The James Webb Space Telescope is often described by what it can see: galaxies forming near the dawn of time, planets around other stars, dust clouds where stars are being born. But the more astonishing part may be how little room there was for error before any of that science could begin.<\/p>\n
Webb had to leave Earth folded inside a rocket, unfold itself in space, fly to a gravitational parking region roughly a million miles away and then operate on about the electrical power of a small kitchen appliance. NASA\u2019s own fact sheet puts Webb in orbit around the Sun-Earth L2 point, 1.5 million kilometres from Earth<\/a>. That is far beyond the kind of astronaut servicing mission that rescued Hubble.<\/p>\n The other number is even more unsettling. Northrop Grumman, Webb\u2019s industry team leader, says the finished observatory carried 344 single-point failures<\/a>, including 295 associated with deployable systems. A single-point failure is a part, action or mechanism whose failure could not simply be worked around. If it did not do its job, the mission could be diminished, crippled or lost.<\/p>\n That is why Webb\u2019s first weeks in space became one of the most watched engineering sequences NASA has ever flown. Before the telescope could become an observatory, it had to become itself.<\/p>\n Webb was too large to launch open<\/p>\n Webb\u2019s scientific power comes from scale and cold. Its primary mirror is 6.5 metres wide, made of 18 gold-coated beryllium segments. Its five-layer sunshield is roughly the size of a tennis court. The cold side of the observatory has to stay extremely cold so its infrared instruments can detect faint heat from distant objects rather than the telescope\u2019s own warmth.<\/p>\n None of that fit inside a rocket in one open piece. NASA\u2019s deployment page says Webb\u2019s operational configuration is about 70 feet long, 47 feet wide and 28 feet tall, far too large for any available launch fairing. It therefore had to be folded compactly inside the Ariane 5 rocket and then unfurled, extended and expanded after launch<\/a>.<\/p>\n The basic idea sounds elegant. The execution was unforgiving. NASA says the deployment process included more than 50 major deployment steps and 178 release mechanisms that all had to work properly. The sunshield alone required membranes, cables, pulleys, motor-driven systems, booms, release devices and tensioning steps to behave in the right order.<\/p>\n On Earth, a jammed mechanism can sometimes be reached by a technician. At L2, it cannot. Webb\u2019s deployment therefore had to be tested, rehearsed and analysed before launch with a level of obsession that matched the risk. Engineers had to know not only how each part worked, but how it behaved after vibration, cold, folding, storage, launch loads and the transition to vacuum.<\/p>\n The 344 number came from real hardware<\/p>\n NASA often described Webb before launch as having \u201cover 300\u201d single-point-failure items. Northrop Grumman later gave the more precise figure of 344. The company\u2019s account says 295 of them were tied to deployable systems, many in the sunshield. Its description of Webb\u2019s testing effort says there were more than 344 possible single points of failure<\/a> in the system.<\/p>\n Those were not abstract spreadsheet anxieties. A membrane release device that failed to release could leave part of the sunshield trapped. A pulley or cable problem could keep a layer from reaching the right shape. A mirror wing that failed to latch could prevent the optical system from becoming a stable telescope. A secondary mirror support structure that did not deploy would leave the primary mirror with nowhere useful to send light.<\/p>\n The phrase \u201csingle point of failure\u201d can make the mission sound reckless, but the opposite is closer to the truth. Webb had single points of failure because it was trying to do something that could not be made simple: launch a giant cryogenic infrared telescope compactly, then deploy it remotely. Engineers spent years reducing risk where possible and proving the remaining risk could be survived.<\/p>\n Northrop\u2019s account of the sunshield notes that 107 membrane release devices were themselves single-point failures. That is a breathtaking sentence because the sunshield was not decorative. It was the thermal foundation of the mission. Without its five layers properly deployed and separated, Webb\u2019s instruments would not have reached the cold conditions required for infrared astronomy.<\/p>\n One kilowatt for a flagship observatory<\/p>\n Webb\u2019s power figure is the part that feels least intuitive. NASA described the telescope\u2019s solar array as its \u201cpowerhouse,\u201d but the total operational demand is small by household standards. NASA wrote in 2020 that one kilowatt is enough to power the largest and most technically advanced telescope ever built, and that Webb would use only 1 kilowatt of power<\/a> while its solar array could generate nearly twice that amount.<\/p>\n