage) into a single column of FL-t800's with 4 more around it and then maybe some boosters in symmetry around them. That should lower your center of mass and make the middle a lot more rigid.

Link to comment
Share on other sites

I built a very simply ship in the demo to see what I could see. I'm a pretty experienced pilot, so I wouldn't expect a new player to do as well as I can with it, but I can fly the linked craft from Kerbin to the Mun's surface and back into Munar orbit before running out of fuel.

http://www./view/2cbqt5zktftmwg6/Munar_Voyager.craft

Part of getting better at this game is learning to make minimal craft - just enough to do the job and not much extra.

Munar_Voyager.jpg

Link to comment
Share on other sites

Okay, I bring good and bad news.

The good news is, I FINALLY MANAGED TO LAND ON THE MÃœN!!!

The bad news is, I don't have fuel to go back. So Bill is stranded there. :(

Congratulation on your 1st successful Mun landing! I know how excited it is, for the 1st time!.

Here are mine. http://forum.kerbalspaceprogram.com/threads/49509-Party-at-the-Mun

Edited by Sirine
typo
Link to comment
Share on other sites

Looks very top-heavy.

Try to make a pyramid, not an hourglass.

You're also using far too many struts, which can cause a ship to explode.

Lots of wobble is bad, but none at all means it breaks instead of bending.

You may consider using this mod to reduce wobble: http://kerbalspaceprogram.com/kerbal-joint-reinforcement/

It's also generally a bad idea to put control surfaces all over your craft.

That can cause it to flip around and wobble, especially at the nose.

You're also using SRBs, which have a tendency to cause instability.

And have you heard of asparagus staging?

If you don't have fuel lines yet, you can still be more efficient with staging.

This image shows different staging methods, including asparagus.

http://imgur.com/WMeQXN8

You also probably don't need that much fuel to get to the mun and back.

Keep in mind that the LV-T45 can lift two large tanks and then a little, max.

And remember that a TWR (thrust to weight ratio) of around 2 is optimal.

Edited by Kerboa
Link to comment
Share on other sites

Ah, the demo...I cut my teeth on the demo.

Your final design is what I rather crudely call a "Phallus 7", a tall, narrow lander that does the job but has a tendency to tip over if you land on a grade. Bingo fuel level on a Phallus 7 is 80 liquid fuel units. Once you get down that far, either get back into orbit or plan on not coming back. Start thinking about an abort when you get to 90.

Now, I know that the smallest tank in the demo is the FL-T400, so I'll forgo my usual advice of "use four tanks to shorten and widen the stack", because I know you're already doing the best you can with what you got. That said, three FL-T400s set radially outboard, with fuel lines going from the outboard tanks to the center and your lander legs attached to those outboard tanks will improve the lander's stability. Just saying. Do not switch to an FL-T800 just for the sake of having more fuel. Trust me on this one...I didn't name that ship the "Flying Death Trap 7" for no reason...

You need to use your radar altimeter when you're landing; it's a gauge that looks like this:

collins-ra.gif

You can get to it via IVA ("C" key, "C" key to get back) and it is present in the Mk1 Command Pod in the demo. Use it to gauge the altitude of the surface.

Starting from a 14k orbit, give yourself a quick puff on the thrusters to bring your periapsis to about 5,000 over your target zone. When you almost get to periapsis, do a hard burn retrograde (make sure your speed gauge is set to "Surface" first) to bring that retrograde marker to vertically up (i.e. you want to kill your horizontal velocity as much as possible). Then kill your burn and go IVA, and watch the radar altimeter. When it starts to twitch downward and gets to an easy mark (say 2,000 or so), switch back to staging view and compare it to the altimeter; you know the surface is 2,000 meters below (so if the altimeter says 4800 when you switch back, you know the surface is at 2800). The rule for the Phallus 7 is that you don't want to be going much faster than 1 m/s per 10 m above the surface if you want to avoid lithobraking. Wait until you're about to that point of no return, then burn; don't burn the whole time, or you'll waste fuel. Watch your fuel level as you descend; I've already told you what to do if it gets to bingo fuel.

If you do happen to add those extra tanks like I mentioned, start burning sooner. Your lander should have enough fuel to get you back to Kerbin without problems but your craft will also decelerate slower.

Good luck.

Edited by capi3101
Link to comment
Share on other sites

The bad news is, I don't have fuel to go back. So Bill is stranded there. :(

Oops.

So, what rocket design did you end up using?

How much fuel do you have left?

How far back is your latest save?

And most importantly, how many tries did it take to land that thing?

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...