1.0.2 - Rocket ascent profile and orbit delta-V

[eviator]

With the 1.0.1 drag changes, I'm having a little trouble finding a close to optimal ascent profile for LKO. I got 1.0.0 down to 3,400 vacuum delta-V, which as I understand it was approximately close to optimal. Now in 1.0.2 my best is about 3,700 vacuum delta-V. Not using Mechjeb. Not gunna. I saw another post where someone claims 3,000 vacuum delta-V in 1.0.2 having gone horizontal at 20km. I've not been able to duplicate that, or anywhere close.

So for those who are doing it much better, what is your ascent profile and vacuum delta-V? Videos and screenshots would be great!

[Foxster]

I'm afraid I've kinda given up trying to figure it out for now. Squad will release another patch tomorrow (probably) that will change it all again, so I'm just sticking to space stuff for now.

[Temeter]

I got somewhat below 3400 in my better launches, although with little experimentation. It's similar to the 1.0 profile: Start your g-turn low, stay in the prograde marker until 20+km, and try to point at the horizon at around 40km, there still is next to no drag at that height. Fast rockets can go a bit lower.

Afaik those 20km horizontal rockets have ridiculously fast t/w ratios and flat profiles, often even SSTOs with no freight. So not much point in copying them.

[Frozen_Heart]

Ok with the same rockets I've tested and got these results.

Gravity turn start - 1.0: 60m/s 1.0.2: 90m/s

dV in orbit - 1.0: 1500m/s dV 1.0.2: 350m/s

[Temeter]

Btw, I recommend using the aerodynamic markers (F12). They tell what parts of your rockets cause drag and the severity. Nice reminder to keep the rocket steady.

edit: Also, a nice try to get something out of your rocket:

Put fins on the end of it, start the rocket, instantly point it between 5 and 10 degree (try it at 5 first).

Then activate the lock to prograde and do... nothing.

Just stage stuff, lower the gimbal when it wobbles, use time acceleration when necessary. It's really quiet relaxing and the results might surprise you. All that maneuvering you do by hand can be rather costly, when a rocket might fly best when left alone.

Edited May 3, 2015 by Temeter

[The Lone Wolfling]

Now if only I could lock it to prograde. Curse you early career mode!

[Temeter]

Now if only I could lock it to prograde. Curse you early career mode!

You'll get there in not time, until then just keep your rocket in the prograde marker. Add fins and half the work will be done by aerodynamics.

[eviator]

With more tweaking I was able to get my best orbit down to 3,550 vacuum delta-V. Staying pointed exactly prograde in the low atmosphere probably made the most difference. Procedural fairings helped a little. Using a single stage didn't help at all.

The balancing point between too vertical (fighting gravity longer) and too horizontal (fighting air resistance longer) seems to be the key. I'm hard pressed to see how my best ascent so far is still at least 150 m/s inefficient. I'm still hoping someone will show a specific example of their best ascents, as so far were just giving general tips.

[severedsolo]

You really do not need to lock it to prograde until you are way up in the atmosphere. This is what works for me:

1) Turn on SAS. Full throttle (but with vessels thrust adjusted as outlined below)

2) at 100m/s pitch 5-10 degrees right.

3) As prograde crosses your vessels current trajectory turn SAS off.

4) Let the rocket fly itself. At 36k, lock to Orbit prograde until you hit 100k AP (or fly it manually).

5) Circularise at AP (although I've heard thats inefficient).

Thats it! Ideally, when the marker switches from surface to orbit (about 36k) your rocket should more or less already be facing orbit prograde. You'll probably have to adjust inclination a bit, but other than that let it fly itself.

If you turn too slowly (ie have a large circularisation burn) turn down your engines thrust in VAB. If you turn too fast (don't make it) turn it up. I regularly do it in 3500 - 3700 m/s - not 100% optimal probably, but it's better than the 4000 that I see quoted elsewhere.

Edited May 4, 2015 by severedsolo

[eviator]

Using all or most of the suggestions to this point my best is down to 3466 dV. That required tinkering with thrust limiter in flight to avoid getting too steep. Has anyone done significantly better than this, and if so can you post how specifically?

[Rokmonkey]

There is no optimal ascent curve and if you pick one you are going to have a bad time. Depending on your upper stages with mass, drag, geometry you may find that a steeper ascent is advantageous. This is also dependent on what engines you are using and where.

The only hard rule I follow is that I wait for my vertical velocity to be >= 50m/s before kicking my gravity turn into gear. Then it's a matter of being more or less aggressive when following prograde to keep your ascent rate ideal.

[EtherDragon]

Btw, I recommend using the aerodynamic markers (F12). They tell what parts of your rockets cause drag and the severity. Nice reminder to keep the rocket steady.

edit: Also, a nice try to get something out of your rocket:

Put fins on the end of it, start the rocket, instantly point it between 5 and 10 degree (try it at 5 first).

Then activate the lock to prograde and do... nothing.

Just stage stuff, lower the gimbal when it wobbles, use time acceleration when necessary. It's really quiet relaxing and the results might surprise you. All that maneuvering you do by hand can be rather costly, when a rocket might fly best when left alone.

