Design, development, static and flight tests of reverse flow multiple nozzle solid rocket motor with high burn rate propellant

The Vikram Sarabhai Space Centre, Thiruvananthapuram has developed a special purpose motor for Human Spaceflight Programme with four reverse flow nozzles, having cant angle of 149 degrees, termed as Low-altitude Escape Motor (LEM). This is a high-thrust short-duration motor having specific envelope constraints. New high burn rate propellant has been developed to achieve the specific mission requirements. In the design, emphasis has been given to smooth turning of internal flow, avoiding sharp edges and corners, to the specified cant angle. It has to satisfy the thermal as well as structural design requirements for the multiple nozzle openings provided, containing itself to minimum external projections and envelope. Since four ellipsoidal-shaped cut-outs from the chamber cause high stress concentrations, welding or some other joining methods are not preferable. The nozzle hardware has to be machined out of 15CDV6 steel forging with high precision. The motor is tested in the vertical mode in order to avoid exhaust gas hitting on the ground and getting deflected back to the motor. This calls for extensive thermal protection requirements for both test stand and motor subsystems. A solid rocket motor with four reverse flow nozzles has been designed, realized and twice static tested successfully. The intricacies involved in the development of LEM are presented in this article.