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.
