What altitude to aerobrake?

[Wizard Kerbal]

     I just launched my duna mission, and I remember the last time I aerobraked at about 40 km, It didn’t help at all, but I didn’t get a single temperature gauge. So I’m wondering what altitude I should use, to save DeltaV and not burn up.

[SpaceFace545]

3 minutes ago, Wizard Kerbal said:

     I just launched my duna mission, and I remember the last time I aerobraked at about 40 km, It didn’t help at all, but I didn’t get a single temperature gauge. So I’m wondering what altitude I should use, to save DeltaV and not burn up.

You need to get low probably 15 km to 20 km. just quicksave before entering dunas soi. also use high drag parts like the inflatable heatshield for more drag.

[Wizard Kerbal]

2 minutes ago, SpaceFace545 said:

You need to get low probably 15 km to 20 km. Quick save before entering dunas soi. also use high drag parts like the inflatable heat shield.

Only my nuclear engine and it’s fuel tanks are optimized for low drag due to the design philosophy they’d be the only part exclusively in a vaccum, so, uhh, oops!

But 20 km sounds good, maybe 25 to completely exterminate the risk of burning up.

[SpaceFace545]

13 minutes ago, Wizard Kerbal said:

Only my nuclear engine and it’s fuel tanks are optimized for low drag due to the design philosophy they’d be the only part exclusively in a vaccum, so, uhh, oops!

But 20 km sounds good, maybe 25 to completely exterminate the risk of burning up.

i'd stick with 13km to 20km you shouldnt burn up

[Curveball Anders]

Keep in mind that optimal pe for nice aero brake also depends on your ap.

(Or rather your initial orbital energy state.)

Starting with an ap just outside the atmosphere or screaming in with an ap outside the soi is two very different cases.

 

[Echo__3]

If you are using a typical Hohmann transfer from Kerbinm, aerobraking around 15km works well. Remember to quick save as you enter Duna's SoI. You can use the mod trajectories to help plan your aerobraking maneuvers.

 

[Curveball Anders]

1 minute ago, Echo__3 said:

 Remember to quick save as you enter Duna's SoI.

Not just for adjusting your optimal pe, there's also that bloody Ike that can thrash the most perfect scenario ...

 

[king of nowhere]

the optimal altitude for aerobrake also depends on the drag/mass ratio of your ship. as a rule of thumb, a big ship is harder to brake than a small ship because of the square cube law. so an altitude that's good for a small ship does not work for a big one.

that said, the first 10 km of the duna's atmosphere brake very little, and the subsequent 10 km are also very thin. you start getting some serious drag below 30 km. I generally aerobrake around 20 km.

[Wizard Kerbal]

At first, I tried 20 km, and I crashed into the surface. Then I raised it to 25, and shot past Duna. 22 km was juuust right, and my apoapsis went from a bad gravity assist to 600 km above sea level. I didn’t want to aerobrake again, So I raised my periapsis above the atmosphere, and will do an engine burn to get to my final orbit.