Nowadays, the thing that takes the longest time in a mission tends to be aerobraking for landing in atmospheres, or circularizing: Dropping my Periapsis into the atmosphere enough to lower my Apoapsis by a considerable amount, without burning up during the process.

For example, right now I do this when returning from the Mun to Kerbin by dropping my Pe to about 50km, then a couple of aerobraking maneuvers later, dropping it to 45km, repeating until I either hit a low enough Ap to circularize at (or near), or to re-enter the atmosphere for a landing at a slow enough speed to avoid burning up on re-entry.

It would be really nice if MechJeb could autocalculate the lowest Pe the craft could take per orbit without breaking up (facing retrograde, since this is usually the optimal re-entry direction to avoid heating), and set up the maneuver node at Ap to lowering it each orbit to aerobrake to lower it as much as possible, either to eventually hit a target Ap, or to land safely.

The thermal stuff in stock is complex and depends on too many parameters for a simulation to find out if a craft will survive a specific reentry.

The landing sim prediction can be used to see the aerobraking effect (activate the landing prediction and check the use node stuff). I could extend it to simulate/show more orbits but not much more.

If you want easymode put in some heatshields and airbrakes, make sure the thing can handle 20~30 G and just DROP it onto KSC.

Stock aero has a huge flaw in the heat system which is exposure, if you just blast through the atmosphere you won't burn up, and if you get it right you can lose 3 km/s easy and get to 500 m/s at 5 km and just chute the rest.

The hardest part is probably finding out the best angle for your craft, but I've dropped probes from minmus that used a 909 as heatshield (rather small S1 probes) and they just blast through and when low enough simply chute the rest.

If anything the addition of a landing angle to target would be nice, aka an "aggression" setting for the landing AP, more aggressive = more straight down instead of as shallow as possible.
Reminds me that I need to test if the latter still makes it derp out because the PE goes below 0 and then gets corrected above 0 again which makes it start all over again.

@sarbian Aye, the landing prediction and aerobrake node in landing guidance are useful - though I use the "Trajectories" mod, since it's always on by default, and doesn't add maneuver nodes to show predictions - but it doesn't help much if your ship is turned into a fine dust once it comes out the other side of the atmosphere :)

It'd be nice to know if we can get more detail about the aero/heating model out of Squad.

@BloodyRain2k That's fine, but I can't stick heatshields over everything - My landers tend to have a docking port on top, and an engine on the bottom, for example. I've not played with the airbrakes much, though, admittedly. I should probably do that to slow me down faster in the atmosphere and reduce my aerobraking orbits.

The problem is not having the model. I know how it works, and I know that I don't want to do that much math for a sim that I need to run fast.

So the "automagically figure out the correct and optimum periapsis" is mathematically highly annoying.

The vastly simpler solution here is that MJ accepts from the user a periapsis value and then automates the process of adjusting to that periapsis, then aerobraking, rising up to the apoapsis and raising the periapsis to the desired value, then repeating until a desired apoapsis target is achieved. Keeping the orientation of the craft correct as it does so.