Final Design Report: MEP - Senior Projects 1: Design Synthesis | ASEN 4018, Study Guides, Projects, Research of Aerospace Engineering

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Martian Environment Pod 0 Final Design Report MEP (Martian Environmental Pod) Final Design Report Fall 2003 Aerospace Engineering Department University of Colorado-Boulder ASEN 4018 Ball, James Stemler, Sara Sullivan, Tod September 8, 2005 Martian Environment Pod 1 Final Design Report Table of Contents Table of Contents .............................................................................................................. 1 List of Figures.................................................................................................................... 3 List of Tables ..................................................................................................................... 4 List of Acronyms ............................................................................................................... 5 1.0 Project Objectives and Requirements................................................................. 6 1.1 Background ........................................................................................................ 6 1.2 Objective ............................................................................................................. 6 1.3 Requirements...................................................................................................... 6 2.0 Development and Assessment of Design Alternatives ....................................... 6 2.1 Thermal Control................................................................................................. 6 2.2 Greenhouse Structure ............................................................................................ 9 2.3 Electronics ............................................................................................................ 12 3.0 Design-To Specifications .................................................................................... 13 3.1 Thermal Shield................................................................................................. 13 3.2 Greenhouse Structure ...................................................................................... 14 3.3 Electrical System .............................................................................................. 15 4.0 System Architecture............................................................................................ 15 4.1 Descoping the Project .......................................................................................... 15 4.2 Overview of Requirements ................................................................................... 15 4.3 System Design ...................................................................................................... 16 5.0 Mechanical Design Elements ............................................................................. 17 5.1 Thermal Shield..................................................................................................... 17 5.2 Mounting Box ...................................................................................................... 21 5.3 Electronics Box .................................................................................................... 22 5.4 Drawing Tree........................................................................................................ 22 5.5 Greenhouse Structure .......................................................................................... 24 6.0 Electrical Design Elements................................................................................. 28 6.1 Power System.................................................................................................... 28 6.2 Sensors.............................................................................................................. 29 6.2.1 Temperature Sensor .................................................................................. 29 6.2.2 Pressure Sensor ........................................................................................ 29 6.3 Thermal Actuation ........................................................................................... 30 6.3.1 DC Motor .................................................................................................. 30 6.3.2 Limit Switch .............................................................................................. 30 6.3.3 Relay ......................................................................................................... 30 6.3.4 Solar Panel................................................................................................ 30 6.3.5 Overall Integration ................................................................................... 30 6.4 Pressure Control .............................................................................................. 31 6.5 Electronics Integration .................................................................................... 31 6.6 Power Analysis ................................................................................................. 32 6.7 Noise Analysis .................................................................................................. 33 7.0 Software Design Elements .................................................................................. 33 8.0 Integration Plan .................................................................................................. 34 8.1 Thermal Shield................................................................................................. 34 Martian Environment Pod 4 Final Design Report List of Tables Table 1 - Heat Sources ........................................................................................................ 