NASA-CR-196030 DESIGN AND SIMULATION OF EVA TOOLS FOR FIRST SERVICING MISSION OF HST By Dipak Naik P.H. DeHoff, P.I. Semi-Annual Report July 15, 1993 - January 14, 1994 NASA Grant NAG 5-2038 Technical Report ME & ES 94-1 Department of Mechanical Engineering & Engineering Science University of North Carolina at Charlotte Charlotte, NC 28223 (NASA-CR-196030) DESIGN AND N94-35266 SIMULATION OF EVA TOOLS FOR FIRST SERVICING MISSION OF HST Semiannual Report, 15 Jul. 1993 - 14 Jan. 1994 Unclas (North Carolina Univ.) 77 D G3/54 0012621 CONTENTS Sr. No. Titl..._.__e Page No. ABSTRACT LIST OF FIGURES (ii) 1 Introduction 1 2 The Data Acquisition System 1 3 Computer Program 1 4 Torque/Angle Tests 2 5 Observations 2 APPENDICES I. Guidelines For PC-Based Data Acquisition 6-9 II. COPE Fasteners Torque/Angle Test Results 10-39 III. PRT Torque/Angle Test Results 40-73 (i) ABSTRACT The Hubble Space Telescope (HST) was launched into near-earth orbit by the Space Shuttle Discovery on April 24, 1990. The payload of two cameras, two spectrographs, and a high-speed photometer is supplemented by three fine-guidance sensors that can be used for astronomy as well as for star tracking. A widely reported spherical aberration in the primary mirror causes HST to produce images of much lower quality than intended. A Space Shuttle repair mission in January 1994 installed small corrective mirrors that restored the full intended optical capability of the HST. The First Servicing Mission (FSM) involved considerable Extra Vehicular Activity (EVA). Special EVA tools for the FSM were designed and developed for this specific purpose. In an earlier report, the details of the Data Acquisition System developed to test the performance of the various EVA tools in ambient as well as simulated space environment were presented. The general schematic of the test setup is reproduced in this report for continuity. Although the data acquisition system was used extensively to test a number of fasteners, only the results of one test each carried on various fasteners and the Power Ratchet Tool are included in this report. Design and Simulation of EVA Tools For First Servicing Mission of HST 1. Introduction The performance of EVA tools in the space environment can be predicted by testing these tools in vacuum and in temperature extremes in space. The performance of EVA tools is based on various benchmarks such as maximum attainable torque, frequency response, and the life of the tools. Of these various benchmarks, torque and speed can be measured by torque transducers and encoders. The data acquisition system designed to test the EVA tools makes use of these two sensors. However, the data acquisition system can be easily modified to incorporate other analog and digital signals with few modifications. 2. The Data Acquisition System: The block diagram of the data acquisition system is shown in Fig. 1. The torque/angle transducer #8241 has built-in strain gages and an encoder to generate analog and digital signals corresponding to torque and speed of the EVA tool being tested. These signals are taken to the GSE 290 Data-Stat, a meter which displays torque as well as angle of rotation, and to a plug-in data acquisition board. This is accomplished by cable #299210-6E080 and a parallel connection cable as shown in Fig. 1. The power to the GSE 290 Data-Stat is supplied through an A/C adapter. The cable carrying the transducer signals to the data acquisition board in a PC is connected to terminal blocks. Two such terminal blocks are used in this system. One is for analog signals which require signal conditioning, and the other is for TTL compatible digital signals which are directly connected to the data acquisition board through a feed-through terminal block, a feed-through panel and the SCX1-1340 MIO-16 cable #776574-40. The analog signals from the torque transducer are connected to the data acquisition board through the SCXl- 1300 terminal block, SCXI-1110 multiplexure-signal conditioner and SCX1-1340 MIO-16 cable. The SCXI-1100 multiplexure-signal conditioner has low pass and high pass filters. The analog signals are conditioned in the form of noise isolation, voltage scaling and signal amplification. An application software package based on NI-DAQ (National Instrument Software System) is developed to control data acquisition functions for the PC based data acquisition boards. The various cable connections for the torque transducer and encoder connector (Bendix-9219) to the data acquisition board connector AT-MIO-16F are shown in Fig. 2. 