This edited description of Lee Scoresby’s balloon from my Definitive Guide draws on both The Golden Compass/Northern Lights and The Subtle Knife. Most relevant chapters are 10-11, 13-15, and 17-22 in the first volume.
Ropes criss-cross the balloon and are secured to an iron ring protected by a sheath of leather; this is the balloon’s suspension ring. On the leather rimmed basket edge, there’s an instrumentation panel with a compass and altimeter. The basket is level with Lyra’s chin. Lee Scoresby carries oxygen tanks and piles of furs to offer some protection from the extreme cold of open-air Arctic flying, sometimes using canvas as a bivouac.
He also travels with a back-up, smaller balloon for emergencies or flying without passengers, for example, surveying for the gyptians as they approach Bolvangar.
Scoresby’s main balloon can handle the weight of himself, two children, and an armored bear.
Lee’s is a hydrogen balloon. He can tell from above if the ground looks promising for refueling. Ground-gas vents near mines are most efficient sources, or he can make the gas from rock-oil or coal. In a pinch, he can pour sulphuric acid over iron filings. At Bolvangar, he helps himself to some from Mrs. Coulter’s zeppelin’s gasbags.
Lee controls buoyancy by a spring-levered gas-valve attached to a rope, which can be looped around a cleat in the suspension ring in order to keep the valve open. He can slowly open sandbags that have been used as ballast around the balloon’s basket to ascend more rapidly. To descend, he can gradually release gas. For a quick landing, as in Bolvangar, he can use a rope to open a flap on the top of the balloon.
One problem is the wind can make a partially deflated balloon into a sail. In an emergency, the aëronaut can use a grapnel, like an anchor, to snag onto a treetop from which he can assess his best next move.
Once landed, the balloonist needs a new source of fuel to get going again.
Weather conditions are the greatest concern. Lightning can cause explosions, and fog makes navigation nearly impossible. Speed and direction depend on prevailing winds. Scoresby was lucky to have Serafina Pekkala’s witch clan drag his balloon against prevailing winds as he approaches Svalbard.
Featured image is Lunar halo and luminescent cross observed during the balloon Zénith’s long distance flight from Paris to Arcachon in March, 1875. https://www.loc.gov/pictures/item/2002716357/. Many balloon pictures are part of the Library of Congress’s Tissandier Collection. http://www.loc.gov/pictures/search/?q=Tissandier%20collection.