  This paper extends the model reduction method by the operator projection to
the three-dimensional special relativistic Boltzmann equation. The derivation
of arbitrary order moment system is built on our careful study of infinite
families of the complicate Grad type orthogonal polynomials depending on a
parameter and the real spherical harmonics. We derive the recurrence relations
of the polynomials, calculate their derivatives with respect to the independent
variable and parameter respectively, and study their zeros. The recurrence
relations and partial derivatives of the real spherical harmonics are also
given. It is proved that our moment system is globally hyperbolic, and linearly
stable. Moreover, the Lorentz covariance is also studied in the 1D space.
