Jeffrey A. Hoffman

Generalized Multicommodity Network Flow Model for the Earth–Moon–Mars Logistics System

Simple logistics strategies such as “carry-along” and Earth-based “resupply” were sufficient for past human space programs. Next-generation space logistics paradigms are expected to be more complex, involving multiple exploration destinations and in situ resource utilization. Optional in situ resource utilization brings additional complexity to the interplanetary supply chain network design problem. This paper presents an interdependent network flow modeling method for determining optimal logistics strategies for space exploration and its application to the human exploration of Mars. It is found that a strategy using lunar resources in the cislunar network may improve overall launch mass to low Earth orbit for recurring missions to Mars compared to NASA’s Mars Design Reference Architecture 5.0, even when including the mass of the in situ resource utilization infrastructures that need to be predeployed. Other findings suggest that chemical propulsion using liquid oxygen/liquid hydrogen, lunar in situ resou...

Ultra-low delta-v objects and the human exploration of asteroids

Abstract Missions to near-Earth objects (NEOs) are key destinations in NASAs new ‘Flexible Path’ approach. NEOs are also of interest for science, for the hazards they pose, and for their resources. We emphasize the importance of ultra-low delta-v from LEO to NEO rendezvous as a target selection criterion, as this choice can greatly increase the payload to the NEO. Few such ultra-low delta-v NEOs are currently known; only 65 of the 6699 known NEOs (March 2010) have delta-v

Expected science return of spatially-extended in-situ exploration at small Solar system bodies

The recent decadal survey report for planetary science (compiled by the National Research Council) has prioritized three main areas for planetary exploration: (1) the characterization of the early Solar system history, (2) the search for planetary habitats, and (3) an improved understanding about the nature of planetary processes. A growing number of ground and space observations suggest that small bodies are ideally suited for addressing all these three priorities. In parallel, several technological advances have been recently made for microgravity rovers, penetrators, and MEMS-based instruments. Motivated by these findings and new technologies, the objective of this paper is to study the expected science return of spatially-extended in-situ exploration at small bodies, as a function of surface covered and in the context of the key science priorities identified by the decadal survey report. Specifically, targets within the scope of our analysis belong to three main classes: main belt asteroids and irregular satellites, Near Earth Objects, and comets. For each class of targets, we identify the corresponding science objectives for potential future exploration, we discuss the types of measurements and instruments that would be required, and we discuss mission architectures (with an emphasis on spatially-extended in-situ exploration) to achieve such objectives. Then, we characterize (notionally) how the science return for two reference targets would scale with the amount (and type) of surface that is expected to be covered by a robotic mobile platform. The conclusion is that spatially-extended in-situ information about the chemical and physical heterogeneity of small bodies has the potential to lead to a much improved understanding about their origin, evolution, and astrobiological relevance.

Options in the solar system for planetary surface exploration via hopping

This paper provides an initial overview of the capabilities of hopping vehicles, and examines planetary bodies in the solar system which might be amenable to exploration via hopping. A hopping vehicle is one which uses ballistic propulsive action, rather than ground contact or action on a surrounding fluid, to propel itself1 2. The paper examines how gravity levels, atmospheric densities, and surface characteristics affect the attractiveness of a planetary body to hopping missions. An initial catalogue of planetary bodies where hopping missions could take place is provided.

Small Lunar Exploration and Delivery System Concept

This paper describes an architectural concept for a Small Lunar Exploration and Delivery System to operate as a platform for emplacing payloads into lunar orbit and onto the lunar surface, while providing mobility for surface exploration, science, and infrastructure. The concept leverages emerging services that are capable of delivering payloads to Low Earth Orbit (LEO), while utilizing new and old technologies to build a platform for transfer to Low Lunar Orbit (LLO). Advances and miniaturization in avionics, navigation, power, and propulsion systems enable a unique opportunity to develop a system that is both capable of landing on the lunar surface and providing surface mobility with the same system.

Further Development and Flight Testing of a Prototype Lunar and Planetary Surface Exploration Hopper: Update on the TALARIS Project

This paper presents an update on the Earth-based hopper prototype for autonomous planetary exploration that MIT and Draper Laboratory are developing as part of the Next Giant Leap teams efforts in the Google Lunar X-Prize. New developments and upgrades, culminating in the second-generation vehicle, are described in this paper, as well as the ongoing test program and experimental results. Recent developments include a redesign of the vehicle structure, an upgrade to the avionics system, the use of an upgraded version of the gravity-offsetting propulsion system (which uses electrically-powered ducted fans) and the incorporation of the secondary spacecraft-emulator propulsion system (which uses compressed nitrogen propellant and cold gas thrusters).

