arkie87

If you are asking me how much deltaV vertical ascent takes? You can look it up in my video? Otherwise, not sure what you are asking.... Also, rather that asserting it is "incorrect", I would appreciate if you explain why, rather than cockily asserting your knowledge trumps mine.

It's not always possible to burn prograde immediately. Examples include if you are in an atmosphere or deep in a crater, you have to burn vertically first to escape dense atmosphere or rise up out of the crater. That said, unless you have infinite TWR, you also cannot burn horizontally since you need to first clear the ground, which requires some wasted deltaV to climb. On the Mun, Ive heard safe altitude is 10 km, so assuming you have to fly up to 10 km before you can turn sideways (or even if you burn 45 degrees or less but still rise up to 10km), it appears vertical and horizontal methods are close enough, that vertical might win under the right conditions.

I have revised OP to reflect this information. By the way, it only enhances my argument... since you are using stock aerodynamics...

That's even better since you do not use FAR... and as we've established, terminal velocity in stock is much lower than FAR, so a vertical ascent will suffer the consequences...

I will try with lower TWR. I assume you will be correct-- since vertical ascent is detrimental for low TWR... A fairer comparison would be for the same payload, what is cheapest (in terms of Kerbucks) way to get to a certain apoapsis? I imagine a skipper would be best for LKO-to-mun approach but strapping loads of SRB's (which are cheap) would be best for vertical ascent approach. I will actually test this and post results. Perhaps, i will also try reducing thrust on SRB's and going for a LKO-to-Mun transfer as well. - - - Updated - - - So you disagree that terminal velocity is optimal ascent velocity? Or what?

Sarcasm much?

I thought we resolved this? Your argument is 100% false with FAR installed. In stock, i would have FAR (pun intended) exceeded terminal velocity, so i would have wasted too much deltaV fighting drag. With FAR installed, I am always wayyyy below terminal velocity, as per this video ( ), and so, I am actually wasting more fuel fighting gravity than drag...

You basically ignored the concrete mathematical numbers i gave in favor of vertical ascent for this case....

In career mode, I think optimizing cost/deltaV ratio for a given payload is what matters, unless you care about pollution on Kerbin and Kerbin global warming If not in career mode, then any of those other definitions can make sense, depending on what you care about...

Wow. Much more complicated than simple scale height

I readily admit that which utilizes Oberth effect "better" is dependent on a lot of factors such as your ship, TWR, and planet you are launching from etc.... Nevertheless, in practice, vertical ascent seem to take <10% more deltaV compared to LKO-to-mun transfer, in my experience. Yeah, but in career mode, we dont care about efficiency-- we care about cost, and in current iteration, SRB's are dirt cheap, and will get you more deltaV/Kerbuck than a more efficient engine will. So #2 stands. Now if they increase price of SRB's or cost of fuel, then the optimum solution will obviously change

Who struggles for a minute to try to attach something In update 0.90, editor has been overhauled so it should make this problem go away for good

Sorry to bring this up again, guys, but I think we have overlooked something. GoSlash27 http://forum.kerbalspaceprogram.com/threads/102606-Transfering-to-Mun-First-to-LKO-or-Directly-to-Mun?p=1593793&viewfull=1#post1593793 said that in his experience with stock aerodynamics, it will take approximately 340 m/s extra deltaV to go vertical ascent directly to the mun vs. performing gravity turn into LKO, then periapsis transfer to the Mun. In my own experience with FAR installed, the difference is smaller, around 70 m/s . The theoretical reason for this difference is that in stock, terminal velocity (which is optimal ascent velocity) is low and easily reachable with low TWR. Thus, there is no benefit of high TWR since it will not be used. In FAR, terminal velocity is essentially unreachable, and thus, there are petential benefits of high TWR craft. Furthermore, the potential for a pilot-induced sub-optimal gravity turn, which could easily bleed off a few hundred m/s deltaV if you raise apoapsis too high upon liftoff or stay too low for too long. Thus, vertical ascent could match gravity turn under the right conditions.Nevertheless, Kerbin isn't the only planet. My question is if you are on the Mun such that Kerbin is perpetually setting (since the Mun is tidally locked) i.e. on the rear-side of the planet w.r.t. Mun's velocity vector, do you want to get into LMO first or go straight vertical to return to Kerbin. My preliminary math shows it takes less deltaV to go straight up (807 m/s) vs. hopping up to 10 km altitude (to avoid hitting terrain) and then burning horizontally until escape velocity is achieved (964 m/s). Since Mun's gravity is small, TWR will inevitably be large so gravitational losses will be small/negligible. What do you guys think? If i am right, it implies that vertical ascent vs. LXO-to-transfer optimality is dependent on the planet/mun and other conditions, rather than always assuming vertical ascent is bad.

I'm not sure if FAR changes atmosphere parameters such as scale height and sea level density. What is your hunch?