7 Table 2 - Phase Change Materials ...................................................................................... 7 Table 3 - Thermal Shields................................................................................................... 8 Table 4 - Petal Materials ..................................................................................................... 8 Table 5 - Actuation Systems ............................................................................................... 9 Table 6 - Transmittance and Tensile Strength .................................................................. 10 Table 7 - Cost and Density Analysis................................................................................. 10 Table 8 - Greenhouse Material Trade Study..................................................................... 11 Table 9 - Pressure Valve Trade Study .............................................................................. 11 Table 10 - Temperature Trade Study................................................................................ 12 Table 11 - Pressure Sensor Trade Study........................................................................... 13 Table 12 - Data Acquisition Trade Study ......................................................................... 13 Table 13 - Drawing Tree................................................................................................... 22 Table 14 - Mass and Cost Distribution ............................................................................. 28 Table 15 - Cost and Mass Distribution ............................................................................. 32 Table 16 - Power Consumption ........................................................................................ 32 Table 17 - S/N Analysis.................................................................................................... 33 Martian Environment Pod 5 Final Design Report List of Acronyms AC – Alternating current ACH – Analog channel CCW – Counter clockwise CW – Clockwise CPU – Central processing unit DC – Direct current DIO – Digital input output DOF – Degrees of freedom EMC – Elastic Memory Composite MAAC – Mars Atmospheric Acquisition and Compression PCM – Phase Change Material SMA – Shape Memory Alloys S/N – Signal to noise ration WBS – Work breakdown structure Martian Environment Pod 6 Final Design Report 1.0 Project Objectives and Requirements 1.1 Background Mars is the fourth planet from the sun. The conditions on Mars vary greatly from the conditions on Earth. The average temperature on Mars is -65° Celsius. A day on Mars is 24 hours and 37 minutes, with a year lasting 687 days. The seasons are similar to Earth’s but are approximately twice as long. The amount of solar radiation falling on Mars is approximately 0.4 that of Earth per square meter. Due to the dust storms on the surface, much less solar radiation can occur. The atmospheric pressure on Mars is 0.1 kPa, which is insufficient for sustaining life. The first step to inhabiting Mars is the understanding of the possibilities of life on the planet. The CO2 content on the planet makes it uninhabitable for humans, but plant life can be sustained with controlled conditions. Plant life on Mars would need a higher temperature, higher pressure, high humidity, high nutrient source, and better growth medium than available on the surface. A miniature greenhouse could be proposed to fly abroad a Mars Lander in the next 5-10 years. The proposed greenhouse can act as the source of the fundamental requirements for the plant life on Mars. The greenhouse would be able to control temperature, pressure, humidity, nutrients, and a platform for the plants to grow. The greenhouse would house Arabidopsis plants and maintain a suitable environment for their survival and growth. 1.2 Objective The overall objective of the proposed project is to conceive, design, fabricate, integrate, test and verify a deployable greenhouse for a robotic Mars Lander. 1.3 Requirements Using an existing Mars Lander, the Beagle 2, design requirements are defined according to the Beagle 2’s available resources. The Beagle 2 Mars Lander can accommodate experiments not exceeding 25” in length, 25” in width, 10” in height, and 3.5 kg (~7.72 lbs) in mass. The Beagle 2 has an on-board power supply, providing 30 W-hrs during the day and 16 W-hrs during the night. There is a gas supply of CO2 that is provided by another on-board experiment, the Mars Atmospheric Acquisition and Compression. The Martian Environmental Pod will be capable of housing an Arabidopsis plant that needs to be sustained for 6 weeks, the life span of the plant, and be maintained at a pressure of 10 - 50 kPa. The internal temperature of the greenhouse must be sustained at a temperature range of 15 - 25° C. The structure will be compact and deployable for transport and will inflate to create a closed system. For operation and inflation, the MEP will use an outside power source and gas supply for testing because that would be provided by the Mars Lander and MAAC experiment. 2.0 Development and Assessment of Design Alternatives The initial requirements break down the project into three subsystems, the greenhouse structure, which includes the pressure system, the thermal controls, and the electronics, which includes actuation and data acquisition. 