It is assigned, but perhaps the function rotate_gondel1() is loaded before rotate_boosterarm, thus boosterpaal is still an empty pointer. That's why you need to wait.
-> is used when you ask an object's attribute through a pointer.
VECTOR vec = nullvector;
VECTOR* vec_pointer;
...
vec_pointer = vec; //give vector reference to the pointer
vec.x = 5; //vector.x is 5
vec_pointer->x = 6; //and now it is 6
