Calculating DV is "hard"??

[LethalDose]

I've still probably spent more time running the math, or building spreadsheets for KSP than I have actually playing the game. I'm not afraid of a calculator, or my paper and pencil, and I have a notebook filled with scribbled diagrams and equations, and derivations.

I don't use in-game mods.

I see a lot of people suggest using mods to make their life easier, or use other mods to watch "and learn" from the way a computer does it, and then try to emulate it. What I have seen as a result is plenty of people who use rules of thumb about how to do things based on some mod mission profile said so, or something they read on the forum, or saw on a video once. But they don't necessarily understand "Why" something is more efficient, and having coached a few twitch players through some of these follies caused by blindly following these rules of thumb, I believe that understanding the "why", and the underlying equations is very powerful.

It allows for much greater flexibility and success, especially when mods aren't available after updates, or haven't been programmed to solve the actual situation you've discovered yourself in.

So what does actually doing the math assist with? I actually understand the numbers that I see. I know where they came from. And the more I play with the equations, the more I can figure out when to apply them, and when to start breaking the rules....because there are times when radial burns are more efficient than pro-grades, and what autopilots do for inclination changes aren't necessarily optimal either. If you understand the math, then you'll know when inclination changes can benefit from a drastic Ap change...and when it's not.

I calculate and plan out my ships ahead of time with spreadsheets I build. Or in a time crunch I use also use pre-generated dV maps, and an Isp/Mass ratio to dV graph and some head cheese math to build up quick ships from the ground up. Neither of these even require a calculator...the two graphs required are available in the community, and the ratio's are simple enough that if you can divide and multiply in 2's and 10's in your head, you're golden.

Don't fear the math, or a little work... because the pay-offs can be awesome. Do the hard things, until they become easy, and the impossible will become merely difficult...(This is a bit of a life philosophy too, btw)

I think this is getting a little far afield from the OP's... whatever that post was, but afield is okay because this kind of discussion is actually useful.

I completely agree that the math isn't hard (as has basically everyone else that has responded to his thread), and using the math leads to insight into what the numbers mean and how to manipulate the equations and systems to your advantages.

Using the math like this always makes me think of this:

But only after you understand what's going on. Anyway, enough diversion. Up to this point, I agree with PurpleTarget's post.

Where I disagree with Purp's post/opinion is that, due to the current state of the game, calculating dV by hand is largely a waste of time. This is because performing the math needed to calculate dV in KSP suffers from two major and related problems: It is impractical, and it is tedious.

KSP gives bovine manure for info during vessel construction. To calculate dV for a staged rocket, you need the following parameters for every stage:

• stage dry mass
  
• stage fuel mass
  
• cumulative vessel mass
  
• engine(s) ISP
  

Currently, we can quickly get one of those values. The others require a butt-load of work to get out of the program, making hand calculations of dV impractical. Further, because of the cascading nature of changes to dV due changes to payload and upper stages, the work may need to be repeated several times.

The calculations are also made tedious since the work has to be repeated for every stage. When students are presented with this kind of tedious, repetitive work, they can quickly lose the forest for the trees. (I'm going to swing credentials here for a second, sorry, but it's needed for perspective) I'm a doctoral candidate in epidemiology and biostats, and I'm defending my dissertation next month. During my time in grad school, I've TA'd nearly 20 quarters of quantitative courses, and I've seen graduate students completely miss the point of many exercises due to the tedium of the math involved in the exercise. IMO, trying to calculate dV from what's presented in game without mods leads to the same problem: so much work has to be put into getting the numbers and running the calculations over and over and over that it's value as a learning exercise is all but ruined.

If the devs ever manage to get over themselves and just give the players the information the need to play the game intelligently (what I've listed above), I'll be able to agree with what Purp is saying up there. If you can get the numbers easily (making it practical), then you can plug them into a spreadsheet (removing the tedium).

But until that time, I'm not going to change my mind that KER/VOID are necessities.

[MGCJerry]

Didn't read past the first page.