Amendment to this suggestion: If you have strong enough aerodynamic fins at the base of your rocket, tip over early (between 60 and 100m/s) and then TURN SAS OFF. You don't need it, just use gravity to execute your gravity turn. Locking Prograde just uses energy to control the rocket that you don't need to expend.

Video Tutorial:

[Deutherius]

5) Circularise at AP (although I've heard thats inefficient).

Where have you heard that? It's not gonna get more efficient than burning right at Ap.

[AmpsterMan]

I didn't even know aero got changed in the new update xD. Does the thicker atmo at low altitudes affect Sea Level thrust much?

[Mister Spock]

What is the relevant delta-V statistic when pondering Kerbal Engineer in the VAB -- the numbers before the slash or after? The lower numbers are in-atmosphere delta-V, and the higher numbers are in-vacuum delta-V, yes? But as a flight to orbit combines atmosphere and space flight, I'm not sure which number people mean when they say it takes 3500 m/s delta-V to get to orbit.

Edit: Doh, I've been mis-reading KER. I used to know this once upon a time, but I'm out of practice! So pushing the 'atmosphere' button toggles between atmosphere/vacuum figures. But that still leaves me uncertain about what numbers should say what. 2500 for the atmospheric stage(s), 1000-plus for the vacuum stage?

Edited May 4, 2015 by Mister Spock

[Rizendell]

you want to use vacuum delta-v and atmospheric TWR.

[Randox]

As fascinating as all this is (and it's been helpful for sure), I am left with questions about optimal speed during ascent to avoid creating excessive drag forces. Previously, I would follow the terminal velocity values, and I've continued doing that into 1.0, but this often results in my going hypersonic (flames) on the way up. Am I going way too fast? Or perhaps it's not such a huge deal anymore and I should just put the hammer down and get to orbit as fast as I can without making anything explode? The rocket I've been doing most of the playing with since the patch can pull 3+ g's the entire way to establishing apoapsis.

I also have to say the more pronounced gravity turn is a bit freaky. It really feels like I'm about to nose dive back into the planet. It's nice to be so close to a circular orbit though from the initial burn. Way less work to do in space, and the short burn creates a more even orbit.

[eviator]

you want to use vacuum delta-v and atmospheric TWR.

After more experimentation, I can definitely see this. I've noticed a significant jump in total vacuum dV needed to orbit if an intermediate stage is too weak. So what atmpospheric TWR should we be shooting for in our stages?

[EtherDragon]

After more experimentation, I can definitely see this. I've noticed a significant jump in total vacuum dV needed to orbit if an intermediate stage is too weak. So what atmpospheric TWR should we be shooting for in our stages?

Lower stages 1.5 to 2.

Upper stages (in atmosphere) around 1.0

[Jarin]

Where have you heard that? It's not gonna get more efficient than burning right at Ap.

I'm pretty sure that burning at AP/PE is only universally efficient when you're already in orbit and have no other considerations. If that was true in all circumstances, we'd be pointing straight up and circularizing at the top of a vertical trajectory.

[Violent Jeb]

Where have you heard that? It's not gonna get more efficient than burning right at Ap.

I'm pretty sure that burning at AP/PE is only universally efficient when you're already in orbit and have no other considerations. If that was true in all circumstances, we'd be pointing straight up and circularizing at the top of a vertical trajectory.

It is certainly the most efficient to burn at Ap or Pe.

During a launch, I try to keep under 200 m/s during the first layer of atmosphere. I always fly almost directly up or 5 degrees at the most during this time.

For the first 7000m (give or take), the average ship @1.5-2.0 will encounter 200-500 µm/s - almost half a m/s being wasted. If you go above this, the resistance makes the craft very hard to control (turn) with so much force acting against it. So anything above 200m/s during the first 7km is not efficient - so much so that I usually dial engines back to keep my speed under 200m/s.

After the first atmospheric "zone", the craft can still be quite prone to tipping if you don't have fins or SAS/monoprop.

After you've cleared this you should have your Ap approaching 1 minute away - and climbing fast. This is the key. Burning with your apoapsis more than 1 minute away means that you are constantly burning in a less efficient spot (especially for turning). 1m is arbitrary, obviously the closer you can get to burning on the Ap is better but I find 1m gives you nice room for correction. As you turn, the time to Apoapsis will slow - keep turning until it remains under 1 minute. Usually by around 20km I am only 20-30 degrees from completely horizontal. At 25km your wind resistance has fallen to less than 1/10th what it was during the first zone, So it doesn't hurt you because you're saving big-time by keeping your turn within 60s of the AP at all times.

I find that by 40-50km, I have begun to fly "into the red" on the navball, just to keep my time to Ap less than 60s. Now we're gaining some serious speed - and the Ap begins to slide. At this time I cut the engines, and do 2 or 3 small burns within 10s of the Ap, directly horizontal.

