U.S. Human Space Transportation Failures

Transcription

1 Trans. JSASS Space Tech. Japan Vol. 7, No. ists26, pp. Tg_1-Tg_1, 9 U.S. Human Space Transportation s By E. Joe TOMEI and I-Shih CHANG The Aerospace Corporation, El Segundo, California, U.S.A. (Received April 17th, 8) The U.S. human space transportation history from 1961 through 7 is reviewed. Past and present U.S. human space programs and human space launch vehicles and spacecraft are briefly discussed. Category and chronological list of U.S. human space missions are presented. The emphasis of the study is on the investigation of mission failures and major anomalies encountered in the U.S. human space transportation history. s and major anomalies by part, root cause, element, function, domain, and component are analyzed. outcome, failure mode, time of failure, and mission reliability relevant to flight safety analysis are examined. Findings and failure mitigation strategy are summarized. Key Words: Space Launch, Human Space Flight, and Anomaly 1. Introduction To expand human presence, activity, and habitation beyond Earth orbit, new launch vehicles and crew exploration vehicles are being developed by several space-fairing nations for human space transportation. The new vehicles will incorporate modern space technologies to meet stringent requirements for crew safety in space launch operation and space flight environment. Anticipated expansion in space tourism to low Earth orbit would also contribute to increased demand for reliable human space transportation systems. Human space launch and flight are dangerous, expensive, and technically challenging. The success of this new endeavor relies upon the application of knowledge and experience gained from prior human space programs. The study is concerned with all U.S. human space missions and is a portion of a continuing effort 1)-14) to investigate the failure causes and corrective actions of the world space launch and flight systems and to provide lessons learned from the past in order to mitigate space mission failures in the future. The prior work has been concentrated on launch vehicle failures. The current project is intended to examine the failure history of all human space flights focusing on transportation and is a subset of overall space missions. The focus of the study is on human space mission failures and major anomalies in order to better understand the ramifications of the human space transportation record on the new human space programs. The objective of the study is to apply knowledge and experience gained from prior U.S. human space programs to the development of reliable human space transportation systems in the future. 2. Overview This paper summarizes the history of U.S. human space transportation failures since the inception of the first human space flight in Past and present U.S. suborbital, orbital, and lunar human space launch systems (Redstone, Atlas, Titan, Saturn, Space Transportation System [STS]) and their associated space flight systems (Mercury, Gemini, Apollo, Shuttle) are considered in the study. Related near-space and suborbital flights with X-15 and commercial suborbital flights with SpaceShipOne (SS1) rocketplanes are also included in the study. The near-space is in the region between 8.5 and 1 km altitude. U.S. astronaut wings are awarded for flights above 8.5 km (5 miles). Human space flight requires an expansion of space transportation systems. For purposes of this study human space flight can be categorized into several transportation phases. They are the launch phase, earth and lunar on-orbit phases, lunar transfer and return phases, surface exploration phase, entry and landing phases, and lunar ascent phase. Human space flight also includes static, in-situ habitation phases both on the lunar surface and on board space stations. There are also a variety of related topics worthy of investigation, including uncrewed flights in support of human space flights (developmental, logistics, etc.), animal space flights, and human satellite deployment. All of these are to be addressed by the larger project being undertaken. This paper will limit its discussion to the primary transportation phases. Several additional papers would be needed to contain all of the collected material. The paper starts with a brief description of U.S. human space transportation history, followed by category and chronological list of U.S. human space missions and identification of space mission failures and major anomalies. Analysis of mission failures and anomalies by part, root cause, element, function, domain, and component are presented. outcome, failure mode, time of failure, and mission reliability relevant to flight safety analysis are examined. Findings and failure mitigation strategy are summarized at end of the paper. 3. U.S. Human Space Transportation History Human space flight started when the USSR launched the Vostok vehicle carrying Yuri Gagarin to a low-earth orbit on Shortly afterwards, the U.S. launched a Redstone vehicle carrying Alan Shepard in a Mercury capsule for a suborbital flight on and Copyright 9 by the Japan Society for Aeronautical and Space Sciences and ISTS. All rights reserved. Tg_1

