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Thread: Aerobraking in Kerbins Atmosphere

  1. #1
    Spacecraft Engineer maro's Avatar
    Join Date
    Jul 2012

    Aerobraking in Kerbins Atmosphere

    Made some Apollo-8 style Missions and all together 10 Aerobraking tests back at Kerbin with my new ship (Aagaeon 239), yesterday and today.

    Here are the results

    Orbit was every time 27.300 AP
    Aerobrakings starting with 3.209m/s at 70.000m
    With PE 60km resulting AP was 22.560km (-17% AP)
    With PE 55km AP resulting into 22.878km (?)
    With PE 48km AP resulting into 14.826km (-45% AP)
    With PE 45km AP resulting into 9.995km (-63% AP)
    With PE 42km AP resulting into 6.314km (-76% AP)
    With PE 40km AP resulting into 4.030km (-85% AP)
    With PE 38km AP resulting into 2.530km (-90% AP)
    With PE 36km AP resulting into 1.385km (-95%AP)
    With PE 35km AP resulting into 1.028km (-96% AP)

    Was a bit surprised at the first try, that cutting 10km into Kerbins atmosphere had so little effect.
    For the moment we do not have som heat effects at reentry - probably it will not be possible after such an upgrade to brake that hard.
    I will do another set of tests when i have a ship that is able for Kerbol star and back, but i am not sure if i can aim that exact to be able to make such entrys interplanetary...(?)

    Therefore i started to look at the atmospheric density - and made some tables:

    Preassure scale (roundings) starts at
    sea level: 1,2
    1000m: 1,0
    2000m: 0,8
    4000m 0,55
    6000m: 0,35
    8000m: 0,25
    10000m: 0,15
    15000m: 0,06
    20000m: 0,02
    25000m: 0,009
    30000m: 0,003
    35000m: 0,001
    40000m: 0,0004
    45000m: 0,0001
    50000m: 0,00006
    55000m: 0,00002
    60000m: 0,000005

  2. #2
    I noticed this as well, it's great you got all that data to back it up. I'm sure the reentry physics will change the game in a big way once they're added, I know for a fact some of my craft do not have sufficient fuel to slow to a realistic reentry speed. That is if the devs decide on very realistic reentry, I'd prefer if the realism was implemented like 'difficulty level' so we can put it on easy for experimental craft, and realistic for missions.

  3. #3
    I might have been more impressed if I had the slightest idea what you're talking about

  4. #4
    to put it simply, he tried "dipping" into the atmosphere to slow down without reentring completely.

    Like they did with the appollo missions that returned from the moon. Those pods carried so much speed that it was impossible for them to enter earth's atmosphere in one go.
    So in stead they enter the upper layer of the atmoshpere, lose some speed, get back out of it to cool down. Rince, repeat untill you lose enough speed to make a safe entry.

  5. #5
    Destructive Field Tester MaverickSawyer's Avatar
    Join Date
    Dec 2011
    Sacramento, CA
    Well done. Very scientific approach to this, and excellent data tables/charts afterward. This will become a go-to source for my aerobrakings when returning from the Mun and beyond.
    Will you update this once 0.17 comes out to include the other planets and moons?
    Quote Originally Posted by RyanRising View Post
    Add-on development is where all the fun stuff happens.
    Never argue with idiots, internet trolls, drunks, or conspiracy nuts. They'll just drag you down to their level, then beat you with experience.

  6. #6
    i havent even tried aerobreaking yet, i really need to, eventually i feel it might be a requirement for certian ship designs, when atmospheric effects are added.

  7. #7
    Spacecraft Engineer maro's Avatar
    Join Date
    Jul 2012
    Quote Originally Posted by spikeyhat09 View Post
    I might have been more impressed if I had the slightest idea what you're talking about
    Arobraking you can do, if you want go into orbit of a planet with atmosphere, comming from another celestrial body.
    And the "gain" of that feature is, you do not need fuel for that braking, only for steering to hit the exact - slight - angle.

    So you came in with a hell of a speed - several 1.000m/s - interplanetary probably also in the 10.000m/s region - and you do not have the fuel and the powerfull engine to slow down for a low orbit - or you want save this fuel for further actions (flight back)...therefore aerobraking. You get it for free. But in reality you would need a heatshield or a other speacial design or you can do it very gently.

    Its very challenging in reality. Because if you are to shallow it could spit you out on a total wrong course. If you go too deep you are doomed and gravity will bring you down finally.

  8. #8
    Junior Rocket Scientist Markus Reese's Avatar
    Join Date
    Jun 2012
    Canada, eh?
    Once you do it, atmospheric braking will be all you will ever do. There are a couple of very strong advantages.

    First is the fuel usage. For example, departing from Minmus, if your departure vector is counter to minmus orbit, you will only be going about 270m/s Kerbin orbit velocity when you reach Minmus escape velocity. As result, it only takes very small amounts of fuel in a short burn to reduce speed to an atmospheric grazing velocity. It is so slow out there that if you wanted, you could completely stall all velocity and set up any orbital capture path you want around kerbin without too much problem.

    Second: Your kerbals always get home

    The main disadvantage is you need to be lined up correctly and get the correct altitude for your braking to prevent complete re-entry. Too low and you don't get to choose landing location. Too high and it can take a few passes. If you want specific landing locations, you need to plan in some maneuvering to get a permanent orbit capture. This can be done by simply burning directly planetside to round out your orbit. My favorite altitude is usually the 35km altitude. I never dip lower than that.

  9. #9
    Galactic God Emperor Tommygun's Avatar
    Join Date
    Aug 2012
    Center of the Universe
    I have been playing around with aerobraking sense you posted those numbers and it's been interesting.
    I just did a direct entry from Mun where I adjusted my Pe to 7,800 meters and with an Ap of 9,700 Km.
    My speed top out at over 3200 m/s as I hit the atmosphere and then dropped quickly, at the same time my Pe lowered into negative numbers.
    With that new Dragon Rider capsule I was able to land within 0.4 km of the launch tower, but that was just blind luck that I was passing directly over head.
    I did use the landing autopilot when I saw that the KSP center was just below though.
    No fuel was needed for de-orbit, just for the last part of the landing as the Dragon has no parachute.
    Last edited by Tommygun; 12th September 2012 at 09:19.

  10. #10
    I have never tried aerobraking before re-entry before, might try it on my next munar mission. Thanks for the help

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