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Need help with rocket design


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I don't know if this thread should be posted on the Support forum, but tell me if it shouldn't.

The title says it all, i read how to design a rocket in the wiki, and also read about Asparagus Staging, but from what i've seen (players rockets and stuff), the tutorials of rocket design in the wiki is basic (or too much text less images, like the Advanced Design page) and i need to know how to build properly, so i need help from you guys.

Edited by Unknow0059
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Are you looking specifically for asparagus staging information or how to generally get stuff into orbit?

One easy way to help you (and get people involved) is to post a pic of your rocket and ask how you can improve it.

P.S. Are you using FAR/RSS?

I'm not using FAR or RSS. My problem is, sometimes when i put engines on the sides of a lander, it gets uncontrollable. I will edit this post and put a picture when i can.

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I'm not using FAR or RSS. My problem is, sometimes when i put engines on the sides of a lander, it gets uncontrollable. I will edit this post and put a picture when i can.

Uncontrollable, as if the ship locks up or you can't control your attitude?

Usually, when people have attitude control issues with landers, it's related to Center of Mass shifting (asymmetrical fuel flow).

or

If your engines are OVER (higher) your Center of Mass, disable the gimbals (or reverse them, depending on the mods). Otherwise, the gimbals will try to correct your attitude by firing toward the wrong side.

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By uncontrollable i meant, the ship starts to go where it's not supposed to go, like, if its pointed somewhere, the ship will go generally left of where is pointed.

If attitude is this, then thanks, i'll see about that when i play again.

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Ensure center of thrust is always in line with center of mass, which for the most part means "build symmetrical rockets dummy". SAS (press T to toggle, F to activate for a moment) stabilizes your craft in its current orientation. As mentioned: watch for CoM shifts as fuel is burnt, and disable gimbals on any engines placed ahead of CoM.

Otherwise, a simple picture of your lander would help a lot.

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As others have suggested: we can't diagnose what we can't see. The more specific you can make your questions and the more relevant information you provide, the better an answer you'll get.

For the pics, it's best to do them in the VAB, looking at the rocket directly from the side (i.e. not at a 3/4 angle that makes it hard to figure out exactly what's where) with the CoM/CoL/CoT indicators turned on.

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Going to point the OP to '>Temstar's principles on building successful asparagus-staged rockets. It's from 0.20 so a few things have changed, the big one being that instead of using an engine cluster you can get away with thrust-limiting a single engine that would otherwise be more powerful than you need. The underlying math is still solid, though.

As for lander design, you might try emulating Geschosskopf's design; that's good for collecting science. Underlying principle there - build a lander wide instead of tall, and make sure it's symmetrical (as others have said). SAS also helps, but only so much if your CoT and CoM are misaligned.

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Ensure center of thrust is always in line with center of mass, which for the most part means "build symmetrical rockets dummy". SAS (press T to toggle, F to activate for a moment) stabilizes your craft in its current orientation. As mentioned: watch for CoM shifts as fuel is burnt, and disable gimbals on any engines placed ahead of CoM.

Otherwise, a simple picture of your lander would help a lot.

As others have suggested: we can't diagnose what we can't see. The more specific you can make your questions and the more relevant information you provide, the better an answer you'll get.

For the pics, it's best to do them in the VAB, looking at the rocket directly from the side (i.e. not at a 3/4 angle that makes it hard to figure out exactly what's where) with the CoM/CoL/CoT indicators turned on.

Yeah i'm very sorry i took time to post the pictures, i was going to sleep when i replied your posts. I don't know how to see my CoM while not in the VAB, i don't think thats possible, but i don't think the problem is the CoM.

