The NASA Interstellar Mapping and Acceleration Probe (IMAP) end-of-mission disposal maneuver will be a single impulsive burn performed to ensure that the spacecraft enters a heliocentric orbit upon passivation and that it does not interfere with future missions to the L1 point or return to the low-Earth orbit (LEO) or geosynchronous equatorial orbit (GEO) regions. These analyses comprise the IMAP mission’s initial investigation into disposal departure behavior; zero velocity curves (ZVC); effective disposal magnitudes and directions; and long-term resonances. The results provide insight into the process of designing an effective single-burn disposal maneuver for a libration point mission.

The Interstellar Mapping and Acceleration Probe is scheduled to launch in February 2025. After a 3.6 month transfer, the spacecraft will enter a Lissajous orbit about the Sun-Earth L1 libration point where it will conduct a 2-year heliophysics mission. After an overview of the IMAP trajectory and design process are presented, the effects of parking orbit coast duration and Lissajous orbit class at insertion on the required Lissajous orbit insertion (LOI) ΔV and launch vehicle separation timing are discussed. Results of higher-fidelity modeling for the LOI maneuver and also presented. Finally, LOI contingency options are presented.

MESSENGER launched on 3 August 2004, entered orbit about Mercury on 18 March 2011 (UTC), and impacted Mercury's surface on 30 April 2015. After a 6.6-year cruise phase with one flyby of Earth, two of Venus, and three of Mercury, MESSENGER spent 4.1 years in orbit about the innermost planet. Initially in a 12-h orbit, MESSENGER maintained periapsis altitudes of 200-505 km before transferring to an 8-h orbit on 20 April 2012. MESSENGER's low-altitude campaign included periapsis altitudes between 15 and 200 km. In its final 44 days, MESSENGER maintained unprecedented minimum altitudes less than 38 km above Mercury's terrain before impact.

Having completed its primary and first extended missions by mid-March 2013, the MESSENGER spacecraft in orbit about Mercury began a 2.1-year final mission extension that brought substantial opportunity for low-altitude science, along with many technical challenges successfully overcome by the flight operations and science teams. After four orbit-correction maneuvers (OCMs) between June 2014 and January 2015 targeted minimum altitudes near 25 km and 15 km, seven OCMs in March and April 2015 maintained minimum altitude between 5 km and 37 km. Engineering challenges at mission end included the efficient utilization of accessible propellant and helium gas pressurant to delay Mercury impact.

After MESSENGER's 18 March 2011 Mercury orbit insertion (MOI), the spacecraft began its year-long primary science mission. Trajectory perturbations from solar gravity, Mercury's gravity field, and solar radiation pressure shift orbit periapsis higher in altitude and Mercury latitude during the primary mission. Five orbit-correction maneuvers (OCMs) will either lower periapsis altitude or increase orbit period. After the primary mission, MESSENGER will either drift until impacting Mercury or begin an extended mission. Extended mission options require OCMs to establish and maintain a new orbit. Final results for MOI and OCM-1 indicate a successful start to the primary mission.

On 18 March 2011, the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft became the first probe to orbit Mercury. The spacecraft's 6.6-year journey to Mercury orbit included six large trajectory-correction maneuvers and six planetary flybys. These planetary gravity assists imparted the vast majority of velocity change required to transform the spacecraft trajectory from Earth orbit departure to Mercury arrival. This paper summarizes the design and performance of all planetary flybys and course-correction maneuvers through orbit insertion, as well as the results of targeting the planetary-flyby aim points using the acceleration on the spacecraft imparted by solar radiation pressure.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission is the seventh mission in NASA's Discovery Program. The spacecraft, launched from Cape Canaveral Air Force Station in August 2004, arrived in orbit about Mercury in March 2011 to begin a one-year scientific investigation. While in orbit, the spacecraft is subject to a variety of forces, including Mercury and solar gravity, solar and planetary radiation effects, and propulsive events associated with orbit correction and momentum desaturation. This paper describes the challenges for navigation in terms of achieving the highest accuracy possible for relevant force models to support orbit determination and reconstruction over the Mercury orbital phase of the MESSENGER mission.

While the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft is in orbit about Mercury, the navigation team will refine a spherical-harmonic gravity-field model that requires accurate estimation of all perturbing accelerations, including those induced by Mercury's surface albedo and infrared radiation. The incident flux on each spacecraft surface is estimated and converted into perturbing accelerations, which are then incorporated into a propagation model within the Satellite Tool Kit Astrogator module. This paper outlines the calculation and predicted effects of these perturbing accelerations on the MESSENGER spacecraft throughout the mission's orbital phase.