arkie87

I think the confusion is the definition of "terminal velocity". The accepted definition of terminal velocity is not the velocity where acceleration is zero (despite it's name) i.e. when a craft under thrust stops accelerating or a gliding craft stops accelerating. It is accepted to mean the velocity where a falling craft stops accelerating due to weight perfectly balancing drag force from air resistance. We are not interested in the "terminal velocity" of a craft under thrust since it has no bearing on optimum launch, and likewise, we are not interested in "terminal velocity" of a gliding craft. What DOES have a bearing on optimal launch is falling terminal velocity i.e. the accepted definition of terminal velocity. It can be shown mathematically that the terminal velocity of a falling object (no thrust) happens to be the optimum ascent velocity to minimize fuel consumption. This is the result of a balance between drag force and gravitational losses (any slower and you are spending too long climbing; any faster, and drag losses are too great). If you dont believe me, look it up in a textbook, or ask me to derive it for you, and i will. The rate at which atmospheric pressure is dropping does matter, and is accounted for in the variation of terminal velocity with altitude. This is not what is meant by terminal velocity. See above.

Yes, and that clearly isnt you, so i suppose there is no point in continuing this debate further, sad to say

I am testing the theory, with videos and math-- as much as you expect me to--and I'm trying to sell it, since it seems correct to me. How else would you like me to "test it"??? Anyway, why are we talking about this and not the issue at hand???? Your own testing is with stock aerodynamics, not FAR. Install FAR and test it if that's what you need to do... And once again, you assert it's wrong without giving a reason, even though we have clear and present evidence that it actually reduces deltaV requirements than the nominal ones required by FAR, and not vice versa...

It might be high enough to cause aerodynamic disassembly, but I have that disabled I'm not sure if GoSlashy would agree with this, and Im not sure I do either... I think it depends on the case... Yes, a similar calculation can be done for LKO-to-Mun ascent, and i think you will find it is significant, though not as large since eventually centripetal forces reduce effective g forces... meanwhile, vertical ascent does not get far enough away from the planet to significantly decrease parasitic gravity losses. I agree 100% and this is my point. In practice, you could and maybe should substitute mainsail for a skipper, in order to get more deltaV from the lighter engine at expense of TWR (though reduced TWR also costs deltaV). EDIT: by the way, the only reason i group it as "LKO-to-Mun" and "vertical ascent" and not low TWR vs high TWR is because with low TWR, LKO-to-mun is easy to perform due to use of thrust-vectoring engines, which allow for much more control during ascent and gravity turn; high TWR seem to lend themselves to favor boosters, which do not have thrust vectoring, and would be harder to steer into a gravity turn, thus, they favor vertical ascent.

I assume KER is either using updated part masses, or is including weight of RCS fuel in command pod, or something else i am not aware of.... either way, the numbers are not far off... In any case, you can assemble the same craft that you see in the video and/or the spreadsheet and check the numbers for the LKO-to-Mun case assuming that i burned out the first stage completely (which is approximately true), and let me know what deltaV you get...

This is true. KER says about 70 m/s... but who knows... but it is about right on target... as i did not use too much of the upper stage... Regardless of the vertical ascent accuracy, your main argument was that the LKO-to-Mun flight was flawed due to it wasting too much energy on atmospheric drag. But given that it comes in below nominal value, that clearly isnt the case, right?

Yes, of course. If you were to start arguing that it's actually 4086.7772342343 instead of 4087, i would lose a bit of respect for you But my main point is that your past conclusion that my craft is inefficient because it creates excess drag is not supported by this deltaV calculation. Though if you would like to still argue that, I am open to hearing arguments...

So then you admit this conclusion is no longer applicable, and my rocket does not produce excess drag...: If that is the case, then my rocket saves ~100 m/s compared to the nominal value required by FAR for this task....

You can use vacuum ISP. That is what i used, though real value is slightly smaller than that. I trusted those values before we got into this discussion, but after investigating and using a spreadsheet (as per your recommendation in another thread), those masses dont make sense to me. Maybe the add on has updated part masses or knows something I dont... Anyway, there are two numbers for mass reported in KER: one is current-stage only value, and one is total value. I think you used stage instead of total. Can you please redo your calculations...

I am making statements that appear to be valid to me based on the math and physics i know. I am seeking mathematical/specific rebuttals if I am wrong. Could you expect any different from a scientist? I appreciate you genuinely trying to answer the questions (though i would prefer less rude responses sometimes ). Let's finish up these calculations. I think we are close to resolving this...

Can you please redo your calculation with the corrected numbers. I think we are finally close to resolving this. Don't tap out now. It is exasperating on my side too Here is my spreadsheet:

KER said 47.428 ton, but I summed parts manually in spreadsheet and came out to only 46.670 ton. Either way, 42.6 ton is incorrect. Similarly, KER said 15.458 ton at burnout, but i calculated 14.67 ton. Don't know where you got 10.7 ton... I think your number here is incorrect because you used incorrect masses. By my calculations, using ISP 320 (at sea level for mainsail), i get 3633 m/s deltaV in lifter stage and using ISP = 360 (vaccum for mainsail), i get 4087 m/s deltaV. Since i only have approx 7 m/s deltaV left for LKO-to-mun burn, lets be conservative and assume, correct deltaV spent is the total of 4087 m/s... I think the values you used were incorrect... Yes, it is a LV-T30 engine to maximize TWR Your conclusions here are misinformed since you used incorrect numbers. See above. I didnt use KER for terminal velocity--only FAR. I admit KER's numbers seem fishy, when it comes to mass and deltaV though....

low quality? It's 1080p...

