Space station troubles

[Ic6500]

Hello I am a relatively inexperienced KSP player lately I have attempted to launch a space station to the Mun but when I launch the rocket it turns the wrong way. I hope some more experienced players can help.

[paul_c]

We would need a pic, but a guess is that its too draggy at the top/front compared to the bottom. Like a shuttlecock, it will try to turn and as speed increases, eventually overcome whatever control (engines gimballing; reaction wheel) you have/had over it.

[king of nowhere]

another possible option is that the station parts you are trying to launch have some probe core mounted backwards, and it is the one controlling the rocket. in that case the rocket will thing forward is backwards and viceversa.

but yes, aerodinamics is generally the main source of flipping rockets, and yes, we can't tell without pictures

[Anonymous49]

how does your rocket even looks like? Any pics pls? Btw, try adding some autostruts.

[jimmymcgoochie]

If you need help with a design, always include pictures of that design- without them we’re just guessing, but with them it becomes a lot easier.

When you say “turns the wrong way” do you mean it flies in the wrong direction or flips backwards? If it keeps going pointy-end up but in the wrong direction it might be fixable by adding a few degrees of angle (so it points at e.g. 87 degrees up and slightly to the east on the launchpad) then just holding prograde for most/all of the launch. If it flips backwards then either your aerodynamics are off (too much drag at the front e.g. a massive fairing, and/or not enough at the back e.g. fins) or your weight distribution is off (too heavy at the back and/or too light at the front) which could be solved by changing the order that your fuel tanks get used so they drain from the bottom up.

Without seeing the rocket in question that’s about as specific as I can get.

[Guest]

To expand on the excellent answers so far, I usually find 2 problems when this happens:

1) too much drag at top (use a fairing, even something oversized/resembling taj mahal is better than nothing at all for things not shaped like end of rocket). Fins at the other end will also help here.

2) because of extra mass involved in lifting station parts, there is a tendency to stick a load of fuel in the first stage (ie lowest point) to boost deltav which is bad, as a rocket doesn't actually act like a pendulum as you might think. One trick I've found is rather than having one huge first stage tank is to have a second smaller one (nearest the end) but have it empty/part empty. This shifts the CoM upwards. Also make sure you've got plenty of reaction wheels, fins and gimbling rockets so if it does start to go you've got more chance of recovering it.

Finally if all the above fails, do the exact opposite and load it up with more fuel and launch straight (ie no gravity turn) until you are up to at least the thinnest part of the atmosphere. It'll use a ton more fuel to circularise but it shouldn't flip on way up (ah the memories of trying to get the largest Alcubierre Drive into orbit coming back now...)

 

[paul_c]

I've said it before (in other threads) but its worth mentioning again:

In an ideal gravity turn, there are no* sideways forces at all!

*Except for the initialisation of the turning (if it were designed to point directly upwards, as rockets are by default when built in the VAB), the gravity turn is like dropping a broom balancing on your fingertips, very gradually, from vertical to horizontal. The sideways imbalance results in the  actual, very slow, rate of turn which occurs as it goes over. In theory you could turn off SAS and let it do its own thing. Indeed, people have demonstrated on YouTube this is possible.

In reality, the closer you can get to this ideal, the less the sideways forces from whatever source, which need to be countered by SAS reaction wheels and/or gimballing engines. KSP doesn't help with its keyboard controls which bang in control inputs at either 0% or 100%, and some engines are very jerky with their gimbal (Thud) so its something you need to work around. But its possible that a beautifully designed rocket can be misflown and go bonkers; or a complete dog is launched in an apparently perfect ascent by an expert (or a good autopilot).

[Spricigo]

1 hour ago, FruitGoose said:

One trick I've found is rather than having one huge first stage tank is to have a second smaller one (nearest the end) but have it empty/part empty.

Mind you, may be tricky trick to pull off due heavy engines at the very bottom of the craft.

1 hour ago, paul_c said:

In theory you could turn off SAS and let it do its own thing. Indeed, people have demonstrated on YouTube this is possible.

In practice, you don't even need to turn SAS on in the first place. (shameless plug: https://kerbalx.com/Spricigo/Yuri250-70 )

Now, certainly is not so easy when carrying a bulky station and dealing with a considerable amount of flexing between the parts. May exist imbalances in drag and weight distribution because of how the station is designed and all the issues due to eventual limitations in tech/facilities available.

A popular solution for the problem is  to build a somewhat  overengineered craft around the station, use plenty of struts/autrostrus to improve structural strength and ascent to a higher altitude before turning to orbit. The idea behing this is that Station tend to be draggy and not so heavy(dense), moving the draggy things back and the heavy things forward helps to improve aerodynamic stability and the  more vertical ascent profile avoid a big chunk of the aerodynamic forces that could otherwise twist the craft out of control or/and into a rapid unplanned disassemble.

Spoiler

Example of one such craft https://kerbalx.com/lolotux/Huge-Lifter-Stock-+-Big-Station-+-Capsule-de-retour-v2

As other said, pictures are welcome.  If you may also inform us about limitations of tech/facilities that is also good.

 

 

 

[Guest]

11 hours ago, Spricigo said:

Mind you, may be tricky trick to pull off due heavy engines at the very bottom of the craft.

True, but not as tricky as trying to get it into orbit without any at all, so a necessary evil unfortunately