March/April 1999

Scope Floats continued

Scientists sometimes describe a research balloon as "a poor man's satellite." Balloons can loft instruments above 99.7 of the atmosphere and remain at high altitudes for several days. (BAM is a short flight because the glare of the Sun makes it difficult to see the microwave background during the day.) A balloon mission generally costs a couple of million dollars, compared to tens of millions of dollars or more for a satellite.

Just as important, a balloon mission is a work in progress until the moment it's launched.

"We have our hands on it hours before it goes and does its experiment," says Halpern. "With a satellite, the turnover time is more like months. We can make the detectors be really cold, do really fiddly, delicate things, get them to work, patch them together — we've got *tape* on our gondola — tune it up just hours before we do it, and it's only got to work overnight."

BAM begins the three-hour climb to its cruising altitude.

NSBF technicians launch about 30 balloons a year. About a half-dozen take flight from the Palestine base, a half-dozen more from another facility in New Mexico, and the rest from sites around the world — from Alaska to the Amazon to the South Pole. The instruments they carry study both Earth's atmosphere and the heavens beyond.

As launch time approaches for BAM, a 135,000-pound tractor, nicknamed "Tiny Tim," carries the payload from its hangar to the center of a concrete launch pad. Halpern climbs inside BAM's silver gondola, suspended about eight feet in the air. He removes lens covers, runs through a checklist with other scientists, and tosses a cricket overboard.

When his work is done, he bicycles back to the hangar and turns control over to the NSBF launch director, who guides a team of about 10 crew members through a step-by-step launch plan that resembles the countdown for a rocket launch. "Learning this business is like learning to dance," notes NSBF manager Dwight Bawcom. "It's not an easy thing to tell somebody how to do it. You just have to do it."

Shortly before sunset, BAM takes flight. The balloon looks like an 800-foot exclamation mark as it springs skyward. As it climbs into thinner air, however, it will puff outward. In about three hours, when it reaches its cruising altitude, the balloon's shape and the slightly pearlescent sheen of its white plastic skin will make it look like a giant onion.

Stronger-than-usual winds at BAM's cruising altitude push it westward at a jaunty clip, so scientists won't get quite as much observing time as they hoped. BAM's detector has flown three times: on a small rocket in 1990, and on balloons in 1995 and 1998. Each flight yielded a brief peek at the birth of the universe. But scientists want to extend BAM's reach through a much longer balloon flight.

In particular, they hope to launch BAM from Alaska or northern Canada in late autumn or early winter, when the Sun remains near or below the horizon. Steering currents would carry the balloon around the globe, bringing it back to its starting point a week or so after launch.

Combined with the shorter flights, scientists say data from a long BAM mission would go a long way toward solving some of the mysteries of the universe — or create new mysteries for them to ponder.

"By really characterizing these brightness differences in the cosmic microwave background, we can measure the parameters which determine the evolution of the universe," says Greg Tucker. "If the theoretical models aren't correct, and we don't measure what we expect, it will really force us to rethink what we know about the universe."

Damond Benningfield is executive editor of StarDate.

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