Piezoelectric Assisted Smart Satellite Structure

Final Report Summary - PEASSS (Piezoelectric Assisted Smart Satellite Structure)

Executive Summary:
European space objectives include Earth Observation to monitor the health of the planet and the impacts of human activities. In addition, Europe seeks to stay on the cutting edge of space technology.
The technologies that will be developed in the PEASSS project directly enable European space observation and in-space activities. The project will create a cutting edge technology based on piezo actuated smart composite panels, which can improve the accuracy and stability of nearly all Earth Observation sensor platforms.
The PEASSS project has a total budget of almost 2.47 M€. The project started on 1 January 2013 end ended on 30 April 2017. To enable the launch the project is suspended for 11 months and an extension of 5 months is granted to finish the flight hardware.

The PEASSS consortium, with its six partners, aligns established aerospace contributing organizations with SME’s and university researchers, including members from Germany (Sonaca Space), The Netherlands (TNO, ISIS) Belgium (Sonaca), as well as Israel (NSL, Technion).

The main objective of the PEASSS project is to develop, manufacture, test and qualify "smart structures" which combine composite panels, piezoelectric materials, and next generation sensors, for autonomously improved pointing accuracy and power generation in space. The smart panels will enable fine angle control, and thermal and vibration compensation, improving all types of future
Earth observations, such as environmental and planetary mapping, border and regional imaging.
The project starts with the design of the CubeSat platform bus, definition of system components, design payload interfaces, satellite configuration, power supply, software and avionics logic. The system components include new nanosatellite electronics, a piezo power generation system, a piezo actuated smart structure, and a fiber-optic sensor and interrogator system. The designs are prototyped into breadboard models for functional development. Following completion of functional and environmental tested operational breadboards, the Flight system components have been designed, manufactured and passed the functional and environmental tests, This has resulted in flight-ready hardware, that is integrated into a working satellite. Once the nanosatellite is assembled and related software is developed, the on ground tests are performed.
Finally the satellite is successful launched on 15 February 2017 with PSLV mission C37 from India. All new developed system components are operational. After commissioning of the platform and the payload, the functional tests in space are performed successful.

Results of the program are disseminated to industry through a project website, papers, courses, and presentations. Actuated “smart structure” technology will take the first steps toward space qualification in the PEASSS project, making it a proven viable technology, with a high TRL available to improve future European space missions. PEASSS technologies will give European space, aviation, and other industries a new tool in their design repertoire.

Project Context and Objectives:
Project context
European space objectives include Earth Observation to monitor the health of the planet and the impacts of human activities, which is increasingly important in this time of climate change and growing industrialization, farming, mining, smuggling, terrorism, illegal immigration, etc. In addition, Europe seeks to stay on the cutting edge of space technology, both for the intrinsic benefits that technology offers in space as well as the benefits generated by the introduction of next generation technologies into the broader economic base.

The application of piezoelectric technology is rapidly growing in daily products as well as in the
high-tech industry, due to the weight and volume savings that it offers, while maintaining a high level of accuracy. Piezoelectric technology can be used as actuator, sensor, and energy harvester. Despite the clear advantages, its application in the Space environment remains at a mostly conceptual level.

The technologies that will be developed in the PEASSS project directly enable European space observation and in-space activities. The project will create a cutting edge technology based on piezo actuated smart composite panels, which can improve the accuracy and stability of nearly all Earth Observation sensor platforms. As described below, the improved pointing accuracy and potential for reduction of mechanical noise stands to improve all types of observations, from environmental and planetary mapping to border and regional observation. Furthermore, the project will advance alternative power generation in space, which stands to enable distributed sensor networks and other next generation space technologies. In addition, this new technology will help keep Europe on the cutting edge of space research, potentially improving the cost and development time for more accurate sensor platforms. Likewise, this new "smart structure" technology may provide positive economic impacts to other industries, such as its utilisation to reduce noise and related fatigue in future aircraft composites.

