An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69's origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.

The Canadian Space Agency (CSA) has contributed to the Origins Spectral Interpretation Resource Identification Security-Regolith Explorer (OSIRIS-REx) spacecraft the OSIRIS-REx Laser Altimeter (OLA). The OSIRIS-REx mission will sample asteroid 101955 Bennu, the first B-type asteroid to be visited by a spacecraft. Bennu is thought to be primitive, carbonaceous, and spectrally most closely related to CI and/or CM meteorites. As a scanning laser altimeter, the OLA instrument will measure the range between the OSIRIS-REx spacecraft and the surface of Bennu to produce digital terrain maps of unprecedented spatial scales for a planetary mission. The digital terrain maps produced will measure ∼7 per pixel globally, and ∼3 per pixel at specific sample sites. In addition, OLA data will be used to constrain and refine the spacecraft trajectories. Global maps and highly accurate spacecraft trajectory estimates are critical to infer the internal structure of the asteroid. The global and regional maps also are key to gain new insights into the surface processes acting across Bennu, which inform the selection of the OSIRIS-REx sample site. These, in turn, are essential for understanding the provenance of the regolith sample collected by the OSIRIS-REx spacecraft. The OLA data also are important for quantifying any hazards near the selected OSIRIS-REx sample site and for evaluating the range of tilts at the sampling site for comparison against the capabilities of the sample acquisition device.

The New Horizons mission, the first mission in NASA's New Frontiers Program, is also the first mission with primary science objectives to explore the Pluto/Charon system. After launch in January 2006 and an interplanetary cruise of more than 9.5 years, New Horizons has completed the approach and flyby of Pluto. This paper presents an overview of the analysis and operational constraints that led to the navigation strategy used. Also presented are operational results for that strategy during this final phase of the prime mission.

The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition, its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.

The New Horizons mission to explore the Pluto/Charon system was launched on January 19, 2006 as the first mission in NASA's New Frontiers Program. The New Horizons mission is led by principal investigator, S. Alan Stem, of the Southwest Research Institute. The project is managed by and the spacecraft was built and is operated by The Johns Hopkins University Applied Physics Laboratory. Navigation for the spacecraft is provided by the Space Navigation and Flight Dynamics Practice of KinetX, Inc., a private corporation. The spacecraft will have its first planetary flyby of Jupiter and its moons on February 28, 2007, and after this the spacecraft will continue for eight-and-one-half years of interplanetary cruise to flyby the Pluto/Charon system on July 14, 2015. This paper gives a description of the navigation system developed for the New Horizons mission, and the navigation results obtained thus far for launch and early interplanetary cruise phases of the mission. Also included are results from calibrating and testing the navigation system, including attitude and small force modeling, trajectory correction maneuver design and reconstruction, and the use of DSN Delta Differential One-way Ranging (Delta-DOR).

