On February 20 1998 two rockets were launched from Puerto Rico as part of t
he Coqui Dos campaign. Data from on-board photometers and ground-based data
from a Na lidar and an airglow imager allowed an estimate to be made, usin
g both the TIME-GCM and MSIS models, of the branching coefficient alpha for
the Na airglow emission. Assuming the hydrogen density is within the range
predicted by the two models the data are consistent with cu being less tha
n 0.05. This value is well below a recent theoretical estimate of 0.67 and
also below the nominally accepted value of 0.1 derived from previous aerono
mic data.