the FEA Model was satisfied by adjusting the spring constants for each mechanism in each direction until  the model matched the test results.  

The only vibration requirement left to satisfy was t he post-vibration visual inspection. The aluminum  tongue in Vespel slot interface of the XYZ mechanism  was of particular concern. The Vespel slot was  initially 0.645-mm (0.254-in) wide and remained 0.645-mm (0 .254-in) wide after X-axis and Y-axis testing.  After Z-axis testing the slot opened up only slightly  to 0.650-mm (0.256-in) wide, which was within  specification. Virtually no debris was collected in  the tent placed around mechanism and no traces of  Vespel were found by contamination inspection. The redesigns made to the other mechanisms also  proved successfully and, aside from minor pusher tip di mpling, there was no significant wear detected in  any of the interfaces. 

Thus, the ETU deployer and ETU spacecraft passed the post-vibration visual inspection requirement and  successfully completed all of the requirements impos ed on it for qualification for space flight use. 

Lessons Learned 

• Transducer-based rate sensors are not the only choice for velocity data. High-speed video gave  direct spin rate information, though data had some pixel-picking error and parallax had to be  accounted for. The photo technician and equipment  rental cost about $10,000 for 2 weeks.  • All parts of a test setup that may lead to discrepancies from a theoretical model should be  considered before testing. Correcting a model afterw ards to match a test is not as convincing.  • Determining the on-orbit spin rate from ground data compounded errors. This would have been  the case even with on board transducers. The mo st straightforward measurement would have  required a Zero-Gravity research lab, with its ow n set of constraints and significantly higher cost.  • When a mechanism is going to face vibration,  sharp edges should always be avoided to reduce  the chances of gouging or chewing up hardware.   • Hard plastics, such as Vespel, could be used in stead of metals if a mechanism shows wear.   • In our drive for miniaturized components, we started with innocently low assumptions for margin  requirements and had to pay for it with extra test ing. Instead of margins in the 1-2 range, 4 is  recommended for initial design. When this extra margin is not achievable due to resource  limitations on micro-satellites, component testi ng must make up the difference in confidence  level.   

Conclusions 

The Frisbee spin up is a viable technique for imparting a mission-critical spin rate to a micro sat. Deck  space is preserved, the design is simple, and rate  precision has been demonstrated to better than ±10%  with low tip-off.  The spin rate was measured by hi gh-speed video frame capture of the target locations on  the deploying spacecraft. The design was demonstrat ed with development hardware and a flight-like  engineering test unit qualified the design.   

Low design margin and heritage was compensated by mo re component-level testing in a “skunkworks”  environment. In the move towards miniaturized spac ecraft for constellation science missions, new ways  of dealing with risk must be adopted. This single-st ring spacecraft mission afforded the opportunity to  research strategies for mechanism development under a less risk-averse atmosphere. Reliable suppliers,  adequate facilities, and experienced personnel made up the balance of the success formula.   

References 

[1] “ST-5 Critical Design Review” Presentation1, Peter Rossoni June 2002  [2] Michael Bokaie and Kevin Barajas: “Non-Explos ive Pinpuller and Rotary Actuators” 32nd Aerospace  Mechanisms Symposium, NASA K ennedy Space Center, May13-15 1998  [3] SAI-ANYS-396 William McGill1, Swales Aerospace, 2003                                                    1  ST-5 internal project document, s ubject to export control restrictions  72