[BwanaNdege]

The software that controls that rocket has to bring the solutions of five or six differential equations all to zero at exactly the same instant in time.

It is similar to making a good, no-hover landing in a helicopter. You have to zero forward velocity, vertical rate of descent and altitude to coincide with a fixed point on the ground. When you manage to do it smoothly, it is quite satisfying.

Especially in a very large helo with stabilization turned off...

:-)

[Steely Tom]

Having done a lot of RC model helicopter flying, I agree with you.

Except add these challenges: the COG of the helicopter is about fifty feet above the skids, and the helicopter’s moment of inertia is about twenty times more than what you’re used to.

[Steely Tom]

It is similar to making a good, no-hover landing in a helicopter. You have to zero forward velocity, vertical rate of descent and altitude to coincide with a fixed point on the ground. When you manage to do it smoothly, it is quite satisfying.

Also, in the SpaceX case, they had to bring yaw and pitch angles and yaw and pitch angular velocities to zero at the same time that they got velocity and vertical rate of decent to zero, with fuel running out at the rate of pounds per second.