Wireless Sensor and Actuators Networks for Intra

Wireless Sensor and Actuators Networks for Intra-Vehicle Applications Charalambos Sergiou∗ and Vasos Vassiliou∗ Dept. of Computer Science, University of Cyprus, Nicosia, Cyprus

Aleksandar Bozic† ArachnoBeeA Project

Christos Panayiotou‡ Cyprus Space Exploration Organization (CSEO)

Aristodemos Paphitis§ Dept. of Electrical and Computer Engineering, Cyprus University of Technology,Limassol, Cyprus

Wireless Sensor and Actuator Networks (WSANs) is a special category of Wireless Ad- Hoc Networks, that bears all the functionality of Wireless Sensor Networks (WSNs) but they are equipped with actuators capable to perform specific tasks. In this work we describe a specific application that indicates how WSANs can facilitate space operations and particularly intra- vehicles applications. The application is based on an autonomous assistant drone that would operate in any kind of spacecraft and assist crew by transporting small cargo for them.

I.

Introduction

Wireless Sensor Networks (WSNs) are a special category of wireless communication networks that consist of a number of wireless nodes equipped with sensors. These nodes form networks in an ad- hoc manner and cooperate in order to perform specific tasks.1 Currently, WSNs are considered as an emerging technology for either manned or unmanned spacecrafts.2 Generally, the applications of WSNs for space operations span from intra-vehicle to inter-vehicle, as well as planetary surface exploration, surface-to-orbiter data communications etc. But most importantly, WSNs can also provide flexibility for many future applications. In this work we focus on intra-vehicle applications. In particular, we initially discuss how this technology can be applied in performing specific tasks, such as monitoring environmental parameters, reducing harness complexity, reducing mass and volume of cabling, as well as facilitating retrofit activities. It is definite that the aforementioned uses of WSNs are primarily applications that monitor and warn about an event and in most cases provide adjusting mechanisms and/or warning mechanisms for event recovery. Bearing this in mind, we move a step forward and we study how to integrate the WSNs with multi-purpose actuators. In particular, we present the “ArachnoBeea” project, an effort that fuses all pre-mentioned technologies together into a flexible all-around system. This integration pushes our research from pure WSNs to Wireless Sensor and Actuators Networks (WSANs). These networks are able to perform a large set of tasks such as transportation of materials, maintenance, repairs etc., either intra- or inter- vehicle environment. Moreover, this system is able, under specific conditions, to substitute human crew in operations held in dangerous or hazardous environments, while in general it can assist in reducing their workload. ∗ email:

sergiou, [email protected]

† email:[email protected] ‡ email:[email protected] § email:[email protected]

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The actuators we present in this work are in the form of autonomous drones capable of flying and walking. These drones are unique in their capability to operate in low-to-none gravity as well as normal and gas-less environments. The research challenges that stem-out of this project are several. Initially, we present how this WSAN network is formed. Then, we present an algorithm of indoor localization. Based on this indoor location system, drones are able to navigate through the spacecraft, avoid collisions, find objects of interest etc. An important aspect of this work is that the applications presented in this work are supported by existing protocols and technologies, a fact which is fundamental for their successful implementation, especially in terms of cost and feasibility. The rest of the paper is organized as follows. In Section II we present how wireless technologies can contribute to space operations. In Section III we focus on Wireless Sensor and Actuators Networks discussing intra- vehicle applications, while in Section IV we briefly present the ArachnoBeea project. Finally we close with conclusions and future work.

II.

Wireless Technologies in Intra- Vehicle Applications

Wireless technologies can contribute in space operations, in several manners. Intra-vehicle applications is a sector where the applications span from the spaceship itself, to the crew, as well as to the mission. In particular, concerning the spaceship, applications of wireless technologies such as WSNs, can lead to reduced wiring and the associated aircraft weight. Bearing in mind the fact that almost every system in a modern space vehicle is controlled using wired communications, the weight saving is not negligible, even if just a redundant wired system is replaced by wireless network. Reduced weight can lead to reduced fuel consumption as well as increased payload. Moreover, wireless technologies can increase the reliability of the vehicle, even if at a first glance, wired connectivity seems to be much more reliable. In the cases of air-vehicles, wires are initially fitted when the vehicle is constructed and due to their complexity are “re-visited” only when a problem appears (fit-andforget). Wires age and as a result chaffing, corrosion, and other similar issues arise. In such cases, wireless technologies can be considered as more reliable since none of these issues exist, while the ability of receiving constantly much more data from aircraft systems is enhanced. Furthermore, the flight safety is improved by providing dissimilar redundancy from various vehicles systems. Concerning the operational efficiency, employment of wireless technologies offers the ability of monitoring systems and flying surfaces that currently cannot be monitored due to the complexity of the cables NASA itself recognizes2 a vast set of candidate applications that can leverage the benefits of wireless technologies and sensors. Below, a number of them is listed: - Inventory monitoring: In this case RFIDs tags can be attached to every equipment and with a simple harware, the position of every item in the vehicle can be monitored. - Environmental monitoring: Using dedicated sensors, several physical parameters like temperature, humidity, pressure, and radiation can be monitored in locations where access is very difficult (e.g outside of the vehicle).3, 4 - Physiological Monitoring: Wireless Sensors can be attached to the uniform of the crew and monitor important health parameters like blood pressure, heart rate etc. All these values can be wirelessly transmitted to a central systems were relevant decisions can be taken.5 - Crew member location tracking.6 - Structural monitoring: Sensors can be embodied into the structure of the vehicle, constantly monitoring any cracks, dents2, 7 etc. - Process monitoring and scientific monitoring and control - Retrofit of existing vehicle with new capabilities: Old vehicles can be retrofitted with new advanced electronics (avionics) systems adding new capabilities, without the constraint of wires routing. Additionally, the combination of energy harvesting technology2 can further prolong the lifespan of wireless