I think you over-simplified a bit. Other advantages of vertical include: (1) Utilization of Oberth effect the entire time (vs. LKO, you waste the initial climbing part when you turn off pro-grade); nevertheless, even theoretically, vertical requires more deltaV than LKO to Mun for this particular case. For other planets/moons, this might not be the case. (2) With FAR, does not require control surfaces or reaction wheels or expensive thrust-vectoring engines to steer the craft into a gravity turn. Thus, strapping loads of SRB's and going vertical might be cheaper (in terms of Kerbucks) than using a mainsail/skipper and using thrust vectoring to get into LKO first. (3) Eyeballing is easy-- just aim 90 degrees in front of the Mun or Minmus; or burn at sunrise/sunset if you are going interplanetary at optimum launch window (4) With FAR, it is possible if you are too aggressive with gravity turn, you craft will spin out of control, thus, ruining the mission. (5) Optimum ascent path to minimize deltaV is very sensitive and its not necessarily so easy to hit every time going to LKO first vs. vertical ascent is easy to hit optimally every time. GoSlash27 predicted approximately 300 m/s wasted deltaV using vertical ascent method, but its possible to waste that going into LKO first, if you accidentally raise your apoapsis too high or do something else sub-optimally...

G's required to get to terminal velocity would be huge, enough to make kerbals require an exoskeleton it's not really feasible to achieve terminal velocity with FAR, nor is it more efficient (in KSP) given the extra required mass of the engines (though it might be cheaper in terms of kerbucks, if you just strap loads of SRB's rather than one mainsail). Also, with FAR, going too fast can result in high dynamic pressure and aerodynamic disassebly from too much drag (though i personally have disabled this feature). Why? Are you trying to get terminal velocity? FAR displays terminal velocity... Also, terminal velocity is a function of attitude, mach number, and weight with FAR...

Yes, it assume vertical launch. If you are horizontal, terminal velocity increases more slowly (as you pointed out); however, the fraction of velocity in the vertical direction also decreases. Nevertheless, for a gravity-turn launch, you dont need to be climbing at terminal velocity the whole time, so the results become less applicable... The main point for the graph is that with stock aerodynamics, TWR of 2 can get you up to terminal velocity fast, and keep you there (until 10 km or so) and even require you to throttle back to not exceed it.

TWR is dimensionless. A TWR of 1.4 will behave the same for a large rocket or a small rocket... (assuming drag is negligible). Your explanation does not make sense. So that makes sense. I, however, have disabled aerodynamic disassebly in FAR so i dont have to worry about falling apart How exactly does it make rocket harder to fly though?

Yes, i think your analysis is spot on. So, you are saying with FAR, i should begin turning instantly? Interesting...perhaps i will experiment with that... And career mode is sort of what sparked this question for me, since the only thing we care about is cost. And SRB's are dirt cheap, but have no throttle or thrust vectoring, making turning them difficult in FAR for that gravity turn, especially before you unlock reaction wheels and control surfaces... so i considered whether it was cheaper/easier to just launch vertically to the mun by strapping on cheap SRB's that didnt NEED to be steered...

Oh, havent a clue what BC is Ask Mr. Ferram Oh i see. I dont have that information, but terminal velocity is always optimum. Perhaps i should try again with mechjeb...

Once you go FAR, you never look back The main reason i switched to FAR is because it enables "skipping" off the atmosphere during re-entry. With stock, i dont think that's possible-- once you start falling, its hard to use lift/AoA to bring your craft back up again. However, i am thinking of switching back to stock, since it's drag simplifications will make this mod (http://forum.kerbalspaceprogram.com/threads/93685-0-24-0-25-Trajectories-v1-0-0-%282014-11-17%29-atmospheric-predictions-FAR-NEAR) that predicts aerobreaking (and with a beautiful GUI!) more accurate/deterministic and less prone to variation due to piloting. FAR makes flying planes more fun and realistic; all it does for rockets is cause them to tumble around during lift off albeit, more realistically. When flying rockets, i'd rather have stock drag; when flying planes, i'd rather have FAR.

Yes, for stock, achieving terminal velocity is easy and doable, since at sea level, its only 100 m/s. Thus, maintaining terminal velocity as you get high is what matters, and that is relatively easy to do even with low TWR until you get to 10 km or so. I actually once made a spreadsheet that calculates required acceleration needed to maintain terminal velocity vs. altitude: (The initial high value at 1 km is based on some assumption of how fast we want to get to terminal velocity from a standing start). Thus, i think you are right. We can save weight by keeping a small TWR in stock aerodynamics, and still be efficient by flying at terminal velocity. In FAR, achieving terminal velocity is impossible (read: not possible without very large TWR), thus, there are potential benefits of higher TWR that might outweigh added weight of more engines...

TBH, I'm kinda surprised you use stock aerodynamics. You seem too technically-literate to be satisfied with the completely unrealistic stock aerodynamics...

But it always seems to lift off so SLOWLY!

Not really sure what you were saying here. What is a "BC value"? The drag loss is the Cd-- coefficient of drag indicator.