Gravity waves, sometimes called buoyancy waves, have dramatic effects on the circulation in planetary atmospheres through the wave drag and diffusion they induce. Because they have small scales compared to the resolution in global models, these effects are parameterized. The importance of including parameterized wave drag has long been recognized as critical to weather prediction, and now researchers are demonstrating new sensitivities to gravity wave drag in simulations of Earth's climate that incorporate trends in greenhouse gases and ozone-depleting chemicals. Modelers using the parameterizations must set numerous poorly constrained parameters that describe wave propagation properties and amplitudes. Key to accurate parameterization of the wave drag is knowledge of the spectrum of wave momentum flux as a function of wave phase speeds and wavenumbers. Global constraints on wave momentum flux are needed that can only come from satellite observations. Gravity wave scales are small compared to typical satellite measurement footprints, yet in the last 15 years detection of atmospheric gravity waves in satellite data are becoming more common. Determination of wave momentum flux from these observations places special demands on the measurements that have only been met with some of the more recent data using innovative analysis techniques. To realize the goal of defining global constraints sufficient for climate modeling requires merging of a collection of measurements from different techniques on different satellites with full characterization of the limitations of each technique as well as the uncertainties.