Efficiency . . . I am Lacking

[SiliconPyro]

Part of my problem is skill, I\'ll work on that. The other part is knowing exactly where and in which direction to burn. Also, is it sometimes better to burn at less than 100%? So I don\'t get vague answers, I\'ll be more specific.

During initial ascent, at what point is it best to turn for a 100km equatorial orbit? I think on my first successful orbit I just waited until I was at about 35-40km up, turned to the horizon and burned 100% until I had an orbit. Of course my momentum contributed to carry me away from Kerbin. It worked, but was it efficient?

Also, at AP, is it more efficient to burn toward the (artificial) horizon or directly prograde to expand your Pe?

[Ydoow]

To expand your PE, it\'s more efficient to burn directly Prograde.

If you had a circular orbit, there would be no difference between burning at the horizon and prograde (horizon is your prograde). In elliptical orbits you aren\'t always perpendicular to Kerbin. I believe the prograde circle is always the heading that\'s perpendicular to the center of the foci.

As for when to turn and how much to burn...

I\'m not exactly sure when to turn. I don\'t think the math has been done yet, but the generally consensus is that turning before you\'re out of the thickest atmosphere is a waste.

A slow, gradual turn is what I keep reading. I generally starting tilting around 15-20km, but again, I don\'t know if this is more efficient and it also depends on how much Y velocity you have (directly up).

100% fuel burn is what seems to be most efficient for a majority of the time.

A few people calculated the math out to determine optimum speeds/fuel consumption. I\'ll brb with the graphs

Edit:

These graphs are for a specific ship, I don\'t exactly think they\'ll apply to everything you build but it should help give an idea/generalization of what\'s going on

TWR = Thrust Weight Ratio

Fg = Force Gravity

Fd = Force Drag

Just gives you an idea of how much Thrust to Weight you should have for your rocket to have a near optimal fuel burn.

Don\'t pay attention too much to the throttle line because this was based off of a very specific ship, and as such this will change with different ships

MET = Time (Mission something Timer) in seconds

This is the most useful one to me. Basically about 10 seconds in you should be going about 100m/s

The sharp peak at the very top is where this craft runs out of fuel. This graph was based off of a challenge to get the highest altitude with limited fuel.

[Kosmo-not]

I always start turning after passing 10km. Depending on how my thrust will change in the future due to staging, I will either keep it more vertical or continue turning.

[SiliconPyro]

Okay, please forgive my ignorance, but is the m/s in your HUD your actual speed? For some reason I may have misread a post and thought it was your relative speed perpendicular to Kerbin/Mun. I don\'t know where that idea came from.

[Kryten]

It shows two different speeds; orbital and surface (toggle by clicking on it). Surface speed is speed (not perpendicular velocity, just speed) relative to the surface of the reference body (currently Kerbin or the Mün), and orbital is your actual speed.

[Ydoow]

Yeah I myself was confused over the speeds shown in game.

As Kryten said, it always shows your speed. The emphasis here is that it\'s overall speed, not just speed east/west/north/south but also includes up/down. That can be misleading if your altitude is still rising.

Surface Speed is relative to Kerbin\'s spin (200m/s I believe) and Orbital is you\'re absolute speed relative to Kerbin\'s revolution around the sun; i.e. it excludes Kerbin\'s spin of 200m/s

Sit on the launch pad and click the speed indicator to switch it from Surface to Orbital and you\'ll see it change from 0m/s to 200m/s

Because sitting there relative to Kerbin\'s spin, you\'re traveling 0m/s. Setting it to Orbital simply ignores Kerbin\'s spin.

[SiliconPyro]

I\'m not going to lie, knowing this earlier may have saved some lives.

[AlexanderB]

Someone did the math:

Altitude (m) Target speed (m/s) - rounded to nearest 5 m/s

0 97.3

500 105

1000 110

2000 120

3000 130 - usually the first benchmark I have time to look at

5000 160

8000 215

10000 260

13000 350

15000 425

16000 470 - most of us are at least thinking about staging and pitchover maneuvers by now!

..

32000 2250 - this is equal to the orbital speed, so by now you should be pushing over hard for orbit, and air drag is not as important above this altitude.

But for most rockets you\'ll notice that going flatout works pretty well anyway, maybe a couple of % less efficient.. Once you\'re in orbit, there is no difference in efficiency between going 100% or burning at part throttle.

[Ydoow]

Generally, fully maxed throttle and I never reach those numbers.

It\'s been noted that not hitting these numbers results in horrendous efficiency.

I noticed I had a crazy amount of fuel left in orbit when I built a craft that could actually meet these numbers

[SiliconPyro]

I\'ve been making attempts at Mun landings and gradually arriving there with more and more fuel as my piloting becomes more and more consistent. I finally landed there moments ago. Thanks for your help, guys.

[MFToast]

I\'m no elite space pilot, but I\'ve noticed that waiting for about 300 m/s vertical velocity, tilting to 45 degrees, waiting for about 800 m/s, then from there staying prograde will generally get you into orbit, given you didn\'t have any problems on the way up.

