Kerbin Orbit

[Buckeye1]

Still working on Kerbin orbit. I've been able to get a periapsis of 21,000 meters and a very large apoapsis. I think this is a product of my rocket being at about a fifty degree angle through the atmosphere. I'm figuring I need to be almost parallel to the ground when I get up to 70,000. Probably don't need full throttle on my engine either. Any tips? I want a circular orbit without having to maneuver after I'm in space.

Edited August 7, 2016 by Buckeye1

[foamyesque]

You've pretty much identified what you're doing wrong. You want to be parallel earlier than 70km, though; where, exactly, depends on your rocket's thrust profile. The Kerbal Engineer Redux mod can give you very important orbital parameters (apoapsis and time to apoapsis, particularly) to help with that; if you can't/won't get it, fly in map mode to see what your apoapsis is. You should be parallel around the time your apoapsis hits 55-60km and your time to apoapsis at that point should be about fifty seconds to one minute.

 

You may need to make one orbital burn to execute a circularization, since a direct continuous ascent to a circular orbit is very difficult to get right every time. It's generally a tiny engine burp done at apoapsis.

[bewing]

Yes, you want to be horizontal somewhat before 70km. You don't need to be fancy about it, though -- it just costs a little extra dV to be early or late. I like 58km as a rule of thumb.

Then, as you burn your Ap will move ahead of you. The further ahead, the faster it rises. Don't let it get very far ahead. If it starts accelerating in front of you, then coast for a while. But you are putting energy into raising the Ap, and you want to be putting it into raising your Pe.

[dafidge9898]

5 hours ago, Buckeye1 said:

Still working on Kerbin orbit. I've been able to get a periapsis of 21,000 meters and a very large apoapsis. I think this is a product of my rocket being at about a fifty degree angle through the atmosphere. I'm figuring I need to be almost parallel to the ground when I get up to 70,000. Probably don't need full throttle on my engine either. Any tips? I want a circular orbit without having to maneuver after I'm in space.

If you mean you want to have a circular orbit without having to coast to apoapsis, that is a very inefficient way of achieving orbit in stock. That is, however, the only way in RO.

[Spricigo]

Previous posters already answered the question, so I will just try to add a bit of perspective. 

We quickly notice,  after few attempts,  reaching orbit it's not so easy as reach space.  That's is because climb to space is a lot easier than to reach orbital speed. To  make it worse the effort to Climb to space don't help at all with Reaching orbital velocity and vice-verse. To climb you thrust up,  to get to orbital velocity you thrust laterally.

This is somewhat hard to realize because our intuition says gravity bounds everything to the ground,  also our intuition is tuned for speeds and distances way lower than what we are dealing here .   We may even know the theory but it takes time until we become confident enough to act accordingly. 

 

Another thing you should notice: since surface it's not plane,  but curved,  burning horizontally  will push the vessel away from the surface. To prevent your apoapsi to raise even further you may point your vessel an bit inward (how much depends on your thrust) 

[Magzimum]

Just to get the problem completely clear: when you pass through the Apoapsis, is it (1) already "very large", or (2) do you pass through apoapsis at normal altitude, but then the apoapsis becomes "very large" afterwards, while you fall back into the atmosphere?

Since your apoapsis is "very large", it sounds like you have enough power. So, you just need to use that power differently.

If we are dealing with:

(1): you basically ascend straight up. Make sure to go horizontal earlier, while you are still in the atmosphere, going up. If you can't, add more control surfaces (e.g. Delta-deluxe Winglet), or make sure that some of your engines have a Gimbal (the nozzle of the engines can be used to steer): Most liquid engines have that, but the solid boosters don't.

(2): you probably need more power. You have enough fuel, but the burn takes too long, and you are already back in the atmosphere by the time you used all the fuel. Solve this by either aiming higher (getting a higher apoapsis), which gives you more time to burn all that fuel while going horizontal, or get a more powerful engine so you can consume the fuel quicker. 

 

[Spricigo]

3 hours ago, Magzimum said:

... or (2) do you pass through apoapsis at normal altitude, but then the apoapsis becomes "very large" afterwards, while you fall back into the atmosphere?

... 

(2): you probably need more power. You have enough fuel, but the burn takes too long, and you are already back in the atmosphere by the time you used all the fuel. Solve this by either aiming higher (getting a higher apoapsis), which gives you more time to burn all that fuel while going horizontal, or get a more powerful engine so you can consume the fuel quicker. 

 

 

IMHO don't look like is the case based in the info given by OP.  But if that is the problem maintening some thrust up on the later ascend and after apoapsis sometimes is enough to keep fighting gravity for sufficient time to reach orbital speed.

Usually one end in this situation because of piloting error at earlier parts of the launch or bad designed rocket.  Fortunately recovery it's possible 

[Reactordrone]

12 hours ago, Buckeye1 said:

 I want a circular orbit without having to maneuver after I'm in space.

This is where you're going to run into problems. Most of the time people will raise apoapsis to the level that they want and then shut down the engine, coast up to that point and relight the engine to raise the periapsis. To get a circular orbit without doing that you'll need to maintain a very low thrust level and time it so that you approach your apoapsis just as you're reaching orbital velocity. From your description what you appear to be doing is trying to raise your periapsis beyond your current altitude while still within the atmosphere but all you're doing is raising your apoapsis and getting a highly elliptical sub-orbital path.