Space @ VT
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In the polar night of early February, at the Poker Flat Research Range north of Fairbanks, Alaska, a Virginia Tech team launched a rocket into an aurora. The team included ECE associate professor Scott Bailey, Chris Hall of aerospace and ocean engineering, two students and a postdoctoral associate, plus colleagues from three other institutions. The 10-minute flight took the rocket 200 miles above the ground and represented the first time a sounding rocket was used for pointing at a star near the horizon and using attenuation of starlight to determine atmospheric constituent concentrations.
Some measurements are harder to obtain than others, and Bailey’s team sometimes must take their measurements by sending special equipment up on rockets. With funding from NASA, the team was aiming at Spica, 260 light years away, in an effort to measure the amount of nitric oxide in the upper atmosphere.
Nitric oxide is important because it can destroy ozone. One of the chemical byproducts of the aurora, nitric oxide is usually found in the thermosphere — at a far higher altitude than the ozone in the stratosphere. However, “in the polar night, there are no solar photons to break up the nitric oxide,” Bailey explains, “so the aurora keeps building it and there’s nothing to take it away. Then it has time to flow downward and destroy large amounts of ozone.”
According to Bailey, “we’ve observed the ozone destruction that we believe occurs from aurorally produced nitric oxide, but we’ve never measured the nitric oxide itself at night, when it must be flowing down. The methods we use for nitric oxide in the daytime don’t work at night.”
The team aimed the sounding rocket at Spica because it shines exceptionally well at wavelengths that only nitric oxide absorbs. With the star in occultation (covered by Earth’s atmosphere), they hoped to measure the density of nitric oxide molecules along the path from the rocket through the atmosphere. They used an ultraviolet spectrograph designed at the University of Colorado to measure the starlight. The more nitric oxide between the rocket and the star, the more the spectrograph signal decreases when viewing through the atmosphere. “It’s tricky to find a star that’s bright at the UV wavelengths that only nitric oxide absorbs.”
It’s also hard to get the rocket pointed at the star, he explains. NASA has equipment that can take the rocket up to space and point it within two arcminutes (one arcminute is 1/60 of a degree), but this only works when the rocket is pointing at a star sufficiently high in the sky. However, to study the atmosphere, the rocket had to actually look toward the Earth’s horizon. To compensate for this, they planned for the rocket to first lock onto a star higher in the sky, then use a gyro system to scan it down mechanically. An internal camera system would then help align it more precisely. “When you look at the whole system, it’s very complicated, but on the other hand, except for the looking near the horizon, this pointing approach is well within the team’s experience,” says Bailey.
Building the Hardware
Building the hardware presented a number of challenges. The experiment was led by Virginia Tech, in collaboration with researchers from the University of Colorado, Utah State University, and Artep Inc. (a small company in Maryland). “It was an interesting challenge bringing together hardware when it came from four different places,” says Bailey. The telescope they used, for example, had been flown on rockets in the 1980s and 1990s, but had been on display in Colorado.
Top: The team tested and integrated all the hardware for the experiment at Virginia Tech, then integrated with NASA subsystems at Wallops flight facility, and installed the motors in Alaska.
The team performed all the testing and integration at Virginia Tech, and then integrated with NASA’s systems at the Wallops Flight Facility on the Eastern shore of Virginia, and then integrated the entire payload with the rocket motors once in Alaska. “It’s a big success for Virginia Tech to get it together and get it launched.”
In addition to Bailey and Hall, the team includes master’s student Padma Thirukoveluri, Ph.D. student Justin Carstens, and postdoctoral associate Brentha Thurairajah.
Even with all the lab tests, Bailey explains that field trials are a vital part of the research. “You think it’s only a small difference from what you’ve done before, but all the new variables come together to make it something different. A failure in the pointing system prevented us from getting pointed at the star,” Bailey explains. Even though this year’s launch didn’t return with the data they had hoped to collect, he remains optimistic. “We’re a long way from being done,” he says.
“We learned a lot about pointing at a star close to earth. It’s the first time a sounding rocket had done that.” The team would like to try again, and hopes in the future to expand the effort to include measurement on the same star, but from a satellite.
Bailey’s team involved a number of undergraduate and graduate students over a couple-year period. Shown here from the left are Brentha Thurairajah (postdoc), graduate students Cissi Lin, Justin Carstens, and Padma Thirukoveluri, and Bailey. The space monkey is a good luck tradition for Artep (not flown).