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Development of an Off-the-Shelf Bus for Small Satellites Garrett D. Chandler, Dale T. McClure, Samuel F. Hishmeh, James E. Lumpp, Jr.

Department of Electrical and Computer Engineering University of Kentucky Lexington, KY 40506

859-257-8042 jel@uky.edu

Jennifer B. Carter, Benjamin K. Malphrus

Space Science Center Morehead State University

Morehead, KY 40351

Daniel M. Erb College of Science, Engineering and Technology

Murray State University Murray, KY 42071

William C. Hutchison, III

Department of Mechanical Engineering University of Louisville Louisville, KY 40292

Gregory R. Strickler

Department of Computer Science Western Kentucky University

Bowling Green, KY 42101

James W. Cutler, Robert J. Twiggs Department of Aeronautics and Astronautics

Stanford University Stanford, CA 94305

Abstract—KySat1 is a 1 kilogram picoclass satellite being developed by college students across the state of Kentucky. To the best of our knowledge, the KySat effort is the first by a state to develop a satellite. The consortium assembled to fund and develop KySat includes public, private and educational partners throughout Kentucky. While the primary mission of KySat1 is educational outreach, the goals of the KySat program include 1) Educational experience for secondary and post secondary students 2) Cultivate an aerospace and satellite technology base in Kentucky 3) Develop a reliable reusable satellite bus that will form the basis for future education and commercial KySat missions. The timeline for KySat1 is aggressive and off-the-shelf technology is leveraged whenever possible. This paper12 overviews the KySat1 design and development.

TABLE OF CONTENTS

1. INTRODUCTION......................................................1 2. BACKGROUND........................................................2 3. SYSTEM DESIGN ....................................................3 4. DISCUSSION .........................................................12 1 1 1-4244-0525-4/07/$20.00 ©2007 IEEE. 2 IEEEAC paper #1365, Version 2, Updated December 13, 2006

5. CONCLUSION....................................................... 14 REFERENCES........................................................... 14 BIOGRAPHY ............................................................ 15

1. INTRODUCTION

Slated for launch in the last quarter of 2007, KySat1 is the first in a planned series of satellites that will emerge from a newly founded partnership among public and private entities across the state of Kentucky. To facilitate future missions, the engineering team for KySat1 is focusing on creating a robust and reusable system architecture that meets the needs of future payloads. To meet the aggressive schedule for KySat1 and to make it possible to rapidly produce future generations of KySat, particular emphasis was placed on the use of commercially available “off-the-shelf” technologies.

To meet the reliability and time constraints under which this project must operate two primary decisions were made at an early stage; to design the system to meet the CubeSat standard and to make an effort to use off-the-shelf subsystems as much as possible. In doing so, the KySat1 team has been able to design a system that only requires a single custom circuit card assembly and a few

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customizations to commercial hardware for specific harnessing and antenna mounts.

2. BACKGROUND

Although the content of this paper is focused on design of KySat1, there are a few associated topics that must be discussed to put this work in perspective. These include an overview and history of the CubeSat standard and the community involved, a discussion of the history and distributed management of the project, and a discussion of the planned mission for KySat1.

CubeSat Standard and Community

The CubeSat standard developed at Stanford University and California Polytechnic State University [1] has become the de facto standard for university-class satellite missions [2]. The standard specifies structural, electrical, operational, and testing requirements for a 1kg, 10 cm cube satellite called a CubeSat. CubeSats are deployed with a standardized launch vehicle interface (LVI) called the Poly Picosatellite Orbital Deployer (P-POD), which holds up to three single CubeSats. The standard was developed after the success of Stanford's OPAL mission that deployed six picosatellite daughterships and demonstrated that standardized structures and LVIs promote the launch of university satellite missions [3].

A growing international community with over 80 universities and corporations are developing CubeSats for training missions and research testbeds. Smaller startup companies such as Pumpkin Inc and Clyde-Space are developing off-the-shelf Cubesat components. Missions have ranged from technology demonstration of various small satellite technologies to ionosphere monitoring with VLF receivers [4].

Since the birth of CubeSats in 1999, there have been four launches placing twenty-four CubeSats into orbit. Six are operational, and fourteen were lost due to a launch vehicle failure in June 2006. Teams from Canada, Denmark, Germany, Japan, Norway, South Korea, and the United States participated in these missions. Currently, over 80 satellites are under development with over four P-PODs currently awaiting launch on a DNEPR mission in 2007 and an upcoming Falcon-1 [5].

KySat Management

Founded in the first quarter of 2006, the KySat consortium is interested in engaging post-secondary students within the state of Kentucky in the challenging work of designing, constructing, launching and operating a satellite system. The grand payoff of this work is to increase the technological capabilities within the state, by providing both an advanced educational experience to those moving

through the public school system and by creating high-tech infrastructure within the state.

Financial interest in this project comes from a variety of public, private, and educational entities. These include five public universities within the state; Morehead State University, Murray State University, Western University, University of Louisville and the University of Kentucky. Non-educational parties include the Kentucky Space Grant Consortium, the Kentucky Council on Post-Secondary Education, and the Kentucky Science and Engineering Foundation. Other partners include the Kentucky Virtual University network, Stanford University, and California Polytechnic State University.

The program is the brainchild of the Kentucky Science and Technology Corporation (KSTC) president Kris Kimel. KSTC continues to serve and direct the project as the managing partner. Between the time that plans for this project were first discussed in meetings between Stanford University professor Robert Twiggs and Mr. Kimel in February of 2006 and the earnest launch of the technical aspects of the project in June of the same year, KSTC was able to assimilate the backers for the project and create the managing framework.

A technical team comprised of seven undergraduate and graduate students from the five universities within the consortium was selected in April of 2006. The disciplines represented include Electrical, Computer, and Mechanical Engineering as well as Engineering Physics, Industrial Engineering Technology, and Computer Science. These students relocated to offices on Moffett Field adjacent to the NASA Ames complex near Mountain View, California in the early part of June. While there they interacted daily with faculty, staff, and students at Stanford University as the design for the satellite was underway. In addition visits were made during this time to the project's launch and integration partner, California Polytechnic State University.

Upon return to Kentucky in August after a 10 week stay in California each team member returned to their respective university to continue the work. The team continues to function as a unit by collaborating and documenting efforts using a web-accessible wiki, participating in virtual meetings using a voice and desktop sharing application and network supplied by the Kentucky Virtual University, and by attending monthly on-site meetings. A central project leader monitors and directs the technical progress while the managing partner, KSTC, handles the financial aspects.

Mission Requirements

The KySat1 design team adopted a mission goal similar to that of a CubeSat project that has been under study for two years at Stanford called KatySat (www.katysat.org). An acronym for "Kids Aren't Too Young for Satellites," the goal of this satellite is to interest kids in careers in

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engineering and science by inspiring them at an early age with advanced technology that has been made easily accessible to them.

