In the discussion on Jons’ last post it was mentioned that seven cores could be used in the VTVL booster technique with the outer six semi-permanently attached as a single unit. If they are close to gas-n-go on landing, then keeping a much larger LV booster together might make economic sense. A very large Reusable Launch Booster (RLB) could make good sense
The thought is that the center core is mated to the three diameter payload shroud on the ground and lowered into position after the six booster is moved to the launch pad and cleared for flight. This would allow for frequent launch of large volume payloads with the expenditure of a single booster.
At right is the landed cluster with a crane lowering the center core and high volume payload shroud into the center position. At left in color is the nozzle layout. The high expansion ratio center nozzle has the lower expansion ratio booster nozzles in close proximity. The outer six nozzle ring entrains air flow to prevent flow separation of the vacuum nozzle at sea level.
The Falcon9 series may not be appropriate for this concept as 63 engines at lift off may be a bit much to deal with as well as the problem of getting the expansion ratios right for the upper stage in a complex layout. Their next engine series may be a different story. I have wondered on occasion why they didn’t go with an aerospike arrangement with all the gas generator exhausts to the middle.
Blue Origin may have a better shot with the single engine cores. The ULA Vulcan in the works may have potential. The Delta might be modified in this manner with a bit of VL development on their part. Atlas and Antaries have the two nozzle boosters which may make it a bit more challenging, though a bit of clever could go a long way.
It should be built into the design of the RLB that individual cores could be changed out fairly rapidly for maintenance or repairs. Also it would allow for transport of the entire vehicle in sections by ground or air. Seaborne transport might carry it as a unit if desired.
If the demand arises, it seems possible for several companies to have 100+ ton LVs with 10+ meter shrouds in the next ten years.