Precision Cleaning of Aerospace Hardware at Martin Marietta

Spacecraft/satellite propulsion components require high levels of cleanliness to ensure reliability in their operating environment. Typical components and their respective cleanliness levels are shown in Table 2 . Cleanliness levels of MIL-STD-1246 25A and 50A have also been required in several systems and have been achieved.

Table 2 Propulsion Components and Cleanliness Requirements

Component	Cleanliness Requirement (MIL-STD-1246)
Tubing/Fittings Valves/Fittings Pressure Transducers Tanks Internal Components Engine Modules Special Components	100A 150A 150A 150A 100A 100A 25A

Precision cleaning of these components has been by ultrasonic immersion in CFC 113 followed by a low pressure CFC 113 or alcohol spray rinse. Medium and large object precision cleaning was accomplished by spray rinsing CFC 113 over a large object ultrasonic cleaner located in a Class 100,000 clean room. Small details and assemblies were precision cleaned with CFC 113 or isopropyl alcohol on a Class 100 laminar flow bench which exhausts to the outside. Filtering of the CFC 113/alcohol (isopropyl) was accomplished using a 10, 5, 2, and 0.2 micron filtration bank (prefilters) and a 0.2 micron filter at the nozzle. These operations were performed in an open spray booth.

Final cleaning of medium and large assemblies is much more difficult and typically accomplished by flow through of CFC 113 or alcohol followed by gaseous nitrogen purges for up to 8 hours. Use of a vacuum drying oven to assist drying was also occasionally used. Cleanliness verification for particulate and non- volatile residue (NVR) was made prior to drying. The purpose of this cleaning scenario is to precision clean the hardware at a low assembly level such that high precision cleanliness levels can still be met for the end product.

The current cleaning process consists of an ultrasonic aqueous degreaser preclean, followed by water rinse and gaseous nitrogen purge (for drying) and finally an isopropyl alcohol (IPA) spray rinse for final cleaning. The use of CFC 113 and other ozone depleting substances in the cleaning process have been eliminated. This process is illustrated in Figure 1 and described in more detail in the next section.