Vertical Ascent vs. To LXO First

[LethalDose]

Furthermore, LethalDoses is both practical and advantageous in every way.

Well, not every way. I expect we're going to hear about that 4.9% mass increase...

Even though you can drain that same 70 kgs from the tank and still beat it in dV (albeit by only 6m/s).

[GoSlash27]

Data, data, data!

http://s52.photobucket.com/user/GoSlash27/slideshow/KSP/munar%201

Vehicle cost: $1,188

Vehicle mass: 1.39 Tonnes

Supplies expended: Fuel: 33.77 units, Oxidizer: 41.27 units

Cost of supplies expended: $27.02 fuel, $2.47 oxidizer= $29.49

Mass of supplies expended: 0.32 tonnes

DV to achieve Kerbin periapsis from trailing edge munar surface: 881 m/sec.

Bonus: Kerbals killed from over-G: 0.

Cheats enabled to disable breaking parts and killing kerbals because I'm accelerating too hard: 0

craft file:

http://wikisend.com/download/411660/munar1.sfs

Best,

-Slashy

Edited December 18, 2014 by GoSlash27

[GoSlash27]

arkie,

Please demonstrate your results and post all of your results as I have done.

Best,

-Slashy

[GoSlash27]

Actually, if you replaced the LV1 in *someones* design with a 48-7s, it gives the craft:

• 1379.4 m/s dV
  
• 1.5125 t mass
  
• 1150 funds cost
  
• Munar sea level TWR of 12.2
  

The engine swap results in a gain of 150 m/s dV, a price reduction of 50 funds, and straight up baller TWR at the expense of 70kg...

I can't see how some could reasonably argue that additional 70 kgs makes this an "impractical" Munar lander. IMO, choosing the LV1 instead of the 48-7s given that comparison is simply idiotic.

Further it very easily pushes the vessel into the range were vertical ascents are reasonable give the data I provided.

LD,

If you wish to play along, you're more than welcome.

Please demonstrate it's ability to achieve an aerocapture and all pertinent data as I have done.

Time to put up or shut up...

-Slashy

[GoSlash27]

All,

This is where the rubber meets the road.

Rather than posting speculation, we're actually comparing the two approaches head-to-head.

The design I posted has not been optimized, it is just a quick 'n' dirty example of a representative lander I slapped together. It was also not expertly flown; I left about 30 m/sec on the table from a theoretically "perfect" flight.

These proposed vertical launch designs can now be fairly compared to the way we've always done it, and the readers can decide for themselves whether this is an avenue worth pursuing or not.

Best,

-Slashy

Edited December 18, 2014 by GoSlash27

[GoSlash27]

I readily admitted that my RT10 example is impractical, but that wasn't the challenge posed by Slashy.

Actually, it *is* the challenge.

You need to build a vertical launch munar escape vehicle, demonstrate it achieving the goal, and post all data related to efficiency for direct comparison to the traditional method.

Shouldn't be difficult, right? All you have to do is hit the space bar. Not like you've got to steer or anything.

There is no penalty in this exercise for needing a monster lander for putting it on the munar surface (although that *is* a pretty important practical factor).

Release the hounds

-Slashy

Edited December 18, 2014 by GoSlash27

[LethalDose]

Quoted for accuracy:

Data, data, data!

http://s52.photobucket.com/user/GoSlash27/slideshow/KSP/munar%201

Vehicle cost: $1,188

Vehicle mass: 1.39 Tonnes

Supplies expended: Fuel: 33.77 units, Oxidizer: 41.27 units

Cost of supplies expended: $27.02 fuel, $2.47 oxidizer= $29.49

Mass of supplies expended: 0.32 tonnes

DV to achieve Kerbin periapsis from trailing edge munar surface: 881 m/sec.

Bonus: Kerbals killed from over-G: 0.