Lfzxbt6.png This is the rocket, we'll get to the lander in a sec. Note: This was the first time (yesterday) i got to another planet. I think this rocket looks horrible, like, seriously (this is why i started this thread), also the take off from the ground is slow. The initial plan for this was to have one manned spacecraft orbiting Duna, and send the unmanned rest of the spacecraft (lander and rover) to the planet, it didn't work because the part that was supposed to keep orbiting Duna had its fuel depleted when it was creating an orbit so i had to push that part of the plan away and just send the lander to the planet. The two small things on the part that was going to keep orbiting Duna are some kind of escape pods that i created for the kerbals to go to the planet if i wanted, but i haven't tested it yet so i dunno if it actually works. My first design of this ship had the manned pod in the part with two escape pods, but if i wanted to plant a flag i had to either put it on the lander, or not.

This is the lander BbsdLPQ.pngOHcjDeI.pngit was kind of "sliding" to the left of where it was supposed to be pointed to, is this normal? From the gravity of the planet? I don't think so.The rover is also horrible, i just made it so i could control it around in the planet.

Also i have this problem too. 4yGvSFK.png

I also have another rocket, i think it's very heavy and not so efficient, it had parts of another mod so i cannot show him until i reinstall the mod. I think i will post this now, if you guys want more pictures let me know.

Edited by Unknow0059
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You can't make circular connections. The only exception is struts which keeps your ship sturdy.

Rover is OK. Do you have a seat or science parts on it? For the note: constant powering is more important than the batteries.

Lander seems too high and can tip over. Though it wouldn't with so much SAS units. Lower your center of mass. Remove unnecessary parts (at least those small SAS units). I don't think that you need such big battery. The part with more weight should go to the bottom.

Check engines Atmo-ISP (You are going to Duna?). Duna landing is easy with parachutes. Just add twice more than on Kerbin.

Something must carry your lander + orbiter to the planet. Usually the lander do not fly by itself. In your design you could change the orbiter to be a tug.

Asparagus design X6 of FL-T400 and three LV-N engines would bring you to the Jool without a launch window.

Launcher is too big. As you said it is too slow. For example:

- LV-T30 engine is best with two FL-T800. The third is just a dead weight.

- Staging asparagus or not - each later stage should be smaller than the previous one. So use of 1.25m LF parts is not the best idea.

- If you lack a bit of trust add Solid Fuel Boosters.

p.s.

Don't strut too much. Parts are not attached to each other by paper glue... Or maybe they are but some wobbling is good.

Edited by DrMonte
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I'm going to talk about your lander. Form the looks of it you have one engine off center from it's partner, this is the cause of your sliding. (The one engine is unbalancing the thrust on the one side) Since you are not using FAR you can ditch the nosecones because they don't really do a whole lot and are just dead weight. I've not seen those engines on your lander before, so I don't know anything about them (Such as gimbaling and whatnot) but you could stand to move them down onto your fuel tank to ensure that they are below the CoM.

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Hmm...I'm also trying to analyze your lander. The engines look like LV-T45s but it's almost like you've got them clipped through something (which I can't identify). Looks like an oversized Aerodynamic nosecone with more power generation than you'll ever need, a Mk2 lander can, a Z-4k battry, a large ASAS module, an X200-8 fuel tank, four LT-2 laner legs, I'ma gonna go with four LV-T45s, 4 pieces of some kind of structural fuselage, 4 inline stabilizers and 4 oversized standard NC cones, plus the rover (which looks like a rovemate, okto2, 2 Z-400 batteries, a shielded solar panel, a gravioli detector, 2 small antennas and six shopping cart wheels) held on with a girder and a TR-18A.

I'd be willing to bet it's that shielded solar panel giving you your steering issues, but that's just a hunch. Where is the center of mass of the rover in relation to the center of mass of the lander?

How close am I on the parts, too? If I've got them right, we can discuss launch vehicle design too.

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Hmm...I'm also trying to analyze your lander. The engines look like LV-T45s but it's almost like you've got them clipped through something (which I can't identify). Looks like an oversized Aerodynamic nosecone with more power generation than you'll ever need, a Mk2 lander can, a Z-4k battry, a large ASAS module, an X200-8 fuel tank, four LT-2 laner legs, I'ma gonna go with four LV-T45s, 4 pieces of some kind of structural fuselage, 4 inline stabilizers and 4 oversized standard NC cones, plus the rover (which looks like a rovemate, okto2, 2 Z-400 batteries, a shielded solar panel, a gravioli detector, 2 small antennas and six shopping cart wheels) held on with a girder and a TR-18A.