From the inspiration that the satellite should be engaging to students in the K-12 age range the KySat1 team created a set of requirements. Analog interaction and low-speed digital communication with the satellite should be done over the VHF and UHF amateur radio bands using the AX.25 communication protocol. This will require a radio and terminal node controller (TNC) capable of operating in these modes. The satellite should be capable of receiving audio files from a ground station and playing these back over the ham radio frequencies when requested by an operator on the ground. Telemetry should be sent periodically in the form of both continues wave (Morse code) and digital beacons as well as when requested from a ground station. When requested, telemetry should also be recorded at a high rate for later download from the spacecraft. When asked, the satellite should also be able report its position to a requestor using a human spoken voice. Lastly, there is a desire to test higher-bandwidth communication radios.

Operation of the satellite will be done with two types of ground stations. The first, referred to as a digital user, would be equipped with a large ground station including high-gain antennas, a computer controlled rotator and tracking system, auto-tuning radios, a terminal node controller, and a custom ground station software package used to move data to and from the satellite. The second, an analog user, would be much less equipped with only a small beam antenna, low-noise receive amplifier, and a handled transceiver. Using the dual-tone multi-frequency (DTMF) capabilities typically found in these types of units allow an easy method for these analog users to command the satellite.

The K-12 targeted educational mission has the added bonus for the KySat consortium that dividends from their investment aimed at increasing the technology within the state are returned twofold. In addition to the post-secondary education and infrastructure creation they are also inspiring young minds to become interested in advanced technology as well.

KySat1 will be placed in low-earth orbit by a launch vehicle to be selected by California Polytechnic State University. As the satellite will be a secondary payload on the launch vehicle, the specific orbit is unknown at this time – although it is important to note that the KySat consortium plans to turn down any ride with an inclination of less than 40 degrees to ensure passes over Kentucky. As a consequence of this unknown orbit, the systems must be designed to handle all possibilities. The targeted operational lifespan of the spacecraft is 18 months, while the physical structure will remain in orbit for another 10 to 15 years.

3. SYSTEM DESIGN

The satellite system consists of the spacecraft bus, spacecraft payloads, mechanical structure, ground station, and flight software. Each of the following sections describes these subsystems in detail.

Spacecraft Systems

Electrical systems onboard the spacecraft are divided into two functional categories – that of the bus and that of the payload. In KySat1 the spacecraft bus consists of a data processing unit and peripherals used for command and data handling, a power system to charge and monitor the secondary batteries and disperse this energy about the craft when needed, and a UHV/VHF radio system with an integrated TNC. Additionally, one custom piece of electronics has been created to augment the bus with a temperature-stable real-time clock with primary battery backup, a DTMF decoding circuit, high-current switches for the antenna deployment and camera systems, a long-period watchdog timer and a supervisor processor. The payloads include a VGA camera system with JPEG compression engine and a S-Band radio system.

Spacecraft Bus—The internal bus hardware consists of primarily of four printed circuit boards; the processor module, the power module, the system support module, and the UHF/VHF radio module. These four boards provide most of the functionality needed for any small satellite mission. The bus system is detailed in Figure 1.

Processing Module——Command execution, data handling, and storage onboard the craft is accomplished using a processor module (part number 705-00193C) purchased from Pumpkin Inc [6]. Fitting within the PC/104 form factor, it contains a Texas Instruments MSP430 microcontroller, a linear power regulation system, over-current protection devices, bus connectors, remove-before-flight and launch switches, level shifters and buffers, a JTAG programming connector, a processor power bus control device, high and low frequency crystal oscillators, an SD flash interface with separator power control and over-current protection, and the means for on-ground diagnostics using a USB port.

Currently these processing modules (referred to as a "flight module" by Pumpkin) ship with an MSP430F1612 installed on them [7], although any device in the 16x series can be custom installed from the supplier. It is expected that more options will become available in the future as Texas Instruments continues to grow the MSP430 product line. The MSP430 is a low-power 16-bit microcontroller achieving up to 8MIPS at a cost of approximately 500uA per megahertz. In addition, the device comes with five additional software-selectable low-power modes that can bring power consumption down to as little as 0.2uA [8].

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As the bus control unit, the MSP430 is a great balance between performance and power consumption. If payloads require additional computing power, this can be added to the payload itself as needed. Looking ahead of the current mission and onto needs in the immediate future is also a significant advantage that the MSP430 has an integrated bootstrap loader that will allow for in-flight reprogrammability. The unit also contains two serial communication interfaces that can be configured to operate as UART, SPI, or I2C bus. Two 12-bit DACs and eight 12-bit ADCs are also contained within the chip to provide analog functionality [8].

In addition to connecting a SD card slot to the MSP430 via a SPI communication path, the Pumpkin flight module also provides power control of this flash memory device – a large power saver as leakage currents on flash memories can be quite significant. With this interface, the non-volatile storage of large amounts of data is easily and cheaply accomplished.

The flight module also includes two critical mechanical switches; the remove-before-flight switch and the launch switch. Although not committed to any particular function by the flight module, these switches are most commonly used to keep the system from powering on until the

launching device ejects the satellite in the target orbit. The “remove-before-flight” switch consists of a plunger that will remain inserted as the satellite is integrated into the launching device. After such time, the launch switch is depressed by the satellites adjacent to it in the deployment mechanism thus preventing power-on as the remove-before-flight plunger is extracted. The satellite electronics are connected to the power system once this final switch is closed upon deployment.

Power System——Power control within the satellite will be accomplished by a "CubeSat power module" from Clyde Space Limited [9]. On this single circuit board are the connectors to up to six solar panels, the battery, charging circuitry, battery temperature control, and 3.3 and 5 volt high-efficiency switching regulators. A monitoring processor and individual rail power on/off control is achieved through an I2C interface.

The solar panels interface to dedicated converters that allow for multiple voltages to be accepted from the solar panels. Although all strings on a single face of the cube must be of equal length, the dedicated converters allow the possibility of different lengths for each face. Each of the interfaces also include peak power point tracking for maximum efficiency. On the input side the system can accept between 3.5 and 25

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volts, will output a max of 0.5 Amps at 9 volts to the charging and regulating system, and is rated at efficiencies of over 90%.

An 8.4 volt lithium-polymer battery with a beginning of life capacity of 7.2 watt-hours is also part of this system. It contains a heater that is autonomously controlled by the power system that monitors the pack temperature using a thermistor. This feature prevents the charging of the battery when outside of its recommended operating temperature – an operation that could cause mechanical failure of the battery system.

The power system also has many other capabilities. It contains over-current and low battery voltage protection on the three power rails and is capable of supplying many telemetry points including currents, voltages, temperatures, and estimated battery charge state. In addition, the unit is capable of resetting or turning off any of the three power lines. Although all of this monitoring and control is available to the satellite controller, it is important to note that the power system can operate fully autonomously and does not require such communications [9].

System Support Module——The system support module is the only custom circuit board in the KySat1 bus design. As the name implies, its function is to provide support to the processor module and other systems throughout the satellite. It includes a real time clock, a watch dog timer, a DTMF receiver, a supervisory microcontroller, high current switches for antenna deployment, as well as header and power control switches for the camera payload and the antenna deployment mechanism.

