Calculating DV is "hard"??

[GoSlash27]

Why does everybody keep saying that?

I see it all the time on this forum. "Leave it to MechJeb". "It's super-complicated". Stuff like that.

Uhh... I ain't exactly a math perfesser, and I solve this equation all the time by hand. Heck, it's easier than most of the math people deal with on a regular basis.

Take "a" and divide it by "b". Now take the natural log of that. Now multiply that by "c" and "d".

What's so difficult about that?? It only takes a few seconds with a scientific calculator, and happens instantly with a spreadsheet.

So what's the big deal? Is it the natural log that scares people? 'Cuz the rest is all just 5th grade multiplication and division, and there's not even much of that.

Curious,

-Slashy

[Superfluous J]

I never said it was hard, though doing natural logs by hand sounds more like punishment than math. I just don't want to do it.

I play KSP to fly rockets, not solve math equations. Also, computers were originally designed to do exactly this kind of drudgery for us, so it seems weird to do the drudgery specifically to do something I wouldn't otherwise be able to do without the computer (Play KSP).

[zekes]

this is my go-to thing. that, and Kerbal Engineer.

http://www.strout.net/info/science/delta-v/

[Starman4308]

It's not hard.

It's tedious, slow (particularly when summing a lot of part/fuel masses), and you have better things to do than manually grind out dV.

[GoSlash27]

I never said it was hard, though doing natural logs by hand sounds more like punishment than math. I just don't want to do it.

I play KSP to fly rockets, not solve math equations. Also, computers were originally designed to do exactly this kind of drudgery for us, so it seems weird to do the drudgery specifically to do something I wouldn't otherwise be able to do without the computer (Play KSP).

I never said that *you* said it was hard

But a lot of people around here portray it as something 3 shades deeper than deciphering heiroglyphics.

Setting aside the solving natural logs by hand (which is something nobody does), it's not "hard". Tedious for sure if you do it throughout the design process just due to sheer repetition, but not anything that could be rightfully described as difficult.

[RainDreamer]

It is not hard. All the equations are already available and numbers just needed to be plugged in. It is just a pain to do, especially for the average person like me who isn't that interested in math. Having a simple, dynamic read out of dV is much more convenient.

[Reactordrone]

It's not hard.

It's tedious, slow (particularly when summing a lot of part/fuel masses), and you have better things to do than manually grind out dV.

There's not much summing to do. The information button in map view gives the vehicle mass and if you know each unit of fuel/oxidizer weighs 0.005t it's easy to work out how much fuel is left in the tank. The only time you really need to sum up part masses is if you're working out mass drops due to staging.

[Specialist290]

It's certainly a legitimate question; however, it's less a gameplay question (EDIT: That is, a "How do / why should I do / what do I need to do [x] in the game?" question) and more one about different player habits. Therefore, I'll be moving this to General Discussion.

Remember to keep things civil

Edited December 10, 2014 by Specialist290
Clarifying note.

[SkyRender]

"Tedious" and "hard" are often terms used interchangeably when it comes to maths. While it is true that it isn't difficult to calculate dV, it does takes far less time to use a mod like Kerbal Engineer Redux to do the calculations for you on the fly. Why spend the extra time doing it by hand when it doesn't add anything to the experience and you can basically have a mod handle it for you?

[JenBurdoo]

It's not difficult, but it's time-consuming, and difficult for a layman to remember. I've never liked math, and I don't want to take several minutes out of my playing time and a bite out of my crappy computer's memory to bring up the formula and calculator, figure out which numbers go where and probably get them wrong...

That's not to say that it isn't useful. If you're using KSP in a classroom, it can even be fun because the student will get to see the result of his calculation. But for an ordinary gamer...

[Red Iron Crown]

None of the math is beyond anyone with a scientific calculator (most smartphones have a suitable app). It is tedious though, especially in a staged setup. I rely on mods to calculate it, makes the game more fun and less like math homework.

That said, I'm glad I learned to do it by hand first. Running it step by step on a few different designs helped me understand the relative importance of mass ratio and Isp and that rockets scale linearly with payload mass for a given delta-V requirement.

Writing a spreadsheet for calculation was also helpful in this regard, and I still use it when designing with dV requirements as a starting point rather than a result (in-game dV calculators only verify results for that sort of design).

[GoSlash27]

"Tedious" and "hard" are often terms used interchangeably when it comes to maths. While it is true that it isn't difficult to calculate dV, it does takes far less time to use a mod like Kerbal Engineer Redux to do the calculations for you on the fly. Why spend the extra time doing it by hand when it doesn't add anything to the experience and you can basically have a mod handle it for you?

Fair question, and here's the answer:

Doing the math the hard and tedious way can help people answer questions that mods like KER cannot answer. Which engine is the best to use for a given stage? How many staging events should I use for my launch vehicle for least mass? At what point does it become economically viable to use liquid boosters instead of solid?

