NDT in the Space Industry

Why space hardware is different

Most engineering relies on margin: make the part a little heavier than it needs to be, and it will tolerate a flaw. Launch vehicles and spacecraft cannot carry much extra mass, so they are designed closer to their limits. Propellant tanks and pressure vessels hold enormous stored energy. Engines see extreme temperatures and vibration. And unlike an aircraft, a satellite in orbit cannot be pulled into a hangar for a look.

The result is that the space industry leans on fracture control — the discipline of assuming a part may contain a flaw, working out the largest flaw it can tolerate for its whole life, and then proving through inspection that no flaw of that size is present. Nondestructive testing is the proving step, which is why the methods, their sensitivity and the qualification of the people applying them are taken so seriously.

The cost of getting it wrong is obvious: a lost vehicle, a lost payload that may represent years of work, and in human spaceflight, lives. Even on the ground, a pressure vessel or propellant line failure during testing can injure people and destroy facilities.

Where NDT is used

• Welds in tanks and structures. Launch vehicle tanks and structures are often welded aluminum alloys. Radiography (RT) and ultrasonic testing (UT), including phased array, examine weld volume, and liquid penetrant testing (PT) checks the surface.
• Pressure vessels and COPVs. Composite overwrapped pressure vessels store high-pressure gases on many vehicles. Their metal liners and composite overwraps are examined with methods chosen for each layer, and acoustic emission (AE) monitoring during pressure testing is one of the approaches used to detect damage growth.
• Engines and turbomachinery. Turbopump parts, injectors and combustion chambers are examined with PT, eddy current testing (ET), UT and radiography, depending on the material and the part.
• Additively manufactured parts. 3D-printed engine and structural parts can have internal porosity, lack of fusion and complex internal passages that other methods cannot reach. Computed tomography (CT) has become a key tool for these parts, alongside surface methods once they are finished.
• Composite structures and thermal protection. Fairings, interstages, satellite panels and thermal protection materials are examined with UT, thermography and shearography to find disbonds, delaminations and impact damage.
• Leak testing. Propulsion systems, valves, fluid lines and sealed spacecraft volumes are leak tested, often with helium mass spectrometry, because even a small leak in space can end a mission.
• Electronics and assemblies. Radiography and CT are used to examine solder joints, connectors and assemblies without taking them apart.

How inspection fits into a program

Raw material and processing. Plate, forgings, castings and powders are inspected before and after processing, because many flaws originate in the material itself.

Fabrication and assembly. Each weld, bond and critical feature has defined inspection points in the traveler, with results recorded against serial numbers so the history of every fracture-critical part can be traced.

Acceptance and proof testing. Pressure vessels and many structures are proof tested, and NDT is often required before and after proof to show no flaw has grown.

Reusable vehicles. Reusability changes the picture. A booster or capsule that flies again needs between-flight inspection, much like an aircraft, and the data from each inspection informs how many more flights a part can safely make.

Standards you will come across

• NASA technical standards, including NASA-STD-5009 on nondestructive evaluation requirements for fracture-critical metallic components, NASA-STD-5019 on fracture control, and NASA-STD-6030 on additive manufacturing for spaceflight hardware. These are publicly available and are widely referenced beyond NASA programs.
• ASTM E-series standard practices for individual methods, and ASTM guides addressing NDT of additively manufactured parts and composite pressure vessels.
• SAE Aerospace Material Specifications (AMS) and aerospace method standards that many space suppliers share with aviation.
• NAS410 for NDT personnel qualification, which uses Level 1, Level 2 and Level 3 and is common across aerospace and space suppliers; some programs use ASNT SNT-TC-1A (Level I, II and III) instead.

Which documents apply depends on the program and customer. A commercial launch provider, a NASA contract and a defense satellite program may each flow down different requirements, so read the contract before assuming.

What this means for buyers and suppliers

For companies buying space hardware, ask to see how NDT sensitivity was demonstrated for the flaw sizes the fracture analysis depends on. "We did penetrant" is not the same as "our penetrant process has been shown to reliably detect a crack of the size this part cannot tolerate." For new processes, especially additive manufacturing, ask how the inspection was validated on representative parts with known defects.

For suppliers moving into space from other industries, the step change is usually documentation and traceability rather than technique: every inspection tied to a serial number, a qualified inspector, a calibrated instrument and a current procedure, and all of it retrievable years later.

How NDT LLC can help

NDT LLC helps space and aerospace suppliers build NDT programs that meet flowed-down requirements, write procedures, qualify personnel under NAS410 or SNT-TC-1A, and prepare for customer audits. If you are entering the space supply chain or qualifying a new process, talk to us.