The ALTAIR (Airborne Laser for Telescopic Atmosperic Interference Reduction) Project provides a precision [0(0.1%) uncertainity] photometric reference calibration using in-situ-calibrated light sources above the atmosphere, in the optical and microwave spectra.
Please see the Talks + References link for a number of talks and papers about the project and its history. The ALTAIR project is presently graciously funded by multiple federal agencies in both the U.S. and Canada, which you can see in the links on the left.
Some ALTAIR photos (site under construction as well) can be found at http://altairphotos.shutterfly.com/pictures .