Focal plane alignment for large format arrays and faster optical systems require enhanced precision methodology and stability over temperature. The increase in focal plane array size continues to drive the alignment capability. Depending on the optical system, the focal plane flatness of less than 25μm (.001”) is required over transition temperatures from ambient to cooled operating temperatures. The focal plane flatness requirement must also be maintained in airborne or launch vibration environments. This paper addresses the challenge of the detector integration into the focal plane module and housing assemblies, the methodology to reduce error terms during integration and the evaluation of thermal effects. The driving factors influencing the alignment accuracy include: datum transfers, material effects over temperature, alignment stability over test, adjustment precision and traceability to NIST standard. The FPA module design and alignment methodology reduces the error terms by minimizing the measurement transfers to the housing. In the design, the proper material selection requires matched coefficient of expansion materials minimizes both the physical shift over temperature as well as lowering the stress induced into the detector. When required, the co-registration of focal planes and filters can achieve submicron relative positioning by applying precision equipment, interferometry and piezoelectric positioning stages. All measurements and characterizations maintain traceability to NIST standards. The metrology characterizes the equipment’s accuracy, repeatability and precision of the measurements.
A key milestone in NASA's Mission to Planet Earth project was achieved with the completion of Environmental Qualification testing of the Protoflight Model (PFM) Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. Completing this task paved the way for MODIS to be integrated onto the EOS AM spacecraft which is to be launched as the keystone of the EOS system. Qualification of the PFM MODIS instrument required conducting an extensive test program in four different test facilities. Accomplishing environmental qualification testing, while meeting the stringent contamination and operational requirements for the MODIS instrument, required us to address a variety of issues and tasks. The main tasks included: developing special ground support test equipment, developing special tenting and handling equipment to protect the instrument from being contaminated during off-site environmental vibration an electromagnetic compatibility testing, designing and developing a state-of-the-art thermal-vacuum test chamber, and defining detailed test operations to fully characterize the instrument's electrical, optical and mechanical performance before, during and after each environmental test sequence. Selected penalty test were streamlined for characterizing the instrument whenever design changes or improved test techniques were incorporated to ensure all requirements had been met while maintaining a fully qualified instrument.
The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument is the key facility instrument on board the NASA-GSFC “Mission-to-Planet Earth” EOS-AM spacecraft. This instrument is designed to study Earth system processes and includes 36 spectral bands for study of oceanographic, atmospheric, and land surface phenomenon. Launch of this 705 km high, polar orbiting platform, mounted atop an Atlas IIAS, is scheduled for June, 1998 from Vandenberg AEB, California. The MODIS Protoflight instrument has been delivered to Lockheed Martin Marietta’s Valley Forge facility for spacecraft integration and testing. The primary structure of the MODIS instrument is the “mainframe” and this paper discusses the geometrical design, material selection and processes, static and dynamic analyses and environmental testing required to ensure spaceflight reliability. Comprehensive studies of candidate materials led to the selection of beryllium made by the “Hot Isostatic Process”.