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Solar-Heated Balloon Carrying APRS Travels from Michigan to New Hampshire

The SD4 shortly after launch from Michigan. [Robert Rochte, KC8UCH, Photo]

NEWINGTON, CT, Mar 3, 2004--Shades of Charlie Brown's perennial bad luck with kites: A solar-heated balloon carrying an Amateur Radio Automatic Position Reporting System (APRS) payload remains in the grasp of greedy tree limbs this week after traveling all the way from the upper Midwest to New England. Robert Rochte, KC8UCH, who's director of technology at The Grosse Pointe Academy in Michigan, reports the flight marked the fourth in a series of what are known as solar "tetroons"--tetrahedral-shaped balloons.

"We've dubbed these tetroons 'Sky Diamonds' from the appearance that they have at altitude," Rochte said. "This particular flight was Sky Diamond 4--SD4."

SD4 took off February 16 at 1434 UTC from Sterling Heights, Michigan. By that evening--0119 UTC on February 17--it had covered some 563 miles, ending up near Peterborough, New Hampshire. "Our tetroons currently have the number 2 and number 3 records for great-circle distance and for duration," Rochte said. "The SimSat balloon in Portugal beat us out of number 1, but we'll take this back in the summer." Ralph Wallio, W0RPK, maintains such statistics on his "Amateur High Altitude Ballooning Mission Records" "Web site.

Rochte said SD4 was equipped with an APRS tracker consisting of a RadioShack Digitraveler GPS, a KPC-3+ and a small RadioShack HTX-245 handheld transceiver. A simple wire ground-plane mounted below the payload provided the antenna. Rochte said the GPS unit failed to report altitude above 10 km, but veteran ham radio balloonist Bill Brown, WB8ELK, estimated the float altitude by correlating speed and bearing data with balloon sounding data gathered earlier in the morning.

A map tracing the relatively straight-line path the SD4 balloon took from Michigan to New Hampshire. Rochte points out that note that tracking was lost during descent through the jetstream. The large red dot marks the actual landing spot.

"Lift for the tetroon is provided entirely by solar heating of the air within the envelope," Rochte explains. "There's no external heat, helium or anything else used to get them off the ground." He said he typically inflates the envelope using a leaf blower, but in the case of SD4, there was more than enough natural surface wind to inflate the envelope by simply aiming its "mouth"--secured open using a rigid "load ring"--into the breeze.

Rochte, who custom designs and builds all of these balloons himself, says each tetroon is made of translucent 9 micron (0.35 mil) high-density polyethylene film. The mouth is held open by a rigid load ring and the payload line attaches from there. He says he's gotten help over the years from well-known balloonist Don Piccard, who suggested the diamond shape. Beyond ease of construction, Rochte says, the shape offers no special advantage.

The SD4 envelope weighs a couple of pounds and contains a total volume of approximately 3000 cubic feet. A clear polyethylene box houses the payload. "The clear box--recommended by APRS guru Bob Bruninga, WB4APR--allowed the sun to keep the payload warm, just like the air inside the tetroon," Rochte noted.

The SD4 balloon remains in the grasp of these trees on private land in New Hampshire.

He says the final APRS packet from SD4 was received when it was still some 250 feet above the ground in New Hampshire. It wasn't until the payload began transmitting again the following afternoon that he was able to pin down its location using the Findu.com and APRSworld.net Web sites. He speculates the transmitter restarted once the payload had been warmed by the sun.

"I searched for nearby APRS stations on Findu and found N1MZX's (Jon Hampson) weather station about five miles away," Rochte said. He contacted Hampson, who offered to go out and look for the balloon. "He was first on the scene around 4 PM or so on February 17," he said. "He called me on his cell while he was walking up to the tree."

The SD4 tetroon stranded in the New Hampshire treetop has been airborne before. Last August, it flew from Detroit to within 50 miles of Pittsburgh. "I retrieved the envelope, patched it using Scotch tape and now it has flown again," Rochte explained.

Hampson has been attempting to contact the landowner, who's out of town, to get permission to fell the tree and retrieve the SD4, but Rochte says it should be able to withstand the elements for up to a year with no problem. "We'll fly it again as soon as we get it back," he said.



Page last modified: 07:39 AM, 03 Mar 2004 ET
Page author: awextra@arrl.org
Copyright 2004, American Radio Relay League, Inc. All Rights Reserved.