I'd be willing to bet it's that shielded solar panel giving you your steering issues, but that's just a hunch. Where is the center of mass of the rover in relation to the center of mass of the lander?

How close am I on the parts, too? If I've got them right, we can discuss launch vehicle design too.

Hahahaha that big power generation is because i rage quited from the first design, which had only the solar panels from the rover. You are right about most of the parts.

I'm going to talk about your lander. Form the looks of it you have one engine off center from it's partner, this is the cause of your sliding. (The one engine is unbalancing the thrust on the one side) Since you are not using FAR you can ditch the nosecones because they don't really do a whole lot and are just dead weight. I've not seen those engines on your lander before, so I don't know anything about them (Such as gimbaling and whatnot) but you could stand to move them down onto your fuel tank to ensure that they are below the CoM.

The Lander's engine is from the FASA mod, the engines can't be off center because i used the angle snap. Out of the VAB, when i right-click the engine there's no gimbaling option so i think it doesn't have. I tested the engine (which is LEM Descent Engine btw) on Kerbin, and it didn't give any trouble. The nosecones are there because they look cool.

You can't make circular connections. The only exception is struts which keeps your ship sturdy.

Rover is OK. Do you have a seat or science parts on it? For the note: constant powering is more important than the batteries.

Lander seems too high and can tip over. Though it wouldn't with so much SAS units. Lower your center of mass. Remove unnecessary parts (at least those small SAS units). I don't think that you need such big battery. The part with more weight should go to the bottom.

Check engines Atmo-ISP (You are going to Duna?). Duna landing is easy with parachutes. Just add twice more than on Kerbin.

Something must carry your lander + orbiter to the planet. Usually the lander do not fly by itself. In your design you could change the orbiter to be a tug.

Asparagus design X6 of FL-T400 and three LV-N engines would bring you to the Jool without a launch window.

Launcher is too big. As you said it is too slow. For example:

- LV-T30 engine is best with two FL-T800. The third is just a dead weight.

- Staging asparagus or not - each later stage should be smaller than the previous one. So use of 1.25m LF parts is not the best idea.

- If you lack a bit of trust add Solid Fuel Boosters.

p.s.

Don't strut too much. Parts are not attached to each other by paper glue... Or maybe they are but some wobbling is good.

I don't have seats or science parts on the rover, i'm in the sandbox mode, i'm tired of career. Idk what's that "tug" design you're talking about.

VeN6jOF.png

This is the new lander, should i go with bigger engines (by bigger i mean normal-size engines like the LV-900 or LV-N, or these engines i said right now but smaller) to land or stick with the LEM Descent ones?

vgSi0uN.png

And this is the "new" launcher (i only changed some things, i accept any suggestion). Actually this "new" design sucks, i changed the small "boosters" to the giant NASA thrusters that have 3000 thrust and even then it's slow to get off of the ground.

Edited by Unknow0059
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30-odd designs and 50-odd missions, from driving a rover around KSC to placing space-stations around all the planets and moons in KSP - link in my signature.

If you don't want to read text you won't like it much though.

THE place to find tutorials is - The Drawing Board.

TV generation - the undoubted (ie; I don't doubt it ^^) master is Scott Manley; many videos on YouTube.

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May want to check to make sure those lander legs stick down past the engine bells of the nukes on the new design - that's one major disadvantage of using the nukes as lander engines.

New design...I'm seeing an inline stabilizer, rocko adapter 2, eight OX-STAT panels, 4 Z-400 batteries, 4 PB-NUKs, an X200-8, a Mk-2 lander can, three FASA bits, three standard NCs, three nukes and three LT-2s. Should be a little over fifteen tonnes of lander - let's say sixteen because I don't known what those FASA bits are). Somewhere around 2400 m/s of delta-V total with 180 kN of thrust, or about 6.9 TWR for Mun landings. A tad short for making it to Mun on its own, though it should be capable of landing on Mun, taking off and making it back to Kerbin by itself.