3. Computer Proqram: An application program (PRT.BAS) developed for testing EVA tools, and particularly the Power Ratchet Tool, is based on a NI-DAQ software system supplied by National Instruments. The applicationsoftware hasthe capabilityto generate sequential data files and to compute torque, angle and speed at pre-programmed torque speed characteristics of the tool. The sequential steps to run this application are shown in Appendix-I. 4. Torque/An,qle Tests: Tests were conducted on COPE (Contingency ORU Protective Enclosure) cover fasteners at various torque Ioadings. The locations of these fasteners are shown in Fig. 3. These fasteners were fastened and unfastened at three settings; 2 Ft. Lbs, 5 Ft. Lbs. and 10 Ft. Lbs. The torques measured on GSE Datastat are tabulated in Table 1. The torque angle readings measured by the Data Acquisition System are shown in Appendix- I1. The Power Ratchet Tool was also tested at various torque and speed profiles. The results of these tests are shown in Appendix-Ill. As a reference point, the programmed torques (desired torque) at these settings are given in the graphs showing the measured torques. 5. Observations: Although the application software package, "PRT.BAS" was developed for testing the Power Ratchet Tool, it can also be used for other applications requiring measurement of torques and rpm as well as the ultimate torque capacities of various fasteners. The following observations can be made concerning the torque/angle tests. The datastat readings were found to be more accurate. The reasons for this being that the datastat records only peak torque reached beyond a set threshold. The threshold for the sensor used in this test set-up is 2.5 Ft. Lbs. As soon as the torque level rises beyond 2.5 Ft. Lbs., only peak torque is recorded along with the corresponding angle reading. The torque angle readings are sampled at a rate of 3.6 KHz. In contrast to datastat, the data acquisition system records every torque and angle reading (as we were interested in examining the torque angle loading cycle of the system). Some time is lost in analog to digital data conversion. This results in missing some readings. Our tests showed that the limit to which this system can measure the data without missing any peaks, is 1.1 KHz. If we were to measure the torque/angle data like the datastat does, (recording only peak readings), the accuracy would have been much better. The reason for this being that in this case we could sample the data as fast as 1 MHz. 2 O x_ o °_,,_ o_,,_ 0 U 0000 _o_ o_ ........t__ ° 0!! '! 11 e , ,. L_ L.---..... FASTENER LOCATIONS © © © © © 3 FASTENTER NO. MTL SETTING (Ft.Lbs) IFASTEN (FLLbs) UNFASTEN (Ft.Lbs) 1 2 2.1 1.6 5 4.6 3.2 10 9.3 5.8 2 2 1.9 1.6 5 5.1 4.7 10 9.3 8 3 2 2.3 1.65 5 4.8 3.8 10 8.9 7.7 4 2 2.3 1.8 5 4.8 3.9 10 9.7 6.8 5 2 2.3 1.3 5 5.1 3.2 10 8.9 5.9 Fig. 3 COPE Fastener Locations APPENDIX - I GUIDELINES FOR PC BASED DATA ACQUISITION Notes: 1. User response is underlined. 2. Comments are in (Italics). 3. Symbol ,[,Stands for Return Key 4. For Any Software Bugs Call Dipak Naik (301-474-0832 OR 286-1324) HARDWARE SETUP: Power On: o a. Computer b. SCXI 1000 (Signal Conditioning Module) c. GSE Data-Stat . The CAPS LOCK and The NUM LOCK Keys On The Computer Keyboard Should be "ON" SOFTWARE SETUP: ° (All The Executable File For Data Acquisition Are In VBDOS Directory. Key-In Following Command To Switch To VBDOS Directory.) C:l> CD VBDOS,[, C:\> VBDOS> . C:\>VBDOS>PRT,I, (Run PRT.EXE) o DATA STORAGE FILE NAME? EVA272_, (Input Data Storage File Name) ° EXEL FILE NAME? EVA272,[, (Input Exel File Name) The Transducer Must Be Unloaded To Scan Initial Offsets 5. If Transducer Is Unloaded Hit 'Y'? Y__ (1. Before Responding To Above, Hit Any Key On GSE:Data-Stat If If Displays "Press any key to continue". 2. Enter 'Y' If Transducer is unloaded. Else Unload It and Then Hit "Y'. User Will Get 5 Chances To Unload The Transducer. After That The Program Will Terminate.)