Cheats enabled to disable breaking parts and killing kerbals because I'm accelerating too hard: 0

craft file:

http://wikisend.com/download/411660/munar1.sfs

Best,

-Slashy

VEHICLE

• Parts: 1 mk 1 pod, 1 48-7s engine, 1 FLT-100 tank, 4 OX-STAT panels
  
• Cost: 1550 (1150 w/o panels)
  
• Starting resources: 10 Mp (forgot to remove it), 55 Ox, 45 LF
  
• Starting mass: 1.5125 t
  
• Dry mass: 1.0125 t
  
• Initial dV: 1379.4 m/s
  
• Initial TWR: 12.4 m/s², local
  

LANDING SITE

• Location: 0^o 16' 25" N, 223^o 50' 40" W
  
• Altitude: 1786 m
  

PARKING ORBIT ESCAPE

• Parking orbit: 10 km x 9 km
  
• dV spent to reach orbit: 575.9 m/s
  
• dV spent on escape: 271.3 m/s
  
• Final Mass: 1.17 t (by info box, 1.18 t by spreadsheet. oh well)
  
• Total dV:: 847.3 m/s
  
• Max acceleration:: 25.4 m/s² (approx 2.6g)
  

VERTICAL ESCAPE

• Final mass:1.17 t
  
• dV spent on escape: 877.6 m/s
  
• Max acceleration:: 25.6 m/s² (approx 2.6g)
  

Images available here.

Videos available

. Apologies for a lack of sound, I didn't realize I had an open mic during recording. If values are too hard to read, I'll re-upload in native 1080p.

Craft available here.

I ran each ascent 3x well, but occasionally forgot screen caps. The values didn't change more than 5 m/s, but only values for which images or video is available are presented here.

I spent 0 time optimizing this craft. I don't need to. I don't plan to. I don't care.

Remainder of post removed

If readers can't figure out what the evidence shows, it's not my problem.

Removed posts have been screenshotted and are available on request.

Edited December 18, 2014 by LethalDose

[arkie87]

Actually, it *is* the challenge.

You need to build a vertical launch munar escape vehicle, demonstrate it achieving the goal, and post all data related to efficiency for direct comparison to the traditional method.

Shouldn't be difficult, right? All you have to do is hit the space bar. Not like you've got to steer or anything.

There is no penalty in this exercise for needing a monster lander for putting it on the munar surface (although that *is* a pretty important practical factor).

Release the hounds

-Slashy

Once again you misunderstand me. The challenge is to obtain a munar escape vehicle. There is no requirement of how it got there in the first place. Thus, SRB is perfectly feasible... Nevertheless, I'd rather go with LethalDose's design since it is a more feasible design given the spirit of the challenge (and it also perfectly illustrates the point I was trying to make-- so thank you LethalDose, have some Rep!)

I will do Lethal's design and post results...

EDIT: Nevermind, he already took care of it!

Bonus: Kerbals killed from over-G: 0.

Cheats enabled to disable breaking parts and killing kerbals because I'm accelerating too hard: 0

Best,

-Slashy

Kerbals will not be killed from over-G in stock (you need to have deadly-re-entry installed for that to happen). Plus, even for TWR = 30 on the Mun (my RT-10 design) will result in 5 g's acceleration, not 30... I don't know why you imply that ill murder Kerbals with my designs...

Parts only break in FAR from aerodynamic stresses. There are obviously none of those on the Mun... Suggesting I'm enabling cheats that prevent breaking parts from a mun launch indicates you either arent reading what im saying in full, or have a severe lack of understanding regarding the things I am saying... Frankly, I'm not sure which is more likely...

Edited December 18, 2014 by arkie87

[LethalDose]

Post Removed. See above.

Edited December 18, 2014 by LethalDose

[arkie87]

*everything i wanted to say and more*

I was in the middle of doing this test as well, but then saw this post, which basically said and did everything i wanted to (and more!)...

Edited December 18, 2014 by arkie87

[LethalDose]

I was in the middle of doing this test as well, but then saw this post, which basically said and did everything i wanted to (and more!)...

Please still do the test and provide your results. I don't feel like getting accused of BS'ing anything. Independent confirmation is required.