Project objectives
The main objective of the PEASSS project is to develop, manufacture, test and qualify "smart structures" which combine composite panels, piezoelectric materials, and next generation sensors, for autonomously improved pointing accuracy and power generation in space. The smart panels will enable fine angle control, and thermal and vibration compensation, improving all types of future
Earth observations, such as environmental and planetary mapping, border and regional imaging. This new technology will help keep Europe on the cutting edge of space research, potentially improving the cost and development time for more accurate future sensor platforms including synthetic aperture optics, moving target detection and identification, and compact radars.

The system components include new nanosatellite electronics, a piezo power generation system, a piezo actuated smart structure, and a fiber-optic sensor and interrogator system. The designs will be prototyped into breadboard models for functional development and testing. Following completion of operational breadboards, components will evolve to flight-test ready hardware and related software, ready to be integrated into a working satellite. Once the nanosatellite is assembled, on ground tests will be performed. Finally, the satellite will be launched and tested in space.

Work package objectives
In total 9 work packages are defined: 1 general management WP, 1 technical management WP, 1 dissemination and exploitation WP and 7 R&D WP’s. The objectives of the R&D WP’s are described below
WP2 System Research & Engineering objectives:
In this WP, NSL satellites and ISIS BV will design the CubeSat platform bus, choose components, design payload interfaces, and satellite configuration, power supply, software and avionics logic. The goal of this WP is to flow system design specifications to component level, perform requirements management, and interface management to help ensure the team’s ability to integrate and accommodate all satellite systems, and deliver a full CubeSat system. The NSL effort regarding provision of guidance and requirements and system engineering to all the payload designs is also covered in this WP.

WP3 Design Development objectives:
The objective of this WP is to execute the design of the innovative payloads of the PEASSS Program. The end result will be to develop designs which can be produced and tested at the breadboard level.

WP4 Breadboard Development and Testing objectives:
The objective of the breadboard development and testing is to implement the design results of WP3 at an initial working-model level, without concern for form factor or other final product requirements. The end result of this effort will be a final confirmation of adequate functionality of the component designs, and a report documenting the test results and changes required to reach functionality.

WP5 Component Fabrication and Testing objectives:
In this WP the various payload elements for this project will be manufactured, assembled and integrated, followed by functional and environmental testing of the individual payload components.

WP6 Satellite integration and on-ground functional testing objectives:
Realize the final integration of the payloads and the spacecraft and perform the flight qualification testing of the spacecraft.

WP7 Space Environment Testing objectives:
To arrange and execute the spacecraft launch, and operate the spacecraft and its experiments in space; or in case launch is not feasible, perform full functional testing in a space representative environment.

Deliverables
In the project 33 deliverables are defined: 26 reports, 1 list with names of members of the advisory board, 1 CAD model of the PEASSS satellite, 1 set of breadboards representing the flight hardware to be developed, 1 operational nano satellite, to be launched in space.

Dissemination
Results of the program are disseminated to industry through a project website, papers, courses, and presentations. Actuated “smart structure” technology will take the first steps toward space qualification in the PEASSS project, making it a proven viable technology, with a high TRL available to improve future European space missions. PEASSS technologies will give European space, aviation, and other industries a new tool in their design repertoire.

Project Results:
main S&T results / foregrounds

The objective of the PEASSS project was to develop, manufacture, test and qualify “smart structures” which combine composite panels, piezoelectric materials and next generation sensors, for autonomously improved pointing accuracy and power generation in space. In order to fulfill these objectives a Cubesat has been designed and build that consisted of the platform bus and payloads. The platform bus should be a reusable Cubesat base design which can be combined with several different payloads. Specifically for this Cubesat platform bus, novel nanosat electronics has been designed consisting of a Payload Data Acquisition Unit (PDAU) and an Electronic Power Supply (EPS) module. The payload for the PEASSS satellite consists of a pyro power generator and a smart structure. The smart structure is a combination of several advanced technologies that together are used to demonstrate the ability to change the tilting angle of a sensor. For demonstration a sun-sensor has been selected that measures that angle of the sun-sensor body with respect to the sun. In order to measure the tilting angle, a second sun-sensor is added on a fixed location of the satellite such that the sun-sensor readings can be compared to determine the tilting angle achieved by the smart structure. Tilting of the sun-sensor by means of the smart structure (also referred to as Optical Bench) is performed by 2 piezo bimorph actuators mounted orthogonally that move a ring and an inner disc in a gimbal setup. The smart panel is made from Carbon Fiber Reinforced Polymer (CFRP) to provide both a lightweight structure and sufficient stiffness.

