PCsat Success! and follow-on payloads

by on 9 June 2015in Technology Development & Demonstration No comment

PCsat was designed and built as a student project at the US Naval Academy and launched on 29 Sept 2001 on the Kodiak Star mission as an experimental communications payload to not only introduce students to space systems engineering, but also to begin a series of experiments in low cost spacecraft telemetry system and data communications for mobile satellite users. An additional unique feature of PCsat was the integration of multiple worldwide Internet linked ground stations allowing around the world access to satellite telemetry and communications live from anywhere. PCsat was a complete success and it has been used by thousands of users in its first 9 months of flight. It has validated the viability of our using off-the-shelf AX.25 for all Telemetry Command and Control as well as supporting a bent-pipe mission. As our first satellite, we have a lot of lessons learned and experiences with spacecraft operations and many ideas for the future. This paper sumarizes the design details for PCsat and highlights of the first year in space including what we have learned and what new experiments we want to do on our nextcommunications mission.

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Planning solar array operations on the international space station

by on 9 June 2015in Technology Development & Demonstration No comment

Flight controllers manage the orientation and modes of eight large solar arrays that power the International Space Station (ISS). The task requires generating plans that balance complex constraints and preferences. These considerations include context-dependent constraints on viable solar array configurations, temporal limits on transitions between configurations, and preferences on which considerations have priority. The Solar Array Constraint Engine (SACE) treats this operations planning problem as a sequence of tractable constrained optimization problems. SACE uses constraint management and automated planning capabilities to reason about the constraints, to find optimal array configurations subject to these constraints and solution preferences, and to automatically generate solar array operations plans. SACE further provides flight controllers with real-time situational awareness and what-if analysis capabilities. SACE is built on the Extensible Universal Remote Operations Planning Architecture (EUROPA) model-based planning system. EUROPA facilitated SACE development by providing model-based planning, built-in constraint reasoning capability, and extensibility. This article formulates the planning problem, explains how EUROPA solves the problem, and provides performance statistics from several planning scenarios. SACE reduces a highly manual process that takes weeks to an automated process that takes tens of minutes.

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Middeck Active Control Experiment Reflight (MACE II) Program: Adventures in Space

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The Middeck Active Control Experiment Reflight (MACE II) Program was the first on-orbit demonstration of adaptive structural control technology and the first active science experiment flown aboard the International Space Station. Our program objectives were to (1) greatly decease the need to modeling and ground testing to develop controllers and (2) allow for autonomous configuration of the control system to changing dynamic characteristics and sensor/actuator failures. This paper discusses the development of the MACE II program, an overview of the technical success of the MACE II mission, and lessons learned from both a technical and programmatic standpoint dealing with the Space Test Program and NASA.

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http://dx.doi.org/10.2514/6.2003-6243

The JPL electronic nose: Monitoring air in the U.S. Lab on the International Space Station

by on 9 June 2015in Technology Development & Demonstration No comment

An electronic nose with a sensor array of 32 conductometric sensors has been developed at the Jet Propulsion Laboratory (JPL) to monitor breathing air in spacecraft habitat. The Third Generation ENose is designed to operate in the environment of the U.S. Lab on the International Space Station (ISS). It detects a selected group of analytes at target concentrations in the ppm regime at an environmental temperature range of 18 – 30<sup>ο</sup>C, relative humidity from 20 75% and pressure from 530 to 760 torr. The monitoring targets are anomalous events such as leaks and spills of solvents, coolants or other fluids. The JPL ENose operated as a technology demonstration for seven months in the U.S. Laboratory Destiny during 2008-2009. Analysis of ENose monitoring data shows that there was regular, periodic rise and fall of humidity and occasional releases of Freon 218 (perfluoropropane), formaldehyde, methanol and ethanol. There were also several events of unknown origin, half of them from the same source. Each event lasted from 20 to 100 minutes, consistent with the air replacement time in the U.S. Lab.

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Nonlinear Control and Synchronization of Multiple Lagrangian Systems with Application to Tethered Formation Flight Spacecraft

by on 9 June 2015in Technology Development & Demonstration No comment

This dissertation focuses on the synchronization of multiple dynamical systems using contraction theory, with applications to cooperative control of multi-agent systems and synchronization of interconnected dynamics such as tethered formation flight. Inspired by stable combinations of biological systems, contraction nonlinear stability theory provides a systematic method to reduce arbitrarily complex systems into simpler elements. One application of oscillation synchronization is a fully decentralized nonlinear control law, which eliminates the need for any inter-satellite communications. We use contraction theory to prove that a nonlinear control law stabilizing a single-tethered spacecraft can also stabilize arbitrarily large circular arrays of tethered spacecraft, as well as a threespacecraft inline configuration. The convergence result is global and exponential due to the nature of contraction analysis. The proposed decentralized control strategy is further extended to robust adaptive control in order to account for model uncertainties. Numerical simulations and experimental results validate the exponential stability of the tethered formation arrays by implementing a tracking control law derived from the reduced dynamics. This thesis also presents a new synchronization framework that can be directly applied to cooperative control of autonomous aerospace vehicles and oscillation synchronization in robotic manipulation and locomotion. We construct a dynamical network of multiple Lagrangian systems by adding diffusive couplings to otherwise freely moving or flying vehicles. The proposed tracking control law synchronizes an arbitrary number of robots into a common trajectory with global exponential convergence. The proposed control law is much simpler than earlier work in terms of both the computational load and the required signals. Furthermore, in contrast with earlier work which used simple double integrator models, the proposed method permits highly nonlinear systems and is further extended to adaptive synchronization, partial-joint coupling, and concurrent synchronization. Another contribution of the dissertation is a novel nonlinear control approach for underactuated tethered formation flight spacecraft. This is motivated by a controllability analysis that indicates that both array resizing and spin-up are fully controllable by the reaction wheels and the tether motor. This work reports the first propellant-free underactuated control results for tethered formation flight. We also fulfill the potential of the proposed strategy by providing a new momentum dumping method. This dissertation work has evolved based on the research philosophy of balancing theoretical work with practicality, aiming at physically intuitive algorithms that can be directly implemented in real systems. In order to validate the effectiveness of the decentralized control and estimation framework, a new suite of hardware has been designed and added to the SPHERES (Synchronize Position Hold Engage and Reorient Experimental Satellite) testbed. Such recent improvements described in this dissertation include a new tether reel mechanism, a force-torque sensor and an air-bearing carriage with a reaction wheel. This thesis also introduces a novel relative attitude estimator, in which a series of Kalman filters incorporate the gyro, force-torque sensor and ultrasound ranging measurements. The closed-loop control experiments can be viewed at http://ssl.mit.edu/spheres/videos.html.

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Propellant-Free Control of Spinning Tethered Formation Flight, Part 1: Linear Control and Experimentation

by on 9 June 2015in Technology Development & Demonstration No comment

We introduce a decentralized attitude control strategy that can dramatically reduce the usage of propellant, by taking full advantage of the physical coupling of the tether. Motivated by a controllability analysis, indicating that both array resizing and spin-up are fully controllable by the reaction wheels and the tether motor, we report the first propellant-free underactuated control results for tethered formation flying spacecraft. This paper also describes the hardware development and experimental validation of the proposed method using the Synchronized Position Hold, Engage, and Reorient Experimental Satellites test bed. In particular, a new relative sensing mechanism that uses six-degree-of-freedom force-torque sensors and rate gyroscopes is introduced and validated in the closed-loop control experiments.

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On-Orbit Measurements of the ISS Atmosphere by the Vehicle Cabin Atmosphere Monitor

by on 9 June 2015in Technology Development & Demonstration No comment

We report on trace gas and major atmospheric constituents results obtained by the Vehicle Cabin Atmosphere Monitor (VCAM) during operations aboard the International Space Station (ISS). VCAM is an autonomous environmental monitor based on a miniature gas chromatograph/mass spectrometer. It was flown to the ISS on shuttle mission STS-131 and commenced operations on 6/10/10. VCAM provides measurements of ppb-to-ppm levels of volatile trace-gas constituents, and of the atmospheric major constituents (nitrogen, oxygen, argon, and carbon dioxide) in a space vehicle or station. It is designed to operate autonomously and maintenance-free, approximately once per day, with a self-contained gas supply sufficient for a one-year lifetime. VCAM is designed to detect and identify 90% of the target compounds at their 180-day Spacecraft Maximum Allowable Concentration levels.

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http://dx.doi.org/10.2514/6.2011-5214

SPHERES Tethered Formation Flight Testbed: Application to NASA's SPECS Mission

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This paper elaborates on theory and experiment of the formation flight control for the future space-borne tethered interferometers. The nonlinear equations of multi-vehicle tethered spacecraft system are derived by Lagrange equations and decoupling method. The preliminary analysis predicts unstable dynamics depending on the direction of the tether motor. The controllability analysis indicates that both array resizing and spin-up are fully controllable only by the reaction wheels and the tether motor, thereby eliminating the need for thrusters. Linear and nonlinear decentralized control techniques have been implemented into the tethered SPHERES testbed, and tested at the NASA MSFC's flat floor facility using two and three SPHERES configurations. The nonlinear control using feedback linearization technique performed successfully in both two SPHERES in-line configuration and three triangular configuration while varying the tether length. The relative metrology system, using the ultra sound metrology system and the inertial sensors as well as the decentralized nonlinear estimator, is developed to provide necessary state information.

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Propellant-Free Control of Spinning Tetherd Formation Flight, Part 2: Nonlinear Underactuated Control

by on 9 June 2015in Technology Development & Demonstration No comment

This is the second in a series of papers that exploit the physical coupling of tethered spacecraft to derive a propellant-free spin-up and attitude control strategy. We take a nonlinear control approach to underactuated tethered formation flying spacecraft, whose lack of full state feedback linearizability, along with their complex nonholonomic behavior, characterizes the difficult nonlinear control problem. We introduce several nonlinear control laws that are more efficient in tracking time-varying trajectories than linear control. We also extend our decentralized control approach to underactuated tethered systems, thereby eliminating the need for any intersatellite communication. To our knowledge, this work reports the first nonlinear control results for underactuated tethered formation flying spacecraft. This article further illustrates the potential of the proposed strategy by providing a new momentum dumping method that does not use torque-generating thrusters.

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