GoSlash27

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 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

^ 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.

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

'Zackly. And I must stress that this isn't shaolin monk level math. Not like I'm tooting my own horn over my uber math genius skillz. It's just really not difficult. Now having said that, understanding how the math works and actually working it by hand (at least for a while) can help you gain insights into the enginerding by answering questions that MechJeb can't answer for you, such as which engine is optimal for a given application or which staging scheme will get you the most DV for the least stage mass. Spreadsheets are invaluable for these answers and being competent (if not stellar) at algebra is very useful in building a better rocketship.

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.

Heck, not even all that tedious, really. It's just 4 numbers and one of those is a constant. It's just barely more time consuming than figuring out a tip at the restaurant. If there's anything that makes it tedious IMO, it's that you have to do it so many times... not that it takes much work (or brains) to do in a single iteration. Best, -Slashy

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

Why does everybody keep saying that calculating DV is "hard"? There's nothing hard about it. It's a straightforward equation. I've never used anything to calculate it for me other than spreadsheets, and in those cases I programmed them myself. I'm not a math genius or anything, it's just really not complicated. Other than a single natural log, it's literally *all* multiplication and division. Not even much of that. a/b. Take the log of that. Multiply the answer by c and d. That's it. Best, -Slashy

This is a matter of docking 2 ships at different energy levels; like sinking a 3 pointer from the other side of the planet. The ship at the higher circular orbit has more velocity than the intercepting ship on the Hohmann transfer from lower orbit. How is one supposed to match speed with all of the standard methods disallowed? I dunno, but it'll be interesting to find out. Best, -Slashy

I'm not a huge sci-fi bookworm, but the stuff I like tends to run more towards "hard" sci-fi. Heinlein and Steele are nearly always good. Have you read The Martian by Andy Weir? Best, -Slashy

The opening lines of the book I'm currently engrossed in are incredibly appropriate here... Seriously, there's not a blessed thing we can do about something like that. We can try to divert it, but we will fail. We can try to get humans off the planet, but they will only die in space. We can try to hunker down in shelters and try to survive long enough for life to reestablish itself outside, but we would merely go extinct. All I can think of worth doing is to stockpile seeds and animals, enough humans and supplies to make it until the sun comes back and then immediately begin repopulating. Best, -Slashy

^This. 10char -Slashy

Also agreed here. Long way around to the point that we all agree on: When we refer to DV, we are actually referring to energy although we do not *express* it as such. It is far more convenient for us to work in terms of DV, much like a pilot will prefer to calculate fuel economy in terms of minutes. Best, -Slashy

To the contrary; *everybody* does that here. The fact that it's incorrect is why we have the Oberth effect. When we refer to DV maps, we are treating m/sec as if they were Joules. When we apply the rocket equation, we are treating m/sec as if they're Joules. When we say "it takes 4,500 m/sec to get to LKO" we are talking about m/sec as if they're Joules. It's incorrect in the same sense that expressing speed in units of distance is incorrect. We all do it even though it's incorrect because it works. Or at least well enough to get by. Best, -Slashy

This is actually precisely what I'm saying, although I must stress that Red Iron Crown is absolutely correct in stating that it's incorrect to use it this way. In addition to describing potential chemical energy in a rocket, we also use it to describe changes in kinetic energy and losses due to gravity and drag. This is not the proper way to use the term either... it's just how it's used. Best, -Slashy

It's a case of the two of us saying the exact same thing from opposite ends. On the "No DV map" thing, You've already answered that. If somebody tells you it takes precisely a certain change in velocity to get to Duna, then you'd point out (correctly) that it's not so. What it *takes* is a precise change in kinetic energy. Nevertheless, we have these DV maps and treat DV as if it's energy. That's my point... Best, -Slashy

You are, of course, 100% correct, so I'll revise the statement: Delta V is *used as* an offhand representation of energy. It *should* only represent a change in velocity, but how it is applied in orbital mechanics (and around here) is as a measure of energy. It is incorrect to use it this way (which is why we have the Oberth effect and variations in the DV maps), but it's how it's done and how it should be thought of. I didn't want to get this far in the weeds, and technically DV is only a change in velocity. Also technically there is no such thing as a "DV map" and rockets do not "have" DV. When we speak of "DV budgets" to complete missions, we're talking about energy. When we talk about a burn to Jool, we're talking about kinetic energy. When we talk about building a rocket to "have" a certain DV, we're talking about potential energy. We use DV as a shorthand description of Joules. It's not correct, it's just how it's done. Best, -Slashy

