The SPHERES Navigation System: from Early Development to On-Orbit Testing

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The MIT Space Systems Laboratory has developed the Synchronized Position Hold Engage and Reorient Experimental Satellites (SPHERES) facility for the testing of formation flight and autonomous docking algorithms inside the International Space Station (ISS), in NASA's reduced gravity aircraft and in a 1-g laboratory environment. To provide SPHERES with reliable and accurate position, velocity, attitude and angular rate estimation, an innovative state estimation system based on ultrasound transmission has been developed. An extended Kalman filter (EKF) processes time-of-flight data collectedby ultrasonic receivers, as well as angular rate measurements provided by gyroscopes, to compute the state estimates required by the satellites when maneuvering. To increase the robustness of the system, the EKF has been augmented with a fault detection capability that uses the filter innovation (residual) to diagnose measurement errors. Two versions of the algorithm were successfully implemented and used on the SPHERES facility onboard the ISS during a series of five test sessions, from May 2006 to November 2006. This paper describes both versions in detail, along with di culties encountered during the implementation on the hardware and their solution. Results from experiments performed in the ISS to validate the algorithms are also presented.

Related URLs:
http://dx.doi.org/10.2514/6.2007-6354

MISSE 6 Polymer Film Tensile Experiment

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The Polymer Film Tensile Experiment (PFTE) was flown as part of Materials International Space Station Experiment 6 (MISSE 6). The purpose of the experiment was to expose a variety of polymer films to the low Earth orbital environment under both relaxed and tension conditions. The polymers selected are those commonly used for spacecraft thermal control and those under consideration for use in spacecraft applications such as sunshields, solar sails, and inflatable and deployable structures. The dog-bone shaped samples of polymers that were flown were exposed on both the side of the MISSE 6 Passive Experiment Container (PEC) that was facing into the ram direction (receiving atomic oxygen, ultraviolet (UV) radiation, ionizing radiation, and thermal cycling) and the wake facing side (which was supposed to have experienced predominantly the same environmental effects except for atomic oxygen which was present due to reorientation of the International Space Station). A few of the tensile samples were coated with vapor deposited aluminum on the back and wired to determine the point in the flight when the tensile sample broke as recorded by a change in voltage that was stored on battery powered data loggers for post flight retrieval and analysis. The data returned on the data loggers was not usable. However, post retrieval observation and analysis of the samples was performed. This paper describes the preliminary analysis and observations of the polymers exposed on the MISSE 6 PFTE.

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SPHERES interact—Human–machine interaction aboard the International Space Station

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The deployment of space robots for servicing and maintenance operations that are teleoperated from the ground is a valuable addition to existing autonomous systems, because it will provide flexibility and robustness in mission operations. In this connection, not only robotic manipulators are of great use, but also free-flying inspector satellites supporting the operations through additional feedback to the ground operator. The manual control of such an inspector satellite at a remote location is challenging, because navigation in three-dimensional space is unfamiliar and large time delays can occur in the communication channel. This paper shows a series of robotic experiments, in which free flyers are controlled by astronauts aboard the International Space Station (ISS). The Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) were utilized to study several aspects of a remotely controlled inspector satellite. The focus in this case study is investigating different approaches to human–spacecraft interaction with varying levels of autonomy under zero-gravity conditions.

