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For additional information about this web page and for feedback please contact
Pietro Bernasconi
Phone: 443 778 8970

Instrument Requirements

To achieve its science objectives, the SBI optical assembly must meet the following technical requirements:

grn ball The telescope must be achromatic over the wavelength range from 0.28 (ultraviolet UV) to 2.6 μm (near infrared NIR) which includes about 96% of the total solar irradiance.

grn ball The system spectral response must be constant to better than ±10% over the above mentioned range. The irradiance of the direct solar image at the focal plane must be reduced to within the acceptable range for the thermal-imaging detector. This is required because of the fixed detector integration time that limits the maximum acceptable intensity to 1 mW/cm².

grn ball The system's angular resolution in the NIR must be sufficient to resolve structures of at least 10 arcsec in size. This is the characteristic size of the enhanced solar photospheric network, which is the smallest structure currently known to contribute significantly to the total irradiance variation. Excessive blurring would decrease the peak intensity of these structures, thus reducing the signal-to-noise ratio.

grn ball The scattered light level must be sufficiently low to enable sunspot and facular contrast measurements of ±10% accuracy.

grn ball The camera's photometric response must be sufficiently well understood and stable to enable photometric measurements of ±10% precision.

grn ball The system must be capable to acquire full disk images.


Other requirements more specifically related to the balloon flights are:

grn ball The balloon must fly at altitudes higher than 24.5 km to avoid molecular band absorption from the Earth's atmosphere that would reduce the spectral coverage. Because of even more strict requirements dictated by the pointing system the goal altitude is actually about 36 km.

grn ball Telescope and detector must be able to operate at the above mentioned altitude, where the air pressure is about 4 mBar, and at temperatures that can range from -50 (during the ascent phase) up to +70 °C (for the Sun facing surfaces). The telescope optics and mount must be able to handle the intense solar heating.