212 There are several heritage aspects of MAIA which are reminiscent of the Multi -angle Imaging  SpectroRadiometer (MISR) mission, which has been using a multi - angle imaging approach to image  aerosols in the atmosphere, imaging targets from nine angles, using nine cameras, since the year 2000.  The reduction of the number of cameras required from nine for MISR to one for MAIA, is largely thanks to  the Bi -Axis Gimbal Assembly (BGA), which articulates the MAIA camera to achieve multi -angle pointing.  

A key heritage item in the MAIA instrument design is the Mini Dual Drive Actuator (MDDA), which is a  single- fault tolerant electromechanical device, used by MISR as its Cover Actuator, and as the North and  South Calibration Plate Actuators. It also flew on Cloudsat and Galaxy Evolution Explorer (GALEX). The  MDDA is valued largely due to its redundancy, providing the high- reliability desired to produce necessary  mission -critical motions. The single- string Mini Uni -Drive Actuator was used on Mars Pathfinder for the High  Gain Antenna Gimbal Actuators. Its design was inspired by the Standard Dual Drive Actuator, originally  designed at JPL by Doug Packard. [ 1] The MAIA MDDAs  will marry the applications of the Mars Pathfinder  gimbal operation and the multi -angle imaging of MI SR, with one MDDA driving each of the two axes of the  MAIA BGA.  

Figure 1. Mini Dual Drive Actuator  

However, the MAIA project seemed to be in luck, as there existed a set of spare Harmonic Drive units in  flight storage, which had been originally purchased by the Cloudsat project. The Cloudsat actuator build  had occurred just following MISR in the 1990s, and used the MDDA as its Reflector Mechanism. As fate  would have it, the lot of flight spare size 10 pancake HD s had been preserved in their  original heat -sealed  packaging, l ocked away in flight stores since their receipt in 1995, as delivered by their namesake  manufacturer who, at that time, was operating under a different ownership than the Harmonic Drive LLC of  today. Flight spare duplex output bearings were also identified, as well as spare Duplex Motors, which  would end up getting sent back to Ducommun  Technologies , their original manufacturer, to be rewound  and have bonds, wires, and Hall sensors replaced, for the new MAIA application.  

MAIA Actuation and the Endurance Test   In flight, the two MAIA MDDAs will drive two slightly different load and speed profiles, with sweeps as well  as stop and stare motions, dependent on the axis for which they are designated and the mode of operation  of the instrument. The nominal expected output loads are around half of the maximum load rating of the  size 10 HD, which  is documented at 5.1 Nm ( 45 in- lb), and the application was one of continuous use  throughout the mission life. Even with heritage and redundancy, no other MDDA application was similar  enough to avoid some testing. T his called for the execution of a new test, with the intention of verifying the  fatigue life of the mechanism and its endurance with  the MAIA operational profiles.  

For simplicity, a hybridized profile was created, to capture both the higher loads and the requirement for  repeated gear tooth engagement of the off-track axis profile, and the higher speed and larger rotational