From October 1984 through August 2005, the NASA Earth Radiation Budget Satellite (ERBS)/Earth Radiation Budget
Experiment (ERBE) nonscanning active cavity radiometers (ACR) were used to monitor long-term changes in the earth
radiation budget components of the incoming total solar irradiance (TSI), earth-reflected TSI, and earth-emitted outgoing
longwave radiation (OLR). From October 1984 through September 1999, using on-board calibration systems, the
ERBS/ERBE ACR sensor response changes, in gains and offsets, were determined from on-orbit calibration sources and
from direct observations of the incoming TSI through calibration solar ports at measurement precision levels
approaching 0.5 Watts-per-squared-meter, at satellite altitudes. On October 6, 1999, the on-board radiometer calibration
system elevation drive failed. Thereafter, special spacecraft maneuvers were performed to observe cold space and the
sun in order to define the post-September 1999 geometry of the radiometer measurements, and to determine the October
1999-September 2003 ERBS sensor response changes. Analyses of these special solar and cold space observations
indicate that the radiometers were pointing approximately 16 degrees away from the spacecraft nadir and on the antisolar
side of the spacecraft after the elevation drive failure. The special observations indicated that the radiometers'
responses were stable at precision levels approaching 0.5 Watts-per-squared-meter. In this paper, determinations of the
measurement geometry [sensor pointing direction] and of the radiometers' gain and offset are presented. These
determinations will permit the accurate processing of the October 1999 through August 2005 ERBE data products at
satellite and top-of-the-atmosphere altitudes.