Jason Keim

Flight-Like Ground Demonstrations of Precision Maneuvers for Spacecraft Formations—Part II

Formations of collaborating spacecraft enable orders-of-magnitude increases in Earth and space science. However, to realize robust, high-performance formations, the complex interactions of distributed guidance, estimation, control, sensing, actuation, and inter-spacecraft communication must be addressed. As in any technology development, such interactions are first dealt with through analysis and simulation. Then system-level, hardware-based demonstrations are needed to validate simulations and provide the technological maturity necessary to proceed with flight demonstrations and, eventually, a mission. This paper and its companion describe such a maturation process and system-level hardware demonstration results for the formation flying control system of NASAs Terrestrial Planet Finder Interferometer (TPF-I). In this paper, first technology and testbed needs are discussed for system-level validation of precision formation control systems. Then the Formation Control Testbed (FCT) is described in detail. The FCT is a ground-based, robotic environment for high-fidelity, six degree-of-freedom validation with flight-like hardware. Finally, the formation control architecture and synchronized rotation guidance algorithm used in the precision formation flying demonstrations are presented. The companion paper gives all the experimental results, traces the ground performance demonstrated to TPF-I flight performance through a simulation-based error budget, and highlights some technology areas for further development.

Field test implementation to evaluate a flash LIDAR as a primary sensor for safe lunar landing

From May 2 through May 7 of 2008, the Autonomous Landing and Hazard Avoidance Technology (ALHAT) Exploration Technology Development Program carried out a helicopter field test to assess the use of a flash LIDAR as a primary sensor during lunar landing. The field test data has been used to evaluate the performance of the LIDAR system and of algorithms for LIDAR Hazard Detection and Avoidance, Hazard Relative Navigation, and Passive Optical Terrain Relative Navigation. Reported here is a comprehensive description of the field test hardware, ground infrastructure and trajectory reconstruction methodologies1,2.

Guaranteed initialization of distributed spacecraft formations

In this paper we present a solution to the formation initialization (FI) problem for N distributed spacecraft located in deep space. Our solution to the FI problem is based on a three-stage sky search procedure that reduces the FI problem for N spacecraft to the simpler problem of initializing a set of sub-formations. An analytical proof demonstrating that our algorithm guarantees formation initialization for N spacecraft constrained to a single plane is presented. An upper bound on the time to initialize a planar formation is also provided. We then demonstrate our FI algorithm in simulation using NASA’s v e-spacecraft Terrestrial Planet Finder mission as an example.

Analysis of flash lidar field test data for safe lunar landing

In May 2008, the Autonomous Landing and Hazard Avoidance Technology (ALHAT) Project conducted a helicopter field test of a commercial flash lidar to assess its applicability to safe lunar landing. The helicopter flew several flights, which covered a variety of slant ranges and viewing angles, over man-made and natural lunar-like terrains. The collected data were analyzed to assess the performance of the sensor and the performance of two algorithms: Hazard Detection (HD) and Hazard Relative Navigation (HRN). The collected flash lidar data were also used to validate a high fidelity flash lidar software model used in ALHAT Monte Carlo simulations. The field test results, combined with prior simulation results, advanced the technology readiness level of the HD algorithm to TRL 5 and the HRN algorithm to TRL 4.12

Spacecraft inertia estimation via constrained least squares

This paper presents a new formulation for spacecraft inertia estimation from flight data. Specifically, the inertia estimation problem is formulated as a constrained least squares minimization problem with explicit bounds on the inertia matrix incorporated as LMIs (linear matrix inequalities). The resulting minimization problem is a semidefinite optimization problem that can be solved efficiently with guaranteed convergence to the global optimum by readily available algorithms. This method is applied to test data collected from a robotic testbed consisting of a free rotating body. The results show that the constrained least squares approach produces more accurate estimates of the inertia matrix than standard unconstrained least squares estimation methods

Test implementation to evaluate technologies for safe lunar landing

From June 20 through July 7 of 2009, the Autonomous Landing and Hazard Avoidance Technology (ALHAT) Exploration Technology Development Program carried out an aircraft field test over Moon like terrains to assess the use of sensors and algorithms being developed for autonomous, safe lunar landing. The field test data has been used to evaluate the performance of a lidar, a passive optical camera system, and associated algorithms for Terrain Relative Navigation. Reported here is a comprehensive description of the field test hardware, ground infrastructure and trajectory reconstruction methodologies1,2.

Modeling and Testing of Phase Transition-Based Deployable Systems for Small Body Sample Capture

This paper summarizes the modeling, simulation, and testing work related to the development of technology to investigate the potential that shape memory actuation has to provide mechanically simple and affordable solutions for delivering assets to a surface and for sample capture and return. We investigate the structural dynamics and controllability aspects of an adaptive beam carrying an end-effector which, by changing equilibrium phases is able to actively decouple the end-effector dynamics from the spacecraft dynamics during the surface contact phase. Asset delivery and sample capture and return are at the heart of several emerging potential missions to small bodies, such as asteroids and comets, and to the surface of large bodies, such as Titan.

Design, Modeling and Control of an Optical Pointing Sensor for the Formation Control Testbed (FCT)

In this paper the design and modeling of a sensor system that gives relative position measurements is described. The position is provided in the form of bearing and range to a retro target placed on a far field target.