Neutral Densities

One of the most challenging aspects of predicting the location of orbiting spacecraft is modeling the neutral density component in Earth’s atmosphere, which is the primary component of the drag force. Drag is the largest force acting on spacecraft in low Earth orbit (LEO), yet remains difficult to characterize. In order to determine neutral densities, we make point measurements in time and space and use models to extrapolate these measurements globally. Consequently, we suffer from a "15% error bound" in our knowledge of neutral densities due to paucity of data, which results in catastrophes such as the Iridium-Kosmos satellite collision in 2009. These types of collisions then create a plethora of orbital debris, which further increases the threat to spacecraft by the possibility of impact damage. The solution to this problem is to improve modeling efforts, and more importantly, collect in situ data. The QB50 project is designed to address this knowledge gap by collecting in situ, multi-point measurements of neutral density. QB50 is an international network of 50 CubeSats that was approved by the European Commission in January 2012 and is set to launch by 2015.


Artist rendition of the QB50 CubeSats (courtesy of Ruedeger Reinhard).

Professor Close has been leading the U.S. component of QB50, called QBUS (i.e. QB50 U.S.), and was elected to be a member of the QB50 International Steering Committee. QBUS is a consortium comprised of Stanford University, Johns Hopkins Applied Physics Laboratory, the University of Colorado at Boulder, and the University of Michigan. We have been tentatively approved to build 4 CubeSats, which will begin in late 2013.