Capability Development for a Next-Generation Planetary
UV Spectrometer 15-9243

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Principal Investigators
S. Alan Stern
David C. Slater
Donald M. Hassler
John R. Scherrer

Inclusive Dates: 01/24/01 - 01/06/03

Background - Southwest Research Institute (SwRI) has established itself as a supplier of miniaturized, high-performance ultraviolet spectrometers (UVSs) for NASA sounding rocket, Space Shuttle, and interplanetary missions. Our current state-of-the-art instrument, ALICE, is a 3-kg, 4-W device with a spectral resolving power of ~100 (λ/Dλ), covering a spectral passband between 700 and 2050 Å The original ALICE design concept was developed with SwRI internal research funding in 1993–1994. ALICE was then selected by NASA in 1995 to fly aboard the European Space Agency (ESA) mission Rosetta, which will rendezvous and orbit comet Wirtanen in 2014 (with a launch in early 2004). In the 7 years since the original ALICE IR development was completed, the performance and mass requirements for interplanetary UV spectrometers have become substantially more demanding. A second flight version of ALICE, PERSI-ALICE, is now being built to support the New Horizons mission to Pluto/Charon with a UV passband of 520-1870 Å. To remain competitive in future instrument selections for interplanetary missions, it is necessary to reduce the mass to 2.5 kg or less, provide solar observing capability, and extend the spectral passband of the UVS.

Approach - This project has successfully accomplished the following goals toward a UV spectrometer for future interplanetary missions: a) extending the spectral passband of the instrument without sacrificing spectral resolution, b) include a solar observing channel integrated into the instrument design, c) study how to lower the instrument mass to < 2.5 kg for an advanced UV spectrometer; and d) study the inclusion of a high-spectral resolution channel (λ/Dλ ~ 20,000). For goal a), we fabricated a dual passband UVS breadboard instrument that extends the existing ALICE passband by nearly 50 percent. This breadboard instrument was tested for radiometric performance within its 500-2400 Å passband, subjected to vibration and thermal-vacuum tests, and repeated these tests to verify performance after flight-like stresses. For goals b, c, and d, detailed studies were pursued, with results summarized in the project's final report.

Accomplishments - All the planned project tasks have been successfully completed, including the final report. A novel design was investigated that includes a dual grating that allows a 50-percent increase in the spectral passband while maintaining spectral resolution performance and the use of a single detector. A high-fidelity optical breadboard was successfully built and tested that demonstrated this novel design approach. The light-weighting option study was completed that shows that the proposed instrument can achieve an overall mass target of 2.4 kg (a 20-percent improvement over the existing Rosetta-ALICE UV spectrometer design). A technique to include a solar observation channel was also developed and is currently the baseline design for the solar occultation channel on the New Horizons PERSI-ALICE Pluto-Kuiper Belt mission instrument that was awarded to SwRI in late-2001; PERSI-Alice will launch in January 2006.

Simultaneous detector image of the emission spectrum of argon (Ar) gas in the UV wavelength range of 1200–2400 Å (Passband I, 1st order–bottom,) and 600–1200 Å (Passband II, 1st order–top) taken with the "dual-grating" breadboard spectrometer. Passband I shows 2nd order Ar lines in the range 600–1200 Å.

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