Structures Sybsystem Progress Report 10/20/95 - A&M

Structures Sybsystem Progress Report 10/20/95 - A&M

This week was spent looking at different design configurations all based on the concept of payload deployment from the top of the lander as described in the CDR. Figure 1 is a diagram of a downward axial thrust structure with fuel tanks and basic bus design. The thrust structure was designed to be primarily in compression when the main engine is firing. The structure in this figure is 85 inches (216 cm) in diameter, allowing space for the stowed landing gear within the 97.7 inch (248 cm) inner diameter of the Delta-II.

Figure 2 is a diagram of a diamond shaped structural bus with the same compression loaded thrust structure as shown in Figure 1. The bottom ring is again 85 inches (216 cm) in diameter attached to a hexagon that is 50 inches (127 cm) across flats. The entire structure is approximately 37 inches high (94 cm, not including structure required for payload support). Also, there is approximately 30 inches (76 cm) between the base of the thrust structure at the point of engine interface and the bottom ring of the spacecraft structure. This coupled with an engine that is around 47 inches (119 cm) long leads to landing gear of more than 6 feet (183 cm) in length. This idea was eliminated.

Figure 3 is a digram of the same bus structure as figure 2 but with the thrust structure reversed. This design places the thrust structure in tension when the main engine is firing. This is a more efficient loading of the thrust structure since composites perform much better in tension than compression. This also raises the point of engine interface and consequently reduces the required length of the landing gear (and total weight). This also brings the lander closer to the ground, reducing the rover and science package deployment distance and simplifying the operation. The primary draw- back of this design is that raising the point of main engine interface reduces the effective moment arm available for attitude control by main engine gimballing (thrust vectoring). The thrust structure in this configuration also has no support at the top to prevent the struts from buckling due to thrust loads. This has been corrected in Figure 4.

Figure 4 shows essentially the same structure as Figure 3 except that the thrust structure extends to meet the upper hexagon. This provides support for the struts against buckling under thrust loads and adds stiffness to the payload platform. The selected design will most likely be a nine-sided or twelve-sided structure. Since three landing legs are desired, the spacecraft should have some multiple of three sides to facilitate a single interface with the legs. More on this as it develops. Further evaluation of the structure will performed in the next few weeks in order to determine the optimum configuration.

Figure 1

Figure 2

Figure 3

Figure 4


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Wednesday, 31-Dec-1969 18:00:00 CST
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