Optimal Ascent Path

[Synapse]

I'm sure this has been done many times before (maybe Mechjeb has it) but heres my attempt at graphing efficient ascent velocities using the wiki info. I use stock only so this should come in handy with my launches:

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Which means the deltaV requirements are:

0-10000m - 200m/s

10-20,000m - 300m/s

20-30,000m - 1800m/2

30-50,000m - ?

50,000m-orbit - ?

[lammatt]

Which means the deltaV requirements are:

0-10000m - 200m/s

10-20,000m - 300m/s

20-30,000m - 1800m/2

30-50,000m - ?

50,000m-orbit - ?

not really i think...

a lot of the thrust is used to counter act the drag in the troposphere

[lammatt]

I'm sure this has been done many times before (maybe Mechjeb has it) but heres my attempt at graphing efficient ascent velocities using the wiki info. I use stock only so this should come in handy with my launches:

i think i saw there was a mod which plots your flight data realtime during flights...(save the tedious job of data inputting to excel or microcal origin...leave it to the bots)

you should try that out you may find it's cool too~

so that you can compare it to these two graph to see if you ascend matches these two.

[Synapse]

Do you know the name of the mod? I've never used mods before..

[NASI Director]

Getting into orbit takes about 4500m/s of dV. Like was said before, most of it is used trying to break out if the the thick lower atmosphere, and another large bit of it is used circularizing.

EDIT: The main mods everybody uses are MechJeb and Kerbal Engineer Redux. MechJeb is like an autopilot that comes with calculations too. Kerbal Engineer Redux is just calculations, however both calculate TWR and dV.

[lammatt]

Do you know the name of the mod? I've never used mods before..

i think it's graphotron or so...

let me check

[Sethnizzle]

i think it's graphotron or so...

let me check

Yep, the Graphotron 2000 is what you are thinking of. I haven't used it but it looks neat. I have used the Telemachus – Telemetry and Flight Control in the Web Browser on my laptop while I play KSP on my desktop a little bit and that mod is awesome. You might be able to find the information you are looking for with it however you might have trouble configuring it depending on your home network and level of familiarity with networking.

[dlmarti]

The optimal assent path depends on the vehicle.

In fact if you are talking about efficiency, when using aerospikes a case can be made for straight up to apo, then turn.

My point is that unless you know what the important factors are, and the vehicle being used, you cannot make any particular claim as to the optimal assent path.

[Synapse]

The optimal assent path depends on the vehicle.

In fact if you are talking about efficiency, when using aerospikes a case can be made for straight up to apo, then turn.

My point is that unless you know what the important factors are, and the vehicle being used, you cannot make any particular claim as to the optimal assent path.

What factors?

[Sof]

The optimal assent path depends on the vehicle.

In fact if you are talking about efficiency, when using aerospikes a case can be made for straight up to apo, then turn.

My point is that unless you know what the important factors are, and the vehicle being used, you cannot make any particular claim as to the optimal assent path.

You're thinking about the gravty turn. Also, surely the case for aerospikes is that you can remain in the upper atmosphere for longer because the ISP doesn't go up as much when reaching space as it does for other rockets. ie the opposite of what you said.

The graph merely shows the optimal speed your rocket should be travelling at a given altitude to maximise the fuel economy. Go faster and you lose out to drag, go slower and you lose against gravity.

[HeadHunter67]

I know it's horribly unscientific, but a good rule of thumb I use for terminal velocities is 110 m/s, plus 10 m/s for every 1000 m of altitude. This works well enough for me at least during the early ascent. By the time you begin your gravity turn, you should be at about 200 m/s.

[arq]

I use Kerbal Engineer Redux for this info. It gives you terminal velocity calculations for your current altitude, so you can simply follow that up. Note that above roughly 15km you need a massive (and unrealistic) TWR to follow the optimal ascent speeds (people always seem to forget that).

[Sof]

I use Kerbal Engineer Redux for this info. It gives you terminal velocity calculations for your current altitude, so you can simply follow that up. Note that above roughly 15km you need a massive (and unrealistic) TWR to follow the optimal ascent speeds (people always seem to forget that).

good rule of thumb is to just accelerate as fast as you can at the start of your gravity turn (~10km). The extra drag you create at the start by exceeding the optimal path is regained by being closer to the terminal velocity at higher altitudes.

[rkman]

Optimal ascent path is more than having the correct velocity at various altitudes.

It is also very much a matter of having the correct ratio of vertical speed versus horizontal speed at various altitudes, which is determined by the pitch angle of the rocket.

You mileage may vary but there are some guidelines i use:

* ~60~70 degrees pitch (20 to 30 degrees off vertical) at 10km, doing 250~300m/s. (requires pitch-over to start at <=5km)

* ~30 degrees pitch (60 degrees off vertical) at 30km, doing ~900~1000m/s.

* close to horizontal at ~50~60km, doing ~1800m/s

I think 20~30 degrees off vertical at 10km is a good compromise between two conflicting factors wrt fuel efficiency: shortest path through the thickest part of the atmosphere, and gaining horizontal speed early.

[lazarus1024]

After much experimenting the optimal I have found is quickly accelerate to 100m/sec by 1,000m. Then slowly accelerate with a velocity target of 200m/sec by 10,000m. Continue slow rate of acceleration (likely goal of about 230-250m/sec) and begin gravity turn at approximately 13-15,000m, turning to 45 degrees. After gravity turn pour on the thrust to max your rocket is structually able to handle. At approximately 40,000m pitch over to about 75 degrees. At about 60,000m finish pitch over to 90 degrees.

Since doing this I tend to maximize payload to orbit and/or orbital height. Give or take a little compared to other methods. Also it has the perk that I almost never cause a structual failure of a rocket that is actually capable of getting off the launch pad without falling apart. A lot of rockets fail because max Q+thrust are way too high. Keep max Q a lot lower, rather than trying to slam your way through the lower atmosphere and it can hold together much better.

[numerobis]

This challenge is relevant: http://forum.kerbalspaceprogram.com/showthread.php/39196-Launch-Efficiency-Exercise-Updated-for-0-21-1/

The best trajectory they've found is basically to start turning slowly at 8km, and mostly finish the turn at 37km. Don't accelerate faster than 22 m/s^2, and in the vertical phase, don't exceed terminal velocity.

I'm trying to automate this, still needs a bit more work.

[Synapse]

My conclusions from the graph are that I should aim for about 100m/s up to 5000m, 200m/s by the time I hit 10,000m and begin the gravity turn. By 20,000m should have reached 800-1000m/s and then just flat out accelerate at the apoapsis (for interplanetary missions)

[theflyingfish]

Sidenote: If you're using FAR, you just turn prograde as fast as possible without flipping your rocket (maintain Angle of Attack < 5 degrees) until pointed East, and thrust till orbit.

[aNewHope]

launching at terminal velocity it not that hard. All my rockets simply have a TWR of about 1.8 -2.2, which means that flying at full throttle u automatically travel at terminal velocity. (because terminal velocity is the speed u reach in an atmosphere by accelerating at 1 G)