For those of us that are not engineers what the piece nightcrawler has posted is talking about modifying the solid fuel to change how it burns.

It omits that different energy solid fuel can also be used as well.

Old rockets used to use solidly packed rocket fuel that burns from the bottom to the top like a sky rocket burns black powder.

The problem with this design in a rather more powerful rocket is that the walls of the rocket needs to be able to withstand very high pressures and high temperatures.

A solution to that was to make the solid fuel truly solid rather than just a powder and then drill a hole right up the centre. This means when the rocket ignites rather than the surface of the base of the solid rocket fuel burning and pushing against the walls of the rocket the entire core of the rocket fuel burns... generating more surface area and more pressure but it is pushing out against the remaining fuel which supports the pressure and absorbs the heat so the rocket motor walls can be made thinner and less strong... in other words lighter.

To increase thrust further instead of drilling a circle you can drill a star shape which increases surface area and therefore burning area further increasing thrust with the same fuel. Obviously there is no free ride... drilling the core and using star shaped core design to maximise surface area also dramatically reduces burn time because the fuel burns faster. The pressure is however much higher and would get a missile to a higher peak speed.

Most solid fuels are actually baked like a cake and as with most cake recipes what they often do is use different energy fuels so the first inner layer that burns first is a high energy fast burning fuel, while the second layer burns slower but much much longer. This means that when you launch a missile the first layer burns rapidly and accelerates the missile up to its max speed. When that burns up the next layer burns and it is not powerful enough to keep accelerating the missile but it burns for much longer than the first layer and helps the missile overcome drag and maintain velocity and energy till it reaches the target. In many ways the second fuel acts like a gas generator to overcome drag like base bleed ammo extends the range of artillery shells.

Anyway what I originally wanted to say is that you can shape the thrust of a solid rocket motor with different fuel types and different fuel shapes, but at the end of the day this is fixed for a solid fuelled rocket.

A solid fuelled rocket like a Phoenix might be optimised to be fired from medium to high altitude at a very long range target but any profile expected for the missile will disadvantage the missile if it is used outside of that expected flight envelope.

For instance the missile is designed to be fired from medium to high altitude and cruise for a period and then dive on the target... If launched at low level at a target that is outside Sparrow range but not by much then the missile will enter its terminal manouver flight stage with a lot of cruise fuel left... so it is over weight, and is generating enough thrust to overcome drag and the initial high energy fuel was not enough to allow it to climb to more than medium altitude so it is flying in much thicker air than was anticipated so it is flying slower on its way too.

Another problem with rocket fuel is that it is either on or off and when it is on you might find that a lot of energy is being wasted.

What I mean by that is that at very low level there are not many objects that can exceed Mach 2 no matter how powerful their rocket motors are. If you launch a Mach 4 AMRAAM at low altitude... it will not be a Mach 4 AMRAAM... it will be a Mach 2 AMRAAM, which greatly reduces its maximum range. The thing is that they both have the same rocket motor and are expending the same amount of energy... the problem is that trying to fly at mach 4 at low altitude is a waste of energy.

A Meteor is a mach 4 or 5 missile and with an engine throttle if launched at low level it will use a reduced throttle and will likely fly at mach 1.5-2 depending on the design and how efficient it is. It wont however be running its engine at full power and full fuel burn and so it should be able to fly rather further than a similar rocket powered missile. The reason is that an onboard computer can optimise the thrust and fuel burn rate to get the most efficient use of fuel.