Bridging the Gap: Collaboration Using Nanosat and CubeSat Platforms Through The Texas 2 STEP (2 Satellite Targeting Experimental Platform) Mission

Transcription

1 SSC08-X-8 Bridging Gap: Collaboration Using Nanosat and CubeSat Platforms Through The Texas 2 STEP (2 Satellite Targeting Experimental Platform) Mission Cinnamon Wright, Dax Garner, Jessica Williams, Henri Kjellberg, E. Glenn Lightsey The University of Texas at Austin, Department of Aerospace Engineering and Engineering Mechanics 210 E. 24 th St. Austin, TX ; Cinnamon.wright@gmail.com ABSTRACT The Texas 2-STEP (2-Satellite Targeting Experimental Platform) mission is University of Texas at Austin's (UT- Austin) entry into University Nanosat-5 (UNP-5) competition, a program sponsored by Air Force Research Laboratory (AFRL), NASA and American Institute of Aeronautics and Astronautics. The 2-STEP mission is to perform an autonomous rendezvous and formation flight demonstration using an innovative and inexpensive GN&C system. Two vehicles will be launched in a joined configuration but will perform a separation maneuver on-orbit to drift apart to a distance of 3 kilometers. When commanded, larger, actively controlled Chaser nanosatellite will autonomously maneuver back to within 100 meters of smaller, passively controlled Target. The Target vehicle is designed based on CubeSat platform, a design solution that merges Nanosat and CubeSat programs in a unique collaboration that has not been previously demonstrated. A standard CubeSat platform has been designed using commercial hardware which can be adapted for a 1U (1-Unit), 2U or 3U CubeSat mission. Use of CubeSat standard is a responsive space solution that incorporates a modular vehicle design for use in multiple university missions. Adoption of this standard also promotes collaboration between Satellite Design Laboratory programs at UT-Austin. This paper will review Texas 2-STEP mission and highlight how Target vehicle is bridging a gap between Nanosat and CubeSat communities. Elements of vehicle design as well as Chaser-Target team cooperation will also be covered. INTRODUCTION The University of Texas at Austin has actively participated in small satellite design, fabrication, and testing for past 10 years. The satellite program at UT-Austin has been formally housed in Satellite Design Laboratory (SDL) since its founding in The SDL is devoted completely to student design, prototype, and flight assembly work, and educational opportunities are offered to students at all seniority levels under faculty supervision. Since laboratory s inception, student satellite program at UT-Austin has expanded to include four distinct satellite missions. Each program in SDL is funded and overseen by a different sponsor, and each has a unique set of mission objectives. Only one vehicle adheres strictly to CubeSat standards; remaining three programs are picosatellite (<5 kg) and nanosatellite (<50 kg) scale vehicles. This paper focuses on Texas 2-STEP mission (2-Satellite Targeting Experimental Platform), which is UT- Austin entry into University Nanosatellite Program (UNP) competition. The Texas 2-STEP mission was adopted from ARTEMIS (Autonomous Rendezvous & Rapid Turnaround Experiment Maneuverable Inspection Satellite) mission, a vehicle designed for an earlier UNP cycle review. Rendezvous mission objectives are to be accomplished using separate Chaser and Target vehicles that are to be launched in a stacked configuration and separated on-orbit. In earlier design, ARTEMIS Target vehicle was essentially a miniaturized version of ARTEMIS Chaser vehicle. At conclusion of ARTEMIS design and commencement of Texas 2-STEP design, decision was made that Target vehicle could be implemented as a 3-Unit (3U) CubeSat and still accomplish mission objectives. The implementation of this concept was highly feasible as a CubeSatstandard vehicle was already under development in SDL. This paper documents development of CubeSatbased hardware components within Satellite Design Laboratory and how y have been uniquely incorporated into Texas 2-STEP nanosatellite mission. Each satellite program in SDL is introduced, and mission objectives and mission sequence for design-stage programs are outlined. The process of adopting CubeSat standard hardware components for 2-STEP is shown, leading to a nearly complete design for Texas 2-STEP Target vehicle. Wright 1 22 nd Annual AIAA/USU