You do it by hand a few times, then decide (rightly) that doing it by hand sucks and gin up a spreadsheet, and then you're building better rockets than you could otherwise build and accomplishing things that you couldn't otherwise do.

The math is tedious and it sucks, but it *is* your friend and it will help you if you let it.

I'm not questioning whether or not the math is drudgery, but rather why people speak of it in awe- struck tones like it's actually difficult.

Best,

-Slashy

[Xavven]

I use a spreadsheet to calculate dV because it gives me more flexibility than KER ever could. That said, I am one of the FEW gamers that go as far as using Excel for ANY game. The vast majority of players out there do not find that level of theory interesting or fun.

It's good to hear that math is something that comes so naturally to you. Hopefully you're in a STEM field or are on your way to starting a career path in STEM. That said, it can't hurt to refrain from belittling people who aren't as good at something as you are. You don't become a good leader by bragging.

[cantab]

The rocket equation is indeed pretty easy to use. The problem is getting the values. As Reactordrone says, you can put the ship on the launchpad and get the full mass, but the method is really non-obvious. Totting up part masses gets very old very fast.

Manual calculation is fine for serially staged rockets. It's also simple, if tedious, for asparagus staging. For non-asparagus parallel staging though it's much more complicated, you need to do fuel drain calculations for the core and possibly weighted Isp averages for when you're flying with the boosters. I'll happily let KER handle that.

Of course there are situations even KER can't handle. Any ship which expends some delta-V with a payload then more without that payload cannot have its delta-V calculated independently of its flight plan. This includes Apollo-style missions.

Edited December 10, 2014 by cantab

[GoSlash27]

None of the math is beyond anyone with a scientific calculator (most smartphones have a suitable app). It is tedious though, especially in a staged setup. I rely on mods to calculate it, makes the game more fun and less like math homework.

That said, I'm glad I learned to do it by hand first. Running it step by step on a few different designs helped me understand the relative importance of mass ratio and Isp and that rockets scale linearly with payload mass for a given delta-V requirement.

Writing a spreadsheet for calculation was also helpful in this regard, and I still use it when designing with dV requirements as a starting point rather than a result (in-game dV calculators only verify results for that sort of design).

^ This about a kajillion. Especially that first sentence.

It's not beyond anyone with a scientific calculator to fathom, and if you're running KSP, then you have access to a scientific calculator. If you can figure out how to program a spreadsheet, then you can already do what the mods do. And if you have a passable knowledge of algebra, then you can do things that the mods can't.

But the overriding sentiment is in that first sentence; it's not "beyond" the average player to grasp the concept. It's not a difficult equation.

[Red Iron Crown]

Of course there are situations even KER can't handle. Any ship which expends some delta-V with a payload then more without that payload cannot have its delta-V calculated independently of its flight plan. This includes Apollo-style missions.

The workaround I use for this is to run a "simulation" in the VAB. Build ship with payload, then remove fuel from the tanks until the point where the payload is meant to be dropped, then remove the payload and KER will calculate the non-payload dV correctly. This technique can be also used for more complex mission profiles, like a lander that undocks from an orbiter and later redocks with less fuel on board. Some manual addition/subtraction is still required, but it's much quicker than doing the whole thing by hand.

Edited December 10, 2014 by Red Iron Crown
Silly typos.

[GoSlash27]

I use a spreadsheet to calculate dV because it gives me more flexibility than KER ever could. That said, I am one of the FEW gamers that go as far as using Excel for ANY game. The vast majority of players out there do not find that level of theory interesting or fun.

It's good to hear that math is something that comes so naturally to you. Hopefully you're in a STEM field or are on your way to starting a career path in STEM. That said, it can't hurt to refrain from belittling people who aren't as good at something as you are. You don't become a good leader by bragging.

I gotta stress this: It ain't about math coming naturally to me or anybody else. You don't have to be RainMan to get how the rocket equation works. Telling others that it's too difficult to understand doesn't really help them. It's not that I or the others here have some super-human abilities to grasp this stuff, it's that it's not as tough as people make it out to be.

Best,

-Slashy

[Xavven]

The workaround I use for this is to run a "simulation" in the VAB. Build ship with payload, the remove fuel from the tanks until the point where the payload is meant to be dropped, then remove the payload and KER will calculate the non-payload dV correctly. This technique can be also used for more complex mission profiles, like a lander that undocks from an orbiter and later redocks with less fuel on board. Some manual addition/subtraction is still required, but it's much quicker than doing the whole thing by hand.

Sincere question here: can KER calculate Bingo fuel level? In other word, the exact reading of liquid fuel and/or oxidizer at which I must abort mission and return to Kerbin?

