Bulky craft to orbit - help :-)

[LiveHereNow]

So, I'm trying to get a drilling rig to orbit... and ultimately to the Mun.  The actual structure is solid... doesn't bend... but it starts to tumble end-over-end around 8k-12k up.  I do get rotation as well, but that's moderately tolerable.  I generally tip it just a few degrees at 500 feet... and then start to lean it a little more over time until I'm about 45 degrees at 23k.  I thought a steeper launch would help but it doesn't.

I'm at a loss... I used to be able to get bulky things up to orbit.  I've tried all sorts of different boosters... with fairing, w/o fairing, slow launch, fast launch, steep, shallow.  It's driving me crazy.

My goal... a driller than can go up/down on Mun (and Minmus, but that's easier) to an orbiting orange tank and hold 1200 ore.  A self-sufficient refueling operation.

My ask... advice... if you think I need to rebuild or redesign, or if you think my launch style is poor... let me know how to get a big driller to the Mun!

Throw advice my way please.

[BananaTime101]

7 minutes ago, LiveHereNow said:

So, I'm trying to get a drilling rig to orbit... and ultimately to the Mun.  The actual structure is solid... doesn't bend... but it starts to tumble end-over-end around 8k-12k up.  I do get rotation as well, but that's moderately tolerable.  I generally tip it just a few degrees at 500 feet... and then start to lean it a little more over time until I'm about 45 degrees at 23k.  I thought a steeper launch would help but it doesn't.

I'm at a loss... I used to be able to get bulky things up to orbit.  I've tried all sorts of different boosters... with fairing, w/o fairing, slow launch, fast launch, steep, shallow.  It's driving me crazy.

My goal... a driller than can go up/down on Mun (and Minmus, but that's easier) to an orbiting orange tank and hold 1200 ore.  A self-sufficient refueling operation.

My ask... advice... if you think I need to rebuild or redesign, or if you think my launch style is poor... let me know how to get a big driller to the Mun!

Throw advice my way please.

Fairing could help. Try it maybe? not to sure though

[ExtremeSquared]

Keep your velocity below 300m/s and completely vertical until 10000m altitude. Then gradually increase velocity. You may not be able to start a gravity turn until 20000m+ depending on how bad the aerodynamics are. It is an inefficient ascent, so plan to waste a couple thousand m/s of deltaV. May want to add a few more reaction wheels to help the craft maintain a vertical ascent. Fairings do not work in 1.05, so launching odd contraptions absolutely requires a 0.23 style ascent.

Edited February 5, 2016 by ExtremeSquared

[Snark]

I'd say, don't bother with a fairing that big.

The thing to do is:  launch vertical and slow.  Go straight up and don't even think about starting a gravity turn until you're at least 10 km up.  Also, go slow.  Drag goes up by a lot around Mach 1, so keep the speed under 300 m/s.

And add big fins to the back.  Big steerable fins.

For a craft that size, "big fin" could mean actual wings.  For example, stick four Delta Wing on the bottom in a "+" configuration, and put a decent-sized elevon on each one.  That'll do wonders for your aero stability.

But that's an extreme-- if you go straight up to 10 km without exceeding Mach 1, you may be okay with just sticking a quartet of AV-R8 winglets on.

Main thing is, whatever wings/fins/control surfaces you put on there, make them as low low low as possible-- you want them really far behind the CoM to give them a decent lever arm to work with.  For example, your radial boosters are sticking way down-- put some fins/wings/whatever down on the bottom of those.

[Vim Razz]

Take a look at the way you've got fuel set up to drain from your tanks.  All the top-most tanks are draining out first, pushing your COM back pretty far down the rocket.  That alongside your reasonably draggy payload isn't helping your stability any.  Your TWR is also extremely high -- especially for a rocket with bad aero.

A quick-and-dirty thing to try might be to shift your asparagus boosters down lower in relation to your core assembly so that you maintain a big chunk of weight out in front more effectively.

Personally, I'd start by putting the orbital orange tank on a poodle instead of a skipper (? - hard to see) and have that entire stage sitting on top of where your 2.5m SAS currently, striping the relevant parts off the current orange tank for it and just letting that remain as part of the launch assembly .  That would keep that chunk of mass way out in front of the rest of the launch assembly while passing through the atmosphere, which should help -- and tbh, it looks like you're overbuilt enough that you can handle the extra weight without substantially redesigning your rocket.

[HebaruSan]

As a start, I'd consider flipping your payload right side up. All those draggy radially attached bits are way out in front of the center of mass, and flipping it around would move them closer to the middle and make it somewhat easier for your rear fins and engine gimbal to compensate.

I've never measured how much it matters, but you also might try using one of the 1.25m-2.5m adapters to avoid abrupt changes in craft diameter near those docking ports. I think you're paying an extra drag penalty right around that big reaction wheel.

Your take-off TWR is pretty high, and your third stage burns much longer than the other two (presumably because it includes Munar transfer and capture). A decent guideline is to try for approximately equal burn lengths for multi-stage rockets (but it's not worth making sacrifices trying to make them exactly equal), and take-off TWR around 1.3-1.7, so you might try moving some of that fuel from the third stage to the first.

Does that upper stage have enough delta V to land on the Mun if you turn off atmospheric mode in KER? I was alarmed at seeing 134 m/s before I noticed that button was pressed.

I'm not sure if those solar panels will supply the power you need to run the drills and converter. You might want to add fuel cells.

[juanml82]

Would putting nosecones on top of the terriers reduce drag?

Also, how about using the vectors for the ascend stage, so you can count on their insane gimbal?

[LiveHereNow]

So, it's now on the Mun drilling!  THANK YOU SO MUCH!

The solution, less thrust with a longer, slower burn... staying well under 300m/s until after 10k to start turning *really helped.  Yeah, it burned a lot of fuel, but really wasn't as bad as I thought.  It took to orbital insertion burns to get it right, but then I had plenty to get to the Mun.  Also, locking fuel in the drill/lander helped the balance as well so the COM didn't go back as quickly.

Now, the efficacy of the actual decent/drill/ascent rig is less than I wanted, but it go there and it does work... so... I count that as progress!  Thanks again!