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Installing a Kevlar liner for Static Test June 27th

The 4 grains had been poured 7 days previously so had setup well in the warm dry Mojave heat of the FAR motor fabrication facility.  The process commenced with the removal of the core mandrels used for the bates grains.  
The motor consists of 4 grains made from 14.5" sections of 7.5" ID x 7.625 OD Sono tube.  The following cores were used:
  • 2" hollow UHMW cylinder
  • 2.25" Solid UHMW cylinder
  • 2.25 to 2.625" tapered hollow aluminum core
  • 2.625" to 3" tapered hollow aluminum core

The 2.25" core and smaller tapered core removed easily.  The larger tapered core had propellant that had migrated up the inside of the mandrel.  The 2" hollow UHMW cylinder seemed to have gone slightly hour glass shaped.  The UHMW hollow core was removed by drilling a hole in the top, passing a piece of rebar through the hole and then pressing a long rod against the rebar to pull the core out of the grain using a 20 ton press.  This was done to keep the grain in tension instead of compression to prevent cracking. 

Use of hollow plastic cores for large diameter grains is not advised for future work. 

The grains were stacked vertically on the prepared stand and wood spacers were used to space the grain stack 2.25" off the surface of the stand plate.  This space was to allow for space for the nozzle and retaining ring to be inserted into the motor tube. 

Vertical alignment was carefully determined using a 4' level and the grain stack was tensioned using the threaded rod through a piece of 1.5" pipe. 

The stack was dry wrapped with a pre-cut piece of Kevlar and the seam was taped with mylar tape.  The Kevlar was then lightly wetted using the very thin MAX CLR epoxy from polymer composites.   After wetting the Kevlar was wrapped tightly using a spool of plastic shipping wrap to obtain good compression.  

Andy and Kale from Virgin Orbital were a great help in this process!

The motor tube was then slid over the Kevlar wrapped grain stack and it was allowed to cure. 
Assembled motor with Rick for scale. 


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