Cleanliness

Cleanliness & Contamination Control

CSL performs qualifications on satellites, space instruments or units by submitting them to environmental space conditions in a perfect clean environment (ISO7 to ISO5).

   

The five thermal vacuum chambers and the two shakers are located in a 1 000 m² clean room area.

CSL works with a strict contamination control program, depending of controlled cleanliness clean rooms standards and specific payload requirements.

Follow-on contamination witnesses (particulate and molecular) are provided and analyzed by CSL for each unit and for each individual test sequence.

Among the different methods and instrumentation for particulate and molecular contamination monitoring, the following ones have been selected by CSL for their practicality and relevance thorough the different on-ground AIV/AIT phases:

Airborne contamination control

An airborne particulate counter (MetOne syst 3400) is available in each main clean room and a third instrument is available as back-up. These instruments are portable and can be installed anywhere they are needed. Results can be collected via PC or memory stick.

Each instrument gets its own internal alarm system, which advices immediately and in real time, the people working in the area where the counter is installed.

Deposited particle (fall-out)

The particle fall-out (PFO) system is measuring the particles that deposit onto surfaces. It is using fall out sensors (black glass plates glued on a holder). The complete holder is open and exposed whenever desired during at least 24 hours. The results (given in ppm [part per million – mm²/m²] per 24 hours) provide the level of contamination of the surface.

This measurement system allows to check the level of contamination at a specimen level either every day, week, etc, or/and for cumulative results.

The PFO counter is located in the main clean room.

    

Molecular contamination

Molecular contamination, as for particulate, is also one of the most major concerns, which can strongly impact on the optics in space.

Therefore, molecular contamination control is also an important part in the cleanliness control.

CSL is using the “Fourier transform infra-red” (FTIR) spectrophotometer Perkin Elmer System 2000. The method used, called “indirect method” and defined in ECSS-Q-ST-70-05C is using polished stainless steel witness plates. After measurement, the results provide a quantitative level of contamination expressed in terms of equivalent surface concentration of reference compound (hydrocarbons, ester, methyl silicons and phenyl silicons species).

The system of measurement is located in a dedicated laboratory next to the clean rooms.

These molecular witnesses are used to follow the contamination during under vacuum tests in the facilities but also to follow the clean room molecular contamination or witnesses following a flight specimen. 

Bake-out tests

Success criterion

Bake-out tests can be realized in the CSL vacuum chambers in order to outgas material and to remove potential contamination as solvents in paintings for example. The materials generally baked are material used for the test set-up in the vacuum test simulation as thermal shrouds, MLI, mechanical welded structures and supports.

Bake-out can also be realized on flight items as filters, MLI, mechanical structure or PTFE powder before sintering.

The material baked is always vacuum compatible (a DML is asked before test) but a bake-out test upgrades its level of contamination.

The bake-out test conditions are to bake the material till 80 °C during at least 72 hours under vacuum.

TQCM use is highly recommended by the European Space Agency (ESA) to demonstrate the effectiveness of a vacuum thermal bake-out.

The stopping criterion is achieved as soon as the variation in the TQCM frequency is < 5% during minimum 3 hours.  The variation in the TQCM frequency is calculated over 5 hours and is defined as following:

 

with the TQCM frequency rate calculated over a period of 30 minutes:

Test realization

To illustrate a bake-out test, a test on Zenith A Powder is presented hereafter. This test was realised in the Focal 6.5 CSL facility. All the activities were performed in class 100.

240 kg of Zenith powder were spread in 16 dedicated stainless steel boxes.

These boxes were integrated in a thermal tent composed of an aluminium structure with several levels.

Infrared lamps of 500 W were installed at about 50 cm of the boxes.

Kapton foils were installed on all the structure to insulate the set-up from the vacuum chamber.

Contamination witnesses were installed close to the set-up: one set (molecular and particulate witnesses) in the thermal tent and one set on the optical bench, outside the tent. A TQCM was installed in the kapton tent.

   

The powder was baked at 80°C during 72h minimum.

 

When the criterion  F"<5% was also reached since 5 hours, the test could be stopped.