Tomas J. Martin-Mur

Telecommunications relay support of the Mars Phoenix Lander mission

The Phoenix Lander, first of NASAs Mars Scout missions, arrived at the Red Planet on May 25, 2008. From the moment the lander separated from its interplanetary cruise stage shortly before entry, the spacecraft could no longer communicate directly with Earth, and was instead entirely dependent on UHF relay communications via an international network of orbiting Mars spacecraft, including NASAs 2001 Mars Odyssey (ODY) and Mars Reconnaissance Orbiter (MRO) spacecraft, as well as ESAs Mars Express (MEX) spacecraft. All three orbiters captured critical event telemetry and/or tracking data during Phoenix entry, descent and landing. During the Phoenix surface mission, ODY and MRO provided command and telemetry services, far surpassing the original data return requirements. The availability of MEX as a backup relay asset enhanced the robustness of the overall relay plan. In addition to telecommunications services, Doppler tracking observables acquired on the UHF link yielded a highly accurate position for the Phoenix landing site.12

Orbit Determination for the 2007 Mars Phoenix Lander

The Phoenix mission is designed to study the arctic region of Mars. To achieve this goal, the spacecraft must be delivered to a narrow corridor at the top of the Martian atmosphere, which is approximately 20 km wide. This paper will discuss the details of the Phoenix orbit determination process and the effort to reduce errors below the level necessary to achieve successful atmospheric entry at Mars. Emphasis will be placed on properly modeling forces that perturb the spacecraft trajectory and the errors and uncertainties associated with those forces. Orbit determination covariance analysis strongly influenced mission operations scenarios, which were chosen to minimize errors and associated uncertainties.

Preliminary Maneuver Analysis for the Europa Clipper Multiple-Flyby Mission

A multiple-flyby mission to the Jovian moon Europa has been proposed. Currently known as the Europa Clipper, the primary objective of this mission would be to observe the science-rich environment of Europa. After a launch in 2021 and a 6.5-year cruise, the Europa Clipper spacecraft would orbit Jupiter’s system for a 3.5-year tour. During the Europa Clipper tour, propulsive maneuvers would be necessary to correct the spacecraft’s trajectory due to flyby dispersions. Maneuvers would be accomplished through the use of two independent propulsion systems. The bi-propellant main engine assembly performs large maneuvers, while the reaction control system thrusters handle small trajectory corrections. This paper presents the feasibility of the proposed tour by producing statistical ∆V results given by the reference trajectory and orbit determination covariance analysis. Preliminary results show that the tour’s statistical ∆V average would be approximately 4 m/s per flyby. This result is comparable to the Cassini Mission at Saturn statistical predictions prior to Saturn Orbit Insertion. However, the number of maneuvers within the typical petal orbit petal duration (i.e. approximately 14 days between Europa flybys) could present challenges to the operational schedule, including the placement of contingency maneuver opportunities. This paper describes the navigation-sensitive portions of the trajectory and offers recommendations to improve robustness.