2.1 Thermal Control Considering the temperature can drop to –65° C at night on the Martian surface, there needs to be an ample supply of heat to sustain the desired temperature range. Heaters, solar radiation, and insulation are outlined in the trade study below, Table 1, to help maintain the range of 15 - 25° C inside the greenhouse. Martian Environment Pod 9 Final Design Report Table 5 - Actuation Systems Paraffin actuators use heat from the surrounding environment and convert it to linear work. The paraffin within the actuator solidifies once the environment’s temperature drops below the actuation temperature and a piston provides a force up to 500 lbs. Because of the many different compositions of paraffin, an actuation temperature can be selected between –70 - 80° C. Shape memory alloys rely on electric current to actuate and only have a stroke length of 4 - 5% of the total length of the wire, which is not enough elongation for how far the petals need to rotate. The mechanical system would be integrated into an actuation system the same way the paraffin actuator would but would consume power. Taking into consideration all properties, the paraffin actuator offers passive actuation at the desired actuation temperature and is selected for the thermal shield actuation system. 2.2 Greenhouse Structure The main factors taken into account in the design of the green house enclosure were the customer requirements, mass, transmissivity, delta pressure, size and strength. Due to customer requirements it was decided that the enclosure be inflatable. This balloon-like enclosure needs to be strong enough to withstand stress created by a difference in pressure of 50 kPa between the inside and outside of the enclosure while allowing as much visible light to enter its walls as possible. The design parameters that most directly determine this design are the selection of materials and structural configuration. For the materials, many thin transparent films were considered. The two main groups of films were urethanes and polyamides. Polyamides were chosen over urethanes due to their optical properties. Polyamides allow a good amount of visible light to pass through them while not allowing potentially harmful UV light to pass. Urethanes do not have this beneficial characteristic. Among the polyamides looked at were Kapton, LaRC-CP1 and CP2, Teflon, and TOR-LM. These materials were compared by their densities, relative costs, tensile strengths and their transmittance. Table 6 and Table 7 below are the tables that summarize these properties. - Weight = 0.071 oz $3.99 0.39 W ------ ~1 sec infinite Mechanical RadioShack SR-3 Motor - Two-way SMA’s do not allow for enough elongation. $7.50/m 5.25 W 60-110°C 1 sec 4-5% of total length Shape Memory Alloy Flexinol d = 0.012” - Passive actuation $3000 0 W -70-80°C 300 secs 1.5” Paraffin Starsys IH-50125 Comments Cost Power Consumption Actuation Temp Actuation Time Stroke Length Martian Environment Pod 10 Final Design Report Table 6 - Transmittance and Tensile Strength Table 7 - Cost and Density Analysis LaRC-CP1 and CP2 had adequate mechanical properties and excellent optical properties while their costs were extremely high. Teflon and TOR did not have as good of mechanical properties as Kapton and LaRC. Kapton was chosen because of its good mechanical properties and its affordable price. The trade study in Table 8 summarizes the positives and drawbacks of each material. Martian Environment Pod 11 Final Design Report Table 8 - Greenhouse Material Trade Study The structural configurations considered included a sphere, hemisphere, cone, cylinder, box and pyramid. The two configurations that were given most consideration were the sphere and the full cylinder. These configurations were given the most consideration due to their high ratios of internal volume to external surface area, which reduces convection, and because thin walled pressure vessels of these shapes have relatively even distribution of stress in the walls of the materials. The sphere was chosen because it has a higher volume to surface area ratio and its stress distribution was more even. To maintain the delta pressure of 10 -50 kPa, it was decided that there needs to be a valve to control the flow of air into the structure and a relief valve to assure that if the inflow valve does not shut off at the right time, pressure can still be released. The control valves considered were the micro-valves by the Lee Company. Characteristics considered were the power consumption, the dispense rate, and the weight. Price was not considered since the most expensive valve micro- valve is in the range of $60. It was decided that the simplest configuration, which was a non- latching 2-way solenoid valve, would suffice. The trade study in Table 9 summarizes the properties relevant to the project of the different valves. Table 9 - Pressure Valve Trade Study Martian Environment Pod 14 Final Design Report The overall configuration for the thermal shield is depicted in Figure 1, with phase change material placed inside of the greenhouse and the thermal shield closing at dusk and opening at dawn. Figure 1 - Thermal Control System The petals are cast into the petal shape using elastic memory composites (EMC), a carbon fiber with memory polymer. In order to heat the petal above it glass transition temperature, nichrome wires that are cast into a fiberglass sheet are cast into and throughout the EMC. When a power of 10 W is supplied to the nichrome wires, the EMC becomes flexible and can be rolled down for storage and flight. Once the system is on Mars and ready for deployment, the necessary power is supplied to the nichrome wires and the petals return to their original cast shape. The actuation system is engaged using the paraffin actuator as the driver. The system incorporates the actuator with a gear drive that moves every petal at the same rate at the same time. This gear drive system will be mounted below the greenhouse while the paraffin actuator is inside the greenhouse. Phase change materials are contained within small packages in the bottom of the greenhouse. They act as a buffer for heat transfer, storing extra energy acquired during the day and giving off that energy when needed at night. 