Best way to achieve orbit?

[nveresdf]

Sometimes I launch my rocket perpendicularly to KSC and I keep it that way through the atmosphere, so I end up having a very high apoapsis and a very eccentric trajectory, so I can't wait until I reach the apoapsis to start doing a burn. Now I'm wondering: what is the best (most fuel efficient) way to achieve an orbit in this case? Should I do a burn along the prograde vector (chasing it) or should I line up the rocket with Kerbin's equator (keeping it that way) and then do a burn to achieve orbit?

[Vanamonde]

There's no simple answer. There is an optimum, of course, but it depends on a lot of complex math involving drag, the thrust/weight ratio of the ship, etc., and will vary a bit from one design to another. There are some challenges in the challenge section of the forum to try to find the most efficient ascent, but I don't know their names. Personally, I turn about 30 degrees prograde as I leave the lowest atmosphere zone (light blue on the gauge), to 60 on leaving the second zone, and then rotate to horizontal fairly quickly after that. But that's just a rule of thumb, and not at all rigorously derived.

[Kosmo-not]

I'll refer you to the first part of my video. It gives you the rundown on the factors involved in getting into orbit.

http://www.youtube.com/watch?v=MBZPH0OOZdY&feature=plcp

I start my turn at 7km and try to end up with an 8° angle above the horizon at around 40km.

[lucidLemon]

This is how I generally do it, it's been fairly successful for me.

During take-off, don't exceed 250 m/s, because by that time your probably wasting fuel to fighting atmospheric drag, once you get above 10 km, it should be OK to fully throttle up.

Start your gravity turn until your above the thickest part of the atmosphere. Again, a good height is 10 km.

Slowly tilt towards the the horizon, in the direction of the planet's rotation. If you are unsure, this is the direction that planes take off from on the KSC runway.

by 30 KM, you should be flying at at least 45 degrees

by 50 KM, you should be flying at at least 20 degrees

It's perfectly fine to have different values for these steps. Just remember to make sure to do a slow, gradual, tilt.

During this entire procedure, be sure to check your map. In fact, it is easiest to use the map view primarily and occasionally check the normal view for fuel. There is a small tab in the bottom center of the map-view, click it to bring up a navball so you can control your ship.

Once reach an apoapsis of 75 km or higher, cut your engines. If you see that your apoapsis is rapidly falling, apply a little power to keep it up.

Wait till you reach the apoapsis (Watch in the map view)

You should be pointed slightly above the horizon, still facing prograde, when you reach the apoapsis.

Once your at the apoapsis, start your engines up again.

If you are going past your apoapsis, point your ship higher up to bring it back to you, if the apoapsis is moving ahead of you, point your ship downwards until you start to catch up.

Stay on the apoapsis like this until you raise your periapsis to 75 km. You'll be able to tell when the PE and AP markers suddenly flip around.

Bam, your in orbit!

[PakledHostage]

There are some challenges in the challenge section of the forum to try to find the most efficient ascent, but I don't know their names.

These might be two of the ones you're thinking of:

Closette's Mini-challenge: max altitude with this supplied spacecraft. The conclusion there seemed to be that climbing at terminal velocity is about optimal (at least in the vertical ascent case). Achieving this profile requires a fair bit of throttle modulation during the climb. There's also the Optimal Ascent Profile for this spacecraft challenge.

These challenges pre-date v0.16 so the performance of the test spacecraft configurations have changed. The designs were intended to be easy to fly, rather than to have peak efficiency. It is also interesting that the human pilots did better than MechJeb in the Optimal Ascent Profile for this spacecraft challenge.

[nveresdf]

Thank you, guys. You were very helpful!

[Aerodynamic Kerbal]

Back to reviving a... 9 year old thread?!?

I start the gravity turn slowly, almost directly after liftoff. When the apoapsis reaches the target altitude, I turn equatorial and sometimes below 0°, until the first stage runs out of fuel. Then I burn prograde (without even using a maneuver node!) until I reach a circular orbit. 

 

[Snark]

Since, as you observe, this is in fact a 9-year-old thread, I think it's safe to assume that everyone involved in the original discussion has long since gotten the problem figured out and moved on to other things.  Not to mention that KSP has changed so much in the meantime that any pre-1.0 advice would be very wrong today. 

Accordingly, locking the thread to prevent further confusion.  If anyone has current questions about how to get to orbit, feel free to spin up a new thread.

Thank you for your understanding.