2.5m Rocket Troubles

[Tex]

Hey gang, try as I might, I can't seem to get any darn 2.5m rockets into any sort of state that will be helpful. Would anyone mind sharing some tips/tricks/info, or simply letting me borrow your rocket designs?

I'm trying to get larger landers to the Mun, Minmus, even some that can go to Duna in the future. I would really like some help, mostly because I also have a Kerbal stuck on the Mun right now!

Thanks, y'all!

Edited September 18, 2013 by Maximus97

[M5000]

I don't have many tips really for such a general question, but, if you'd like to look at a 2.5m rocket design, the Soyuz replica in my signature will get you well into an orbit. It comes with its own space capsule and everything. I've heard from users that it's very easy to fly. Also it's all stock so don't worry about whether or not you have the mods to use it.

-M5K

[UmbralRaptor]

In no particular order:

* The size 2 parts have a lot more wobble and structural failure issues, so struts (especially between vertically attached tanks) are necessary.

* Attaching a Mainsail directly to an orange tank will give you a great deal of heat issues. Put a gray tank, structural plate, or octagonal strut in between.

* Giving a mainsail only a single orange tank worth of fuel is also a waste. Aiming for ~2 (or the equivalent in smaller tanks) will get you substantially more ÃŽâ€V, and only costs TWR that you can't use anyway.

* The Poodle is rarely a good choice for smaller (<50 tonne) craft. Try an LV-T30 instead.

[Specialist290]

I can sympathize: I remember having similar problems myself adjusting when I made the leap to bigger rockets, which resulted in a few interesting failures.

Here's the Mun lander that I'm currently playing around with:

It can reliably get me to the Mun safely and back without any real need for super-precise piloting.* All parts are stock, aside from the Kerbal Engineer chip that gives me the handy data readout. The launcher has a Mainsail fed by Jumbo-64 + a white "hockey puck" for the core, with radial Skippers mounted on Jumbo-64s for boosters, which all feed into the central tank during the first stages of the flight; it had no need for any fancy asparagus staging to put me in orbit, so I didn't set that up. The Munar Injection stage has a Poodle, and it has enough "oomph" to get me to the Mun, circularize, and get a nice head start on the landing. The lander itself has an LVT-45 (which is probably overkill on the thrust for the Mun and Minmus and definitely less efficient than the LV-909, but I wasn't thinking about that at the time I designed it) and enough fuel to land, take off again, and get back to Kerbin. The LES isn't strictly necessary, but I like to add a dedicated abort system to my crewed vessels "just in case." (Efficiency experts might undoubtedly notice some other areas I could tweak this design to get it to perform better, but it works well enough to suit my purposes.)

In general, the same principles apply as they would for any rocket. Make sure your initial engines can actually lift the ship off the pad. Try to front-load as much of the total weight as possible onto stages that drop early so that the later stages don't have as much to lift. The lighter your final payload, the smaller your total launcher can be... And so on.

If you really want to delve into the nuts and bolts so you don't have to purely rely on trial and error, I'd highly advise learning how to calculate your rocket's performance statistics (delta-v capacity, thrust-to-weight ratio, etc.) yourself. It may seem daunting at first, but the Atomic Rockets website has some very helpful pages that explain the basics in layman's terms, and the KSP Wiki has all the necessary statistics for individual parts. There are helpful plugins that tell you these stats as well, but running the numbers by hand a few times and playing around with different layouts and arrangements is a great way to make sure you actually understand what they mean.

Finally, feel free to continue asking questions as the need arises, and don't forget to take a look at some of the resources listed in the Drawing Board, which is linked in my signature.

Hope this helps

* At least not "super-precise" by my own standards; I am slightly OCD about efficient transfers and getting the most out of my maneuvers, though.

Edited September 17, 2013 by Specialist290
Missed a closing tag for the URLs. Drat.

[Guest]

Struts, struts, and more struts. Strut tanks together, strut between tanks, strut to the payload. You might be able to see what I'm talking about in the picture below. Part of all that strutting is to handle lifting a payload by its two long engines; decouplers are very wobbly.

Same principles apply to large landers.

[Tex]

Thanks all! It does really help, and to Specialist290, I've actually tried a rocket design that looked almost exactly like yours O.o

Thanks a million!

[Toxicterror]

the asparagus design helped me alot with bigger rockets

[SRV Ron]

Stitching tanks together is a must on those large diameter tanks or else they just fall apart. However, it doesn't seem to be an issue on some parts as this kid built five stack, 1.25 x 30 meter design flew single stage to escape velocity with hardly a wobble.