[arkie87]

Please still do the test and provide your results. I don't feel like getting accused of BS'ing anything. Independent confirmation is required.

Fine. I'll post the image gallery, if that's ok...

I was having trouble matching numbers with the design i had on paper... my command pod weighed about 200 kg more than what is written on the wiki... i thought maybe 0.90 updated some part specs... but then i realized i had deadly-re-entry installed and command pod had an additional 200 kg of ablative heat shielding .... once i removed heat shield and monopropellant, i matched paper values quite nicely

Javascript is disabled. View full album

Also, it feels kinda cheaty that all of us are supposed to get a Kerbin capture but none of us have a parachute... i guess, we'll just have to land Jeb on his head... That still works, right?

Edited December 18, 2014 by arkie87

[The_Rocketeer]

There is STILL way too much hostility in these posts. This is now (at last) a question of FACT and not browbeating.

LD all you've proved is that parking escape is still 30m/s more efficient than vertical launch, even with a rocket optimised designed for vertical launch!

Slashy's rocket isn't optimised whereas any vertical launch is already optimised simply by having high TWR and high FMR.

Slashy's rocket has 500 kerbucks of SOLAR PANELS on it! (Maybe if you weren't so hostile and prejudice to him and his views you'd have noticed that.)

[arkie87]

LD all you've proved is that parking escape is still 30m/s more efficient than vertical launch, even with a rocket optimised designed for vertical launch!

The challenge was about if a craft with high TWR can be cheaper than one with a low TWR, since that was a highly contested point by Slashy (see LethalDose's post on page 21). Not necessarily about which method of returning to Kerbin used less deltaV, though admittedly, the horizontal burn approach seemed better than i would have imagined given he got into LMO first. I assume he burned straight horizontal to raise apoapsis, stayed low, burned hard, and was very very careful not to overshoot.

Either way, now i know that i really shouldnt climb at all when launching from the Mun horizontally unless i have to.

Slashy's rocket isn't optimised whereas any vertical launch is already optimised simply by having high TWR and high FMR.

So let him optimize it, if he cares... there are only a finite number of ways to combine the parts... and ive tested every other engine, and the one LethalDose used is the best for both TWR and deltaV.

[LethalDose]

Post removed. See above.

Edited December 18, 2014 by LethalDose

[The_Rocketeer]

You post your way, I'll post mine. When you're a mod, you can tell me how to post.

From a mod:

Gents, while I can read very interesting and valuable opinions and ideas from all who posted lately on this thread, the discussion seems also to be descending to a rather hostile level at times.

Please, keep it in the most civil way possible. Really, there is no need to show a lack of respect for the opinions of others.

I'm done with this thread.

Thank God.

FMR would be fuel/mass ratio.

I'm not getting drawn back into this debate, but I will say that your attitude is your problem here. Slashy is still and always has been basically right, even if the differences are more marginal than he suggested. Sorry if that fact smarts.

[arkie87]

From a mod:

Thank God.

FMR would be fuel/mass ratio.

I'm not getting drawn back into this debate, but I will say that your attitude is your problem here. Slashy is still and always has been basically right, even if the differences are more marginal than he suggested. Sorry if that fact smarts.

We were never arguing over which was more efficient, but rather, if the difference is significant for this case, which it clearly is not.

If Slashy had taken a more balanced approach and said "yes, horizontal is more efficient, but under certain conditions, efficiency gains would be marginal" acknowledged even once that horizontal is not even always possible from within a deep crater, and in general actually addressed the logical arguments that were provided instead of (condescendingly) dismissing them with literally no reason given, then this thread would never have made it past 3 pages...

Anyway, I think it's time to label this question answered. Thank you LethalDose and Slashy for building and testing ships and providing results to us here for all to see.

I think in the future, I will post my theoretical questions in the Science Labs, rather than here, since here, I tend to get more advice of what to do (after all, this sub-forum is about gameplay questions so it is usually noobs asking for advice from experts) rather than a discussion, which is what i am after (in my defense, I think a Mod moved this discussion to this sub-forum).