Transfer stage - based on the mass of your new lander, a transfer stage consisting of a Rockomax Decoupler, a single X200-16 tank and a Poodle engine should give you what you need. You can add a probe core to guide it into a Munar impact when you're done with it if you so choose; the x200-16 actually gives you a fair amount more fuel than you really need for the job.

With that lander and that transfer stage, you're up to twenty-five tonnes of payload, give or take. For the booster -

A 4STOa (four stage asparagus design - that's a core and three pairs of boosters) for that payload would require about 2690 kN of thrust, 592.9 in the core and 350.35 on the sides. A core consisting of a single Skipper set at 92% thrust should do the trick. For the boosters, you can use a Bi-Adapter with two LV-T30s (set at 81.5% thrust) each for 2.6 tonnes a pop - which will give you some mass savings over a Skipper there. A single X200-32 tank in each stack (core + boosters) should give you the fuel you need to make orbit (actually the X200-32 is about half-a-tonne too heavy, but you can set the engines for slightly higher thrust levels to offset the extra mass).

For a SSR (single stage rocket) instead - you'll want 7350 kN of thrust, which you can get with five Mainsails or three KR-2Ls firing in concert; I'd recommend the Mainsails as they're the lighter option. Five stacks (with three orange tanks and an X200-8 each) should do the trick.

You've still got way more power generation than you need on that lander - the four PB-NUKs by themselves would do the trick regardless of location, while the batts and panels would be the lighter option.

Edited by capi3101
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Hello Unknow0059 and welcome,

I'm in work so I haven't had time to read everything. Looking at the pictures. I see that your lander got smaller. That's good. The more you can do with the less parts the better. I would put the lander can on top of the fuel tank though. That would make it more bottom heavy. Have you thought about using parachutes? They will help you slow down on Duna. That'll save you some fuel. I don't use nuclear engines on small landers myself. They are too darned long. But they are really, really great at getting you from one planet to another and back. Have you tried them for that yet? Do you really need those two big RCS tanks on your launcher? Those things are heavy. I only use RCS gas when docking. It looks to me like you have way too much. I see you have Mechjeb. Are you using it in the VAB to help with designing?

Have you thought about splitting up the load? Put the lander in orbit around Kerbin with one rocket. Then everything else you need on one or two more. Dock them all together and off ya go. To infinity and beyond.

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I think i might need example images for the launcher (i don't remember parts by their name), the lander can land so its already good (the landing legs work perfectly).

Sorry about that. Uh....I'm at work so I can't build the boosters and show them to you outright, but I can link you to the images on the wiki so you at least have a notion of what I'm talking about.

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If going to Duna with that lander, then three things:

1: You'll want parachutes.

2: Nukes won't do in atmosphere. They are great in a vacuum, but not where there is some air. No matter how toxic and deprived of oxygen.

3: Still too big - or underpowered. Either or.

Landing on Duna - and getting back to orbit - you'll need about 2100dV. 600 going down, 1500 getting back up. It's the getting back up bit that is tricky. And why size matters. Not only do you need a ship capable of hauling the lander to Duna from Low Kerbin Orbit (about 1800dV for mothershipship with Lander attached - one way), but you also need some good Oomph, a technical term for high Thrust to Weight Ratio, on the Lander so as to make the trip back to orbit from Duna as efficient as possible.

Saving weight on the lander achieves both. First, your transfer vessel won't need as much fuel or as many heavy engines. Secondly, getting something neat and light-weight to gain speed is a lot easier than something big and ungainly.

When doing interplanetary, a 'moar boosters' design is more work and effort than a 'small is beautiful' design.

This for instance is a tiny Duna lander, with Life Support and plenty of Science instruments that add a couple of tons to it. If not caring about Science gear and don't play with Life Support, you'll get even more dV out of a similar design:

31CHA3v.png

High Duna TWR, and in atmosphere dV of 2100 and change. Mass is under 10 Tons fully fueled and with some RCS for docking back with the mothership. Hauling that thing to Duna orbit from LKO and back won't take more than a Orange Jumbo and a couple of nukes.

