Calculating DV is "hard"??

[Hary R]

I will say that the answer is simple, anyone can do the calculation but does everyone have the will to do it. It have been said multiple time (beware no pun intended), it's time consuming and in ksp, time is what we don't have.

I speak for myself but i'm using mechjeb dv reading just because i don't have time to do the math. I don't have hours and hours of free time to do one launch and make all NASA type preparation with all the math involve.

Well in short, the math may be simple (and it is) but I (myself) don't have time to bother with that.

[Rusty6899]

It's easier to do the calculations yourself. You can set up an excel spreadsheet with cells for the required variables. Pick an engine, put in your payload and required delta-V for the stage, and rearrange the Tsiolkovsky equation to give you the required amount of fuel to get there. This way you can design your rocket and know how far it will go before you even get to the VAB.

[Xavven]

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

I don't mean to be rude, but what I've been trying to hint at is that, the equation itself aside, saying, "man, I don't get why it's so hard for you guys" is not going to win you many friends. I devote about 5% - 10% of my workweek training new and veteran employees alike on concepts I learned early in my career and consider elementary and second nature to me. I've learned that it's important to be respectful of my teammates no matter their age and experience. Someone always knows something you don't, so a little humility goes a long way. Just trying to help.

[Hannu]

It's easier to do the calculations yourself. You can set up an excel spreadsheet with cells for the required variables. Pick an engine, put in your payload and required delta-V for the stage, and rearrange the Tsiolkovsky equation to give you the required amount of fuel to get there. This way you can design your rocket and know how far it will go before you even get to the VAB.

What do you mean when you say "easy"? Of course you can do Excel sheets or separate programs, but I do not see any easier things on them than mod which shows automatically a window with wanted information. You do not have to put values to any other program. And when you change the vessel, the mod updates information immediately. If you use separate sheet, you have to update masses by hand after every change. Especially if you have a complicated staging sequence and fuel lines, things will be very complicated and probability of error is high. And again, Mechjeb or other mod calculates everything in a microsecond and shows results in very clear format.

What is easy in mathematical sense varies. Even basic school math is difficult to most adults who are not interested in maths and do not need it in their works. On the other hand, rocket equation is theoretically very easy thing to them, who have scientific education, but as many have said, it needs lot of work and errorless transfer of many values from game to calculation.

[MockKnizzle]

OP: "Here's a generalization."

Everyone else: "Well, from my experience that generalization isn't really true."

OP: "But that's just you, here's the same generalization anyways."

"Hard" is relative. Looking at a number that's already on my screen is easier than typing lots of numbers into a calculator or spreadsheet. Thus, hand-calculation is harder.

[Cirocco]

okay, my two cents.

to see wether or not calculating delta-V by hand is hard, we first need to define what "hard" is. Personally, I go by the definition that if it is not easy to correctly and repeatedly attain the desired result, then something is hard. Note that this is very different from something being complex. If doing something involves a task that is extremely simple, but needs to be executed a very large amount of times with a 100% accuracy and no room for error, then the overall task is very hard even though it is made up of extremely simple parts (humans very easily make mistakes when performing repetitive tasks).

That is I think the case with calculating delta-V. As slashy stated before, it's not super complex: once you have your input data, it's just one logarithmic function and a couple of very simple calculations. Thing is, in order to get the desired input data (wet mass, dry mass, etc), you need to do a LOT of addition of different parts of your ship. That is a very tedious task in which it is extremely easy to make a mistake (I speak from experience. My first Eve return vehicle designs were laughably underpowered because I forgot to add the mass of a part here or there on the final ascent stage). Add to that the complexity that comes in when you start using asparagus or some other more intricate staging, and it becomes (in my experience) best left to mechjeb/KER/other software because said software will do all these calculations for you without error.

And of course once you go into an atmosphere, delta-V calculations get very complex very quickly. We're talking differential equations if you want to be accurate over a full ascent profile in atmosphere.

in short: are Delta-V calculations too complex to do by hand? Not if you got the hang of it and have all the needed input data. Is it difficult to reliably achieve a high degree of accuracy when done by hand? Yeah, pretty much.

