by George Denniston
Last March, Troy Bradley resigned his spot on the Dymocks Odyssey Flyer, the helium balloon planning to go around the world west to east in the stratosphere. The Dymocks Flyer is preparing to take off from central Australia sometime after early November, the beginning of the Australian summer.
Raven is building the envelope of thin polyethylene film. The table they use to build such balloons is 700 feet long. On the ground, it will be filled with 170,000 cubic feet of helium. As it ascends into the stratosphere, the helium will expand to 39.5 million cubic feet. Below the envelope hangs a large parachute, and below it, the capsule.
The balloon will ascend into the stratosphere, which begins around 50,000 feet MSL. It will continue up to a maximum of 130,000 feet, as the helium, warmed by the sun, and encountering less pressure, expands. When night comes, the helium will begin to contract with the cold, and the balloon will begin a slow descent. By morning, when the sun returns, hopefully it will not have descended below 80,000 feet. This is known as Raccooning, which is short for RAdiation-CONtrolled Ballooning. In this manner, having to carry and drop large amounts of ballast is avoided.
Winds in the stratosphere travel about 50 mph, maximum. At some levels it is calm. This can make for a longer trip than at lower levels. The balloon can travel a maximum of 1200 miles per 24 hours, and more likely 800-900 miles per day. Since the minimum distance for a legal around the world flight is approximately 16,000 miles, the journey can take three weeks.
The balloon would cross half of Australia, the Indian Ocean, southern Africa, the south Atlantic, South America, and the Pacific Ocean. Then it must land west of a north-south line through the center of Australia (Alice Springs).
Launching a balloon of this size and thinness requires equipment and skill. Near the town of Palestine, in eastern Texas, where large unmanned scientific balloons are routinely launched (Balloon Life, June, 1988), a 10 ton diesel-powered launch vehicle picks up the payload, and drives it slowly to the launch pad. The envelope is brought out in a box atop its own truck, and laid out in a long straight line. A tie-down truck and a helium truck are also present.
The tie-down truck has arms that grasp the envelope ever so gently just below the top. Two men begin filling the top with helium through plastic filling tubes. When they have completed putting what appears to be a relatively small amount of helium into the top, the tie-down truck releases its grasp, and the top of the envelope lifts off rapidly. The launch vehicle races to keep the payload directly under the envelope, and releases it quickly. If the envelope has been damaged during the preparations or launch, a tear will appear, and the entire balloon ruptures at takeoff. If the envelope has not been damaged, the balloon is on its way.
Balloon Life recently interviewed Troy Bradley to discover why he left the Dymocks Odyssey project and to uncover some of the challenges of stratospheric balloon flight.
Balloon Life: Why did you decide to leave the project?
Troy Bradley:: I have no problem with the theory behind this flight. I think it is a very valid concept. I think this concept may be the one with the greatest likelihood of succeeding, the way the first round the world flight is finally accomplished.
The problem is that it is a space shot. When I left, we simply did not have the financing to solve all of the problems.
BL Is the project still continuing?
Bradley:: Yes it is. Bob Martin of Albuquerque and John Wallington of Australia are continuing with their plans right now.
BL What is the status of the project now?
Bradley:: The capsule has already been built. It is sound. It is pressurized by gases. Liquid nitrogen and oxygen canisters are on the outside of the capsule, and one can manipulate regulators on the inside to adjust the percentage of each gas, and its pressure. Lithium hydroxide scrubbers remove CO2 from the cabin air, as they do in the space shuttle.
BL How do they plan to keep warm?
Bradley:: One might think that the problem would be keeping warm at the high altitudes where the Dymocks Flyer will be traveling, and it may be, because the outside air temperature in the summer is between -50C and -60C. But the real problem is keeping cool in the daytime. To help with this, the capsule is painted with a special white paint that reflects a maximum amount of sunlight. Underneath the paint is ethofoam for insulation that routinely keeps unmanned balloon equipment within reasonable ranges of temperature.
But if the capsule were to overheat, it cannot be ventilated to the outside due to the pressure difference. So it may be necessary to have a heat exchanger.
BL Does the Flyer have a heat exchanger?
Bradley:: No. But they are planning to have air conditioning, with solar panels to supply the electricity.
BL What happens if the huge thin polyethylene balloon ruptures at altitude?
Bradley:: There is a parachute between the balloon and the capsule. Supposedly that will take you down OK, but if not, you bail out. At present, you must wait until you are down to a lower altitude before bailing out. The crew is not equipped with space suits.
BL When the big chute opens, we have heard that the capsule and its occupants may pull as many as 12 G's. Is that correct?
Bradley:: Yes, the capsule has been stressed so that it can withstand 12 G's. The occupants would be sitting in special aircraft seats, designed to help a human survive the G forces expected. These seats have helped humans survive more than 12 G's.
BL What do you do if you are over water?
Bradley:: You ride the capsule all the way to the water. I checked with the person who is calculating various trajectories, and he tells me that the rate of descent at landing will be under 1000 fpm. That's very survivable.
