Like a trusty watch counting up the minutes, the Landsat 5 satellite keeps on ticking, orbit after orbit around Earth. Still observing the Earth after 25 years — 22 beyond its three-year primary mission lifetime — Landsat 5 collects valuable scientific data daily. Some attribute the satellite’s longevity to over-engineering. Others say it’s a long run of good luck. Whatever the reason, no one who attended the satellite’s March 1984 launch could have expected it would still be working today.