13
The Material Available
Solar composition by mass
Element   % by #         % by mass
  H    91.0      70.9
  He    8.9      27.4
  O     0.07      0.8
  C     0.03      0.3
  Ne    0.01      0.2 
  N     0.008     0.1
  Fe    0.003     0.1
  Si    0.003     0.07
  Mg    0.003     0.06
  S     0.002     0.04
•Inner solar system dominated by silicate rocks
–SiO2 (quartz)     Mg2SiO4  Fe2SiO4 (olivine)     etc.
•Outer solar system dominated by H2, He, ice (H2O)