Related URLs:
http://dx.doi.org/10.1002/rob.21419

Micrometeoroid and Orbital Debris impact Damage Recording System

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Damage from Micrometeoroid and Orbital Debris (MMOD) impacts poses a substantial risk for the loss of crew for the currently planned CEV missions to the International Space Station (ISS). The Columbia Space Shuttle accident in 2003 spurred an investigation that led to the requirement of an active impact monitoring system on the Shuttle Orbiter. The MMOD impact Damage Recording System (DRS) presents a reliable, mass- and power-efficient Thermal Protection System (TPS) impact detection system that can be readily integrated with manned and robotic spacecraft. Thus, the Crew Exploration Vehicle (CEV) is considering inclusion of active MMOD detection systems for monitoring damage to the backshell TPS. MMOD impact detection systems have been developed and flown on satellites and probes dating back to the 1960s. These technologies were designed primarily to understand and characterize the MMOD environment found in low earth orbit (LEO). The only impact monitoring system qualified for use on manned spacecraft is the wing leading edge impact detection system (WLE IDS). During Shuttle ascent, the WLE IDS monitors impacts due to insulating foam shed from the external fuel tank onto the WLE. The WLE is particularly vulnerable due to the high heating environment experienced during reentry. Ever-increasing accumulation of man-made debris is magnifying this threat to shuttle and other spacecrafts operating in LEO. Therefore, the development of on-orbit impact monitoring systems that aid in the mitigation of the threat to manned spacecraft is needed. This paper describes the development and testing of the DRS, a massand power-efficient wireless MMOD impact detection system designed for potential incorporation into the backshell of the CEV. The DRS utilizes wireless data acquisition via custom designed wireless nodes. The DRS wireless nodes determine MMOD impact damage by employing an Embedded Damage Recorder (EDR) sensor. A variety of EDR sensor designs were considered based upon d- – ifferent damage detection and TPS integration requirements. The DRS system design was recently tested at the University of Dayton Research Institute's hypervelocity impact range. During this test series, seven hypervelocity impacts were conducted using aluminum and nylon projectiles to simulate MMOD impacts to representative models of the CEV backshell TPS. The TPS models were fabricated in a flight-like configuration integrating the EDR sensor at the bondline. The DRS accurately indicated damage to the TPS models on all seven hypervelocity impact tests. These results have confirmed the feasibility of the DRS employing the EDR sensor as a viable MMOD impact sensing solution. Vehicle integration and further space environment testing remain critical steps in maturing this technology to flight qualification.

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SPHERES Reconfigurable Control Allocation for Autonomous Assembly

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Current research on control allocation emphasizes reconfiguration for adapting to thruster failures. However, in the application of autonomous assembly, the reconfiguration is necessitated by changing physical properties. For the scenario of an assembler tug constructing a large space structure, every docking and undocking maneuver used for the tug to move an individual payload causes a large shift in the dynamics of the tug. Not only do the mass properties change, but so does the thruster configuration. Changes in the center of mass, mass, and inertia of the tug-payload system, causes changes in the equivalent force exerted by each thruster. This paper explores reconfigurable control allocation to adapt to changes in the mass properties. Specifically considered are changes to the center of mass and thruster configuration (number, location, and active thrusters). Results are presented from the implementation of a reconfigurable control allocation algorithm on the SPHERES (Synchronized Position Hold Engage Reorient Experimental Satellites) testbed aboard the International Space Station. Results demonstrate controllability for configurations with large center of mass shifts, varying number of thrusters, as well as maintaining performance from the baseline non-reconfigurable control allocation algorithm on SPHERES.

Related URLs:
http://dx.doi.org/10.2514/6.2008-7468

Advanced ISS Air Monitoring — The ANITA and ANITA2 Missions

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After 11 months of successful operation onboard the ISS US laboratory Destiny, the air quality monitors ANITA (Analyzing Interferometer for Ambient Air) was brought back to Earth on STS126 (ULF2). ANITA is a technology demonstrator flight experiment for continuous air quality monitoring inside the crewed cabin of the ISS with low detection limits and high time resolution. For the first time, the dynamics of the detected trace gas concentrations could be directly resolved by ANITA and correlated to gas events in the cabin. The system is the result of a long term ESA technology development programme initiated more than seventeen years ago. The ANITA mission was a cooperative project between ESA and NASA. ESA's responsibilities were the provision of the H/W, the data acquisition and the data evaluation. NASA was responsible for the launch, accommodation and operation onboard ISS, data download and the transportation of ANITA back to the Earth. ANITA was calibrated to detect and quantify 30 trace gases simultaneously with down to sub-ppm (parts per million) detection limits in addition to the always present background gases carbon dioxide and water vapour. The results of the mission are summarised in [ 1 ]. Further, with a specially developed gas bag hand pump system also gas analyses were performed on air samples from Node 1 of the Space Station. ANITA is a precursor for a permanent continuous trace gas monitoring system ANITA2 for ISS and future space vehicles. At the time of the conference the follow-on study on ANITA2 will have been initiated. This paper describes the measurement system, the lessons learned during the mission on ISS, and the planned follow-on activities. The work described has been performed under contract of the European Space Agency.

