How do I use the Ascent Path editor on Mechjeb2??

[lyndonguitar]

I am using mechjeb to get many ships to orbit easily and I have done it many times, In the ascent path editor, most of the time I just enter a guessed value or use the default and it seems to work, however I don't really know how to use it properly, maybe i could save some more fuel by knowing how to use it.

I tried experimenting different values to understand what it does but I don't get it.

Can someone explain it to me? thanks

[EndlessWaves]

It should be fairly self explanatory. Start and end values determine when mechjeb starts and stops turning your ship and the curve shape determines how it'll apply steering input between those values.

[Gniuz]

it changes the amount of turning in the curve when climbing to orbit, so start at the small end around 5% and it will turn harshly use it around 80% and the turn becomes alot slower good for when your seperating a few parts during ascent as its more gentle on the turn. Best bet is play about with it.

G.

[lyndonguitar]

it changes the amount of turning in the curve when climbing to orbit, so start at the small end around 5% and it will turn harshly use it around 80% and the turn becomes alot slower good for when your seperating a few parts during ascent as its more gentle on the turn. Best bet is play about with it.

G.

thanks, how about the start turn and end turn? I don't quite get it in relation to the orbit altitute.

For example, if I set my orbital altitude at 100 km, should I put my end turn at 100, <100, or >100?

Also how can I use ascend guidance to jump directly into solar orbit? or in the trajectory to the moon

note: I know how to do this all manually, just looking for a way to do it automatically so I can leave it running

[numerobis]

The default settings are adequate for Kerbin, so you don't need to change them.

For other bodies, the general idea is that you want to burn horizontally in the end to make your orbit (vertical speed is useless at that task). The only reasons to go up are atmospheric drag, and mountains. If there's no atmosphere, make a quick turn just above the mountains. If there's atmosphere, start turning about 8-10km on Kerbin or its equivalent on your new planet, since that's about when drag gets low enough.

[lyndonguitar]

The default settings are adequate for Kerbin, so you don't need to change them.

For other bodies, the general idea is that you want to burn horizontally in the end to make your orbit (vertical speed is useless at that task). The only reasons to go up are atmospheric drag, and mountains. If there's no atmosphere, make a quick turn just above the mountains. If there's atmosphere, start turning about 8-10km on Kerbin or its equivalent on your new planet, since that's about when drag gets low enough.

Thanks!! I kinda get it now

[lyndonguitar]

Another question, If I want to escape kerbin SOI right directly from launch, do I tell it to fly straight up and input orbit as 85000km? (thats the soi range)

[HoY]

I've never done that personally but it sounds like you have the right idea.

Another note about turn shape and turn end alt and angle.

Depending on the TWR of your ship you will have to change the angle. For High (2.0+) TWR ships anything between 35% and 50% is fine. For ships with lower TWR's you need to ascend at a steeper angle more like 60-70%. This doesn't always hold true but low thrust (talking about below 1.3 TWR) ships have a tendency of flipping end over end if you angle over too much at lower altitudes.

About end turn altitude and angle. 9 times out of 10 setting turn end angle to 0 is optimal, and if your only aiming for a standard LKO launch and orbit your end altitude should be 65,000 or 70,000 meters. I sometimes use even lower altitudes because I have the deltaV to spare to lose another 10points to drag. What this does in the end is increases your orbital speed sooner, raising your pariapsis faster. Which in turn means that once your apoapsis hits your target you will have a much shorter burn to make to make it circular.

[numerobis]

Another question, If I want to escape kerbin SOI right directly from launch, do I tell it to fly straight up and input orbit as 85000km? (thats the soi range)

That's not the most efficient way: you always want to be burning perpendicular to the surface, to minimize losses to gravity. So you want to do that turn. Pre-purge there was a challenge of how fast could you reach the moon (and go splat); I burned vertically with giant rockets, and got edged out by a much smaller rocket that did a turn.

The easiest way is to get a very low orbit, maybe as low as 70km. Then do a transfer burn from there.

The harder but slightly more efficient way into launch at just the right time and just keep burning at full throttle -- set the apoapsis super high and take manual control once you're burning below the horizon. Then turn the rockets back on at full throttle and keep going prograde. MechJeb has some help with timing this, but it's limited (it's intended for a rendezvous, which would get you to an orbiting station or a moon, but isn't quite what you need for interplanetary).

[LeathalMeatball]

You should really try and learn to fly into an orbit without mechjeb first, it can easily become a crutch

[lyndonguitar]

You should really try and learn to fly into an orbit without mechjeb first, it can easily become a crutch

I know how to, I just want to do it automatically, so I can launch and watch, nOW I've perfected the mechjeb ascent guidance, I can launch it and leave the pc, eat some snacks and when I return I get a nice good orbit