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, led by principal investigator Sean C. Solomon of the Carnegie Institution of Washington, is the seventh mission in NASA’s Discovery Program. The spacecraft was launched from Cape Canaveral Air Force Station on August 3, 2004 to begin its six-and-one-half-year interplanetary cruise to arrive in orbit about Mercury beginning in March 2011. The cruise phase includes planetary gravity-assist flybys of Earth (in August 2005), Venus (in October 2006 and June 2007) and Mercury (in January and October 2008, and September 2009). This paper describes the navigation results for the interval from Earth flyby through Venus flyby 1, and focuses on orbit determination results, navigation analyses supporting statistical trajectory correction maneuvers, and maneuver reconstruction results for this interval. Also included are preliminary results from several tests performed for optical navigation imaging and Delta-Differential One-way Ranging (Delta-DOR) tracking data types taken on approach to Venus flyby 1.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, led by principal investigator Sean C. Solomon of the Carnegie Institution of Washington, is the seventh mission in NASA's Discovery Program. The spacecraft was launched from Cape Canaveral Air Force Station on August 3, 2004 to begin its six-and-one-half-year interplanetary cruise to arrive in orbit about Mercury beginning in March 2011. The cruise phase includes planetary gravity-assist flybys of Earth (in August 2005), Venus (in October 2006 and June 2007) and Mercury (in January and October 2008, and September 2009). This paper describes the navigation results for the interval from Earth flyby through Venus flyby 1, and focuses on orbit determination results, navigation analyses supporting statistical trajectory correction maneuvers, and maneuver reconstruction results for this interval. Also included are preliminary results from several tests performed for optical navigation imaging and Delta-Differential One-way Ranging (Delta-DOR) tracking data types taken on approach to Venus flyby 1.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission is being flown as the seventh mission in NASA’s Discovery Program. The MESSENGER mission is led by the principal investigator, Sean C. Solomon, of the Carnegie Institution of Washington. The project is managed by and the spacecraft was built and is operated by The Johns Hopkins University Applied Physics Laboratory. Navigation for the spacecraft is provided by the Space Navigation and Flight Dynamics Practice of KinetX, Inc., a private corporation. Navigation for launch and interplanetary cruise makes use of radio metric tracking data from NASA’s Deep Space Network in addition to optical navigation from on-board images of planet flybys. The spacecraft was launched August 3, 2004, to begin its six and one-half year interplanetary cruise leading to rendezvous with and orbit of the planet Mercury beginning in March 2011. Once in orbit, MESSENGER will perform detailed science observations of Mercury for at least one Earth year. This paper gives a description of the navigation system developed for the MESSENGER mission, along with the navigation results obtained thus far for launch and the early interplanetary cruise phase of the mission. Also included are plans for calibrating and testing the navigation system during the remaining years of cruise to prepare for support of the science operations in orbit about Mercury.

Radio Doppler data from the Galileo spacecraft's encounter with Amalthea, one of Jupiter's small inner moons, on 5 November 2002 yield a mass of (2.08 ± 0.15) × 10 18 kilograms. Images of Amalthea from two Voyager spacecraft in 1979 and Galileo imaging between November 1996 and June 1997 yield a volume of (2.43 ± 0.22) × 10 6 cubic kilometers. The satellite thus has a density of 857 ± 99 kilograms per cubic meter. We suggest that Amalthea is porous and composed of water ice, as well as rocky material, and thus formed in a cold region of the solar system, possibly not at its present location near Jupiter.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission is being flown as the seventh mission in NASA's Discovery Program. The MESSENGER mission is led by the principal investigator, Sean C. Solomon, of the Carnegie Institution of Washington. The project is managed by and the spacecraft was built and is operated by The Johns Hopkins University Applied Physics Laboratory. Navigation for the spacecraft is provided by the Space Navigation and Flight Dynamics Practice of KinetX, Inc., a private corporation. Navigation for launch and interplanetary cruise makes use of radio metric tracking data from NASA's Deep Space Network in addition to optical navigation from on-board images of planet flybys. The spacecraft was launched August 3, 2004, to begin its six and one-half year interplanetary cruise leading to rendezvous with and orbit of the planet Mercury beginning in March 2011. Once in orbit, MESSENGER will perform detailed science observations of Mercury for at least one Earth year. This paper gives a description of the navigation system developed for the MESSENGER mission, along with the navigation results obtained thus far for launch and the early interplanetary cruise phase of the mission. Also included are plans for calibrating and testing the navigation system during the remaining years of cruise to prepare for support of the science operations in orbit about Mercury.

ON 8 February 1992, the Ulysses spacecraft flew by Jupiter at a distance of 5.4 AU from the Sun. During the encounter, the spacecraft was deflected into a new orbit, inclined at about 80° to the ecliptic plane, which will ultimately lead Ulysses over the polar regions of the Sun1. Within 1 AU from Jupiter, the onboard dust detector2 recorded periodic bursts of submicrometre dust particles, with durations ranging from several hours to two days, and occurring at approximately monthly intervals (28 ± 3 days). These particles arrived at Ulysses in collimated streams radiating from close to the line-of-sight direction to Jupiter, suggesting a jovian origin for the periodic bursts. Ulysses also detected a flux of micrometre-sized dust particles moving in high-velocity (⩾ =26 km s-1) retrograde orbits (opposite to the motion of the planets); we identify these grains as being of interstellar origin.