I play games to have fun. After being buried in math all day, gaming is an escape especially since my free-time is highly limited. Sure, I could sit down and spend time to do all these calculations but I'm wasting my time. Plus, I don't like math.

I can do it, but I don't want to do it. However I do kind of want to do it by hand now that MJ & VOID give me 2 different ÃŽâ€v readings (VOID is 10dv smaller than Mechjeb) so I can find which is more accurate. However, on the other hand I don't care about 10 ÃŽâ€v difference is that significant enough for me to sweat over.

The math that is hard is "Taxes", but that's an entirely prohibited topic...

[Aphobius]

I bet that most people who are saying how easy it is, lack the intellectual ability (shouldn't be taken as an insult .... it's rocket science after all) to calculate the delta-v even for a simple rocket (that uses both liquid fuel rockets and SRBs).

PS: Since most of you will probably think I'm a troll that just wants to insult the highly intelligent people from here. I'll give a short explanation of why calculating the delta-v for that simple rocket is harder than most of the people here thought it is (else they wouldn't have said how easy it is to solve that "simple equation").

In the hypothetical situation where you have a single liquid fuel tank and SRBs that finish burning before the liquid fuel is over. Assuming that the SRBs have different ISP from the liquid fuel rocket, you have to calculate the delta-v for the first part of the burn (until the SRBs are done burning) and after that calculate the delta-v for the rest of the rocket (without SRBs and with the remaining liquid fuel after dropping the SRBs) and add the obtained values. To do this you have take into consideration the burn time of the SRBs and the flow rate of the liquid fuel engine.

And I don't even mention the variation of the ISP with the altitude while inside of an atmosphere. I doubt that ANYONE runs high precision missions in this game. You people should just use grossly overpowered rockets and stop talking about how easy rocket science is. (I don't say you should stop discussing, but if you want to learn more about rocket science, saying how easy it is, when you hardly know anything about it, is not a good way to start doing it.)

[Red Iron Crown]

That's definitely a situation where it becomes more complex. Parallel non-crossfed staging requires net Isp to be calculated and the burn time as well, but those things are not insurmountable. Tedious, but not overly difficult.

I think just about everyone who calculates manually assumes a fixed atmospheric pressure, even the dV calculator mods do this.

[AbhChallenger]

Hey OP. Do you mind not judging the way players choose to play their game? Thanks

[bakanando]

KSP gives bovine manure for info during vessel construction. To calculate dV for a staged rocket, you need the following parameters for every stage:

• stage dry mass
  
• stage fuel mass
  
• cumulative vessel mass
  
• engine(s) ISP
  

Currently, we can quickly get one of those values. The others require a butt-load of work to get out of the program, making hand calculations of dV impractical. Further, because of the cascading nature of changes to dV due changes to payload and upper stages, the work may need to be repeated several times.

This. Even if only the total mass of the vessel was displayed, it would help a lot.

[Fiddlestyx]

Dear OP, why is this an issue? Does the way I play a game affect your life? Does the color of my underpants matter to you?

Edited December 10, 2014 by Fiddlestyx

[DrD]

OP just wants to know, and has sparked an interesting discussion. And maybe wanted to show off a bit. So 'tis allright by me. (I'm sure you're all very relieved ha ha.)

[Dunbaratu]

My point is that it's really not "tricky"

Incorrect.

Even if the math operations are simple a process can still be accurately called "tricky" if the information you input into it is hard to assemble together and easy to make a mistake. Finding the sum of 10 numbers? Easy. Finding the sum of 10 numbers taken from a set of 100 numbers, which are hidden from view except one at a time so you have to keep notes on the side to do it - is extremely error-prone and therefore quite accurate to describe as "tricky".

The tedious nature of the work *causes* it to be tricky, because it activates the thing human beings are bad at - repetitive rote operations.

Human beings are actually good at math. What they're bad at, is *arithmetic*. It's a distinction people often fail to make.

When you use a tool to do dV for you, you're not doing it to save yourself from the math, although it has that side effect. You're doing it to save yourself from the arithmetic.