I've got a few different crafts up with VERY close to 3000m/s to 0.0 circular orbit, 70-73km. I'm going to say an optimal ascent could be 2800. I can't tell you the actual profile but I follow the Ap exclusively.

I'm flying manual on career mode - mechjeb is giving me the drag/Ap values i've been using. These observations are based on 1.0.2 flights

Edited May 4, 2015 by Violent Jeb

[eviator]

Okay Jeb, I'll give this a shot. If I am correct MechJeb gives you atmpospheric dV, which is difficult to plan for during the building stage, so I've been using the vacuum dV values provided by KER. I've read on these forums that taking vacuum dV and accounting for drag, you get an atmospheric dV 15 to 20% less. Using your 3000 m/s, that would be vacuum dV of around 3.5km/s

[DJK]

Indeed, 3000 dV vaccum seems a bit too little.. however, 3000 atmospheric is probably right. I've been needing roughly 3680 m/s vaccum to 100x100 orbit (de-orbit burn included, roughly 45-50 m/s dV vacc), which translates to 3100 atmospheric.

My rockets have a 1.25 TWR on the pad and i do a 3-5 deg. turn @ 50 m/s. By the time i finish this turn the ship already has ~100 m/s speed and an altitude of roughly 1200m. I turn off SAS and let it slowly do its gravity turn, lowering throttle so that my Ap also stays within less than a minute, usually keeping a 1.6-1.8 TWR does the trick. I don't touch anything except the throttle until i reach 35km altitude, when the surface speed switches to orbit. Note that when the switch occurs, the surface prograde marker & orbit prograde marker are nearly in the same place. There is little to no deviation between them. I've noticed that this is extremely important. After 35km i turn on SAS (have a pilot follow prograde if available) and continue to burn with very low thrust until desired Ap.

For 100km Ap, the burn lasts throughout the entire atmosphere, then coast to said Ap and circularize. Note that when the Ap reaches 100km, the Pe is somewhere around 25km in the atmosphere already, needing less than 100 m/s dV vacc. to circularize. That leaves me with ~50 m/s dV to de-orbit.

[Violent Jeb]

Mechjeb will give both different readings atmo and vac so i'm probably referring to atmospheric. Either figure is somewhat rough because atmospheric data assumes a constant atmo isp though it is almost gone after 15k and vac dv is consumed faster in atmo, so it ends up between those two readings either way it's significantly less than what was needed in .90, but the aero makes it more of a challenge.

I'm actually satisfied because it implies that the round trip mission to eve might be a little more possible - haven't got out there yet to find out.

Edited May 5, 2015 by Violent Jeb

[Slugy]

It is certainly the most efficient to burn at Ap or Pe.

During a launch, I try to keep under 200 m/s during the first layer of atmosphere. I always fly almost directly up or 5 degrees at the most during this time.

For the first 7000m (give or take), the average ship @1.5-2.0 will encounter 200-500 µm/s - almost half a m/s being wasted. If you go above this, the resistance makes the craft very hard to control (turn) with so much force acting against it. So anything above 200m/s during the first 7km is not efficient - so much so that I usually dial engines back to keep my speed under 200m/s.

After the first atmospheric "zone", the craft can still be quite prone to tipping if you don't have fins or SAS/monoprop.

After you've cleared this you should have your Ap approaching 1 minute away - and climbing fast. This is the key. Burning with your apoapsis more than 1 minute away means that you are constantly burning in a less efficient spot (especially for turning). 1m is arbitrary, obviously the closer you can get to burning on the Ap is better but I find 1m gives you nice room for correction. As you turn, the time to Apoapsis will slow - keep turning until it remains under 1 minute. Usually by around 20km I am only 20-30 degrees from completely horizontal. At 25km your wind resistance has fallen to less than 1/10th what it was during the first zone, So it doesn't hurt you because you're saving big-time by keeping your turn within 60s of the AP at all times.

I find that by 40-50km, I have begun to fly "into the red" on the navball, just to keep my time to Ap less than 60s. Now we're gaining some serious speed - and the Ap begins to slide. At this time I cut the engines, and do 2 or 3 small burns within 10s of the Ap, directly horizontal.

I've got a few different crafts up with VERY close to 3000m/s to 0.0 circular orbit, 70-73km. I'm going to say an optimal ascent could be 2800. I can't tell you the actual profile but I follow the Ap exclusively.

I'm flying manual on career mode - mechjeb is giving me the drag/Ap values i've been using. These observations are based on 1.0.2 flights

Some confusion here - burning as fast as possible, as low as possible, is always the most efficient, if there is no atmosphere.

This is very much what you describe: your orbit should be generally be near circular as you finish burning, any time spent coasting to an AP circularisation burn (particularly if periapsis is still low so a large burn is needed) means you will be going slower and losing efficiency (Oberth effect), and that you have probably more engine than you need.

Pretty much everyone uses vacuum dV for comparison, would be helpful if you post the vacuum dV numbers.

It looks like gravity loses are around 85%+ of the total, which makes aero loses much larger than on Earth launches.

I'd say 3400m/s dV looks to be around the minimum - but I'd love to be proved wrong