May 16, 2013
NASA Calls on APL to "Catch" a Comet
When astronomers announced last September 24 that they had discovered Comet C/2012 S1, predicted to swing past the Sun in late 2013, it meant a combination of excitement (the chance to study a new and rarely observed type of comet) and anxiety (there was barely a year to prepare for the observations).
For a team of about 30 APL staffers, it soon meant a fast scramble to meet an urgent need from NASA. The agency wanted to know whether APL could develop a payload and gondola for a balloon mission to study the comet — named ISON after the Russian institution from which it was first observed — during a window of mid-September to mid-October 2013.
Program Manager Dewey Adams, of APL’s Space Department, says such a program would normally take 18–24 months to develop. After some fast studies and deliberations at the Laboratory and discussions with the Southwest Research Institute (SwRI), APL told NASA it could be done. The Balloon Rapid Response for comet ISON (BRRISON) project was born; the project is led by NASA’s Glenn Research Center in Cleveland. “We’re going to do it in 10 months, on schedule, and with a high level of science,” says Adams.
“This is the kind of rapid response project that APL has a good record of doing,” says the Space Department’s chief scientist and BRRISON Principal Investigator Andy Cheng. “NASA already had a study in progress at APL and SwRI about the possibility of doing decadal planetary science from a balloon, but this is the real thing. It’s amazing to think that the first scheduled decadal science balloon study will be on a comet, one that goes from being discovered to observed in only 13 months.”
The arrival presents a fantastic chance to do fundamental science, with one big problem: No one knew comet ISON was on its way until late last year. While other space assets will attempt to observe many of ISON’s characteristics, it’s important to measure certain specific aspects of the comet. “Getting [BRISSON’s] instruments above the atmosphere is critical,” Adams says.
The only way to make the deadline is to use a lot of existing hardware, experience, and knowledge. APL’s successful Stratospheric Terahertz Observatory (STO) balloon mission, which studied the Milky Way in early 2012, proved key when the team was examining how to make BRRISON a reality.
BRRISON’s planned mission will use much of the hardware and knowledge from STO to soar some 120,000 feet (about 23 miles) high on a balloon that eventually expands to the size of a football field, carrying an aluminum-frame gondola the size of a small cottage that will place two instruments sharing a 0.8-meter telescope above 99.5% of Earth’s atmosphere. This altitude removes almost all barriers to clear observations, providing many of the benefits of a space-based instrument but at far lower cost.
“We’re reusing a lot of hardware built for STO” and other balloon missions, says the Space Department’s Pietro Bernasconi, APL’s resident balloon expert and BRRISON gondola lead. He adds that the team is developing new technical items for improved positioning stability, because gondolas on balloons oscillate from side to side. BRRISON will carry a new mechanism to reduce oscillation and provide the best stability ever achieved on a balloon mission of this type.
That stability will benefit the two instruments, one that covers visible light (now being built and provided by SwRI) and one for infrared. APL is reusing and improving STO’s infrared instrument. “In some ways, we’re reflying STO with a new instrument package,” says Karl Hibbitts, BRRISON deputy principal investigator and infrared telescope lead. “Almost everything is a legacy system or very simple; that’s the only way this works. Plus, Pietro has shown he can fly with positional accuracy on an object that’s not the Sun.” Given the distance to ISON and the comet’s dim and diffuse light properties, that capability will prove invaluable, he adds.
When completed (scheduled for early September), BRRISON’s gondola and attached science payload will be trucked to NASA’s Scientific Balloon Flight Facility in Fort Sumner, New Mexico, where it will be joined to a balloon. A few weeks later, the team will attempt to launch; just like a spacecraft launches, balloon launches are subject to weather and cloud restrictions that can delay scheduled ascents. If all goes well and BRRISON can perform its mission, it will spend only about 20 hours aloft before returning to Earth; the proximity of population centers makes longer flights too risky.
Hibbitts, like the rest of the team, says the project is a mix of tension and fun. “This is why I’m at APL,” he explains. “This is what APL does. We have the institutional mentality to tackle this.”