A B C D  Figure 7. Antenna Deployment with Motorized System  After the deployment system demonstrated successfully, the next key challenge was to prove the design  through  vibration  testing.  The  antenna  was  vibed  at 14.1  GRMS in three  axis,  which  is the General  Environmental  Verification  Spectrum  qualification  level,  as no launch  had been  determined  at that  point.  After  the vibration  in the first axis,  the antenna  was  deployed  to ensure  everything  worked  as planned.  However, the deployment revealed a problem with the design. The mid-rib hinges, actuated by the constant  force spring did not deploy. This resulted in the deployed antenna stopping in position illustrated in Figure  7C. While it was known the mid-rib hinges had a low torque margin, prior deployments had never failed to  deploy the antenna. The root cause was found to be a combination of friction and gravity from a number of  test runs  with  an extra  hinge.  When  the antenna  was  stowed,  the constant  force  spring  is unrolled  and  pulled  across  the root  portion  of the mid-hinge.  The  friction  on the spring  prevents  it from  fully  relaxing,  resulting in tension. But  vibration shifted the spring  into lowest energy state, resulting in friction that  was  originally  providing  additional  tension,  now  resisting  the deployment.  In addition,  in the configuration  the  antenna  was  deployed,  the mid  rib hinges  had to deploy  against  gravity.  The combination  of gravity  and  additional friction resulted in a negative torque margin.   After  the failed  deployment,  kick-off  springs  were  added  under  the constant  force  springs  to ensure  the  antenna deployed. Vibration test proceeded in the remaining two axes, and afterward the antenna deployed  successfully. Once, again, the antenna was taken to the RF range for testing, and found to achieve a gain  of 42.7 dBi.   One final note on the engineering model antenna: during a subsequent deployment, after the RF test, one  of the kick off springs became jammed in a closed rib which prevented the antenna from fully deploying.  Thus, a more permanent solution was required.  Flight Model  After the completion of vibration testing on the engineering model , construction of the flight model began  for the RainCube Spacecraft , a 6U CubeSat. RainCube is a precipitation radar and will be the first active  instrument in the CubeSa t form factor . Some redesign efforts were required, the firs t and foremost being  changing the rib mid-hinge geometry to allow the constant force spring to generate more torque . Other  changes included features t o better hold the ribs in the stowed position, switches for deployment  verification, and vacuum-compatible grease in all components. During construction of the fligh t model, the  torque margin was checked on th e mid-rib hinges , and found t o be more than adequate when compared to  the engineering model design.   After  construction  of the flight  model,  it was  first deployed  and then  tested  on the RF range,  once  again  achieving  a gain  of 42.6  dBi.  Next  it was  stowed  and  then  deployed  in thermal  vacuum  (TVAC)  at a  temperature  of 65°C.  In general,  antennas  are not fully  deployed  in thermal  vacuum  due  to size,  but  because KaPDA was intended for a CubeSat, it was easy to find a chamber which could accommodate a  © 2018 All Rights Reserved. Government sponsorship acknowledged.  NASA/CP—2018-219887 369