Mission design of the Global Lidar Altimetry Mission (GLAMIS)

The Global Lidar Altimetry Mission (GLAMIS) proposes a distributed network of novel spaceborne lidar to provide a regularly updated global lidar map that could be employed by governments and businesses for applications such as flood modelling, urban planning and commercial forestry. The very narrow swath of a lidar instrument makes achieving global coverage a significant challenge. Unlike with most Earth observation technologies, the swath width of a lidar system increases as the orbit altitude decreases, due to the reduction in energy per shot needed to get a measurable return for each pulse. Because of this, Very Low Earth Orbits (VLEOs) offer the possibility to significantly decrease the number of spacecraft required for GLAMIS to achieve global coverage in a given time. This paper presents the analysis of a range of mission architectures, showing that the performance improvement at VLEO altitudes is significant. Assuming a desired imaging probability of >80% (when accounting for cloud cover), 14 500 kg spacecraft at a 200 km altitude would provide the desired coverage at 20m resolution to 95% of the Earth's land in one year. Using a 400 km altitude orbit, 63 spacecraft would be required to provide the same coverage. As such, the use of a VLEO 200 km altitude orbit could provide a reduction in mission cost of approximately 70%, from $355M to $96M. If a propulsion system that could maintain the VLEO altitude could be integrated for less than this cost difference, then GLAMIS could see significant cost savings.