1) Just wasteful. 2) The delta v represents energy. It's the chemical potential energy in your rocket and also the kinetic energy of orbit+ energy lost as heat and noise during the ascent. the formula is the Isp of your engine(s) x 9.81 x the natural log of ( the mass of your rocket fully fueled/ the mass of your rocket dry). 3) It's for a low orbit. Best, -Slashy

I fed your post into Google Translate and I get the gist of it. IMO the best fix for long burn times is reducing the payload. It looks like you're bringing a lot more mass to Jool than you really need. Likewise, you're bringing a lot more fuel to burn pushing that extra mass, and then still more fuel and structure to push that extra fuel. That all translates into extra workload for your engines, which means longer burn times. The best way to go about it is to figure out your DV budget for each phase of the mission, add maybe 10% for safety factor, and then build to the minimum mass that will accomplish that goal. Always look for ways to trim off excess weight. Other than that, you will have to live with longer burn times. You can help mitigate that by breaking up the burn into multiple passes. Instead of 1 burn in 1 orbit for 15 minutes, do 3 burns in 3 orbits of 5 minutes each. Trickier to get your timing right that way, but much more efficient. Best, -Slashy

Tsevion, -Slashy

I'm looking forward to this movie. I enjoyed his re-spins of the Star Trek franchise for all the reasons so many Star Trek fans hated them. The old Star Trek movies were boring, his weren't. Likewise, I can tell from the teaser that he's fixed what I hated about Star Wars: Lucas has ADD and it was only the technical and budget limitations that enabled him to make the first couple movies watchable. Abrams has simplified things, gone back to the "used universe" concept, and put the focus back on special effects. The only bad news is I gotta wait a whole year to see it YMMV, -Slashy

This gets into personal preference, but from a standpoint of maximum efficiency... SSTO spaceplanes are really only optimized for making the trip from KSC to LKO and back with kerbals and/ or supplies. Any mission beyond that is best- served with a craft optimized for the task. If I'm going to Laythe, I will 1) Lift the sections of a Kerbin-> Laythe mass mover and assemble them in orbit using an SSTO bulk lifter 2) Lift a Laythe SSTO spaceplane as payload using an SSTO bulk lifter 3) Get the crew and supplies into orbit using an SSTO spaceplane 4) Use the mass-mover to handle interplanetary logistics. Of course, the beauty of KSP is that it allows you the freedom to tackle the challenges as you want. Best, -Slashy

Wandering off into the weeds, and sadly... I'm leading the way. 17* is the best lift/ drag, whereas 26* is the max lift. So if anyone is wondering, this is why I set 22* as the maximum angle of attack for launch envelopes. Best, -Slashy

We've got the balance that we want, so first we remove all intakes and engines. Now with symmetry turned off, we place only the intakes meant to feed the left engine. Next, we place only the left engine. Then we repeat the process for each remaining engine. Place only the intakes for the right engine Finally, place only the right engine. This helps trick the game into doing what we intended. Now it will 1) Draw air from the left intakes 2) Feed the left engine 3) Draw air from the right intakes and 4) Feed the right engine. Let's give it a go. It now gets much higher and faster without spinning out of control. We still have some yaw starvation effects, but they are tempered down enough to where they are manageable. This is because excess air still gets carried over to the universal pool and one engine will always flame- out first. There's no way around this limitation in the game engine, but there are ways to mitigate it's effects... 1) Don't go multi- engine if you don't have to. Feeding one engine is easier to manage. 2) Place your engines as close to centerline as you can. When one engine dies, it won't yaw so bad. 3) Use some reaction wheels for yaw authority. When one engine flames out, it won't spin you as quickly. 4) Throttle down earlier to keep the engines from flaming out. No flameout= no yaw and finally... 5) Set it up so that the engines closest to the centerline flame out first. Maybe give them a little less intake area... Stay thirsty, my friends! -Slashy