2 Figure 1: SDL Design concepts and hardware realization for picosatellite and nanosatellite vehicles. BACKGROUND The SDL has housed and currently supports four vehicles thatt are part of national design competitions, government sponsored missions, and departmental concepts. These programs are knownn as CubeSat,, Texas 2-STEP, and FASTRAC. Thesee vehicles are shown in Figure 1. The laboratory space features soldering stations, hardware cabinets, and Flat Sat testing configurations for all current and future vehicles. The CubeSat project is a bench top CubeSat satellitee that has been independently supported by Department of Aerospace Engineering since The purpose of CubeSat project is to develop, build, test and operate an affordable plug and play satellite system that will create an infrastructure for future UT-Austin CubeSat missions. (Platform for Autonomous Rendezvous and Docking with Innovative GN&C Methods) is a collaborative picosatellite mission with Texas A&M University that is sponsored by NASA s Johnson Space Center (JSC). Each university is contributing a picosatellite to mission that willl be launched onboard Space Shuttle mission STS-127 in April The primary mission objective is to collect and downlink one complete orbit of Dragon GPS receiverr data, a receiver that is built by NASA JSC. has a mass of no more than 3.5 kg and conforms to 5 x 5 x 5 inch volume allocated in Space Shuttle Picosatellite Launcher (SSPL). It adheres to Shuttle launch and safety requirements. The Texas 2-STEP (2-Satellite Targeting Experimental Platform) is UT-Austin The purpose of Texas 2-STEP is to entry into UNP-5 competition. perform autonomous, on-orbit, proximity operations with a rapidly producible nanosatellite; this shall be accomplished by maneuvering a Chaser satellite from a stand-off distance to a station keeping orbit about a cooperating Target satellite. Texas 2-STEP is participating in a Proto-Qualification Review (PQR) as part of UNP-5 competition at 22nd Annual AIAA/USU in August Finally, FASTRAC (Formation Autonomy Spacecraft with Thrust, Relnav, Attitude and Crosslink) is winner of University Nanosat-3 (UNP-3) competition that was held in January The purpose of FASTRAC is to investigate enabling technologies for satellite formations. The FASTRAC design is largely completed and is awaiting integration to its launch vehicle. FASTRAC has been manifested for launch by US Air Force in December The FASTRAC vehicle design was completed before start of CubeSat,, and Texas 2-STEP programs. Wright 2 22 nd Annual AIAA/USU

3 with two o lithium polym mer batteries. The battery packs are able to t hold a maxim mum potential of 8.2 V. The EPS board han ndles all neecessary functiions to regulatee output vooltage to 5 Volts V and 3.3 Volts, as welll as charge th he batteries from m solar pan nels. PICOSATELLITE PROG GRAMS U of Texas T at Austinn As previously stated, The University p cale programs. has participaated in two picosatellite-sc The history of o CubeSatt and PARADIIGM programss are briefly described, wiith key missiion objectivess highlighted. The vehicle designs d are alsoo described, ass well as e flow of haardware choicces from onee picosatellite program p to anoor. CubeSat The Univerrsity of Texxas at Austtin started a departmentallly-funded CubbeSat project thhat has evolvedd through threee stages over time. t The origiinal mission off CubeS Sat was to implement a wirelesss communicatiion system bettween subsysteems in order too fulfill neeed for eliminatting complex wire w harnessingg in satellites. At this timee, CubeSaat project wass named WipSat. The program n evvolved into a mission that would fulfill t need for a reusable plug-and-play Cu ubesat bus thaat would utilizze a LabVIEW W Embedded RTOS. R The puurpose of e mission nn became to op perate sateellite bus on-orrbit in order too increase technology reeadiness level (TRL) of e hardware com mponents andd to increase thhe TRL of e ground statioon in preparattion for 2009 launch off FASTRAC. At A this time, th he bus design for f originaal 1U CubeSat had been adappted into a 3U form factor inn order to servve as Targeet spacecraft foor Texas 2STEP missiion. This keey design meerger initiatedd additional program collaborations within SDL. Figure 2: ClydeSpacce 1-Unit CubeeSat EPS Board with on ne battery pacck. The Sten nsat Group, LLC L produces a UHF/V VHF radio whhich has a