FTS CubeSat Constellation Providing 3D Winds

A novel small satellite constellation utilizing a Fourier Transform Spectrometer (FTS) instrument onboard 6U CubeSats would allow weather forecasters to have unprecedented understanding of global tropospheric wind observations from space; enabling more accurate, reliable, and longer-term weather forecasts. Three FTS CubeSats flying in formation and separated by a known time delay would provide cooperative measurements and overlay scenes necessary to compile vertical profiles of the wind field. A constellation of formation-flying FTS CubeSats would allow measurement of the global wind field; providing unparalleled coverage and allowing longer-term weather forecasts. This paper will describe the recent advancements in CubeSat capabilities and future work required to meet the objectives of the FTS mission. The innovative approach the Exelis/University of Michigan team is taking to power, attitude determination and control, communications, and constellation formations will also be discussed. System and subsystem trades were optimized with emphasis on science mission requirements while balancing overall mission cost. 3D WINDS MISSION BACKGROUND The 2007 Earth Science Decadal Survey established the need for three dimensional (3D) wind knowledge to improve weather forecasts. According to the survey, “tropospheric winds are the number-one unmet measurement objective for improving weather forecasts” and “would provide direct and measurable societal and economic effects”. The survey calls for a 3D Winds demo mission using a Doppler lidar in a sunsynchronous (SSO) low earth orbit (LEO). Anticipated launch would be in the later half of this decade at an estimated cost of $650M. 1 3D Winds from On-Orbit Instruments To address the unmet need of 3D winds, there have been efforts to improve upon data products from existing on-orbit assets. While wind field estimation using visible/infrared imagers like GOES, AVHRR and MODIS is well documented, they are unable to resolve the vertical structure of cloud tops and upper tropospheric water vapor distributions. As a result, these products are usually provided for three layers of the troposphere, are spatially discontinuous, and cannot adequately support Numerical Weather Prediction (NWP). 2,3 Current 3D Winds Development Efforts The two major ongoing efforts for 3D Winds mission, TWiLiTE and OAWL, have used a Doppler Lidar instrument via airborne platform as recommended by the decadal survey. 4,5 The Doppler lidar profiles winds by transmitting a laser pulse through the atmosphere, a fraction of which is backscattered by molecules and aerosols in the air and then detected by a Doppler receiver in the instrument. The received signal is then analyzed to determine the frequency shift introduced by the mean velocity of the scatterers, which yields the horizontal wind velocity of the air. 4 The issue with a Doppler lidar system is that it has never been proven on a spaceborne platform, requires large volume and power, and is still in development testing. Currently, there is no published plan to move either instrument from airborne testing to spaceborne operation. This paper speculates that a $650M+ demo mission for a spaceborne Doppler lidar mission is unlikely in the current fiscal environment for terrestrial observation platforms within NASA and NOAA. Yet the need for 3D winds data remains critical for NWP.