The general theory of porcupines, perfect and imperfect
  Porcupines are networks of gravitational wave detectors in which the
detectors and the distances between them are short relative to the
gravitational wavelengths of interest. Perfect porcupines are special
configurations whose sensitivity to a gravitational plane wave is independent
of the propagation direction or polarization of the wave. I develop the theory
of porcupines, including the optimal estimator \hat{h}^{ij} for the
gravitational wave field; useful formulae for the spin-averaged and
rotationally-averaged SNR^{2}; and a simple derivation of the properties of
perfect porcupines. I apply these results to the interesting class of
``simple'' porcupines, and mention some open problems.
