You have created an optical experiment that is to be mounted on an Earth Observa

Question

You have created an optical experiment that is to be mounted on an Earth Observation satellite. You are concerned that your primary telescope mirror that has a diameter of 10cm, will be impacted bv a contaminated lm diameter radiator plate that has a 100nm molecular film on it. The film is expected to completely be removed in 2 weeks by the absorption of solar radiation. The material is expected to adhere to your cooled infrared mirror. If the plate is at an angle of 30 degrees to the optical axis of your mirror and its centre is directly in line with your mirror (you are staring straight at it). You will not move into your observational configuration until after one month is up. How thick will the film be on your mirror. The distance between the plate and the lens is 5m. Make your initial estimate assuming point source approximations.

Explanation / Answer

For a simple (point source) estimate M = 1 * 10E-7 * A = 1 * 10E-7 * pi * .5^2 = 7.85 * 10E-8 Mass to be removed assuming a unit density Area of mirror a = pi * .05^2 = 7.85 * 10E-3 m^2 Area of mirror perpendicular to axis of plate = 7.85 * 10E-3 * cos 30 a' = 6.8 * 10E-3 Area of hemisphere of 5 m radius = 2 * pi * 25 = 157 Fraction of mass intercepted = 6.8 * 10E-3 / 157 = 4.33 * 10E-5 m = 7.85 * 10E-8 * 4.33 * 10E-5 = 3.4 * 10E-12 m = a t t = 3.4 * 10E-12 / 7.85 * 10E-3 = 4.33 * 10E-10 = .43 nm

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