What percent throttle do you use on take off?

[PDCWolf]

I start at 75%, depending on how much speed per second I gain I either go up or down, that way, when I separate the boosters I don't lose speed.

[buzzles]

Depends on the rocket and if I've been bothered enough to keep tweaking to get to the lowest possible engine amount.

Normally it's a varied throttle amount on a per rocket basis up to 10-15km, then full throttle while turning until 65-70ish km.

[NFK]

I've just been doing full throttle the whole time, with the exception of mainsails which I dial back a few ticks to keep the overheat bar from going past about two-thirds full. So I guess I've been running inefficient launches the whole time.

Not surprising really, my entire space program can be summed up by the word inefficient. I don't think the Kerbals care.

[RawChicken]

It all depends on the drag your ship is making. I always keep ot aroun 100 m/s to 1500 m/s till i get 10 km, then i throttle up, but still wait till I clear the second third of the atmo to throttle at 100%

[sgtscuba]

zero to start with as I use SRB's to get to 6km, but after that I usually need 75% throttle for a while in order to be able to gain speed whilst climbing.

[buzzles]

I've just been doing full throttle the whole time, with the exception of mainsails which I dial back a few ticks to keep the overheat bar from going past about two-thirds full. So I guess I've been running inefficient launches the whole time.

Stick one of the smallest 2m tanks (Rocko 16?) between the Mainsail and any other fuel tanks. Heat issue solved

[brandoncormier4]

I usually go with 100% unless I'm using the mainsail which tends to over heat. I also often use solid fuel rockets to get out of the atmosphere, so no need to to worry about throttle. But what do I know, I'm still new here!

[Railsmith]

In real life, running at a lower throttle often causes incomplete burning and lower efficiency. However, in KSP we're burning some sort of highly energetic hypergolic bipropellant that never over- or underexpands a nozzle, so we can essentially throw most of the real-life throttle restrictions away.

When I'm flying a design for the first time, I start off with full throttle to ensure that I get off the pad. Then the throttle goes down so I get a TWR of just over 1. I'm sure a policy like this results in grossly underloaded rockets, but it's good to have a meganewton or three of thrust to spare in case of an emergency.

[krbl]

Whatever gets my rocket off the ground.

[scotty93]

I always try to give my rockets a very high thrust to weight ratio, so I can have a lot of room for throttle adjustments. But I usually keep my rockets at 75% through the thick parts of the atmosphere and then throttle up to 100% at 10,000M.

[ComradeGoat]

My interplanetary workhorse vehicle, which is powered by 2 NERVAs and a 12 (count 'em) mainsail powered heavy lifter is balanced so that you can more or less sit it on the pad, select 100% throttle, and do a near fuel-optimal ascent without shifting it from there right the way to the end of the ascent. Careful tweaking of the weight, asparagus staging, and the TWR or each stage ensures that it stays close to terminal velocity all the way up to 10K.

Ultimately, where you set the throttle to get a fuel optimal ascent will depend on how you've designed your ship, and the granularity of the staging (large stages produce much more thrust when they're nearly burned out because they're a lot lighter).

[tomf]

For maximum efficiency you want to be traveling at terminal velocity the whole way. If you are going faster then your drag climbs rapidly and you are wasting deltav. Any slower and you are loosing to much deltav supporting the rocket against gravity. Approximate terminal velocities for Kerbin are shown on the wiki page http://wiki.kerbalspaceprogram.com/wiki/Kerbin, although it does vary with rocket.

Normally you want to get to terminal velocity as quickly as possible so throttle to 100%. As soon as you reach it you can find a throttle level that keeps your speed climbing at the same rate as the terminal velocity at your altitude climbs.

If you have a TWR of just above 2 then at 100% throttle the rocket will tend to naturally travel at terminal velocity and you aren't carrying more engines than you need.

[Epthelyn]

100% on takeoff down to ~50% depending on the power of the rocket.

[azazel1024]

Most of my designs since they use some amount of staging at each level and SRBs, I tend to launch at 100% throttle for maybe 4-6s and then I throttle back to about 80% until the SRBs burn out and seperate, then I throttle up to the limit that the main sails can handle.

That way the SRBs burn out a couple of seconds before the inital main sail stage seperation occurs.

My design for the first stage is generally 7 rockomax jumbos with mainsails, 6 around 1. 4 of them feed in to the central tank and the two other outer tanks, once dry the 4 outer tanks seperate, leaving center and 2 outers which burn until empty.

This arrangement seems to, to me anyway, maximize heavy lifting capability with high thrust and plenty of dV. I used to do a 7 engine/tank first stage without cross feeding or seperation and I'd generally be able to deliver about 6-8mt less to the same orbit.

Anyway, if I burn at 100%, first I'd blow the mainsails, but even if I throttle to about 92% thrust to keep them on the edge of burnout, the outer tanks will run dry a couple of seconds before the SRBs would run dry, hence a few seconds of 100% throttle to get my velocity up as quickly as possible, and then throttling back to around 80% or so to time it for SRB burn out right before first stage seperation.

[zekes]

I always go 100%. No exceptions.

[Flymetothemun]

100% throttle until i hit 150 M/S, then i throttle back to try to hit 200 M/S by 10,000 Metres.

[RoboRay]

One of the nice things with MJ2 is that it can display the actual terminal velocity for your current altitude. This makes it very easy to stay just below it with a little throttle management.

[AmpsterMan]

I adjust to keep the "G" counter at about 2. Then after 30 km or so when I am nearly horizontal I let myself go to like 3. Never beyond that. I like my Kosmokerbs to have a relatively comfortable ride to LKO

[UmbralRaptor]

100% until I push up against terminal velocity, then down as needed to avoid going to fast. Post-staging and high altitude (>25 km) throttleups may be necessary.

[SmallChange]

So, here are the results of a quick, not so scientific experiment. All numbers shown are max altitude. All flights switched to max throttle at 10km. Test configuration was the Mark 1 Command Pod, one FL-T400 tank, and an LV-T45:

Full throttle: 16040

Hold at 150m/s before 10km: 22694 (141% of full throttle)

Keep at 100, raise to 200 (1km - 100, 7km 170 etc): 23917 (149% of full throttle)

So, as you can see, the fuel savings are pretty significant.

In my previous post mentioned the "rule of thumb" that I use. Anybody else have a trick?

[UmbralRaptor]

My rule of thumb is 100 m/s at sea level, doubling every 7 km. (This should run very slightly behind the actual terminal velocity)

[skendzie]

Wow, tons of replies! Thanks for the advise everyone. I will be more conscience about terminal velocity. I knew about the lighting thickness of the atmosphere, but I didn't connect it with TV. Thanks!

[CobraA1]

I've been using MechJeb to throttle my engines - but I have noticed that terminal velocity isn't generally an issue unless my craft has a pretty high thrust/weight ratio. Most of my launches these days have been using heavy lifters to launch heavy loads, so the smaller, lightweight craft I haven't used in a while.

[AmpsterMan]

I've been using MechJeb to throttle my engines - but I have noticed that terminal velocity isn't generally an issue unless my craft has a pretty high thrust/weight ratio. Most of my launches these days have been using heavy lifters to launch heavy loads, so the smaller, lightweight craft I haven't used in a while.

I have a craft that has a starting TWR of 1.2 and have noticed that terminal velocity is not usually a problem for me either. Still, it is important to keep in mind.

[foamyesque]

My throttle is the VAB. If I have to throttle back, it means I'm carrying dead weight in the form of extra engines-- so I remove some and/or rejig the staging so's to jettison them sooner.