The engineering design of the REXIS Solar X-ray Monitor and risk management considerations for resource constrained payload development

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.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Aeronautics and Astronautics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2015

Author dc:creator

• Jones, Michael P., Second Lieutenant (Michael Paul)

Advisor dc:contributor.advisor

• Rebecca A. Masterson and David W. Miller.

• Aeronautics and Astronautics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/98688

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/98688