LambdaCactus

Something with a highly elliptical orbit like a comet would be fun.

Cut some slack, it's part of a process to eventually do the full thing... You yourself edited parts to simulate the same thing from Kerbin, so what's the difference?

Well, no. He's upfront about the parameters of the challenge so I wouldn't call it cheating: it's only restricted to the scenario of getting off of Eve. The next step in the challenge would obviously be to deliver the lander to the surface there, and the final challenge would be a full round-trip.

I'm thinking of an orbit such as when transferring from Kerbin down to Moho. When the destination at Moho is below the solar plane, what's the best way to transfer there? In a circular orbit, it's easy to think of plane changes as "twisting" around a line from the craft to the planet's center of mass, and the same happens in an elliptical orbit: If I add some "North" component to my ejection velocity at Kerbin (the apoapsis of my transfer orbit), then the plane of the transfer orbit will be inclined through the Kerbin-Sun line: the craft makes a rising arc above the solar plane as it falls towards Moho, but the periapsis will just be back on the solar plane again. Yes, I could look for a launch opportunity when Kerbin is lined up with Moho's ascending/descending nodes and do that. But let's say I launch 90° from there. In other words, the Kerbin-Moho transfer apoapsis needs to end up really far north of Kerbin, in order to get aligned with Moho's orbital plane. I'm guessing this requires more than one impulse?

What I do is plane change from a Kerbin equatorial orbit. It\'s pretty accurate and doesn\'t take much fuel. Here\'s how: 1. Get into a circular equatorial orbit 2. Focusing the map view on your craft, zoom out until both the front and back lines of the moon orbit are in your view. Line them up so you\'re looking at the moon\'s orbit 'edge-on'. You should see Kerbin in the middle, and a horizontal white line going across it for the moon\'s orbit. 3. Turn your view until the Minmus orbital plane crosses behind Kerbin (You may need to zoom out a bit more). You are now looking directly at the intersection of the two planes. 4. Check which way you need to burn: at your craft\'s next crossing of the intersection, you will either need to burn north or south to change the angle. You can orient your craft to put the navball on the horizon at 0° north or 180° south and lock it there. You can set this up ahead of time: unlike when pointing prograde in orbit, these points on the navball won\'t move, they\'ll just rotate about your ship\'s axis. 5. Zoom in until you can see the sphere of Kerbin fill the top and bottom of the screen. If you\'ve focused the map view on your craft, Kerbin will move across your view from side to side while your craft stays centered. You\'ll know you\'re at the intersection when the space on either side of Kerbin is equal. 6. When you reach the intersection, burn full power. You\'ll have to zoom out to see the Minmus orbit, and zoom back in to overlay your craft orbit. Check a few times until your orbits look like the same angle. Cut the engines. As for exactly when to start your transfer burn to Minmus, I\'m not sure. I can usually get it pretty close, but I still have to sweep around with small radial burns mid-course until I find an intercept.

Thanks for the correction, yes that\'s what I meant. I hope that part made sense anyway.

I did it! My mission parameters: [li]Stock parts[/li] [li]No calculator or other nav add-ons: totally kowboy[/li] [li]Circular(ish) orbit at Kerbin before transfer burn[/li] [li]Orbital insertion at Mun (i.e. controlled speed/low perigee landing)[/li] [li]Nice atmospheric re-entry[/li] I was just able to complete this after a few tries. It\'s actually quite thrilling to fly totally seat of the pants. I had a rough idea of the kind of numbers I would need, so I did the whole run by feel. 3 attempts total: The first attempt looked good until I skimmed into lunar terrain... that little lander engine was too little too late once I noticed my orbit insertion was going to be sub-surface. Second attempt, I had a good efficient launch with a bit of a low orbit. I was mostly circular around 75k, but then misjudged the velocity I\'d need for lunar transfer. I was aiming for 3000m/s which might be fine from 120-150k altitude, but a lot of that speed bleeds off coming up from a low orbit... I ended up in a long elliptical orbit to about 6000km. I was a bit surprised at first when I noticed I was no longer climbing, so I peeked at the map to see how far off I was (it was a failed pass anyway). Ok, maybe just get these guys home then: I made a short burn to drop my periapsis down from 75k into the atmosphere, thinking I would just come back for a landing. However, once I was in the atmosphere I could see my speed was still too high and I would skim off. At 45km my descent levelled out and my speed dropped to 2300-ish. This is too perfect! I still had plenty of fuel, and I could circularize this and make another run! I managed to get the aerobraking pass circularized around 100k, waited for the mun to come around again, and then screwed up the burn again: still too slow! I left the crew in elliptical orbit as a souvenir of a failed but really fun double-attempt. Successful mission spoilers below. Final attempt: good on launch but I was too slow to accelerate into orbit: I missed the apogee and dropped back into the atmosphere a bit. Still, I saved it and set up a slow climb up from 63km. At moonrise I was nearly level around 75km, and accelerated to 3150m/s. I reached the lunar gravity going a bit fast so I made a bit of retro-burn so I wouldn\'t just pass by. I watched my altitude drop until about 720km where it levelled out. I took a wild guess: retrograde burn, 160m/s sounds good. Honestly this was such a lucky guess that I couldn\'t believe it... I just checked the numbers in Orbit Mechanic and I was dead on! This would bring me in to a low perigee at 3 km above the surface: perfect! I still had my second stage with some fuel for slowing down, and when I burned it up, I was sitting 3km up, in level flight, going 65m/s. Couldn\'t have done it any better. Here\'s how I actually checked if that approach from 720km was sane as I was coming in: when you\'re in an elliptical orbit, the prograde/retrograde markers oscillate up and down in a sine wave: at apogee/perigee they are on the horizon, and at the ascending/descending nodes (half way between apogee/perigee at the steepest descent or climb), the markers reach the furthest away from the horizon. Let\'s say it oscillates between 40 degrees above the horizon and 40 degrees below the horizon... like a sine wave, it slows down as it reaches the highest and lowest points, and it passes through the horizon quickest. I knew I had to get from my horizon at 720km altitude to my low horizon somewhere near the surface. This means the prograde marker would dive down to some angle, pause there, and start returning to the horizon as I approach perigee. I watched that marker as it dipped. I could see it pause at -40 degrees, and I checked my altitude once I confirmed that it slowly started returning: the altitude was 350km, so I knew I was close since this is half-way between 720km and zero. This is harder to do when the approach is not so steep since the movements are smaller... If you want precision instead of seat-of-the-pants flying, use a calculator! My lander had full fuel at touchdown because of that perfect approach... Return trip: I knew Kerbin was just over the horizon from my landing spot and I was near the equator, so the direction I needed to go was straight up (perpendicular from the Mun-Kerbin line, aka the horizon). With 2 full tanks of fuel, I could just burn straight up instead of doing the more efficient method of orbiting before transferring off. I accelerated to 900m/s, which left me about 60m/s Kerbin-relative speed after leaving mun gravity (actually it was too much the other way, I was coming back retrograde). This set me up for a really steep descent, Ideally I would\'ve liked to decelerate in the high atmosphere rather than coming straight down... oh well, still landed by parachute. Fun! The map feels like cheating now.

