capi3101

I'm positive they're flowing the right direction; I include fuel ducts with almost all of my desigs, so I am pretty well versed in how they function. I did the math on that one. TWR at Stage 2 seperation is 1.2 with the Mk-55s and 0.9 without; it's the whole reason why I included them in the first place. I actually had given that idea some thought; I've noticed a lot of wobble in the central engine during takeoff, no doubt due to the plethora of gimballing engines I've got on the design. I haven't crunched the numbers on putting in a cluster yet; might be worth investigating. I am familar with Temstar's heavy booster designs; whole reason why I'm trying a 120 tonne payload. I finally know it's in the realm of possibilities... "Onion"-staging, huh? I'll remember that. Meantime I'll do what y'all have suggested and report what happens.

So here's one I don't understand...I've got "ringed" asparagus staging going on between my stage rockets if I understand the term correctly; the third stage feeds off the second stage which feeds off the first. 8 mainsails in the first stage, 8 mainsails in the second stage and the third stage (the central stack) is one mainsail with 8 Mark 55s (without which the third stage TWR would only be 0.9 if I've done the math correctly). I've checked the fuel ducts and they're all running in the right direction. Launch at 80% thrust and the first stage runs out of gas just before 10k following a fuel-optimal ascent profile; I eject it and throttle up. Twice now, when I get to about 14,000, the center engine shuts off because it's out of gas. You know, my third stage - the one that's supposed to make the orbital insertion burn and should be drawing off the fuel supplies of 16 mainsails. Any ideas on what might be happening? I'll try to post the .craft file and some screenshots in the near future; still haven't found a repository I like yet. Maybe some crappy ASCII art would be helpful? â–‘ â–‘ â–‘ ââ€Ëœ ↓ ââ€â€ â–“ â–“ â–“ ââ€ËœÃ¢â€ “ââ€â€ â–‘>>â–“>>â–ˆ<<â–“<<â–‘ ââ€Â↑ââ€Å’ â–“ â–“ â–“ ââ€Â ↑ ââ€Å’ â–‘ â–‘ â–‘ â–‘ STAGE 1 â–“ STAGE 2 â–ˆ STAGE 3 EVERYTHING ELSE IS A FUEL DUCT

You really shouldn't try to jinx yourself like that... show-off

Quick note for a substitution - assuming you've got a Mk-I on your rocket right now, a Probodobodyne OKTO and 4 PB-NUKs have the same mass; swapping one out for the other = no net effect on delta-V or TWR.

http://wiki.kerbalspaceprogram.com/wiki/Controls

So here's one I don't understand...I've got "ringed asparagus staging" going on between my stage rockets if I understand the term correctly; the third stage feeds off the second stage which feeds off the first. 8 mainsails in the first stage, 8 mainsails in the second stage and the third stage (the central stack) is one mainsail with 8 Mark 55s (without which the third stage TWR would only be 0.9 if I've done the math correctly). I've checked the fuel ducts and they're all running in the right direction. Launch at 80% thrust and the first stage runs out of gas just before 10k following a fuel-optimal ascent profile; I eject it and throttle up. Twice now, when I get to about 14,000, the center engine shuts off because it's out of gas. You know, my third stage - the one that's supposed to make the orbital insertion burn and should be drawing off the fuel supplies of 16 mainsails. Any ideas on what might be happening? I'll try to post the .craft file and some screenshots in the near future; still haven't found a repository I like yet.

With the great forum nuking last month, the boards currently do not have attachment functionality. You'll have to put your materials on another site and link them in on the forums here. A lot of folks are using dropbox and imgur.

Pretty much what I said earlier; payload's just under 120 tonnes. I've designed a TSTO booster for it using the orange tanks - looking at TWRs of 1.75 on the first stage, 1.68 on the second, and 1.24 on the third. total mass at launch is looking at a little over 1500 tonnes with about 4601 delta-V. So...I've built this design at this point and I didn't know you could stitch the tanks together, so as y'all can imagine I've been treated to some fairly spectacular unplanned vehicular disassemblies this evening. I think my record for skipping a Standard Canard across the KSC is maybe half a dozen bounces so far. You know it's bad when the TT-18-As get knocked over; yet the Probodobodyne OKTO sitting at the top of the third stage survived. Even still had a PB-NUK attached. Actually did get the design into the air once and it did pretty well up until first stage separation. That's when I realized I hadn't put any control surfaces on the second stage... Good thing that A) the designers have yet to account for radioactivity from exploding PB-NUKs and LV-Ns and I was doing all this in the "Construction Basics" tutorial, so I didn't clutter up my persistent game with moar junk...

Okay; I've actually got several stacks of two planned in my design... When you say I should "be prepared to add a dozen struts", is that between the two tanks or between them and the tanks surrounding them? I.e. can you put struts between two tanks with one on top of the other? I've tried and haven't had much success in that regard.

