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loss of the telescope. Although the data still have to be analyzed, “weaccomplished all the goals of the flight and then some,” said University ofPennsylvania professor Mark Devlin, the U.S. principal investigator of BLAST.Given the hazards of the Antarctic environment, it is natural to wonder why thetelescope was launched there in the first place. The answer can be found in aneven more inhospitable place—galaxies at the far reaches of the universe.The two-metre telescope, known as BLAST (Balloon-borne Large-Aperture SubmillimetreTelescope), was designed to address important questions about theformation and evolution of stars and galaxies by collecting data at sub-millimetrewavelengths with an unequalled sensitivity. These wavelengths are largelyblocked by the Earth’s atmosphere; in fact, on Earth, the telescope could “barelysee across the street, let alone into space” in one of the frequency bands it wasdesigned to study, Netterfield noted. “You’ve got to get out of the atmosphere.”Perhaps the obvious way to do this is to launch a telescope into orbit, but it is farless expensive to carry it aloft on a balloon. At about $5-million, the BLASTproject, jointly sponsored by Canada and the U.S., the U.K. and Mexico, cost atiny fraction of the hundreds of millions of dollars it typically costs to operate asatellite. Canada’s contribution to the multinational program, largely funded bythe Canadian Space Agency (CSA), was to develop and build the pointing controlsystem, the electronics, the software, and the gondola that carried the telescope.The work was done at the University of Toronto and the University of BritishColumbia (UBC).A balloon launch presents certain technical challenges of its own. The goal wasto get BLAST into the upper stratosphere, above atmospheric interference, andkeep it there as long as possible. Because atmospheric pressure drops withaltitude, gases in the balloon expand as it rises. If you entirely fill the balloon atground level, the expanding gases could burst it as it rises, so these balloons arelaunched only about one half of one percent full. “At 38 kilometres altitude, it’scompletely full,” Netterfield said.However, the volume of gases in the balloon is also affected by temperature;come sunset and cooling temperatures, the volume would shrink and the balloonwould drop. If it dropped low enough, this would create several problems thatwould interfere with the telescope’s ability to collect the desired data. “If you wantto get these really long flights, you’d have a hard time doing it without constantsunlight on the balloon,” Netterfield said.An elegant solution to this problem was developed in the late 1980s by NASA’sColumbia Scientific Balloon Facility. It involves launching a giant balloon near the44
poles during periods when it would experience 24-hour sunlight. This is whyBLAST was launched from McMurdo in December 2006. In June 2005, aprevious five-day BLAST mission was launched over the Arctic from Sweden forthe same reason.BLAST’s primary goal was to study starburst galaxies, where star formationoccurs at a dramatic pace. These galaxies are important in understanding thestructure and evolution of the universe. To find them, BLAST must observe atsub-millimetre wavelengths. Located between the infrared and microwaveregions of the electromagnetic spectrum, these wavelengths provide a windowthrough clouds of dust that hide the star-forming areas of galaxies from othertypes of telescopes, such as optical telescopes that observe wavelengths in thevisible range.Netterfield said that galaxies are filled with dust. “The stars are producing carbonfrom hydrogen and helium and just spewing it out.” This dust plays an essentialrole in further star formation, he noted. In order for a star to form, a cloud of gasmust collapse under its own gravity so it becomes dense enough to start nuclearfusion, the stellar power source. This will not happen unless the gas cools down.“A really excellent way to cool the gas is to have it mixed with dust,” saidNetterfield. Dust radiates heat away, cooling both itself and the gas it lives in,enabling the gas to collapse enough to form a star. “You always find starformation buried in dust clouds.”Unfortunately, he noted, the dust “also masks everything behind it. You can’t seethrough it in visible light.” Thus, it blocks the view of conventional telescopes.BLAST, however, can pierce right through the dust and can also measure itsproperties and behaviour. Sub-millimetre telescopes can reveal what is going onby measuring the temperature of the surrounding dust cloud, which is warmed bythe process of star formation. By measuring the average temperature of the dust,scientists can estimate “the total power emitted by the new, bright, short-livedstars and therefore the rate of star formation,” Netterfield said.BLAST provides a new window on star formation “from relatively nearby stellarnurseries to the most extreme star-bursting galaxies, at ages most of the wayback to the beginning of time,” said UBC professor Douglas Scott, anothermember of the BLAST team. “This has been an extraordinary flight and the datawill be very exciting.”Another key purpose of the BLAST program is to pave the way for the EuropeanSpace Agency’s Herschel Space Observatory, a telescope scheduled for launch45
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