A DS1388 real-time clock from Dallas Semiconductor keeps track of UTC time for time stamping events and for executing commands at specific times. As the temperatures experienced by the satellite would vary greatly, it was decided to use a temperature compensated crystal oscillator (TCXO). The DS32KHz, also from Dallas Semiconductor, will provide a time base expected to be ± 4 minutes per year at the temperature extremes expected. The real time clock and TCXO are both backed up with primary batteries. Although once in orbit and in while in the sun, these devices will run off of the secondary energy from the main batteries, the clock will be able to run for up to 3 years while waiting for launch or once the main battery fails.

A watchdog timer is also included on the DS1388 device that will be used to provide automatic resets to the main processor [10]. Although the MSP430 has an internal watchdog timer, it requires a frequent “tickle” and can only soft-reset the processor. The ability to power cycle the flight processor was added as an additional layer of reliability with the option of a much longer period of up to 99 seconds. If the main processor does not reset the external watchdog, the system support module will do a full-power reset of the main processor.

To offload the decoding of DTMF tones from the processor and to allow DTMF tones to be used to initiate a system reset, a hardware receiver is included on the SSM. The MT88L70 manufactured by Zarlink Semiconductors can take an analog DTMF signal from the VHF/UHF radio and convert it to a digital representation. Thus it can be used to control the satellite from the ground without the need for a computer and TNC interface. It will also be used as another way to reset the flight computer. To achieve this, the radio will feed the analog signal to the DTMF receiver where they are decoded and passed to the supervisor processor and main processor. A pre-flight reprogrammable sequence of tones will signal the supervisor processor to reset the main processor. The DTMF receiver is designed to ignore analog signals that are not DTMF tones and are not held steady for a selectable period of time for enhanced reliability.

The microcontroller on the SSM is a MSP430F1132. It is in the same family as the main processor but consumes much less space. Its function is to invert logic signals and decode the sequence of digital codes given to it by the DTMF receiver resulting in a reset the processor power bus if need be. A trade study was conducted to compare the use of discrete logic, a FPGA solution, and a microcontroller for this purpose. It was found that the microcontroller option consumed the least power and has maximum flexibility.

Specific to the KySat1 mission are the interface for the camera and the antenna deployment system. The camera interface includes a power switching device to completely disconnect the camera module from the bus to conserve power. The antenna deployment system is one of the most critical systems onboard the craft. Dual paths of a pair of high-side and low-side switches remove the possibility of system failure should one of the switching device stop fail into either the open or closed state.

VHF/UHF Radio—An amateur band radio from Stensat, designed to conform to the CubeSat standard and specifically configured to interface with the Pumpkin CubeSatKit, is being used. This module houses sending and receiving TNCs and modulator/demodulators conforming to the AX.25 specifications, a RF transmitter, a RF amplifier, and a RF receiver [11].

The transmitter side of the unit is interfaced using a TTL level UART at 1200 baud using the AX.25 packet framing and contents specification. The radio is rated at an effective radiated isotropic power (ERIP) of 1/4 watt. Stensat is currently working on including an amplifier stage that will boost the ERIP to one watt. On the receive side, the TNC demodulates and interprets the 1200 baud AX.25 stream and returns it to the system processor at 4800 baud.

Spacecraft Payloads—Because it is a goal to fly a fully functional satellite in around a year, it was decided that a camera would provide a maximal cost-benefit ratio. The second payload was initially considered as the primary

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communication radio, but because of potential problems it was moved into the payload category. Both of these payloads are discussed in the following sections.

Camera——For a low-mass and high-effectiveness camera the C328-7640 from CO Media was selected [12]. The device weighs roughly 5 grams and is capable of producing both JPEG compressed images and uncompressed bitmaps at a range of resolutions from VGA (640x480) to 80x64. It is directly compatible with the power system on the spacecraft requiring a supply of 3.3 volts and consumes 60mA.

One challenge of using this camera system is its narrow specified operating temperature; 0 to 25 Celsius. To ensure that use of the camera will produce useable images the temperature of the device will be monitored and heat applied to the camera to bring it up to temperature.

As KySat1 will not be actively stabilized, considerations will be made in the spacecraft software to assist in ensuring that valuable images are received from the satellite. Upon capturing each frame, the image will be requested from the compression engine at four different resolutions (640x480, 320x240, 160x128, and 80x64) and stored on the SD flash card. Employing this method, one can quickly download the smaller image to manually determine if it is worth committing the transmission time required to get larger versions. Each image will be stored permanently in the file system once it is captured so it will be possible to retrieve these pictures at any time and in any order over the lifetime of the craft.

S-Band Radio——The radio system used is the MHX2400 manufactured by Microhard Systems and weighs 75 grams. It runs at 5 volts and consumes 200mA and 700mA for RX and TX respectively [13]. Like the camera, the power supply to the S-Band radio will be completely cut when it is not in use. Fortunately the radio is specified to operate throughout the range of -40 to 90 Celsius and thus does not need a heating system.

Once the satellite is on orbit the S-Band radio can be fully tested to see if it can handle some of the anticipated problems including Doppler shifts and the high noise floor in the 2.4 GHz spectrum. As it is a secondary communication system, if the radio turns out to be non-functional the low-bandwidth communications can still occur on the UHF/VHF system. If it does in fact work the upload and download of information will be possible at much higher rates.

Mechanical Integration

The frame assembly for KySat1 is made up of commercial off-the-shelf (COTS) components wherever possible to reduce the engineering effort required. Certain modifications to the COTS items are deemed necessary and

prudent as outlined below and in the antenna and solar cell sections of this paper, but this approach still provides a rapid path to both engineering models and a flight worthy picosatellite. As a result of this process, few of the systems on KySat1 are optimized for the highest efficiency or lightest weight. Rather, given a short design, test, and build timeline as well as a fixed budget, the COTS approach appeared workable. The KySat1 team also believed a COTS approach increased the likelihood of success because fewer new technologies or novel solutions would have to be engineered, tested, and possibly iterated.

Frame—The bulk of the frame assembly, the main frame itself, is a standard "skeletonized" single CubeSat assembly that measures 10 x 10 x 10 cm. The frame is constructed of 5052-H32 sheet aluminum and is hard-anodized for gall protection when in contact with the rails of a CubeSat launcher. The anodized areas are non conductive, but the balance of the frame is allodyned to provide Faraday-cage shielding to the interior electronics. The frame is provided with two spring separators that increase the distance between multiple CubeSats upon orbit insertion from a P-POD deployment device or launcher.

The interior arrangement for the mounting of most printed circuit boards within the cube consists of threaded standoffs or the equivalent with spacing based on the PC/104 standard. The flight module that holds the MSP430 processor and flash storage will be installed adjacent to the base plate; all subsequent PCBs are installed on top of the flight module and connect to each other using the CubeSatKit bus header. The frame base plate has rivet-nuts installed to accommodate the hole pattern of the PC/104 standard. The only connection and mounting deviation from the aforementioned is with the Microhard MHX-2400. This device has special-purpose header and mounting standoffs on the flight module.