And manually tracking all the data is part of the boring arithmetic.

You know - the **tricky** part.

[Superfluous J]

Spreadsheets can be tedious, but using MechJeb or KER can be equally tedious. If the ship already exists, a mod can quickly tell how much delta-v it has, at least if the staging is simple enough and the ship never separates into multiple parts that continue the mission. On the other hand, a simple spreadsheet can quickly tell, whether a hypothetical design can satisfy mission requirements, or what kind of ship would be needed to satisfy the requirements. With MechJeb or KER, you'll have to proceed by trial and error and actually build a prototype.

I do not see the functional difference between spending an hour flipping numbes around in a spreadsheet or spending an hour in the VAB moving tanks and engines and stages around. Other than that the spreadsheet sounds like a terrible bore and the VAB is fun and there are little guys driving around and great music.

[Caelib]

Convenience.

[GoSlash27]

OP just wants to know, and has sparked an interesting discussion. And maybe wanted to show off a bit. So 'tis allright by me. (I'm sure you're all very relieved ha ha.)

Well, thanks... I guess :/

Inasmuch as it did spark a discussion, it wasn't the discussion I was intending. The relative merits of doing the math yourself vs. letting KER do it isn't the point. How other people prefer to play the game isn't the point.

I'm just saying that calling the process "hard" and steering people towards a mod is kinda absurd.

It would be the same thing if someone asked a question about flying planes and people were to say "flying planes is tricky. You should just get a mod with an autopilot".

Uhh... flying planes really isn't all that tricky; a lot of us do it all the time. Not bragging, not belittling those who have trouble flying planes. Not telling everyone else that they shouldn't use autopilots. Just sayin' "Maybe people who are asking for help in piloting would be better served with assistance in learning to fly a plane than they are by being immediately steered towards an autopilot mod."

Best,

-Slashy

Edited December 10, 2014 by GoSlash27

[Xavven]

I understand and appreciate that, but it's not what I'm saying.

I'm not a super math whiz and all the folks who have piped up in this thread and said it's not hard are not super math- whizzes (presumably). It just plain doesn't take a super math whiz to run this equation.

And yet... whenever somebody posts a help thread asking about DV, somebody will invariably come along and post (and this is a *direct quote*) "Calculating delta V is very tricky and it's best to get KER."

I would cite specific examples, but I believe it's bad form to call out other members personally.

My point is that it's really not "tricky" at all and it's doing a disservice to the guy asking advice to tell him it's hard and he should get a mod to do it for him.

People learn by doing, right? Why dissuade somebody from attempting to learn?

As several people here have pointed out, doing the math themselves opens up possibilities that they just plain wouldn't have with mods.

Best,

-Slashy

So what you really meant to do by posting this thread was to counter those folks discouraging people from learning how to calculate dV by hand. That's a totally amiable goal. If it were me, I'd have tried a different approach in my original post -- more like:

Hey, everyone! For those of you were were wondering how those mods like KER and MechJeb calculate delta-v, it's actually a pretty easy equation. If you want to do it by hand, by calculator, or by spreadsheet, and learn how this simple but powerful equation works, I encourage you to read my/this-other-guy's tutorial.

etc...

By now you've seen how your current approach has worked out for you. It has undertones of a condescending nature that riled up the forums a bit.

[Jouni]

Consider these four scenarios, where you might want to calculate delta-v and related quantities:

1. I want to fly a direct ascent mission to Duna. Does this rocket have enough delta-v to do it?
   
2. I want to fly an Apollo-style mission to Duna. Does this rocket have enough delta-v to do it?
   
3. The rocket didn't have enough delta-v. Can I scale it up to meet the mission requirements, or do I need a different design?
   
4. How large rocket would I need to meet the mission requirements?
   

Mods such as KER and MechJeb work well in scenario 1. In scenario 2, they do most of the work for you, but they can't tell whether the ship has enough fuel for the return trip. In scenarios 3 and 4, using the mods becomes tedious, as you have to build prototype rockets and proceed by trial and error.

