567 The FOT needed to develop an option that would allow GPM to control eccentricity  growth without violating  the geodetic height  requirements, or at least one that would minimize loss of science for the remainder of  the prime mission. Solution proposed was to increase GPM’s drag area profile by unfeathering the solar  arrays panels. Similar to how the array profile was changed during early orbit check out to reduce drag, the  FOT could change the array profile to one that could create sufficient drag needed to l ower the spacecraft’s  geodetic height faster than the growth of the eccentricity. The benefit would be that no additional maneuvers  would be required to maintain orbit requirements. The predicted analysis showed that using the largest drag  profile, profile G, the eccentricity requirement could be maintained for several months . Hence, as shown in  Figure 16, in August 2016 the Tracking Pr ofile was changed back to G  [5]. 

Figure 16. -Y and +Y SADA Tracking Profiles used since launch date  

When using Profile G, trending was showing the SA profile induced additional cycles on the SA actuators ,  thus putting an unnecessary strain and risk to the spacecraft. Pre- launch analysis predicted that 3- years  into the mission the Solar Arrays would cycle  (out and back) around 18,000 times per wing . This was seen  as unnecessary and so a switch was made to profile K . Due to the switc hing from the Profile G to the  Profile  K control table early after launch the +Y gimbal had only reached just under 5000 cycles, and the   -Y gimbal had reached just under 9000 cycles. While the FOT trending of the systems shows no signs of  motor degradation or slippage, the concern for staying on Profile G indefinitely was that the result in a large  number of cycles could potenti ally lead to a solar array drive failure before the fuel projected mission end  of life  [5]. 

The concern was prompted from lessons learned from GPM’s predec essor TRMM. Returning to the G  Profile to increase drag was resulting in a faster increase in the number of cycles which increased the  chance of solar array drive failure before fuel ran out. The rate can be observed in Figure 16, where the  green trend represents the number of cycles that would have been encountered if cont inuous tracking had  been  used since launch and the red trend is what was actually used when the FOT switched between G  and K with G  being the portion with higher  slope . While the orbit requirements w ere being maintained under  Profile  G, in addition to the increased number of cycles , Profile G was discovered to cause hardware  concerns with the solar arrays at certain beta angles  as sunlight was able to reach parts of the SC that had  not previously when solar arrays were fixed,  resulting to temperature s pikes on SADA  [5]. 

The decision to move away from  Profile G was finally aided by the fact that while the increase in drag  helped in maintaining the requirements for the first eight months after implementation, future predictions  showed that the continual drop in solar activity would ultimately result in repeated violations of the mission  requirements starting in early spring of 2017. Therefore, in May of 2017, the tracking profile was switched  back to Profile K and continued since. This current profile maximizes the amount of feathering, aimed to   reduce the drag caused by the large solar panels during flight by strategically positioning the two wings  alternatively depending on the beta angle variations . Feathering the wings minimizes the projected area in  G  G  K  K  K  K  G  G