FINAL REPORT SYSTEM DESIGN OF THE PIONEER VENUS SPACECRAFT VOLUME 2 SCIENCE U a By L.K. ACHESON NET AL. P 0 JUL1974 E-4 (d U ,L) July 1973 R ECFIvJ_ o w 0 (v Prepared Under Contract No.. i a - 750 W0 By 'PPli HUGHES AIRCRAFT COMPANY me o EL SEGUNDO, CALIFORNIA AME S For I AMES RESEARCH CENTER NATIONAL AERONAUTICS AND SPACE ADMINISTRATION . ErZ4 C) IS~ PREFACE The Hughes Aircraft Company Pioneer Venus final report is based on study task reports prepared during performance of the "System Design Study of the Pioneer Spacecraft. " These task reports were forwarded to Ames Research Center as they were completed during the nine months study phase. The significant results from these task reports, along with study results developed after task report publication dates, are reviewed in this final report to provide complete study documentation. Wherever appropriate, the task reports are cited by referencing a task number and Hughes report refer- ence number. The task reports can be made available to the reader specific- ally interested in the details omitted in the final report for the sake of brevity. This Pioneer Venus Study final report describes the following baseline configurations: * "Thor/Delta Spacecraft Baseline" is the baseline presented at the midterm review on 26 February 1973. * "Atlas/Centaur Spacecraft Baseline" is the baseline resulting from studies conducted since the midterm, but prior to receipt of the NASA execution phase RFP, and subsequent to decisions to launch both the multiprobe and orbiter missions in 1978 and use the Atlas/Centaur launch vehicle. * "Atlas/Centaur Spacecraft Midterm Baseline" is the baseline presented at the 26 February 1973 review and is only used in the launch vehicle utilization trade study. The use of the International System of Units (SI) followed by other units in parentheses implies that the principal measurements or calculations were made in units other than SI. The use of SI units alone implies that the principal measurements or calculations were made in SI units. All conver- sion factors were obtained or derived from NASA SP-7012 (1969). The Hughes Aircraft Company final report consists of the following documents: Volume 1 - Executive Summary -provides a summary of the major issues and decisions reached during the course of the study. A brief description of the Pioneer Venus Atlas/Centaur baseline spacecraft and probes is also presented. iii PRCEDING PAGE BLANK NOT FILMED Volume 2 - Science - reviews science requirements, documents the science peculiar trade studies and describes the Hughes approach for science implementation. Volume 3 - Systems Analysis - documents the mission, systems, operations, ground systems, and reliability analysis conducted on the Thor/Deta iaseline design. Volume 4 - Probe Bus and Orbiter Spacecraft Vehicle Studies - presents the configuration, structure, thermal control and cabling studies for the probe bus and orbiter. Thor/Delta'and Atlas/Centaur baseline descriptions are also presented. Volume 5 - Probe Vehicle Studies - presents configuration, aerodynamic and structure studies for the large and small probes pressure vessel modules and deceleration modules. Pressure vessel module thermal control and science integration are discussed. Deceleration module heat shield, parachute and separation/despin are presented. Thor/Delta and Atlas/Centaur baseline descriptions are provided. Volume 6 - Power Subsystem Studies Volume 7 - Communication Subsystem Studies Volume 8 - Command/Data Handling Subsystems Studies Volume 9 - Altitude Control/Mechanisms Subsystem Studies Volume 10 - Propulsion/Orbit Insertion Subsystem Studies Volumes 6 through 10 - discuss the respective subsystems for the probe bus, probes, and orbiter. Each volume presents the sub- system requirements, trade and design studies, Thor/Delta baseline descriptions, and Atlas/Centaur baseline descriptions. Volume 11 - Launch Vehicle Utilization - provides the comparison between the Pioneer Venus spacecraft system for the two launch vehicles, Thor/Delta and Atlas/Centaur. Cost analysis data is presented also. Volume 12 - International Cooperation - documents Hughes suggested alternatives to implement a cooperative effort with ESRO for the orbiter mission. Recommendations were formulated prior to the deletion of international 'cooperation. Volume 13 - Preliminary Development Plans - provides the development and program management plans. iv Volume 14 - Test Planning Trades -documents studies conducted to determine the desirable testing approach for the Thor/Delta space- craft system. Final Atlas/Centaur test plans are presented in Volume 13. Volume 15 - Hughes IRD Documentation - provides Hughes internal documents generated on independent research and development money which relates to some aspects of the Pioneer Venus program. These documents are referenced within the final report and are provided for ready access by the reader. Data Book -presents the latest Atlas/Centaur Baseline design in an informal tabular and sketch format. The informal approach is used to provide the customer with the most current design with the final report. V CONTENTS Page 1. SUMMARY 1-1 2. INTRODUCTION 2-1 3. MULTIPROBE MISSION 3-1 3. 