After years of tests and development, NASA's Balloon Program team is on the cusp of expanding the envelope in high-altitude, heavy-lift ballooning with its super pressure balloon (SPB) technology. NASA's scientific balloon experts are in Wanaka, New Zealand, prepping for the fourth flight of an 18.8 million-cubic-foot (532,000 cubic-meter) balloon, with the ambitious goal of achieving an ultra-long-duration flight of up to 100 days at mid-latitudes.

Launch of the pumpkin-shaped, football stadium-size balloon is scheduled for sometime after April 1, 2016, from Wanaka Airport, pending final checkouts and flight readiness of the balloon and supporting systems.

Once launched, the SPB, which is made from 22-acres of polyethylene film - similar to a sandwich bag, but stronger and more durable - will ascend to a nearly constant float altitude of 110,000 feet (33.5 km). The balloon will travel eastward carrying a 2,260-pound (1,025 kg) payload consisting of tracking, communications and scientific instruments. NASA expects the SPB to circumnavigate the globe once every one to three weeks, depending on wind speeds in the stratosphere.

"We are thrilled to be back in New Zealand for another test flight of this critical, potentially game-changing technology," said Debbie Fairbrother, NASA's Balloon Program Office chief. "This could be the flight for the record books."

Up to a hundred days at float could shatter the current SPB flight duration record of 54 days, which occurred over Antarctica in 2009. To achieve this goal flying at mid-latitudes, where the balloon endures pressure changes due to the heating and cooling of the day-night cycle, the SPB flight must do what no other balloon has accomplished before.

Longer-duration flights enable longer observations of scientific phenomena, the ability to survey more sources, and more time to observe weak or subtle sources. In addition, mid-latitude flights are essential for making observations at night, a requirement for certain types of scientific investigations. These two aspects greatly enhance the return on science, and combined with the relatively low-cost of balloon missions, SPB could become a competitive platform for a number of scientific investigations that would otherwise need to launch into orbit.

COSI flying as mission of opportunity
One group familiar with the potential of SPBs is the Compton Spectrometer and Imager (COSI) team from the University of California, Berkeley. COSI is a NASA-funded telescope designed to probe the mysterious origins of galactic positrons, study the creation of new elements in the galaxy, and perform pioneering studies of gamma-ray bursts and black holes. Long-duration flights are vital to these types of studies.

"SPBs enable completely new types of science investigations, such as we are attempting with COSI," said Steven Boggs, professor of physics at Berkeley and leader of the COSI collaboration. "The long duration and night-time observation capabilities of SPBs are transformative. COSI is just the first science payload to take advantage of these new capabilities." The COSI payload is flying on the SPB test flight as a mission of opportunity. COSI last flew on an SPB that launched from McMurdo Station, Antarctica, Dec. 28, 2014. Unfortunately, that balloon developed a small leak, leading to an early flight termination just one day and 20 hours after launch. Lessons learned from that mission have been applied to the upcoming SPB flight from Wanaka.

Lessons learned from 2015
This year's SPB campaign marks NASA's second year in Wanaka, which appears to be an ideal location for launching mid-latitude flights. The first SPB flight from Wanaka, which launched March 26, 2015, flew 32 days, five hours, and 51 minutes, taking it nearly around the world in what was the most rigorous test of the SPB to date, according to Fairbrother.

Officials terminated the balloon's flight over a remote area of the Australian Outback after detecting a leak in the balloon. Back on the ground, the team recovered the balloon and shipped it back to the United States for analysis. The ensuing investigation concluded that the most likely cause of the leak was a gradual slipping of the balloon material at the metal fittings on the base and top of the balloon structure.

To address this issue, the team has implemented subtle modifications to the balloon flying in this year's campaign. For example, the team changed the way the balloon is clamped at the metal fittings by adding a gasket material. In addition, they've increased the clamping force at the fittings.

"I'm confident in the changes we've implemented in our design, and I'm excited to see SPB take flight again from Wanaka," said Fairbrother.

Wanaka 2016
In much the same way U.S. rocket launches draw crowds at nearby viewing sites, NASA's 2015 SPB launch from Wanaka drew a similar degree of attention from New Zealanders.

"It was incredible to see the interest in our balloon flight last year, with hundreds of people coming out to viewing locations or climbing nearby Mt. Iron to see our launch," said Fairbrother. "All that buzz seems to be building up once again, and we're looking forward to engaging the community even more."

The balloon team has a number of outreach events planned during this year's campaign. Most notably, the team will exhibit during the Warbirds Over Wanaka Airshow, providing information on the upcoming mission and guest speaker presentations.

"We're looking forward to welcoming the team back again this year and are delighted that NASA will play a part in the biennial Warbirds show," said Ralph Fegan, Wanaka Airport Operations Manager. "With more than 50,000 attendees over three days, the event is the largest Warbird airshow in the southern hemisphere, so associating it with NASA's new launch program will provide fantastic national and international exposure."

As the balloon travels around Earth, it may be visible from the ground - particularly at sunrise and sunset - to those who live in the southern hemisphere's mid-latitudes, such as New Zealand, Argentina, Australia and South Africa. Anyone may track the progress of the flight via a map showing the balloon's real-time location, at: http://www.csbf.nasa.gov/newzealand/wanaka.htm

NASA's scientific balloons offer low-cost, near-space access for scientific payloads in the approximately 1,000-pound or more weight class for conducting scientific investigations in fields such as astrophysics, heliophysics and atmospheric research.