Another View on U.S. Treasury Term Premiums

The consensus suggests that subdued nominal U.S. Treasury yields on balance since the onset of the global financial crisis primarily reflect exceptionally low, if not occasionally negative, term premiums as opposed to low anticipated short rates. Depressed term premiums plausibly owe to unconventional Federal Reserve policy as well as to net flight-to-quality flows after 2007. However, two strands of evidence raise questions about this story. First, a purely survey-based expected forward term premium measure, as opposed to an approximate spot estimate, has increased rather than decreased in recent years. Second, with respect to the time-series dynamics of factors underlying affine term structure models, simple econometrics of recent data produce not only a more persistent level of the term structure but also a depressed long-run mean, which in turn implies an implausibly low expected short rate path. Strong caveats aside, an implication for central bankers is that unconventional monetary policy measures may have worked in more conventional ways, and an inference for investors is that longer-dated yields embed meaningful compensation for bearing duration risk

Calculation of Operations Efficiency Factors for Mars Surface Missions

The duration of a mission--and subsequently, the minimum spacecraft lifetime--is a key component in designing the capabilities of a spacecraft during mission formulation. However, determining the duration is not simply a function of how long it will take the spacecraft to execute the activities needed to achieve mission objectives. Instead, the effects of the interaction between the spacecraft and ground operators must also be taken into account. This paper describes a method, using "operations efficiency factors", to account for these effects for Mars surface missions. Typically, this level of analysis has not been performed until much later in the mission development cycle, and has not been able to influence mission or spacecraft design. Further, the notion of moving to sustainable operations during Prime Mission--and the effect that change would have on operations productivity and mission objective choices--has not been encountered until the most recent rover missions (MSL, the (now-cancelled) joint NASA-ESA 2018 Mars rover, and the proposed rover for Mars 2020). Since MSL had a single control center and sun-synchronous relay assets (like MER), estimates of productivity derived from MER prime and extended missions were used. However, Mars 2018's anticipated complexity (there would have been control centers in California and Italy, and a non-sun-synchronous relay asset) required the development of an explicit model of operations efficiency that could handle these complexities. In the case of the proposed Mars 2018 mission, the model was employed to assess the mission return of competing operations concepts, and as an input to component lifetime requirements. In this paper we provide examples of how to calculate the operations efficiency factor for a given operational configuration, and how to apply the factors to surface mission scenarios. This model can be applied to future missions to enable early effective trades between operations design, science mission planning, and spacecraft design

Theory and experiments in autonomous sensor-based motion planning with applications for flight planetary microrovers

With the success of Mars Pathfinder's Sojourner rover, a new era of planetary exploration has opened, with demand for highly capable mobile robots. These robots must be able to traverse long distances over rough, unknown terrain autonomously, under severe resource constraints. Much prior work in mobile robot path planning has been based on assumptions that are not truly applicable to navigation through planetary terrains. Based on the author's firsthand experience with the Mars Pathfinder mission, this work reviews issues which are critical for successful autonomous navigation of planetary rovers. No current methodology addresses all of these constraints. We next develop the sensor-based "Wedgebug" motion- planning algorithm. This algorithm is complete, correct, requires minimal memory for storage of its world model, and uses only on-board sensors, which are guided by the algorithm to efficiently sense only the data needed for motion planning, while avoiding unnecessary robot motion. The planner has the additional advantage of producing locally-optimal paths, and is suitable for robots with a field-of-view limited in both downrange and angular scope, for a variety of applications including planetary navigation. This work includes the proof of completeness and correctness of the Wedgebug algorithm, and in particular provides a corrected, detailed proof of a key result required for the proof of completeness of the Wedgebug algorithm (and for the TangentBug algorithm which inspired this approach). In addition, we extend this result to a broader class of environments. The implementation of a version of Wedgebug, called "RoverBug," on the Rocky7 Mars Rover prototype at the Jet Propulsion Laboratory (JPL) is described, and experimental results from operation in simulated martian terrain are presented

From Prime to Extended Mission: Evolution of the MER Tactical Uplink Process

To support a 90-day surface mission for two robotic rovers, the Mars Exploration Rover mission designed and implemented an intensive tactical operations process, enabling daily commanding of each rover. Using a combination of new processes, custom software tools, a Mars-time staffing schedule, and seven-day-a-week operations, the MER team was able to compress the traditional weeks-long command-turnaround for a deep space robotic mission to about 18 hours. However, the pace of this process was never intended to be continued indefinitely. Even before the end of the three-month prime mission, MER operations began evolving towards greater sustainability. A combination of continued software tool development, increasing team experience, and availability of reusable sequences first reduced the mean process duration to approximately 11 hours. The number of workshifts required to perform the process dropped, and the team returned to a modified 'Earth-time' schedule. Additional process and tool adaptation eventually provided the option of planning multiple Martian days of activity within a single workshift, making 5-day-a-week operations possible. The vast majority of the science team returned to their home institutions, continuing to participate fully in the tactical operations process remotely. MER has continued to operate for over two Earth-years as many of its key personnel have moved on to other projects, the operations team and budget have shrunk, and the rovers have begun to exhibit symptoms of aging

Evolution of the Scope and Capabilities of Uplink Support Software for Mars Surface Operations

In January of 2004 both of the Mars Exploration Rover spacecraft landed safely, initiating daily surface operations at the Jet Propulsion Laboratory for what was anticipated to be approximately three months of mobile exploration. The longevity of this mission, still ongoing after ten years, has provided not only a tremendous return of scientific data but also the opportunity to refine and improve the methodology by which robotic Mars surface missions are commanded. Since the landing of the Mars Science Laboratory spacecraft in August of 2012, this methodology has been successfully applied to operate a Martian rover which is both similar to, and quite different from, its predecessors. For MER and MSL, daily uplink operations can be most broadly viewed as converting the combined interests of both the science and engineering teams into a spacecraft-safe set of transmittable command files. In order to accomplish these ends a discrete set of mission-critical software tools were developed which not only allowed for conformation to established JPL standards and practices but also enabled innovative technologies specific to each mission. Although these primary programs provided the requisite capabilities for meeting the high-level goals of each distinct phase of the uplink process, there was little in the way of secondary software to support the smooth flow of data from one phase to the next. In order to address this shortcoming a suite of small software tools was developed to aid in phase transitions, as well as to automate some of the more laborious and error-prone aspects of uplink operations. This paper describes the evolution of this software suite, from its initial attempts to merely shorten the duration of the operator's shift, to its current role as an indispensable tool enforcing workflow of the uplink operations process and agilely responding to the new and unexpected challenges of missions which can, and have, lasted many years longer than originally anticipated

An autonomous path planner implemented on the rocky7 prototype microrover

Much prior work in mobile robot path planning har been based on assumptions that are not really applicable for exploration of planetary terrains. Based on the first author’s experience with the recent Mars Pathfinder mission, this paper reviews the issues that are critical for successful autonomous navigation of planetary rovers. No currently proposed methodology accurately addresses ali of these issues. We next report on an extension of the recently proposed “Tangent Bug ” algorithm. The implementation of this extended algorithm on the Rocky 7 Mars Rover prototype at the Jet Propulsion Laboratory is described, and experimental results are presented. In addition, experience with the limitations encountered by the Sojourner rover in actual Marh’an terrain suggest that terrain traversability must be more accurately handled in autonomous planning algorithms for interplanetary rovers. 1

A Retrospective Snapshot of the Planning Processes in MER Operations After 5 Years

No abstract availabl