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About sebjf

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    Bottle Rocketeer

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  1. Thanks again for the great responses! I added more wing area, to start with, on my Mk 2 craft. I built an Aerospike version. For this I need to use its high TWR to get out of the atmosphere quickly but I can get it into a (regular) orbit with about 550 m/s of dV to spare. I added even more lift to the Nuke version, but with two engines it just can't accelerate quickly enough once in the upper atmosphere, before the plane falls back down (after which the drag becomes overpowering and it loses speed). Looking at AeroGav's designs I think I am just using too many Mk2 parts. Based on this thread I also created a Mk 1 plane that successfully achieves retrograde orbit with enough dV to rendezvous! It took a long time, partly because I spent days trying to figure out why my efficiency dropped precipitously between two game sessions, only to realise that somehow at some point the cooler had become Mounted BACKWARDS! I then had to figure out how to get it back to Kerbin without exploding... It may not be pretty, but finally I have a craft that can de-orbit my Kerbals! Interestingly, I still find the best ascent for the above plane is: Take off at 10-20 deg. Increase speed to ~1200 m/s by 10 km. At 10 km pull up gently (30 deg) At 20 km engage Nukes Continue at 30 deg until Alt. reaches 40 km Level out and push forwards until orbit is achieved I tried the just fly faster approach, but I get into orbit with much less dV. I am not sure why. In fact, I find using the jets to throw up the AP while they still can at high speed/low altitude the best ascent for all my planes. I wonder if there's a quirk or mistake I am repeating in all of them, since I can't seem to figure out how to make good use of the high wing area. I've never been able to push the PE high enough while in the atmosphere at all regardless of engine. (Actually, I have trouble getting to any speed that can present temperature problems with the Mk 2 craft - is this a sign that the craft is too draggy to make it?) Yes I originally started this because I had Kerbals on ships without re-entry pods and it felt super wasteful to send up rockets just to de-orbit them. These planes have taken so much time, and have been frustrating, but once they started to work as Signo says there's so much to explore in different ways to tweak and fly them.
  2. Thank you for all the great replies! I'm glad to hear it is a tough problem, opposed to a really simple mistake! I've tried to improve my ascent efficiency but am still having trouble. Here is a video of my attempt to do a high-altitude speed run with the NERVs: High Altitude Speed Run-1.m4v?dl=0. I don't seem to have a good TWR for long enough to get the AP high enough. Is there an obvious place its going wrong? Still so far the only way I've managed to orbit, is to accelerate to Mach 4 at 1-2 km, then throw the plane up at a high pitch, using the entirety of the air-breathing altitude (+ NERVS after 9 km) with the supersonic performance of the Whiplashes to build up enough vertical speed such that it leaves the atmosphere, even after the TWR drops. But that only works pro-grade. I am in career mode and don't have RAPIERS yet, but I did redesign the plane to use Aerospikes, thinking that the higher TWR would be more forgiving when doing high-altitude speed runs. Unfortunately I don't seem to do much better! I achieve Mach 4 at ~18km before engaging the rockets, but it seems they have too much work to do and I barely make orbit. High Altitude Speed Run-1.m4v?dl=0] Signo seems to do much better with engines that are less efficient than the Aerospikes if I am correct, so this must be a problem with the ascent? I have tried with a sharp and shallow pitch. With a sharp pitch I can indeed push the AP to 70, but the PE is so low I don't have enough fuel to circularise. On the other hand if I try not to fight gravity it seems I waste a lot pushing against the atmosphere and end up with less dV than with the NERVs. I will try again with some combinations of pitches over time...
  3. Thank you all for the advice!! I have replaced the wings. I have also tried the new ascent, but I don't think I am doing it correctly. I aggressively get to 15km (by starting at 45 deg or so, keeping speed at about 250 m/s) before leveling out. The air engines to push the speed 1300-1400 m/s, before I engage the nukes. The speed continues to increase and I rise slightly to keep from overheating. The problem comes when the plane reaches about 21 km and the air breathing engines cut out. At this point the surface speed (1500 m/s or so) continues to increase but too slowly, and the time to AP (a few seconds to a minute) decreases. I encounter AP before gaining enough speed and the plane falls back into the atmosphere. Then its a case of either burning up, or letting the nukes push against the atmosphere until fuel is exhausted. I can push the AP away by pitching up, but then surface speed doesn't increase at all. If I aim the plane down, surface speed increases quickly, but the time to AP decreases even quicker! I don't think my nukes have enough thrust to overcome the drag, which is why I need to ensure the trajectory had the AP above 50km before the air-engines cut out in my original ascent. I have tried this many times, I managed to get into orbit by starting a speed run at 10k and pushing up at 20 deg with nukes, but with no more dv than originally Is it a reasonable conclusion that my rockets don't have enough thrust? Apparently people have got planes up with just one LV-N.
  4. So that's why its double, thank you! But still, if I can get into orbit with ~800 m/s to spare east, where does the other ~500 go? Obviously I could be flying badly, but I have tried *many* times and I can get no where near orbit like I can east. I can't even get the AP above 40km at any point, let alone raise it high enough and keep it there to escape the atmosphere and achieve orbit. Is there something else about going west that I've missed?
  5. Hi, I am trying to make a spaceplane. I've managed a couple of craft that can get into orbit with 500-1000 m/s dv remaining, but when I try to launch westward (to pick up crews from Asteroid intercepts), I cannot get into orbit at all. Below is the latest. The ascent profile I aim for is to get to 1300-1400 m/s around 1-2km, then pitch up to 20 deg, and around 9km engage the nukes. (I just tried it just now - 1200 m/s by 3km, engaged the nukes at 12km, burned all engines at 20 deg until the air breathing engines ran out, then burned prograde until AP hit 70km. Orbit established with 830 m/s dv remaining.) When I aim west though it doesn't work. I can never get the AP as high before reaching it as I do going east. I know I have to fly against the rotation of Kerbin, but thought that was only 175 m/s or so to cancel the initial rotation? Can anyone see where my plane is going wrong? Here is a picture of it, and the craft file: I haven't unlocked RAPIERS yet. Sj
  6. Thanks for the replies everyone! Right, Δv != Δv/t, D'oh! OK this is what I am doing wrong! Below is a screenshot of my trajectory (different PC so didn't have it yesterday). I will try again without shooting right past it...
  7. Hi, I am on my first Minmus mission. The delta-v maps say that I should require ~180 m/s^2 to get into orbit. I can get onto an intercept trajectory with the suggested delta-v of about 930, but when I place a manoeuvre node at the periapsis it takes over 400 m/s^2 to capture. I have tried launching a number of times but always the result is the same. My trajectory isn't being perturbed by Mun. I am getting to within 65-100 km of Minmus. I was wondering if that estimate expects a free-return trajectory, but none of the tutorials say that? What about my trajectory can change the capture speed? Sj