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Remote Monitoring of a Heterogeneous Sensor Network for Biomedical Research in Space Keywords: sensor network, microgravity, space station, biomedical research Kathy J. Liszka ** presenter / contact The University of Akron Dept. of Computer Science Akron, Ohio 44325-4002 (On site at NASA Glenn Research Center) Office: (216) 433-5110 Fax: (216) 433-8000 [email protected] David W. York NASA Glenn Research Center MS 86-11 21000 Brookpark Road Cleveland, Ohio 44135 Office: (216) 433-3162 Fax: (216) 433-8000 [email protected] Michael A. Mackin NASA Glenn Research Center MS 86-11 21000 Brookpark Road Cleveland, Ohio 44135 Office: (216) 433-5326 Fax: (216) 433-8000 [email protected] Michael J. Lichter NASA Glenn Research Center MS 86-5 21000 Brookpark Road Cleveland, Ohio 44135 Office: (216) 433-8588 Fax: (216) 433-8000 [email protected] Abstract The objective of this research is to present the design and development of a heterogeneous sensor network and remote experiment server with personality modules to service microgravity research in biomedical engineering. We present the architecture for cardiac, metabolic and ocular research to be conducted on the International Space Station. The purpose of this project is to assess, understand, mitigate, and manage the risks associated with long-term exposure to the space environment. It is anticipated that the ground-based, spin-off use of the experiments will contribute to the improvement of health care for the people on Earth. 1. Mars or Bust! NASA has launched astronauts into space for more than four decades. Alan Shepard’s historical flight in 1961 lasted 15 minutes 22 seconds. Skylab was home to three crews from 1973-74, the longest lasting 84 days, proving that humans could potentially live and work in space for extended periods. However, this was not enough to even begin to assess long term effects of microgravity on humans. It wasn’t until 1995 when a succession of seven astronauts joined Russian cosmonauts on the MIR space station, that we had the opportunity to begin serious research on how to sustain long-term space expeditions in preparation for permanent operations on the International Space Station (ISS). Significant studies on human adaptation to space have been conducted on the Space Shuttle, but long term scientific data cannot be collected in this manner. Missions are limited to roughly two weeks because of the effects of microgravity on the vestibular system that regulates the body’s equilibrium. 2 The shuttle is a reusable launch vehicle requiring a piloted landing operation. Somewhere between the third and fourth weeks, the accumulated effects of microgravity alter an astronaut’s perception of spatial orientation enough to make manual landing maneuvers too risky to attempt. When Expedition One docked at ISS in November 2000, it marked the beginning of a new era of space exploration with a permanent human presence in space. Today, while orbiting the earth at an average altitude of 354 kilometers (220 miles) for up to six months at a time, astronauts defy a hostile, oxygen-less environment of freezing temperatures and lethal radiation levels. Yet in order to embark on the long-term missions suggested in the current Administration’s new agenda, we must overcome additional hurdles that keep us earthbound. NASA has been tasked to extend human presence across the solar system, starting with a human return to the Moon by the year 2020 in preparation for human exploration of Mars and other destinations. Our primary concern is the fact that prolonged exposure to microgravity will cause major physiological changes to the human body. The John Glenn Biomedical Engineering Consortium (JGBEC) focuses on health related countermeasures for astronaut crews. Project Rescue, a part of JGBEC, serves two purposes. The first is to design and build a space-based specialized sensor network for embedded, real-time systems to support biomedical experiments that can be monitored and/or controlled either locally or remotely. The second objective is a biomedical experiment that concentrates on studying electrophysiological changes in the heart as a way to understand how the body’s conduction system works. 2. Architecture The system objective of Project Rescue is to provide an interoperable framework for accessing and controlling sensor and sensor systems in space via standard web protocols. Figure 1 shows the basic on-board configuration. Two experiments in addition to Rescue have been identified to work with the system. PUMA measures metabolism with a portable unit, which can be carried by the human subject. INI-Tech looks for physiological anomalies through various non-invasive examinations of the eyes. Sensor data is transmitted via a shorthaul network to a personality module processor dedicated for that experiment. A serial link with standard connections will be immediately implemented. Wireless transmission is the ultimate goal but may not be available for the first experiment because it is subject to stringent safety requirements. 3 ISS is a closely monitored environment with many hardware, software and communication systems on board. Their interactions and potential conflicts with each other must not impact the safety of the crew or station. The personality module is a processor board with enough storage for up to 6 hours of archived data. Incorporating new sensors can be done almost seamlessly and without reengineering the design. This module is responsible for running algorithms and signal analyses unique to their sensor measurements. Installed in each module is an embedded web server with stored HTML and embedded Java applets for remote command and telemetry access. The boards plug into a CompactPCI backplane, a high performance industrial bus based on the standard PCI electrical specification in rugged 3U or 6U packaging. Personality modules are inserted from the front of the chassis. The experiment processor is the contact point for the system and is responsible for the remote access protocols