1.0.4 Getting a scanner into Kerbin orbit

[kfsone]

Relatively new to KSP, playing career mode and trying to get a probe into [polar] orbit around Kerbin. I figure I need to aim for a little more than 4k dV, so I experimented with liquid and solid boosters, but my problem is that as soon as I stick a scanner onto the top of my rocket, I lose control and tip around 2500m, whether I throttle down at 300m/s or not.

The liquid version of the ship:

probe1.craft file (dropbox)

I've tried raising and lowering the CoM, but that doesn't seem to help: my hunch, from the before the first launch, was that the scanner was going to have a lousy aero profile.

TL;DR How the heck do you launch a scanner? Are there fairings? Is there a way to hide it in a structural fueselage, or is there some way I need to tweak my rocket to counter the tipping and just live with the drag?

(Incidentally: The reason I'm trying to do this is that I need more science to get out of a rut where I desperately need to research parts of the tech tree for landing etc but I can't earn the science I need to research them, I've been to the Mun and Minmus but to really get further I need a couple of improvements; c.f I have the Mk1-2 but I don't have a heatshield to be able to land it with, which means my landers all tend to bounce uncontrollably, fall over during landing, or be incapable of return to orbit)

Edited November 6, 2015 by kfsone

[eggymatrix]

There indeed are fairings!

In the aero parts menu take the 1.25 fairing ring (AE-FF1 aerostream proctective shell) and place it under your upper decoupler. As soon as you place it you can build your fairing by left-clicking for each segment.

[kfsone]

Ok - the problem is I don't have those yet (I'm playing in career mode).

Also, part of the problem seems to be that the TR-18A is broken...

Try this:

OKTO (or HEXS),

FL-T800,

LV-T30,

TR-18A,

FL-T800,

FL-T800,

Tricoupler,

add 3 swivel engines to the tricoupler,

TT18-A attached to upper T800 to support well off the ground

Now launch. Notice the gap betwteen the decoupler and the second set of T800s...

https://dl.dropboxusercontent.com/u/109944963/gap.jpg

If I build basically the same rocket with the rockomax tanks/engines, I don't have the same problems, it's only when I try to build complex with the FL tanks and components.

[kfsone]

There indeed are fairings!

In the aero parts menu take the 1.25 fairing ring (AE-FF1 aerostream proctective shell) and place it under your upper decoupler. As soon as you place it you can build your fairing by left-clicking for each segment.

Awesome - managed to scrape just enough science out of KSC from the runway to pay for that so I think I'm good now

[Harry Rhodan]

I lose control and tip around 2500m, whether I throttle down at 300m/s or not.

I've tried raising and lowering the CoM, but that doesn't seem to help:

A low CoM will make you less stable, you have to keep it high. The easiest way would be building a simple two stage rocket with a heavy upper stage. Those boosters might look funky but they will only make you go too fast too soon and keep your CoM low.

[ElWanderer]

Bigger fins (those basic ones are very small) on the bottom might help too.

[Acet]

Less launch TWR - 3.86 is way too much. For a liquid fuel launch stage around 1.4 - 1.5 is right.

You are probably getting to higher supersonic levels (mach 3+) in the lower atmosphere - you can tell it by the flames around the ship - which is pretty bad for controlling it, especially given that without any fairings the aerodynamic profile at the front of your rocket could best be described as something which wants to get out of the way of the airstream ASAP. Furthermore, an excessive ascent speed means you're wasting too much fuel purely on compensating for aerodynamic drag.

You should probably get rid of at least half the engines (drop two side stages, possibly move some of their fuel to the remaining ones) and add an AE-FF1 aerostream proctective shell just below the middle decoupler to make a fairing around the satellite stage.

[kfsone]

Appreciate the answers, but the thing that had been keeping me from figuring any of these out was the bug with the TR-18A: if the stuff below one is too heavy, you get a gap which behaves like more than a visual artifact once you launch. It seems to be a factor in why really tall rockets are so oddly "bendy".

As a result, everything I tried (fwd/mid/rear com, manually keeping below terminal by throttling back at 300m/s, etc) resulted in tipping, wobbling or - one time - the top half of the rocket simply slid off...

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You are probably getting to higher supersonic levels (mach 3+) in the lower atmosphere - you can tell it by the flames around the ship - which is pretty bad for controlling it, especially given that without any fairings the aerodynamic profile at the front of your rocket could best be described as something which wants to get out of the way of the airstream ASAP. Furthermore, an excessive ascent speed means you're wasting too much fuel purely on compensating for aerodynamic drag.

I generally ride the throttle once I hit 300m/s, but my scanner-rockets were all suffering tipping the moment I touched the throttle or directional controls; I tried a various staging approaches with boosters etc to get me to 300ms and then leave me with a simple liquid fuel to ease me above 10-15k before kicking in a second stage with more boosters and a reliant engine. I tried an all-liquid approach which used the less powerful Swivel for the early part of the launch with a tank just enough to get me to 14k so that I was riding it's full potential until I ditched it so that I didn't need to play throttles.

The problem with these builds was they made the rocket very tall - or very unstable if I built them outward - until I went to the Rockomax components. I was assuming it was because of the Scanner until I got a bit crazy and built a really heavy rocket and spotted the hole under the decoupler. It's very easy to repro, so now I know it's not just me

[DeMatt]

...that gap is because you have heavy stuff stretching your rocket out from where it's supported. Try taking away the launch clamps (just let it rest on the engines) and see whether there's still a gap.

As to your rocket design, yes, as mentioned you'll need a fairing for the scanner. I would further suggest increasing the size of your side boosters from FL-T400's to FL-T800's, and putting much larger steerable fins on them; fire just the side boosters to get you off the launch pad, then keep the throttle and speed low and your steering gentle until you've gotten out of the thick atmosphere, say 12km altitude.

[radonek]

Yeah KSPs physics is stretchy, but you hardly ever see this. With engines pushing stuff in front of them, you are more likely to see parts buried into each other. And it's not like you have to look far - your own creation with five Reliants in first stage must have sky high TWR and is likely to experience this. Don't worry much about that, it's games way of (not) visualising physics. Game engine can compute stretching and bending for parts subject to force, but it can't display it because visual models are unflexible. If you don't push your luck too hard, everything will settle back. Should you need to enforce some joint, just move camera "inside" parts and apply struts liberaly.

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Just looking at KER numbers in your screen - you start with TWR of 3.8 (read: way too much), which raises to more then six (oh my god) as you burn through fuel weight, then drop to 2.0 with stagging (still too much), only to raise back to 5.2 (ouch). Now, if you were lifting off some airless body like Moho or Tylo, this would be "only" rough ride of high G's and wasted fuel. but in atmosphere... you are traveling back and forth through you max-Q at crazy-ass speeds. If you did this with real rocket, it would not be "unstable". It would be shred to pieces!

Picking right TWR is kinda black magic depending heavily on your ascent profile. But general rules are:

1) if you see red flames, you are going too fast and can/should throttle down.

2) if you throttle down, you could do with smaller engine as well

3) smaller engine == less weight == higher TWR (!) and more delta-v in the end.

When shopping for engine, do not ask "can I use more power" because answer is invariably yes. Ask "If I take difference in weight as extra fuel, where will it get me?"

[GoSlash27]

Wait... you have the scanner but *not* the 1.25m procedural fairing?? How is that possible?

The fairing is tech level 5 and the scanner is tech level 7. *Scratches head*

Best,

-Slashy