buuilt-in TNC and a abilityy to receive at a 1200 baud aand transmit at a 9600 baud. The radio cusstom produced for PARADIG GM by Stensatt has utilizes UHF U bands ffor both uplinnk and downnlink transmisssions. The boaard communicaates over a UA ART interface and has variabble output poweer up to 1 wattt. The originaal CubeSat bus design utilized twoo commercial off shelff products: a Clyde Spacee ower System (EPS) board and a Stensaat Electrical Po Group, LLC C. UHF/VHF radio. These are shown inn Figure 2 and d Figure 3. A custom comm mand and dataa handling sysstem was desiggned to be run n by a Blackfinn microprocesssor running LabVIEW L Embbedded RTOS. Hardware co omponents arre connected to each orr using a PC C-104 connecttor stack. Paassive on-orbit vehicle stabiilization is obbtained by a combination c off hysteresis rod ds and perman nent magnets. dio for CubeS Sat Figure 3: Stensat Grroup, LLC rad UHF/VHF communicaation. The Clyde Sp pace 1-Unit Cu ubesat EPS booard has provedd to be a robuust and durablee product. Thee EPS board iss capable of holding h two 1.25 Ah batterry packs, eachh Wright 3 22nd Annual A AIAA/U USU

4 Figure 4: PARADIG GM Concept off Operations. componeents would alsoo fulfill ir mission m needs. The PARADIIGM team choose to inherit CubeSat bus design even e though t satellite has h approximaately twice volume of a sttandard CubeS Sat. M The PARAD DIGM projecct is a seriees of NASA A sponsored jooint picosatelllite missions designed andd fabricated by y UT-Austin and a Texas A& &M Universityy. The program m aims to fulfill NASA A s need forr autonomous rendezvous and dock king in e Constellation n program s innfrastructure. The T goal of e M program is to accomplish this using twoo small satellites each with w a form m factor off approximatelly 5 x 5 x 5. ge change wass made to standardized bus. One larg Instead of utilizing LabVIEW Embedded, PARADIIGM team oppted to run thhe same Blacckfin microprocessor with Linnux Embeddedd in order to obbtain e more control over thhe operating environment. The Commannd and Data Haandling (CDH)) board is a cusstom design prrototyped at UT-Austin. It ho olds a Bluetechhnix Blackfin Core Module, a Mini SD carrd for data storrage, and vario ous signal coonditioning cirrcuits to optim mize communiication to subsystems. s A voltage regulaation circuit has h been deveeloped to inccrease ouutput voltage from f poweer board to up to 12 Volts. This T custom soolution is pictuured in Figure 5. 5 The first mission in seriies consists of 2 picosatellitess o a minim mum of two orbits o worth off that aim to obtain GPS data fro om a NASA deesigned GPS receiver r knownn as Dragon. The T two satellittes cooperativeely interface inn Space Shhuttle Picosatelllite Launcher (SSPL), ( but flyy independentlly after ejection n. The Concept of Operationss for this misssion is shownn in Figure 4. 4 The currennt mission is inn final fabrrication stage, with a launchh date schedulled for April Future missions m in e M series will require r implem menting activee attitude conttrol and thrusting capabilitiies to perform m rendezvous and a docking maaneuvers. Both M and CubeeSat vehicless encompassed d similar hardw ware componennts in a slightlyy different form m factor. In ordder to maximizze utility off limited maanpower resoources, CubeSat andd M teams were consolidated into a singlee team whosee current fo ocus is to complete e M vehicle. M Adaptation Figurre 5: Custom U UT-Austin CD DH board with h Bluetechnix B Blackfin Coree Module The hardwarre design usedd for CubbeSat was nn adopted by progrram as see Wright 4 22nd Annual A AIAA/U USU

5 Utilization of UT-Austin CubeSat bus with commercial off shelf products has allowed development teams to focus on ir satellite s system design rar than on developing custom hardware solutions. SATELLITE DESIGN LABORATORY COLLABORATION Each SDL program has, until 2007, operated independently from one anor. Though teams have worked essentially side by side, collaboration between teams has occurred only when requested. As three programs currently under design (Texas 2-STEP,, and CubeSat) continued to develop, design obstacles and team management challenges encountered by each independent team were not unique. Commercial hardware selection for a low-budget space vehicle was incredibly limited, and recruiting and maintaining student personnel was an annual setback. Each