Adam Hibberd
In my latest research, I have been considering the case of using laser structures in space to accelerate space laser sails to sufficient speed so that they will ultimately reach the first discovered interstellar object, 1I/'Oumuamua, within a matter of years from launch, or even as soon as a year. This is clearly a great saving in time compared to using chemical propulsion, which would take 20-30 years from launch, with launch probably in the early '30s.
Such so-called 'Directed Energy' systems are not the ravings of a lunatic scientist, it is more than likely they will genuinely come to fruition, of course if the human race lasts long enough to allow the necessary technological advances to be made. Thus there appears to be no 'theoretical limitations' which would eliminate them from becoming real, indeed the famous 'law of accelerating returns' will almost ensure that the tech will arise, and much of it even is available to us at this very moment in time.
If you have read my previous blog on the matter (here), you will know that I have experimented with the technique of 'Evolutionary Neurocontrol' to solve the laser sail attitude problem - that is, how the normal to the sail should be orientated over time as it is being accelerated by the laser beam.
To summarise, Evolutionary Neurocontrol attempts to evolve a 'brain' to minimize the beaming time. The reasoning behind this is that, since the power output is constant, and of course Energy = Power x Time, it will also minimize the total energy required by the laser.
This is achieved by constructing a population of Artificial Neural Networks (ANN) each of which has two inputs: (a) the current state of the sail and (b) the target state - i.e. the required velocity vector. In turn the purpose of the ANN is to output the current required attitude of the laser sail.
By trying many such ANNs, retaining the most successful ones and ditching the least successful ones (so they are out of the gene-pool), then followed by engaging the elite in a process of mutation and crossover to spawn a new and better generation, we eventually reach by iteration the ultimate ANN - the most effective one satisying the constraints, i.e. eventually intercepting 'Oumuamua.