The engineering design of the REXIS Solar X-ray Monitor and risk management considerations for resource constrained payload development
Author(s)
Jones, Michael P., Second Lieutenant (Michael Paul)
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Alternative title
Risk management and mission assurance techniques for high-risk, low-cost payload development
Other Contributors
Massachusetts Institute of Technology. Department of Aeronautics and Astronautics.
Advisor
Rebecca A. Masterson and David W. Miller.
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The REgolith X-ray Imaging Spectrometer (REXIS) is a student collaboration instrument aboard the NASA New Frontiers Program's OSIRIS-REx spacecraft. Set to launch in 2016 OSIRIS-REx will travel to, survey, and return a sample from the near-earth asteroid Bennu. One of five hosted payloads, REXIS images the asteroid in the soft x-ray spectrum. The REXIS science goals are to classify Bennu among the meteorite groups and spatially map surface elemental distributions. To accomplish this, REXIS carries 4 CCID-41 detectors sensitive from 0.5 keV to 7.0 keV, in order to observe fluoresced x-rays from the surface of the asteroid. Fluoresced x-rays are dependent on the incident solar x-rays; therefore, REXIS includes a secondary detector to image the solar spectrum simultaneous with REXIS observations of Bennu. This secondary detector, the Solar X-ray Monitor (SXM), consists of a silicon drift diode (SDD) that faces the sun while the REXIS detectors face the asteroid. The SXM provides an energy histogram of x-ray events between 0.6 keV and 6.0 keV that is fit to known solar spectral data to provide accurate knowledge of the incident x-ray spectrum at Bennu. As a student collaboration, the REXIS instrument is classified as a high-risk and low-cost payload. The high level requirements for REXIS mission success are to provide students experience in engineering design and project execution, and to do no harm to the host spacecraft. In addition the REXIS project is highly resource constrained in budget, schedule, and personnel. The higher risk posture adopted by the REXIS mission is evidenced in the SXM design. The SDD is a commercial, off-the-shelf (COTS) component, and the SXM leverages design heritage from other missions. As an independent subassembly within the REXIS instrument that incorporates many aspects of the REXIS risk posture, including COTS components and design heritage, the SXM can provide insights into the application of risk management to high-risk payload development in general. This thesis presents the engineering design of the REXIS SXM. Overviews are given of structural and thermal components, electronics hardware, and software elements of the design. Additionally this thesis explores the difficulties inherent in creating a balanced risk posture for highly-constrained payload development. First, background on current risk management techniques and applications to high-risk missions are discussed, especially in the context of NASA. Examples of difficulties in high-risk missions are drawn from the REXIS SXM, especially its use of COTS parts and design heritage from other missions. Finally, some conclusions about the risk management of highly constrained missions and suggestions for future work towards a more balanced risk approach are presented.
Description
Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. Cataloged from PDF version of thesis. Includes bibliographical references (pages 111-117).
Date issued
2015Department
Massachusetts Institute of Technology. Department of Aeronautics and AstronauticsPublisher
Massachusetts Institute of Technology
Keywords
Aeronautics and Astronautics.