Design considerations for satellite optics.
We are reading new reports of the benefits of optical satellite imaging in applications including inspection, navigation, remote sensing, and telecommunications, as well as ground-breaking scientific space research.
Most optical satellites operate passively taking images in the visible or near-visible portion of the electromagnetic spectrum, using the sun’s radiation as it reflects off the Earth and atmosphere. By comparison, radar satellites operate actively, as they emit their own microwaves or radio waves, and usually require much more processing to get an image that makes sense to the human eye. Optical satellites also offer another significant advantage over radar satellites in that they require much less energy, making them cheaper to use. Other advantages of optical satellites over radar satellites are that they offer improved bandwidth, smaller size and weight, electromagnetic interference immunity as well as higher transmission and processing speeds.
Optics designed to be ‘space ready’ for use in an optical satellite must meet some strict requirements. These requirements are often determined by international space organisations, such as NASA or the ESA, with the aim of ensuring that any optical components used in satellites can withstand the rigors of launch and the harsh environment of space.
When designing optics for satellite applications, one of the first things you need to consider is whether the optics need to use radiation tolerant (non-browning) glass. There are two main factors that will affect this decision. The first is the Earth orbit that your satellite will be deployed into. The levels of radiation that an optical satellite will be exposed to in low earth orbit (LEO) are much lower than a satellite operating in a higher orbit. The second key consideration is the length of time that these optics need to remain operational for. If the mission is short (a few months), then the level of radiation absorbed by the optics may not be enough to have any significant effect on transmission. In this optical satellite application, there should be no requirement to use non-browning glass.
Operating space on optical satellites is typically extremely limited so the lens / optical systems must be designed to fit within the available space envelope and to reduce launch costs under the maximum weight requirements. Other key considerations when designing lenses to be incorporated into optical satellite systems includes how they react to the vibration and shock of launch, extremes of temperature, and the high vacuum environment that is encountered in space.
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