New NASA Balloon May Carry Large Telescopes to the Edge of Space
Contact:
Christopher Wanjek
wanjek@gsfc.nasa.gov
301-286-4453June 13, 2000
Wallops Island, Va. -- NASA successfully launched and demonstrated a long-duration balloon prototype that may ultimately carry large, powerful telescopes to the brink of space for 100 days or more by 2002. Such a balloon launch would cost considerably less than a rocket, and the payload could be retrieved and launched again.
The 30-hour test flight from Ft. Sumner, New Mexico, on June 4-5 tested the durability and functionality of the balloon's unique pumpkin-shaped design and its novel material, a lightweight polyethylene film made especially for the project. The Ultra-Long Duration Balloon (ULDB) was developed by Physical Science Laboratory in Las Cruces, N.M., and Raven Industries in Sioux Falls, S.D., under the direction of NASA Goddard Space Flight Center's Wallops Flight Facility, Wallops Island, Va.
"The test flight was a resounding and unmitigated success," said Dr. Steve Smith, ULDB Project Manager. "By chance, the balloon flew over a very bad thunder storm at night, the worst-case condition in terms of cold weather and tricky winds. Yet we maintained a stable altitude for the duration of the flight."
The flight, the largest single-cell, super-pressure (fully sealed) balloon ever flown, also tested the capabilities of the balloon vehicle and recovery systems. The ULDB team will now move forward with a full-scale, global balloon test flight this winter from Australia.
When fully inflated, the massive ULDB would barely fit in a football stadium. It will soar with a 3,500-pound (1,588 kilogram) payload above 99.9% of the atmosphere, up to 22 miles high (35 kilometers) or 3-4 times higher than passenger planes. The Ft. Sumner test flight -- with a balloon similar in design to the proposed ULDB but roughly 1/10 the volume -- reached a height of around 17.5 miles (28.3 kilometers) carrying a 1,660-pound (753 kilogram) payload.
The ability to fly balloons for months or years at a time will create a multitude of scientific and business opportunities, Smith said. Conventional high-altitude balloon flights typically last a few days to a week because atmospheric temperature changes from day to night ultimately cause the balloon to lose altitude. During the day, the sun hits the balloon, gas warms up and expands, and the excess expanding gas is vented out to the atmosphere. When the sun sets, the gas cools and contracts; the balloon volume decreases and the balloon sinks. Dropping ballast can raise the balloon again, but soon the ballast is depleted.
Flights from Antarctica or above the Arctic Circle can last up to 21 days, for the daylight (or nighttime) is six months long and there is very little atmospheric or temperature change. The balloon eventually sinks, however, as gas leaks out.
The ULDB differs from conventional scientific balloons now being flown because it is completely sealed, so gas is not vented to relieve pressure. Smith said the new balloon material is strong enough to maintain pressure differences; secure enough to resist leaking; durable enough to hold up to prolonged UV radiation in the high atmosphere; and tough enough to survive high winds and fast-flying dust particles. The test flight, in fact, remained at a constant altitude for the entire flight despite drastic temperature changes.
The ULBD material, developed by Raven Industries for this project, is a co-extruded polyethylene film with a high-density layer sandwiched between two linear low-density layers -- about the thickness of plastic food wrap, 0.0381 mm. The high-density part provides strength and stiffness; the linear-low density part provides toughness and sealability
The ULDB design, in the shape of a pumpkin, shifts the entire payload carrying function and most of the pressure load to the load tendons. This puts less stress on the balloon material itself and allows the balloon to utilize a lighter, more-durable material to carry the kind of loads that heavier, less-durable balloon materials often carry. The Commendable Apex Package, developed by PSL, allowed for pressure monitoring and control of the balloon. This along with the redesign of a new subsystem by PSL and Raven were crucial to the success of this recent mission.
The first fully operational ULDB flight with a scientific payload is currently scheduled for December 2001 from New Zealand, a year after this winter's full-scale test.
The ULDB was highlighted in the National Research Council's decadal survey, "Astronomy and Astrophysics in the New Millennium," and has an important role in providing inexpensive access to a near-space environment. For more information and images, refer to http://www.wff.nasa.gov/~code820/.
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