Wiring, Harnessing and Staking—Secondary wiring that is not included in the CubeSat busses, such as for connecting the six individual solar arrays will be insulated with PTFE Teflon for high temperature protection, slippery surface, and small diameter that is likely to ease installation (part number MIL-W-16878/6 Type ET, Mil-Spec Wire Products, Inc., Syossett, NY) [14]. The solar cell array wires will be hand tied into bundled wiring harnesses. The RF conduit, or shielded antenna cable, is also non-bus wiring and was selected for its flexibility, small diameter, and low outgassing properties [15]. Otherwise loose wiring will be anchored to the frame or other nearby robust component with staking compound to reduce the likelihood of vibration.

Solar Cells, Arrays and Solar Cell Protection—The solar arrays are based on a low-cost individual cell with advanced performance: 27 ± 3% absolute efficiency and are of improved triple-junction GaAs construction [16]. These cells are the peripheral corner "leftovers" resulting from

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manufacturing rectangular or square cells from large circular wafers of base material. Thus the cells are triangular in shape. Two cells may be fitted hypotenuse-to-hypotenuse to form a rectangle. Even so, some array area must be used to allow spacing between the rather high number of individual cells (88 in total). Another drawback to these cells is the need for an electrical connection to the top of each cell which tends to make cover glass fabrication difficult as the cover glass must be notched to accommodate the top connection.

In the space environment built-in cover glass provides a hermetic seal to the solar cell as well as protection from radiation and micrometeorite damage. KySat1 is designed for a low earth orbit (LEO) where radiation damage to the solar cells in unlikely during its mission life [17]. In light of the difficulties likely to be encountered with the use of cover glass on KySat1, along with a marginal need for radiation protection, its use or exclusion will be determined based on vibration tests, mechanical strength and/or damping requirements and mass budget margins. However, at minimum, cover glass will be used for abrasion protection during launch on the individual cells located beneath the stowed antennas.

Figure 2. KySat1 Solid Model

The adhesive used to attach cover glass to solar cells is typically referred to as encapsulant, a high-clarity and low viscosity silicone rubber. Other than attaching cover glass, encapsulant also protects the solar cell current collection "fingers" from attack by atomic oxygen and thus may be brushed onto the solar cells alone, if need be. Three space-rated formulations of encapsulant have been identified (part number DC 93-500 family, Dow Corning, Midland, MI, part number RTV-S 690 family, Wacker Chemie AG, München, Germany, and part number CV-2500, NuSil Silicone Technology, Carpinteria, CA).

Solar cell array board attachment clips (part number 711-00346, Pumpkin, Inc., San Francisco, CA) are used to retain

the corners of the arrays. Additional centrally-mounted screw attachment(s) to the frame for each array are planned to counter warping and to hold the arrays planar, as well as to encourage a large thermal path and provide damping to the arrays during launch vibration. Solar cell array board designs are planned based on Pumpkin, Inc. artwork, which currently exists for a single face only.

Antennas, Stowage, Mounting and Deployment—KySat1 has three antennas, all of which are mounted orthogonal to one plane as shown in Figure 2. The antenna mounting plane is located between the launch rails of the P-POD where an additional 6.5mm of clearance is allowed on each side of the CubeSat (this is in addition to the standard “maximum” 10 x 10 x 10cm CubeSat measurements). In the stowed configuration the longest antenna will be wrapped closely around the exterior of the satellite and will thus hold the remaining shorter stowed antennas beneath it. Kapton tape will be applied to prevent cold-welding of the layers of antenna before deployment. Recessed notches in the edges of the solar array boards will prevent out-of-plane or side-to-side movement of the antennas during launch vibration. A small number of smooth-sided pins or bollards will be incorporated into the solar cell printed circuit board array designs (soldered into place at the edges of the stowed antenna footprints) to further limit side-to-side movement of the antennas between the notches. The notches in the solar array boards along with the underlying frame will be radiused in the antenna plane to avoid a permanent set of the spring steel antenna material while stowed. Small-scale experiments were conducted to determine the minimum bend radius of the antenna material so that it will flex back into its original shape.

The antennas are made of one-half inch wide concave steel measuring tape (part number 939521, Sears, Roebuck and Company, Chicago, IL). The original tape measure paint finish was burned off with a low flame from a propane torch. The raw spring steel was then hand burnished, deburred and polished. After being cut to approximate final length, they were then gold plated. A copper eyelet (part number 110907, LPKF Laser and Electronics AG, Garbsen Germany) will be installed close to the free end of the antenna during final assembly to protect the deployment line from the thin steel edge of the antenna itself. The antennas mounts are machined of ULTEM® resin (part number ULTEM 1000, General Electric, Pittsfield, MA). The longest antenna has an exterior mount and is attached to the frame with a ¼ inch Nylon screw. The remaining two shorter antennas have interior mounts and protrude through suitable openings machined into both the frame and the top solar cell array panel. Interior mounts for these antennas were deemed necessary so that the frame may act as a ground plane.

Many CubeSats have used a coil of resistance wire to sever a line, through the action of heat, for antenna deployment or for other deployables. The arrangement of parts is typically

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a wound coil of nichrome wire loosely threaded over a deployment line. The drawbacks of this arrangement are as follows: 1) only one cut of the line is likely; 2) turn-to-turn electrical shorts are possible in the nichrome coil; 3) depending on the severing amperage available, the necessary diameter or gauge of the nichrome wire (to reach a cutting or melting temperature) may limit the minimum coil-forming diameter and thus there may be a significant gap between the deployment line and the coil. All of these drawbacks adversely affect cutting performance. Of additional concern is the fragility of a small coil of resistance wire that may be easily damaged.

KySat1 has adopted an improvement of the “traditional” CubeSat line-cutter designed to minimize the above drawbacks. First, the deployment line and nichrome wire are to be threaded side-by-side into a ~0.045 inch diameter glass tube (part number 22-260-943, Fisher Scientific, Pittsburgh, PA) of suitable length. A small piece of cotton fabric is also threaded onto each end of the wire and line, along with one or more lengths of PTFE heat-shrink tubing. The deployment line is then tensioned between its anchorage point on the CubeSat frame and the free end of the stowed antenna. Next, the nichrome wire may be wound around the tight deployment line within the glass tube (rather in the form of a helix as opposed to a coil). The fabric patches may then be stretched over both ends of the glass tube and, finally, the heat shrink tubing is shrink-fitted to hold the loose ends of the fabric tightly in place against the sides of the glass tube. The helix form of the coil increases the effective coil diameter and allows multiple and redundant cuts of line with a single line-cutter. The fabric patches act like filters in that they capture debris from multiple cuts yet they allow the cut line to slide through the cutter package easily. The glass tube withstands the heat generated and forces intimate contact between the nichrome wire and the deployment line. And, in addition to holding the fabric patches in place, the heat shrink tubing holds the glass tube together in case it breaks during launch stress (however, this is unlikely because the glass tube is suspended on the taut deployment line and the fabric patches serve as bumpers between the glass tube and the CubeSat frame or solar array). This form of line-cutter also offers a rather substantial package to position, hold or move compared to a loose coil of nichrome wire.

