Design Considerations/Engineering Support

When a new system is being built for airborne applications, developing an early understanding of design constraints and considerations will greatly facilitate its timely airworthiness approval, and overall chances for operational success.

Each aircraft project has a designated payload engineering representative, so it is strongly suggested that new instrument teams contact them directly to understand their unique requirements, before finalizing a design. The Airborne Science & Technology Lab (ASTL) at NASA Ames is also available to answer general engineering questions, as well to as to assist with the implementation of the specific requirements imposed by a particular aircraft platform. For further information contact the ASTL at (650) 604-6252 .

The following are some general examples of considerations to take into account when building a new system, or adapting an existing one to a NASA platform:

Prohibited materials and Safety Concerns

PVC electrical wire insulation is prohibited in most cases, due to toxic fumes in case of fire, as are some types of thermal insulation.

Gas bottles and pressure vessels may need to be certified, and/or require secondary containment, particularly if they contain hazardous gasses.

High-powered lasers require adequate safety measures, for both ground and in-flight operation.

Mechanical strength
Systems must be packaged and mounted to resist various g-force loading contingencies. These design limits may vary between aircraft. A mechanical stress analysis is generally required before approval to fly. Commercial or laboratory-type equipment enclosures are generally not considered adequate.

Electrical power
Most of these aircraft have either 28V DC or 115V/400hz electrical power. Standard 115V/60hz power is typically not available. There is typically adequate power availability, but in the case of some large systems (e.g. Lidars) this should be confirmed as part of the platform selection process.

Environmental Parameters
Unless a system is intended for a pressurized cabin environment, instrument operating conditions are an important consideration. The high-altitude, un-pressurized environment imposes unique problems of thermal management, as the air is thin and convective cooling is often inadequate. This may particularly affect electronic components. Moisture condensation upon descent is also a concern, as is the mechanical stability of precision optical systems. Vibration and shock isolation is also generally needed for airborne instruments, and is partly dependent on the aircraft type being used.

Summary
This is not a comprehensive list of requirements, and is intended only to give a idea of some of the considerations involved in building and certifying an instrument for operation on a NASA or NASA-affiliated aircraft. Specifics should be sought from the engineering team for a particular aircraft project. The ASTL engineering team in some cases can assist with instrument packaging, mounting, or the performance of mechanical stress analyses. They have also developed some generic pressure housings for electronic components, and have extensive practical experience with electronic and optical systems in high altitude environments. There is also an informal network of instrument teams that have successfully operated a variety of instrument types, which are generally willing to share their experiences.

For further questions please contact Jeff Myers at (650) 604-3598