As with all things in this game: play however you prefer and don't feel a single bit bad if other people do it differently.

[J.Random]

Why does everybody keep saying that?

Who exactly is this Everybody you're talking about? I don't know this guy.

[Red Iron Crown]

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?

Not as far as I know, at least not directly. KER doesn't calculate dV requirements for any maneuvers at all, it just gives information about the vessel.

[GoSlash27]

I don't mean to be rude, but what I've been trying to hint at is that, the equation itself aside, saying, "man, I don't get why it's so hard for you guys" is not going to win you many friends. I devote about 5% - 10% of my workweek training new and veteran employees alike on concepts I learned early in my career and consider elementary and second nature to me. I've learned that it's important to be respectful of my teammates no matter their age and experience. Someone always knows something you don't, so a little humility goes a long way. Just trying to help.

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

Edited December 10, 2014 by GoSlash27

[rkman]

It only takes a few seconds with a scientific calculator, and happens instantly with a spreadsheet.

So the difference with Mechjeb is that MJ is in the game, not outside if it, and it has the formula already programmed.

So what's the big deal?

Most people don't do math, so having a major aspect of the game depend on calculations to be made outside of the game is a bad idea.

[John FX]

Well the formula really really is not difficult. It can be done many ways easily.

It`s not a game though, it`s working out the same formula.

How many times can you put numbers into the same formula and find it fun or interesting?

Obviously there are some people that can do it all day over and over but a lot of people don`t find that fun the first time and most people don`t find it fun to do more than a few times.

They think all day for their jobs and want to play something fun when they get home, like a video game.

A lot of people who think for a living have a passing interest in space and rockets and find them fun.

They want to build rockets, have displays similar to the ones in a space program and do fun missions.

Using office is not fun if you use office for your job. Spreadsheets are not fun or a game, they are like work.

What people are saying is it is `too hard to get fun from` and a game is supposed to be fun.

So the situation can arise where it can be too hard to be fun in a game but not hard to do.

TL;DR

I hope that helps understand why people say "it is too hard."

It`s not hard, it`s just not fun.

They are saying

"It is too hard (to be fun so I do not want to do it)"

not

"It is too hard (and I am unable to do it)"

[Comet Tail]

It's tedious. I use Mechjeb.

The fun is in calculating mission delta-vee's. Hohmann transfers, descent/ascent trajectory dv costs... But the best stuff has to be when you've got a non-Hohmann transfer and it's time to crunch some real numerical solutions on a spreadsheet, or trying to work powershot trajectories

Dv(1) = Sqrt(u/r₁)(Sqrt(2r₂/(r₁+r₂))-1)

(u = GM, r₁ = radius if smaller orbit, r₂ = radius of larger orbit)

v² = u (2/r - 1/a )

(r = current radial distance to center of major body, a = semi-major axis, u = GM, v = current velocity)

When you have Hohmann transfer and the vis-viva equations memorized, then you're on your way to becoming a hardcore aerospace enthusiast

[NeMeSiS]

You do it by hand a few times, then decide (rightly) that doing it by hand sucks and gin up a spreadsheet,

You dont make a spreadsheet, you write some code that calculates deltav for you ingame while building your rocket.

Edited December 10, 2014 by NeMeSiS

[Superfluous J]

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."

It all depends on what the people ask. "How do I find the dV of my rocket" or (more common) "How can I tell how far my rocket will go?" is a very different question than "could someone detail out the rocket equation for me?"

The former two questions want the number. They - like the vast majority of us, don't care how the numbers are derived so long as they're accurate. Pointing them at the rocket equation is doing them as much a disservice as would be telling the latter to "just use Kerbal Engineer."

[Red Iron Crown]

You dont make a spreadsheet, you write some code that calculates it for you ingame while building your rocket.