program was essentially faced with same challenges while developing a vehicle platform to carry out a unique mission. Within SDL, it became apparent that numerous elements of each vehicle design, especially key bus components, could be duplicated not only but among or satellite projects as well. Although and CubeSat vehicles are an order of magnitude smaller than Texas 2-STEP vehicle, unique nature of Texas 2-STEP mission permitted Target vehicle to be designed at a comparable scale to that of picosatellite missions under development. Within growing CubeSat community, bus hardware components have become increasingly commercialized. For example, Pumpkin, Inc. CubeSat Kit TM permits a CubeSat vehicle to be assembled virtually off shelf. 2 Several commercial components, including Clyde Space Power Board, have already been integrated into UT-Austin CubeSat vehicle design. 3 The use of CubeSat hardware n flowed to vehicle, and n to Texas 2-STEP Target vehicle. NANOSATELLITE PROGRAMS community. First, re is a need for satellites that can perform on-orbit operations with or space vehicles. For many satellites, minimal communication with ground makes complex maneuvers impossible, so some operations must be autonomous. This capability is driven by vehicles which have needs that include refueling, repairs, maintenance, inspection, upgrades, parts replacement, science, and communications, among or services. Additionally, a global need exists to be able to build and launch satellites into orbit quickly. A university level program also needs to reduce amount of work necessary to perform a new mission. Developing a re-usable satellite bus design which includes structure, command and data handling, electrical power systems, communication and experimental subsystems is one step toward fulfilling se needs. The first step toward developing a maneuverable proximity operations satellite is to develop a satellite which can perform controlled maneuvers, under constraints defined by University Nanosatellite Program. A good starting point in developing this technology is to launch two satellites toger, separate m in orbit, let m drift to a defined distance, and n perform controlled maneuver such as a rendezvous with two satellites. Thus, first goal for Texas 2-STEP mission is to perform a coordinated onorbit maneuver, such as separation and rendezvous. Here, rendezvous is defined as bringing two satellites back to within a defined separation distance relative to each or. A second goal is to develop a reusable satellite bus design for future missions, especially for satellite program at The University of Texas at Austin. To fulfill se goals, purpose of Texas 2-STEP is to perform six degree-of-freedom autonomous, on-orbit, proximity operations between two nanosatellites. For greater program efficiency, a standard, re-usable satellite bus design shall also be created. This design should be well documented so that anor student team could easily build satellite bus simply by following documentation. Texas 2-STEP Mission Overview The Texas 2-STEP mission was created in response to two clear needs expressed by nanosatellite Wright 5 22 nd Annual AIAA/USU

6 1 Launch/Orbital Insertion 2 LV Separation 3 Checkout T 0 = 0:00 T LVsep = T 0 + min T Health = days Downlink Uplink 4 Chaser/Target Sep. T C/Tsep = T LVsep + days 5 Drift T drift = 1 hr 6 Initiate Rendezvous T ren = T C/Tsep + 1 hr Xlink Xlink ~3 km 7 Controlled Return T ret = 1 hr 8 Station Keeping T prox = days 9 Extended Mission/End of Life T end = T months min. ~150 m Figure 6: Texas 2-STEP Concept of Operations. The concept of operations for Texas 2-STEP mission is depicted in Figure 6. In launch vehicle, Texas 2-STEP satellites shall be housed as a secondary payload. The launch vehicle will carry both Target and Chaser satellites in a stacked configuration, with satellites inhibited and powered off. The launch vehicle separation phase begins with a mechanical detachment of stacked Texas 2-STEP nanosatellite from launch vehicle. The check-out phase begins when satellite is at least 90% charged and continues until it has been confirmed that each subsystem is working properly or until a maximum amount of time has elapsed. This could take several days. The Chaser/Target separation phase is initiated when signal is sent from ground to separation system. This phase lasts only seconds. When Chaser satellite confirms