Semiautomatic orbit (no MechJeb)

[RealGecko]

With 1.2 version (still prerelease) SAS holding is fixed and we can finally use it.

I'm going to show now how we can easily reach LKO in semiautomatic mode using only ingame SAS.

For that we will need two things: stable rocket and level 1 pilot (or probe core capable of SAS prograde hold)

Let's start with rocket, it's a simple rocket consisting of only stock parts. It has LV-909 "Terrier" engin in the upper stage:

And LV-T45 "Swivel" in the first stage:

Overall it looks like this, and as you can see it's really chip rocket:

Let's go! On the launch pad:

1. Throttle up to max
2. Switch navbal speed indicator to orbit mode
3. Turn on SAS

Main engin start!

Keep going straight up until you reach 300 m/s of orbital speed (Yes ORBITAL speed!) and then throttle your engine down to keep your speed ~300 m/s:

And keep that speed until you're at 10 km height, as soon as you reach this height hit prograde in your SAS control panel and throttle to max again:

Keep burning, a quick thing to note: if your first stage is still pushing you at 20 km above Kerbin, then your rocket design is good:

As soon as your first stage is depleted, separate it and start the "Terrier":

Pretty goooooood, now go to map mode and keep an eye on your apoapsis:

As soon your apoapsis is above atmosphere, cut the engine down. Note that orbital speed at LKO is approximately 2300 m/s and we already have 2100:

Our speed will go down as we reach AP, but hey, we'll have to burn only ~300 m/s:

As soon as we're close enough to AP we can throttle up again, if your TS is upgraded you can place maneuver node to be more accurate:

As soon as AP and PE are approximately 90 degrees behind you and before you shut down your engine:

Congratulations, we're in orbit!

Not perfect, but stable

And with plenty of fuel!

Have fun!!!

[Pecan]

The return of "straight up to 10km, then turn right"?

[OrbitalBuzzsaw]

11 minutes ago, Pecan said:

The return of "straight up to 10km, then turn right"?

Yep.

[Avonix]

Ah the good old days of burning straight up and then doing a neckbreaking 45 degree turn. I missed you so.

 

Good idea, I never would have thought to use orbital speed on ascent (might borrow that for future reference!).

[RealGecko]

On 10.10.2016 at 10:45 PM, Avonix said:

Good idea, I never would have thought to use orbital speed on ascent

Yep, our initial orbital velocity is 175 m/s due to Kerbin rotation and if we go up 300 m/s our orbital velocity vector will be ~350 m/s with ~60 degree angle.

300 m/s straight up visualisation (a = vertical velocity, b = initial orbital speed, c = resultant orbital vector)

And if we keep our orbital velocity at 300 m/s, then our OV vector will have only ~54.3 inclination

300 m/s orbital visualisation (a = vertical velocity, b = initial orbital speed, c = resultant orbital vector)

Ideal angle of course is 45, but when we're still deep inside the atmosphere it may deadly due to air resistance.

And of course I completely omit dynamic pressure in this tutorial

[John Cochran]

Another method of doing an efficient launch to orbit.

Take off vertically and when you get to a velocity of about 100 m/s, tilt over about 10 degrees. Then go into prograde hold on you SAS.

Now pay close attention to hold long it is until you reach apoapsis. What you want is to adjust your throttle to keep the time 'til apoapsis at 40 seconds.

If it's less than 40 seconds and climbing, just keep your throttle where it is.

If it's less than 40 seconds and dropping, increase your throttle. If you're already at max throttle, nose up a bit until it start climbing, gradually drop the nose until you're going prograde again.

If you're going prograde and the time 'til apoapsis is greater than 40, reduce your throttle.

WARNING: Performing this procedure manually is extremely tedious. It's quite efficient, but also quite tedious. Also you may need to apply more throttle when you're about 40km to get above 50 km before overheating your vehicle too much and exploding. The ideal launch will cause your vehicle to almost, but not quite explode from overheating. The mod GravityTurn performs this kind of launch and you can find the thread on it within this forum. I'm rather surprised that the mod isn't on curse.

[RealGecko]

5 hours ago, John Cochran said:

The mod GravityTurn performs this kind of launch

Yeah, GraviyTurn is the best ascent autopilot for KSP. It once helped me to ascend science vessel with tiny amount of fuel left from the Mun surface to 8km stable orbit, where I and MechJeb failed miserably