Solar Ultraviolet Radiation Measurement Apparatus (SURMA)HASP Experiment

By D. Bordelon1, J. Brady2, J. Causey3, J. Collins2, A. Davis3, V. Fernandez-Kim3, S. Harb1, B. Landry3, B. Stutzman2

1Department of Computer Science and Engineering at LSU, 2Department of Electrical and Computer Engineering at LSU, 3Department of Mechanical and Industrial Engineering at LSU

Scientific Background

Acknowledgements: Supported by the Louisiana Space Consortium. Special thanks to the LaSPACE staff: T.G. Guzik, D. Granger, M. Stewart, B. Ellison, C. Fava, J.P. Wefel, D. Browne, D. Smith. Special thanks to the Columbia Scientific Balloon Facility and their personnel. In memory of Jack Brady.

280.00 289.50 299.00 308.50 318.00 327.50 337.00 346.50 356.00 365.50 375.00 384.50 394.001E-27

1E-24

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1000Expected Irradiance per Wavelength at Altitude

0km 15 km 25 km 30 km 35 kmWavelength (nm)

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Figure 1: Irradiance results calculated for 0, 15, 25, 30, and 35 km. Note that the magnitude of UVB-band wavelengths are dramatically affected by the atmosphere at different altitudes. The magnitude of UVA-band wavelengths remain fairly constant through the flight profile. Data computed using SMARTS.

Figure 2: Expected irradiance per UV band. Note the emergence of UVC (black) at 30 km altitude. UVA (blue) and UVB (red) are present through the entire flight profile. (Source data from SMARTS simulations and URUA payload measurements.)

AbstractThe goal of the SURMA experiment was to detect, measure, and timestamp solar ultraviolet (UV) intensities to model the breakdown of broadband UV, UV-A, UV-B, and UV-C spectrums as a function of altitude. Studying the breakdown of solar UV irradiance measurements is significant for understanding the survival of high-altitude, extreme-environment bacterium; meteorological studies in the atmosphere; and assessment of deterioration of high altitude aircraft or spacecraft. The objective of this experiment was to utilize a balloon-borne orientation system equipped with UV detectors to track the position of the sun and obtain optimal irradiance flux.

ConclusionInitial SURMA analysis is promising. The payload operated for a significant portion of the expected flight operation time and successfully gathered irradiance data. Through the following months, the raw collected UV irradiance readings will be correlated with environmental readings, image processing, expected results, sensor calibration tests, and post-flight payload analysis. Refining of the raw UV irradiance will provide a representation of the corrected irradiance as a function of altitude. Lastly, the mission experience will be assessed and a final science report detailing data analysis and the lessons learned will be submitted in December 2015.

Launch and Preliminary Results

Figure 8: Processed Solar Tracking Image. The onboard camera took pictures throughout the flight. Each of these pictures was analyzed to determine SURMAs tracking accuracy. The image processing functioned by first locating the sun in an image, adding an overlay greet line, and calculating the angle of offset and angle of declension from the sun from this line. The angle offset will account for UV irradiance attenuation as a function of the viewing angle.

On September 7th, 2015 SURMA and 11 other student payloads were launched on HASP in Fort Sumner, NM. At about 11 AM CT SURMA reached a peak altitude of 120,000 ft. The platform and onboard payloads stayed at this float altitude for 23 hours until termination at 10 AM CT, September 8th.

SURMA was designed to operate from launch until sunset yielding a total of 12 hours of analyzable data. For approximately 50 percent of the payload operation time, SURMA successfully tracked the sun, recorded data points, and downlinked data packets. The UV data analysis is still being conducted and cannot yet be presented. Images captured by SURMA’s onboard camera have been analyzed to determine data points where the payload was not pointing toward the sun. An image processing software has also been used to estimate the payloads viewing angle of the sun (Figure 8). This will be used in our data analysis to account for UV attenuation due to off-normal irradiance incidence.

Several issues were identified during the flight. Tracking operated well under normal conditions; however, it failed when shadows and reflections interfered with the photodiode output. The interior payload overheated due to prolonged solar exposure and inadequate heat dissipation.

Experimental Setup

Figure 4: Full Payload Assembly

Figure 5: Electronics Bay Internal Cross-Sectional View

Figure 3: High Level System Diagram

SURMA was designed to be mounted to the High Altitude Student Platform (HASP). HASP provided both power for the payload and communication channels that allowed for telemetric control of the payload. SURMA regulated the 30V supplied by HASP through its own internal power subsystem. The communication channels were used to broadcast the payload’s current status, various sensor readings, and any detected operation errors. The connections to HASP and all major subsystem interfaces of the payload are detailed in Figure 3.

The mechanical structure of the payload was divided into the rotational assembly, the electronics bay, and the sensor enclosure (Figure 4). The rotational assembly contained a slip ring that allowed the payload to rotate azimuthally. The electronics bay housed the payload’s electronics, a servomotor, and a linear actuator (Figure 5). The sensor enclosure contained two light sensitive photodiodes, a camera, and four UV-filter photodiodes.

Tracking was accomplished by comparing solar photodiode outputs and rotating the payload in the direction that would equalize them. The elevation angle of the sensor enclosure was controlled by the linear actuator extending or retracting based on relative position of the payload to the sun during the flight profile.

SURMA recorded a data point every 14 seconds. Each data point included an image capture, UV irradiance values, solar photodiode outputs, payload temperatures, and a timestamp. After recording the data point into onboard storage, the payload downlinked data packets through HASP to provide live status updates.

Figure 6: SURMA mounted on HASP before launch

Figure 7: SURMA tracking the sun onboard HASP at altitude

Ultraviolet radiation (UV) is electromagnetic waves with a wavelength from 100 to 400 nm. UV is broken up into three categories based on its wavelength: UV-A (320 – 400 nm), UV-B (280 – 320 nm), and UV-C (100 – 280 nm).

UV-B and UV-C are filtered out by the atmosphere. Figure 1 and Figure 2 show the irradiance present at select altitudes.