Small diameter coil springs may be used to tension both the deployment line and the nichrome wire and to further encourage intimate contact. The springs will also provide a non-destructive secondary means of removing the stowed antennas and line-cutter from the satellite without actuating or deploying them.

KySat1 has also adopted the use of cotton antenna deployment line as opposed to monofilament Nylon “fishing” line. The drawbacks to the use of Nylon are as follows: 1) melted Nylon line tends to form a small ball at the severed ends, which may catch on something and

prevent deployment; 2) Nylon is somewhat difficult to knot; 3) Nylon is difficult to stretch so tensioning typically involves putting the material close to its elastic limit; 4) Nylon tends to have a very small diameter, which makes intimate contact with a coil of nichrome wire unlikely; and, 5) Nylon degrades in the space environment. Nevertheless, we are incorporating a short link of very fine Nylon monofilament in our antenna deployment line as an eventual fail-safe back-up; if our line-cutter fails, the Nylon link will eventually degrade and deploy the antennas. Although cotton deployment line has apparently been successfully used on at least one previous small satellite mission [18], we envision a dedicated thermal and vacuum test of our improved cotton line-cutter design.

Perhaps the optimum line-cutter would employ side force so that the deployment line is held under tension against one or more lengths of resistance wire; very similarly, as in weaving, to the way the warp of a fabric is held against the weft. Thus, as the heated resistance wire severs individual fibers, tension in the deployment line forces the remaining uncut fibers into direct contact with the cutter.

Cotton deployment line avoids all of the drawbacks of Nylon line as listed above. Cotton line also offers an additional advantage of being fibrous. To take advantage of this, a resistance wire may be woven, threaded or otherwise inserted between individual or bulk fiber layer(s); perhaps as a core around which a short segment of the cotton line is originally built or laid up.

Mass Budget— A conservative approach to the mass budget was adopted early in the design. Where components were published with values such as "< 5 grams", the weight was always up rounded up to the nearest significant figure and therefore some inflated margin was built into the total. Weights of items such as encapsulant, staking compound and other adhesives were also inflated primarily due lack of experience with them. This approach quickly led to an overweight spacecraft budget, but also encouraged “weight-awareness” in the entire KySat1 Team. As the budget was updated with more accurate masses, design iterations were dictated. Using this conservative approach, as of October 2006 KySat1 was 25 grams over the target weight of 1000 grams. As a result of being overweight, in September the team decided to reduce the solar panel board thickness from 0.062 inches to 0.031 inches. With the weight savings from this one decision our estimated weight is now 845 grams. If problems arise during thermal, vacuum, vibration or deployment testing, we now have an ample underweight margin to design-in a solution.

Ground Station

Although KySat1’s communications subsystem provides the satellite with the ability to downlink data to and receive commands from many different UHF/VHF ground stations, KySat1’s primary ground station is located at the Space

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Science Center at Morehead State University. KySat1 is designed to communicate with both the 21 Meter parabolic dish located in Morehead, Kentucky, as well as simple Yagi-type amateur radio ground communications systems around the world. The KySat consortium will encourage schools and individuals worldwide to set up their own low-cost ground stations to send and receive data from KySat1. Secondary ground stations will be located at participating universities as well as several middle and high schools participating in the project. In addition, Ham operators are encouraged to participate in the project using their own equipment.

The satellite system has two transceivers (UHF/VHF and S-band) requiring two ground stations to be maintained. A Microhard MHX 2400 transceiver handles communications in the S-band (2.4 GHz) at high data rates (2,400 to 115,200 baud) and a UHF/VHF transceiver communicating at 1200 baud will be utilized for educational and amateur radio communications. Each system and its associated ground station, is described briefly below.

VHF/UHF Radio System—A VHF frequency in the 2 meter band (~144 MHz) will be used as the uplink frequency and a UHF frequency in the 70 centimeter band (~433 MHz) will be used as the downlink frequency. The UHF/VHF ground stations will consist of a UHF/VHF Yagi array used in conjunction with a motorized azimuth and elevation array rotator, back-end receivers (similar to the ones on-board the satellite), and tracking software to track and control the satellite. In-house software is currently being designed to aid in commanding the satellite and reassembling the received data. The system will be responsible for commanding all available actions including all transmissions from the satellite such as transmitting telemetry as well as commanding the camera to take a photograph or to control the various satellite subsystems.

In this ground station, a transceiver such as an ICOM America IC-910H (100W transmit power on VHF) will be required to transmit and receive the audio frequency-shift keyed (AFSK) signal. A preamplifier such as the ICOM America AG-35 70cm preamp will be used to boost the incoming signal in conjunction with a 2 meter linear amplifier to boost the transmitted signal strength. The KySat recommended power supply is a 50 Amp/13 volt Astron power supply to be used in conjunction with a PacComm PicoPacket TNC. The tracking device consists of a Yaesu Antenna rotator (azimuth and elevation) and a ZL2AMD rotator/radio controller for auto tracking and Doppler tuning.

Two pieces of software will be used in tracking, SatPC32 and Mercury Ground Station. SatPC32 satellite tracking software, provided by AMSAT, supplies a graphical representation of the pass including the footprint of the satellite and the "view" range of the ground station. Mercury Ground Station is a software system developed by

James Cutler of Stanford University. Mercury Ground Station is based on a network of university ground stations accessible via the Internet called the Mercury Ground Station Network (MGSN). Accommodating MGSN is an open-source reference ground station control system, called Mercury, which automates routine ground station services and provides secure Internet access. The communication protocol of the MGSN is software called Ground Station Mark-up Language (GSML). Mercury is an open-source implementation of the GSML API and is built on the Apache web-server, MySQL database, PHP scripting language, and custom Java applications for controlling ground station hardware and automation services. Ground station users will use the access server for agent-based GSML commanding, the HTTPS GUI for human commanding, and the data server for accessing satellite communications.

An in-house beacon decoder will be added to the system to demodulate the beacon and report telemetry and health of the satellite. In-house software systems will be used to process the data into an appropriate end-user format and to distribute data to the end-users.

S-band Radio System — The secondary transceiver on the satellite operates in the S-band (2.400 – 2.4835 GHz). Due to the challenges associated with the use of S-band frequencies (limited output transmission, significant noise floor, directionality of antennas designed for this frequency, etc.) significantly larger gain is required to communicate with the S-band radio.

Morehead State University's 21 Meter Space Tracking Antenna will be used to support the KySat1 S-band mission. The 21 meter dish (Figure 3) is a research and education instrument that supports two generic missions; a research program in radio frequency astrophysics and space tracking services (telemetry, tracking, and control) for satellite telecommunications applications. The facility provides a state-of-the art laboratory for researchers and students in astrophysics, satellite telecommunications, engineering, and software development.

