Docking clamps have very little shear strength, so I suspect if we just changed the decoupler into two docking clamps, your cockpit would fall off during the ascent.
It's a bit more complicated to replace decouplers with docking ports; decouplers just fire off of your current stage, and stick to the stage you might want to return to. That doesn't work so well when you want the decoupler to detach from BOTH stages, leaving the docking port free for later use.
So what you want is:
- A docking port on top of your fuel tanks.
- A decoupler on it, upside-down, so your lander detaches from your extra fuel.
- A decoupler on top of the other one, right side up, under your engine, that will fire both decouplers off of your lander, and into space somewhere.
- A docking port somewhere on your lander. On the nose, if possible. Anywhere else will require you to dock on your side, which will make controlling it more difficult.
Pictures of this will be forthcoming shortly.
This setup will allow you to take it back to Kerbin (if you have enough fuel remaining), and leave it in orbit for future use.
Kerbals can't die for any other reason than lithobraking (just like aerobraking, only difference is that you replace the atmosphere with the ground) and a collision with an object.
When you're in control of the command module, try switching to Neil by using the [ and ] keys. Unless there's a lot of debris near by, it should only switch between the module, flag and any kerbals on EVA.
If taking control of Neil doesn't work while you are in control of another object, you can go back to the space center and enter the tracking station. There you will be able to select your kerbal from the list on the left and press the "Fly" button.
The only thing that could prevent you from taking control of that poor kerbal is a bug.
In this case, basic troubleshooting. Reload your save file. If that fails, restart the game. If this fails, well, assume that Neil met the kraken.
You could also try bumping him so some of its variables in the code are changed.
If all fail, well, roleplay it. He died of hunger while you pressed the big red button in the tracking station.
Best Answer
The only difference between RCS thrusters and ordinary thrusters is the control scheme, the forces they apply work the same way:
Any time a thruster is fired, it applies linear momentum to the ship (which is the same as translation or changing the ship speed). The amount is independent of where the thruster is placed.
If the center of thrust does not align perfectly with the center of mass, it will also apply angular momentum (which is the same as rotation or applying torque) to the ship. The further away it is from the center of mass (CoM), the more angular momentum will be produced.
So, in the case of RCS, what you generally want is for it to be far away from the CoM, but balanced around it (placed symmetrically around the CoM). This makes both RCS modes work well:
If you use RCS to rotate, the thrusters on the opposite ends of the ship will fire in different directions, cancelling out the linear momentum, and adding up the angular momentum, resulting in rotation but unchanged speed.
If you use RCS to translate, the thrusters will fire in the same direction, adding up the linear momentum and cancelling out the angular momentum, resulting in no rotation, but changed speed.
Side note: If all you need is rotation, using reaction wheels is a reasonable alternative - reaction wheels never change the speed of the ship, only rotate it, and do not use any fuel, only electricity. They are more effective if you place them near the CoM, but will work anywhere, too. The trade-off is that they are bulkier and, for short missions, heavier (for similar power) than RCS, and cannot be used to translate (which is usually needed for docking).
Summary: Place RCS symmetrically around the CoM, but far away from it, for best results.