Figure 1, Design drawing of the Smart Structure with a fixed sun-sensor and a second sun-sensor mounted on a gimballed structure that can be tilted by means of 2 piezo bimorph actuators located at the back side of the panel

The tilting angle measurement by means of the 2 sun-sensors is used as a reference measurement. The objective is to be able to tilt any kind of sensor on the gimballed platform to a pre-defined angle. The piezo actuators used however show a hysteresis effect which makes forward control difficult. Therefore strain is measured on the surface of these piezo beams which makes feed-back control possible to cancel out the piezo hysteresis. Strain is not measured by means of traditional resistive strain gauges but by means of Fiber Bragg Gratings (FBG’s). The use of FBG’s is especially attractive because a single fiber can be used for several strain measurements at different locations which significantly reduces the number of wires of fibers. This beneficial characteristic is used in the PEASSS satellite because a single fiber runs over both piezo beams as presented in the next figure. Actually two fibers are used to measure strain on both the front- and the back side of the piezo beams. This measurement on the front- and the back side of the piezo beam makes it possible to perform a differential measurement which cancels out the sensitivity of FBG’s to temperature change. This temperature sensitivity of FBG’s is however also used to demonstrate the use as a temperature sensor.

Measurement of temperature or strain by means of FBG’s is attractive because a tiny fiber can be used instead of numerous electrical wires. Compared to an electrical measurement, an optical measurement is also not sensitive to EM interference. The drawback is that a rather complex interrogator is necessary to be able to measure the wave length of the FBG’s and to convert this into temperature or strain. For the PEASSS satellite a new interrogator has been designed and build that fits in the limited dimensions available within the cubesat and that is also compatible with the space environment and the vibration loads that occur during launch. Compatibility with the space environment means for instance that all components have to operate in vacuum which also includes a different thermal environment without convection. The dimensions of the interrogator are 110 x 50 x 40 mm.

Figure 3, space compatible miniature interrogator (110 x 50 x 40 mm aluminum box) mounted in a test frame. The back side of the smart panel mounted in a separate test frame is also visible

The pointing mechanism of the smart panel in which thin piezo beams are used, is quite a delicate structure. The violent vibrations during launch would destroy these parts unless they are protected by a launch-lock. An innovative launch-lock was designed that secured the position of the gimballed ring and disc by means of Shape Memory Alloy (SMA) beam. In space the launch-lock was released by applying electric power to a heating wire wound around the SMA beam. The temperature rise then makes that the SMA beam returns to its pre-programmed S-shape which frees the ring and disc for tilting.

Figure 4, launch-lock for the smart panel based on an SMA beam that blocks the gimballed ring and disc during launch (left). When heated the SMA beam returns to its pre-programmed S-shape releasing the lock (right)

Figure 5, flight ready PEASSS satellite with visible in the left picture the 2 sun-sensors and in the right picture the 2 black pyro power generator elements
When in-orbit first the launch-lock of the smart panel was successfully released, followed by the execution of several experiments during which the sun-sensor mounted on the smart panel was tilted over 2 orthogonal rotation axis. Actuation of the smart panel was performed by adjusting the voltage on the 2 piezo beams between -200 and +200 Volt. The resulting strain on the piezo beams was measured by the FBG strain sensors and a classical resistive strain gauge for reference purposes. The resulting tilting angle was measured by comparison of the readings from the fixed and the tilting sun-sensors which required that the experiment was performed with the sun in the field of view of the sun-sensors. It was demonstrated that the sun-sensor could be tilted in micro steps over both orthogonal tilting angles over a range of more than 1 degree.
In-orbit also the performance of the pyro power generator was assessed. The pyro power generator consists of 2 sets of piezo plates which are embedded in an aluminum tray by means of an epoxy filler. Temperature changes applied to the pyro power generator result in the generation of electrical power. The generated electrical power is determined by measuring the generated voltage over a connected load resistor. Laboratory tests during the development showed that the generated power is a function of the rate of the temperature change. This effect was confirmed in space where temperature changes were the result of the slow tumbling of the satellite and the eclipse when the satellite moves into the shadow of the earth during every orbit of about 100 minutes. The figure below shows the effect of these cycles on the temperature of the solar panels which are located on all sides of the satellite. It was demonstrated that electric power can be generated from temperature changes by means of a pyro power generator. The actual power level was relatively low but it is expected that this can be raised in the future by an improved design and tuning of / to the rate of change of the temperature.

