This paper presents the initial results of lander and rover localization and topographic mapping of the MER 2003 mission (by Sol 225 for Spirit and Sol 206 for Opportunity). The Spirit rover has traversed a distance of 3.2 km (actual distance traveled instead of odometry) and Opportunity at 1.2 km. We localized the landers in the Gusev Crater and on the Meridiani Planum using two-way Doppler radio positioning technology and cartographic triangulations through landmarks visible in both orbital and ground images. Additional high-resolution orbital images were taken to verify the determined lander positions. Visual odometry and bundleadjustment technologies were applied to overcome wheel slippages, azimuthal angle drift and other navigation errors (as large as 21 percent). We generated timely topographic products including 68 orthophoto maps and 3D Digital Terrain Models, eight horizontal rover traverse maps, vertical traverse profiles up to Sol 214 for Spirit and Sol 62 for

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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 exploration 1 and the Global Positioning System (GPS) 2 and as scientific tools for addressing questions in fundamental physics 3,4,5,6 . 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 operation 7 . The invention of methods to electromagnetically trap and cool ions has revolutionized atomic clock performance 8,9,10,11,12,13 . Terrestrial trapped ion clocks have achieved orders of magnitude improvements in performance over their predecessors and have become a key component in national metrology laboratories 13 . 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 magnitude 14,15,16 . 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 possible 17 .

Prior results have developed a methodology for selecting a long-lived constellation of three satellites that provide persistent, stable coverage to either the North or South Pole with no requirement for stationkeeping under the influence of only gravitational perturbations. In the present study, the sensitivity of this coverage in the presence of nongravitational forces is determined, and a design strategy is formulated that minimizes any potential sensitivity to these accelerations. The class of orbits and methods are extended to the search for global coverage constellations of six satellites. Two constellations are designed that provide 99.999% global coverage for a ten-year period also without the need for any deterministic orbit maintenance.

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