FAR aerobraking calculator?

[cicatrix]

Hello, recently I've added FAR to play with aircraft, but I noticed, that the tool I use for calculations about how deep should I put my periapsis into the atmosphere for aerobraking stopped producing reliable results. I use aerobraking a lot and in some cases it's very important due to limited dV budget to slow down in a single pass through the atmosphere. I noticed that with FAR I should go deeper than with the stock aerodynamics, but right now it's trial and error. I wonder is there any similar aerobraking calculator that takes FAR model into account?

Or at least, can anyone explain the math involved in calculations? I suppose I need density/altitude curves for every planet with an atmosphere to do math, am I right?

Edited December 7, 2014 by cicatrix

[Signo]

You could try to give a go to the MechJeb "show aerobrake nodes" option. I used it with NEAR and it works properly so it should be good for FAR too.

[Vectura]

Or use the Trajectories mod, it shows your path through atmosphere, so it will also show your predicted landing spot on any given atmospheric body. It works a treat.

[cicatrix]

It's not necessary to land. Sometimes, I only need to slow down and enter the low orbit. As far as I know, MJ only does that in 'landing mode' and it messes thing anyway with FAR. I'll give a look at Trajectories, although I sometimes I only need aerocapture no actual landing.

[Signo]

It's not necessary to land. Sometimes, I only need to slow down and enter the low orbit. As far as I know, MJ only does that in 'landing mode' and it messes thing anyway with FAR. I'll give a look at Trajectories, although I sometimes I only need aerocapture no actual landing.

The option shows up in the autolanding UI, but you can edit it to show up wherever you want. Moreover, you do not need to switch on the autopilot for it to show up the nodes. You can then eyeball the correct Ap you want to obtain. The D/v you can read from the navball is the speed you will leave in the aerobrake.

[cicatrix]

Hm, I'll give it a try, but nevertheless, MJ's only considers stock aerodynamics which means I could still be on the escape trajectory on leaving the atmosphere or I could very well do a lithocapture

I looked at the Trajectories mod, it appears it supports FAR and does precisely what I want.

Still I simply got used to the idea that I know exactly what my periapsis should be given my ship's speed and altitude in order to enter a near-circular orbit.

[-ELF-]

I will second the Trajectories mod. Super useful and pretty easy to use.

Edited December 1, 2014 by [ELF]
link added

[Yakky]

;1571427']I will second the Trajectories mod. Super useful and pretty easy to use.

And I'll add a third endorsement. Amazingly useful mod, best and easiest solution I've found.

[prophet_01]

Same here. Trajectories mod is pretty awesome

[cicatrix]

I tried Trajectories and found they're inaccurate as well. It showed pretty near-circularized resulting orbit before aerobrake but in the end I ended up in suborbital flight. It appears the only 'reliable' method to calculate aerocapture with FAR is by trial and error.

[How2FoldSoup]

I tried Trajectories and found they're inaccurate as well. It showed pretty near-circularized resulting orbit before aerobrake but in the end I ended up in suborbital flight. It appears the only 'reliable' method to calculate aerocapture with FAR is by trial and error.

You can recalculate with your current AoA. Your AoA determines how much drag is experienced when you fly through the atmosphere and will determine the trajectory that you have inside/outside the atmo. Are you sure you used a fixed AoA for your craft and updated trajectories to account for that?

[cicatrix]

You can recalculate with your current AoA. Your AoA determines how much drag is experienced when you fly through the atmosphere and will determine the trajectory that you have inside/outside the atmo. Are you sure you used a fixed AoA for your craft and updated trajectories to account for that?

Ehm, can you elaborate a little bit more?

[prophet_01]

If you want to use the trajectories mod, you have to keep in mind how FAR works. You are getting vastly different results depending on the orientation of your vessel. Even a craft without wings will create lift. AoA (angle of attack) basically describes the orientation of your vessel relative to the direction it travels. It directly affects how much lift will be created.

Regarding aerobreaking: if you point your nose upwards you get a positive angle of attack and lift, which will reduce the effect of aerobreaking (you won't dive as deep down into the thick air and therefore you are not losing as much speed; the lift will keep you higher in the atmosphere -> less drag).

If you point your nose down you will dive deeper tlinto the air and will experience more drag. That will slow you down and it might even get you suborbital. The trajectories mod usually gets it about right but you will still have to check it in map mode while you are passing the atmosphere. You can change your AoA to stay in control and do some corrections. And btw if you don't do that, your craft might bounce, whoble or changes it's orientation as a result of drag, lift, etc on it's own. As explained above, that affects your aerobreaking result (significantly).

That could be an explaination, but I can only guess depending on what you wrote earlyer.

Anyway, precise aerobreaking with FAR can be very difficult to predict depending on the craft. I usually don't do aerobreaking with FAR within one maneuver as it leaves too little space for unpredicted stuff. I pass the atmosphere multiple times (with a higher periapsis on every pass). That leaves enough room for correction and makes everything easyer if you use deadly reentry like I do

[Vectura]

A quick example, to show why you should change the settings in Trajectories depending on orientation: Try a taking the small black command pod into lko. Start to re-enter 'bottom first' (ie navball should show you pointing retrograde). You should see the trajectories line moving because it thinks your craft is pointing prograde.. However, if you open the Trajectories window, change every slider to 180, then the trajectories line will no longer move because it has calculated the trajectory of your craft which is technically flipped 180* (I used this exmple because DRE is not forgiving when you re-enter the wrong way round ).

[cicatrix]

Oh, I found it, thanks. I should experiment with that.