Figure 6, measured temperature of the solar panels on the satellite sides: x, y and z of the satellite (p and n side) as a function of time. The graph shows the slow temperature change resulting from the eclipse in the ~100 minute orbit cycle and the faster temperature changes related to tumbling of the satellite.

The temperature change is as described an important aspect for the performance of the pyro power generator. Temperature is in general of great importance for a satellite due to the extremes that can occur in space resulting from solar illumination on one side and exposure to the cold deep space off the opposite side. The thermal design of the satellite has to be such that the components of the satellite operate in their respective applicable temperature ranges. For the PEASSS satellite the most critical component in that respect is the light source within the interrogator which has to be within +15 to +25 degC for optimal performance. Compared to the bigger satellites, in general much less attention is given to the thermal design of the cubesats. During the design of the PEASSS satellite however a dedicated task was reserved for thermal modelling. During the Bread Board test measurements were performed in a thermal vacuum test facility to validate the thermal model. Finally the temperature measurements gathered during operation in-orbit were again compared with the model predictions. The resulting errors were in line with the maturity of the model and showed the value of thermal modelling for cubesats.
The technologies demonstrated in the payloads made use of the cubesat satellite platform. Most of the components of this cubesat were previously demonstrated in other space missions. However part of the PEASSS project was the design of novel nanosat electronics for this cubesat platform bus. Two modules were designed and build: a Payload Data Acquisition Unit (PDAU) and an Electronic Power Supply (EPS) module. The EPS is an essential part of the satellite because it provides a stable bus voltage for all other components. Electric power is received from the solar panels and is stored in batteries such that the satellite can also operate during the eclipse periods when the satellite is in the shadow of the earth. In order to operate the solar panels at maximum efficiency, the EPS is equipped with a Maximum Power Point Tracker. This more complex system compared to the systems used in conventional satellites provide optimal use of the available solar panel area especially at the end of life phase. The use of batteries in a satellite is of course attractive to keep it operational during eclipse but also introduces a number of challenges. For protection and in order to guaranty the required number of charge/discharge cycles, the batteries have to be ‘managed’ by the EPS which includes current and voltage control and cell balancing. The new EPS in combination with solar panels and batteries was extensively tested during on-ground tests. After launch the EPS functioned flawlessly in space and provided the bases for the correct operation of all other components of the satellite.
The Payload Data Acquisition Unit (PDAU) developed for the PEASSS project proofed to be a valuable component between the On Board Computer (OBC) and the different payloads. This way the OBC can be offloaded from the payload specific processing tasks that are different for each mission. The OBC software can be kept more generic which improves reliability and reduces risk. In the PEASSS mission the newly developed PDAU proved its advantage by the ease of programming the different tilting experiments that were performed with the piezo actuated smart panel.

Figure 7, Generic Cubesat Payload Data Acquisition Unit (PDAU) developed for offloading the On Board Computer (OBC) from payload specific processing tasks.

Potential Impact:
Potential impact
European space objectives include Earth Observation to monitor the health of the planet and the impacts of human activities, which is increasingly important in this time of climate change and growing industrialization, farming, mining, smuggling, terrorism, illegal immigration, etc. In addition, Europe seeks to stay on the cutting edge of space technology, both for the intrinsic benefits that technology offers in space as well as the benefits generated by the introduction of next generation technologies into the broader economic base.

