Initial SPHERES Operations aboard the International Space Station

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

The Satellite Position Hold Engage Reorient Experimental Satellites (SPHERES) program, developed by the MIT Space Systems Laboratory, began operations aboard the International Space Station (ISS) on May 2006. SPHERES was designed as a research facility to demonstrate metrology, control, and autonomy algorithms for distributed satellites systems. By operating in the risk-tolerant environment of the ISS, SPHERES allows researchers to push the limits of their algorithms. Five test sessions, conducted during 2006, achieved multiple objectives for the different areas under study. The first test session was dedicated to hardware checkout. The second test session demonstrated basic 6DOF closed-loop control of the satellites. Fault detection and isolation algorithms were also tested, successfully using the inertial measurement system to detect simulated faults in space. Formation flight tests during the fourth and fifth session demonstrated two types of control architectures. Following the principle of incremental algorithm development, demonstrations of multiple scenarios of spacecraft docking occurred during test sessions one through four; the last session demonstrated docking to a tumbling spacecraft. The results of these test sessions are the basis upon which substantial more research will be conducted in the following years.

Related URLs:

International Space Station acoustics – a status report

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

It is important to control acoustic noise aboard the International Space Station (ISS) to provide a satisfactory environment for voice communications, crew productivity, and restful sleep, and to minimize the risk for temporary and permanent hearing loss. Acoustic monitoring is an important part of the noise control process on ISS, providing critical data for trend analysis, noise exposure analysis, validation of acoustic analysis and predictions, and to provide strong evidence for ensuring crew health and safety, thus allowing Flight Certification. To this purpose, sound level meter (SLM) measurements and acoustic noise dosimetry are routinely performed. And since the primary noise sources on ISS include the environmental control and life support system (fans and airflow) and active thermal control system (pumps and water flow), acoustic monitoring will indicate changes in hardware noise emissions that may indicate system degradation or performance issues. This paper provides the current acoustic levels in the ISS modules and sleep stations, and is an update to the status presented in 20031. Many new modules, and sleep stations have been added to the ISS since that time. In addition, noise mitigation efforts have reduced noise levels in some areas. As a result, the acoustic levels on the ISS have improved.

Related URLs:

SPHERES: a platform for formation-flight research

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

New space missions, such as the Terrestrial Planet Finder (TPF) and Darwin programs, call for the use of spacecraft which maintain precise formation to achieve the effective aperture of a much larger spacecraft. Achieving this requires the development of several new space technologies. The SPHERES program was specifically designed to develop a wide range of algorithms in support of formation flight systems. Specifically, SPHERES allows the incremental development of metrology, control, autonomy, artificial intelligence, and communications algorithms. To achieve this, SPHERES exhibits a wide array of features to 1) facilitate the iterative research process, 2) support experiments, 3)support multiple scientists, and 4) enable reconfiguration and modularity. The effectiveness of these aspects of the facility have been demonstrated by several programs including development of system identification routines, coarse formation flight control algorithms, and demonstration of tethered systems.

Related URLs:

Physical and Biological Organ Dosimetry Analysis for International Space Station Astronauts

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

In this study, we analyzed the biological and physical organ dose equivalents for International Space Station (ISS) astronauts. Individual physical dosimetry is difficult in space due to the complexity of the space radiation environment, which consists of protons, heavy ions and secondary neutrons, and the modification of these radiation types in tissue as well as limitations in dosimeter devices that can be worn for several months in outer space. Astronauts returning from missions to the ISS undergo biodosimetry assessment of chromosomal damage in lymphocyte cells using the multicolor fluorescence in situ hybridization (FISH) technique. Individual-based pre-flight dose responses for lymphocyte exposure in vitro to γ rays were compared to those exposed to space radiation in vivo to determine an equivalent biological dose. We compared the ISS biodosimetry results, NASA's space radiation transport models of organ dose equivalents, and results from ISS and space shuttle phantom torso experiments. Physical and biological doses for 19 ISS astronauts yielded average effective doses and individual or population-based biological doses for the approximately 6-month missions of 72 mSv and 85 or 81 mGy-Eq, respectively. Analyses showed that 80% or more of organ dose equivalents on the ISS are from galactic cosmic rays and only a small contribution is from trapped protons and that GCR doses were decreased by the high level of solar activity in recent years. Comparisons of models to data showed that space radiation effective doses can be predicted to within about a ±10% accuracy by space radiation transport models. Finally, effective dose estimates for all previous NASA missions are summarized.

