The peeling aerospike

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The peeling aerospike

Solid propellant rocket motors have many advantages and some drawbacks. One of these drawbacks is the propellant needs to be contained inside a huge and though reservoir. This text proposes a way to get rid of the reservoir. It has not been tested.

It relies on the aerospike principle. The rocket booster should be made of layers of very fast burning solid propellant and very slow burning propellant:

The fast burning propellant layers are meant to burn from the inside towards the outside:

The sizes displayed in above pictures are inadequate. The propellant layers should be thiner. Maybe a few millimeters thick. Otherwise there would be a severe energy loss when the burning zone of a layer reaches the end outside diameter. Also I can't figure how the inside part should exactly be made to get the maximum yield. A third concern is whether a third kind of layer (a lightweight and insulating one) should be used in order to get a better burn front profile. Most puzzling concern is wether the gasses flowing out of the fast propellant burn front will go supersonic.

Should this concept be effective then it may have following advantages:

The motor's weight decreases while it burns, down to zero. There is no dead mass. The booster can be made of layers with a decreasing diameter so the thrust decreases while the booster burns up, in order to get a constant acceleration. That way a single booster is needed to get into orbit. There is no waste falling back on Earth or staying in orbit.
The slow propellant (or the insulating layer) can be chosen so each fast propellant layer has to be ignited by an electric trigger. That way the motor can be halted and reignited at will, using a set of layers at a time.
The booster can easily be made of several segments. On the launch pad the segments are piled up and glued together. This makes tuning the booster easy as the amount of layers can be chosen.
The bottom of the booster can easily be made quite wide. So a strong acceleration can be attained from the start on. This increases the yield by lowering the impact of Earth gravitation.
Security: no moving parts, no pressurized reservoirs.
Maybe steerability can be attained by asymmetric ignition of the layers.

On second thought, maybe the burning fronts should be directed towards the supersonic flow, in order to be compressed:

I have no idea how far this can be simplified. Maybe thin layers of propellants with different properties can allow the necessary shock fronts to compress the burning fronts and erode towards the adequate shape to allow the supersonic acceleration of the compressed gas (which would not be the acute angles shown below).

Eric Brasseur - April 14 2004 till January 5 2011