In that case, I think you are misunderstanding Slashy's answer

TWR = 2 doesnt mean you are at terminal velocity-- it just means its physically impossible to exceed it. If you are in space, terminal velocity is infinity, and TWR will not make you reach infinity.... As i said before, in stock, terminal velocity is small--only 100 m/s at sea level-- so TWR = 2 will make you reach terminal velocity quite quickly. From then on, its only a matter of maintaing terminal velocity, which changes with air density in stock. In FAR, terminal velocity starts out much higher, due to low density of atmosphere relative to density of spaceship. It is much harder to get to without huge TWR. I do agree terminal velocity is optimal. And i can prove it mathematically (albeit for a simple case) if you are interested . I am positive I am under terminal velocity. FAR itself calculates terminal velocity-- and I get all reading from FAR itself. I was not, and never was, using MechJeb (don't know where you got that from) nor was i getting any numbers from there...

Actually, i think numbers changed due to ISP changing because of atmosphere density...

I could make the same argument for you that you are just arguing and not listening. We obviously both think we are right... But the difference is, when i argue, i make an argument with math or logic rather than claim the other side is wrong. Claiming the other side is wrong without supporting evidence is pointless... From my side, it seems you arent listening either. You repeatedly use arguments that i've argued apply to stock aero only, and not FAR, even after ive explained why and how stock and FAR are different. Furthermore, you've never addressed the terminal velocity argument other than claiming its wrong without providing a reason. Please follow community rules, as per B787_300. And the fact that my rocket is glowing from re-entry effects on liftoff says nothing. You still haven't refuted my claim that terminal velocity is what matters-- not rerentry effects.

Yeah, something weird is happening in KER, since during launch, deltaV values for upper stage were changing when they shouldnt be since the fuel wasnt being shared... From KER, i think the numbers are as follows (KER reports two numbers. I assume the first is current stage and second is total, so i report total): Initial Mass (both cases): 47428 kg LKO-to-Mun: 15458 kg (only lower stage burned; upper stage untouched) Vertical Ascent: 4688 kg (lower stage used completely) Let me know what you find. I will crunch numbers too.

Oh. I read below. See below for response. Where did TWR = 2 come from? Unless you are above terminal velocity, throttling down is not the right option since you want to get into orbit ASAP... Who mentioned this? This is exactly what I am saying.... Yeah, this is the problem. It wont happen on Mun often, since you would have to land in the right spot since it's tidally locked. But still. It's a hypothetical argument... My numbers say vertical ascent is 70 m/s worse than horizontal in FAR (not the other way around), which, IMHO, isnt much. I'm not saying you should do vertical ascent or vertical ascent is more efficient (which GoSlash27 for some reason thinks I am saying), but the common knowledge that vertical is woefully inefficient isnt true in this case. Furthermore, for the case we are discussing in this thread, it seems that vertical ascent is more efficient....

Really? you think terminal velocity is not optimal? Please explain why not? I already provided the equations which suggest it is... My dV doesnt suck so bad. I posted the numbers (which you could have gotten yourself), what now? Once again, you arent using FAR... I've already explained that terminal velocity is easy to hit in stock aerodynamics

First of all, you are being rude. You mentioned somewhere that you like helping people. If that is true, and your intentions are that, then you should really tone down the rudeness. As i have said many times in other threads where we argued, I dont care if I am right or wrong. I want to know why. So if you want to help me, tell me why I am wrong. Not start putting words in my mouth or otherwise insult me. That is no way to behave on the forums. And for the love of god, I dont claim it is more efficient. I am just trying to highlight its advantages, since conventional knowledge recommends avoiding it at all costs. But even according to your results, it only costs less than 10% more deltaV.

I wont say because you can get them yourself since i posted the video with those numbers. But since you insist, here are the numbers: Vertical ascent: 3313 m/s LKO-to-Mun: 3241 m/s Using readouts from KER. Your numbers: Vertical ascent: Vertical: 5570 m/s LKO-to-Mun: 5230 m/s Now what is your point?

Should be the most efficient; also a way to get kerbal's blood pumping (do they have blood? green blood?) You want you climb as little as needed and burn as horizontally as possible as fast as possible, if you arent going the vertical approach.

I dont think you've debunked that notion at all. So by all means, debunk away. Terminal velocity here is infinity. Terminal velocity with FAR installed, is essentially infinity as well... Once again, stop asserting your answer is correct and PROVE it.

The reason i started a new one is because I wanted to start out with a more refined statement of the problem, so that people dont chime in with information they think is new or will resolve the issue, despite it being mentioned 5 pages ago, and we are currently debating something else...