Aerobrake Calculations

[nholzric]

One aspect of orbital flight that remains a mystery in KSP is aerobraking. How low should my periapsis be to capture but not crash? If you get this question wrong you have the potential of spoiling hours of work which is not fun. Are there any tools out there to calculate aerobraking maneuvers? Better yet, has anyone built a table of sample aeorbrakes?

I built this little tool in MATLAB for ye-olde-KSP before there were periapsis markers and time-warp. It was designed to take a snapshot of flight info and determine if you were in orbit and if so a few orbital parameters.

I've modified it based on drag information from the wiki to "calculate" aerobrake maneuvers. I put "calculate" in scare quotes because aerobraking is an extremely finicky maneuver, made worse by having to read flight information out of KSP (can you pull an angle off the nav ball down to a degree, a tenth of a degree, a hundredth of a degree??) in real time. All this when some fraction of a degree can make the difference between escape and crash. So, is my drag model correct? Maybe. Is the tool so dependent on precise measurements that it will never be useful? Probably. These are things I worry about; my question for you is, do you know of a set of data with which I can test my model?

Thanks for your help!

[EtherDragon]

I wondered the same thing - a table of useful Aerocapture periapsis would be very useful! In your case, I say Quick Save - and experiment...

[Black_Tomcat]

Well, you could just compare your results with the results the aerobraking calculator gives if you input similar/the same data (might be difficult because both require different inputs).

[nholzric]

Well, you could just compare your results with the results the aerobraking calculator gives if you input similar/the same data (might be difficult because both require different inputs).

Nice, using the example in the screen shot I entered 800km Altitude, 2450 m/s velocity, 33 km periapsis, with an apoapsis at 290 km into the aerobraking calculator you linked to. The periapsis and apoapsis are outputs from my tool. The aerobraking calculator gives a thrust angle of 50 deg which matches the input to my tool. So, that's good evidence that my model works. Thank you!

I'm still interested if anyone has a table of aerobrakes out there!

[Surefoot]

Note that using FAR, or future stock aerodynamics, will completely mess up these calculations.

[Specialist290]

I've actually been doing some work on a similar project myself with another user. The best way to go about verifying your numbers is simply to run tests within the game itself, using mods that output telemetry data (like MechJeb, Logomatic and similar mods) to track your craft's progress for easy comparison to your projected path.

If you want more information on the coding angle, I can try to get you in touch with the other fellow I've been working with.