[VincentMcConnell]

MET = Time (Mission something Timer) in seconds

Mission Elapsed Time

[Geeny]

Question: Why does one need to turn, anyways? Like, you already have a velocity vector going up, can\'t you just turn to the horizon and burn until you have a desire AP, and then burn at / before the AP to make an orbit???

[VincentMcConnell]

Question: Why does one need to turn, anyways? Like, you already have a velocity vector going up, can\'t you just turn to the horizon and burn until you have a desire AP, and then burn at / before the AP to make an orbit???

Because the AP does slowly rise. Your orbit will become highly elliptical.

[Geeny]

Ahh, makes sense. So, if your orbit goal is very high, it does not make a difference?

[SiliconPyro]

Ahh, makes sense. So, if your orbit goal is very high, it does not make a difference?

Depending on how high you\'re talking, it might be easier to just head straight out, watching your AP (which will be in front of you. When it gets close to where you want your orbit, turn and burn toward the artificial horizon, watching your Pe rise. This doesn\'t work as well for me because I\'m shooting for a 100km orbit with a weak second stage, so if I just turn and burn when i reach around 80km, I\'ll fall back to Kerbin before I have an orbit. I know from experience. So I turn gradually and it\'s been working pretty darn well. I have a successful Mun mission as evidence.

How high are you talking?

[Geeny]

I just meant relatively. My orbits seem to be at the 200k range.

[Kosmo-not]

My standard orbit these days is 75km. With the rockets I like to fly, there is no way I can burn straight up and then immediately to the horizon before I run out of time and start sinking back towards the ground. My efficient rockets won\'t go far burning straight up. They have too little thrust to continue vertically after the first stage separation.

[Xivios]

Efficiency is highly overrated =P

I will take a reliable and easy to use rocket over an efficient one any day.

[SiliconPyro]

Efficiency is highly overrated =P

I will take a reliable and easy to use rocket over an efficient one any day.

Well, I was speaking more of my piloting rather than my design schemes. If a budget is ever implemented though, efficiency in design will become a huge deal!

[Xivios]

Depends on how the budget is set up. One of my favorite PS2 games is called 'Warship Gunner 2', it\'s a sequel to Naval Ops: Warship Gunner. These games let you build your own warships, ranging from small and agile Destroyers to massive Battleships and Aircraft Carriers. The first game (which I don\'t have, but want) made you pay for each part for each ship - expensive enough for reusable ships that were only built once, and a scheme that would prove to be a real drain on any money-making with one-time use space ships.

But the second game had a scheme that I think would (with suitable tweaking) work very well with KSP. Parts were researched, not purchased, in an R&D menu, and cash earned in missions was used to start and speed up research - once researched a part would be freely available in unlimited quantities and would (usually - some parts had prerequesits) unlock the next part in the research tree. Singular parts would also be collected as the missions passed, and could be used in limited quantities until the part had been researched properly. This game had 1500 different parts though, I don\'t know how well the idea would work with much less parts.

[cardgame]

If I burn straight up and get a PE of ~75k (just outside of the atmo), could I/should I shut off the engines and burn completely horizontal when I get near that point?

[closette]

Just a couple of points:

- As the 'someone who did the math' http://kerbalspaceprogram.com/forum/index.php?topic=7161.msg106460#msg106460 I feel I should point out that the efficiency vs. ascent speed curve is fairly broad around the maximum so you need not follow those speeds exactly - plus or minus 20% is OK. In fact I fly my usual craft faster than the most efficient speed at the beginning of its launch (so as to burn off some fuel weight ), but I still end up about 20% slower than optimal by 12000m. Not a big deal.

- As for 2D optimal trajectories from Kerbin to orbit, I\'ve been doing a lot of reading about optimal control theory, gravity turns, linear tangent steering etc. and it\'s not an easy problem to solve. (Even the lunar ascent profile with no atmosphere is difficult enough). For Kerbin, turn too early or too flat and you\'ll waste fuel scraping through a long path length of the atmosphere. Turn too late or too little and you\'ll get a nice sub-orbital flight but no orbit.

I tend to wait until about 25km to begin my gravity turns, which is higher than many of you, but can get me into an ~85km orbit if I do it right. For a higher orbit, I just Hohmann transfer from there, although that takes more time than a direct insertion.

If someone else (an aerospace engineer) can come up with an efficient launch-to-orbit rule-of-thumb as I did for vertical ascent, we\'d all be very interested to see it!

[AlexanderB]

turning around 20-25 is what I do too, works for me first turn t0 20-25 degrees, then in gradual steps of about 5 untill my AP reaches target altitude, then I really level the rocket.

If I burn straight up and get a PE of ~75k (just outside of the atmo), could I/should I shut off the engines and burn completely horizontal when I get near that point?

yes, given that you have enough thrust-per-weight, else you\'ll fall back like a brick before you reach 2300+ m/s. (but I\'m not sure about the efficiency, burning all the way up seems the way to go, as you need to reach ~2300 m/s horizontal anyway)

[Kosmo-not]

I usually start my turn shortly after 10km. Depending on my TWR and known future TWR for the ascent, I may keep it more or less vertical.

Fore the 2D ascent problem, I think doing a 'backward' calculation would be the best approach to it (starting from orbit burning in a retrograde direction with increasing fuel quantity).