to and from the ground facilities. Astronauts will be able to plug a laptop computer directly into the system to give commands and retrieve data for each experiment. The experiment processor provides functions common to all personality modules. These include long term (greater than 4 days) archival of data, Embedded Web Technology (EWT) and a communications interface to the spacecraft TCP/IP or CCSDS1 data link [1]. A researcher is not constrained by operating system or hardware requirements to remotely interact with their experiment. We only require a connection to the network with a standard network card and a standard Web browser. Command and telemetry links to the personality modules are available as URLs. The experiment processor is designed for mounting in a Lab standard payload rack or an Express rack. Figure 2 shows the communication paths from Project Rescue to the scientists on the ground. Digital sensor data is packetized at the application level on the personality modules. The experiment server holds the packets until data downlink is scheduled based on availability of bandwidth of the Tracking and Data Relay Satellite System (TDRSS) and Space Station resources. The Space Station Command and Data Handling system (C&DH) is comprised of several components with different operational capabilities and objectives [2]. The experiment server will provide 1 CCSDS (Consultative Committee for Space Data Systems) is the protocol used for spacebased telemetry handling. According to the ISS OD/Avionics and Software office of ISS, conversions from CCSDS to TCP/IP, Phase 2, is scheduled for completion in May 2005. 4 communications hardware and software interfaces compatible with the ISS Medium Rate Data Link (MRDL), an Ethernet local area network provided for telemetry. The TDRSS system uses two geosynchronous satellites for space-toground communications. The Ku-band communication link operates at 43.2 Mbps and is used for transmission of video and high-speed data to earth. The S-band communication link operates at 57 Kbps. This link is used for transmission of twoway voice commands to the space station and telemetry from the space station to the ground. Once on the ground, the Payload Data Services System (PDSS) at Marshall stores and distributes the data to experiment principle investigators running a thin client. 3. Biomedical Sensors A plethora of biomedical sensors are available to detect and measure physical, chemical and biological phenomena. Their use in space has yielded varying degrees of success. The sensor systems selected for Project Rescue are not tiny, certainly not on the scale of motes2, but they are reasonably portable. Size and weight are significant in light of the cost to send payloads to the Space Station, sharing precious space packed with food, water and oxygen. Astronaut mobility in tight quarters is another factor. The experiment most likely to be manifested for flight first is the cardiology part of Rescue. This is, in part, due to the fact that the special ECG unit made by Cambridge Heart, a partner in this project, is already available. Medical protocols have already been developed for the experiment by cardiologists at the MetroHealth Campus of Case Western Reserve University. 2 A mote is a tiny electronic device that contains a tiny computer, radio, sensors and a power supply. Another consideration is the time and effort to install and test the communication system before loading the rest of the personality modules. PUMA and INI-Tech are NASA technology still under test and development. 3.1 Rescue: T-Wave Alternans Rosenbaum, et. al., [5] established the significance of T-wave alternans (TWAs) as a predictor of life threatening cardiac arrhythmia. Cardiologists are unsure how these affect the electrical activity of the heart on return to earth. What they do know is that the heart changes electrically as a function of time in orbit. In basic terms, the heart is simply an electrically controlled mechanical pump. Electrical activity normally spreads out in an organized manner. If this pattern is disturbed, due to functional or anatomical blocks, an 5 arrhythmia results that can be lethal if left untreated. More commonly known as a sudden heart attack, it is the one of the more common causes of death in the United States. Now consider an astronaut after 30 days of prolonged exposure to microgravity. The heart has become larger, thinner, and as the result of other physiological changes, pumps less efficiently and does not get enough blood. Flight surgeons also know that the heart changes electrically as a function of time in orbit. Astronauts have experienced episodes of cardiac arrhythmias (an abnormal rhythm of the heart beat) in space [3, 4]. This is extremely dangerous, as it can result in brief loss of consciousness, endangering the whole crew and compromising successful completion of a mission. The Cambridge Heart unit will be used to detect microvolt TWAs and prolonged QT intervals. It uses a 14-lead ECG sensor lead-set (7 conventional, 7 multi-segment), generating 32 channels of data. All standard ECG measurements can be derived from this configuration as well. Historical ECG data collected from astronauts has had questionable value because the heart shifts in location in addition to the other changes experienced in orbit. The orthogonal lead system on this unit mitigates those effects so that lead placement on the body does not have to be as accurate in order to make comparable measurements over a time series. The personality module built for this experiment will contain TWA signal analysis software supplied by Cambridge Heart. The purpose of the first flight will be to prove that we can make the required microvolt measurements, analyze, store and transmit the resulting data to researchers on the ground. When this is confirmed, longterm signal collection will provide medical researchers with a way to understand how the conduction system works as a function of microgravity and time in flight. If this can be done, then it may be possible to create and deploy effective counter-measures for astronauts who may, for example, be on the moon 239,000 miles away. It may also be an effective screening tool for selection of astronauts for long terms missions in the future. 