Brent Buffington

EUROPA multiple-flyby trajectory design

As reinforced by the 2011 NRC Decadal Survey, Europa remains one of the most scientifically intriguing targets in planetary science due to its potential suitability for life. However, based on JEO cost estimates and current budgetary constraints, the Decadal Survey recommended-and later directed by NASA Headquarters-a more affordable pathway to Europa exploration be derived. In response, a flyby-only proof-of-concept trajectory has been developed to investigate Europa. The trajectory, enabled by employing a novel combination of new mission design techniques, successfully fulfills a set of Science Definition Team derived scientific objectives carried out by a notional payload including ice penetrating radar, topographic imaging, and short wavelength infrared observations, and ion neutral mass spectrometry in-situ measurements. The current baseline trajectory, referred to as 11-F5, consists of 34 Europa and 9 Ganymede flybys executed over the course of 2.4 years, reached a maximum inclination of 15 degrees, has a deterministic delta v of 157 m/s (post-PJR), and has a total ionizing dose of 2.06 Mrad (Si behind 100 mil Al, spherical shell). The 11-F5 trajectory and more generally speaking, flyby-only trajectories-exhibit a number of potential advantages over an Europa orbiter mission.

The Cassini Extended Mission

Based on the overwhelming success of the Cassini/Huygens 4-year tour of Saturn from July 2004 to June 2008, NASA Headquarters approved at least two years of extended mission for continued study of the target-rich Saturnian system. After a rigorous phase of science objective definition and trajectory design and analysis, the Cassini project initiated an efficient, scientifically intense and operationally challenging mission phase, including 60 orbits around Saturn, 26 close Titan flybys, and 10 close icy satellite flybys — including seven more flybys of Enceladus. At the conclusion of the 2-year extended mission, substantial operating margins should be present with some fascinating options for further extensions

Europa mission update: Beyond payload selection

Europa, the fourth largest moon of Jupiter, is believed to be one of the best places in the solar system to look for extant life beyond Earth. The 2011 Planetary Decadal Survey, Vision and Voyages, states: “Because of this oceans potential suitability for life, Europa is one of the most important targets in all of planetary science.” Exploring Europa to investigate its habitability is the goal of the planned Europa Mission. This exploration is intimately tied to understanding the three “ingredients” for life: liquid water, chemistry, and energy. The Europa Mission would investigate these ingredients by comprehensively exploring Europas ice shell and liquid ocean interface, surface geology and surface composition to glean insight into the inner workings of this fascinating moon. In addition, a lander mission is seen as a possible future step, but current data about the Jovian radiation environment and about potential landing site hazards and potential safe landing zones is insufficient. Therefore an additional goal of the mission would be to characterize the radiation environment near Europa and investigate scientifically compelling sites for hazards, to inform a potential future landed mission. The Europa Mission envisions sending a flight system, consisting of a spacecraft equipped with a payload of NASA-selected scientific instruments, to execute numerous flybys of Europa while in Jupiter orbit. A key challenge is that the flight system must survive and operate in the intense Jovian radiation environment, which is especially harsh at Europa. The innovative design of this multiple-flyby tour is an enabling feature of this mission: by minimizing the time spent in the radiation environment the spacecraft complexity and cost has been significantly reduced compared to previous mission concepts. The spacecraft would launch from Kennedy Space Center (KSC), Cape Canaveral, Florida, USA, on a NASA supplied launch vehicle, no earlier than 2022. The formulation and implementation of the proposed mission is led by a joint Jet Propulsion Laboratory (JPL) and Applied Physics Laboratory (APL) Project team. In June 2015, NASA announced the selection of a highly capable suite of 10 scientific investigations to be flown on the Europa Mission. Since the announcement, the Europa Mission Team has updated the spacecraft design in order to fully accommodate this instrument suite — a significant challenge. After completing a successful System Requirements Review and Mission Definition Review in January of 2017, the project is currently transitioning from the concept development phase to the preliminary design phase of the mission. This paper will describe the progress of the Europa Mission since 2015, including maturation of the spacecraft design, requirements, system analyses, and mission trajectories.

Dual Satellite-Aided Planetary Capture with Interplanetary Trajectory Constraints

The system entry problem entails the capture of a spacecraft about a planet by way of propulsive maneuver(s) or flyby(s) of a planetary satellite(s), or both. In the case of the Jovian system, a balance is sought between the interplanetary time-of-flight, orbit insertion maneuver magnitude, mass delivered to the system, capture orbit period, radiation dose, and mission complexity. Based on a nominal asymptote, this paper introduces the analytical equations necessary to solve the phase-free, singly aided and doubly aided capture problems, with a focus on the doubly aided capture problem in the Jovian system. An analytical approximation for the required phasing is derived and the implications of the Laplace resonance are discussed. Analytical approximations are used to seamlessly seed a multiple-shooting algorithm in order to arrive at the converged high-fidelity solution space for the Europa Mission.

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.