sensors and minimize maintenance operations on the wireless network.

III.

Wireless Sensor and Actuators Networks

Wireless Sensor and Actuators Networks is a special category of Wireless Ad- Hoc Networks where wireless sensors are accompanied with actuators in order to perform specific tasks.8 This technology is based on the notion of incorporating mechanical actuators in WSNs, which are able to perform actions, based on the input they collect from several sensors. This functionality provides an important capability, as it enables the reaction within the operating environment, utilizing the data it collects and ultimately manipulates them towards a specific output. The concept of equipping Wireless Sensor Networks with electronically-controlled actuators, first appeared in literature in 1998.9 Since then, it has been widely accepted and praised by the research community; whereas the academia and industry have embraced the field for its vast applicability and promising prospect. WSANs are regarded as a vital part of the vision for the near future, which envisions cyber-physical systems to be in the centre of technological progress.9 As one of the most rapidly evolving fields, Space Exploration Research and Development can easily be considered as one of the fields that will be highly benefited from the evolution of WSANs. The extremely unique environmental conditions -which are correlated with a high probability of failure- demand a trustworthy system of monitoring several operations. This system should be able to adapt to the dynamic environmental conditions, and also perform specific tasks for maintaining the integrity of the vehicle, ensuring the adequateness of the intra-vehicle environment, and also for assisting the crew in performing specific tasks. The expansion of automation through a reliable system of WSANs, and the subsequent reduction of the probability for human error, is of great importance in any technological endeavour, and particularly in Space missions, where the margin for error is slight and the magnitude of the financial cost is inversely proportional The Quality of Service (QoS) of WSANs is of particular significance, in terms of incorporating the technology in Space Exploration. The precision and reliability of the system have to be ensured before utilising it into any Space vehicle. This creates the need for further addressing a series of issues that arise, such as performance, reliability and security. The incorporated system has to be able to meet the certain specifications for delivery and robustness, in order to be adequate for the high requirements of a Space mission. Several measures of satisfaction for the QoS should be introduced, such as the throughput, the delay, the jitter and the packet loss rate, which will provide an assessment of the overall responsiveness of the system.9 Furthermore, the energy efficiency of the system should be ensured. Energy constraints are directly correlated to low system performance- including limited mobility of actuators, poor transmission rates and delay. Insufficiency of energy resources will restrict the ability of the WSAN to perform in an autonomous manner, affecting the mobility of the actuators. Hence, mobile sensors, which may act as gateways and middleware to connected local topologies, will not be able to traverse throughout their respected physical spaces; therefore forming “routing holes” and affecting the overall coverage and availability of the network.10

IV.

ArachnoBeeA project

In this section we briefly present the ArachnoBeea Project which is an integrated system of actuators and sensors capable to operate in every type of spacecraft in order to assist the crew by transporting small cargoes to them. The challenge in this project is the building of an autonomous assistant drone, which serves as the transportation mean for these cargoes. A.

