arkie87

100% agree. But for this case, i have explicitly stated that I am below terminal velocity (this was specified in the OP--emphasis added): It almost certainly will, but that is not what was suggested. What was suggested was limiting thrust, even though the additional thrust/TWR comes at no additional mass/deltaV penalty since the heavier engine is already ON the ship (and since it is below terminal velocity). From your answer here, it seems like you agree that if you are below terminal velocity, you do not want to limit thrust...

I dont mean to be rude, but i dont think our discussion is going anywhere. None of your comments actually address the points i've made or "refute" an imaginary point i never made... from my perspective, it seems like you arent actually reading what i am writing, but rather, just typing your response to imaginary arguments. I'm not sure you should continue responding to my threads, as we dont seem to communicate well.

I never claimed vertical was always better. I was wondering if it COULD be better with a high TWR in FAR. I dont see where all the animosity and condescension is coming from. Every time i say "could" or "might" people interpret that as "IS 100% WITHOUT A DOUBT" and i'm getting kind of sick of it... Second, I also was trying to suggest that it definitely isnt as bad as people say-- my craft cost about 20% more and can do just about the same task (i also overshot and had to correct a few times, but those were minimal). 20% isnt the 100%+ inefficiencies that people claim. Plus, it happens to be loads more fun That said, i dont think your pencil craft is particularly well suited to vertical launch due to low TWR. Can you give me details about how exactly your fly it so i can try to replicate it. If you can steer this pencil, then i should be able to steer all of the craft ive made, given they all have lower moment of inertia. Also, please comment on my suggestion for improvement by using lv909 instead of 48-7s... In an unrelated note, maybe its a good that this forum was moved to challenges so no one will come in and derail it...

You think its more fuel efficient to throttle SRB's down? If I had a mainsail, would you tell me I should throttle it down to a skipper even though i already have the extra mass? - - - Updated - - - I'm using FAR though...?

See spreadsheet below for a case study of where a higher TWR also happens to be more fuel efficient i.e. larger deltaV

Your point about it being impractical is conventional wisdom; however, this thread will show that it is possible to have a high TWR craft that is also quite cheap/competitive (that is sort of the point of the linked thread): http://forum.kerbalspaceprogram.com/threads/103449-A-New-Thread-to-Discuss-5thHorseman-s-Challenge?p=1606814&viewfull=1#post1606814 and http://forum.kerbalspaceprogram.com/threads/103449-A-New-Thread-to-Discuss-5thHorseman-s-Challenge?p=1607366&viewfull=1#post1607366 Second, I am not trying to stack the deck in favor of anything. I merely want to understand under what conditions conventional wisdom is correct (i.e. horizontal burn) and under what conditions vertical is better... Furthermore, even if for an ideal launch conventional wisdom is better, it is important to know how badly one needs to mess it up to offset its gains. I was surprised to learn that the values were so low for the Mun case-- for TWR 3, if you get your craft up to 7.5 km, it is more efficient to have just launched vertically... i dont know about anyone else, but when i launch from the moon, i first climb up to a parking orbit at least 10km high... i dont skim across the surface like a daredevil... it is possible that climbing up to this height actually makes the gains less. Finally, if you are in a crater, it might easily be better to launch vertical... And my last point--for heavy landers, the difference in mass between a rockomax 48-7s and the lv-909 is large, but the different mass is negligible on the scale of the large craft. So the ISP gains from switch to LV-909 actually favor using the LV-909, since the LV-909 will give more deltaV... so it's entirely possible that a higher TWR craft will be both cheaper and have more deltaV. For the example of a craft where this is the case, see:

But the much nicer, redesigned rocket is so much cooler. I call it "The Pencil" and it's as simple as it gets. The hardest part is actually falling East but it's pretty forgiving in the first 200m/s or so, so you can wrestle it into place so long as you don't let it wander too far. And you can't argue with the $9322 price tag (Including payload!) [defunct site link removed by moderator] I've filmed the 2nd ship but won't be able to post it today. Rest assured, it got into a 28x25km orbit with (again) over 200m/s to spare, even though I screwed up the ejection bur and had to turn around and slow down a bit. Then I overshot THAT and had to speed up a little again. Probably 10-15 m/s total though so no bigs. I may have had 300m/s in the tank when all was said and done, which is actually better than the above monstrosity. I dont know if we can absolutely rely on KER deltaV readouts, but if we can, my craft has 4629 m/s deltaV, while your first craft has 4964 m/s and 4830 m/s, so the 200 m/s of remaining fuel could easily be because it started with more (though both are cheaper than mine, so that might not matter). In terms of aesthetics though, i'd say mine wins Let me know how flying mine with a horizontal burn goes.... if you can do it, i'd like to learn what im doing wrong...(though if you could turn your monstrosities, then i assume i can turn mine...) And FYI: for the last stage before the lander/payload, i had the same design using that smaller engine (rockomax 48-7s), but i noticed i actually get more deltaV from the LV-909 since its ISP is larger; the increase in mass of the LV-909 to the total package isnt significant enough to offset its increased ISP.

But the much nicer, redesigned rocket is so much cooler. I call it "The Pencil" and it's as simple as it gets. The hardest part is actually falling East but it's pretty forgiving in the first 200m/s or so, so you can wrestle it into place so long as you don't let it wander too far. And you can't argue with the $9322 price tag (Including payload!) [defunct site link removed by moderator] I've filmed the 2nd ship but won't be able to post it today. Rest assured, it got into a 28x25km orbit with (again) over 200m/s to spare, even though I screwed up the ejection bur and had to turn around and slow down a bit. Then I overshot THAT and had to speed up a little again. Probably 10-15 m/s total though so no bigs. I may have had 300m/s in the tank when all was said and done, which is actually better than the above monstrosity. So you are saying that both of these ships are easy to turn, despite having only one reaction wheel at the top i.e. the worst point to turn the vehicle from? ....Maybe I am doing something wrong then... do you hold down the turn key or let the vehicle turn itself? I know you are supposed to bank 5-10 degrees instantly upon liftoff, but then you just leave the rocket alone or turn slightly (with a joystick or keyboard)? I will build your crafts and fly them both ways... Also, I will try firing my liquid engine during liftoff to see if that saves fuel since I am still below terminal velocity in FAR. For some reason, ShadowPlay stopped working for me (seems to happen every time there is a new driver or new version of NVIDIA Experience), so i wont be able to record it though...

that is VERY IMPORTANT to know.... Thanks for sharing! Have some rep!

Interesting. I would think in stock, since terminal velocity is so painfully low, you really really want to be going at it. In FAR, since terminal velocity is so high anyway, the gain in ISP might be much more significant, so you might want to keep it for later....

I actually tried flying my rocket in horizontal mode configuration--- i was trying to lower nose down towards east the whole time (my finger was smooshed down on the keyboard) but the rocket wouldnt turn!!! I tried raising the large boosters higher up, but that was a big mistake --- rocket flipped the $%^#$ out...

Let's say you have a craft like this with FAR aerodynamics (aerodynamic disassebly is disabled), such that if you begin thrusting with only the two boosters, you will be below terminal velocity, do you want to ignite the liquid engine? Liquid engine ISP is higher than SRB's, but I've heard that it's better to burn lower ISP fuel first. Which effect is worse on deltaV? Being below terminal velocity or burning low ISP and high ISP fuel together? EDIT: Answer: FURTHER EDIT: Actually, the above answer is only correct if one is not allowed to drop the SRB's; if one is, then it should've been obvious that dropping the SRB's before turning on LFE is more efficient since LFE will be pushing drastically less dry mass, as pointed out by Starman:

By definition, if you burn horizontally up to an altitude, you pass through a circular orbit (assuming impulse burns) with periapsis on the ground. This is what i meant by LMO.... If both have roughly the same fuel left and cost roughly the same amount, then each player can decide which method is better for them, by weighing the pros and cons. Whatever they decide, more information is better than less information. If you think this discussion is pointless, please bow out, and stop derailing this discussion (after all, lots of other people in this thread derailed the discussion, and then you blamed me for the fact that you were confused about what exactly we are debating).

