Atomic clocks, which lock the frequency of an oscillator to the extremely stable quantized energy levels of atoms, are essential for navigation applications such as deep space exploration1 and the Global Positioning System (GPS)2 and as scientific tools for addressing questions in fundamental physics3,4,5,6. Atomic clocks that can be launched into space are an enabling technology for GPS, but to date have not been applied to deep space navigation and have seen only limited application to scientific questions due to performance constraints imposed by the rigors of space launch and operation7. The invention of methods to electromagnetically trap and cool ions has revolutionized atomic clock performance8,9,10,11,12,13. Terrestrial trapped ion clocks have achieved orders of magnitude improvements in performance over their predecessors and have become a key component in national metrology laboratories13. However, transporting this new technology into space has remained elusive. Here we show the results from the first-ever trapped ion atomic clock to operate in space. Launched in 2019, NASA’s Deep Space Atomic Clock (DSAC) has operated for more than 12 months, demonstrating a short-term fractional frequency stability of between 1 and 2 x 10-13 at 1 second of averaging time (measured on the ground), a long-term stability of 3 x 10-15 at 23 days, and an estimated drift of 3.0(0.7) x 10-16 per day. Each of these exceeds current space clock performance by as much as an order of magnitude14,15,16. We found the DSAC clock to be particularly amenable to the space environment, having low sensitivities to variations in radiation, temperature, and magnetic fields, and we were able to characterize these in detail. This level of space clock performance will enable new types of space navigation. In particular, the DSAC mission has demonstrated a process called one-way navigation whereby signal delay times are measured in-situ making near-real-time deep space probe navigation possible17.