99   The qualification tests used REACT as the release mechanism within a solar array (HDRM). HDRMs are  used by SSTL to secure deployable solar panels against the spacecraft during launch, and release once  commanded in orbit. SSTL specifically adapted the HDRM design and qualification test set up to integrate  the REACT actuator. Historically, many of the release actuators used by SSTL are not resettable by the  end user and are must  be returned to the manufacturer after one use, causing large impacts on schedules.  REACT has the advantage of being easy to reset and non- explosive.  

The qualification test plan was driven by the requir ements set out at the start of the project. This included  testing the 35- kN preload, making sure the release and reset functions were as expected, and verifying that   there was no degradation in performance after experiencing simulated in- orbit environments  through  vibration and thermal vacuum testing.  

After first confirming that  the actuator received met expected properties such as mass, dimensions and wire  resistance, it was set up in a tensile test machine to verify  it could hold the maximum preload (Figure 14  left). The actuator was fixed in the machine using bespoke MGSE which held the actuator down and pulled  a load of 35 kN on a bolt fixed within the mechanism, and held for a period of time. This was repeated  including application of a low no- fire cur rent of 0.8 A on primary and secondary circuits to make sure that a  small accidental current would not inadvertently cause deployment. Tests showed that the actuator held  the load perfectly with no reduction in load.  

The actuator was fitted into SSTL ’s solar array deployment test setup (Figure 15 center). The actuator was  mounted within a hold down and release system incorporating a cup (spacecraft side) and cone (array  side), kick- off springs to help separation, and a bolt catcher to trap the deployed bol t from the actuator.  REACT was attached to the cup within the setup. The final deployment angle was  set by SSTL tape spring  hinges. Deployment was confirmed by an integrated micro- switch, which allowed for measurement of the  mechanism ’s actuation time. The functional tests were carried out using preloads of 16, 22 and 35 kN on  both primary and secondary circuits . During these tests, shock was measured with the use of two  accelerometers attached to the system. Each planned functional test successfully deploy ed the panel, and  shock values remained under the required limit.  

After the successful deployment tests, the system set up was moved to the vibration test machine and  underwent low level sine tests, qualification sine tests and random vibration in all three axes, at a nominal  preload of 22 kN. The system passed all vibration  qualification tests. The preload on the REACT mechanism  did not decrease during testing and the deployments performed post testing were successful.  

The final qualification tests occurred whi le attached to a thermal plate within a vacuum chamber over a  period of 4 days. Initially, one full thermal cycle at vacuum was carried out, with a maximum temperature  of 60°C and minimum of - 85°C, after which deployment tests occurred at a nominal  preload of 22 kN at hot,  cold and ambient. All thermal vacuum tests were successful with actuation time varying with temperature  as expected. Ambient pressure and temperature deployment tests on primary and secondary circuits  were  carried out after the thermal vacuum testing to prove function had not been compromised. Both tests were  eventually successful, although the primary test required an increase of voltage to the actuator to get a  successful deployment.  

Conclusion   The REACT mechanism successfully completed qualification testing whilst integrated within an SSTL  HDRM for a small satellite deployable solar panel. The qualification testing demonstrated that the  mechanism could perform as required during all stages of operation on ground and in simulated orbital  environments. There were some occasions in which difficulty was experienced in actuating the device due  to lack of margin between expected actuation time and maximum allowed pulse duration, however, with a  more flight representative electrical setup, these issues would most likely be removed.