Material Compatibility Assessment of Spacecraft Oxidizer Systems

Recently designed oxidizer systems used in spacecraft propulsion are pushing the limits of materials 

and operating conditions. As a result, nitrogen tetroxide (NTO) oxidizer systems are exhibiting failures 

driven by ignition mechanisms similar to oxygen systems. Oxidizer systems (e.g., O2, N2O4, N2O, H2O2) 

have generally been designed and operated within industry experience for material corrosion concerns 

without a thorough understanding of potential material ignition and burning. To compound the problem, 

the effects of varying parameters on ignition and the kindling chain have not been studied, and there 

is a very limited amount of published data to help with the understanding. NASA-sponsored testing is 

actively researching ignition mechanisms, determining thresholds, and defining operating envelopes to 

inform the aerospace community. 

NASA Engineering and Safety Center Technical Bulletin No. 20-06

National Aeronautics and Space Administration

www.nasa.gov

Applicability

The information in this technical bulletin is applicable 

to spacecraft oxidizer systems found to be situationally 

flammable with oxidizers. Titanium was the focus of 

recent work in the presence of NTO, but other metals 

such as certain thicknesses of stainless steel and 

also soft goods may be susceptible as well in the right 

configuration. 

Background

Recent testing found that traditionally acceptable materials of construction (titanium and certain thicknesses 

of stainless steel) are flammable and ignitable in NTO. 

Literature searches, flammability testing, and ignition 

testing confirmed that these materials are sensitive to 

ignition in much the same way as they are in oxygen 

systems. Flammability and ignition susceptibility have 

traditionally not been evaluated for these types of propulsion oxidizer systems other than oxygen.

Discussion

Recent testing has identified the need for compatibility 

assessments in all oxidizer systems consistent with 

oxygen systems per NASA-STD-6016A. As a result, NASASTD-6016A has been updated with this requirement. The 

recommended oxidizer compatibility evaluation process 

for NTO and other oxidizers is based on the existing 

oxygen compatibility assessment process per NASA/TM2007-213740. Materials evaluation testing is performed 

per NASA-STD-6001B. 

The intent of the oxidizer compatibility assessment 

process is to identify the likelihood of ignition for 

flammable materials through system interrogation. High 

probability ignition sources can be further assessed 

through targeted testing at the material, component, or 

system level. The process also identifies potential hazard 

controls through material change, system configuration, 

or operation.

Path Forward

NASA-STD-6016B now requires all spacecraft oxidizer 

systems to be evaluated per NASA/TM-2007-213740. 

NASA-sponsored testing is actively researching ignition 

mechanisms, determining thresholds, and defining operating envelopes to inform the aerospace community. 

For information, contact Gregory J. Harrigan at gregory.j.harrigan@nasa.gov.

07/27/2020

Successful static fire test with incorporated lessons learned

References

1. NASA-STD-6016B Standard Materials and Processes 

Requirements for Spacecraft

2. NASA/TM-2007-213740 Guide for Oxygen 

Compatibility Assessments on Oxygen Components 

and Systems

3. NASA-STD-6001B Flammability, Offgassing, and 

Compatibility Requirements and Test Procedures