In the 1960's, with its Surveyor program, NASA mastered the technology of using a solid rocket motor to decelarate a lander, removing over 90% of its speed to allow a relatively small liquid-fuel propulsion system to make the final descent and landing.
To help with the design of your solid rocket motor breaking stage, you might like to check out Rogers Aeroscience who has recently published some useful reference materials. The following articles are available from their website http://www.rasaero.com/;
- Performance Analysis of the Ideal Rocket Motor.
- Departures from Ideal Performance for Conical Nozzles and Bell Nozzles, Straight-Cut Throats and Rounded Throats.
- Erosive Burning Design Criteria for High Power and Experimental/Amateur Solid Rocket Motors.