In some ways, the last place you’d want to put the James Webb Space Telescope is, well, in space. If you owned a $10 billion car, you wouldn’t leave it out in a hail storm, and while there’s no hail in space, there are plenty of micrometeoroids—high speed debris no bigger than a dust grain but moving so fast they can pack a true destructive wallop. Every day, millions of such fragments rain down on Earth, but they incinerate in the atmosphere long before they reach the ground. The Webb, parked in a spot in space 1.6 million km (1 million mi.) from Earth, has no such protection. And as NASA and others have reported in the past week, its mirror—the heart of the space telescope—has already been dinged five times by tiny space flecks, the most recent of which has done real, but correctable, damage.
The Webb’s mirror is an exquisite piece of engineering. Measuring 6.5 m (21 ft., 4 in.) across, it’s made up of 18 hexagonal segments, each of which can be moved along seven different axes to allow controllers to focus the overall instrument. Together, the segments, made of beryllium, have an area of 25 sq. meters (269 sq. ft.). All of them are covered with reflective gold, but in a film so thin that if it were peeled off and tamped down into a sphere, it would measure no bigger than a golf ball. Meanwhile, the beryllium is so smoothly polished that if it were expanded to the size of the United States, its biggest imperfection would be 7.6 cm (3 in.). That’s a heck of a piece of hardware to leave exposed to the space elements. But if you’re going to do your work where Webb does, it’s a risk …read more
Source:: Time – Science