SAMPE Journal - May/June 2020 - 11

INTRODUCTION
Background
The NASA Composite Technology for Exploration
(CTE) Project has been developing and demonstrating critical composite technologies with a
focus on joints; incorporating materials, design/
analysis, manufacturing, and tests that utilize
NASA expertise and capabilities. The CTE project
kicked off in 2017 and is a multi-Center project
led by Marshall Space Flight Center (MSFC) and
supported by Glenn Research Center (GRC), Goddard Space Flight Center (GSFC), Kennedy Space
Center (KSC), and the Langley Research Center
(LaRC). The project has been funded by the Game
Changing Development (GCD) Program in the
Space Technology Mission Directorate (STMD)
and the Spacecraft Payload Integration and Evolution (SPIE) Office in the Space Launch System
(SLS) Program. The project has goals of advancing
composite technologies and providing lightweight
structures to support future NASA exploration missions. In particular, the CTE project has plans to
demonstrate weight-saving, performance-enhancing composite bonded joint technology for Space
Launch System (SLS)-scale composite hardware.
Advancements from the CTE project may be incorporated as future block upgrades for SLS structural
components. Further, the project will advance the
state of the art in the detailed analyses of composite bonded joints for joint failure prediction. The
CTE project builds upon composite design and
manufacturing knowledge obtained from earlier
NASA programs1-5.
For the first two years of the project, the CTE
project focused on the development of composite
longitudinal bonded joint technologies for conical structures such as the SLS Payload Attach Fitting (PAF) due to challenging joint geometries and

loads compared to cylindrical jointed structures.
As shown in Figure 1, the conical PAF resides within the Universal Stage Adapter (USA) in the Exploration Upper Stage (EUS) of the SLS. Payloads for
the SLS are mounted atop the PAF. Alternative SLS
configurations also allow for payload only missions
with a fairing instead of the USA. The diameter of
the conical PAF at its bottom circumferential joint
is 8.4 meters, making the PAF too large to manufacture as one piece in all but the largest autoclaves;
therefore, the PAF is being designed to be manufactured in eight sections connected with longitudinal joints (see Figure 1). As part of this focus on
longitudinal bonded joint technologies for conical
structures, the CTE project worked with the SLS/
PAF team to develop a generic PAF design called
the CTE Point Design with a goal of advancing
manufacturing and analysis prediction technologies for composite longitudinal bonded joints. A
description of this development effort for the longitudinal bonded joint is included in reference6.
Objectives
The focus of this paper will be on the sub-element joint testing and analysis correlation for the
CTE project. This paper is organized as follows.
First, a section that provides a brief description of
the structural design of a composite longitudinal
bonded joint and the sub-element joint test coupons is covered. Then, the next discussion presents
a description of the sub-element joint testing for
various loading conditions and includes a summary of the test results and test/analysis correlation
for pre-test and post-test predictions. A description of the analysis methodology is also presented.
Finally, a summary of the effort is presented in the
final overview of results.

Figure 1. Exploded view of SLS showing
PAF.

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SAMPE Journal - May/June 2020

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