3.2 Greenhouse Structure The performance parameters which drive the design of the greenhouse are mass, strength, size, heat transfer characteristics and transmittance. The shape that was chosen is the sphere because of its high internal volume to surface area ratio and the even distribution of stress with the walls of the enclosure. Things that will need to be purchased are the uncoated Kapton and the DP105 epoxy. The ring will make it possible for the enclosure to be removed for maintenance or anything else that will require removal of the enclosure. The ring will fit inside the bottom of the enclosure and glued with epoxy. The rubber O-ring is meant to eliminate leakage between the ring and the thermal control structure and will be the exact same size of as the ring but half as thick. Martian Environment Pod 15 Final Design Report The control valve must have low power consumption in order to meet the daily power allotment and must be small enough to fit inside the thermal control structure without interfering with any of the other systems. It must also be capable of maintaining the delta pressure. The valve that will be purchased is the LIF series 2-way solenoid valve from the Lee Company. The relief valve needs to crack at a pressure above the required delta pressure but below the pressure that will cause the greenhouse to rupture. For this the CCPI5510069S check valve by the Lee Company, which cracks at 69 kPa, will be purchased. 3.3 Electrical System Given the pressure range of inside of the greenhouse a sensor was needed that could span the range of 50 kPa. Also, because of the feedback response for the control valve the time response had to be at least 5 ms and a resolution of at least 1 kPa. The power consumption limit constituted the choice of pressure sensor will low power consumption. The Omega PX139 was selected because its specifications met all of the design requirements. The PX139 has a resolution of 0.5 kPa, a time response of 2 - 3 ms, and a power consumption of only 0.01 W. The required temperature range for the system is 15 to 25 °C. The resolution required is 0.5 °C. Due to the fact that the temperature is only for data acquisition and is not in a feedback loop the time constants only need to be at least 15 s. The Omega 44000 series thermistor was chosen because it meets those specifications. The 44000 series thermistor has a time constant of 10 s, a power consumption of 0.0075 W, and a resolution of 0.1 °C. The calculated torque was 367 oz-in. The DC motor was selected based upon the torque rating, power consumption, mass, and size. The Faulhaber 2342-006CR with a 23/1 989:1 planetary gearbox was chosen because it meets all of the criteria. The motor meets the required torque while only consuming 6.25 W of power. The total mass of the motor is only 0.45 lbs. 4.0 System Architecture 4.1 Descoping the Project After assessing the work required for a passive actuation system and maintaining the temperature inside the greenhouse at a desired range, it was concluded that the project needed to be scaled back. The initial requirement of maintaining the temperature inside the greenhouse at 15 - 25° C was adjusted to requiring the system to monitor the temperature inside the greenhouse and retard the heat loss at night. With this change in the requirements, the thermal shielding system was reduced to one DOF from two DOF, simplifying the design of the actuation system. Although a paraffin actuator would provide a passive actuation, the cost and complexity of incorporating it into the design is too great. Therefore, the thermal shield will be actuated using a mechanical system, including a motor and shaft. Since the temperature does not need to be sustained around room temperature, the phase change materials are no longer necessary. The “flower configuration” for the structure of the thermal shield was originally considered because it offered the option of reflectors for concentrating light. Seeing as the light concentration is not a requirement for the system, the configuration for the structure was redesigned. In order to fit the MEP in the Mars Lander, the greenhouse shape was changed from a sphere to a cylinder. 4.2 Overview of Requirements The Martian Environmental Pod will be capable of housing an Arabidopsis plant that needs to be sustained for 6 weeks, the life span of the plant, and be maintained at a pressure of 10 - 50 kPa. The internal temperature of the greenhouse will be monitored and heat loss will be reduced. The structure will be compact and deployable for transport and will inflate to create a closed system. For operation and inflation, the MEP will use an outside power source and gas supply for testing because that would be provided by the Mars Lander and MAAC experiment. Martian Environment Pod 16 Final Design Report 4.3 System Design The overall system design includes the greenhouse structure, the thermal shielding, and the electronics package. The overall architecture includes the main platform which everything is mounted to, a mounting box on top of the platform for the greenhouse, a bottom box for the electronics package and the motor, and the thermal shielding petals. Because the MEP will be transported on-board a Mars Lander, the system must have a compact configuration for flight, a deployed configuration for the daytime, and a fully deployed configuration for night. In Figure 2, the stowed system for flight and daytime configuration are depicted. Figure 2 - Stowed System The SolidWorks model accurately depicts the configuration during the day when the thermal shield is open. To accurately depict the flight configuration, the greenhouse would be deflated. Figure 3 depicts the MEP fully deployed at night. Martian Environment Pod 19 Final Design Report Figure 5 - Torque Analysis The total torque produced by the petals on the axle was calculated to be 367 oz-in, meaning the motor is sized to the torque required. Using the shear stress equation, the diameter of the axle needs to be greater than 0.083”. A diameter of 0.25” is chosen for the diameter of the axle due to availability, offering a safety factor of three. By calculating the polar moment of inertia for a hollow axle versus a solid axle, a hollow axle was chosen because it lower