| Acquisition Program: | PMA-265, F/A-18 |
Objective: | Design and develop an optically polished, tangent ogive, infrared-transmitting dome made of polycrystalline alumina or other material with thermal shock resistance, durability, and infrared bandpass similar to or greater than that of sapphire. When fitted with an appropriate nosetip, the dome should survive hypersonic flight (Mach 6 at 20 km altitude).
| Description: | Hemispheric infrared-transmitting domes are not capable of surviving the thermal shock associated with hypersonic flight. An aerodynamic shape, such as an ogive, with a durable material at the nose, could survive in hypersonic flight if the infrared-transparent material had at least as great a thermal shock resistance as sapphire. Infrared-transparent, polycrystalline alumina with thermal and mechanical properties similar to those of sapphire was demonstrated in 2003 [1-3]. The front of the dome will be left open for eventual attachment of a durable nosetip that will enable flight at hypersonic speeds.
Near-net-shape casting of infrared-transparent, polycrystalline alumina (or a superior material) should be in the form of a tangent ogive whose finished dimensions will be a base diameter of 130 mm, a thickness of 2 mm, and a height of 195 mm. The outside and inside of the dome should be ground and polished to an optical quality finish.
| | PHASE I: Demonstrate the feasibility of near-net-shape casting of polycrystalline alumina (or a material with similar or better thermal, mechanical, and infrared properties). The infrared transmittance of polished, flat witness samples should be within 2 percent of that of sapphire in the 3-5-µm wavelength region. Cast a subscale tangent ogive with a base diameter of 50 mm, a height of 50 mm, and a thickness of at least 2 mm. Determine the feasibility of optical polishing and figuring of the outside of the ogive. Develop a plan for how the inside of an ogive can be optically polished.
| | PHASE II: Demonstrate the optical polishing of the inside of the subscale ogive fabricated in Phase I. Cast three full-scale, near-net-shape, tangent ogive domes with a base diameter of 130 mm, a thickness of 2 mm, and a height of 195 mm. Develop methods for optical polishing of the outside and inside surfaces of the full scale dome and deliver two fully polished, full-scale domes. Provide measures of optical figure and surface quality.
| | PHASE III: Demonstrate commercial production capability for casting and polishing full-scale domes.
| | PRIVATE SECTOR COMMERCIAL POTENTIAL: Optical quality polycrystalline alumina has commercial potential as the lamp element for high intensity automobile headlights.
| References: |
1. Krell A., Blank, P., Ma, H., Hutzler, T., Van Bruggen, M. P. B., and Apetz, R. “Transparent Sintered Corundum with High Hardness and Strength.” J. Am. Ceram. Soc., 86, 2003, pp. 12-18.
2. Krell A., Blank, P., Ma, H., Hutzler, T., and Nebelung, M. “Processing of High-Density Submicrometer Al2O3 for New Applications.” J. Am. Ceram. Soc., 86, 2003, pp. 546-553.
3. Krell, A., Baur, G., and Dähne, C. “Transparent Sintered Sub-µm Al2O3 with IR Transmissivity Equal to Sapphire.” Proc. SPIE, Volume 5078, 2003.
| | Keywords: | Missile Dome; Infrared Dome; Hypersonic Missile; Polycrystalline Alumina; Polishing; Ceramic Fabrication
|