Planned a TSTO using the orange tanks - looking at 1.75 on the first stage, 1.68 on the second, and 1.24 on the third. Payload's just under 120 tonnes; total mass at launch is looking at a little over 1500 tonnes with about 4601 delta-V and around 275 parts. That's assuming all the math's right. Haven't built it yet, obviously.

I've built most of my heavy designs using Rockomax X200-32 Fuel Tanks because I've heard repeatedly that there are some significant disadvantages with the Rockomax Jumbo 64 in the current version. As I'm wanting to launch heavier payloads, though, and I'm noticing that my part counts are starting to make my CPU smoke a bit, I can't help but wonder if I should switch out. I've also seen you guys use the orange tanks a lot, so I have to ask: are they really all that bad?

You have to be pretty close before the bracket keys work, usually within a kilometer or so.

Well, I had a notion for getting there and back but my son wanted me to go to Ike instead; don't know if it's got enough juice for a return trip at this point. Haven't tried yet, either. It's unmanned in any event. Probodobodyne OKTO and 4 PB-NUKs have the same mass as a Mk-I Command Pod, incidentally; makes a good dummy mass. The trick is that if you're not using mods, you have to eyeball it. I don't care how good you are, if you're eyeballing everything you're not going to hit Duna at the precise phase/ejection angle to get an optimal trip. So you've got to add a pretty big fudge factor. And probably the best way to handle that is to build a multi-part ship in orbit - a main thruster pack, a service module, and a lander. Good luck.

Heavy lifter's kind of vague...what's the mass of your payload? Are you looking for one to build yourself or are you just wanting one someone else has already built?

If you also use Subloader Assembly module, what you could do is put together a dummy payload that has a similar mass to your desired payload (say...an probe chassis with an orange tank, BUT NO ROCKETS, if your payload is somewhere around 36/37 tonnes); Mechjeb oughta tell you that you have no delta-V, which would be right since you haven't got a rocket on it yet. You can then build a lifter with 4500 delta-V off of that. When you get there, save the lifter portion of the rocket (the part without the dummy payload) with Subloader, switch to your actual payload and simply attach the lifter to it.

RCS should work; thrust down on contact. You might also try widening the base of your lander; if you make it low and squat, it's less likely to tip over. I'd also recommend making sure the grade of your landing site is as level as possible.

The trick in short, as many would eloquently put it, is MOAR BOOSTERS. Yes, there is a diminishing return on how much you can put into orbit as once; it's more often than not a limitation of your memory, though. The key is to have plenty of stages, to make sure you follow a fuel-optimal ascent (by keeping your speed close to Kerbin's terminal velocities), and to make sure your TWR is close to optimal the entire way up (1.2-2.5, I'd say). Struts and control surfaces are also essential, particularly for the lower stages. RCS is helpful once you've finished the ascent burn to get the payload on the desired trajectory for the orbital insertion burn. I've put up as much as 130 tonnes in one go with stock parts; it is possible and there are folks here who will gladly help you your designs if you need them.

Eh...it adds mass. In makes steering harder in that sense.

We ever get an answer on how long a periapsis kick burn should last? One minute? Two?

Shouldn't; if anything, adding more SAS to a large ship will make it less likely to turn (SAS's function is to counter unwanted rotation). To make a tub more maneuverable in space, you've got to go with more RCS.

Well, the Aerospike has a comparable Isp in vacuum; it's Isp is superior to the LV-909 in atmosphere and it can produce more thrust. That may be a consideration depending on the intended target. Just saying.

Stack separators have an annoying tendency to collide with my modules after separation; probably from the way it's placed on my rocket. Necessary evil. So far nothing catastrophic has occurred; usually the separator is destroyed while the module remains intact. Hopefully that trend will continue...

Try throttling back a bit; I have a DSTO rocket that has an initial stage TWR of greater than 2.2 and it spins like mad if I go full burn. Plus it wastes fuel; ideally you want your launches to follow the terminal velocity curve of Kerbin's atmosphere. It also increases the risk of catastrophic failure by telescoping stack. What I usually have to do is burn at two-thirds, pitch over to 45 degrees on heading 090 around 10,000m, wait for Stage 1 to flame out, throttle up and seperate; the second stage's TWR is usually around 1.5 by that point and she's stable the rest of the way up.

You could try boosting up a seperate transfer stage, dock that to a fueling module and then dock all that to your lander before you head out that way. I might also suggest a rocket with a higher Isp than the LV-909 on the lander...an Aerospike, perhaps (you haven't got anything under the lander engine anyway). It'd have more thrust than you'd need for a landing, sure, but you'd get more delta-V out of the engine; perhaps enough to actually land. Only other thing I would suggest is adding another set of fuel tanks to the LV-Ns. And more struts if it falls apart on you. I'm sure someone around here will tell you that you should be using all your engines from the get go...

If you're looking for hard data, we'd need either to see your rocket, get an accurate parts list or have access to the .craft file. If you're wanting to do the work yourself, you've got the options folks have already said: count 'em up or install Mechjeb.