When traveling beyond the earth’s atmosphere, it’s crucial to be able to adequately measure the level of various gases that may seep into the spacecraft. The danger is especially severe during long missions, when contaminants can build up in the air supply, threatening the health of any crew members and the functioning of sophisticated instrumentation. Scientists at NASA Ames Research Center (ARC) and Goddard Space Flight Center are combating the problem with a new chemical nanosensor, the first of its kind to be tested in space. Each sensor is either made of carbon nanotubes or nanowires, giving it high sensitivity.
In March, the nanosensor chip, weighing only a couple of grams, traveled into space in an electronic and mechanical package aboard the Naval Academy’s Midstar-1 satellite, and was put to the test in late May. According to Jing Li, the principal investigator and a senior scientist at NASA Ames, the sensor was able to endure the intense conditions, including temperature and pressure cycles, in space, as well as the extreme vibrations and gravity changes that occur during launch.
Making a chemical sensor for space travel using nano components “is very significant,” says Joseph Stetter, director of the Microsystems Innovation Center at SRI International, in Menlo Park, CA. “This is a valuable way to approach things and solve problems in space.”
NASA scientists built the nanosensors by coating carbon nanotubes with different polymers that react with various chemicals, or by doping the carbon nanotubes and nanowires with different catalytic metal particles that act as the sensing material. There are 32 sensing channels on a chip; depending on the chemical to be detected, various nanostructure materials, carbon nanotubes, or metal-oxide nanowires–coated or uncoated–are put in each channel. When a small amount of the targeted chemical touches the sensing materials, it triggers a reaction that causes the electric current flowing through the sensor to increase or decrease. The different responses will form a pattern, which the sensor can use to identify a gas.
To test the nanosensor, the scientists injected nitrogen dioxide into the chamber holding the nanosensor. Once the nitrogen dioxide made contact with the sensing materials, the sensor was able to measure the change in electricity passing through it. Thus far, scientists have tested more than 15 chemicals, including ammonia, hydrogen peroxide, hydrogen chloride, and formaldehyde.
Using carbon nanotubes to sense the chemicals “may have significant advantages,” says Jiri Janata, a professor in the school of chemistry and biochemistry at the Georgia Institute of Technology. For one, using the nanostructure materials increases the surface-area-to-volume ratio, allowing the materials to absorb more gas and thus improve sensitivity.
In addition to the potential increased sensitivity, the nanosensors are solid-state devices. This gives the sensor a shelf life of up to five years, compared with the six-to-twelve-month lifetime of existing electrochemical sensors.
The sensor chip itself is one centimeter squared. In its electronic package it is about 5.1 centimeters by 6.4 centimeters by 2.5 centimeters, and it’s wireless: it can transmit sensor data from one corner of a room to another, or a distance of 30 meters. “Low power, small size, and light weight are very important in outer space,” says Stetter. “The idea is, we want more functionality in smaller packages, especially given the cost to lift something into space.”
NASA scientists hope to eventually place the nanosensor aboard the shuttle, the International Space Station, and other vehicles destined for space. Engineers at the Kennedy Space Center have also shown interest in the sensor for placement in the launch-pad area to monitor fuel leaks and chemical dispersion along the radius.
The technology for the sensors are ready for space, says Li, but before they can fly in a mission, they will have to be modified according to the chemicals that NASA is interested in detecting. The sensors will also have to go through NASA’s space qualification process, which can be a lengthy adventure all by itself.