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Excerpts from a larger technical report, linked below.
Executive Summary
This report details a photobiological hazard assessment of the general concept of Orbital Solar Reflectors (OSRs). A recent proposal, Reflect Orbital’s proposed Earendil-1 satellite is used as an exemplar. The analysis was conducted following IEC 62471:2006 Photobiological Safety of Lamps and Lamp Systems. OSRs are intended to provide primary or supplemental lighting and thus a photobiological safety assessment should be a prerequisite to launch and operation. This assessment demonstrates that in general OSRs pose a significant photobiological risk to persons at ground level and would be classified as Risk Group 3. As such, it would require significant warning and safety considerations before deployment.
Introduction
The ocular hazards associated with unprotected viewing of an eclipse proximal to totality are well known.[1],[2],[3],[4] The high intensity and high levels of illuminance provide some inherent degree of protection from sunlight due to maximal constriction of the pupil and discomfort and aversion reflexes. However, during an eclipse, only a fraction of the sun is visible resulting in significant reduction in illuminance and dilation of the pupils. This minimizes or reduces aversion reflexes which mean that the solar surface can be directly imaged on the retina for extended periods of time. Additionally, there are no pain receptors in the retina so there is no conscious indication of damage.
Orbital Solar Reflectors (OSRs) are large reflective surfaces in orbit above the earth that are expressly intended to reflect sunlight towards the earth for supplemental lighting.[5] Even at the lowest orbital altitudes OSRs subtend visual angles significantly smaller than the sun. The sun subtends a visible angle of 0.52°. While a 100 m OSR in an implausibly low 500 km orbit would subtend a visible angle of 0.011°. The difference in apparent size between the sun and this hypothetical OSR would be more than a factor of 2000x. Both would have similar surface brightness and viewing the OSR would be similar to viewing a solar eclipse just before or just after totality.
Conclusion
Delivery of light from an OSR has been shown to be a potential photobiological hazard that should require warnings and safety interlocks before delivery of light. However, as of yet, no mechanism has been identified that would even allow a warning for all persond within the target illumination zone of an OSR.
Visually, the appearance of an OSR is equivalent to a laser. Both are high intensity light sources that subtend an extremely small solid angle. Because of the known hazards of laser devices, legal penalties apply to individuals who knowingly point a laser at an aircraft or vehicle. The laws regarding safety of or interference with traffic in some countries are broad enough that light from an OSR directed toward the operator of an aircraft, train, ship, or vehicle would constitute a criminal offense.
The full technical report can be found here. Special thanks to the All Things Lighting Association (ATLA). Excerpt republished with permission.
Image above: Courtesy of ATLA.
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