© 2020 Lockheed Martin Corporation   375  

Figure 11 - Orbit Raising with Deployed MM Solar Arrays  

Lessons Learned Overview  

During the design, development, qualification, and production of the MM Solar Array, many valuable  lessons were learned. Lessons learned were plentiful during development  and qualification, but some of  the most important lessons were learned during the production of the flight MM Solar Array s. Some lessons  were still being learned during the production of the fifth and sixth MM Solar Arrays.  

Thermal  Testing  of Complex Assemblies  

The Deployer Assembly is a complex subassembly  of the MM Solar Array. It contains structural panels  made from carbon- fiber facesheets with aluminum honeycomb core, precision mechanisms such as the  drive actuators , large aluminum sleeves that guide the mast during deployment , and the mast  itself. The  mast of the MM Solar Array is a composite lenticular strut  that is based on work originally done by Dr.  George Herzl , a co- founder of the Aerospace Mechanisms Symposia. When deployed the mast is in a  stress- free state. But when stowed, i.e. , flattened and w rapped up around a drum, the mast is in its most   stressed  state . The Mast is in its stowed state during thermal cycling of the Deployer Assembly. Before  starting the qualification thermal cycle test of the Deployer Assembly, the hot and cold temperature  extremes needed to be established for the test. A thermal model was used to determine the temperature  extremes that would be experienced by each part of the Deployer Assembly during the mission. The  analysis showed that the structur al panels of the Deployer Assembly were the driving components, so t he  thermal extremes of the Deployer Assembly thermal cycle test were established based on these p anel  temperatures. Once this assessment was complete, it was noted that t he drive actuators would have to be  removed from this test because they contained circuit cards with electronic components that could not  survive the planned temperature extremes  (during flight, heaters are used to maintain the temperature of  these circuit  cards) . However, the team forgot to assess whether any other parts of the Deployer Assembly   had any temperature restrictions. Instead, the team went forward with the qualification thermal cycle test  and every remaining component in the Deployer Assembly w as tested to the predicted temperature  extremes  of the structural panels . Upon completion of the test, the mast was unrolled and deformities in the  mast were observed. Further investigation revealed that the deformities were caused by subjecting the  stowed mast, i.e. , the stressed structure, to a hot temperature extreme that was above the glass transition  temperature of the composite resin . Certain members of the team were aware of this limitation, but this was  not communicated to the team member that wrote the test plan. There are multiple lessons learned in this  example. The first is that a stressed composite structure should not be thermal cycled above its  glass  transition temperature. Two is that the limitations of all components in complex assemblies must be known  prior to beginning a thermal cycle test  or any other test . And three is that all members of the team should  be involved in establishing the thermal extremes for a thermal cycle test  of a complex assembly .