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The Mars Exploration Rovers Spirit and Opportunity successfully landed respectively at Gusev Crater and Meridiani Planum in January 2004. The rovers are essentially robotic geologists, sent on a mission to search for evidence in the rocks and soil pertaining to the historical presence of water and the ability to possibly sustain life. In order to conduct NASA's "follow the water" strategy on opposite sides of the planet Mars, an interplanetary journey of over 300 million miles culminated with historic navigation precision. Rigorous trajectory targeting and control was necessary to achieve the atmospheric entry requirements for the selected landing sites. The propulsive maneuver design challenge was to meet or exceed these requirements while preserving the necessary design margin to accommodate additional project concerns. Landing site flexibility was maintained for both missions after launch, and even after the first trajectory correction maneuver for Spirit. The final targeting strategy was modified to improve delivery performance and reduce risk after revealing constraining trajectory control characteristics. Flight results are examined and summarized for the six trajectory correction maneuvers that were planned for each mission.

The MER Project will launch two spacecraft (MER-A and MER-B) to Mars in 2003 with the objective of delivering two Rovers to different landing sites on Mars to study the surface composition and to look for evidence of present or past water. This paper describes the methods used to estimate the statistical AV and propellant requirements for propulsive maneuvers necessary to deliver the two Rovers while ensuring that planetary protection requirements are satisfied. Maneuver analysis results for four different trajectories, open and close of launch periods for each of the two MER missions, are presented. The results for the two representative landing sites (MER-A: Melas Chasma, MER-B: Hematite) indicate that the MER-A Open case has the most demanding propellant requirement (-45 kg), and that the inertial atmospheric entry flight path angle delivery requirements of-1 1.550.17 (3 0) deg for MER-A and-1 1.550.20 (30) deg for MER-B are achievable.

On May 25, 2008, the Mars Phoenix Lander (PHX) successfully landed in the northern planes of Mars in order to continue and complement NASA's "follow the water" theme as its predecessor Mars missions, such as Mars Odyssey (ODY) and Mars Exploration Rovers, have done in recent years. Instruments on the lander, through a robotic arm able to deliver soil samples to the deck, will perform in-situ and remote-sensing investigations to characterize the chemistry of materials at the local surface, subsurface, and atmosphere. Lander instruments will also identify the potential history of key indicator elements of significance to the biological potential of Mars, including potential organics within any accessible water ice. Precise trajectory control and targeting were necessary in order to achieve the accurate atmospheric entry conditions required for arriving at the desired landing site. The challenge for the trajectory control maneuver design was to meet or exceed these requirements in the presence of spacecraft limitations as well as other mission constraints. This paper describes the strategies used, including the specialized targeting specifically developed for PHX, in order to design and successfully execute the propulsive maneuvers that delivered the spacecraft to its targeted landing site while satisfying the planetary protection requirements in the presence of flight system constraints.

The Mars Exploration Rover (MER) project successfully landed two identical rovers on Mars in order to remotely conduct geologic investigations, including characterization of rocks and soils that may bold clues to past water activity. Two landing sites, Gusev crater and Meridiani Planum, were selected out of nearly 200 candidate sites after balancing science returns and flight system engineering and safety. Precise trajectory targeting and control was necessary to achieve the atmospheric entry requirements for the selected landing sites within the flight system constraints. This paper discusses the expected and achieved launch vehicle performance and the impacts of that performance on the first Trajectory Correction Maneuver (TCM-1) while maintaining targeting flexibility in accommodating additional project concerns about landing site safety and possible in-flight retargeting to alternate landing sites.