Mun rocket with 3 stages

[Gunhed]

Hi,

I try to build a Mun rocket with 3 stages with default items.

Every time I lift off I encounter at a hight between 10 - 20km problems that let to a fatal flight path.

On X2 Speed I can see that the Rocket starts to swing, as the lower part pushes against the last stage.

I tried different shapes and different combination of S:A:S usage with no success.

Can someone point me in the right direction, even if it\'s another thread?

Kind regards and thanks in advance,

Matthias

[sal_vager]

Hi Gunhed, welcome to the community.

While I can\'t help much with the swinging without testing your craft myself, I can see a few things you really should change.

First off, you only need 1 ASAS, any more than that is redundant, also you have fitted your SAS units to your engines, they will not be able to provide thrust with the SAS units in the way, so swap them around with the decouplers below them.

You may need more struts but really apart from those two things, your rocket looks okay to me.

Hope this helps

[sss]

Hi Gunhed, welcome to the community.

While I can\'t help much with the swinging without testing your craft myself, I can see a few things you really should change.

First off, you only need 1 ASAS, any more than that is redundant, also you have fitted your SAS units to your engines, they will not be able to provide thrust with the SAS units in the way, so swap them around with the decouplers below them.

You may need more struts but really apart from those two things, your rocket looks okay to me.

Hope this helps

he is correct. also it looks a bit tall for its width, so add more struts.

[closette]

Matthias - Welcome, and check out the 'stock repository' in the spacecraft exchange for a wide array of modifiable, stock, Mun-capable ships which can inspire your own designs.

One of the latest additions, 'EZ Minimun II', is a lot of fun to fly despite its minimalist approach. I\'ve modified it a bit so that the pod+RCS stay together as a 'lifeboat' if my poor piloting skills cause me to run out of main engine fuel.

As for the 'swinging' when using x2 warp, many of my ships do that too. As you ascend, fuel drains out of the tanks causing the ship\'s center of gravity to move down(*), while at the same time the atmosphere gets thinner making control surfaces (such as fins) less effective, so you\'ll find that torques can amplify very quickly and possibly even flip your rocket. My solution is just to go back to 1x time, especially for manual staging or pitchover maneuvers, and hope that the SAS can counteract the torque buildup.

(*) For stability, the center of gravity for a rocket should be well above the 'center of pressure', where the aerodynamic forces act, hence the fins are usually placed on the lowest part of the rocket. A good explanation is here: http://exploration.grc.nasa.gov/education/rocket/rktstab.html

[Endeavour]

You should take off one of the ASAS because more than one can sometimes mess things up. And if control is an issue, try the gimballed engines. They give much better control. Otherwise I think that rocket looks just fine.

[Gunhed]

Good thing first.

[list type=decimal]

[li]Lift of successful[/li]

[li]entering orbit (could be better, but it was an orbit) [/li]

[li]Flew to the moon Yay[/li]

[li]Lost orientation while approaching the moon...[/li]

[li]De acceleration wasn\'t (play of words) the burner...[/li]

[li]Landed on the moon (impact had a length of 1 km[/li]

At least the rocket was successful, now I have to work on my skills

I changed 3 of the middle LV-T30 to LV-T45 and redone the strut connector to make it stop wobble around while flying.

[sss]

Good thing first.

[list type=decimal]

[li]Lift of successful[/li]

[li]entering orbit (could be better, but it was an orbit [/li]

[li]Flew to the moon Yay[/li]

[li]Lost orientation while approaching the moon...[/li]

[li]De acceleration wasn\'t (play of words) the burner...[/li]

[li]Landed on the moon (impact had a length of 1 km[/li]

At least the rocket was successful, now I have to work on my skills

I suggest landing legs, if you have the demo, get the novapunch pack.

[Gunhed]

I suggest landing legs, if you have the demo, get the novapunch pack.

I have the hope to successfully land on the fins, without destroying them.

[RC1062]

I suggest landing legs, if you have the demo, get the novapunch pack.

The door is open, he\'s got 0.15. ;D

[Gunhed]

The door is open, he\'s got 0.15. ;D

Yeah, I had so much fun destroying my rockets that I had to buy it.

[Kosmo-not]

Here\'s my example of a simple 3 stage Mun rocket that looks more like a traditional rocket.

[Cryphonus]

Good thing first.

[list type=decimal]

[li]Lift of successful[/li]

[li]entering orbit (could be better, but it was an orbit) [/li]

[li]Flew to the moon Yay[/li]

[li]Lost orientation while approaching the moon...[/li]

[li]De acceleration wasn\'t (play of words) the burner...[/li]

[li]Landed on the moon (impact had a length of 1 km[/li]

At least the rocket was successful, now I have to work on my skills

I changed 3 of the middle LV-T30 to LV-T45 and redone the strut connector to make it stop wobble around while flying.

You can prevent the swing if you add struts from the first stage to the third stage vertically, also from the 2nd stage to 3rd stage. This will kill the swing.

[Gunhed]

I thought about it, but isn\'t it a problem when you separate the lower stage, or does it just snap?

[Gunhed]

Here\'s my example of a simple 3 stage Mun rocket that looks more like a traditional rocket.

I can\'t see RCS thrusters, isn\'t that a problem, or does the S.A.S take care of?

[UmbralRaptor]

I thought about it, but isn\'t it a problem when you separate the lower stage, or does it just snap?

Struts should just deactivate when the stage decouples.

I can\'t see RCS thrusters, isn\'t that a problem, or does the S.A.S take care of?

It looks like it would be marginal for the first stage (though the SAS might be enough). After that, the low mass + vectoring engines + ASAS would be plenty.

