When balloon and basket are sitting quietly, waiting for lift-off, the whole contraption will reach a height of about 126 feet. The balloon alone will measure 72 feet in diameter and hold 5,790 cubic meters of helium, a nonflammable gas.
Alexander "Pete" Hoskins, zoo president, said the ride would afford visitors unusual views of the zoo's 42-acre site, as well as spectacular vistas encompassing "Philadelphia's illustrious skyline."
Joseph D. Moore, the zoo's chief operating officer, said the project would cost about $1.6 million. The Delaware River Port Authority provided a grant of $500,000 to kick-start construction; the rest will come from the zoo's capital budget, Moore said.
The advent of the balloon, however, will mean the end of the zoo's monorail system, which has not operated since 1998 because of an increasing number of mechanical problems.
The monorail was built in 1968. Rather than replace its system, which is "very invasive" as it meanders through the zoo, Moore said, officials decided to take a look at other possible attractions.
The balloon, scheduled to operate in the evening, Thursdays through Saturdays, will lift off from the former monorail station near the zoo shop.
"In Philadelphia, there aren't many opportunities to get up high and see the whole region," Moore said. "There's no Sears Tower. No Space Needle. City Hall is about the closest thing."
He said officials hoped the balloon rides would accommodate 75,000 passengers its first season.
Stephan Salisbury's e-mail address is firstname.lastname@example.org.