stress and less weight. In order to reduce the torque needed from the motor, a set of two gears with a ratio of 4:1 is integrated to quarter the torque necessary to actuate the petals. A 2” diameter gear is fixed to the center of the axle and a 0.25” diameter gear is fixed on the gear shaft. The thermal shield is the structural backbone for the entire system. It consists of the platform, axle, gear drive, and ten petals varying in size. All subassemblies are mounted to the platform and it is constructed from 0.096” thick acrylic. The following figure, Figure 6, shows the platform with axle mounts fixed on either side. Figure 6 - Platform Limit Switch Mounting Box Gear Electronics Box Axle Mount Motor Mount Martian Environment Pod 20 Final Design Report The thermal shielding petals are all placed along the axle with a 2” diameter gear secured in the center of the axle. The gear passes through a slot in the middle of the platform with the axle supported by the axle mounts. Each petal varies dimensionally but is scaled to the same design so that they store within each other. The outer most petal (Petal 1), which pulls the subsequent petal during actuation in both directions and hits the limit switch to stop the motor during deployment of the shielding, is depicted in Figure 7. Figure 7 - Petal 1 Petal 1 is fixed to the axle for rotation while the remaining nine petals are free to rotate about the axle. When the motor begins rotating, Petal 1 moves with the axle whereas each subsequent petal is caught by the tabs running the width of the petals. Upon retraction, tabs’ running along the length of Petal 1 catches all petals as the axle rotates in the reverse direction. The motor is mounted below the main platform and using two gears, the rotation of the motor is translated to the axial motion to actuate the retractable structure. The petals vary in length from 7.5”-14.25” at 0.75” intervals and vary in width from 6.5”-8.3” at 0.2” intervals. The inner most petal (Petal 10) is shown below in Figure 8 and has a limit switch tab to stop the motor during retraction of the thermal shield. Figure 8 - Petal 10 Figure 9 shows the full assembly of all ten petals with the gear secured on the axle and the axle fixed to the outer most petal. The tolerance in the width direction is 0.04”, allowing room for rotation and the tolerance in the lengthwise direction is approximately 0.15”. Martian Environment Pod 21 Final Design Report Figure 9 - Full Petal Assembly 5.2 Mounting Box Figure 10 shows the mounting box for the greenhouse. Figure 10 - Mounting Box Once the greenhouse enclosure is constructed, it is fixed to a mounting ring that screws into the mounting box. The greenhouse and mounting ring are screwed into the mounting box from underneath. This mounting box also allows for the check valve to be inside the greenhouse and the thermistor, pressure sensor, and gas line to run up into the greenhouse from the lower electronics box. The tabs are located on the outside of the box to allow for easy access during testing. The small openings on the side of the box are for the axle to run through. Martian Environment Pod 24 Final Design Report MEP-021210 Cap 9 1 Make MEP-021220 Petal Side 9 2 Make MEP-021230 Top Tab 9 1 Make MEP-021240 Bottom Tab 9 1 Make MEP-021300 Assembly, Petal 10 1 Make MEP-021310 Cap 10 1 Make MEP-021320 Petal Side 10 2 Make MEP-021330 Top Tab 10 1 Make MEP-021340 Switch Tab 10 1 Make MEP-021350 Bottom Tab 10 1 Make MEP-030000 Assembly, Electronics Box 1 Make MEP-030100 Assembly, Box 1 Make MEP-030110 Bottom Plate 1 Make MEP-030120 Assembly, Box Ring 1 Make MEP-030121 Plate, Side, Lengthwise 2 Make MEP-030122 Plate, Side, Widthwise 2 Make MEP-030123 Bottom Box Tab 4 Make MEP-030200 Assembly, Electronics Package 1 Make MEP-030210 Assembly, Circuit 1 Make MEP-030211 Relay Switch 1 Buy MEP-030212 Resistor 3 Buy MEP-030220 Pressure Valve 1 Buy MEP-030230 Pressure Sensor 1 Buy MEP-030240 Thermistor 1 Buy MEP-040000 Assembly, Mounting Box 1 Make MEP-040100 Plate, Side, Axle Opening 2 Make MEP-040200 Plate, Side 2 Make MEP-040300 Plate, Top 1 Make MEP-040400 Tab 8 Make MEP-040500 Check Valve 1 Buy 5.5 Greenhouse Structure The enclosure will be a cylinder made out of Kapton with one open end. It was decided since PDR that this enclosure be a cylinder. Even though a sphere has a high volume-to-surface area ratio, it was decided that the cylinder it be more practical to manufacture and its inflated size would be more narrow. Therefore, it would be easier to cover with a thermal shield. However, the objectives have not changed since PDR and are that the greenhouse must be large enough to house one Arabidopsis plant but no larger to reduce mass, and strong enough to withstand a delta pressure of 50 kPa. Martian Environment Pod 25 Final Design Report Figure 12 - Greenhouse Stress Analysis Figure 12 shows how the longitudinal and hoop stress change in a thin-walled cylindrical pressure vessel as the internal pressure increases. The following equations were used to make these graphs: Eq.1 Eq.2 For cylindrical pressure vessel eight inches tall, six inches in diameter and with a wall thickness of 5 mil,, the longitudinal stress is 15 MPa and the hoop stress is 30 MPa. These stresses are well below the tensile stress of Kapton which is 165 MPa. This enclosure will be a cylinder 8 inches tall, 6 inches in diameter and its walls will be 5 mil (127 µm) thick. It will be constructed out of Kapton and glued together using 3M DP105, which is an industrial grade epoxy. The cylinder will be achieved by taking a rectangular piece of Kapton and rapping it around so that it forms a hollow cylinder. A circular piece of Kapton will then be glued to one end of the cylinder using DP105. This assembly is shown in Figure 13. MPa t MPa t t l 30 Pr 15 2 Pr == == σ σ Martian Environment Pod 26 Final Design Report Figure 13 - Greenhouse Enclosure The mounting hardware will include an acrylic ring that will