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Background
Research
Anti-Shock Material
• 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)
• HARP is paint coated with tiny conductive flakes of copper and
aluminum
Telescope
Teflon
Steel
Image: telescope nailed down
into steel wrapped with Teflon
Material for a Filter
• 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 m2 x 1 frames/30s = 0.0111W/m2
but the solar intensity on Mars is 590W/m2
37nJ/cm2
- maximum energy/cm2 for the DALSA 2M-30
1/(0.01)2 m2 - unit conversion from cm2 to m2
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
100
Transmission
%
Transmission curve: This
type of transmission can
usually be obtained by a
combination of Schott
glasses
61%
Transmission
50
250
500
Wavelength (nm)
750
• to find the amount of attenuation needed, Fourier optics is used
Fourier
far away
light source
optics will be discussed in more detail later
Instead of a perfect point,
a blurspot is formed due
to diffraction effects
• on the pixel array, the image of the sun appears with an
intensity of
I(0)
 2 J 1( ka sin  ) 
I  I (0) 

 ka sin  
2
I
kasin
is the maximum intensity and is directly related to the
parameters of the first lens in the telescope
J1 is the Bessel function and its value may be found in
mathematic tables
kasin is the radius from the center point of a blurspot
• 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
100
Transmission
%
40%
Transmission
50
250
500
Transmission curve:
AgPd particles
deposits in glass
750
Wavelength (nm)
• 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
1
• for thin lenses: nm nm
s0

si
 (nl  nm )
f
nm
is the index of refraction of the surrounding medium
nl is the index of refraction of the lens
s0
is the distance from the object to the lens
si is the distance from the lens to the image
f
is the focal length of the lens
• magnification of lens:
si
MT  
so
Object
So
Si
Image
• ray tracing
lens
principal
plane
parallel
focal
ray: refracted through focus F
ray: goes through focus F and then refracted parallel
to the principal plane
central ray: passes through center of 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
coma
• pincushion and barrel distortions - caused by imperfections in
the lens
original
pincushion
barrel
Preliminary Design of Telescope
• the minimum allowable diameter of the lens is first calculated
• diameter is limited by angular resolution and collecting power
122
. 

D

(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  8.644  10
power of lens
10

D
4
2
 8.644x102 W/m2
- the
minimum power of a star
with the Signal-to-Noise Ratio >= 10,
D >= 0.3648cm
• considered thin lenses when lens thickness<<focal length and
the diameter of lens<<2 x radius of curvature of lens
3cm radius of curvature
example:
3cm
3cm
3cm radius
of curvature
1cm << 6cm
1cm lens diameter
4.5cm lens diameter
plano-convex lens
negligible
thickness
not negligible
thickness
Design:
f = 1cm
f = 3cm
parallel rays:
image at infinity
1.247cm
CCD
7.06cm
3cm
both
lens diameter =1cm
blurspot size after first lens = 2.44/D = 3.66x10-6m
Blurspot - central part of Airy disk
desired
7.4m
blurspot size (to span 4
pixels) = 2x7.4m = 14.8x10-6m
magnification factor needed = 4.044