With spreadsheets, making the initial template takes some effort every time you start using a different kind of staging. If the template already exists, reusing it is quick and easy. Filling in the part stats may initially feel tedious, but there are a lot of things that make it easier. You'll quickly learn the stats of the parts you use frequently. Almost all fuel tanks in the game are just multiples of the FL-T100 and the S3-3600, so you can treat them as such, making launch vehicles and transfer stages really simple. Most small parts are massless, so you can just ignore them in your calculations. You can always approximate: a lander with a Mk2 lander can and a lot of fluff could be a lander with 4 tonnes of payload. Finally, KER and MechJeb are useful tools, even if you are using spreadsheets.

I do not see the functional difference between spending an hour flipping numbes around in a spreadsheet or spending an hour in the VAB moving tanks and engines and stages around. Other than that the spreadsheet sounds like a terrible bore and the VAB is fun and there are little guys driving around and great music.

The next time you end up in a similar situation, you can either spend the hour in the VAB, or find the answer in a couple of minutes by reusing an existing template. You don't have to be a programmer to use a computer, but thinking like one certainly helps.

Besides, spreadsheets have much better UIs than the VAB.

[arkie87]

With spreadsheets, making the initial template takes some effort every time you start using a different kind of staging. If the template already exists, reusing it is quick and easy. Filling in the part stats may initially feel tedious, but there are a lot of things that make it easier. You'll quickly learn the stats of the parts you use frequently. Almost all fuel tanks in the game are just multiples of the FL-T100 and the S3-3600, so you can treat them as such, making launch vehicles and transfer stages really simple. Most small parts are massless, so you can just ignore them in your calculations. You can always approximate: a lander with a Mk2 lander can and a lot of fluff could be a lander with 4 tonnes of payload. Finally, KER and MechJeb are useful tools, even if you are using spreadsheets.

The next time you end up in a similar situation, you can either spend the hour in the VAB, or find the answer in a couple of minutes by reusing an existing template. You don't have to be a programmer to use a computer, but thinking like one certainly helps.

Besides, spreadsheets have much better UIs than the VAB.

I have to agree with 5thHorseman.

How exactly is a spreadsheet different than the VAB? A spreadsheet has a UI whereas the VAB has a GUI, so i would vote VAB is easier to use and more interactive.

Furthermore, a "template" for a spreadsheet is equivalent to a "saved craft" in the VAB, so i fail to see the advantage of a spreadsheet (other than learning how to calculate the numbers, and therefore, understanding the best/easiest/cheapest etc.. way to increase deltaV)

[Bill Phil]

Well, DV for a maneuver is hard if you take into account gravity losses. But DV of a vehicle is easy to calculate.

Ve(ln ( m1/m2) ) = DV

Ve = g * isp

[arkie87]

Well, DV for a maneuver is hard if you take into account gravity losses. But DV of a vehicle is easy to calculate.

Ve(ln ( m1/m2) ) = DV

Ve = g * isp

For a single stage rocket, with few parts, calculations are simple. But in the real world, it easily gets much more complicated than that...

As others have pointed out: what is dV for a craft with multiple engines, each with its own fuel mass burn rate and ISP?

And i think the reason it is "difficult", as others have said, is due to the looking up of information regarding the parts, and making sure to put them in the right column etc... the best analogy is it's like doing your taxes-- it's not necessarily "difficult" in terms of intellectual capability, but it is "difficult" to get the right answer, in the sense that it is easy to make a mistake...

[GoSlash27]

I have to agree with 5thHorseman.

How exactly is a spreadsheet different than the VAB? A spreadsheet has a UI whereas the VAB has a GUI, so i would vote VAB is easier to use and more interactive.

Furthermore, a "template" for a spreadsheet is equivalent to a "saved craft" in the VAB, so i fail to see the advantage of a spreadsheet (other than learning how to calculate the numbers, and therefore, understanding the best/easiest/cheapest etc.. way to increase deltaV)

The difference in this approach is that you can simulate the process of trial and error in the VAB that would take weeks or even months instantly with a spreadsheet.