be glued with epoxy inside the open end of the ring, and a rubber o-ring to be placed between the acrylic ring and the thermal structure to prevent leaks. The ring and o-ring are shown in Figure 14. Figure 14 - Acrylic Ring and Rubber O-ring The acrylic ring will be mounted inside the open end of this enclosure and bonded there using DP105 epoxy. The Kapton will be slightly wrapped around the bottom of the ring for increased bond strength. This is shown in Figure 15. Figure 15 - Ring Enclosure Assembly The acrylic ring, as well as the rubber o-ring will have four screw holes each and each screw hole will be about 0.3 inches in diameter and will be placed evenly around the rings. The rubber o-ring will be placed in between the acrylic ring and the thermal control structure. The screws will fasten from below the thermal control structure up through the o-ring and will thread into the acrylic ring. The screws can not pass all the way through the acrylic ring or else they pose the threat of puncturing the Kapton. Martian Environment Pod 29 Final Design Report 6.2 Sensors 6.2.1 Temperature Sensor The Omega 44000 series thermistor will be connected in series with 1000 Ohm resistor. A 5 V power supply will be supplied to the thermistor. Figure 19 shows the wiring diagram of the temperature sensor. The voltage drop across the thermistor will be measured and used to calculate the temperature. The thermistor will be located inside of the greenhouse. The thermistor will provide a resolution of 0.1 °C. Figure 19 - Thermistor Wiring Diagram 6.2.2 Pressure Sensor The Omega PX139 differential pressure sensor will measure the pressure difference between the outside air and the air inside of the greenhouse. The pressure sensor will be powered by a 5 V power supply. Figure 20 below shows the wiring diagram of the pressure sensor. Figure 20 - Pressure Sensor Wiring Diagram The voltage output will be connected to the BNC terminal block using a BNC connector. The output spans from 0.25 V to 4.25 V. A silicone tube will connect the pressure sensor to the inside of the greenhouse. The pressure sensor will provide a resolution of 0.5 kPa. Martian Environment Pod 30 Final Design Report 6.3 Thermal Actuation 6.3.1 DC Motor The Faulhaber 2342-006CR with 23/1 989:1 planetary gearbox will actuate the thermal shield. A 5 V power supply will be connected to the motor through a relay switch. The motor will draw a maximum current of 2 A. The motor is capable of providing the required torque. The wiring of the thermal actuation system will be discussed in section 6.3.2 Limit Switch Two limit switches will be used to stop the motor. The limit switches are rated to a maximum current draw of 3 A. The limit switches are normal closed and are momentary push button switches. This provides an open circuit when pressure is applied to the perspective switch. 6.3.3 Relay The Potter & Brumfield R10E1Y2S200 DPDT relay will reverse the polarity on the motor. The relay is rated to a current of 2 A. The coil is actuated by a 5 V supply from a solar panel acting as a sun sensor. 6.3.4 Solar Panel The solar panel from Solar World will supply a voltage of 5 V when in the sun. This 5 V actuates the coil of the relay. The panel will be hard wired to the relay. 6.3.5 Overall Integration The thermal actuation is a complex integration between the DC motor, limit switch, relay and solar panel. Figure 21 below shows the flow chart of the wiring. Figure 21 - Thermal Actuation Overview Martian Environment Pod 31 Final Design Report The DC motor is connect to two circuit; one 5 V circuit and the other -5 V. The relay is the switch between each circuit. The DC motor remains connected to the circuit until the relay is actuated. This occurs at the transition from day to night and night to day, based upon the sun sensor. The limit switch prevent the continue operation of the motor. They act as a break in the circuit when the thermal shield hits the switch. The power to the motor is supplied from the same power supply as the sensors, the Tektronix PS280. 6.4 Pressure Control The pressure valve will be actuated by the LabView software. This valve from the Lee Company is controlled by a 5 V signal to open the valve and is normally closed. 6.5 Electronics Integration The electronic package consists of a laptop computer, pressure sensor, pressure valve, temperature sensor, thermal actuation system, and power supply. Below, Figure 22 shows the overview of the electronics integration. Figure 22 - Electronics Integration Martian Environment Pod 34 Final Design Report difference coming in on the analog channels. One channel is dedicated to the temperature sensor and the other is dedicated to the pressure sensor. The program will convert the voltage input from the thermistor’s ACH and convert it into a temperature reading. This reading will be stored to a file and then plotted versus time. The pressure sensor voltage input will be converted into a pressure value. The corresponding pressure will run through an if/then statement to control the pressure valve. If the pressure reads greater than or equal to 50 kPa the DIO signal is set to 0 V. If the pressure reads less than 50 kPa the DIO signal is set to 5 V. This process opens the valve if the pressure drops below 50 kPa and does nothing if the pressure is above 50 kPa. The data stored to a file from the pressure read out will also be plotted versus time. Figure 24 is a flow diagram of the software design. Figure 24 - LabView Flow Chart The data will be processed using a 12 bit DAQ card and a BNC terminal block will interface between the DAQ card and the electronics package. 