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1 Introduction

This handbook provides a description of the Far Ultraviolet Spectroscopic Explorer (FUSE) science instrument, focusing on its design and performance from the perspective of an archival scientist interested in the impact of the instrument on the data quality. This approach is targeted primarily to the archival data miner, but much of the technical information may be of interest to future instrument builders as well. To address these audiences, we have organized this presentation with the main body of the document containing the information of most direct relevance to data users, and the technical details contained in the extensive Appendices attached. For an in-depth description of the FUSE data products and the CalFUSE data reduction pipeline, the reader is referred to the companion volume: The FUSE Archival Data Handbook (2009).

FUSE was a NASA-funded far ultraviolet (FUV) space telescope that was operated for NASA by The Johns Hopkins University Department of Physics and Astronomy in Baltimore, MD. The satellite was launched on a Delta-II rocket from Cape Canaveral on June 24, 1999, at 11:44 a.m. EDT into a circular 760 km (475 mile) orbit inclined 25 degrees to the equator, with an orbital period of 100 minutes.

The FUSE scientific instrument was designed to provide high resolution spectra ( &lambda/Δλ ≥ 20,000) across the 905 - 1187 Å FUV spectral bandpass. The parabolic telescope mirror and Rowland circle spectrograph design maximized instrument efficiency by employing only two reflections prior to photon detection.

FUSE operated until it was decommissioned on October 18, 2007, after the loss of the fourth and final reaction wheel assembly in mid-2007 caused the termination of nominal science operations.

This handbook was written with two goals in mind: to provide an overview of the instrument and a characterization of instrument effects that affect the data quality and, secondly, to provide a more detailed description of the instrument design as well as some results from the integration, ground test, in-orbit performance of the instrument.  On-orbit performance anomalies and the operational procedures for mitigating their effect on the data quality are also discussed.

Below we provide an outline of each chapter's contents with an indication of the primary target audience for each.  The designations are either "General" (of interest to all) or if appropriate, broken out for a casual user, advanced user, or as an instrument designer/builder, to facilitate locating relevant information at the desired level of detail.

Chapter 1:  (Audience: General) contains this introduction.

Chapter 2: (Audience: General) provides an overview of the FUSE instrument. Basic aspects of the instrument design and functional characteristics are presented for each of the instrument subsystems: telescope, spectrograph, focal plane arrays, guide system camera, and the detector.

Chapter 3: (Audience: General) presents an overview of the FUSE spacecraft. A brief overview of the Command and Data Handling system and the Attitude Control System (ACS) performance is presented. Post-launch spacecraft anomalies, such as the loss of reaction wheels and its effect on operations, are discussed in Section 7 of the technical appendix.

Chapter 4: (Audience: General) discusses the post-launch instrument performance.  The mirror motion alignment anomaly (section 4.1, etc.), spectral motion (section 4.3) and detector performance (sections 4.4, etc.) are described here, with additional details presented in the technical appendix (Section 6).

Chapter 5: (Audience: Advanced archive user) presents a description of various  overbright target observing strategies, only some of which were used operationally.  Since some of these test data are available in the archive, this chapter is included for completeness.

Chapter 6 (Appendix A): (Audience: Instrument designer/builder, advanced user) – presents many details of the instrument design, detector characterization and operation,  FES performance, telescope and spectrograph focus, and channel alignment behavior and operational mitigation.

Chapter 7 (Appendix B): (Audience: Instrument designer/builder, advanced user) – presents information on the Attitude Control System on-orbit performance, including the gyro and reaction wheel failures, and the flight software and target acquisition strategies employed to operate despite these limitations.

Chapter 8 (Appendix C): (Audience: Instrument designer/builder, advanced user) Coordinate Transformations.

Chapter 9 (Appendix D): (Audience: Instrument designer/builder, advanced user) Airglow appendix.

Chapter 10 (Appendix E): (Audience: All) Members of the development and operations teams.

Chapter 11: (Audience: All) Acronym List

Chapter 12: (Audience: All)  References.  This section provides a extensive list of references to papers describing the instrument subsystems, and the modifications to the instrument and ACS software made during the mission. There are also references to a subset of science papers that provide useful information on instrument performance.

This instrument handbook is one of two primary archival support documents describing the FUSE instrument and its data products.  For information specific to the pipeline processing and analysis of FUSE data, readers are referred to this handbook’s  companion volume: The FUSE Archival Data Handbook (2009).

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