Step 5 - Arriving at Jool
A small probe aerobraking in Jool's dense atmosphere.
When you get into Jool's SOI, you basically have two options for getting into orbit.
1- Play it safe and burn retrograde at periapsis, but risk running out of fuel
2- Aerobrake, save some fuel but risk burning up in Jool's atmosphere
Option 1- When you arrive into Jool's SOI, make sure your periapsis is is above 200km. Simply point and burn retrograde at periapsis until you get into a stable orbit.
Option 2- A few days before you arrive in Jool's SOI, play with a maneuver node and get your periapsis under 200km, inside Jool's atmosphere. The height of the periapsis is totally up to you, but I recommend not to go under 160km. Then, enter Jool's atmosphere pointing retrograde. Try to keep your ship as stable as possible and not flip around, or else you could burn up. Once you have exited the atmosphere, burn retrograde for a bit if you are not in a stable orbit.
Congratulations! You have reached Jool!