© 2020 Lockheed Martin Corporation   369 Lessons Learned D uring the  Development , Qualification , and   Production of the  MM S olar Array 

Thomas B. Pace* 

Abstract  

The Multi -mission Modular Solar Array (MM Solar Array) is Lockheed Martin’s fourth generation flex array.  The MM Solar Array was designed to be a high- powered solar array , 7.5-12.5 kW and higher  per Wing    (15-25 kW and higher with 2 Wings per  spacecraft ), that is easily configurable for a number of different  missions. The prime objectives  during the design process were a  finished product that was cost -effectiv e,  easy to manufacture , and modular.  

Like previous generations of Lockheed Martin flex arrays, the MM Solar Array Z -folds the blanket and stows  it between two rectangular composite structures that protect the blanket during ascent on the launch  vehicle. Once on orbit, the MM Solar Array deploys in two phases. During phase one of the deployment,  the launch locks are released, and hinges move the MM Solar Array away from the vehicle and position the  blanket for deployment. During phase two of the deployment, motorized actuators are energized and the  mast is deployed, which in turns pulls the Z -folded blanket open. At the end of the deployment, two blanket  tensioning mechanisms are engaged. These mechanisms ensure the blanket behaves as a planar   membrane throughout the life of the vehicle, thus cr eating a stiff structure that can survive vehicle engine  and thruster firings. Once deployed, the MM Solar Array measures approximately 23 meters (75  feet) from  the base of the solar array to the tip. O ne of the bigger design challenges with the MM Solar Array was to  survive an orbit -raising maneuver , i.e.,  an apogee engine burn , with two 23 -meter ( 75-foot) long MM Solar  Arrays fully deployed on opposite sides of the vehicle. The structure and the hinges  of the MM Solar Array  had to be designed to survive this high loading condition.  

During the development, qualification, and production of the MM Solar Array many lessons were learned.  In composite manufacturing, a critical lesson regarding cure profiles and how small variations can adversely   change the behavior of a composite structure were learned. In mechanisms, proper handling of springdriven devices so as not to damage the device were learned. In test, a simple but important lesson was  learned on est ablishing the correct test temperatures for a thermal cycle test of a complicated mechanical  assembly. Also in test, the degradation of the strength of composite structures at cold temperatures was  investigated. In the supply chain realm, lessons were learned about how one supplier  might interpret what  was thought to be a clear requirement completely differently than another supplier . During failure  investigations, an important lesson was learned about obtain ing an independent perspective of the failure  at hand. Some positive lessons were also learned, such as getting manufacturing and tooling involved early  in the design process  led to a smooth manufacturing process. Another positive lesson was that requalificati on of a heritage mechanism is a good idea, especially if the mechanism has not been built in over  15 years.  

The lessons learned in the development, qualification, and production of the MM Solar Array resulted in a  cost-efficient and manufacturable solar array design that can be easily configured for any number of highpowered missions. Four MM Solar Array Wing Assemblies are currently in- orbit on two different vehicles.  The launch of Wings 5 & 6 is  scheduled for early 2020 . 

* Lockheed Martin Space, Sunnyvale, CA;  tom.b.pace@lmco.com  

Proceedings of the 45th Aerospace Mechanisms Symposium, NASA Johnson Space Center, 2020