The 21 meter system has a drive system that is capable of tracking LEO satellites at an altitude of 350 nautical miles and a maximum elevation angle of 77º. The primary challenges of this requirement are azimuth drive speeds and the development of controlling software. The secant elevation coordinate transformation factor from the cross-El to the Azimuth plane is often referred to as the "Keyhole effect". A solution to ameliorate this effect is based on compensating azimuth drive speeds and accelerations at Keyhole and compensating via software strategies. To handle 350 NM passes without link breakage up to 77º elevation, a field weakening algorithm (and circuit) will be employed to enable the azimuth axis to slew up to a velocity of 3º/s. The algorithm is a horsepower limitation algorithm and does not add to the peak power demand on the power

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line. Analysis of the satellite trajectories shows that the period of overspeed above 2º/s only lasts for about 30 seconds and the wind loading about the azimuth axis is minimal due to the high look angle in elevation during the flyby. The algorithm only weakens the field when needed and maintains maximum torque capacity at all times it is needed. Thus, optimum loop performance exists during sidereal rate star tracking and LEO tracking. This strategy provides an instrument with great flexibility to support both the satellite tracking missions and the radio astronomy research programs.

Figure 3. Morehead State University 21-Meter Dish

The S-band radio system consists of a MHX-2400 Microhard Radio (identical to one on the spacecraft) mounted at the prime focus of the 21 meter system. The MHX-2400 is a high-performance embedded wireless data transceiver, operating in the 2.4000 to 2.4835 GHz ISM band. This frequency-hopping spread-spectrum module is capable of providing wireless data transfer using an asynchronous serial interface. The transceiver has a data rate of between 2,400 and 115,200 bps sent uncompressed in a half-duplex transmission scheme and approximately 100 kbps sustained in intelligent asymmetrical full-duplex transmission mode. The transceiver has a system gain of 135 dB, sensitivity of 105 dBm, and a selectable output power of 1 to 1000 mW. The transceiver is connected to a cross dipole inside the feed termination (resonant cavity) of a corrugated S-band feed designed to uniformly illuminate the 21 meter parabola.

Ground Station Software—Two software systems will be utilized to support the S-band mission, one to model the trajectory of the satellite across the local sky, and one to command the antenna servo systems. The RF system is essentially separate, and utilizes software developed in-house (previously described). A control program developed

by VertexRSI (primary contractor of the 21 meter system) will operate the Antenna Control Unit (ACU) and drive the antennas servo system to continuously position the antenna system. The software system accepts 2 line orbital Keplerian elements and uses these to model a trajectory over the local sky. This "sat-track mode" is a form of program tracking that does not use feedback from the RF system but relies exclusively on the orbital elements. Future versions may incorporate a feedback loop based on the amplitude of the RF signal received by the S-band transceiver. As with the UHF/VHF system, in-house software systems will be used to process the data into an appropriate end-user format and to distribute data to the end-users.

Spacecraft Software

Although the COTS approach of KySat1 was carried even into the software aspect of the design, this portion of the design requires much customization. The baseline software architecture has been developed and will be discussed herein.

Software Requirements—The software requirements include deploying the antennas, managing power, reporting the system status, taking photographs, playing audio files, uploading and downloading files, and storing data. Management of the incoming and outgoing radios channels is required, as is monitoring the health of the satellite system and adapting as necessary.

Software Specifications—In the early stages of the project time was spent carefully examining the radio systems, the capabilities of the MSP430 microcontroller, and the functionality of the operating system. From this analysis a set of software specifications was created. These include the data encoding standards for the data path over the VHF/UHF radios, the packet framing specification, a set of commands and expected responses, and details on remote integration with the spacecraft file system and telemetry.

Data Encoding——Limitations imposed by the AX.25 protocol require that the data moving across this channel exclude certain control characters. Although a more efficient custom coder/decoding (codec) methodology could have been created, it was decided to use a codec that would satisfy the exclusion of these restricted characters and be readily implemented in the languages used to create the software. For this reason the system uses a base 64 codec scheme using the standard MIME character set.

One custom extension to the MIME codec has been specified for use on the satellite that uses the same character set to move a variable-space limited (6-bit) integer through the data channel in a single ASCII character. This custom encoding is referred to as KS64 and can be seen on the 3rd row of Figure 4.

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TNC2 Header Header Delimiter TNC2 Payload Packet Delimiter20 bytes : 0 to 64 bytes \r

Source Delimiter Destination Delimiter Path6 bytes > 6 bytes , 6 bytes

APRS Identifiers KCOM Data2 bytes <= 62 bytes

Frame Identifier Encoded Payload Frame Length1 byte (0 to 15) * 4 bytes 1 byte

KS64 Encoded MIME Encoded KS64 Encoded

Command Unencoded Arguments6 bits 0 to 45 bytes

File ID Directory ID Packet ID4 bytes 1 byte 2 bytes

Data<= 38 bytes

Year6 bits

Month4 bits

Day5 bits

Hour5 bits

Minute6 bits

Second6 bitsKySat Packet Framing.vsd

V1.0 - 061002

Figure 4. Data Packaging and Framing Expansion

Finally, a timestamp encoding was devised to allow the year, month, day, hour, minute, and second to be stored in four bytes. To achieve this, portions of this array of 32 bits are sectioned off and used for the individual fields. Six bits for the year (0-63), four for the month (1-12), five for the day (1-31), five for the hour (0-32), six for the minute (0-59), and six for the second (0-59). This will allow timestamps to be efficiently and effectively passed around the satellite system and in communications with the ground stations.

Data Packaging——A data packaging standard was devised for digital interactions with the satellite. This specification was specifically designed to work around the limitations of the radio and TNC systems.

Each data frame to/from the satellite will consist of a TNC2 header, a header delimiter, the TNC2 payload, and a packet delimiter. From the TNC2 header the source, destination, and path HAM radio callsigns can be extracted. As for the TNC2 payload, it contains 2 bytes of APRS identification characters to allow these packets cooperate with the APRS-IS system already in place on the internet and allow distributed collection of the data, as well as up to 62 bytes of informational payload, referred to as KCOM data.

Within every KCOM data frame there are three distinct sections; the frame identifier, the encoded payload, and the frame length specifier. After each of these sections goes though its respective decoding stages the result is a command, the unencoded raw data associated with that command, and for use by the packet error checking mechanisms, a number specifying how long the packet should be. Figure 4 shows this structure.

Operating System——To deal with the events occurring in the system as well as provide a management strategy in producing a significant amount of code by many distributed developers we are using a real time operating system (RTOS). In the case of KySat1, Salvo from Pumpkin Inc. was selected.

Salvo is shipped as part of the larger CubeSatKit from Pumpkin. This level of integration and vendor knowledge about both systems greatly enhanced the speed at which we were able to produce code. Salvo uses a minimal amount of flash memory (less than a typical printf() implementation) and requires only 5 bytes of RAM per task. It is also important to note that Salvo is a cooperative non-preemptive operating system. Naturally, tradeoffs exist between these two types of systems but it has been found that in this system Salvo has been fully capable.

Although not distributed as part of the operating system per-se, a FAT12/16/32 file system was also purchased from Pumpkin. This COTS software component will greatly simplify iterations with the SD/MMC mass storage device.

Information Flow—Figure 5 shows the software structure for KySat1. Digital data arrives on either the VHF or S-Band radio systems. The demodulated analog signal received from the VHF radio is passed both to a TNC that is a part of the same system as well as the DTMF decoder stage. The S-Band radio is only used for digital transmissions. As a result, any of the three devices can add data to the satellite input queue.