separation, drift phase begins. Here, satellites will drift approximately 3 kilometers apart over a time period of about 1 hour. After drift mode is complete, Chaser will gain an attitude lock for projected path to Target. Once desired attitude is obtained, thrusters will fire to initiate return to Target. Once Target and Chaser are within 150 meters, Chaser will establish a relative orbit around Target for proximity operations. The end-of-life segment begins once one successful rendezvous has been completed or propellant has been depleted to a specified level. It is during this phase that data from rendezvous maneuver will be down-linked. If enough propellant remains, n more propulsion experiments will be performed. Adequate fuel should also be reserved in order to perform an end-of-life separation burn. In interest of outreach and education, satellites will n be opened to Amateur Radio Community and possibly or Wright 6 22 nd Annual AIAA/USU

7 educational organizations. Texas 2-STEP is currently in development phase as project begins fabrication and finalizes satellite design in preparation for PQR in August Texas 2-STEP Vehicles The Texas 2-STEP vehicle is composed of two satellites, larger Chaser and smaller Target. Texas 2-STEP is comprised of 2 satellites, Chaser and Target. The Chaser satellite is designed to actively separate and autonomously rendezvous with cooperating Target satellite. (In this cooperativee relationship Target will have no control but will send out position data to Chaser). These vehicles have been designed by students at UT- Austin. The design for Chaser vehicle is now described. Figure 7 displays stacked vehiclee configuration. The Mk II II Poly Picosatellite Orbital Deployer (P-POD) device, manufactured by Californiaa Polytechnic University, is mounted to Chaser spacecraft and will be used to separate Target from Chaser on-orbit. 4 The Target is held within P- POD; Chaser will be attached to launch vehiclee through Lightband separation system. still limited both teams due to time and manpower. Now re is a separatee Target team, within 2-STEP in which team collaborates with and uses as much of baselinee CubeSat design as possible. Texas 2-STEP Chaser The Chaser vehicle design uses an R-134A, refrigerant based, cold-gas thruster system to provide attitude control and total ΔV neededd to perform rendezvous. A Bluegiga WT11 Bluetooth device will independently verify that Chaser and Target have separated and accomplished rendezvous. The Chaser s structure is derived from UNP-2 competition winner, Three Corner Sat. Fifteen Sanyo Cadnica Ni-Cd N-4000DRL batteries and GaInP2/GaAs/Ge Triple Junction solar cells will power Chaser. For communicating to Target and ground, Chaser willl employ a Stensat radio. The command and data handling subsystem (CDH) used for Texas 2-STEP is composed of two separate computers. An Arcom Viper 400MHz PXA255 XScale RISC processor will manage communication of Chaser with Target and ground station as well as control power subsystem, verification subsystem, and any or internal functions not related to GN&C activities. The Embedded Planet 8280 computer using a Freescalee PowerQUICC II PowerPC processor will support guidance, navigation and control algorithms and willl command thruster subsystem. The computer will have a hard real-time QNX operating system to handle GNC specific computations necessary to maneuver Chaser. For GN&C system, a suite of relatively inexpensive sensors are used. These include a Honeywell 3-axis magnetometer, an X Sense MEMS IMU, an Orion GPS, and an Optical Energy Sun. 6,7,8 These are shown in Figure 8. Sensor information will be combined in an Extendedd Kalman Filter to estimate position of Chaser satellite relativee to Target. Figure 7: Texas 2-STEP stacked configuration without solar panels The 2-STEP team was originally one single team whose job was to design, build, and test both Chaser and Target satellites. Each member belonged to a subsystem whose responsibility was to design that subsystem for Chaser and Target satellites. With this system it seems that progress was only being made on Chaser satellite. The next step was to have CubeSat team also design Target satellite, since designs weree so similar. This worked much better, but Figure 8: Sensor Selection for Texas 2-STEP nanosatellite. Wright 7 22 nd Annual AIAA/USU

