418 • It had to work correctly at temperatures ranging from 243K, reached when passing through the  Earth’s shadow, to 353K, reached during launch.  • It needed dimensional stability so that dilations and contractions did not cause tension at the  mechanical interfaces of the attachments. At the same time, if the material over-contracted at  minimum temperature, this could squeeze the antenna and prevent them from full or partial deployment.  • It needed acceptable resistance to radiation and ultrav iolet radiation, both of which are present in  the satellite’s working environment. According to re search in the literature , the e-beam radiation  effect on the polyamide would be to increase its elastic limit and decrease its elongation, neither of which poses a problem for prope r operation. As for UV radiation,  the metallic-based paint cover  used to dissipate static charges would notably in crease resistance to this type of radiation.  • It had to be extremely light. The final sub-chassis weight is 5 or 6 grams and the attachment  elements another 5 grams, which, when added to the weight of the antenna, the electrical  resistance, the thermoplastic envelope sheet, t he switch and storage thread, meant the whole  mechanism weighs in at less than 12 grams.  • Over-fragility had to be avoided to prev ent vibration problems during launch.  • It had to be as dissipative as possible so as  not to become electrostatically charged when  passing through orbital areas with high ion densities and so avoid the risk of experiencing electrostatic discharge that could affect the sub-chassis itself or other elements of the  mechanism. To improve dissipation,  the sub-chassis would be covered by zinc- or silver-based  dissipative paint, except in areas of antenna cont act. In this way, dissipation is increased in  ionized environments and there is al so increased resistance to ultraviolet radiation and, to a  lesser extent, to nuclear radiation.  • Last, but not least in importance, it had to  be simple, and if possible, cheap to make.   It was finally decided to make the sub-chassis from polyamide (PA6, PA66) using a selective laser sintering process to obtain parts designed by CAD without losing the initial properties of the polyamide produced. This material was able to acceptably fulfill the above requirements. 

Antenna Attachment   As described, the antenna had to be located in the center of each shielding edge and have a deployment angle of 45º to this edge. It was thus decided to design a hole in the sub-chassis going through the whole piece, from the outside of it s profile to the oppo sing side. This drill hole is loca ted in the central area of the  edge and as close as possible to the sub-chassis atta chment to the shielding as this gave the whole  assembly more rigidity. Figure 3 shows the location of  the entry hole for the antenna attachment bolt from  the outside of the profile to fac ilitate assembly. Figure 4 is a cut away showing the antenna attachment  and the area in which it is located. It can be seen  how the antenna attachment is adjacent to the subchassis attachment to the shielding (yellow piece), as this is the most rigid area of the whole assembly.    With regards to the approach used for attachment, a hole was made at the base of the antenna, through  which the attachment bolt was introduced. This bolt se rved as the axle for the washer, the antenna itself,  and the conducting wire in contact with the antenna. T he conducting wire transmits signals both from the  antenna to the satellite and vice versa.  On the other side of the attachment bolt is a nut, also M2, which is  inserted into the sub-chassis and whose function is to keep the whole assembly of antenna, connection  cable and washer together, as once the bolt is tightened the assembly will be kept fixed by the tension between the nut and the sub-ch assis it is embedded in. 

NASA/CP-2010-216272