Rather than simply telling you what a rocket you have already built can do (which is all these mods are capable of) it can instantly tell you far more important things, such as "which engine is best for this stage", Exactly how much mass this stage will have using the selected engine, and exactly which staging scheme is the least massive, or cheapest, etc.

Learning/ applying the math and using spreadsheets instead of mods allows you to design an optimal vehicle for a mission in a matter of minutes before you even get into the VAB. No trial and error, no assembly and disassembly, no nuthin'. Just plug in the requirements, pick your options, and you know exactly what you need to build before you start.

That's the power of using the math instead of a mod.

Best,

-Slashy

[Red Iron Crown]

How exactly is a spreadsheet different than the VAB? A spreadsheet has a UI whereas the VAB has a GUI, so i would vote VAB is easier to use and more interactive.

The spreadsheet lets you solve the equation quickly for different variables. The mods answer one question: How much delta-V and TWR does this design have? For that, the mods are faster, easier, and less error prone.

But there are other interesting questions. Like:

How many tons of tanks do I need to give this payload 2000m/s of delta-V?

How many tons of tanks and how many tons of engines do I need to give this payload 2000m/s of delta-V and a TWR of 0.5?

The spreadsheet can solve these quickly, whereas in-game it must be done by trial and error until the mods produce the numbers you desire. I'm not saying people shouldn't use the mods (I certainly use them and feel the game is incomplete without them), but they're not a complete replacement for spreadsheets. They're all tools in the toolbox of an amateur rocket scientist.

[Jouni]

I have to agree with 5thHorseman.

How exactly is a spreadsheet different than the VAB? A spreadsheet has a UI whereas the VAB has a GUI, so i would vote VAB is easier to use and more interactive.

Furthermore, a "template" for a spreadsheet is equivalent to a "saved craft" in the VAB, so i fail to see the advantage of a spreadsheet (other than learning how to calculate the numbers, and therefore, understanding the best/easiest/cheapest etc.. way to increase deltaV)

As I said, thinking like a programmer certainly helps.

In a spreadsheet, this rocket is essentially the same as this one, with a few numerical details changed. If you have built a launch vehicle with two pairs of asparagus boosters, you can reuse the same template to determine, whether it's worth having nine pairs of boosters in a 7-kerbal Eve lander, or would a simpler design with the same boosters arranged in three onion stages work well enough. It's much easier to reuse your earlier work, if you don't have to worry about superficial details, such as rockets and payloads.

[GoSlash27]

^ A very simple example to illustrate the point...

You are designing a mission to Duna and currently assembling the transstage. Your payload for this stage is 35 tonnes and you need to impart 1,500 m/sec at 1G acceleration.

To keep it simple for this example, we will just use 1 stage to do this job and assume vacuum Isp.

The question: What combination of parts will accomplish this task with the minimum stage mass?

KER won't answer this for you. How long will it take you in the VAB to answer this question?

A spreadsheet can answer this instantly, tell you exactly how many engines to use in the stage, how many tanks of what type to use, and tally up the stage mass and overall mass to apply for your booster stage.

Best,

-Slashy

*edit: double ninja'd!*

Edited December 10, 2014 by GoSlash27

[arkie87]

The difference in this approach is that you can simulate the process of trial and error in the VAB that would take weeks or even months instantly with a spreadsheet.

Rather than simply telling you what a rocket you have already built can do (which is all these mods are capable of) it can instantly tell you far more important things, such as "which engine is best for this stage", Exactly how much mass this stage will have using the selected engine, and exactly which staging scheme is the least massive, or cheapest, etc.

Learning/ applying the math and using spreadsheets instead of mods allows you to design an optimal vehicle for a mission in a matter of minutes before you even get into the VAB. No trial and error, no assembly and disassembly, no nuthin'. Just plug in the requirements, pick your options, and you know exactly what you need to build before you start.

That's the power of using the math instead of a mod.

