Fiber-Optic Pyrometer for Thermal Protection Systems

Award Information
Agency: National Aeronautics and Space Administration
Branch: N/A
Contract: NNX13CA28P
Agency Tracking Number: 125465
Amount: $124,935.00
Phase: Phase I
Program: SBIR
Awards Year: 2013
Solicitation Year: 2012
Solicitation Topic Code: H7.01
Solicitation Number: N/A
Small Business Information
MI, Ann Arbor, MI, 48105-1570
DUNS: 610511334
HUBZone Owned: N
Woman Owned: N
Socially and Economically Disadvantaged: Y
Principal Investigator
 Christopher Davis
 Business Operations Manager
 (734) 786-1434
 zagel@edapplications.com
Business Contact
 Jonathan Zagel
Title: Business Official
Phone: (734) 786-1434
Email: info@edapplications.com
Research Institution
 Stub
Abstract
Surface temperatures in atmospheric reentry simulations range from 1500-2300 K, while stagnation temperature on the leading edge of a Mach 6 flight vehicle at 25 km altitude is 1817 K. Sensors that can operate at temperatures well above 1273 K are needed to provide reliable validation data for TPS modeling and design tools.We propose to develop a low-intrusive fiber-optical pyrometer capable of measuring temperature profiles within an ablating thermal protection system (TPS). In this concept a bundle of parallel sapphire fibers is embedded in a step-wise manner into a multilayered "plug" of TPS material. The sensing tip of each fiber consists of a metallic coating, forming an isothermal cavity; graybody emission from this cavity is transmitted through the fiber to a fiber-optic multiplexer, and thence to a compact near-infrared (NIR) spectrometer. By fitting the thermal spectrum from the shortest fiber to a Planck distribution (adjusted to account for spectral absorption in the sapphire fiber), a cold-side temperature can be inferred first. The next longest fiber can use this temperature to estimate the distorting effects of self-emission in the heated fiber. Sequential evaluation of fiber tip temperatures at known locations along the bundle will allow effective estimation of temperature gradient and subsequent calculation of heat flux.The proposed fiber-optic sensors are thermally and physically robust, lightweight, electrically passive, and immune to electromagnetic and radio-frequency interference. Additionally, our proposed fiber-optic pyrometer is optimized for high temperatures. As the TPS-embedded sensing tip temperature increases, the wavelength peak for the thermal emission spectrum moves from 2634 nm (at 1000 K) to 1260 nm (at the sapphire melting point of 2300 K), while the integrated spectral intensity increases as the 4th power of the temperature. Both effects improve the pyrometer signal-to-noise ratio.

* Information listed above is at the time of submission. *

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