Ah, that\'s what I was wondering... so you basically skipped trying to orbit the mun. (Not criticizing, I\'m just trying to understand the parameters of your challenge.) Well, since the mun\'s orbital speed around kerbin is about 540 m/s, you want to burn away from the mun so you basically follow its orbital trail backwards and effectively cancel out that orbital speed and fall into kerbin... (If kerbin is straight overhead in the sky at your landing spot, that means burn east.) You also need to launch with more speed so you get 500m/s at the edge of the SOI (2400km) altitude. A hofmann transfer to just pop out of the mun\'s SOI sounds like it\'s a bit too soft... I expect you\'d end up in an elliptical orbit, and like you said, burn a lot of fuel to slow down at the bottom. Sure, I would watch it! I\'m off to try this myself...

Yes, this makes sense... it can be worked out with some trial and error and approximate numbers too. 2250m/s to orbit Kerbin; 3000m/s to shoot for the moon; 600m/s to orbit the moon. (Just off the top of my head, might be off a little bit.) Mmm, yes a little bit, but not really. For orbital insertion, you will know your speed, but not your true vector. Given the same speed, it\'s either a collision into the moon, or a flyby. Small difference in angle, big difference in results. But I wouldn\'t want to hit the moon. :-( Ok, I just thought of something. If you watch the prograde marker as you reach the moon\'s gravity, it will either be near 90° straight down, or off by some degrees. (Straight down is bad.) A burn to the side should move it off to an angle, but I have no idea how much, how far out. A good approach means the marker will slowly move away from -90° as you come around, eventually crossing the horizon at perigee... (retro-burn here). So if you watch your approach rate towards the moon along with the movement of the marker, you might be able to kind of estimate which one will happen sooner: impact, or marker on the horizon. Very rough idea, but it might be doable.

This is awesome. I can guess at how most of it can be done, but how did you accomplish orbital insertion? (Or did you skip it?) What I mean is, how can you tell if you\'re coming in for a low perigee or an impact, and how do you know which way to correct for that?

I\'ve done this. The trick is to build more horizontal speed early, then reduce thrust as you approach your orbital altitude. What I do: [list type=decimal] [li]Slowly start pitch-over at 10-15km, depending on the ship\'s speed and stability.[/li] [li]Maintain a slow pitch-over, your thrust vector ('nose') should follow your prograde marker as it falls over toward the horizon. You\'ll want to time it so you\'re pretty much horizontal around 50-60km. You can aim higher, it depends how high you want to establish your orbit. Just remember you will keep burning and climb up to it by building horizontal velocity.[/li] [li]When approaching horizontal attitude, reduce thrust so you\'re just pushing the Apoapsis ahead of you, perhaps gaining on it slowly, but not pushing it any further away.[/li] [li]Keep adjusting your attitude to point at the horizon. Keep low thrust. As long as you keep apoapsis slightly ahead of you, you will be climbing. If you have a longer way to climb, you can push apoapsis further ahead: just don\'t let it get too far away from you, or you\'ll get too elliptical, and that means cuttiing the engines for a while.[/li] [li]The trick to finish it off is to reduce thrust so you approach and hit apoapsis at your target altitude with zero thrust. Since you\'ve been burning horizontally the whole time and slowly gaining orbital speed, it should be pretty much circular when you get there. Check your periapsis and add a little burn if necessary.[/li]

As long as you\'re just dropping SRB\'s for takeoff assistance then yes.

That was a beautiful video, the music was a nice touch. What does the 21.8° refer to?

I assume 'get into orbit' means to establish the orbital trajectory, not complete the whole orbit: I got Apogee 108k, perigee 72k, then immediately deorbited. Total time to splashdown: 12:16 (game clock).

Either that or the silvery 'water' is very dense!