Once data is in the input queue, the Packet Rx task filters and decodes the data. When a packet is detected, Packet Rx performs error checking on the packet. If all fields are to be intact, then Packet Rx decodes the packet.

Next the decoded data portion of the packet is passed to the Command Executor queue. The Command Executor task controls the execution of all incoming commands. It performs such operations as saving a file, reading and sending a file, signaling to take a picture, signaling to play an audio file, and adding commands to the command scheduler.

As the satellite will not always be in view of a ground station it will be helpful to be able to instruct the satellite to execute a command, such as taking a picture, at some time in the future. The satellite will have a Command Scheduler task that stores commands, arguments, and a timestamp that specifies when to execute that command. The Command Scheduler will compare the requested time with the real-time clock located on the System Support Module and when the timestamp has passed the Command Scheduler will move the command to the Command Executor queue.

A beacon task will gather satellite information, such as temperature, battery voltage, and location, and then transmit

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these results at a periodic interval. To gather and report system information with a higher rate, a Telemetry Gatherer task takes a specified number of samples of a specific telemetry point at a requested frequency. The task will then save these results to the mass storage device to be retrieved at a later time.

To send files and the immediate responses to some of the commands, the satellite will have a Packet Tx task that will pull data from a send queue and then perform the necessary MIME and KS64 encoding on the data to form a packet. The new packet is then sent on to either the UHF or S-Band radio, depending on which radio is currently in use.

In the case of transmitting an audio file the satellite will use one of the digital to analog converters (DAC) on the MSP430 to create the analog signal from the specified wave file. In this case the Command Executor will signal the Audio Playback task to play a specific file. The Audio Playback task will open that file, pass the raw data to a DAC driver convert the file into analog data, and then send the data over the UHF radio.

4. DISCUSSION

This section focuses on some specific aspects of the design of KySat1 that have posed particular problems. It includes a discussion of the anticipated problems with the S-Band communication system, the design of the spacecraft antennas, and mention of the electrical power system (EPS).

S-Band Communication

The S-Band radio system offers high data transfer rates and several highly customizable features such as adjustable data rates and changeable frequency hopping patterns. If this radio proves to be a reliable method of orbital communication the capabilities of KySat1 and future satellites will benefit greatly. However, there still remain a few unanswered questions about how well it will perform in space as it has not yet been used for this type of application previously. After researching the possible risks of using this S-Band system, several issues were uncovered.

The first possible problem with the S-Band radio transceiver is its low output power. Although this radio can transmit at user selectable levels ranging from 1mW to 1W in its use on KySat1 its output will be configured to supply as much power as possible. Even at 1 Watt, the current link budget suggests that it is possible the radio may not have the power necessary to be heard on earth. Estimates show that the S-Band ground station antenna will need to have at least 44dBi of gain. Although the antenna that will be used for testing this radio is the 21 meter dish at Morehead State University this antenna currently does not have an S-Band feed horn, so its gain at the 2.4 GHz band is currently unknown.

The second possible issue with this radio is the fact that it does not account for Doppler shift. A plot of expected Doppler shift magnitude versus ground station antenna elevation angle and azimuth angle is shown in Figure 6.

The VHF/UHF radio system on KySat1 uses standard Ham radio frequencies and modulation, so Doppler shift can be compensated for by adjusting the transmit and receive frequencies on standard ground station equipment. This is

CommandScheduler Audio

Playback

Beacon

Packet Tx

S-BandRx

VHFRadio

SSM

TelemetryGatherer

CameraControl

Camera

Packet Rx CommandExecutor

S-BandTx

UHFRadio

Figure 5. Data Flow Diagram

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however not the case for the S-Band radio. The transceiver employs automatic handshaking and is a frequency hopping spread spectrum (FHSS) device. This makes using a customized ground transceiver and modem very difficult because the custom modem/transceiver setup would be required to match the modulation, handshaking protocols, and frequency hopping pattern of the radio in the satellite. An alternative to this method involves processing the signal prior to entering and leaving the S-Band ground station transceiver using radio frequency mixers and a variety of filters and amplifiers. This would compensate for Doppler shift but could also introduce losses in the already weak communication link.

Figure 6. Doppler Shift Surface Plot

Overall, the S-Band system should provide an excellent opportunity for experimentation and education given its reconfigurable nature. Also, if it is proven to work well in space, the knowledge gained about this system will benefit the CubeSat community as a whole.

Radio Antennas

The antenna systems onboard KySat1 proved to be an interesting design problem. This was due in part to the extreme size and mass limitations of a CubeSat. Also, because there will be only passive attitude control of the satellite, directionality of these antennas must be low to reduce radio dropouts as the satellite tumbles. The ideal antenna radiation pattern would be completely spherical and omnidirectional, but to achieve this, a phased array or phased cross-dipoles would need to be necessary. In an effort to save time, reduce deployment and integration complexity, as well as increase reliability, a simplified antenna system was used.

All radios on KySat1 will use a separate monopole antenna. Using separate antennas for all three radios will eliminate the need for additional antenna switching circuitry, and monopole antennas will provide a reasonably omnidirectional pattern. The only null in a monopole

radiation pattern will occur when looking straight into the end of the antenna. After analyzing orbital simulations, it was decided that this null will affect communication very rarely if ever. As an added benefit, monopole antennas also require only minimal matching circuitry. After simulating the radiation patterns using the satellite as a ground plane the images shown in Figures 7 and 8 were produced. As can be seen, the patterns of the VHF and UHF antennas are uniform and the only null is looking into the end of the antenna as estimated. The S-Band pattern looks somewhat questionable due to its non-uniformity.

Figure 7. Simulated VHF Antenna Pattern

Figure 8. Simulated S-Band Antenna Pattern

The antenna systems of KySat1 are simple, but this design has been used with success in previous CubeSats. For this reason, the design using monopole antennas can be trusted, and the time needed to design a complex phased antenna array can be spent improving other systems onboard KySat1.

Power System

The power system employed by KySat1 will consist of solar cells, a rechargeable battery, and an electrical power system (EPS) control board. Due to the small external surface area of KySat1, space for solar cells is very limited. In addition, the solar cells purchased for KySat1 come only in small pieces. This means that rather than having one or two large

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solar cells on each face of the satellite, there will be 8 to 16 small cells per face. Using smaller cells is costs less because factory remnant cells can be used. The downside of this method is a diminished packing factor because extra circuitry is required to control the cells. After calculating the expected output power and compensating for cell inefficiencies and poor packing factor, an average power of 0.25W has been estimated. This should be sufficient power as long as radio duty cycle remains low.

Due to the tight schedule of KySat1, it is hoped a COTS EPS module will be used. This board is being developed by Clyde Space. The Clyde Space EPS will control battery charging and battery temperature via onboard analog circuitry, requiring no external microprocessor input. This is an advantage because even in the event of a microprocessor crash, power systems will remain unaffected. This EPS module will accept power from a wide range of solar cell array configurations and should operate at 90% efficiency independent of the solar cell input voltage.

