Background Research

material selection for launching of telescope; must be soft, able to absorb vibration, fit within the appropriate temperature range and durable under radiation use steel wrapped in PTFE (teflon) and coated with Halpern Anti-Radiation Paint (HARP) Anti-Shock Material HARP is paint coated with tiny conductive flakes of copper and aluminum Teflon Steel Telescope Image: telescope nailed down into steel wrapped with Teflon

Mars is exposed to high levels of solar radiation telescope to be used in conjunction with a charged coupled device (CCD) CCD’s maximum allowable light intensity is: 37nJ x 1/(0.01) 2 m 2 x 1 frames/30s = W/m 2 but the solar intensity on Mars is 590W/m 2 Material for a Filter  37nJ/cm 2 - maximum energy/cm 2 for the DALSA 2M-30  1/(0.01) 2 m 2 - unit conversion from cm 2 to m 2  1 frames/30s - CCD’s frame rate

solar radiation will cause electron well saturation (blooming) or permanent damage to the CCD each individual pixel is a quantum electron well as wells fill up (saturate), the probability of trapping an electron greatly decreases and electrons spread onto adjacent pixels (blooming) instead of filling into the correct pixel Image: white streaks (saturation trails) produced due to spillovers to adjacent wells

a filter is designed to attenuate visible light wavelengths and eliminate all infrared and ultraviolet light CCD is most effective around =500nm Eliminate below 300nm and above 700nm Transmission % Wavelength (nm) Transmission curve: This type of transmission can usually be obtained by a combination of Schott glasses 61% Transmission

to find the amount of attenuation needed, Fourier optics is used  Fourier optics will be discussed in more detail later on the pixel array, the image of the sun appears with an intensity of  I(0) is the maximum intensity and is directly related to the parameters of the first lens in the telescope  J 1 is the Bessel function and its value may be found in mathematic tables  kasin  is the radius from the center point of a blurspot Instead of a perfect point, a blurspot is formed due to diffraction effects far away light source kasin  I

to prevent electron well saturation, only 0.01 or 1% of the solar light coming in can be transmitted photosensitive glass with gold-palladium particles used Transmission % Wavelength (nm) 40% Transmission Transmission curve: AgPd particles deposits in glass with the above filter in conjunction with the IR and UV filter, only 1% of the light will be transmitted

Geometric Optics ideal optics - every point or object is perfectly imaged for thin lenses:  n m is the index of refraction of the surrounding medium  n l is the index of refraction of the lens  s 0 is the distance from the object to the lens  s i is the distance from the lens to the image  f is the focal length of the lens magnification of lens: SoSo SiSi Object Image

ray tracing  parallel ray: refracted through focus F  focal ray: goes through focus F and then refracted parallel to the principal plane  central ray: passes through center of lens principal plane lens

Fourier Optics when plane waves of light hit a lens, only a fraction of the light is collected because no lens or object can be infinitely large the diffraction pattern formed by the lens can be found by taking the Fourier transform of the aperture and convoluting with the Fourier transform of the original image (object) Distant point source such as a star (delta function) Image of point source produced by a circular lens is often called an Airy disk: top view Airy disk: side view

Aberrations departures from the idealized conditions of geometric optics chromatic aberrations Result of a lens focusing different wavelengths of light at different points Distortion in image colouring occurs Possible correction method

monochromatic aberrations include coma, spherical aberration and astigmatism - focus points do not all coincide on the principal axis pincushion and barrel distortions - caused by imperfections in the lens originalpincushionbarrel coma

Preliminary Design of Telescope the minimum allowable diameter of the lens is first calculated diameter is limited by angular resolution and collecting power   (in radians) - angular resolution  D - diameter with a required angular resolution of 22.5 arcseconds, D = 1.22(500nm)/(22.5/3600 x  /180) = 0.56cm collecting power of lens  8.644x10 2 W/m 2 - the minimum power of a star with the Signal-to-Noise Ratio >= 10, D >= cm

considered thin lenses when lens thickness<<focal length and the diameter of lens<<2 x radius of curvature of lens example: 3cm radius of curvature 3cm 1cm lens diameter plano-convex lens negligible thickness 3cm radius of curvature 4.5cm lens diameter not negligible thickness 1cm << 6cm

Design:  both lens diameter =1cm f = 3cm f = 1cm parallel rays: image at infinity 3cm 1.247cm7.06cm Blurspot - central part of Airy disk 7.4  m  blurspot size after first lens = 2.44 /D = 3.66x10 -6 m  desired blurspot size (to span 4 pixels) = 2x7.4  m = 14.8x10 -6 m  magnification factor needed = CCD