The Crew Exploration Vehicle, or Orion, will replace the space shuttle for ferrying crews to and from the International Space Station; and in the future, it is planned to take part in manned lunar and Mars missions. The spacecraft consists of three components (see part (a) of the figure beginning on the next page): (1) the Launch Abort System, (2) the Crew Module (CM), and (3) the Service Module. Although Orion will ultimately be constructed by Lockheed Martin Corporation, NASA developed an independent CM design as part of a smart buyer exercise. The current design is predominantly metallic, relying heavily on NASA’s past experience with the Apollo program configuration. Early in 2006, the NASA Engineering and Safety Center assembled a team to examine the possibility of an alternative composite-dominated CM design. As part of this activity, NASA Glenn Research Center personnel and contractors took the lead on designing and sizing a potential monocoque CM concept and performed sizing analysis on a geometrically stiffened CM concept designed by the NASA Ames Research Center (see parts (b) to (e) of the figure).
Proposed design for composite crew module. (a) Orion. (b) Monocoque CM design led by Glenn. (c) Geometrically stiffened CM design led by Ames. (d) Sized webcore sandwich panel core thickness for monocoque CM design. (e) Sized webcore sandwich panel core thickness for geometrically stiffened CM design (one-fourth model)
Long description of figure.
The NASTRAN finite-element code and the HyperSizer structural sizing code were used for the design and sizing (ref. 1). HyperSizer identifies structural components (e.g., beams, bars, and panels) from a finite-element model and, on the basis of the loads on each component from the finite-element analysis results, along with specified factors of safety, sizes the components for minimum weight. Specializing in composite materials and stiffened sandwich panels, HyperSizer checks a large number of static failure and buckling criteria, enabling rapid design with a high level of confidence. HyperSizer’s new HyperFEA module (ref. 2), which automates the process of sizing all components in a structure and of iterating with NASTRAN to capture the effects of load redistribution, was employed for rapid turnaround. Load cases representing internal pressure, 15g Launch Abort System acceleration, and 16g late abort reentry deceleration were considered in the analyses.
The monocoque composite CM concept combines the CM aeroshell and pressure vessel over part of the CM acreage (see part (b)). Starting with an existing CM finite-element model provided by the NASA Langley Research Center that had a separate aeroshell and pressure vessel, the pressure vessel wall was moved outward to merge with the aeroshell as shown. The original conceptual design involved TEEK (low-density polyimide closed-cell foam designed and patented at Langley) sandwich panels with hybrid composite laminate facesheets composed of IM7/8552 graphite/epoxy, Kevlar (DuPont)/epoxy, glass/epoxy, and T300/934 carbon/epoxy plies. The facesheet construction was chosen to provide micrometeoroid impact resistance. A total CM weight of 1965 lb resulted from the HyperSizer-NASTRAN sizing of the CM with these TEEK sandwich panels. Next, an alternative design involving webcore (ref. 3) sandwich panels with identical facesheets was sized. The resulting weight was 1538 lb--427 lb less than the original sandwich construction concept. Finally, a third design was considered involving IM7/977-2 graphite/epoxy face-sheets in conjunction with webcore sandwich panels. The resulting weight was 1081 lb--an additional savings of 457 lb. Part (d) shows the webcore sandwich panel core thickness resulting from the sizing.
The geometrically stiffened CM concept is based on corrugating the top and bottom of the pressure vessel (similar to the bottom of a plastic 2-liter soft drink bottle) to derive stiffness from the geometry itself (see parts (c) and (e)). Ames designed this concept and provided a NASTRAN finite-element model for the concept to Glenn. Glenn performed the HyperSizer-NASTRAN sizing. The original concept for the geometrically stiffened design called for the pressure vessel to be composed almost exclusively of solid IM7/977-2 graphite/epoxy laminates rather than sandwich panels. This configuration resulted in a total sized CM weight of 1851 lb. As an alternative design, webcore sandwich panels with IM7/977-2 graphite/epoxy facesheets were introduced, reducing the sized CM weight to 1330 lb--a weight savings of 520 lb. Part (e) shows the webcore sandwich panel core thickness resulting from the sizing.
Last updated: December 15, 2007
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