[Gunhed]

Struts should just deactivate when the stage decouples.

It looks like it would be marginal for the first stage (though the SAS might be enough). After that, the low mass + vectoring engines + ASAS would be plenty.

I see. Have to wrap my head around of the vectoring engines, but makes sense.

I have two silly question left,

[list type=decimal]

[li]how do you activate / use the landing gear? Does it only work, when it\'s at the certain stage?[/li]

[li]What is the best approach for the moon? I had the choice between what looked like a slingshot route and a wide open one. I didn\'t know what was the best one. Maybe the between version? [/li]

I guess after this question the only thing left to do is try it out.

[Melfice]

I see. Have to wrap my head around of the vectoring engines, but makes sense.

I have two silly question left,

[list type=decimal]

[li]how do you activate / use the landing gear? Does it only work, when it\'s at the certain stage?[/li]

[li]What is the best approach for the moon? I had the choice between what looked like a slingshot route and a wide open one. I didn\'t know what was the best one. Maybe the between version? [/li]

I guess after this question the only thing left to do is try it out.

1) 'g' button activates the gear.

2) One way, and probably NOT the best way, is to get into an orbit around Kerbin - any orbit will do! I suggest around 100 km, but less is fine too. From there, wait until you see the moon rise above Kerbin\'s horizon. Aim straight for the moon and start burning your engine at full throttle (Remember to activate the ASAS to avoid drastic changes in your course).

Switch to map-mode (m) and cut off your engine when you reach an apoapsis just under the moon\'s orbit. If all goes well, you\'ll see the map update with your current flight-path which will show the place where you\'ll get captured in Mün\'s sphere of influence.

[Gunhed]

1) 'g' button activates the gear.

2) One way, and probably NOT the best way, is to get into an orbit around Kerbin - any orbit will do! I suggest around 100 km, but less is fine too. From there, wait until you see the moon rise above Kerbin\'s horizon. Aim straight for the moon and start burning your engine at full throttle (Remember to activate the ASAS to avoid drastic changes in your course).

Switch to map-mode (m) and cut off your engine when you reach an apoapsis just under the moon\'s orbit. If all goes well, you\'ll see the map update with your current flight-path which will show the place where you\'ll get captured in Mün\'s sphere of influence.

Hmm G that\'s actual so obvious, that i didn\'t thought of.

Thanks a lot! I\'ll let you all know how it went.

[Kosmo-not]

2) One way, and probably NOT the best way, is to get into an orbit around Kerbin - any orbit will do! I suggest around 100 km, but less is fine too. From there, wait until you see the moon rise above Kerbin\'s horizon. Aim straight for the moon and start burning your engine at full throttle (Remember to activate the ASAS to avoid drastic changes in your course).

Switch to map-mode (m) and cut off your engine when you reach an apoapsis just under the moon\'s orbit. If all goes well, you\'ll see the map update with your current flight-path which will show the place where you\'ll get captured in Mün\'s sphere of influence.

Almost. Aim prograde, not straight at the Mun.

[Melfice]

Almost. Aim prograde, not straight at the Mun.

Comes almost down to the same thing, unless you\'re launching retrograde.

Aiming straight at the moon as it\'s just peeping over the horizon has always worked for me, however. Seeing as that\'s pretty much aiming prograde.

[rkman]

Good thing first.

[list type=decimal]

[li]Lift of successful[/li]

[li]entering orbit (could be better, but it was an orbit) [/li]

[li]Flew to the moon Yay[/li]

[li]Lost orientation while approaching the moon...[/li]

[li]De acceleration wasn\'t (play of words) the burner...[/li]

[li]Landed on the moon (impact had a length of 1 km[/li]

At least the rocket was successful, now I have to work on my skills

I changed 3 of the middle LV-T30 to LV-T45 and redone the strut connector to make it stop wobble around while flying.

The craft still has 2 ASAS. Remove the one in the 2nd stage.

You have SAS directly below the engines of the 2nd stage. Move those to below the stack decouplers - or remove them completely: it probably does not need 6 SAS on the first stage. I\'d remove all 6 and replace with one SAS on top of the 2nd stage below the decoupler.

3rd/final stage:

I\'d remove all RSC tanks and -blocks, replace one fuel tank with a 1/2 fuel tank, and replace the enigine with the small engine (LV909). Then the wings can work as landing legs (put the radial decouplers that the wings are attached to in a seperate staging group above the commandpod/parachute group so that you can\'t accidentally detach them when you still need \'m).

I tried a craft like that and was still using the 2nd stage on final approach for Mun landing. Conclusion: it\'s functional but over-designed.

[Monkthespy]

...I do three stage Mun craft all the time...

My design is pretty simple. A small lander is hooked up on top (just a parachute asas fuel tank and engine with landing legs), and a decoupler below the engine, where a stage which orbits you, does the Munar orbit, etc. And then radial decouplers (four of them) have about 3 fuel tanks with aerospikes.

Hard to explain, let me get a picture up in a sec.

EDIT: Here it is, it\'s quite forgiving.

EDIT2: Do not believe the staging on the side. It could be edited just to be three stages.

[Gunhed]

Yesterday I had my first successfully munlanding. My problem so far was, that I only had 3 landing legs, what was very unstable while landing.

[Monkthespy]

Yesterday I had my first successfully munlanding. My problem so far was, that I only had 3 landing legs, what was very unstable while landing.

Usually when that happens you just want to land on your engine, it may be risky but sometimes it\'s just a better idea.

[dogon11]

Also, if you still feel like landing on your wings, or if you are using the flimsy landing legs from .14, do 6x or 8x symmetry for them. They like to break off.