1 Science Objectives 3-1 Large Probe 3-3 Small Probes 3-3 Probe Bus 3-3 Targeting Requirements 3-5 3.2 Science Payload 3-7 Large Probe 3-9 Small Probe 3-17 Probe Bus 3-17 3. 3 Tradeoff Studies 3-33 Payload Design Integration (EX2) 3-33 Experiment Window Design (PB39) 3-37 Experiments/Structure Interaction Design Study (PB29) 3-43 Externally Mounting High Altitude Sensors (EX10) 3-46 External Sensors Alignment/Stability Study (EX11) 3-59 Magnetometer Studies (EX15) 3-65 Payload Tradeoff Analysis (EX1) 3-69 Wind Velocity Measurement Study (EX8) 3-78 Experiment Integration Plan (PL1O) 3-97 Probe Spacecraft/Experiment Interface Specification (SP4) 3-101 3.4 Science Payload Accommodations 3-103 Large Probe 3-103 Small Probe 3-117 Probe Bus 3-131 Additional Accommodation Considerations 3-145 Supplement 3-1: Pioneer Venus Instrument Data EXLP-3 3-149 4. ORBITER MISSION 4-1 4. 1 Science Objectives and Requirements 4-1 4. 2 Science Payload 4-6 XD VG Tvii 4. 3 Tradeoff Studies 4-11 Spin Axis Orientation/Science Requirements (EXlZ) 4-11 1978 Orbiter Transit Trajectory Selection (MS25) 4-30 Payload Design Integration (EX2) 4-37 Orbiter Radio Science Impact on Communication Subsystems (CM19) 4-40 Payload Tradeoff Analysis (EX1l 4-43 Orbiter Spacecraft/Experiment Inte rface Specification (SP4) 4-46 4. 4 Science Payload Accommodations 4-47 Magnetometer 4-53 Solar Wind Analyzer 4-60 Electron Temperature Probe 4-60 Neutral Mass Spectrometer 4-60 Ion Mass Spectrometer 4-61 UV Spectrometer 4-61 IR Radiometer 4-61 X Band Occultation 4-61 Radar Altimeter 4-62 Thermal Control Considerations 4-62 Electrical Power 4-64 REFERENCES R-1 APPENDIX: Science Trip Reports A-i viii 1. SUMMARY The objectives of the low-cost Pioneer Venus program have been established by steering groups in a series of meetings over the last few years. Information on Venus gathered by Earth-based observers and by U. S. and Soviet interplanetary fly-by and probe missions have served to define a number of problems requiring a carefully coordinated series of multiprobe and orbiter missions to resolve. The purpose of this volume is to describe the mission science requirements and demonstrate how well Hughes has succeeded in design- ing a spacecraft which satisfies these requirements in a cost effective way. The Atlas/Centaur will be used to launch both the multiprobe mission (probe bus, large probe, and three small probes) and the orbiter mission, utilizing its larger payload capability to achieve a lower cost system than could be achieved with the smaller Thor/Delta launch vehicle. Both missions are currently scheduled for launch in 1978, although it is possible that one or both might slip to 1980. Section 2 of this volume reviews the basic scientific questions about Venus. Section 3 discusses the multiprobe mission, and Section 4 the orbiter mission. Both sections are organized the same way. Science objectives are described in subsection 3. 1 and the science payload in subsection 3. 2, first in terms of the initial payloads defined for the Thor/Delta launch vehicle, and then the current payload for the Atlas/Centaur. The science experiments have been in the review and selection process over the period of the present study, hence nominal payloads have been specified, along with other candidate instruments. During the study a number of specific study tasks were carried out to resolve alternative design approaches. These studies are summarized in sub- section 3. 3. An experiment engineering data book was compiled on all instru- ments to identify payload accommodation problems. In the course of gathering data on the experiments, visits were made to a large number of scientists to improve our understanding of the experiment requirements and characteristics. The resulting science trip reports are included as an appendix to this volume. The purpose of the spacecraft and probes is to provide a suitable envir- onment (or laboratory) for the science instruments to function in while they make observations of the planet. The purpose of the study carried out by Hughes is to design the lowest cost, technically effective equipment and labor- atory. The entire study is in this sense completely science oriented. However, specific tasks related to key science instrument accommodation on the multiprobe mission include: preliminary design approaches to meet the