Edited December 18, 2014 by arkie87

[LethalDose]

Thank God.

Well, you said you were done, but you're still here, so...

Slashy is still and always has been basically right, even if the differences are more marginal than he suggested. Sorry if that fact smarts.

Nope, he was, and is, "basically" wrong, and further dishonest to boot.

The "differences being more marginal than he suggested" was basically the point the whole time.

You want to listen to his nonsense, that's your problem. Not mine. If you're going to ignore facts, and theory, and accurate simulation, you're as much of a waste of time as he is.

Edited December 18, 2014 by LethalDose

[The_Rocketeer]

The only reason for writing this post is this thread has been changed to "answered", but I think the "answers" here are not addressing the OP.

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.

So what you've said is that "under the right conditions", as in, if you goof your gravity turn profile from Kerbin, you can waste enough dV to make a vertical ascent worthwhile. Well duh. This is why it's worthwhile to practice.

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.

You still want to go to LMO first. Everything, including the recent tests has shown this is more efficient and therefore more optimal.

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.

Yes, but as was point out some time ago this flight profile is absurd. Gravity losses are never negligible, if you don't account for them in designing your dV allowance your flight will fail.

What do you guys think?

A little tip here: Lots of people told you what they thought and you shut them all down for lack of evidence. If you want evidence, ask for it in the OP, don't ask for thoughts or opinions.

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.

You are wrong.

"Optimal" is the absolute BEST way to do it. It doesn't depend on the planet or situation. The best way is always Slashy's way (prograde/gravity/LKO/LMO/LXO/horizontal and all other terms used for it - NOT vertical). All the tests and statistics show this. Vertical ascent is ALWAYS worse. It may not be much worse if your TWR is outrageous and you have near zero payload, but every flight has some payload and most flights have quite a lot of it. In very nearly every practical case pilots/designers will not be able to reach TWRs anything like as high as you've used as benchmark tests - tests which still showed vertical is sub-optimal.

This is the question you asked. These are the answers to this question, regardless of all other tangents and petty squabbling, personal distaste and irrelevancies.

We are done.

Edited December 18, 2014 by The_Rocketeer

[diomedea]

Gents, I see again some hostility surfacing. While all your opinions are worth the utmost respect, it seems they are still motive for personal attacks.

Beyond opinions, there are theoretical and practical demonstrations of your ideas, now published in this thread. Who got it right is shown by comparing those demonstrations, not by blindly shooting "you are wrong". If anyone has a different opinion, fine, but would be better if he checks the results instead of repeating what is common knowledge (that is sometimes not accurate enough).

I'd like if the subject of this thread could be considered answered, as the tag suggests. And therefore this thread could be closed for good (leaving open in the meantime in case somebody still has something relevant to say, but certainly not to give further opportunities for showing fists).

[GoSlash27]

The only reason for writing this post is this thread has been changed to "answered", but I think the "answers" here are not addressing the OP.

So what you've said is that "under the right conditions", as in, if you goof your gravity turn profile from Kerbin, you can waste enough dV to make a vertical ascent worthwhile. Well duh. This is why it's worthwhile to practice.

You still want to go to LMO first. Everything, including the recent tests has shown this is more efficient and therefore more optimal.

Yes, but as was point out some time ago this flight profile is absurd. Gravity losses are never negligible, if you don't account for them in designing your dV allowance your flight will fail.

A little tip here: Lots of people told you what they thought and you shut them all down for lack of evidence. If you want evidence, ask for it in the OP, don't ask for thoughts or opinions.

You are wrong.

"Optimal" is the absolute BEST way to do it. It doesn't depend on the planet or situation. The best way is always Slashy's way (prograde/gravity/LKO/LMO/LXO/horizontal and all other terms used for it - NOT vertical). All the tests and statistics show this. Vertical ascent is ALWAYS worse. It may not be much worse if your TWR is outrageous and you have near zero payload, but every flight has some payload and most flights have quite a lot of it. In very nearly every practical case pilots/designers will not be able to reach TWRs anything like as high as you've used as benchmark tests - tests which still showed vertical is sub-optimal.