Review and Synthesis of Considerations in Architecting Heterogeneous Teams of Humans and Robots for Optimal Space Exploration

Human-robot systems will play a critical role in space exploration, should NASA embark on missions to the Moon and Mars. A unified framework to optimally leverage the capabilities of humans and robots in space exploration will be an invaluable tool for mission planning. Although there is a growing body of literature on human-robot interactions, there is not yet a framework that lends itself both to a formal representation of heterogeneous teams of humans and robots, and to an evaluation of such teams across a series of common, task-based metrics. In this paper, we review the literature, and synthesize multiple considerations for architecting heterogeneous teams of humans and robots. We discuss considerations related to formally specifying tasks and representing human--robot systems, enumerating task allocations, and evaluating human--robot systems against common, task-based metrics. Our objective is to lay the foundations of a unified framework for architecting human--robot systems for optimal task performance given a set metrics.

Internally-actuated rovers for all-access surface mobility: Theory and experimentation

The future exploration of small Solar System bodies will, in part, depend on the availability of mobility platforms capable of performing both large surface coverage and short traverses to specific locations. Weak gravitational fields, however, make the adoption of traditional mobility systems difficult. In this paper we present a planetary mobility platform (called “spacecraft/rover hybrid”) that relies on internal actuation. A hybrid is a small (~ 5 kg), multi-faceted robot enclosing three mutually orthogonal flywheels and surrounded by external spikes or contact surfaces. By accelerating/decelerating the flywheels and by exploiting the low-gravity environment, such a platform can perform both long excursions (by hopping) and short, precise traverses (through controlled “tumbles”). This concept has the potential to lead to small, quasi-expendable, yet maneuverable rovers that are robust as they have no external moving parts. In the first part of the paper we characterize the dynamics of such platforms (including fundamental limitations of performance) and we discuss control and planning algorithms. In the second part, we discuss the development of a prototype and present experimental results both in simulations and on physical test stands emulating low-gravity environments. Collectively, our results lay the foundations for the design of internally-actuated rovers with controlled mobility (as opposed to random hopping motion).

An Integrated Traverse Planner and Analysis Tool for Planetary Exploration

Future planetary explorations will require surface traverses of unprecedented frequency, length, and duration. As a result, there is need for exploration support tools to maximize productivity, scientific return, and safety. The Massachusetts Institute of Technology is currently developing such a system, called the Surface Exploration Traverse Analysis and Navigation Tool (SEXTANT). The goal of this system is twofold: to allow for realistic simulations of traverses in order to assist with hardware design, and to give astronauts an aid that will allow for more autonomy in traverse planning and re-planning. SEXTANT is a MATLAB-based tool that incorporates a lunar elevation model created from data from the Lunar Orbiter Laser Altimeter instrument aboard the Lunar Reconnaissance Orbiter spacecraft. To assist in traverse planning, SEXTANT determines the most efficient path across a planetary surface for astronauts or transportation rovers between user-specified Activity Points. The path efficiency is derived from any number of metrics: the traverse distance, traverse time, or the explorer’s energy consumption. The generated path, display of traverse obstacles, and selection of Activity Points are visualized in a 3D mapping interface. After a traverse has been planned, SEXTANT is capable of computing the most efficient path back home, or “walkback”, from any point along the traverse – an important capability for emergency operations. SEXTANT also has the ability to determine shadowed and sunlit areas along a lunar traverse. This data is used to compute the thermal load on suited astronauts and the solar power generation capacity of rovers over the entire traverse. These both relate directly to the explorer’s consumables, which place strict constraints on the traverse. This paper concludes by presenting three example traverses, detailing how SEXTANT can be used to plan and modify paths for both explorer types.

Design of Power Systems for Extensible Surface Mobility Systems on the Moon and Mars

This paper presents the power system model description and sample studies for extensible surface mobility systems on the Moon and Mars. The mathematical model of power systems for planetary vehicles was developed in order to estimate power system configuration with given mission parameters and vehicle specifications. The state-of-art power source technologies for space application were used for constructing the model; batteries, fuel cells, and photovoltaic systems were considered in this paper. The Sequential Quadratic Programming method was used to find the optimal power system configurations based on the concept of a previous MIT study. Several case studies on the Moon and Mars were carried out to show the usefulness of the model and to recommend power system configurations for 7-day off-base exploration missions on the Moon and Mars. For the lunar mission, photovoltaic and fuel cell hybrid power systems were suggested. In addition, vehicles with photovoltaic/fuel cell hybrid systems could be operated without recharging when they were driving in shadowed regions. For the Mars mission, both fuel cell single power systems and photovoltaic/fuel cell hybrid systems were acceptable for short missions of only a few days. However, if long, sustainable missions were considered, photovoltaic/fuel cell hybrid systems were required.