Best,

-Slashy

I agree a spreadsheet is better for constrained optimization, but, for using trial and error to design a craft (which is the case i thought we were talking about), i think spreadsheets and mods to calculate delta-V are at the very least equals, though i think VAB is more user-friendly.

Returning to optimization: in my humble opinion, having a spreadsheet to automatically calculate the optimum spaceship/staging/TWR/deltaV/everything takes the fun out of the game, though, i would understand, if part of the fun for you was writing the code/making the spreadsheet template that would do those calculations/designs for you

[arkie87]

As I said, thinking like a programmer certainly helps.

In a spreadsheet, this rocket is essentially the same as this one, with a few numerical details changed. If you have built a launch vehicle with two pairs of asparagus boosters, you can reuse the same template to determine, whether it's worth having nine pairs of boosters in a 7-kerbal Eve lander, or would a simpler design with the same boosters arranged in three onion stages work well enough. It's much easier to reuse your earlier work, if you don't have to worry about superficial details, such as rockets and payloads.

At present, you are right, it is easier to substitute X fuel tank for Y fuel tank in a spreadsheet than in stock VAB.

However, if you use tweakscale (or if ever stock changed such that you only had one "fuel tank" part and used tweakables to adjust texture/length/diameter/fuel-type etc...) then VAB would be equivalent to a spreadsheet, no?

[GoSlash27]

I agree a spreadsheet is better for constrained optimization, but, for using trial and error to design a craft (which is the case i thought we were talking about), i think spreadsheets and mods to calculate delta-V are at the very least equals, though i think VAB is more user-friendly.

Returning to optimization: in my humble opinion, having a spreadsheet to automatically calculate the optimum spaceship/staging/TWR/deltaV/everything takes the fun out of the game, though, i would understand, if part of the fun for you was writing the code/making the spreadsheet template that would do those calculations/designs for you

Honestly, I allowed myself to get sucked into the discussion of which approach is "better" and that wasn't the point of why I brought this up.

You set your own criteria for which is the best way to play the game for you. It's not my place to dictate that to you.

Me *personally*, I get the most enjoyment from this game by achieving the most difficult goals in the most efficient manner possible with no guesswork, trial and error, or failures.

Turning the tables on that thought, would you find the game more enjoyable by not using KER and having no idea what your DV is, or less enjoyable? Some people actually prefer playing that way.

Your mileage may (and should) vary

Best,

-Slashy

[Superfluous J]

Amusingly, all the past few pages have given me is a desire for an in-game implementation of what you're all doing with spreadsheets.

I suppose I can see a spreadsheet instantly telling you how much fuel you'd need or whatnot, but so does a few seconds of alt-clicking your fuel tanks. And I use KER to estimate entire complex missions all the time, by building each piece of the mission backwards in time from landing on Kerbin to launching from Kerbin, and making sure the dV is sufficient at each stage.

I do agree that it all comes down to what you prefer. I have a friend who refused to use any info mods on his Eve lander and return. He also refused to use HyperEdit or any other way to test the ship other than launching each test from Kerbin. It took him months of fairly dedicated play. I have no clue how many hours but I'd not be surprised if it was triple digits. That is as distasteful to me as having so much information pre-flight that I may as well not even bother doing the mission. I like the middle ground where I can be pretty sure the ship CAN do it with the fuel it has, but all kinds of things along the way can cause all sorts of mayhem.

And with that I'll bow out, as this thread from the get-go has been off topic as Xavven mentioned a few pages back.

So what you really meant to do by posting this thread was to counter those folks discouraging people from learning how to calculate dV by hand. That's a totally amiable goal. If it were me, I'd have tried a different approach in my original post -- more like:

Hey, everyone! For those of you were were wondering how those mods like KER and MechJeb calculate delta-v, it's actually a pretty easy equation. If you want to do it by hand, by calculator, or by spreadsheet, and learn how this simple but powerful equation works, I encourage you to read my/this-other-guy's tutorial.

Edited December 10, 2014 by 5thHorseman