B-2 Tests Super-TIGER Balloon Payload to Investigate Cosmic Questions
When scientists and engineers want to study some of the great questions of the universe, they often construct elaborate machines that travel great distances to gather data. Years of labor and research, and millions of dollars are spent creating these technical wonders. But, before launch, they must go through rigorous testing to ensure everything on board works.
This summer, a truck bearing a 6,000 lb. payload arrived at the Spacecraft Propulsion Research Facility (B-2) at Plum Brook Station in Sandusky, a testing facility operated by NASA's Glenn Research Center (GRC). B-2 is a huge thermal-vacuum stainless steel chamber, 38 feet in diameter by 62 feet tall, which can simulate temperature and atmospheric conditions simultaneously.
The payload, called Super-TIGER (Trans-Iron Galactic Element Recorder), is a structure jammed with electronics that will be hitched to a huge, atmospheric balloon and launched in December over Antarctica. It will rise to 120-130 thousand feet and stay there for 30-45 days measuring cosmic ray elements from massive stars in our galaxy that exploded and sent particles zipping through Earth’s atmosphere.
"Funny things can happen to electronics when you put them in the low pressure, low temperature environment of the upper atmosphere," says Rachel Maynard, GRC engineer and manager of the Super-TIGER tests. "We can help investigators identify these problems on the ground so they can fix them before the mission launches."
When a payload arrives at the B-2, a crane lifts it onto a platform inside the cylindrical chamber. After investigators connect all the electronics, the chamber is sealed and the tests begin. "We start with conditions at ambient pressure and room temperature and slowly change the conditions in the chamber to those that the payload will encounter," explains Maynard.
In the case of Super-TIGER, the payload will need to withstand conditions down to minus 10 degrees F and low pressure of 4 Torr (sea level is 760 Torr). However, the payload could also heat up to well over 100 degrees F during transportation to Antarctica.
Over the course of three 24- hour cycles, Maynard and the B-2 team repeatedly changed the temperature and pressure conditions in the chamber from ambient to upper atmosphere, while monitoring the payload components.
"We are able to lower temperatures by pumping liquid nitrogen into a copper wall that lines the chamber. The cooling process can take up to eight hours because air doesn’t transfer heat very well at such low-pressure conditions. Then, when we want to raise the temperature, the wall is drained and heater panels are engaged to create higher temperatures," explains Maynard.
"B-2 was the perfect test facility for our needs," said Bob Binns, principal investigator at Washington University in St. Louis, who, in partnership with NASA's Goddard Space Flight Center, CalTech and University of Minnesota, developed Super-TIGER.
"Historically, we tested these payloads on short flights in New Mexico, but it was risky because landing and recovery could damage it and the conditions weren't nearly the same," explains Binns. "Testing at B-2 not only simulates Antarctic conditions but we also remove the early risk of flight damage by keeping it grounded."
The staff at Plum Brook is becoming quite experienced at balloon payload tests. In just the last year, NASA's Wallops Flight Facility balloon program has shipped three payloads to B-2 for pre-flight tests. And in each case, problems were uncovered that could have adversely affected the mission. Crews fixed the issues prior to launch.
"Our test was a success in that we were able to find several problems with our electronic systems," says Binns. "We can fix these issues now, giving us a better chance for a successful overall mission."
"What we monitor varies from payload to payload because they are all designed for different investigations," says Hal Weaver, test manager of the B-2 facility. "But while they have different objectives, we will always be well-suited to test them because we can simulate the conditions they experience during flight- pressure, temperature, and also solar effects when required."
Originally built in the mid-60s, B-2 was designed to test the upper stages of rockets, including firing engines in the chamber. It continued to test newer engines in the 90s and the landing bags for Mars rovers. With balloon payloads being launched each December, the B-2 facility will continue to aid in this important research.
"We plan to use the Super-TIGER payload at least twice," says Binns. "Once this year, then we will refurbish it and fly it in another two years. I expect we will return to Plum Brook and B-2 before flying again."
Nancy Smith Kilkenny, SGT Inc.
NASA’s Glenn Research Center