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We perform a Fisher matrix calculation of the predicted uncertainties onestimates of the cosmic string tension Gmu from upcoming observational data(namely, cosmic microwave background power spectra from the Planck satelliteand an idealized future polarization experiment). We employ simulations thatare more general than others commonly used in the literature, leaving the meanvelocity of strings, correlation length of the string network, and "wiggliness"(which parametrizes smaller-scale structure along the strings) as freeparameters that can be observationally measured. In a new code, StringFast, weimplement a method for efficient computation of the C_l spectra induced by anetwork of strings, which is fast enough to be used in Markov Chain Monte Carloanalyses of future data. Performing a calculation with the string parametersleft free results in projected constraints on Gmu that are larger than thoseobtained by fixing their values a priori, typically by a factor of ~2-7. Wealso find that if Gmu is equal to the current observational maximum, Planckwill be able to make a confident detection of strings. However, if Gmu is twoorders of magnitude smaller, even a perfect, lensing-free measurement ofpolarization power spectra will not be able to detect a nonzero string tensionat better than 2 sigma confidence.

Predicted Constraints on Cosmic String Tension from Planck and Future CMB Polarization Measurements