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ANITA Air Monitoring on the International Space Station Part 1: The Mission

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After the launch to the International Space Station with The Space Shuttle flight STS 118 13A.1 on August 9th 2007 and the accommodation in the US lab Destiny, the air quality monitor ANITA (Analyzing Interferometer for Ambient Air) has been successfully put into operation. ANITA is a technology demonstrator flight experiment being able to continuously monitor with high time resolution the air conditions within the crewed cabins of the ISS (International Space Station). The system has its origin in a long term ESA (European Space Agency) technology development program. The ANITA mission itself is an ESA-NASA cooperative project. ESA is responsible for the provision of the HW (Hardware), the data acquisition and data evaluation. NASA's responsibilities are launch, accommodation in the US Lab Destiny, operation and data download. The ANITA air analyser is designed to detect and quantify online and with high time resolution 30 trace gases simultaneously with down to sub-ppm (parts per million) detection limits in addition to the always present background gases carbon dioxide and water vapour. The air analyser thus monitors the trace gas dynamics of the spacecraft's atmosphere in providing continuous air monitoring as well as crew warning capability in case of malfunctions. Beside continuous measurements in the vicinity of the gas monitor, air samples from remote places in the International Space Station can be analyzed using gas bags and a hand pump. However, considering the experimental character of ANITA, the measurements are not on-line visible to the Crew. ANITA is an on-orbit test experiment and a precursor for a permanent continuous trace gas monitoring system on the ISS – ANITA II. It further represents a precursor system for future air monitoring in crewed vehicles being developed for the Human Space Exploration program. This is the first paper of two describing the measurement principle, the HW and the mission on the ISS. Finally, an outlook into the future highlights the potential of the ANITA technology for the Exploration program. The work described has been performed under contract of the European Space Agency.

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Change in skin physiological parameters in space–report on and results of the first study on man

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Astronauts often show skin reactions in space. Systematic tests, e.g. with noninvasive skin physiological test methods, have not yet been done. In an interdisciplinary cooperation, a test series with skin physiological measurements was carried out before, during and after a long-term mission in the International Space Station. The hydration of the stratum corneum (Corneometer), transepidermal water loss (Tewameter), and the surface structure of the skin (SkinVisiometer) were measured. In order to record cutaneous states, the suction elasticity was measured (Cutometer), and an ultrasound measurement with 20 MHz (DermaScan) was also made. In addition, one measuring field of the two inner forearms was treated with a skin care emulsion. There were indications of a delayed epidermal proliferation of the cells, which would correspond to the clinical symptoms. Hydration and TEWL values are improved by respective skin care. On the cutaneous level, the elasticity measurements and the ultrasound picture showed results which correspond to a significant loss of elasticity of the skin. Further examinations are necessary to validate these preliminary results.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/18663342

Experimental evaluation of on-board, visual mapping of an object spinning in micro-gravity aboard the International Space Station

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Spacecraft proximity operations near an unknown and uncooperative and spinning target object is a challenging problem. One of the key steps in ensuring safe operations is building a map of the target object. Additionally, it is useful to estimate the relative position, orientation, linear and angular velocities of the object as well as its center of mass, principal axes of inertia and ratios of inertia so that the object's pose can be accurately propagated forward in time. This paper reviews an approach for building a map of an unknown and spinning object, and presents experimental results of this algorithm when it was run onboard the Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) and Visual Estimation for Relative Tracking and Inspection of Generic Objects (VERTIGO) Goggles that are operating within the International Space Station. To the best of the authors' knowledge, this is the first time a solution to a Simultaneous Localization and Mapping (SLAM) problem has been run on a computer that is in space.

Related URLs:
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6942878

Mold species in dust from the International Space Station identified and quantified by mold-specific quantitative PCR

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Dust was collected over a period of several weeks in 2007 from HEPA filters in the U.S. Laboratory Module of the International Space Station (ISS). The dust was returned on the Space Shuttle Atlantis, mixed, sieved and the DNA was extracted. Using a DNA-based method called mold-specific quantitative PCR (MSQPCR), 39 molds were measured in the dust. Potential opportunistic pathogens Aspergillus flavus and Aspergillus niger and potential moderate toxin producers Penicillium chrysogenum and Penicillium brevicompactum were noteworthy. No cells of the potential opportunistic pathogens Aspergillus fumigatus, Aspergillus terreus, Fusarium solani or Candida albicans were detected.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S0923250808000892