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Figure 5: Diaphragm Pump
2.3.4.1 Pump types For a medium vacuum, the most used and reliable
type of pumps are rotary-vane and diaphragm pumps.
The team of Stratospheric Census decided to use a diaphragm pump
(figure 5) , for the following reasons:
• Diaphragm pumps are dry pumps, they do not outgas oil.
• The diaphragm itself insulates the air stream against contamination
from the rest of the pump.
• Diaphragm pumps are reliable, readily available and economic.
• There is less friction than in rotary-vane pumps.
• A diaphragm pump has already been used successfully on a BEXUS
balloon in the very similar SADFACE experiment [7].
Possible disadvantages of diaphragm pumps:
• Depending on the material of the diaphragm, it might become brittle
in the cold and could therefore break.
Decision has been made to use the N 89 KNDC from KNF [16].
2.3.5
Filter and Sensor Subsystem (Payload)
2.3.5.1 Filter requirements To get a meaningful detection, the mass
of the caught particles needs to make up at least 1 ppb (parts per billion) of
the mass of the filter.
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