8.0 Integration Plan 8.1 Thermal Shield Below, Figure 25 is the exploded view of the thermal shield with the parts in their initial positions. Martian Environment Pod 35 Final Design Report Figure 25 - Thermal Shield The assembly of the thermal shield begins with the petals. Each petal is assembled and then slid onto the axle on one side. The 2” diameter gear is then fixed onto the center of the axle and the remaining side of the petals is slid on. The axle mounts then secure the axle to the platform. The motor, with the 0.25” diameter gear fixed on the motor shaft, is lined up with the larger gear in the center of the platform. The motor is fastened onto the bottom of the platform and the thermal shield is complete. 8.2 Final Integration The thermal shield forms the base of the structure. The mounting box for the greenhouse is secured on top of the platform, while the electronics box is secured to the bottom of the platform. The overall assembly is shown in Figure 26. Axle Mount Motor Mounting Axle Platform 2” diameter gear Motor Thermal Martian Environment Pod 36 Final Design Report Figure 26 - Final Integration The thermal shield forms the base of the structure. The mounting box for the greenhouse is secured on top of the platform, while the electronics box is secured to the bottom of the platform. Initially, the electronics package, pressure sensor, check valve and motor are then attached to the bottom of the platform. The limit switches are placed in the holes on either end of the platform and the wiring ran back to the electronics package. The wiring is then fed through the platform and up into the greenhouse. Then, the greenhouse is attached to the mounting box and the mounting box screwed down to the platform. Once the thermistor and tubing for the pressure sensor are in place, the electronics box ring is screwed into the bottom side of the platform. After all adjustments are made to the electronics and the external power and gas supply is run through the electronics box, the bottom plate to the electronics package is screwed on. 9.0 Verification and Test Plan 9.1 Thermal Shield The testing and verification of the thermal shield includes verifying that the shield actuates, analyzing the torque produced by petals, and the rate of heat transfer at varying temperatures. 9.1.1 Structural Operation The hypothesis is that the thermal shield will open and close in approximately 10 seconds. The system will be verified through examining the opening and closing of the thermal shield system and the deployment of the petals will be timed. The test will be run in a controlled, stagnate environment, with the pressure at approximately 1.0 atm and the temperature at 22° C. The purpose of the test in to ensure that the thermal shield can open and close based on the structural design. Martian Environment Pod 39 Final Design Report 9.3.2 Verification Testing The motor circuit, pressure sensor, and temperature sensor will be tested by verification. All components will be tested prior to the integration. The motor circuit will be tested by verifying the operation of the relay, motor direction, and motor reversal. The hypothesis for the relay is when 5 V is supplied to the relay the output will be 5 V and when 0 V is supplied to the relay the output will be -5 V. The procedure for testing the relay is as follows: 1. Hook up power supply to relay. 2. Supply 5 V to coil using lab station power supply. 3. Measure output with voltmeter. 4. Check the output to verify 5 V out. 5. Supply 0 V to coil using lab station power supply. 6. Measure output with voltmeter. 7. Check the output to verify -5 V out. The hypothesis for the motor direction is when 5 V is supplied to the positive terminal the output is CW and when 5 V is supplied to the negative terminal the output is CCW. The testing procedure is as follows: 1. Hook up 5 V to positive terminal from lab station power supply. 2. Hook up ground to negative terminal. 3. Turn power on. 4. Record motor rotation. 5. Reverse terminal connection. 6. Record motor rotation. The motor reversal test is testing the integration of the relay and motor circuit. The hypothesis for the motor reversal is when 5 V is supplied to the relay coil the motor rotates CW and when -5 V is supplied to the relay the motor rotates CCW. The testing procedure is as follows: 1. Using a bread board connect 5 V to relay. 2. Connect the motor to the relay outputs. 3. Supply 5 V to the coil. 4. Record motor direction. 5. Supply 0 V to the coil. 6. Record motor direction. The pressure sensor is going to be tested prior to use to verify its functionality. The hypothesis is when the sensors is power the voltage output is 2.25 V. The procedure is as follows: 1. Supply 5 V to sensor using lab station 2. Connect sensor output to voltmeter. 3. Record output. The temperature sensor will be test prior to integration. The procedure is as follows: 1. Supply 5 V to the thermistors. 2. Using a voltmeter measure the voltage across the assembly. 3. Using the conversion from the supply calculate the air temperature. 4. Record ambient air temperature. 5. Compare to thermistors reading. 6. Place thermistors in an ice bath. 7. Measure voltage across thermistors. Martian Environment Pod 40 Final Design Report 8. Convert to temperature reading. 9. Compare the 0 °C. 10.0 Risk Assessment When calculating the leakage rate of the enclosure, it was not taken into account the bonded seems of the enclosure. It was assumed that the enclosure has no seems. There is a possibility that seems will be major source of leakage, which will cause the enclosure to lose much more gas than previously predicted. In this case, it will be necessary to increase the frequency at which the valve is opened to maintain the required pressure. This of course will increase the amount of power consumed during any given day. Originally it was planned to use a latching type control valve, which requires 5.5 milliwatts to open the valve and the valve is then kept open by a battery powered magnet until 5.5 milliwatts is applied to close the valve. To eliminate the battery powered magnet, it was decided that a non-latching type control valve will be sufficient. However, the non-latching valve requires 280 milliwatts to operate it. Right now this is considered to be a minor increase in power draw, and it is believed that it will be possible to operate this valve while staying within the daily power allotment. If in fact this takes more power than allotted for each day then the power allotment will need to be increased. Kapton is almost ideal for use as the greenhouse material. One concern is that it is very brittle and hard to work with. It has a tendency to form small pin holes that can cause leaks. If Kapton proves to be too difficult to use there is an alternative. Transparent window insulation, which can be purchased at any hardware store, will work just fine for this. It is stronger and more malleable but will not allow for as much visible light transmittance. 