  We describe the technique used to develop on-orbit calibrators for IRAC and
validate the method for either K0-M0III or A0-A5V stars. For SIRTF, the
approach uses all available optical, NIR, and MIR photometry, and yields
absolute spectra from UV to MIR. One set of stars is from Landolt's network of
optical standards, the other from Carter-Meadows IR standards. Traceability to
the Cohen-Walker- Witteborn framework of absolute photometry and spectra is
assured. The method is based on using either "supertemplates" to represent the
intrinsic shapes of the spectra of K0-M0IIIs from 1150A to 35 um, or Kurucz
synthetic spectra for A0-5V stars. Each supertemplate/model is reddened
according to a star's extinction and normalized by characterized optical
photometry. This paper tests our ability to predict NIR (JHK) magnitudes from
supertemplates or models constrained by Hippa- rcos/Tycho or precision
ground-based optical data. We offer absolute calibrated spectra of 33 optical
standards to demonstrate the viability of this technique for a set of IR
calibrators 100-1000 times fainter than we have previously publ- ished. We
calculate the absolute uncertainties associated with predicting IRAC mags for
the faintest cool giant and hot dwarf in this new set of calibrators.
