4: The IR camera
Our mission was to study dust clouds around young stars.
It can provide information about planet formation around these young stars.
Because of nearby star that's blending it's better to observe the dust's IR radiation. The wavelength range was 1 to 20 microns.
A special camera had been developed for this, the sensor had about 192 x 244 pixels, this kind of IR sensors are normally used in heat seeking missiles.
The camera's internal relay lens is made of Germanium, it has a non-transparent gray color in visual wavelengths.
In order to observe in the infrared wavelength it has to be used a special technique with the telescope.
First, there is a mirror in front of the sensor that oscillates between two positions, several times a second,
taking picture and subtracts the background continuously. Sub exposures are thus very short,
but they added up to correspond to several minutes of effective exposure.
Every few minutes the telescope also moves for a short time and takes second calibration images.
The camera could only work when it's chilled thoroughly, right down to 4K. It is done in two steps,
first with nitrogen to about 77K (-196 degrees C),
then take an inner chamber over with liquid helium and cools down to the final goal 4K.
The helium tank was complicated and an expensive part. The tank was big, maybe more than one cubic meter, with massive insulation around it,
and it was an explosion risk and because of that it could not be transported normally.
If it would form an ice plug in evaporation tubes the overpressure that arises can become so large that the entire gas tank can explode.
The French people that was with us studied the dust around Hale Bopp.
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