The EPS system of KySat1 will provide stable, efficient power to all components. It will automatically charge the onboard lithium ion batteries upon entering the sun, and each solar cell voltage at current can be monitored via its I2C interface. Its main advantages lay the lack of required input for operation, as well as its high operating efficiency. Overall, this system is not overly complex and is similar to working EPS in current use by other CubeSats. For these reasons, it will be an excellent solution for KySat1.

5. CONCLUSION

This paper introduced the KySat Project, the mission goals for KySat and the current status of the design. While the CubeSat standard offers great potential for rapid development of spacecraft, the availability of commercial components and subsystems is critical to rapid prototyping and development of CubeSats. Because the KySat1 design philosophy emphasizes rapid development, KySat1 is testing the limits of the use of commercial off-the-shelf components for CubeSat designs. While the primary mission for KySat1 is outreach and K-12 education, the effort will result in a bus standard that will serve as a basis for future KySat missions. In addition, KySat1 will verify the feasibility of the use of several new and existing off-the-shelf technologies in spacecraft. The development of the KySat1 bus continues with integration and system level testing scheduled for the fourth quarter of 2006. The flight model will be assembled and ready for launch in 2007.

REFERENCES

[1] H. Heidt, J. Puig-Suari, A.S. Moore, S. Nakasuka, R.J. Heidt, “CubeSat: A new Generation of Picosatellite for Education and Industry Low-Cost Space Experimentation,” 14th Annual/USU Conference on Small Satellites, August 2000.

[2] Michael Swartwout, “University-Class Satellites: From Marginal Utility to 'Disruptive' Research Platforms," 18th Annual AIAA/USU Conference on Small Satellites, Logan, UT, August 2004, SSC04-II-5.

[3] James Cutler, Gregory Hutchins, “Opal: Smaller, Simpler, Luckier,” 14th Annual AIAA/USU Small Satellite Conference, Logan, UT, September, 2000.

[4] Scott Flagg, “Using Nanosats as a Proof of Concept for Space Science Missions: QuakeSat as an Operational Example,” 18th Annual/USU Conference on Small Satellites, Logan, UT, August 2004.

[5] W. Lan, J. Brown, A. Toorian, R. Coelbo, L. Brooks, and J. Puig-Suari, “CubeSat Development in Education and into Industry,” AIAA Space 2006 Conference, San Jose, California, AIAA-2006-7296.

[6] Pumpkin, http://www.pumpkinc.com/

[7] CubeSatKit, http://www.cubesatkit.com/

[8] Texas Instruments, http://www.ti.com/

[9] Clyde Space, http://www.clydespace.com/

[10] Dallas Semiconductor, http://www.maxim-ic.com/

[11] The Stensat Group, http://www.stensat.org/

[12] COMedia, http://home.pacific.net.hk/~comedia/

[13] Microhard Systems, http://microhardcorp.com/

[14] Allied Wire and Cable, http://www.awcwire.com/

[15] Accu-Glass Products, http://accuglassproducts.com/

[16] Spectrolab Products, http://www.spectrolab.com/

[17] W.J. Larsen, J.R. Wertz, Space Mision Analysis and Design, Third Edition, El Segundo, CA: Microcosm Press, 1999.

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[18] K. Nakara, K. Konoue, H. Sawada, K. Ui, H. Okada, N. Miyashita, M. Iai, T. Urabe, N. Yamaguchi and M. Kashiwa, “Tokyo Tech CubeSat: CUTE-I – Design & Development of Flight Model And Future Plan”, 21st AIAA International Communications Satellite Systems Conference and Exhibit, Yokohama, Japan 2003, AIAA 2003-2388.

BIOGRAPHY

Garrett D. Chandler is currently pursuing a Doctorate of Philosophy degree in Electrical Engineering at the University of Kentucky. He completed the requirements for his Master of Science in Biosystems Engineering at UK in January of 2006. Prior to attending UK he obtained a Bachelor of Science degree in Agricultural Engineering from Texas A&M University in 2003. His current research focus is in

design, dynamic reconfiguration, and reliability management of embedded system architectures.

Jennifer B. Carter is a graduate student in Industrial Engineering at Morehead State University (MSU) where she is Graduate Assistant for the Space Science Center. She received her BS in Mathematics from Morehead in the spring of 2003.

Professor James W. Cutler's research involves development of enabling technologies and instruments for space systems. His current interests include robust computing infrastructure, global ground station networks, and ionospheric monitoring from low Earth orbit. His primary responsibility is teaching AA236--Spacecraft Design at Stanford University where students have launched nine satellites in the last ten years.

Daniel M. Erb is a student at Murray State University and is currently pursuing a BS in Engineering Physics. He will graduate in May of 2007 and will continue on towards a Masters Degree in Electrical Engineering.

Samuel F. Hishmeh is a graduate student at the University of Kentucky pursuing a Master of Science degree in Electrical Engineering. He completed his undergraduate career at the University of Kentucky in spring 2006, with Bachelor’s degrees in Computer Science and Computer Engineering. His research consists of embedded systems programming with a focus in fault-tolerance. He is currently the lead Software

Architect for the KySat project.

William C. Hutchison, III is currently pursuing a Masters degree in Mechanical Engineering at the University of Louisville, KY, and intends to seek a Doctorate of Philosophy in Mechanical Engineering as well. In 1981 he was granted a Bachelors degree in Aeronautical Engineering from Embry-Riddle Aeronautical University, Daytona Beach, FL.

Dr. James E. Lumpp, Jr. is an Associate Professor in the Department of Electrical and Computer Engineering at the University of Kentucky. He received the BSEE and MSEE degrees from the School of Electrical Engineering at Purdue University in 1988 and 1989 respectively, and the PhD from the

Department of Electrical and Computer Engineering at the University of Iowa in 1993. He joined the faculty at the University of Kentucky in 1993. His research interests include distributed embedded systems, safety critical systems, and high-performance distributed computing.

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Dr. Benjamin K. Malphrus is Professor of Space Science at Morehead State University where he also directs the Morehead State University Space Science Center. He served as project director of the design and construction of the 13 M Morehead Radio Telescope and the 21 M Space Tracking Antenna operated by the Center.

Dale T. McClure is a student at the University of Kentucky and is currently working towards a BS in Electrical Engineering. Upon graduation in the fall of 2006 he will begin pursuing a Masters of Science in the same area. He holds an amateur radio operator’s license and his research interests include long range RF communication, embedded systems, and digital signal processing.

Gregory R. Strickler is a graduate student at Western Kentucky where he is pursuing a Master of Science degree in Computer Science. He received his Bachelors degree in Computer Science from Western Kentucky in the spring of 2005. His interests include graphical and web based programming.

Professor Robert J. Twiggs came to Stanford University in 1994 from Weber State University in Ogden, Utah. His primary interest is in the development, launch and operation of small low-cost satellites for space applications feasibility demonstrations and the space qualification of new spacecraft components. He is also interested

in the development of low-cost satellite communications for command, control and data acquisition at remote earth locations, and in the miniaturization development of space experiments for low-cost spacecraft missions.