Tips for Aerobraking

[Greenhornet553]

So I've been playing KSP for some time now and I've only recently tried doing an interplanetary mission after reading a bunch of mission reports and stuff. Most of those mission reports that had interplanetary missions always had aerobraking in it! So I tried doing it on my Duna mission but all I knew about aerobraking was lowering my periapsis down towards the atmosphere and hoping I don't explode so I ended up doing a braking burn whilst aerobraking anyways since I didn't know how ti aerobrake properly. Sooooooo I'm just going to sit here and ask for tips on aerobraking so I don't make the same mistakes I made on my Duna mission.

[Guest]

I think you may be confusing aerobraking and aerocapture. You have already successfully completed an aerobraking maneuver by just entering the atmosphere. Aerocapture is the process of using the atmosphere to slow down or aerobrake enough to remain in the target body's sphere of influence. Completing a successful aerocapture requires a ship to be designed such that it can create enough drag to reduce orbital speed to the point that you remain in the target's soi while not blowing up from overheating. The ship's design is what is key here. So a ship that is designed to fly efficiently through Kerbin's atmosphere is going to be terrible at aerocapture at Duna. For a ship to be good at creating enough drag to aerocapture at Duna, you have to make it wider rather than taller. Think short and fat. Also, some screenshots of some of the craft you have already tried would help people help you.

[Snark]

So there are, generally speaking, two challenges with aerobraking:

• Making the ship tough enough that it doesn't burn up from reentry heating
• Judging the altitude right so that you get the desired amount of dV change (i.e. not too much or too little)

For the tough-enough problem:  mainly, make sure you're behind a heat shield with nothing important and/or heat-intolerant peeking out from behind the shield.  In general you'll do better with short, fat designs, which have the most square meters of heat shield per ton of ship.

As for judging the altitude:  that can be just about impossible to work out in advance, since, 1. the "right" altitude totally depends on the mass and shape of your ship, and, 2. aerobraking altitude can be very sensitive, i.e. just a very small amount of altitude change can be the difference between "too much" and "not enough".

The only real solution to that is trial-and-error.  That is, as you're approaching the target planet, do a quicksave when you're still far away (like way out on the SoI boundary), so that it's cheap and easy to make a minor correction to adjust your periapsis altitude.  Then just pick an altitude and try it.  If you get too little braking (and fly off into space), then reload the save and try again with a slightly lower altitude.  If you get too much braking (and go down to the surface when what you wanted to do was slow just enough to be captured to orbit)), try again with a slightly higher altitude.

[MagicFireCaster]

if your ship is heat resistant enough you can do multiple aerobraking to get your desired orbit, but you need at least the first one to close your orbit around the planet, then repeat the process adjusting your orbit until you get the desired ammount, you will consume a little extra fuel, but it can help you until you're expert enough, remember to adjust your periapsis, you don't want to get land on your second aerobraking.