What a satellite can do, balloons can do cheaper.
- By T. A. Heppenheimer
- Air & Space magazine, January 2002
(Page 6 of 8)
The balloon, folded tightly in a large wooden box, arrives on a trailer pulled by a pickup truck. It takes four people to lift the balloon from the box and unfold it into a long strip of polyethylene, still folded lengthwise and protected by a red wrap. When it's stretched to its full length, technicians attach a parachute; the other end of the parachute is attached to the payload, which has thick pads of corrugated cardboard to cushion its impact when it lands.
With a loud hiss, helium begins to flow from the canisters through metal sleeves and into long plastic tubes feeding the balloon's upper area. Slowly the top of the balloon takes the shape of an inverted teardrop. Most of the balloon continues to lie along canvas until the rising action of the helium-filled end of the balloon releases it from a restraint. The filled end rises and pulls the rest of the balloon's length upward, then lifts the parachute as well. The payload is still attached to the mobile crane; its operator watches for any breeze that will waft the helium-filled teardrop overhead. Then, with his diesel engine rumbling, he drives slowly across the pavement, following the direction of the wind and keeping the balloon directly overhead. When he is satisfied that the balloon has taken up the weight of the payload, he releases it. There is no countdown and no turning back.
Immediately after liftoff, the balloon typically rises at several hundred feet per minute. Still, it seems to hang in the air. While scientists in the hangar follow the data that now is beginning to come in, other specialists head for the control tower, where they will track the balloon during the next several hours.
Assembling a Giant
Raven Industries, a maker of balloons of all types, including many that fly in the Macy's Thanksgiving Day parade, assembles the giants that carry science instruments to altitudes of 25 miles. The balloons are made in a building just off Interstate 30, about 80 miles east of Dallas. Inside, the work area is nearly a thousand feet long, with rows of tables stretching end to end. On the tables are the long gores, or segments, that form a science balloon. The largest use nearly a million square feet—20 acres—of polyethylene film, less than a thousandth of an inch thick.
Mike Zimmerman, Raven's chief of quality control, says, "We inspect every inch." Before the balloon is assembled, an inspector scans the film with polarized light to check for holes or weaknesses. Push your thumb into a sample of film; the dent is not easily seen. Yet it shows up clearly under the light.
A balloon of 40 million cubic feet has 172 gores and takes about three weeks to assemble. Raven's workers unroll sheets of polyethylene film, which comes folded lengthwise in rolls of 54 inches wide, down the length of a table. They then run a sealing machine down the edges where two gores join; the machine uses heat to fuse the film and form gas-tight seams. The panels are cut along a curve, marked on the work tables with tape. As workers join the gores, they install load-bearing tapes that run the length of the balloon. The balloon stays folded during construction and prior to launch. It expands to full size only at altitude.
Ravens build about 20 balloons a year. Most of their instrument packages tip the scales at a ton and more.