The basic concept has been articulated but we don't seem to be progressing the challenges within it very quickly and I thought I would set out the pros and cons of some aspects as I see them.
1. Getting the cruisers into the air. If the concept is to work it assumes that the cruiser will be a very large aircraft and we need to start with some assumptions. Let us hypothesise that it is a 2000 seat cruiser. If we take some sort of payload proportion and extrapolate to a 2000 seat aircraft we might end up with a an MTOW aircraft around 2000 tonnes. Refining this will depend on many factors but let us assume this figure temporarily. Getting it airborne might be best achieved at a lowest safe operating weight i.e. with no passengers and minimum fuel and this would reduce the weight by about 400 tonnes or more. It would also be very large with a wingspan perhaps around 1.5 times the A380 if of similar configuration , say 1.3 for a BWB which might indicate circa 100-110 metres unless its cruising role indicated higher aspect ratio wings which might send this up to maybe 140 metres.
T/O would, of course, require more power than cruising and there is room for some further innovation in working out how the extra weight of of propulsion can be reduced after it is "on station". Could it be enabled by fitting dischargable rocket boosters, or jettisonable engines, or even having another large aircraft tow it on T/O? How would this work in practical terms?
2. The propulsion system: early thoughts turned to nuclear power - this was tried in the 1950's and has more recently been tried again by the USA/NASA. It seems that the weight of the power plant can be got down to feasible levels (below 80 tonnes) but the issues of perception, risk, system failure, shielding etc still remain largely unsolved. How could these challenges be addressed on a very large aircraft like the cruiser? Its size would allow some extra flexibility but the size is not very greatly more than an A380 - would this have a major influence? Could the design of the a/c be approached in a new way to allow a greater barrier of distance or shielding to be accomodated? It seems superficially quite hard to do this for a large civil aircraft without undermining its whole design concept. Could the weight of the reactor, though admissible in simple weight terms, be arranged to be at a less diffiuclt place than close to the CG? It doesn't immediately seem very feasible but what do the weights actually look like?
3. Non-nuclear power: Really drives the solution to be a similar concept to present day high thrust turbo-fans. By careful design it might be possible to configure a VLA of this type to be economical at a lower speed than the 0.82M that we have become accostomed to and let in the design of turbo-prop cruising engines to the consideration. What would be the fuel consumption of an economical large aircraft of this kind be? How much fuel would it be economical to carry between air-refueliing? How would the cost of the fuel carried be offset against the cost of re-fuelling and optimised? What is likely to be the driver of lifetime return on capital employed?
4. The concept relies upon smaller feeder aircraft "joining" the cruiser but how this might be achieved has not been much studied. The economics of cruiser operation suggest that it should not vary its speed by very much so the feeder aircraft could dock if the speeds were aligned - how should they dock. The vortex flow over the wing of such a large aircraft as the cruiser could be damaging to an aircraft perhaps a tenth of its weight. In which direction shoudl the feeder approach the cruiser and what mechanism of docking should be provided. How should the final few metres of the relative distance be managed - the feeder would need to adjust speed, height above the cruiser, lateral position and to do this within both the turbulence of the cruiser and the natural weather turbulence. Could the feeder fly into a catching latch that once secure would wind the feeder up or down into the cruiser main dock? If the cruiser was a BWB could the feeder approach from behind and above and enter the high speed airstream over the upper wing accelerating to set down on a docking platform. There seems to be a handling problem analagous to flight refuelling that if the feeder goes out of the "tube" it immediately finds itself flying too fast or too slowly.