Spinel - Domes
Magnesium aluminate Spinel is a durable, broadband, electro-optical material that can be readily manufactured into transparent domes for multimode seeker applications. Spinel offers the high temperature and thermal shock resistance, hardness, scratch and rain erosion resistance that are prerequisites for missile windows, in addition to excellent optical properties. Legacy window materials such as zinc sulfide, magnesium fluoride, and calcium aluminate offer excellent optical properties, but their strength and hardness are deemed inadequate for increasingly severe applications.
Three transparent ceramic materials, polycrystalline Spinel, single crystal sapphire, and polycrystalline aluminum oxynitride (AlON) are capable of meeting severe duty requirements. Of these, Spinel offers both a cost advantage and better optical performance. TA&T has developed a robust manufacturing process for Spinel dome blanks that can be generated and polished into high performance domes. TA&T is ready to meet the challenge of manufacturing thousands of transparent Spinel dome blanks for new and legacy missile programs.
TA&T produced Spinel dome held against the sky
The difficulty of designing windows and other components that operate reliably in harsh aerodynamic heating environments is complicated further because future designs must anticipate transition into the hypersonic flight regime. At room temperature Spinel possesses measurably better transmission than AlON and slightly better than sapphire in the mid IR. The transmission advantage of Spinel in the mid IR increases with flight-imposed aerodynamic heating. The transmission curves for Spinel, sapphire and AlON at room temperature, 250°C and 500°C shown above are shown superimposed over a typical exhaust spectrum with its characteristic emission at 4.8 microns. The cubic crystal lattice and associated optical isotropy of Spinel give it an additional advantage of image quality over sapphire, whose hexagonal crystal structure makes it optically bi-refringent; i.e., light does not travel at the same speed in all directions through sapphire.
Transmission curves for Spinel, sapphire, and AlON at typical exhaust temperatures
Ta&T news
Annapolis, MD – November 29, 2011 – Ceramic Stereolithography (CSL), a unique manufacturing process developed by Technology Assessment and Transfer, Inc. (TA&T) under multiple SBIR and internally funded programs, was used to make ceramic heater bodies that are onboard the recently launched Mars rover named Curiosity.
Contracted by the NASA Goddard Space Flight Center, TA&T fabricated alumina pyrolysis oven housings that are being used in the Sample Analysis at Mars (SAM) suite of instruments. Patrick Jordan, a NASA engineer, explained that due to the complex nature of the housing, traditional machining of the ceramic was too expensive to undertake. The major impediment to machining the housing is a series of 52 closely spaced, small diameter (.012”) holes through which heating elements are placed. Impressively, the CSL process was able to create fully functional prototypes that survived the rapid heating to >1,000°C. The parts passed thermal shock and thermal cycle durability testing, and will be used on Mars to heat soil samples to determine the presence of water and organic compounds that indicate the possibility of life on Mars.
The CSL process has applications beyond space exploration, including those which have consumer and industrial applications. The process requires no tooling and therefore allows rapid prototyping of fully-functional ceramic parts. TA&T has been involved in the development of rocket engine fuel injectors, heat exchangers for cooling electronics in hybrid electric vehicles, ceramic molds for turbine engine blades, and electrosurgical medical device tips, among other development projects.
Photographs of the TA&T produced ceramic heater housing for the Mars Science Laboratory can be found in the Ceramic Stereolithography gallery.
Additional information about the Mars Science Laboratory mission can be found at http://www.nasa.gov/mission_pages/msl/index.html.
Annapolis, MD – November 21, 2011 – Technology Assessment & Transfer, Inc. has just completed a kickoff meeting as a prime contractor on an Air Force SBIR Phase II.
Led by Dr. James Hom, the Air Force Phase II effort is focused on advanced cooling and packaging designs for electronic components within an aircraft's power electronic converter. The proposed component level solutions substantially reduce the thermal resistances between the highest heat producing components (e.g., the power switching modules, magnetic inductors, and capacitors) and the coolant. These solutions will be integrated into an existing power electronic converter and tested in a simulated aircraft environment. An increase in maximum allowable inlet coolant temperature of at least 30°C is expected.
