Upholding the SPIRIT II precedent, sandwich composite deckplates were built for this payload. The SPIRIT II plates were studied after the payload was recovered and learned of their successful traits and found areas for improvement. Bruce Davis and Brian Pomeroy let this effort and wrote a paper, published by the European Space Agency on the advantages of composite plates over their aluminum counterparts as well as lessons learned.
The SPIRIT III deckplates are lighter and stronger then the SPIRIT II plates. The use of plastic inserts, new cutting methods and the elimination of filler material has simplified the manufacturing process and saved in material costs. The SPIRIT III payload will have 9 composite decks saving approximately 18 pounds when compared the the standard aluminum plate used by NASA.
ESA Paper Abstract
Flight Qualification Test