This is the question you asked. These are the answers to this question, regardless of all other tangents and petty squabbling, personal distaste and irrelevancies.

We are done.

Pretty much all of this, but a few things I'd like to add:

1) LD's example proves that a high thrust design with a vertical launch *can* (under very limited circumstances) approach (and I still maintain even possibly *exceed*) the DV of an orbital escape burn. He didn't achieve surpassing it (and arkie, I totally understand that you never said it would), but *I* believe he could if the t/w is high enough.

2) I learned a few very interesting things in this exercise:

2a) I had grossly overestimated the difficulty of constructing a reasonably sized vehicle with high t/w in low gravity environments.

2b) I had grossly underestimated the gravity losses incurred from using low t/w in airless environments.

2c) given the two points above, I realize now that I have been going about this the completely wrong way. I need to start considering high t/w as a potential DV saver when working in airless environments. It would probably not have worked out to a lighter or cheaper vehicle this time, but it's something to keep in mind. (edited above after running the numbers to confirm this)

arkie, I have learned a lot from this exercise (bickering notwithstanding) so I thank you for that.

So to summarize:

*No, in any realistic situation, vertical launch will not out-perform the standard orbital transfer mode and isn't liable to be close.

*Yes, the advantage of going orbital -> ejection can be marginal (or even possibly negative), but only if the launch vehicle happens to be perfectly situated in an ideal spot for it at the time, which is highly unlikely.

*Going to a higher t/w may be worth doing on an airless body(especially if the higher thrust engine has better Isp) if the additional mass and cost of the engine are offset by the resultant fuel savings.

*Going to orbital altitude and then accelerating prograde is inefficient, and there is never any circumstance where you can't go prograde immediately on an airless body unless you happen to be down a mohole at the time, which is highly unlikely. If there's terrain in the way, clear it as you go.

I think this one can be put to bed now if arkie is satisfied that all of his questions in the OP have been answered, but I'm kinda curious to see if a reasonably sized and priced munar lander can be made to outperform orbital mode in this scenario. I'm thinking it just might be possible...

Best,

-Slashy

Edited December 18, 2014 by GoSlash27

[sal_vager]

This thread seems to have gone as far as it's going to and has just turned into a vehicle for argument, peoples posting style should not be used to back up or belittle ones claims whether right or wrong.

Take peoples data on its own merit and don't turn this thread to any more personal attacks please.

[arkie87]

Pretty much all of this, but a few things I'd like to add:

1) LD's example proves that a high thrust design with a vertical launch *can* (under very limited circumstances) approach (and I still maintain even possibly *exceed*) the DV of an orbital escape burn. He didn't achieve surpassing it (and arkie, I totally understand that you never said it would), but *I* believe he could if the t/w is high enough.

2) I learned a few very interesting things in this exercise:

2a) I had grossly overestimated the difficulty of constructing a reasonably sized vehicle with high t/w in low gravity environments.

2b) I had grossly underestimated the gravity losses incurred from using low t/w in airless environments.

2c) given the two points above, I realize now that I have been going about this the completely wrong way. I need to start considering high t/w as a potential DV saver when working in airless environments. It would probably not have worked out to a lighter or cheaper vehicle this time, but it's something to keep in mind. (edited above after running the numbers to confirm this)

arkie, I have learned a lot from this exercise (bickering notwithstanding) so I thank you for that.

So to summarize:

*No, in any realistic situation, vertical launch will not out-perform the standard orbital transfer mode and isn't liable to be close.

*Yes, the advantage of going orbital -> ejection can be marginal (or even possibly negative), but only if the launch vehicle happens to be perfectly situated in an ideal spot for it at the time, which is highly unlikely.

*Going to a higher t/w may be worth doing on an airless body(especially if the higher thrust engine has better Isp) if the additional mass and cost of the engine are offset by the resultant fuel savings.

