Test and development of advanced solutions for future space missions, such as SiPM technology.
At present, the project has been approved:
The experiment will be performed with one instrument "Wide angle UV detector of nighttime atmosphere", located inside the Service Module of the RS of the ISS in the window made of quartz glass.
|Wide angle UV detector (left) and The UV transparent window of the RS of the ISS made of quartz glass (right)|
Photosensitive element of a photo detector is a multi-anode photomultiplier tube (MAPMT), which provides high sensitivity and the possibility of detection of fast signals in the UV range. A focal surface of an array of 36 MAOMT, each of which contains 64 channels. The total number of pixels - 2304.
MAPMT R11265-M64 manufactured by Hamamatsu is considered as the main options (it is shown in the photo below). This PMT is designed for a project JEM-EUSO, has bialkali photocathode with quantum efficiency of about 35%. Individual pixel size 2.88 × 2.88 mm, maximum sensitive area of MAPMT is about 23.04 × 23.04 mm. This PMT passed a number of flight tests, in particular, has been used successfully in the balloon experiment to study the background of the nighttime atmosphere (EUSO-Balloon experiment).
The optical system (OS) of the detector is designed for imaging the object (lightning, TLE etc) in the field of view. The main requirement for the OS is that a spot size of the light beam should not exceed the size of a single pixel of the photo detector in that the entire field of view (up to about 40 degrees in diameter).
OS is a two-lens telescope. Each of the Fresnel lenses is double-sided. Diameter of the first (front) lens is 250 mm, the diameter of the second (rear) - 290 mm (it is selected so that the light collection efficiency does not decrease significantly with increasing of field angle up to 20˚). The thickness of both lenses is only 5 mm, material - special UV-transparent plastic PMMA-000 (a refractive index in the near-UV is approximately 1.5). The presence of four Fresnel surfaces allowed to meet the basic requirement for the signal focusing. The effective focal length of the resulting system is approximately equal to 268 mm, F-number (the ratio of the focal length to the diameter of the entrance pupil) is 1.07, relative aperture (inverse F-number) - 0.93.
Left figure shows the result of sequential ray tracing performed in the software package ZEMAX. The figure shows the optical system itself and the path of UV rays for field angles of 0˚, 5˚, 10˚, 15˚, 18˚ and 20˚. Right figure shows a spot diagram - the image in the focal plane for the same angles. The spot size, expressed as RMS-diameter is not more than 2 mm. It is smaller than a pixel of the photo detector.
|Sequential ray tracing, field angles: 0˚, 5˚, 10˚, 15˚, 18˚ и 20˚||Spot diagram for field angles 0˚, 5˚, 10˚, 15˚, 18˚ и 20˚|