Reverse Asparagus Lifter

[Beeburgers]

I've been working on a way to make a more efficient launch module, and, after a lot of trial and error, I've come up with this:

I've been calling it a reverse or inverted asparagus launcher. Basically, instead of the outside dropping away, it stays and the inner tanks drop. The central idea is to lose the heavy fuel tanks without losing the engines that would otherwise be attached. In theory, it seems pretty sound. In practice:

And:

And then I got desperate and just started slapping engines and struts to it...

So yeah... Even with a bunch of RCS, extra thrust vectoring and fins, it as an attitude problem. And by that I mean it won't fly straight until you ditch most of the tanks, and that kind of defeats the purpose. If anyone knows what I'm doing wrong, or, and this is more important mind you, why it won't fly straight! I'd greatly appreciate it.

Craftfile.

[eskimo]

So you've got your engines forward of the center of mass, your yaw/pitch movements are going to be reversed. See what happens when you turn off SAS, and see if you can't keep it in mind that the controls are reversededed.

[sgt_flyer]

yup, in this configuration, SAS will try to correct in the wrong direction, and as the rocket turns, the SAS want to compensate even more in the wrong direction... resulting in kerbal style flight for the rocket

[shand]

So you've got your engines forward of the center of mass, your yaw/pitch movements are going to be reversed. See what happens when you turn off SAS, and see if you can't keep it in mind that the controls are reversededed.

I think this was corrected - at least with aero parts, i dont know for certain regarding gimble.

Either way, having your thrust higher then your mass will make your rocket unstable.

the premise of your rocket is sound though, but consider instead of mounting the engines either side of a dropping central stack, having a short central stack with many engines clustered onto it with sidepods that drop off.

Personally i'm having good success with my launch vehicles that have no fuel lines at all, each stage has a combination of rockets and fuel that lasts the same period of time. KISS.

[Darth Lazarus]

first of all : the outer smaller tanks are not getting empty at the same time -> the result is a shifitng center of mass to the side and teh rocket tumbles. second during the burntime the center of mass moves from the tail over teh center of trust to the top -> going to be instable during the moment where center of mass is equal to center of trust -> small correctioninoputs to the flypath will have a big inpact

[Beeburgers]

Okay, I've made some adjustments, primarily involving shifting the weight higher, and Now we have this:

I've been informed by our top sciencey team that this constitutes a 98% decrease in explosions and unwanted ground/craft rendezvous compared to the previous design. Good job boys! That's what we like to hear. Now... make it bigger!

The trick to this design is as follows: as you add weight to the bottom set of fuel tanks, you have to add equal or greater weight to the ring of tanks around the engines. Other than a few minor problems with fuel flow the Mk II has also been a success. Primarily we've had an issue with one engine running out of gas before the others. The good news is that the fuel tanks can be dropped early with no detriment to thrust, nor do we need to flip the engines off for the dump. (this makes these catastrophic problems slightly less catastrophic.) And look what happened:

Maybe next time we'll remember to do a gravity turn... Also, we had another issue:

That's one of the RCS tanks splitting from the others for what seems to be no apparent reason. In fact, "No apparent reason..." were the exact words used by our sciencey team and they seem pretty on the ball. Jeb was quoted at saying "Betcha I can catch back up with it!"

"HA! Told ya!"

Reverse Asparagus Lifter MkI New and improved!

Reverse Asparagus Lifter MkII

I'm not sure if either of these are any more efficient than a standard asparagus model lifter, and with Mech Jeb still on the outs with my computer, I don't really have ay way of testing it, but if it helps you toss some Kerbals into space then that's got to count for something...

[shand]

to help with the one engine running out before others - keep fuel lines running "many to few" OR "few to many". if fuel runs "many to few to many" then it wont drain right and will cause issues.

Also i've found the RCS tanks have rubbish join strength - i think they fixed the similar issue with the large ASAS mind. so connecting 2 big RCS tanks may be dangerous. why do you need so much RCS?! thats probably about 10-15 minutes worth of thrusting.

Glad we've managed to fix a few of the issues

[Beeburgers]

to help with the one engine running out before others - keep fuel lines running "many to few" OR "few to many". if fuel runs "many to few to many" then it wont drain right and will cause issues.

Also i've found the RCS tanks have rubbish join strength - i think they fixed the similar issue with the large ASAS mind. so connecting 2 big RCS tanks may be dangerous. why do you need so much RCS?! thats probably about 10-15 minutes worth of thrusting.

Glad we've managed to fix a few of the issues

The fuel issue is in the last stages, and I think it has to do with a missing fuel line somewhere. (The complexity of this launcher makes every change an intensive process) I am thinking about making the tanks act more like the asparagus (that being dropping off in pairs, rather than all at once) to improve the MPG of this little beast, but that's probably a ways off.

The RCS was initially just there to help with the whole "wobbling around like a hamster on a marble" thing. After that was solved, I just left it there for ballast. Because there's weight bellow the rockets, removing weight at the top can make it unstable all over again. Plus it gave me an excuse to have Jebbidiah go back and try to rendezvous with destitute craft. Also: I feel I should take some of the blame for that. I told the guys in engineering to start crafting the joints from Paper Mache to save on cost and weight and I feel this may be the result... oops.

Thanks for all your help, and no the SAS wasn't the problem, it was the weight. Even with the SAS off, this thing just meandered across the Gimbal like a drunk on New Years Eve, whilst riding a unicycle, during an earthquake... with a blindfold over his eyes.

[shand]

Even with the SAS off, this thing just meandered across the Gimbal like a drunk on New Years Eve, whilst riding a unicycle, during an earthquake... with a blindfold over his eyes.

^^ Made my day ^^^

if you fancy a larger challenge try to make a rocket with the thrust WELL ABOVE the CoM - as you saw here, having the thrust very close to the CoM makes everything tricky, but feasibly you could have an upside down rocket. It wont be more stable then a traditional style (Pendulum rocket fallacy) but it is much more flexability in some ways. it is my preferred style for landers for example, but i've only once attempted an inital ascent stage that way.

the logic behind my use of it: well usually my return stage IS my LES, also i dont want my kerbals to have to climb down long ladders, they've just spent 10 hours in a tiny cabin for goodness sake!

[Exothermos]

I did something similar with this design that I posted over on the heavy lifters thread.

http://forum.kerbalspaceprogram.com/showthread.php/25701-Post-your-heavy-lifters%21?p=592686&viewfull=1#post592686

It works well. It was a fun experiment at least. I kept my engines at the bottom to alleviate a lot of those problems you are having.

[Slugy]

You might find this thread interesting:

I have a large stock stable rocket in post 26, and in 27 numerobis has made a mod to make gimballed engines work properly when higher than the centre of mass!