8 Figure 9. Design evolution of Target vehicle for ARTEMIS and Texas 2-STEP programs. Texas 2-STEP Target The Texas 2-STEP Target vehicle is a fully functional vehicle that can operate independently of Chaser vehicle while in orbit. Developing Texas 2-STEP Target vehicle as a 3-Unit CubeSat essentially makes it a fifth SDL vehicle even though it is not part of a separate program. The Texas 2- STEP Target vehicle bridges a gap between University Nanosatellite Program and CubeSat communities by developing a program that adheres to both UNP and CubeSat standards. With selection and development of key bus components by CubeSat and programs, se design choices were now investigated as hardware components for 2-STEP Target design. First, original target design for ARTEMIS program is outlined; evolution of Texas 2-STEP Target design in conjunction with CubeSat hardware development is n explored. Artemis Target Design Heritage Most of focus during earlierr ARTEMIS mission was directed toward design of larger and more complex Chaser satellite. This was primarily due to lack of personnel relative to number of satellite projects that were under development at SDL. Because of this lack of focus, only Target satellite design components that progressed to competition were outer structure and solar panel layout. The original structure design is shown in left side of Figure 9. The original design of Target structure was n designed as a scaled version of Chaser satellite in order to better match ballistic coefficients of two satellites and increase accuracy for Guidance Navigation and Control (GNC) system. This updated Target design is shown in center of Figure 9. Toward end of UNP-4 competition, as result of a desire to minimize amount of work being duplicated on multiple satellite projects, Target satellite also began adopting parts of CubeSat team s design in a similar fashion as was done for. The CubeSat s hardware components that were incorporated included passive attitude stabilization using magnets, and Blackfin Microprocessor. Texas 2-STEP Target Design For entry into UNP-5 competition it was realized that several of UT-Austin satellite projects needed similar basic capabilities and decision was made to unite programs to maximize productivity and likelihood of success for all of satellitee projects. Therefore, it was decided thatt Target satellite should be a unit (3U) version of CubeSat design thatt was already in progress. The CubeSat team n took on design of 2 STEP Target satellite in addition to ir original CubeSat project. Wright 8 22 nd Annual AIAA/USU

9 receiver used will be receiver which was used on FASTRAC, which was Orion GPS receiver shown in Figure 11. Figure 10: Current 2 STEP Target Satellite Design. However, addition of Target satellite as an additional user of shared UT-Austin CubeSat bus changed framework of UT satellite program and aided greatly in design of 2-STEP Target satellite. The Target design is now nearing completion as UNP-5 competition comes to a close. The current design is shown on right side of Figure 10. Not every aspect of CubeSat design was acceptable for 2-STEP program, and numerous subsystem components required a custom solution to accomplish mission objectives. For vehicle structure, Target is using Pumpkin, Inc. 3-Unit CubeSat skeletonized structure. This is only UT-Austin vehicle that utilizes this 3U hardware component. The Target is may or may not utilize Clyde Space EPS board, as Lithium Polymer batteries that are standard for Clyde Space board must be modified to meet UNP-5 requirements. These requirements necessitate using Nickel Cadmium batteries. The passive attitude stabilization system utilized by CubeSat and by have also been removed since 2- STEP mission levies no attitude requirements on Target spacecraft. Figure 11: Orion GPS Receiver. Since sensors and software used to perform rendezvous maneuvers have not been tested in space, an independent system is needed to verify rendezvous. The verification system used onboard both Chaser and Target spacecraft is Bluegiga Bluetooth Chip WT previously described for Chaser shown in Figure 12. This system can provide an estimate of position of chaser satellite relative to target satellite up to 300 meters. If satellites can link to one anor using se Bluetooth modules n it is certain that y are within 300 meters from one anor. Also, a linear relationship, between power of received Bluetooth signal and relative distance of two satellites can be established. This can be used to verify that position data from sensors is accurate. For vehicle communication, 2-STEP mission requires Target to transmit position data to Chaser vehicle, so an additional inter-satellite communication system is needed. As a result of this need, custom CDH board must be modified in order to support all of functionality needed for updated communication system, GPS receiver, and verification system. The Blackfin processor, however, can still be used. The GPS Wright 9 22 nd Annual AIAA/USU

10 Program. Figure 13 depicts experimental set-up for microgravity flight. Previous studies have investigated separation dynamics where separation takes place along axis of symmetry. FASTRAC is an excellent example of a mission using separation in this direction of motion; however, nanosatellite missions need not be limited to axisymmetric separations. Since P- POD does not eject target vehicle along axis of symmetry a rotational force will be imparted on Chaser vehicle. This force is difficult to accurately estimate refore it is useful to measure this force aboard C-9. The measurements from this experiment can n be used in software simulations and can help answer critical design questions. Figure 12: Bluegiga Bluetooth Module. NANOSAT AND CUBESAT COOPERATION Areas of cooperation between Nanosat and CubeSat design standards are not limited to vehicle hardware components. The SDL has utilized P- POD launcher as a separation system for Texas 2- STEP mission, and has also jointly tested Nanosat and CubeSat hardware via UNP Student Hands On Training (SHOT) workshop. Texas 2-Step Separation System Regardless of choice for size or components of Target satellite, re is still a need to develop a system to separate Target from Chaser. A creative design solution uses P-POD as a separation device between two satellites once it was decided that Target would follow CubeSat standards. Microgravity Experiment The P-POD is primarily intended as a separation device between CubeSat payloads and a launch vehicle. However use of P-POD as a separation device between two satellites on-orbit, as proposed by Texas 2-STEP, is unprecedented. Therefore, re is a need to understand vehicle dynamics during separation. In July 2008, an undergraduate student team will focus on one aspect of problem: free-fall separation dynamics and resulting linear and angular motions of separating satellites. The experiment will fly as a free floating experiment on modified C-9 aircraft as a participant in NASA Microgravity University Figure 13: P-POD Separation Experiment Set-up. The experiment will be valuable to entire small satellite community, which includes CubeSat designers all over world. CubeSats are becoming a very popular satellite design choice for industry and student projects due to ir relatively low cost and standardized features such as P-POD separation device. 1 The data will also be useful to many members of aerospace industry as well as scientific research community. Separation systems similar to one microgravity team proposes to test will be necessary for a variety of nanosatellites. The data will help engineers predict resulting separation motion of se systems not only for Texas 2-STEP but for any or missions as well. Wright nd Annual AIAA/USU

11 SHOT Collaboration As a result of utilizing similar satellite busses between nanosatellite and picosatellite programs, and Texas 2-STEP teams were able to collaborate on a high-altitude balloon launch through Students Hands-On Training (SHOT) program in June This program was made available through University Nanosat Program. The purpose of SHOT program is for members of each university competing in UNP to design and fabricate a balloon payload to test certain subsystems within ir nanosatellite s design. The unique combination between and Texas 2- STEP projects allowed one balloon payload to flight test Clyde Space EPS Board, Stensat Group, LLC. radio, and Blackfin microprocessor benefitting both projects. The payload is shown in Figure 14. Figure 14: SHOT II Payload. BENEFITS Adopting common bus hardware components into a new vehicle design, particularly components that have been developed, tested, and documented, partially eliminates need for duplicate subsystem design work to be performed by limited number of students who work in Satellite Design Laboratory. A goal of UNP program, as well as satellite community, is responsive space, which enables a space vehicle to be quickly designed, built, and launched in order to accomplish a pressing objective. Adopting a generic CubeSat-based bus for SDL allows a new SDL vehicle to quickly go from concept to design and into hardware fabrication in a shorter amount of time. Future designs have benefit of what has gone before. CONSIDERATIONS Adopting CubeSat hardware components among non- CubeSat standard programs has not been without some drawbacks. In particular, challenges have been encountered within Texas 2-STEP mission and within concept of a common vehicle bus. These drawbacks are managed as y are encountered and ultimately have not undermined this resource-sharing system. One noteworthy problem with using CubeSat based hardware, and especially hardware components that have heritage in SDL, was that se hardware components did not always meet standards required by Nanosatellite program that always were levied by United States Air Force. For example, Nanosatellite vehicles cannot utilize Lithium Polymer batteries in ir design due to safety restrictions. As a consequence, proposed Target vehicle must use Nickel Cadmium batteries in design, a bulky alternative that requires much of available internal volume within 3U CubeSat. This is shown in central portion of Figure 10. However, since hardware needed to achieve Texas 2-STEP mission objectives occupies only 1U of 3U form factor, this increased volume allocation for battery space has been accommodated within vehicle. In addition, each program must ensure that ir mission objectives can be accomplished by adopting a particular hardware component that has flowed from generic bus design. It is tempting to adopt work merely because it has already been performed. Past trade studies among hardware choices must be re-investigated and compared to current mission needs to reaffirm that hardware choice is appropriate. For most part, only generic hardware components that function almost identically with regard to a vehicle s mission objectives are shared. As CubeSat community grows, commercial hardware components continue to both improve and become more readily available. The SDL programs must examine newly available technology and weigh se options against convenience of using a preexisting design. However, once a subsystem been proven successful in space, re is strong incentive to continue its use.. FUTURE PROGRAMS With advent of a generic CubeSat hardware bus as developed by UT-Austin, a skeleton framework for future picosatellite scale missions is in place. The laboratory can now make use of CubeSat standard Wright nd Annual AIAA/USU

12 hardware components which are easily adapted and customized to meet individual program mission objectives. ACKNOWLEDGMENTS The authors wish to thank all students who have worked in Satellite Design Laboratory over years have put in countless hours of work to make each program possible. The UT Satellite Program has allowed many students to get hands-on experience and greatly expand ir wealth of knowledge gained from this department. This would not have been possible without our advisors Dr. E. Glenn Lightsey, Dr. Robert H. Bishop, Mrs. Lisa Guerra, Dr. Cesar Ocampo, and Dr. Sean Buckley. Thank you to NASA, AIAA, and The Air Force Research Laboratories for ir continued sponsorship of programs in SDL and for ir support, advice, and criticism. These have improved programs here at UT greatly. Also, thank you to students and advisors and California Polytechnic State University for ir help and cooperation with CubeSat and use of ir P-POD separation system. REFERENCES 1. Toorian, Armen, et al. "CubeSats As Responsive Satellites." AIAA Proceedings, Long Beach, California, August 30, Pumpkin CubeSat Kit TM. Pumpkin, Inc. accessed, May U CubeSat Power Datasheet. Clyde Space Ltd. accessed, June Poly Picosatellite Orbital Deployer Mk III ICD California Polytechic University POD%20Mk%20III%20ICD.pdf accessed, June IMI-101 Miniature 3-Axis Reaction Wheel Product Specification. IntelliTech Microsystems, Inc. Autonomous Vehicle Technologies. space.html accessed, June MTi Miniature Attitude and Heading Reference System XSENS Motion Technologies. accessed, June Sun Sensors Optical Enegy Technologies Inc. accessed, June Three Axis Magnetic Sensor Hybrid Honeywell. tasheets/hmc2003.pdf accessed, June Wright nd Annual AIAA/USU