Lock Din details  Once the rings are bonded to the tubes, the locking pins / rollers are installed into precision radial bores in  these inner and outer rings. When the segment locks, the pins are pushed into the sockets by custom  wound torsion springs, two for each pin. The ‘arms’ of the springs also  provide alignment for the pins, keeping the roller in the groove. The pin /  roller combination allows any tube dimensional change to be insignificant  during the deployment, as the spring compliance takes up any bumps or  dips. When the tube section reaches end of travel, the locking pins are  pushed into tapered holes, causing the tubes to become rigid with  respect to each other. Guide ramps are provided at the end of travel to  ensure that the pins are aligned with the sockets. Each locking pin has a  slight taper (i.e., <20° included angle) that fits into the corresponding  tapered socket. This gives a ‘self-locking’ feature to the pin, offering  increased rigidity and prevents the pins from backing out under slight  vibrations. With six lock pins engaged per joint, three inward acting, three  outward, the boom exhibits great rigidity, and offers redundancy in the  event that one pin (or more, up to three maximum, as long as they are not in same ring) does not lock. Figure 9. 50-mm Tube  End Lock Pins (EM)  Rollers are fitted to the tips of the locking pins to minimize deployment drag when rolling in the tube’s  grooves. Repeated deployments have shown no signs of wear to the tube or the rollers. To provide  conductivity, the tapered portion of the pins and sockets were Alodined, while the sliding cylindrical parts  were Type Ill black anodized to give good wear and low friction sliding properties. The Gr/E exhibits a low  surface resistance too, enabling the boom to easily meet the surface resistance requirement of <lo8  ohms per square, throughout its stroke. The drag was measured to be 3.1 N on average for the  assemblies. The main function of the rollers is to keep the tubes aligned during deployment, so that the  pin engagement is virtually guaranteed at the end of stroke.  Shape Memorv Allov Release (SMAR) details  The SMAR uses the interesting phase change properties of a 50% titanium - 50% nickel alloy (trade  named Nitinol initially) to provide the actuation of the Impact Boom. This device, pioneered by TiNi  Aerospace‘ in cooperation with UCB-SSL, takes advantage of the -4% dimensional change in the drawn  alloy wire when heated above its transformation temperature to let a ball detent assembly release a large  spring loaded retracting pin. Since there was a large design load (50 Gs), >2.5 kN retraction force was  needed. A force amplifier was added to the TiNi standard P50 (-200-N [50-  Ib] pin puller). The force amplifier contains a stack of Belleville washers,  preloaded and held by the P50 pin in another ball detent assembly,  providing a final pull force exceeding 3 kN. When an electric current is  passed though the Ti-Ni wire, it changes phase, elongates, releasing the  primary pin, which then retracts and releases the main pin, which retracts  with great force, allowing the Stacer to deploy. The main benefit of using an  SMAR, aside from increased safety as no explosives are used, is that the  flight unit can be tested over and over again (hundreds of cycles), and is  simply resetable with a hand tool, with no temperature or time dependant  constraints. I  1 a  Flvweiaht Brake Figure 10. Shape  After the SMAR has been triggered, kick springs push the tubes out of the  combs and the deployment assist device pushes the Stacer out of the  canister with a force of -90 N, giving the assembly a good initial velocity.  The Stacer continues to provide force throughout the travel, so the deployment velocity would continue to  increase until a balance between drag and push is achieved. This balance is never reached by the boom,  so the deployment velocity reaches a ‘run-away’ condition rapidly, with the possible issues of lock pin  shearing, ring-tube separation or other damage as consequences. As with every Stacer, a means to limit  deployment velocity is incorporated. For the Impact Boom, a flyweight brake mechanism is attached to Memory Alloy Release  Assembly  TiNi Aerospace, San Leandro, CA 94577 6  55