The spreadsheet lets you do more, though. You can start with payload mass, dV requirement, and minimum TWR and have it calculate how much tank and engine mass are required.

[moogoob]

Sure, I *could* do the delta-v calculations if I wanted to, but Mechjeb not only does that for the vessel, but for each stage as well AND gives surface TWR and burn time on top. And I don't have to reach for paper and a calculator. Sure it's simple algebra (with a tiny bit of trig) but that's why I don't do it by hand - there's a much more convenient method out there and that's why it's one of the whole 2 mods I have installed. (the other being Fine Print)

[Jouni]

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.

[zarakon]

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.

There are a couple of "tricky" things about it

- It's easy to make a mistake when adding up numbers from a large number of parts

- Staging that involves crossfeed, droptanks, and/or detachable boosters gets kind of complicated

[Norpo]

I don't do it because I don't want to get the statistics from ALL the parts in a single stage (Which could be a LOT for larger rockets), add all that up, and then patch it through the rocket equation. This could take minutes (And then i'd have to change the rocket if the numbers were inadequite). Next, do that for every stage. 6 minutes. not TOO long, but then i'd have to recalculate some stages after I change them to be more effecient. 10 minutes. This makes making rockets LONGER, almost twice as long. It's not too hard, but remembering all the values of the parts is just tedious.

Sure, I could, but KER can do it for me in 2 seconds, so why bother?

[brdavis]

Sure, I could, but KER can do it for me in 2 seconds, so why bother?

If all you are interested in is the quickest least-bothersome way of doing something…

…go watch other people play on Youtube

Seriously, for some of us the "fun" of something like KSP is very much a DIY attitude: I have to build the ship. I have to do the staging, and throttle control, and plan maneuver nodes, etc., etc. ALL those things take effort… and ALL those things can be automated. But if all you want is automation… this is probably not the sandbox you're looking for.

My son (high school senior), like me, designs all his rockets using paper and pencil and a simple calculator. He's bugging me to teach him how to calculate ejection angles (he already knows simple transfers, how to calculate when a launch window is, different ways of changing inclinations). The joy for some of us is in working out the details.

And, as a consequence, when it comes time to plan a multi-component mission to Duna and back with the spacecraft being reconfigured and refueled, with strap-on cross-fed boosters and complex stain schemes… it's not only doable, but doesn't involved a bunch of experimentation and trails and error. I'm not limited to what a tool like KER can provide me with… I can do anything I want, and it's not even a huge step in complexity.

People don't run marathons because they need to get to someplace 26.2 miles away. The way you get there is (in many cases) even more important than the destination.

[UmbralRaptor]

Brushing off the equation as excessively complicated seems like a bad approach -- it's only excessively complex if your rockets are. I would lean towards introducing formula first, the major consequences, and then mentioning MJ/KER/VOID/whatever.

[lajoswinkler]

Why would you need to calculate it? If you have Kerbal Engineer Redux installed which shows you delta v and TWR, and you peek into one of those KSP apps which calculate the needed delta v for an orbital maneuver, you're good to go.

[purpletarget]

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)

[GoSlash27]

Brushing off the equation as excessively complicated seems like a bad approach -- it's only excessively complex if your rockets are. I would lean towards introducing formula first, the major consequences, and then mentioning MJ/KER/VOID/whatever.

All of this to get this^ point, which is what I've been trying to say.

Thank you!

-Slashy

[Vaporo]

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.

This about sums up my opinion of it. Actually doing the calculations isn't difficult, but if you're changing your rocket a lot and you want to know how much Dv you have, it's tedious to have to A: Launch the rocket. B: Get the rocket's mass. C. Run the calculation. EVERY TIME you want to check to be sure that those seperatrons you added didn't take your Dv below the minimum required for the mission. And asparagus staging... I would imagine that calculating Dv for an asparagus rocket would be comically tedious. If I didn't already have MechJeb, I might even have looked into learning C# and making my own Dv calculator plugin.