Thrust Shaping and Grain Configuration Design for a Strapon Solid Motor- a Case Study
- Paper number
IAC-07-C4.2.05
- Author
Mr. Jayaprakash Janardhanan Nair, Indian Space Research Organisation (ISRO), VSSC, India
- Coauthor
Dr. M.S. Padmanabhan, Indian Space Research Organisation (ISRO), VSSC, India
- Year
2007
- Abstract
For a new launcher being developed by ISRO for putting 4 ton-class satellites in geo-synchronous orbit, the booster stage comprises two solid strap-on motors (S200). These 3.2 m diameter motor with 207 t propellant mass each are the largest solid rocket motors being developed in India. Evolving the optimum grain configuration design for this large solid strap-on booster motor was the outcome of trade-off considering several aspects like controllability, flight dynamic pressure, vehicle acceleration and payload combined with the constraints of propellant process ability and structural integrity. Performance requirements include take-off thrust, peak thrust, thrust just before start of tail-off, nominal action time, action time dispersion and thrust fall rate during various zones of tail-off performance. The approach adopted for arriving at the optimum grain configuration design for each segment, method of controlling dynamic pressure and maximum acceleration, and optimization of motor chamber pressure and nozzle area-ratio is discussed in this paper. Propellant initial grain port dimensions are fixed considering minimum required vehicle lift-off acceleration and structural margin for all operating conditions of the segment and assembled motor. The short fore end segment provides more than fifty percent of initial thrust. Number of star branches and star geometry is based on peak thrust and maximum dynamic pressure. Port dimensions of central and aft segments are fixed to limit vehicle maximum acceleration and thrust fall rates during tail-off region. Mission study carried out to optimize chamber pressure and nozzle area-ratio. For the current strap-on configuration, MEOP = 5.88 MPa and nozzle area-ratio = 14 is found to be optimum. Any further change from this design value may result in reduction of payload fraction. Impact of segments aft end burning on vehicle acceleration and payload is also addressed. In order to size the vehicle control system and to ensure effective control on the vehicle during strap-on burn phase, it is necessary to have firm specification limits on the differential performance of the strap-on motors. The critical performance parameter in this regard is the differential thrust between the motors, especially during tail-off and ignition phases and it is predominantly controlled by the burning rate dispersion between the two pair motors. A number of iteration were done before finalizing the design.
- Abstract document
- Manuscript document
IAC-07-C4.2.05.pdf (🔒 authorized access only).
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