3.2 PUMA Astronaut fitness is a major concern for NASA, especially during longer duration missions. Without the natural loading of gravity, bones and muscles weaken, causing problems when crewmembers return to earth. Studies of MIR and ISS missions reveal a reduction in bone mass at the rate of 1 to 1.5% per month [6]. Although the 6 metabolic function is measured on astronauts to collect data, it requires a large, cumbersome and stationary set of instruments to which the crew must literally be attached to with tethers. Dietrich, et. al., [7] are developing a Portable Unit for Metabolic Analysis (PUMA) that will quantify metabolic function by measuring temperature, flow, and pressure during respiration using prototype oxygen, CO2 and flow sensors. The portable device will enable measurements during various crew activities without tethers when the wireless portion of the communication interface to the personality module is implemented. 3.3 INI-Tech Radiation probably poses the greatest danger to astronauts. We are protected on Earth because the magnetic field attenuates its harmful effects. Increased exposure to cosmic radiation during long duration space exploration damages the basic cell DNA structure and causes gene mutation. Even relatively low doses of radiation cause an increased risk of retinal detachment and cataracts. Ansari, et. al., [8] have developed and are testing an instrument that will detect early, subtle signs of changes in the fluids, tissues, and blood vessels of the eye and brain. Noninvasive optical measurements have the potential to provide health indices not just for these organs, but also for the entire body. Resembling night-vision goggles, the apparatus will house miniaturized fiber optic probes to collect health data that may detect ocular and systemic abnormalities long before clinical symptoms appear. 4. Becoming Flight-worthy Before something can fly on a Shuttle or the Space Station, it must undergo a lengthy process of modification and testing. Although the prototype Rescue system is not intended for flight, it will, where practical, be designed with spaceflight environment requirements relating to electromagnetic interference and compatibility (EMI/EMC), vibration, microgravity effects, packaging, training and launch loads. The fidelity of this system will be equivalent to an Engineering Model (form, fit, and function). The design goal is to produce a system which can be qualified for flight with minor modifications. Hardware problems that may occur must be anticipated and allowed for. Software must also run reliably, and be reconfigurable from the ground. In short, whether you are orbiting the earth at 250 miles or on your way to Mars, consistency and reliability is the best choice every time! INI-Tech: Perhaps the most diverse experiment, additional benefits on earth, include early detection of changes in the eye associated with infection, allergic reactions, autoimmune diseases, glaucoma, age-related macular degeneration, and diabetic retinopathy. Early cataract formation and diabetes diagnosis can also be detected using this technology. 5. Down to Earth We are grateful to Dr. Leslie R. Balkany, for his editorial and technical comments. The John Glenn BioEngineering Consortium at the NASA Glenn Research Center funded this work. In our quest to explore an inhospitable universe, we improve the quality of our lives on earth. Science, medicine, and communications have benefited tremendously from NASA funded research programs. These experiments will be no exception. Rescue: An earth-based system would allow patients to be monitored for arrhythmias in near real time outside the hospital. Patients become mobile, continuing their daily lives at home, at work and on the road. This technology could potentially save many lives each year. PUMA: Convalescing patients could use the portable metabolic measurement device to measure their physical response to exercise. Athletes in training could increase their endurance by making ensuring their workout keeps them working at the top of their capacity. 7 A crewed mission to Mars currently lies outside of our technological and physiological abilities. We know that Project Rescue can contribute to the realization of this ambition by providing the network and communication infrastructure to advance research with new and unique sensors. 6. Acknowledgements 7. References [1] Ponyik, J. G. and York, D. W., “Embedded Web Technology: Applying World Wide Web Standards to Embedded Systems,” NASA TM-2002211199, AIAA-2001-5107, March 2002. [2] Mortonson, M. W., “ISS Enhanced Payload Data Network for International Space Station utilization on-orbit,” AIP Conference Proceedings, Jan. 2000, vol. 504(1) pp. 649-654. [3] Baisden, D. L. and Jones, M. M., “Cardiac Dysrhythmia Analysis on Flights STS-1- STS 61C,” Houston NASA, 1988. [4] Fritsh-Yelle, J. M., Rossum, A. C., Brown, T. E., Leuenberger, U. A., D’Aunno, D. S., Josephson, M. E. and [5] [6] [7] [8] Goldberger, A. L., “An episode of VT during long duration spaceflight,” American Journal of Cardiology, 1998, 81:1391-92. Rosenbaum, D. S., Jackson, L. E., Smith, J. M., Garan, H., Ruskin, J. N. and Cohen, R. J., “Electrical alternans and vulnerability to ventricular arrhythmias,” New England Journal of Medicine, Jan 27, 1994, 330:235-41. Turner, R. T., “Physiology of a Microgravity Environment: Invited Review: What do we know about the effects of spaceflight on bone?,” J. Appl. Physiology, Aug. 2000; 89: 840 - 847. Dietrich, D., Piltch, N., Cabrera, M., Struk, P., and Pettegrew, R., Development of a Portable Unit for Metabolic Analysis (PUMA), http://microgravity.grc.nasa.gov/grcbio/f itness.html. Ansari, R. and Carbrera, M., Integrating Non-Invasive Technologies to Enable Effective Countermeasures during Prolonged Space Flight, http://microgravity.grc.nasa.gov/grcbio/e ye.html. 8