11.0 Project Plan 11.1 Organizational Chart The chart shown in Figure 27 outlines the projects management and subsystem allotment. Figure 27 - Organizational Chart Martian Environmental Pod Project Manager Sara Stemler Advisors Prof. Jean Koster Prof. Jim Maslanik Project Advisory Board Chief Financial Officer Tod Sullivan Webmaster Tod Sullivan Safety Engineer James Ball Electronics/ Data Acquisition Tod Sullivan Greenhouse Structure James Ball Thermal Shielding/Assembly Sara Stemler Martian Environment Pod 41 Final Design Report 11.2 Work Breakdown Structure The top level WBS is shown in Figure 28. Figure 28 - Work Breakdown Structure Martian Environment Pod 44 Final Design Report 13.0 Appendices 13.1 Omega PX139 Specifications Martian Environment Pod 45 Final Design Report 13.2 Omega 44000 Series Thermistor Specifications Thermistor Elements Compatible Instrumentation DP25-TH Panel Meter See Section M (CN3000 Series Controllers See Section P 44000 Series Thermistor Elements Individual Precision Interchangeable pas Sensors, Available +0.2°C & #0.1°C Accuracy ore ue Epoxy encapsulated, precision matched to standardized resistance temperature curves, providing predicted “ean szowe temperature accuracy based on resistance values and Jug, “BEE* tolerances shown. For Teflon® encased elements, change the middle digt to a “1°, and increase price by 518 for en 0.2°C interchangeable elements or TW a $49 for 0.1°C interchangeable elements. = Se Resistance | Maximum | Storage & Working Color Price Model @25°C ‘Working Temp. for Best Code Each Number (Ohms) Temp (°C) ‘Stability (°C) Body | End 4004 2,252 150 80 to +120 Black | Yellow | $15 202°C (44005 3,000 150 -80 to +120 ‘Black Green 15 Interchangeability | 44007 5,000 150 -80 to #120 Black | Violet | 15 OC 44006 10,000 150 20 to +120 Black | Blue 15 44008 30,000 150 20 to +120 Black | Gray 45 “44033 2,252 75 “80 to +75 ‘Grange | Grange| 22 201°C 44030 3,000 75 -80 to +75 ‘Orange | Black 22 Interchangeability | 44034 5,000 75 “80 to 475 ‘Grange | Yellow | 22 75S 44031 10,000 75 -80 to +75 ‘Grange | Brown | 22 44032 30,000 75 -80 to +75 ‘Orange | Red 2 Typical Thermometric Drift (+0.2°C Elements) ‘Operating Temp. _|10 months) 100 months oc <D.0re 0.01°C 25°C <o.0re 002°C fours | 0.20" 0.326 150°C 15°C [not recommended| Martian Environment Pod 46 Final Design Report Martian Environment Pod 49 Final Design Report 13.4 MATLAB Code for Heat Transfer Rate k_Kapton = 0.12; %Thermal conductivity of Kapton (W/m*K) k_acrylic = 0.2; %Thermal conductivity of acrylic (W/m*K) array = [ -23, 1.413, 0.0181, 1.14*10^-5, 0.724; 7, 1.271, 0.0246, 1.40*10^-5, 0.717; 17, 1.224, 0.0253, 1.48*10^-5, 0.714; 27, 1.177, 0.0261, 1.57*10^-5, 0.712; 37, 1.143, 0.0268, 1.67*10^-5, 0.711; 47, 1.110, 0.0275, 1.77*10^-5, 0.710; 57, 1.076, 0.0283, 1.86*10^-5, 0.708]; %T density conductivity viscosity Pr %K kg/m^3 W/(m*C) m^2/s %For thermal shield t_acrylic = 0.0254; %m A_cylinder = 0.030968; %m^2 t_Kapton = 0.000127; %m A_Kapton = 0.030968; %m^2 t_air = 0.04445; %m A_air = 0.030968; %m^2 V = 30; %m/s L = 0.1524; %m A = 0.030968; %m^2 t_inside = 0.04445; %m A_inside = 0.03096768; %m^2 for i = 1:7 Re_L(i) = (V*L)/array(i,4); Nu(i) = 0.664*Re_L(i)^0.5*array(i,5)^(1/3); h(i) = (array(i,3)*Nu(i))/L; R_outside(i) = 1/(h(i)*A); R_1(i) = t_acrylic/(k_acrylic*A_cylinder); R_2(i) = t_air/(array(i,3)*A_air); R_3(i) = t_Kapton/(k_Kapton*A_Kapton); R_total(i) = R_outside(i) + R_1(i) + R_2(i) + R_3(i); Q(i) = (20 - array(i,1))/R_total(i); end temp = [-23,7,17,27,37,47,57]; plot(temp,Q, 'red') hold xlabel('Temperature (C)') ylabel('Heat transfer (W)') title('Heat transfer rate for interal temp = 20 C') %For greenhouse without shield A_cylinder = 0.030968; %m^2 t1_air = 0.04445; %m A_air = 0.030968; %m^2 V = 30; %m/s L = 0.1524; %m A = 0.030968; %m^2 t_inside = 0.04445; %m A_inside = 0.03096768; %m^2 for i = 1:7 Martian Environment Pod 50 Final Design Report Re_L2(i) = (V*L)/array(i,4); Nu2(i) = 0.664*Re_L2(i)^0.5*array(i,5)^(1/3); h2(i) = (array(i,3)*Nu2(i))/L; R_outside2(i) = 1/(h2(i)*A); R2(i) = t_Kapton/(k_Kapton*A_Kapton); R_total2(i) = R_outside2(i) + R2(i); Q2(i) = (20 - array(i,1))/R_total2(i); end plot(temp,Q2,'b') legend('With Thermal Shield','Without Thermal Shield',2) 13.5 MATLAB Code for Torque Analysis mass = 0.3003*0.45359; %kg g = 9.807; %m/s^2 total_torsion = 0; dimension = [ 0.1651, 0.1905, 0.0697992; 0.17018, 0.20955, 0.07051; 0.17526, 0.2286, 0.07691; 0.18034, 0.24765, 0.08329; 0.18542, 0.2667, 0.089687; 0.1905, 0.28575, 0.096088; 0.19558, 0.3048, 0.102641; 0.20066, 0.32385, 0.108915; 0.20574, 0.3429, 0.115341; 0.21082, 0.36195, 0.121742]; for i = 1:10 area_endcap(i)= dimension(i,1)*dimension(i,3); area_petal(i) = dimension(i,2)*dimension(i,3); total_area(i) = area_endcap(i) + area_petal(i); mp_endcap(i) = area_endcap(i)/total_area(i); mp_petal(i) = area_petal(i)/total_area(i); mass_endcap(i) = mass*mp_endcap(i); mass_petal(i) = mass*mp_petal(i); torsion(i) =mass_endcap(i)*dimension(i,2)*g+0.5*mass_petal(i)*dimension(i,2)*g; total_torsion = total_torsion + torsion(i); end total_torsion i = [1:10]; plot(dimension(i,2)*39.37,torsion(i)*141.6119) xlabel('Length of petal (m)') ylabel('Torsion on axle (oz-in)') title('Torque vs. Petal Length')