When testing deployables, the desire is to prove beyond question that the mechanism will deploy in  space, however, it must be tested here on the ground first. How many times? GEVS provides a minimum,  and each program defines how many additional operations. This brings up  wear margin: the design must show that it is sufficiently robust to survive  testing and flight without degradation. The EM served this purpose, getting  many deployments more than the FMs did. After identifying these values, a  test plan was developed, reviewed and implemented.  Testing large deployables in a simulated space environment is difficult, and  ensuring that the test actually verifies functionality is critical. Deploying the  boom horizontally was initially considered since it is easier to develop a 6-m-  long test rig that rests on the floor. After a few small efforts in this orientation,  it was realized that the only way to ensure that roller drag on the tubes was  representative of actual orbital deployment would be to deploy the boom  vertically. While several interim off load pulley systems were used, all the  verification deployments were performed on the thermal vacuum gantry.  To this end, a tall vacuum chamber was designed and built to allow the tests  to be performed (Figures 14 & 15). Inside the chamber ‘chimney’ a gantry  that allowed a counterbalance pulley system to provide G negation was  installed (Figure 16). The distance from the top of the boom to the pulley was  maximized to provide the least possible restorative (centering) force to the I  sections of the boom during deployment.  Figure 16. Gantry  Detail  Counterweiaht DescriDtion  To demonstrate the force (torque) margin, the masses to be used for the counterbalance force had to be  chosen to show that the Stacer would be energetic enough to deploy the boom. The mass of each of the  tubes (in flight configuration) was added to give neutral balance, plus the Stacer neutralization mass  (determined by bare Stacer vertical deployments to be 164 9). This mass (5214 g) was decreased by 213  of the Stacer minimum force (31 N * 0.67 = 20.7 N, converted to kg: 20.7 N / 9.98 kgm/s2 = 2.07 kg) and  subtracted from the counterweights. All 10 verification deployments were ‘force margin’ deployments and  were successful. After deployment, each boom was inspected for wear, with no signs of degradation of  rollers or Gr/E. The EM has been deployed -20 times, and is still in good condition.  Initially, the counterweights far exceed the G negation requirements for deployment as only one tube is  being deployed, while it is being pulled by the counter weight for 4 tubes. This is not invalid for our testing  needs, as the flyweight brake dissipates the extra force, keeping the velocity in correct range. The area of  interest is the very end of travel, where the Stacer force is lowest, and the full mass is being acted on. It  was this point that the gantry design was built on.  Maanetometer Alicmment Verification  After deployment, the alignment of the Mag needed to be measured to determine compliance with the  specification. A very accurate digital level (resolution: 0.01 degree a.02) was used for this activity. The  measurements were taken relative to the origin and coordinate system established in the Interface  Control Document (ICD)’ for the boom. The relative angles for the mounting feet for the X - 2 and X - Y  planes were recorded at the mounting foot. The angles for the same planes (translated out to the Mag  tray) were then measured. The difference was taken, yielding the deviation of the Mag tray from the  mounting plane. Figure 17 shows the measured differences of the deviations for the FMs for each plane.  See Appendix A for ICD Details 9  60