Kim R. Reh

Wind-Based Navigation of a Hot-air Balloon on Titan: A Feasibility Study

Current analysis of data streamed back to Earth by the Cassini spacecraft features Titan as one of the most exciting places in the solar system. NASA centers and universities around the US, as well as the European Space Agency, are studying the possibility of sending, as part of the next mission to this giant moon of Saturn, a hot-air balloon (Montgolfier-type) for further and more in-depth exploration. The basic idea would be to design a reliable, semi-autonomous, and yet cheap Montgolfier capable of using continuous flow of waste heat from a power source to lift the balloon and sustain its altitude in the Titan environment. In this paper we study the problem of locally navigating a hot-air balloon in the nitrogen-based Titan atmosphere. The basic idea is to define a strategy (i.e. design of a suitable guidance system) that allows autonomous and semi-autonomous navigation of the balloon using the available (and partial) knowledge of the wind structure blowing on the saturnian satellite surface. Starting from first principles we determined the appropriate thermal and dynamical models describing (a) the vertical dynamics of the balloon and (b) the dynamics of the balloon moving on a vertical plane (2-D motion). Next, various non-linear fuzzy-based control strategies have been evaluated, analyzed and implemented in MATLAB to numerically simulate the capability of the system to simultaneously maintain altitude, as well as a scientifically desirable trajectory. We also looked at the ability of the balloon to perform station keeping. The results of the simulation are encouraging and show the effectiveness of such a system to cheaply and effectively perform semi-autonomous exploration of Titan.

Experiences in managing the Prometheus Project

Congress authorized NASAs Prometheus Project in February 2003, with the first Prometheus mission slated to explore the icy moons of Jupiter. The Project had two major objectives: (1) to develop a nuclear reactor that would provide unprecedented levels of power and show that it could be processed safely and operated reliably in space for long-duration, deep-space exploration and (2) to explore the three icy moons of Jupiter - Callisto, Ganymede, and Europa - and return science data that would meet the scientific goals as set forth in the Decadal Survey Report of the National Academy of Sciences. Early in project planning, it was determined that the development of the Prometheus nuclear powered spaceship would be complex and require the intellectual knowledge residing at numerous organizations across the country. In addition, because of the complex nature of the project and the multiple partners, approaches beyond those successfully used to manage a typical JPL project would be needed. This paper, describes the key experiences in managing Prometheus which should prove useful for future projects of similar scope and magnitude

Lunar Fission Surface Power System Design and Implementation Concept

At the request of NASA’s Exploration Systems Mission Directorate (ESMD) in May of 2005, a team was assembled within the Prometheus Project to investigate lunar surface nuclear power architectures and provide design and implementation concept inputs to NASA’s Exploration Systems Architecture 60‐day Study (ESAS) team. System engineering tasks were undertaken to investigate the design and implementation of a Fission Surface Power System (FSPS) that could be launched as early as 2019 as part of a possible initial Lunar Base architecture. As a result of this activity, the Prometheus team evaluated a number of design and implementation concepts as well as a significant number of trades associated with lunar surface power, all culminating in a recommended approach. This paper presents the results of that study, including a recommended FSPS design and implementation concept.

The "Billion Dollar Box" Study of Science Missions to Saturnian Satellites

Cassini/Huygens (C/H) mission investigations verify Saturnian satellites Titan and Enceladus as objects of intense interest to planetary scientists and astrobiologists. Recently NASA commissioned a study of potential relatively low-cost missions to these icy satellites, led by the Jet Propulsion Laboratory (JPL) with science and engineering teams from prominent universities, FFRDCs, and NASA centers. NASA was interested in determining whether there are scientifically viable missions to Titan or Enceladus within the constraints of a (possibly slightly expanded) New Frontiers mission. The C/H missions extremely capable instrumentation and thorough investigation of the Saturn system make that a difficult, though not obviously impossible, task. Any such mission must exceed C/H capabilities (in, for instance, imaging coverage or resolution, or range of constituents identifiable) to be scientifically worthwhile. Beginning in October 2006 these teams assessed science objectives for the two destinations and surveyed architectural options for implementing worthwhile subsets of the global lists of science objectives, attempting to find mission concepts both scientifically justifiable and within New Frontiers constraints. These studies were completed in early 2007 and the somewhat surprising results, that there appear to be no such missions, reported to NASA. This presentation gives the results of the studies and examines interesting individual missions.