Amagi82

I'm having some difficulty figuring out the math for transferring from orbit around one planet/moon to the orbit around another. I know about all the charts that provide the approximate values, but I'd like to know the mathematical equations necessary to calculate the exact values. So far, using the Vis-viva equation, along with Hohmann transfer calculations, I've managed to get accurate values from the surface to orbit around a body at a specific altitude, with or without atmosphere, I can calculate orbital velocity at a specific altitude, I can calculate the speed I need to be traveling when I leave the SOI to reach another planet/moon, and I know the speed I will be traveling when I enter the SOI of the target body. What I have not been able to calculate is exactly how much delta V I'll have to expend at a given periapsis altitude to escape at the desired velocity. Re-arranging the Vis-viva equation, with a as the semi-major axis, I get: a= 1/((2/r)-(v^2/u)). But this is giving me incorrect values for a from what I know to be the correct answer. Anybody know the math and willing to walk me through it here? Thanks!

What's the exact equation being used here? It's been a long time since math class. I managed to figure out everything before this part, but I've tried several different equations here and I keep getting wildly incorrect results. Oh, and I know I'm dredging up an old thread, but thanks for posting this! I've been learning a lot.

From sea level, with a perfect ascent, just barely clearing Eve's atmosphere, you need: 11,582.77 dV From Eve's highest peak, at 7,526m, with a perfect ascent, just barely clearing Eve's atmosphere, you need: 5,263.15 dV You aren't going to have a perfect ascent, so I'd recommend bringing more than that. Shoot for a thrust to weight ratio of around 2.0, and make sure you're getting Eve TWR, not Kerbin TWR. The above math just goes to show you how huge the difference is between a surface ascent and an ascent from high altitude.

// Delta V to reach orbit around a body with no atmosphere, from sea level, r1 is the equatorial radius public static double getToOrbit(double gravParameter, double r1, double orbitHeight, double siderealRotationVelocity) { double r2 = r1 + orbitHeight; return Math.sqrt(gravParameter / r1) * Math.sqrt((2 * r2) / (r1 + r2)) + (Math.sqrt(gravParameter / r2) * (1 - (Math.sqrt((2 * r1) / (r1 + r2))))) - siderealRotationVelocity; } // Additional Delta V to reach orbit around a body with an atmosphere public static double getToOrbitAtmo(double surfaceGravity, double scaleHeight, double terminalVelocity) { return (4 * surfaceGravity * scaleHeight) / terminalVelocity; } // Get terminal velocity at a specific altitude. public static double getTerminalVelocity(double surfacePressure, double altitude, double scaleHeight, double planetMass, double equatorialRadius) { double G = 6.67e-11; // Gravitational constant double r = equatorialRadius + altitude; double atmosphericDensity = 1.2230948554874 * surfacePressure * Math.exp(-altitude / scaleHeight); return Math.sqrt((1250 * G * planetMass) / (r * r * atmosphericDensity)); } For Kerbin: Double toOrbit4 = (getToOrbit(3.5316000e12, 600000, 69078 + mClearanceValue, 174.53) + getToOrbitAtmo(9.81, 5000, 100.2)); For a 69,079m orbit, the absolute minimum possible with a flawless ascent, this returns just over 4,338.2 dV For a 100km orbit, mClearanceValue = 30922, so with a perfect ascent, to a circular 100km orbit, this returns: 4389.4 dV

Yeah, I run Ubuntu and it works just fine. Check your graphics settings, particularly anti-aliasing.

Thanks! I'll plug some numbers into that formula after I get some sleep here. Many of the fancy calculators I've seen give a few values I know to be completely wrong, which makes me question the accuracy of all the other values. Unless someone beats me to it, I'll post the numbers when I finish.

The problem with that delta v map is that it is Kerbin-based, and doesn't allow for a direct trip from, say, Moho to Jool. Have you seen anything, for KSP or otherwise, that lets you just plug in raw data and get accurate results, using teh maths?

I'm working on making a newer, shinier, better Android app, and I was planning to include the requred Delta V for a transfer and a landing to and from each celestial body. I've found plenty of resources on Kerbin to elsewhere, but nothing on other planets. Anyone have this, or remember the calculations necessary to figure them out? Thanks!

The bar has been raised! 2119 tons. 29 stages. Top speed over 7km/s. A super gentle, friendly touchdown. 37:13

Argh, impressive! Okay, it's ON.

Omg, adorbs

52:27 571 tons on the launch pad, and max velocity of over 5 km/s. The deceleration burn took over 10 minutes, and I ran out of fuel at around 20m/s, a couple dozen meters above the surface of the mun, but the engine + fuel tank did a lovely job protecting the capsule on impact, which miraculously survived its harrowing journey. I realized after I built the entire 20 stage rocket that 3 landing cans would have been considerably lighter than the single 3-man capsule, but oh well- just more opportunity for someone to beat me. I also timed the trip poorly, and had to waste fuel making sure I wouldn't overshoot the mun. I'd say it's certainly possible to break 45 mins.

Also, I found a how-to for the costumes! http://imgur.com/a/tGaxR#GaAXr4Q

I was in Atlanta for DragonCon a couple weeks ago, and turned around to discover this! Was anyone on the forums responsible for this awesomeness?

The Kerbal Auto Racing League is going interplanetary! KARL needs you to transport the finest of Kerbal racing vehicles to the most scenic landscapes in the system, where brave Kerbals will race for glory and a large cash prize, thanks to our sponsors. It's your job to transport the vehicles to your planet of choice, and set up the racing track. Rules: 1) At least 4 cars must be present for a race, in close enough proximity to each other for a picture. 2) Cars must be manned by one Kerbal each, in an external chair 3) You must set up some manner of race course, either by placing objects to drive around, or however else seems logical to you. If you can justify it in the description, it's good enough. 4) The race course must have some sort of defined start/finish line. This can be a flat object in the roadway, or two beacons placed side by side- whatever makes sense to you. 5) Mods are allowed, but cheating is not. Kerbal challenges should be fun, not exercises in rules lawyering. 6) Get some good shots of the race! 7) You can use whatever launch vehicles you want, or however many you want. Whatever works and makes you happy. 8) If there's not a rule against it, and it isn't douchey, you can do it. (I swear every time I make one of these, like 30 people ask for clarifications on little nuances of the rules, rather than just getting in there and having fun with it.) Scoring: 1pt for each car transported safely, up to a max of 40 (as in still race-worthy after it lands) 1pt for each car safely returned to Kerbin after the race (score not modified) 1-10pts for racetrack setup, car coolness, and general epicness of the photoshoot, based purely on my subjective judgment. 2pts for having a comm sat in orbit around the planet you choose so the Kerbals back home can watch the race in HD. Modifiers: x0.1 for Kerbin x1 for the Mun or Minmus x2 for Duna, Ike, Eve, or Gilly x3 for Moho, Laythe, Bop, or Pol x4 for Dres or Eeloo x5 for Vall x6 for Tylo If you hold the race on multiple planets with the same cars and equipment, you get to add your scores together. Here's my crappy proof of concept (there's a fourth car on the Mun, but I forgot to grab enough kerbals before I left like a moron, so I'm going to have to send a second vessel). By happy accident I landed right next to the arch, which formed a delightful start/finish line. Track setup is still in-progress. I'll make a much sexier attempt when I have a little more time over the next week.