As NASA begins development of launch systems for space exploration, the need for space-ready technology that enables safe, automated, and autonomous operation is significant. One major safety system associated with the present space shuttle has been the leak-detection system that is meant to ensure that hazardous conditions do not occur. The space shuttle uses gases such as hydrogen and oxygen, and leaks of these gases can potentially result in explosive conditions. The present shuttle leak-detection system is based on mass spectrometers on the ground or sample bottles in flight. Although these shuttle systems provide significant information related to safety conditions, the shuttle systems have their limitations, especially in providing continuous, real-time information as the vehicle is launched. For a number of years, the NASA Glenn Research Center has been developing smart leak-detection systems (SLDSs) to augment ground systems and to provide real-time data for flight systems. This year, steps were taken to prepare these SLDSs for a possible Crew Launch Vehicle (CLV) application.
SLDSs are based on microsystems technology; that is, they are miniaturized systems fabricated using silicon semiconductor processing technology for minimal size, weight, and power consumption. The SLDS is composed of microsensors to detect leaks and supporting electronic hardware for data processing and temperature control. The approach has been to develop a smart “lick and stick” leak-detection system of near postage stamp size that could be applied wherever safety information is needed.
Left: Silicon-based hydrogen sensor. The palladium (Pd) alloy Schottky diode (rectangular regions) resides symmetrically on either side of a heater and temperature detector. The Pd alloy resistor is included for high-concentration measurements. Right: Packaged sensor.
One example of an SLDS microsensor is the hydrogen sensor. The preceding figure shows the microfabricated hydrogen sensor design on the left and a photograph of a packaged sensor on the right. The structure includes two different hydrogen-sensing elements (Schottky diode and resistor), a temperature detector, and a heater incorporated in the same silicon chip. The Schottky diode and resistor have different sensing mechanisms combining to allow hydrogen detection over a wide concentration range. Glenn has been involved in years of testing the sensor and developed the alloy used in the sensor structure. This hydrogen sensor has been demonstrated in the space shuttle, and it has qualified for an International Space Station criticality 1 function.
The following photograph shows a prototype SLDS that uses hydrogen, oxygen, and hydrocarbon sensors. A range of capabilities were built into this lick-and-stick system, including a microcontroller, signal conditioning and temperature control, wireless or wired communications, operation from a 3- to 5-V power source or battery, internal temperature and pressure measurement, and operation of up to three chemical sensors.
Prototype version of a lick-and-stick SLDS with hydrogen, hydrocarbon, and oxygen detection capabilities combined with supporting electronics.
Glenn has led the efforts to turn this promising technology into a sensor system that can be integrated into the CLV. This year’s SLDS activities involved testing and documentation to verify that the existing system has the basic capabilities to meet CLV application needs, especially concentrating on hydrogen- and oxygen-sensing capabilities. These efforts included Glenn involvement in the maturation of the oxygen sensor technology. Other efforts included verifying that space-qualifiable parts are being used and performing fault analysis on component parts to understand failure mechanisms.
Overall, this CLV work represents steps toward the implementation of “smart” system technology into NASA’s Exploration program. As with the introduction of any new technology, challenges exist in showing benefits and gaining acceptance. However, given the future needs of space exploration systems, the introduction of smart system technology could be a significant enabler of the Vision for Space Exploration.
Last updated: December 14, 2007
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