[Xavven]

I gotta stress this: It ain't about math coming naturally to me or anybody else. You don't have to be RainMan to get how the rocket equation works. Telling others that it's too difficult to understand doesn't really help them. It's not that I or the others here have some super-human abilities to grasp this stuff, it's that it's not as tough as people make it out to be.

Best,

-Slashy

Think of it this way... a car mechanic is thinking the same thing when he hands me the $1000 invoice to fix my car. I'm sure I could learn how to undo a few bolts and replace my timing belt, but I don't have the time or the patience to learn that. Similarly, my employer pays me to do stuff that I personally feel is easy. But as it happens, my skillset is rare enough that it pays well.

[klgraham1013]

I used to calculate it by hand when I was anti-mod. I finally grew tired of the tedium and installed Engineer. In the end, it's made building multistage, complex rockets much more enjoyable.

[GoSlash27]

Think of it this way... a car mechanic is thinking the same thing when he hands me the $1000 invoice to fix my car. I'm sure I could learn how to undo a few bolts and replace my timing belt, but I don't have the time or the patience to learn that. Similarly, my employer pays me to do stuff that I personally feel is easy. But as it happens, my skillset is rare enough that it pays well.

Where the analogy falls flat is the differentiation of what various individuals find "easy".

My niece just called me to verify her math homework, and it's more difficult than solving a DV equation.

She's 9 years old. And not like she's in an advanced class or anything, this is just regular old elementary school arithmetic.

I can understand that the rocket equation is tedious/ sucks/ you don't wanna do it and I agree, but "difficult"? It's not at all difficult.

And please understand when I say "you" but I don't really mean *you* personally. Just something that I see around here a lot from people in general.

Best,

-Slashy

[Jason Patterson]

The issue isn't that the rocket equation itself is hard. It's that it's very easy to make a mistake when you're dealing with a staged rocket (which we all are nearly every time we're building a rocket) with hundreds of parts and engines with multiple Isp, and some of the parts are physicless and shouldn't be included in the total, though the game doesn't tell you which.

Can I do the math? Absolutely, and I agree that for anyone who wants to be sufficiently careful, it's not particularly difficult to do any one step in the process. Do I feel that it's valuable to understand the math? Absolutely. Do I feel that it's worth any of our time to actually do the calculation (for a complicated rocket) with anything short of a spreadsheet? No, not even a little bit, unless that person enjoys doing arithmetic for fun. Doing it with a calculator alone seems like a route to frustration when you repeatedly miss a part or mistype a mass.

There are good tools to do the job. If there is some particular value that you wish to know that is not given by one of those tools (or, again, if you just enjoy the DIY of it all) then go for it, but doing this yourself is on par with doing long division by hand. We all know how to do it, but if we have a calculator, there is little reason to go through the steps.

[FITorion]

Why does everybody keep saying that?

I see it all the time on this forum. "Leave it to MechJeb". "It's super-complicated". Stuff like that.

Uhh... I ain't exactly a math perfesser, and I solve this equation all the time by hand. Heck, it's easier than most of the math people deal with on a regular basis.

Take "a" and divide it by "b". Now take the natural log of that. Now multiply that by "c" and "d".

What's so difficult about that?? It only takes a few seconds with a scientific calculator, and happens instantly with a spreadsheet.

So what's the big deal? Is it the natural log that scares people? 'Cuz the rest is all just 5th grade multiplication and division, and there's not even much of that.

Curious,

-Slashy

Can you do it in your head? No. Then it's hard.

Do I need to look away from the game and do something else with my hands or a different program? Yes? Then it's hard.

Even just adding up all the masses of the craft is too hard to do while still playing the game. That's where all the mods come in. They do the ... not so complicated yet time consuming... calculations for you instantly and present the results to you. So you don't have to pause the game and go do math or set up a spread sheet when you otherwise could have been playing the game.

Edited December 10, 2014 by FITorion

[LethalDose]

The question in the OP has been answered multiple times:

• It's not hard, it's tedious
  
• The requisite information is a headache to get without mods
  
• It takes time away from playing the game
  

Basically, anyone who understands the rocket equation well enough to use it isn't going to find it technically challenging to solve, but there are other reasons to not want to calculate the values by hand for every stage in the rocket, namely the tedium.

You're just generalizing this "Everyone says ..." again, even though it's nowhere near accurate. And everytime a specific person answers the questions, you answer "not you", but then still refer back to "the general community". It appears as if there's simply no-one that you'll actually accept answer from...

Seriously, this thread just need to be locked. It's just trolling.

Edited December 10, 2014 by LethalDose

[zarakon]

It's just tedious

First of all, the stock editor doesn't make the full mass and dry mass readily available. Add in staging, especially asparagus, and just getting all the mass numbers is a big pain

It also becomes tricky and even more tedious when you have fuel crossfeed and/or multiple engine types to figure out.