Tasks

The autonomous assistant drone solution was tackled by setting and solving certain high level requirements, such as: The tasks that were assigned to the team members were the following: • autonomy • multi-purpose • adaptability 3 of 8 American Institute of Aeronautics and Astronautics

• ease of maintenance and deployment • robustness Each task is briefly explained below: - Autonomy: This characteristic was obtained by incorporating on-board Accessible Interface (AI) with on-board sensory system (ultrasound and laser distance measuring sensors, accelerometers, heat and imaging sensors etc.) and off-board systems (positioning system, space-mapping database, inventory tracking system, etc.). - Multi-purpose: Apart from just transporting small cargo to and from members of the crew, the drone was designed to do a variety of other tasks, such as: repairs and maintenance, rescue, and measuring of environmental parameters; while the entire solution should be able to solve the problem of tracking the position of the crew and tracking in real-time of the all the important inventory objects. - Ease of maintenance and deployment: For easy deployment of the drone, special attention was given in finding subsystems and proposing solutions that are easily adaptable to the already existing infrastructure. Bearing this in mind, special designs have been proposed for the charging ports, the integration of indoor-location systems (electrically and mechanically) into already existing environments, and the deployment of RFID readers into parts of the spacecraft. Each of the components design should be simple and easily maintainable, yet robust. - Robustness: The majority subsystems have been designed as fail-safe ( fail safe design responds in a way that will cause no harm, or at least a minimum of harm, to other devices or to personnel), and tried to make a design as redundant as possible. As an example, drone would have thrust vectorization and four propellers to enable robustness to fails and redundancy while moving. Also, the indoor-location system would have redundant anchors/tags, to increase precision and give redundancy. Also most of the technology used will be the one that is already proven through the years of use and development. B.

Solutions

The problems that needed to be solved were the following: Task acquisition: The first challenge was to program the drone to accept and process instructions (or commands). A multi- input system has been proposed. The input could be given in the form of voice commands, visual explanation (command gestures)or devised by the system autonomously. -Voice command: This is achieved by voice recognition algorithms, integrated with a personnel/inventory tracking system. A member of personnel could, with a voice command, define a mission. After defining a mission, the system (drone) should query the human for additional information needed for completing the task, (parameters such as the description of object to be retrieved, the name of the object, physical properties or ID of the object, and possibly the destination and/or place of origin of object). Upon receiving such information the system should proceed by executing the task. -Visual commands: This is achieved by pointing to the object that needs to be operated/transported and defining an operation via pre-defined hand gestures. System would have to be able to recognize these gestures and interpret the operation correctly. This could be done via a system internal cameras. Visual commands could prove useful in a mission, since they could be unable to communicate verbally e.g. in decompressed module. Object finding: Once identifying the correct object, the drone has to discover the location of the object. This can be done by searching in the database of objects and their associated locations. Integrated inventorying system should be able to track, in real time, and also update, the location of every object of importance. Inventory tracking system consists of RFID sticker tags (that should be placed on all objects of interest) and RFID readers that should be placed at every “choking point” around a space station or spacecraft. While operating aboard the spacecraft, the crew normally moves objects around, quite often, even from compartment to compartment, and to do so they pass through airlocks, compartment boundaries, narrow corridors and through doors. When doing so, these readers will be able to read the ID of the object and update, in real time,the inventory database with the updated location. This should provide a rough, “low resolution” estimate of the object’s position. For a more precise location of the object, a more sophisticated mechanism is required. One of the proposals made by the ArachnoBeeA team is to measure RTT (round trip time) and to establish the distance towards the object (via its RFID). Since RFIDs are passive devices, they answer only upon receiving enough external 4 of 8 American Institute of Aeronautics and Astronautics

EMF energy. This energy is emitted by a reader on-board the drone. By measuring the distance to the RFID tag, from several points inside the compartment, with a correct probability model and algorithm based on multilateration, more precise position can be calculated. Instead of measuring RTT, this “finer” stationing can be done also by measuring the strength of the signal. The closer the drone is to the tag, the stronger the radiation will be. But this method, due to reflections, can be, sometimes, quite inaccurate. In the last stage of finding the object, a drone can use its visual sensors (multiple cameras in different spectra, as an example) to take one or more pictures and recognize the object based on reference data retrieved from the inventory database. The inventory database construction would have to account for multiple types of data on every object, such as: objects photos from multiple angles, audio “tags” for each of the objects so it can recognize the command, rfID of the object, current position etc. Indoor location system: This subsystem is needed for the drone in order to become able to acquire its position in 3D dimensional space, thus being able to orientate itself and navigate, in order to complete the task in most efficient manner. This subsystem can be also used for tracking crew members inside the craft. In this proposal, the indoorlocation system is based on radio technology. This technology was favoured over ultrasound based systems because of flexibility (ability to work in vacuum), but a trade-off may exist concerning precision. Currently, available solutions give pretty accurate precisions even for radio based systems. Commercially available system, like the onr produced by DecaWave (www.decawave.com) provide precision at the range of 10cm. The system is based on at least 4 “anchor” that are placed in firm locations in the vehicle known to the drone in advance (reference points). To determine its position, the drone employs tags attached to it. One tag is needed in order to specify its position relatively to the anchors, while three tags are required in order to calculate the plane in which it resides. Thus, in order to accurately specify its position and its orientation, 4 tags are required.

Figure 1. Indoor Location System.

