We derive a yes/no requirement for the usefulness of an O2 lidar as part of the ASCENDS mission that incorporates errors due to atmospheric state misspecification as well as instrumental noise. We find that the larger the CO2 instrument's sensitivity to surface pressure errors, the lower the precision requirement for the O2 instrument to be useful. In particular, the 2um CO2 instrument would benefit the most from the inclusion of an O2 lidar with high precision retrievals of surface pressure.