Reusable First Stage Rocket with Substages

I was previously in favor of larger but small number of engines. However, in order to achieve high efficiency, the engines should be operated at maximum pressure. In order to achieve varying thrust, multiple engines would be operated and they would be shut down one by one to reduce the thrust. Therefore, now I am in favor of multiple engine approach. I would like to enhance this concept further by changing the propellent tank structure. I propose multiple tank groups to be stacked one above the other so that the consumed section can be ejected to reduce weight.

The engines of the first stage of the rocket would be placed on the outer edge of the rocket. External propellent pipes would feed the propellent to the engine. The pipes would also enforce the sides of the propellent tanks to withstand high pressure. Each group of tanks would be consisting of cascaded fuel and oxidizer tanks with a pressurizing hydrogen tank above. Cascaded tank design doubles as a support between the tanks top and bottom. Else the top and bottom of the tank would be in dome shape which would increase the height of the tank group.

Once the tank group’s propellant is depleted, it will be disconnected from the main pipes and ejected from the rocket. After ejection, empty tank will deploy a parachute to slow down its descent. The hydrogen filling the tanks will also be released to slow down the rocket. The empty tank will splash down on sea and will be refurbished and reused. Reducing the overall weight of the rocket during its ascent by releasing the empty tanks will reduce its fuel consumption.

Once, all but the last fuel group is depleted the first stage will disengage from the second stage and will start falling. Lincoln hat shaped inner void of the rocket will function like a parachute and slow down the rocket during descent. Additionally, the air filling the gap will be released from the top ventilation holes in a controlled manner to maneuver rocket without using any fuel, foldable fins or gimbled nozzles. Finally, the fuel in the last tank will be consumed to stop the rocket and let it touch down safely.

I propose this concept to work on a first stage which only lifts the upper stages to an altitude above the Kármán line. It will be a vertical only trajectory with no lateral speed. This would allow a much larger diameter rocket with less aerodynamic design. Also, simplify the rocket and the tanks recovery.