*Going to orbital altitude and then accelerating prograde is inefficient, and there is never any circumstance where you can't go prograde immediately on an airless body unless you happen to be down a mohole at the time, which is highly unlikely. If there's terrain in the way, clear it as you go.

I think this one can be put to bed now if arkie is satisfied that all of his questions in the OP have been answered, but I'm kinda curious to see if a reasonably sized and priced munar lander can be made to outperform orbital mode in this scenario. I'm thinking it just might be possible...

Best,

-Slashy

I have learned a few things as well, particularly, just how bad it is to raise apoapsis at all by going vertical at all if you plan to go horizontal to get into orbit. From now on, i will tap throttle to get off surfaces and then aim as horizontal as possible

Also, the only reason the cheapest (in terms of kerbucks) Mun lander also happens to have high TWR and more deltaV then lightest Mun lander is due to the way squad balanced the game. So perhaps one could argue that this result is unrealistic. In the real world, higher thrust, more efficient engines should be more expensive... but my point was that we arent in the real world, we are in KSP, and the optimum solutions must be constructed from the parts that are available, however unrealistic or imbalanced they might be-- and this might result in *interesting* solutions.

I still think Rocketeer's last post is missing the point. This was a theoretical scientific discussion (admittedly, the science labs is a better place than "gameplay questions and tutorials" for that, but like i said, a mod moved this thread to this sub-forum), so, it doesnt matter how unlikely it is. I wanted to know what to do in this scenario, and i think it should be obvious that i want a reason/justification (though, i think most people felt they didnt need to give a reason because this was in "gameplay questions and tutorials" sub-forum, where people are usually just asking what to do, not looking for scientific discussion). In the OP itself, i even ask if there are even any better scenarios that people are aware of where the two approaches might be similar.

I assume Rocketeer will categorically assert: "no, never". (don't mean to put words in your mouth if you wouldnt say this... so feel free to correct me)

But that is clearly not the answer I am looking for, since that answer, based on orbital mechanics, doesnt account for real-world problems. There could easily be an example in the Kerbol System where one is inside a deep crater somewhere, where, given how much distance they have to go vertically, it will pay to just continue. Or there can be another place in the Kerbol system, where, due to reasons I am unfamiliar with, it would pay to go vertical. This is what i was asking for in the OP-- if others were aware of any or could calculate any.

The only example that comes to mind is Gilly-- since it is so misshapen (surface roughness-to-diameter ratio is the largest of any body in the Kerbol System), that you can rarely launch east without also climbing. However, you could also throw a ball into orbit around it, so any deltaV savings would be minimal.

This is a much better answer than a categorical "no" because it illustrates how ugly the planet/moon would have to be for this effect to dominate, and since it is only likely to occur on smaller bodies, any deltaV savings would be minimal anyway. This is what i was looking to investigate-- if there are any other cases in the Kerbol system where this would be practical-- and in examining the Mun problem with you guys, I think it made the Gilly answer clear.

Edited December 18, 2014 by arkie87

[GoSlash27]

*edit* I totally misunderstood what you said, and wasted a lot of time. *facepalm*

Yeah, agreed.

Take care,

-Slashy

Edited December 18, 2014 by GoSlash27

[arkie87]

arkie,

I'd be careful drawing that conclusion; Remember that neither lifter had been optimized.

I ran the numbers for an actual optimized lander with the same payload, and the lightest and least expensive option is still the LV-1. It ends up burning a little more fuel, but not enough to make up for the extra mass and cost of the 48-7S for the same mission.

But it's certainly not unlikely that such a situation could arise; a heavier and more expensive engine ends up making a smaller and cheaper overall vehicle. In fact, this happens fairly often, but I had never considered factoring gravity losses into that before.

I see a lot of testing in my future...

As for the rest of it, yeah, I'm right with you.

Take care,

-Slashy

I assume by optimization you mean starting fuel in the lander? It's good to know that you are willing to do so many tests to find the optimum...

I'll be sure next time i need something rigorously tested to get you interested in the problem so that you will perform the tests