This system can also be used for tracking crew around the station/spacecraft, by placing the tag on each of the crew members. This way, if an object needs to be brought to a member of the crew, the drone would know, in real time, where this member is. This tracking system would help the drone, following the movements of the crew, to map the entire spacecraft even without actually flying through it. By being able to read the proper sensory data, and doing some basic processing and streaming these data to off-board mainframe computer of the vehicle, drone would not have to do any calculations, hence increasing autonomy, through lesser power consumption. This means that navigation and collision detection and avoidance can be centralized and not done by the drone itself, but the set of commands to fly it would be sent to it from the main computer, after analysing real-time telemetry data. Navigation could be done based on so called “Bug 2” algorithm,11 which should help avoid local “minima” in solving the problem of autonomous navigation. Situational Awareness: By the term “situational awareness” a full sensory coverage of the space surrounding the drone is considered. This provides to the drone the capability to (locally) navigate through spacecraft, around the obstacles and avoid collision. In order to detect possible objects in the vicinity, the drone should be equipped with an array of sensors (stereoscopic camera system, laser distance measurement unit, ultrasonic proximity sensors, etc). The navigation path can be planed, in high level, with an indoor-location system, but the problem has to be solved


also locally. Upon setting the global path, the drone has to take responsibility to autonomously search the environment and to be able to safely and efficiently navigate it. Grabbing the object: In order to grab the object of interest, the issue was not only the mechanical design. Considerations were made also for trying to find new solutions in materials that could help with solving the problem. One of the possible solutions is using electro-adhesive materials.12

Figure 2. Grabbing the object.

Walking: In order the drone to be able to dock itself in an efficient manner to any surface and also to be able to move itself, the research team investigated several solutions, bearing in mind the lack of gravity that exists in space. Apart from the already mentioned electro-adhesion method, which has the disadvantage of relatively high energy utilization, the team investigated a number of interesting approaches that are already employed by research groups across the globe. One of the most promising, was based on mimicking the nature by copying the nano-structure of material on the feet of some lizards.13

Figure 3. Walking in zero gravity Environment.

A major advantage of this approach is the fact that it is highly energy efficient, because it does not utilize energy to maintain the contact with the surface. Charging: To recharge itself, the drone needs a simple, yet reliable mechanism to dock to an already existing power network of charge ports in the vehicle. To be able to do this, the team proposed a small modification so that the drone would have easy access handles for docking. The fine docking/locking to the socket itself, should be done electromagnetically. Multi-purpose hand design: The proposed drone has high adaptability and multiple purpose, thanks to the design of its main tool, which is the robotic arm. The “wrist” of the arm should be easily detachable and interchangeable with other modules. Modules are proposed for grabbing, soldering, cutting, screwdriver module, welding etc. Modules are placed on the drone itself or at easily accessible places. The mechanism of attachment/detachment is simple and reliable. Thrust vectorization: Since the drone needs an efficient way to propel itself, to be able to do fast route corrections and to navigate in possibly narrow and tight space of the vehicle, thrust vectorization is considered as the best


solution. This could be done by changing the geometry of the drone. Each of the four carriers for the propellers could be elevated and rolled to different positions, giving the possibility to direct air/propellant flow in a certain direction. This would greatly increase the agility of the platform, its manoeuvrability, and its power efficiency. In tight places, the geometrical configuration of the drone could be significantly changed, thus helping it to reach otherwise unreachable spaces. This could also reduce the storage space for drone.

V.

Conclusion and Future Work

Wireless Sensor and Actuators networks is a prominent technology that it can provide several solution to space-related issues. The example of the ArachoBeeA project is an application that shows some of the countless features of WSANs. This project imposed several challenges to the research team. A lot of these challenges appeared and solved during the implementation of this drone, but the fact is that ArachnoBeeA team proposed a generic solution that can apply in a lot of fields. Our future work is guided by this concept. Similar solutions are already being designed and smart, space related solution are going to be presented in the near future.

Acknowledgments This work has been partially conducted during NASA International SpaceApps Challenge 2015, by the ArachnobeeA team and has been awarded as the “Best Mission Concept project in the competition” https://2015.spaceappschallenge.org/project/arachnobeea/. The team members are: Aleksandar Bozic, Computer Science Engineer Nikola Gacic, Electronics Engineer Ljubodrag Bozic, Student of Electrical Engineering, Department of Electronics Visnja Djurovic, Telecommunications Engineer Dragan Colovic, Mechanical Engineer Dusan Colovic, Civil Engineer Mihailo Kitanovic, Industrial Designer Christos Antoniou, Mechanical Engineer Charalambos Leventis, Computer Science Engineer Adrian Carlan, Computer Science Engineer Iurii Fomenko, Computer Science Engineer

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