Can you post a pic? I would like to see what you did, and try to fly it vertical and horizontal and see what happens. As it is, my craft was wobbling around like crazy during ascent-- i had to spin it around in circles really fast to stabilize it so i'm wondering how you managed to get it to turn without flipping out

Yeah, it makes sense that it would be cheating. The lander is a payload. Payload cannot be used.

So I was able to do it with $11,352 with some fuel remaining (~70 m/s, but i was also significantly below 30km x 30km mark). Screenshot of rocket design and results: What does yours look like?

Are you sure about this? That's surprising....

I honestly dont know how you can say this? Have you even read this thread? I have done plenty of my own simulations, and used the equations that LethalDose has used in my OP. I have also done plenty of tests making videos when asked (though not for this case yet since i have been busy doing others). I agree that experiments can usually trump theory, since theory makes simplifications (such as impulse burns), but experiments also have severe handicaps: while it can take me 5 min to simulate 1000 different cases to see which one is best and/or understand its behavior, it would take me days to fly all of them. And even if i flew all of them, i am still relying on my ability to perfectly execute all of them. Maybe an "ideal burn" (whatever that is for any given case) would be much more efficient, but in reality, if i make a slight mistake, it will actually require the same deltaV as a "less efficient" maneuver, but one that is much easier to execute and/or much less difficult to screw-up. This is the question i am investigating... And if i provide a mathematical proof why X is better for a given case (which i have in OP), then i expect a mathematical proof of why its not. If you only "proof" is that its not because "orbital mechanics says so", then that doesnt help anyone understand why. I am interested in and trying to figure out the "why", and if you cannot provide that to me, then please stop telling me the "what".

I assume by horizontal launch from the leading edge of the Mun, you are referring to a horizontal burn to LMO that goes directly into the burn to leave Mun SoI (i.e. the lower limit that LethalDose is referring to). I think we all agree this is most efficient, but like LethalDose said, my question is about a craft on the trailing edge, so the "lower limit--horizontal from the leading edge" is not available since the Mun is tidally locked (I can start a new thread for non-tidally locked moons ). Also, Like what LethalDose said, the question isnt necessarily which is more efficient, but whether the difference is worth it, given the pros and cons of each method.

Please see my response above. You misunderstood what dogma i was referring to....(though i do not understand why you would think cost was the dogma?) I'm still working our first challenge...but i think doing a test from an airless body would be an interesting test since I seem to be hitting terminal velocity in FAR... which severely limits benefits of TWR.... wait-- did you use a gravity assist to get cost below 10k$? If so, i would like to forbid that as well, since gravity assists can be performed using both methods... i.e. you cannot leave Mun's SoI once you enter it...

Sorry, even though i quoted you, what i was referring to was a bit vague... This should clear it up... This is an assertion without any proof whatsoever. So even if it is 100% true, you will never convince us unless you expect us to just believe you, which is not science. It's dogma. This is dogma. I am asking you to prove it, not just assert it. If you cannot prove it, then dont let yourself get drawn into it, since you cannot help.

Ok, i wasnt sure if we were allowed to use the lander fuel. I need to redesign then I will revise OP to incorporate this fact.

This is an assertion without any proof whatsoever. So even if it is 100% true, you will never convince us unless you expect us to just believe you, which is not science. It's dogma.

Oh. My bad. I betrayed my own source.... oh well. Please do share this new equation....

HOW DARE YOU NOT CALL AN ANGLE THETA! ARE YOU SOME KIND OF BARBARIAN???? DEATH TO PHI!!!!