A Prototype Mini-EUV Imager to Provide Space Weather Monitoring for NASA's Exploration Initiative, 15-9539

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Principal Investigator
Donald M. Hassler

Inclusive Dates:  06/01/05 – 05/31/06

Background - This goal of this project is to build an engineering prototype mini-Space Weather EUV imager "proof-of-concept" to test and demonstrate feasibility, heritage (specifically design and mass maturity), and Technical Readiness Level (TRL) to reduce future risk to NASA. High heritage and TRL levels are crucial to winning inclusion of a flight version of this prototype instrument on several future mission opportunities as part of the new NASA Exploration Initiative. As a member of several NASA strategic planning committees responsible for charting the course and implementing the new “vision” for exploration, it is becoming increasingly clear that high-TRL, low-risk instruments have a strong competitive advantage on rapid turn-around mission opportunities such as are being currently planned. To achieve these goals, we are building an engineering prototype instrument to demonstrate capability and measurement sensitivity, as well as mission resource parameters such as mass, power, and telemetry needs. We will also perform environmental testing necessary to reduce future risk to NASA and achieve a TRL of six or higher. Such an instrument would not only demonstrate capability, but heritage and commitment, developed completely with SwRI internal research and development support. As an added bonus, but beyond the one-year scope of this project, our prototype space weather imager will have a flight of opportunity on the RAISE sounding rocket flight 36.219, scheduled for launch in June 2006, raising the TRL of the instrument to eight.

Approach - The approach of this project is to detail design, build, test, and characterize a prototype space weather imager to provide reliable remote-sensing observation of the impulsive solar disturbances from remote locations to enable local space weather forecasting for future Exploration missions. We will also perform sufficient environmental testing on the prototype imager to achieve a TRL of six, which is necessary to reduce overall project risk for future NASA missions.

Breadboard Optical Testing and Characterization. We will evaluate the performance of the imager through a series of rigorous test and calibration activities, both in air on an optical bench and under vacuum in SwRI’s Vacuum Calibration Facility. We will fully characterize the performance of this mini-EUV imager, with both bench-level and vacuum optical tests. The vacuum tests will be performed in a vacuum calibration facility in San Antonio.

Environmental Testing. We will perform environmental testing (vibration, thermal-vac, and accelerated life-testing) on the imager sufficient to achieve a TRL of six.

Vibration Testing. A single-axis sine sweep (along the optical axis) followed by a random vibration in all three axes will be performed on the imager. The vibration levels will comply with standard Qualification level testing (random vibration level: 9.2 g’s RMS). This test will be performed at the SwRI vibration test facility. Following the vibration tests, the instrument system will undergo a bench optical testing to check its stability.

Thermal-Vac Testing. Following the bench optical tests and the vibration test, the imager will be installed in the thermal-vacuum chamber for a three-cycle thermal-vacuum test. The temperature excursions will run from –30°C to +50°C at high vacuum levels (i.e. <5 x 10-6 Torr). At each temperature plateau (i.e. at –30°C and +50°C), the imager will be powered on and stimulated with an ultraviolet (UV) light source. Data will be taken and compared with room temperature data taken prior to the thermal-vacuum test start. At the conclusion of the thermal-vacuum test, the instrument will undergo a final bench and vacuum level photometric characterization to again check the optical stability of the system.

Accelerated Life Testing. After environmental testing, we will perform accelerated life testing on the imager to simulate operational duty cycle comparable to both a 2-year and 10-year mission life, assuming a flight operational duty cycle of 4x per day. For a 10-year comparable mission life, this corresponds to 10 days of testing with a duty cycle of 1x per minute.

Accomplishments - We have made substantial progress on several aspects of this project, discussed below, and the APS detector procurement order has been placed. We have finalized the optical design and are currently conducting detailed mechanical design in preparation for fabrication. Quotes for the grating, telescope optics, and filters are being procured. The current Space Weather Imager design has been modified to view the +1 and -1 orders using two detectors. This modification has involved replacing the spherical secondary mirror with a grating. Figures 1 through 3 show the imager design that fits well within the volume envelope. The total field of view is 0.6 ´ 0.6 degrees. The detector contains 1,024 ´ 1,024 pixels that are 22 micrometers wide. The image quality is two or three pixels, with a plate scale of 2.5 arcseconds per pixel. The resolution is 60 kilometers per second (km/sec) for a 1.25-inch OAP and 75 km/sec for a 1-inch OAP. This design has been carefully sized to be able to use a commercial off-the-shelf grating with uniform spacing. This current design fits in an envelope of 3.5 in. x 4.125 in. x 18 in. fly on the RAISE sounding rocket.

Figure 1. Three-dimensional view of the current Space Weather Imager design, which images both the +1 and –1 spectral orders using an objective grating in place of the secondary mirror.

Figure 2. View of the external housing of the Space Weather Imager prototype. The next step is to complete this detailed mechanical design and begin fabrication.

Figure 3. External dimensions of Space Weather Imager prototype instrument.

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