As for the lifter you got designed, it looks a bit like it'll only stay together by plenty of struts and some good luck. Way too many parts. And what is the deal with all that RCS fuel? That stuff is heavy, and more important not necessary. Only your lander need RCS to dock, and it'll not need more than 40 units tops. Your mothership certainly do not need 1500 units of RCS. Only thing that ever need even half that, is Fuel Depots and Re-Supply ships that service a whole gaggle of other ships.

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Hello Unknow0059 and welcome,

I'm in work so I haven't had time to read everything. Looking at the pictures. I see that your lander got smaller. That's good. The more you can do with the less parts the better. I would put the lander can on top of the fuel tank though. That would make it more bottom heavy. Have you thought about using parachutes? They will help you slow down on Duna. That'll save you some fuel. I don't use nuclear engines on small landers myself. They are too darned long. But they are really, really great at getting you from one planet to another and back. Have you tried them for that yet? Do you really need those two big RCS tanks on your launcher? Those things are heavy. I only use RCS gas when docking. It looks to me like you have way too much. I see you have Mechjeb. Are you using it in the VAB to help with designing?

Have you thought about splitting up the load? Put the lander in orbit around Kerbin with one rocket. Then everything else you need on one or two more. Dock them all together and off ya go. To infinity and beyond.

Once i'm done re-designing the ship with the help of you guys, it will be my first time using these nuclear engines, so no i haven't tried that yet. I don't know if i really need these RCS tanks, someone said it was going to be good to make my orbiter as a "tug", google images showed ships like that big orange part above the launcher, so i just created a copy.

I haven't thought about splitting the load, that might be good. I'm using MechJeb for the autopilot because i really suck at landing and stopping the burn while going to other planets/moons.

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If going to Duna with that lander, then three things:

1: You'll want parachutes.

2: Nukes won't do in atmosphere. They are great in a vacuum, but not where there is some air. No matter how toxic and deprived of oxygen.

3: Still too big - or underpowered. Either or.

Landing on Duna - and getting back to orbit - you'll need about 2100dV. 600 going down, 1500 getting back up. It's the getting back up bit that is tricky. And why size matters. Not only do you need a ship capable of hauling the lander to Duna from Low Kerbin Orbit (about 1800dV for mothershipship with Lander attached - one way), but you also need some good Oomph, a technical term for high Thrust to Weight Ratio, on the Lander so as to make the trip back to orbit from Duna as efficient as possible.

Saving weight on the lander achieves both. First, your transfer vessel won't need as much fuel or as many heavy engines. Secondly, getting something neat and light-weight to gain speed is a lot easier than something big and ungainly.

When doing interplanetary, a 'moar boosters' design is more work and effort than a 'small is beautiful' design.

This for instance is a tiny Duna lander, with Life Support and plenty of Science instruments that add a couple of tons to it. If not caring about Science gear and don't play with Life Support, you'll get even more dV out of a similar design:

http://i.imgur.com/31CHA3v.png

High Duna TWR, and in atmosphere dV of 2100 and change. Mass is under 10 Tons fully fueled and with some RCS for docking back with the mothership. Hauling that thing to Duna orbit from LKO and back won't take more than a Orange Jumbo and a couple of nukes.

As for the lifter you got designed, it looks a bit like it'll only stay together by plenty of struts and some good luck. Way too many parts. And what is the deal with all that RCS fuel? That stuff is heavy, and more important not necessary. Only your lander need RCS to dock, and it'll not need more than 40 units tops. Your mothership certainly do not need 1500 units of RCS. Only thing that ever need even half that, is Fuel Depots and Re-Supply ships that service a whole gaggle of other ships.

Thanks for the help with the image, i will make another lander and post it here when i play the game again.

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I think Duna's pressure is low enough that nukes aren't a bad option ... you're pretty much out of the major drag areas even 4-6 km above the zero-point. Still, it's much more lander than you're likely to need.

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