Design and Functional Validation of a Mechanism for Dual -Spinning CubeSats Eric Peters*, Pratik Dave, Ryan Kingsbury, Anne Marinan, Evan Wise, Chris Pong, Meghan Prinkey,  Kerri Cahoy, David W. Miller, Devon Sklair, Joshua Emig William J. Blackwell**,G. Allen, C. Galbraith, R. Leslie, I. Osaretin, M. Shields, E. Thompson, D. Toher, D. Townzen and A. Vogel Abstract The mission of the Micro-sized Microwave Atmospheric Satellite (MicroMAS) is to collect useful  atmospheric images using a miniature passive microwave radiometer payload hosted on a low-cost  CubeSat platform. In order to collect this data, the microwave radiometer payload must rotate to scan the ground-track perpendicular to the satellite’s direction of travel. A custom motor assembly was developed to facilitate the rotation of the payload while allowing the spacecraft bus to remained fixed in the localvertical, local-horizontal (LVLH) frame for increased pointing accuracy. This paper describes the mechanism used to enable this dual-spinning operation for CubeSats, and the lessons learned during the  design, fabrication, integration, and testing phases of the mechanism’s development lifecycle. Introduction The Micro-sized Microwave Atmospheric Satellite (MicroMAS) project is a three-unit (3U) CubeSat under  joint development by the MIT Space Systems Laboratory and MIT Lincoln Laboratory, currentlyscheduled to launch in May 2014. Its mission to deliver useful images of hurricanes, cyclones, and  tropical storms using a low-cost satellite stretches the limit of what has been previously accomplished  using the CubeSat platform. The payload is a multispectral passive microwave radiometer that has been  developed by MIT Lincoln Laboratory in collaboration with the University of Massachusetts-Amherst. The  payload is contained within a standard 1U CubeSat structure, occupying one-third of the total vehicle volume. All spacecraft support functions are integrated within the remaining 2U volume as part of a  separate bus structure that has been developed by the MIT Space Systems Laboratory (SSL).  In order to effectively collect data with the radiometer sensor, the spacecraft must simultaneously sweep  the radiometer field of view perpendicular to the ground-track while maintaining sub-degree pointing accuracy fixed in the local-vertical, local-horizontal (LVLH) frame. A satellite stabilized in this way is  considered a “dual-spinning” spacecraft. Figure 1 illustrates how MicroMAS will be oriented during on-orbit operations. The following sections discuss the development of the mechanism, dubbed the Scanner Assembly (SA), used to enable this motion – including design requirements; early prototypes and design  trades; and functional validation. Motivation for Dual-Spinning Design    Preliminary design analyses 1,2determined that precessing the angular momentum of an entire spinning  CubeSat as it progresses through its orbit would require torque in excess of the capabilities of available commercial, off-the-shelf (COTS) CubeSat mechanisms for attitude control. This includes the MAI-400 unit, developed by Maryland Aerospace, Inc. (Crofton, MD), which was selected for MicroMAS attitude determination and control. The MAI-400 incorporates an attitude computer, a 3-axis reaction wheel set, a 3-axis magnetorquer set, and earth-horizon sensors in a single package. 3To maintain the spacecraft’s  alignment with the LVLH frame, MicroMAS would need to slew at a rate equal to the angular velocity of  *Space Systems Laboratory, Massachusetts Institute of Technology, Cambridge, MA **Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA /g51/g85/g82/g70/g72/g72/g71/g76/g81/g74/g86/g3/g82/g73/g3/g87/g75/g72/g3/g23/g21/g81/g71/g3/g36/g72/g85/g82/g86/g83/g68/g70/g72/g3/g48/g72/g70/g75/g68/g81/g76/g86/g80/g86/g3/g54/g92/g80/g83/g82/g86/g76/g88/g80/g15/g3/g49/g36/g54/g36/g3/g42/g82/g71/g71/g68/g85 /g71/g3/g54/g83/g68/g70/g72/g3/g41/g79/g76/g74/g75/g87/g3/g38/g72/g81/g87/g72/g85/g15/g3/g48/g68/g92/g3/g20/g23/g16/g20/g25/g15/g3/g21/g19/g20/g23/g3 523