NASA's Swift space telescope is about to crash to Earth. Where will it fall?

NASA's Neil Gehrels Swift Observatory will reenter Earth's atmosphere in an uncontrolled descent within days after a robotic rescue mission failed to boost the telescope to a higher orbit. The roughly 3,300-pound observatory launched in November 2004 and spent two decades studying gamma-ray bursts using three instruments: a Burst Alert Telescope, an X-Ray Telescope, and an Ultraviolet/Optical Telescope. Swift's orbit had decayed to 171 miles above Earth by October 20, when NASA reported the spacecraft could no longer compensate for atmospheric drag. Swift's operations team at Pennsylvania State University sent a command ending the mission ahead of reentry.

The exact timing and location of Swift's reentry remain unclear. The observatory's orbit passes only within about 21 degrees of the equator, crossing mostly ocean but also populated regions in Africa, South and Southeast Asia, and Latin America. Most of Swift will disintegrate during reentry. Surviving pieces will likely be small, dense, and heat-resistant materials such as titanium, steel, and glass. Dean Sladen, an aerospace engineer, identified probable survivors as Swift's six reaction wheels and telescope components like lenses and mirrors. The spacecraft's roughly 52,000 lead tiles in its mask will almost certainly melt.

Darren McKnight, a senior technical fellow at LeoLabs, stated that Swift will likely disintegrate sufficiently to pose no ground casualty hazard, though internal parts of the X-ray and optical telescopes might survive. Sladen noted that most of Swift's aluminum body, wiring, and electronics melt during reentry. NASA's orbital debris requirements state the risk of human casualty from surviving debris shall not exceed one in 10,000. Sladen said the real concern is the long-term trend, as the number of uncontrolled reentries grows with more satellite launches.