mathmavin

[spoiler=]

I just burned in the same direction as Kerbin's orbit around the sun. I got a very high exit velocity relative to kerbin, and I got to skip out on the transit time towards and then away from Kerbol. My upper stage was a single one of the small liquid engines and 13 tanks, staged to release empties 2 at a time, so I had a very good mass fraction and the highest ISP engine, so I got a ton of delta V out of it. I had about 10 km/s relative to Kerbin when I left its sphere of influence. I thought about doing a run like you did where I do a close pass of Kerbol, but you also lose a bunch of speed dropping your orbit, so it negates a lot of your gains there, and adds a good chunk of time. Edit to add: also, the last stage was burning for over an hour at max thrust, so I didn't really feel like investing that much time into another run >_<

710 days. http://imgur.com/Wf2Ew

I think I've discovered a fuel bug with Nao's design (and probably mine, but I haven't retested mine yet). The first three tanks have 1200 units of fuel, and the aerospikes consume about 13.1 L/s each while the small engine consumes around 1.2 L/s in atmosphere. The three tanks should last for only about 45 seconds, but they last for well over a minute. If you remove the small engine, they only last for about 45 seconds (which is how long they should last). I think having that extra engine somehow reduces the fuel consumption. I don't have an entirely dissimilar setup on my rocket, so it's quite possible I've inadvertently exploited this as well. I'll run some tests/do some number crunching tomorrow when it's not late to see if my fuel usage lines up with the consumption rates for the engines. I also don't know if this is a known fuel bug, but if it is not, someone should look into it. Edit to add: I did a test run to see what kind of performance you could get if you wanted to really exploit the bug - I ended up with this: http://imgur.com/a/oC6fk Altitude: 2954 km Burnout speed: 6803 m/s Orbital Energy: 22.1 MJ/kg Keep in these are BUGGED RESULTS. Upon reviewing my design from my previous run, the small engine and the aerospikes never draw from the same fuel source, and the aerospike powered tanks burn out at 46 seconds, 1:17 seconds, and 1:47 seconds, for 3, 2, and 2 tanks, respectively. At a burn rate of 13.1 L/s, it should take 45.8 seconds, 30.5 seconds, and 30.5 seconds for each of those stages, which match up quite nicely with the timings on my ship.

Last one tonight, I promise. I did one more redesign. Basically, I took one of the fuel tanks normally attached to the aerospikes and stuck it on the top of the central stack, and made it so the fuel systems for the aerospikes and the low-powered engine in the middle were separate. I had to do some weird stuff with the positioning since I was left with 7 tanks total for the aerospikes, so I ended up with tanks in a 3-way symmetry below the aerospikes in such a way that none of them were in line with the engines. At burnout for the aerospikes, there's about 2 and 2/3 tanks left in the central stackup. At this point, the craft can barely make orbit - it actually goes past apogee and starts heading back down before it can get enough speed to raise the periapsis above the atmosphere. I ended up with this result: http://imgur.com/a/12jwg Altitude: 1149 km Burnout speed: 5782 m/s Orbital Energy: 14.70 MJ/kg The high energy and speed are a result of having 2 and 2/3 tanks running at a vacuum ISP of 400, as well as basically doing a powered slingshot maneuver around Kerbin, compared to most other hyperbolic escape trajectories from launch. I'm not sure how to attach files here, otherwise I'd post my craft files. I'd love for someone to duplicate my results to help verify my sanity. I'm hoping between my description here and the images that someone'll be able to do it.

I took another go at the challenge and tweaked my design slightly to give it just a little bit better performance - basically, I split up the 2 tank final stage from my earlier ship by sticking one of the tanks to the front using a decoupler and adding a couple of fuel lines. I calculated that it would give me roughly 270 m/s better delta V, with a more or less negligible effect on the rest of craft's performance in the earlier stages. The final stage has a low enough thrust that you can kick the fuel tank off sideways and get back on course within a second or so while always staying at full throttle, so you don't lose more than a few m/s there. I also added a MechJeb unit which I used for information and for the final stage to keep the craft pointed prograde for the ~13 minutes of burn that the final stages take. It's easy enough, but rather tedious, to keep the craft pointed manually. Everything prior was fully manual, though. Here is screenshot of the result and the craft: http://imgur.com/a/HYLgN Final statistics are: Altitude: 1562 km Burnout speed: 5468.4 m/s Orbital Energy: 13.3 MJ/kg

I think I was somewhere around 60 km? I don't remember off the top of my head.

I think I've got a ship that beats the current records for both altitude and energy. I came pretty close to the velocity record on one run, too - it's possible that a tweaked trajectory could allow for this ship to pass it, but it's a 15:02 flight time, so I only did 2 runs - I'm sure I don't have perfectly optimal trajectories in either the highest altitude or the highest energy cases. http://imgur.com/a/bEdet Difference between the two runs was pretty much how much I angled the craft when I started my gravity turn at ~10 km. For the altitude run, the screen shot has 1493 km, but I think I took it 1 or 2 seconds after burnout, so if you account for the current velocity and direction of flight, it'd probably be something between 1485 and 1489 km. The energy run has an altitude at burnout of 1456 km and a velocity of 5239 m/s. This gives an end result of 12.0 MJ/kg, if my math is right.