Related URLs:
http://dx.doi.org/10.1667/RR1330.1

Distributed Satellite Systems Algorithm Maturation with SPHERES Aboard the ISS

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

Since beginning operations aboard the International Space Station (ISS) in May 2006, the Synchronized Position Hold Engage Re-orient Experimental Satellites (SPHERES) facility has completed a total of twelve test session with over 150 tests. The operational lessons learned from the first year of tests were presented at the 2007 IAC conference; this new paper will present a summary of the most relevant results of SPHERES research aboard the ISS. As a testing environment for distributed satellites systems, SPHERES research concentrates on the development of estimation, control, and autonomy algorithms for missions that include docking, formation flight, close proximity operations, and in-space assembly. By operating in the risk-tolerant environment created by the ISS, the SPHERES scientists can push the limits of the algorithms and attempt tests which would never be conducted as part of normal missions. In this manner SPHERES complements missions such as Orbital Express, while at the same time paving the way to future missions such as TPF, Darwin, and in-space assembly of large space structures, such as an inter-planetary stack. The first four test sessions (through August 2006) helped to validate the operation of the hardware and allowed the team to become efficient during each test session. Since then eight more test sessions have taken place. During these test sessions the SPHERES team has achieved multiple space-firsts, such as: docking to a tumbling target, demonstrated plume impingement effects in spacecraft of similar size, on-line path planning for a docking maneuver, coordinated formation flight of three satellites in microgravity, and formation reconfigurations. The team has also began tests of reconfiguration algorithms which allow the satellites to control each other after docking. Further, research has started on tests that simulate robotic inspection of other satellites. This research has been supplemented by demonstrations of obstacle avoidance algorithms operating in real-time. This paper will present results of the most advanced research of SPHERES by the time of publication in each of the principal areas of research: docking, in-space assembly, formation flight, and robotic inspection. The presentation of the results will be accompanied by high level descriptions of the algorithms used in each test, with references to other publications with detailed explanations of the algorithms. The applicability of the algorithms to future missions will be presented. The paper will conclude with a description of future test sessions to complete the goals of this phase of the SPHERES program.

Related URLs:

SPHERES Demonstrations of Satellite Formations aboard the ISS

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

Starting in 2007 the SPHERES team expanded its research operations aboard the ISS to include algorithms for formation flight systems. Based on the experiences learned by developing complex docking algorithms, the team began research to mature algorithms to perform imaging maneuvers and add autonomy to allow a formation system initialization and safing in case of failures. The imaging maneuvers research started with basic circular motion of independent satellites; these tests were highly successful. Next spiral maneuvers were performed. These proved more challenging as two things were changed in the tests: the dynamics of the system and the controller. Initial fixes to the controller improved performance, but not sufficiently. A distributed control algorithm, cyclic pursuit, was implemented, yielding high quality results. The autonomy algorithms included formation initialization from random locations and in random orders. The tests were partially successful, allowing the team to propose a potential algorithm and providing insight into potential failures modes of such algorithms (which were not exhibited during simulation). The scatter of a formation was demonstrated and subsequently used in the recovery part of a simulated thruster failure. A communications failure algorithm was implemented, but the tests aboard the ISS were not successful. A collision avoidance algorithm with low overhead was demonstrated. The data obtained from this test enables the team to validate the methods used to determine the size of safety areas between the satellites in a formation flight system, especially during reconfiguration of the constellation.