Technological impact
The technologies that will be developed in the PEASSS project directly enable European space observation and in-space activities. The project will create a cutting edge technology based on piezo actuated smart composite panels, which can improve the accuracy and stability of nearly all Earth Observation sensor platforms.
The improved pointing accuracy and potential for reduction of mechanical noise stands to improve all types of observations, from environmental and planetary mapping to border and regional observation. Furthermore, the project will advance alternative power generation in space, which stands to enable distributed sensor networks and other next generation space technologies.
In addition, this new technology will help keep Europe on the cutting edge of space research, potentially improving the cost and development time for more accurate sensor platforms. Likewise, this new "smart structure" technology may provide positive economic impacts to other industries, such as its utilisation to reduce noise and related fatigue in future aircraft composites.

Impact on competitiveness of Proposers
The technologies developed in this program will put the partner companies in the forefront of new technologies dealing with "smart structures" and innovative pointing and power generation techniques. The use of piezoelectric technology will increase the competitiveness of the proposers since it puts them ahead of the current state of the art in accurate control and sensing systems.

European Impact
• Related European Research
The development of more stable platforms with FBG sensor systems adds value for Europe by potentially improving all sensing platforms. The developments expected in the PEASSS project, including space qualification of a miniaturized FBG interrogator and embedment of FBG fibres into smart composites, will help lay the groundwork for further development and utilisation of these cutting edge sensors.
• Aviation
Aerospace applications of Aerodynamic structures where warping and changing of angles are part of flight will also benefit from PEASSS technologies. For example, wingtips, helicopter blades and rudders face natural warping which can be counteracted by piezo-actuated composites. The embedded, lightweight FBG sensor system can further enable these applications. In addition, PEASSS smart materials could sense icing conditions on composite airplane wing structures, and actuate vibration of the wing surface for de-icing. Use of smart composites can also be used to reduce drag, by forming smoother and continuous aerodynamic surfaces. This technology stands to make a significant impact to the Aeronautics industry, especially as the role of composites grows, reducing the need for mass and power consuming moving surfaces and drive motors.
• International competition / cooperation
The benefits of PEASSS smart composite technology can lead Europe to an advantage in Earth and other International space missions. In addition, Europe could be a step advanced to other nations in "smart structures" actuation design and implementation.
Reaching the market with space-proven products based on composites embedded with piezoelectric actuators and FBG sensors will give ESA and Europe a competitive advantage, since it will take the competitors three to five years to reach the level of confidence the proposers shall have in using piezoelectric technology in space in the PEASSS project. Europe, through the PEASSS project, can become the world leader in this field and thus be at the cutting edge of new technologies, potentially leading to participation and sub-contracting with many ESA, NASA, and other agency missions around the world. ESA future missions of deep space planetary observation and telescopes will benefit widely from this technology, giving Europe a technology-hub role in the areas of smart structures and imaging optic benches.
• Lower cost mission solutions
New innovative technologies for lowering mass, volume and cost are in need. Smaller satellites and reduced need for thermal and/or pointing systems will reduce mass and thus project costs dramatically (launch costs will be significantly lower). With PEASSS, such technologies include smart piezoelectric structure that can improve imaging accuracy, reduce the need for motors to tilt surfaces and generate power.
By enabling continuing and lower cost Earth Observation satellites, the PEASSS Technologies have the potential to broaden environmental monitoring. The development of PEASSS Technologies will provide ITAR-free, European developed, game-changing technologies in the areas of satellite instrument pointing and power generation. The specific application of these technologies to nanosatellites enables more advanced functions on smaller, lower-cost platforms, enabling Europe to continue to develop new Earth Observation Platforms with lower budgets and financial risk. The project creates European non-dependent solutions to improved Earth Observation platforms.
List of Websites:
project website: www.peasss.eu
project coordinator: Han Oosterling
TNO, Stieltjesweg 1
2628 CK Delft
han.oosterling@tno.nl
tel +31 888665582

Final Report Summary - PEASSS (Piezoelectric Assisted Smart Satellite Structure)

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