Late Launch Spinout Problem

[ToThaMun!]

Hey guys. New player to Kerbal here and have been working toward getting to the Mun on my own. I've gotten several craft into orbit and space but I'm working on a solution to actually do the above and be able to get to the moon with fuel left over. Been trying to maximize thrust and lighten my ship perhaps or just throw in a ton of fuel pods. I'm doing career mode btw. Currently unlocked the " Advanced " areas.

Pic of the current rocket I'm working with. The thing is, and its been an issue with a lot of rockets I've made. The thing goes straight up just fine, but when it hits about 7Km or 10Km or so it starts to pitch up and it is completely uncontrollable and it eventually just leads to a pure spin.

Any ideas on how to get this rocket to stay stable throughout the gravity manuever and all that? This thing has enough thrust to get me into at the very least the last part of the atmosphere before I decouple and go into my space rocket with triple small boosters with fuel on its own. I use that rocket for actual space travel. If I can stabalize the launch I'll work on giving my main rocket enough fuel for the Mun but atm just trying to figure out this constant pitch problem at 7-10Km. Ir has happened with a lot of other rocket builds too. Around the same time frame. 7-10Km.

[Phil deCube]

In the Tutorials sub-folder underneath this one you'll find this tutorial.

Edited October 30, 2015 by Phil deCube

[DeMatt]

For a craft intended to orbit the Mun, but not land on it, I see the following issues:

• You have two decouplers for each of the solid rocket boosters. Don't do that, the SRBs only attach to one - the one you click the SRB into place on. Feel free to use struts if you have problems with them wobbling - they'll automatically break when the decoupler fires.
  
• Needs solar panels and batteries to power the reaction wheels in the capsule.
  
• Radiator's unnecessary. Use a heat shield, and dump everything but the capsule before reentry.
  
• The Mk1 Command Pod is both cheaper and lighter than the Mk1 Cockpit, and it even has a node for precisely the parachute capable of landing it.
  
• You lack fins. A set of AV-R8's will give you extra steering authority in the atmosphere.
  
• The Thud engines are unnecessary for the LKO-Mun-and-back part of the flight, and poorly designed for the launch-to-LKO part.
  
• I assume the decoupler beneath the center LV-909 is there for adding another stage, and you're not trying to fly with it.

[Rath]

Another thing I see--By using the good 'ol Mk1 eyeball I can tell that it probably doesnt have enough Delta V

[ToThaMun!]

Thanks for the answers and the tips guys! I pretty much scrapped that design and went with something a bit different. Actually made it to the Mun! I didn't have enough fuel to orbit or anything but I got pretty close and was able to land back on Kerbal with my ship intact. I felt like one of those dudes from NASA pumping my fist and hopping up and down once I actually landed safely. Didn't think it was going to happen as I ran out of fuel on approach and was coming in at 3100km/s lol.

Heres the one that got me there this time. I'm going to take what you guys have said and see if I can get the OP type out of orbit next. I'd like to be able to build a full on spaceship and get it into orbit with the boosters and then detach and see what happens from there. Kind of what I did above though really.

[CrashTestDanny]

One word... FINS... If you are losing control during atmospheric flight, fins are probably the answer.

Danny

[LTrotsky]

1. Loss of Control During Kerbin Ascent.

Assuming you haven't built and aerodynamic disaster, this is almost always due to overthrust. The aero model now isn't very tolerant of vehicles moving fast through the atmosphere where the center of mass is closer to the top than the bottom of the vehicle. The more thrust you are applying to the vehicle, the worse it gets. If you have a craft applying 3g accel, and the thrust is at the bottom and the center of mass is at the top, you will flip in atmosphere. Most vehicles do not need more than 2g accel capability for 3 minutes to get into orbit. Anything beyond 2g is probably wasting fuel bigtime due to drag ('pushing wind').

2. Overengineering.

You can get to the Mun with much much less than you are building. Try something much simpler, and arrange your staging for specific functions. In most cases, you should have 2 stages to get into LKO, 1 for the heavy lift off the pad at between 1.5 and 1.8g, and a second stage (which I call the Orbit Build stage) which can provide around 2g accel until you build a 75k orbit. Remember the 10Kn to 1ton ratio: for every 1 ton of vehicle, you need 10Kn to provide 1g. If your vehicle has 40tons on the pad, you need 800Kn for 2g, etc. Your third stage should be a transit stage, and you may need an additional stage for return, depending on what you are doing. Getting to the Mun requires about 860 Dv, but remember that Orbit Capture requires around 300Dv, depending on your approach velocity. Escape and return to Kerbin requires no more than 300Dv.

Use Korolev's Rocket Formula to calculate Dv in each stage. For this to be useful, you need to know how much Dv you need for each stage to complete it's function.

Stage 1 - Heavy Lift (or Launch Boost) = 2000 to 2500 Dv.

Stage 2 - Orbit Build = 2000 to 2500 Dv.

Stage 3 - Transit and Orbit Capture = 1300 Dv

Stage 4 - Kerbin Return = 300 Dv.

Say you have a 4 stage rocket. In the VAB, note the mass in the Engineer's report (that number is now M1). Now empty all the tanks in the first stage, and check the new mass. That number is now M2.

Find your Dv by : ln(M1/M2) * ISP * 9.81 = Dv for that stage.

[AlextheBodacious]

If you test your rockets in the demo (or any early) version your in-game experience will multiply x10.

[Superfluous J]

If you want to eyeball your craft without doing a ton of math, you can see your TWR on launch. The G meter on the right side of the navball has a tick for each 1G of acceleration your ship is under. On the launchpad, it's a 1G. When you launch, you want it to be about halfway up between that and the next tick.