Related URLs:

Characterization of Unknown Events Observed by the Third Generation JPL Electronic Nose Using Sensor Response Models

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

The Third Generation Electronic Nose (ENose) from the Jet Propulsion Laboratory operated continuously and autonomously on the International Space Station (ISS) for more than 6 months during 2008-2009. During this time, the ENose monitored air quality in the US lab and recorded anomalous events. The data gathered and analyzed showed that in addition to detecting several analytes on the target list (ethanol, methanol, Freon 218 and formaldehyde), many events caused by chemical species outside the target list were observed and these were classified as “unknown.” We report an investigation to identify the chemical nature of the analyte(s) producing “unknown” events. The identification is achieved by using sensor response models based on molecular principles developed using Quantitative Structure Activity Relationships (QSAR) and First Principles Molecular Dynamics approaches. Molecular descriptors calculated from the models include dipole, hydrogen bond characteristics, molar refractivity, molar volume, and solubility parameters. Calculated molecular descriptors were then compared with descriptors of analytes in the Spacecraft Maximum Allowable Concentration (SMAC) database. The results indicate that a possible identification of the unknown response is sulfur hexafluoride (SF).

Related URLs:
http://dx.doi.org/10.2514/6.2010-6122

Dual-purpose resonate actuators for electromagnetic formation flight and wireless power transfer

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

This paper describes the development and demonstration of a single set of hardware to perform both electromagnetic formation flight (EMFF) maneuvers and wireless power transfer (WPT). The hardware uses resonant coils to generate electromagnetic fields, which in one mode interact to provide for control of a spacecraft cluster without expending propellant, and in another mode couple to inductively transfer power. Developed under the project name RINGS, standing for Resonant Inductive Near-field Generation System, the hardware attaches to the formation flight test facility on-board the International Space Station, called SPHERES (Synchronized Position Hold, Engage, Reorient, Experimental Satellites). It is the first system to utilize dual-purpose hardware to achieve both EMFF and WPT, and this is the first time that such a capability has been demonstrated in a micro-gravity, six-degree of freedom environment. The RINGS system serves primarily as a testbed for EMFF control algorithm development, and operation onboard the ISS allows for more complicated and realistic algorithms to be tested compared to the restrictive dynamic environment of flat floor facilities on the ground, or the limited duration reduced gravity flights. Design and development of the support hardware and electronics, as well as test results from ground testing, a parabolic flight campaign, and the preliminary results from the International Space Station hardware checkout are presented.

Related URLs:

Two-stage path planning approach for solving multiple spacecraft reconfiguration maneuvers

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

The paper presents a two-stage approach for designing optimal reconfiguration maneuvers for multiple spacecraft in close proximity. These maneuvers involve well-coordinated and highly-coupled motions of the entire fleet of spacecraft while satisfying an arbitrary number of constraints. This problem is complicated by the nonlinearity of the attitude dynamics, the non-convexity of some of the constraints, and the coupling that exists in some of the constraints between the positions and attitudes of all spacecraft. While there has been significant research to solve for the translation and/or rotation trajectories for the multiple spacecraft reconfiguration problem, the approach presented in this paper is more general and on a larger scale than the problems considered previously. The essential feature of the solution approach is the separation into two stages, the first using a simplified planning approach to obtain a feasible solution, which is then significantly improved using a smoothing stage. The first stage is solved using a bidirectional Rapidly-exploring Random Tree (RRT) planner. Then the second step optimizes the trajectories by solving an optimal control problem using the Gauss pseudospectral method (GPM). Several examples are presented to demonstrate the effectiveness of the approach for designing spacecraft reconfiguration maneuvers.

Related URLs:
http://dx.doi.org/10.1007/BF03256564

Monitoring Pre-Combustion Event Markers by Heating Electrical Wires

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

Simultaneous measurements were made for particle releases and off-gassing products produced by heating electrical wires. The wire samples in these experiments were heated to selected temperatures in a heating chamber and responses to vapor releases were recorded by the JPL Electronic Nose (ENose) and an Industrial Scientific ITX gas-monitor; particles released were detected by a TSI P-Trak particle counter. The temperature range considered for the experiment is room temperature (24−26°C) to 500 °C. The results were analyzed by overlapping responses from the ENose, ITX gas sensors and P-Trak, to understand the events (particle release/off-gassing) and sequence of events as a function of temperature and to determine qualitatively whether ENose may be used to detect pre-combustion event markers.

Related URLs: