Simplified Dynamic Model Generation and Vibration Analysis, of the International Space Station Mission 12A José J. Granda §, Louis Nguyen†, Montu Raval§ § California State University, Sacramento. Department of Mechanical Engineering Sacramento, California, 95819 † NASA Johnson Space Center Integrated Navigation, Guidance and Control Analysis Branch, Houston, TX 77058 ABSTRACT The use of computer models to predict the dynamic behavior of Space Vehicles is now a well accepted technique used to understand the natural frequencies and dynamic system responses of a complex flexible multibody system such as the International Space Station. Each new mission of the Space Shuttle after STS114, is destined to build the remaining of the International Space Station (ISS) and each new mission presents new challenges that need to be confronted during flight. One of those is the contingency plan for inspection, repair of the shuttle known as Orbiter Repair Maneuvers. The complete physical system needs to be modeled on a computer to understand the modes of vibration and to design a control system capable of controlling the proposed maneuvers. Building on the theoretical principles and procedures established in Granda, Nguyen1, the authors present the development of a computer model of ISS Mission 12A. As the station is built in space, here on earth, the authors build the components from scratch from generation of each component to assembly and dynamic analysis of ISS Mission12A configuration. The authors propose a simplified modeling technique compared to the actual methods currently in place at NASA and test their model with data from real flights. Such process and results are presented here using a technique that mixes solid modeling and dynamic finite element modeling. Software packages such as SOLIDWORKS, NASTRAN4D, MATLAB and SIMULINK have been incorporated in the process. Since the International Space Station is a combination of rigid and flexible bodies, a dynamic finite element model is appropriate instead of a standard rigid multi body model. Flexible members are analyzed as distributed systems with an infinite set of vibration modes. Once the model has acquired a level of detail in accordance with the actual station, tests are conducted for modal analysis, guidance and control of flight and Orbiter Repair Maneuvers. This research proposes a new method for producing a new generation of simplified computer models while still preserving significant dynamics information. I. INTRODUCTION The international Space Station is a project supported by twelve nations in which the United States and Russia play a central role. It may be helpful for the reader not familiar with the details of the construction of the Space Station to go over the initial missions already accomplished until we reach Mission 12A which is the objective of this paper. In doing this the authors also familiarize the reader with the assembly of the sequential computer models that had to be generated for prior missions in order to reach Mission 12A. Just as in the building of ISS, the computer models of modules were put together until the configuration reached Mission 12A. Missions have either and A or an R designation in their names, the A stands for American, the R stands for Russian. The following flights and configurations are listed in the order of launch2. __________________________ § Professor, Department of Mechanical Engineering, email: [email protected] AIAA Member * Integrated Navigation, Guidance and Control Analysis Branch, email:[email protected] AIAA Member § Graduate Student, Department of Mechanical Engineering email: [email protected] 1 A. FLIGHT BACKGROUND INFORMATION 1. Flight 1A/R (Russian Proton Rocket). The first element launched was the Control Module named Zarya, the Russian word for “sunrise.” Zarya provides propulsion control capability and power through the early assembly stage. It also provides fuel storage and rendezvous and docking capability to the Service Module. The 18,182- kilogram pressurized spacecraft was launched on a Russian Proton rocket. As assembly continues, Zarya provided orbital control, communications, and power for the U.S.-built Node 1, Unity. During this period, Zarya controlled the motion and maintained the altitude of the Space Station’s orbit. It also generated and distributed electrical power and provides ground communications. In the later stages of ISS assembly, Zarya primarily provide storage capacity. It be used throughout the life of the Space Station. 2.. Flight 2A (Shuttle Flight). On flight 2A, Unity and Pressurized Mating Adapters (PMA) 1 and 2 were launched in 1998. The PMA-1 connects the U.S. and Russian elements. The PMA-2 provides a Shuttle docking location. Unity’s six ports provide connecting points for Zarya, as well as the Z1 truss, airlock, cupola, Node 2, and the Multi-Purpose Logistics Module, to be delivered later. Unity is a connecting passageway to the living and working areas of the ISS—the U.S. Habitation and Laboratory Modules—and airlock. It is the first major U.S.-built component of the ISS. It contains more than 50,000 mechanical items, 216 lines to carry fluids and gases, and 121 internal and external electrical cables using 9.7 kilometers of wire. 3. Flight 1R (Russian Proton Rocket). Flight 1R launched the Russian Service Module, the primary Russian element. The Service Module provided the Environmental Control and Life Support System elements and was the primary docking port for the Progress resupply vehicles. It also provided propulsive attitude control and reboost capabilities, early Space Station living quarters, electrical power distribution, the data processing system, the flight control system, and communications. Although many of these systems will be supplemented or replaced by later U.S. ISS components, the Service Module will always remain the structural and functional center of the Russian segment of the ISS. 4. Flight 2A.1 (Shuttle Flight). The flight element for 2A.1 is the Spacehab Logistics Double Module. The purpose of the double spacehab flight is to provide a logistics flight for the early assembly missions. It carried equipment to further outfit the Service Module and equipment that can be off-loaded from the early U.S. assembly flights. The Double Module has the capacity to hold up to 4,536 kilograms as well as the ability to accommodate powered payloads. 5. Flight 3A (Shuttle Flight). Flight 3A delivered the Integrated Truss Structure (ITS) Z1. The Z1 truss is used as a mounting location for the P6 Truss Segment and Photovoltaic (solar array) Module. This Photovoltaic Module provides power for the early science that will be done on the ISS. Also being delivered on this flight was the third Pressurized Mating Adapter and the Control Moment Gyros (these provide non propulsive attitude control). In addition, the Ku-band communications system was be installed on this flight (and later activated on flight 6A). This system provided video capabilities to support ISS scientific research and television transmissions. 6. Flight 2R (Russian Soyuz Rocket). This launch established the first ISS three-person crew, or Expedition I. The Commander was a U.S. Astronaut and the other two crew members were Russian Cosmonauts. The Soyuz vehicle provided crew return capability without the Shuttle present. The first crew will spend 5 months on the ISS. 7. Flight 4A (Shuttle Flight). The completion of this flight reflects the temporary installation and activation of the P6 truss segment. The P6 Photovoltaic Module is the first of four U.S. solar based power sources. It moved and permanently attached to the P5 truss after flight 13A. Two Photovoltaic Thermal Control System radiators will provide early active thermal control. Also, the S-band communications system will be activated. This will provide radio communications on a specific frequency and the capability of transferring data. 8. Flight 5A (Shuttle Flight). Flight 5A delivered the U.S. Laboratory Module. This lab provided a shirtsleeve environment for research, technology development, and repairs by the on orbit crew. The U.S. Laboratory will distribute several systems, including Life Support, Electrical Power, Command and Data Handling, Thermal Control, Communications, and Flight Crew Systems. There will be a total of 24 racks for experiments in the U.S. Laboratory. 2 9. Flight 12A (Shuttle Flight). Space Shuttle mission 12A resumed assembly of the ISS by delivering the P3/P4 truss segment to the port side of the ISS integrated truss assembly. The 17-and-a-half ton truss segment contains a new set of photovoltaic solar array wing, the Solar Alpha Rotary Joint (SARJ), and the Beta Gimbal Assembly to position the solar arrays for electrical power generation. When the solar arrays are unfurled to their full length of 240 feet, they will provide additional power for the station in preparation for the delivery of international science modules. II PRINCIPLES OF SOLID MODELING-FINITE ELEMENTS DYNAMIC ANALYSIS The flow chart (Fig.1) 22 shows a brief summary of the proposed procedure to mix Solid Modeling and the Finite Element Method. First Step is to build a solid model using SOLIDWORKS OR PRO ENGINEER. The authors experimented with both of these programs in order to initiate the generation of ISS modules. Both software packages have great capabilities to build the 3D part as well as an Assembly. SOLIDWORKS was found more user friendly. The models generated by SOLIWORKS were saved and an interface to VISUAL NASTRAN4D was investigated. The second step was to translate the *.Prt(*.sdprt) and *.assemb(*.sdassemb) to a standard file format which could be read by another program such as NASTRAN4D. Once in the NASTRAN4D environment, a mesh for FEA was generated. NASTRAN4D joins the best of worlds, the Finite Element Analysis and the Multi Body analysis. After translating the file to the format like *.STEP,*.IGES or any other format which can be recognized by the FEA software, The constraints, which in this case are the joints between modules and the interface with the solar arrays were generated for each body in VISUAL NASTRAN4D.