2 Trans. JSASS Space Tech. Japan Vol. 7, No. ists26 (9) an Atlas LV-3B carrying John Glenn for an orbital flight on In addition to low-earth-orbit flights, the U.S. is the only country that has conducted human lunar flights with the mighty Saturn V rocket and Apollo spacecraft and landed the first humans, Neil Armstrong and Buzz Aldrin on the Moon launching on The U.S. human orbital space programs include Mercury, Gemini, Apollo, and Shuttle. The Mercury program started in The first human suborbital mission with a Mercury/Redstone was carried out in The orbital mission with a Mercury/Atlas was carried out in 1962; and the last Mercury/Atlas occurred in The Gemini program started in 1962 and extended the U.S. human space program to two-man space flights to develop multi-human capsule, extravehicular operations, and rendezvous and docking techniques critical to the Apollo lunar program. The first Gemini/Titan II human orbital mission was carried out in 1965; and the last occurred in Gemini included dual launches of Gemini spacecraft from Titan II launch vehicles with Atlas/Agena target vehicles to allow on-orbit rendezvous operations. The Apollo program started in 1961 and was devoted to land humans on the Moon and bring them safely back to Earth. The first human orbital mission with an Apollo/Saturn IB was carried out in 1968, and the first lunar orbital mission with an Apollo/Saturn V occurred in The first lunar landing mission with the Apollo 11 was conducted in The Apollo program ended after the launch of a Saturn IB vehicle in The Space Shuttle program started in 1972 and was dedicated to develop a space transportation system (STS) that can shuttle repeatedly from Earth to orbit and back. The first human orbital mission with shuttle Columbia was carried out in The Space Shuttle is a unique dual mode vehicle that serves as part of the launch vehicle during ascent to earth orbit and as a spaceplane for the rest of the mission. The Space Shuttle is still in use today, but is planned to be retired in 1. In addition, the X-15 rocketplane program started in 1955, flew its first human near-space flight in 1962, suborbital flight in 1963, and ended in Recently, the first privately developed human rocketplane SS1 successfully completed three suborbital flights in 4. Other than the successful programs mentioned in the previous paragraph, there were also cancelled human space programs, namely Man-In-Space-Soonest ( ), X- Dyna-Soar ( ), Manned Orbiting Laboratory ( ), X-3 NASP ( ), and X-33/Venturestar (1996-1). Currently, there are new human space programs under development in the U.S.: NASA Constellation program, Virgin Galactic (U.K.) sponsored SpaceShipTwo project, and XCOR Aerospace Lynx program. The space habitation programs involving Skylab ( ) and International Space Station (1993-present) are part of the overall project, but will not be considered in this paper. Fig. 1 shows the U.S. human space launch systems and spacecraft. The Redstone rocket was used for suborbital and the Atlas for orbital space launches of the Mercury spacecraft. The Titan II rocket was used for orbital space launches of the Gemini spacecraft. The Saturn I vehicle was used for suborbital, and the Saturn IB and V for orbital space launches of the Apollo spacecraft. The Apollo spacecraft included a Lunar Module for landing/habitation/ascent and a Lunar Rover for surface exploration. The STS consists of Space Shuttle, External Tank, Solid Rocket Booster (SRB) and was used to launch the Shuttle to low-earth orbit. The Shuttle payload bay can accommodate upper-stages for delivering satellites to higher orbits. Shown also in the figure are the X-15 and Fig. 1. U.S. human space launch vehicles, spacecraft, lunar module and rover (drawings reprinted courtesy of NASA) Tg_2

3 E. J. TOMEI and I-S. CHANG: U.S. Human Space Transportation s SS1 rocketplanes. The X-15 was air launched from a B-52 aircraft at 14 km for conducting hypersonic research and evaluating pilot performance and physiology during exit from and reentry to the atmosphere. The SS1 was air launched from the White Knight carrier vehicle at 14 km and was the first successful privately funded human suborbital reusable rocketplane. The SS1 won the $1-million Ansari X-prize by reaching 1 km in altitude twice in a two-week period. 4. U.S. Human Space Missions As of , U.S. human space exploration mission count is 168, which includes 11 near-space, 7 suborbital, 141 orbital, and 9 lunar missions. The 168 human space flights consist of 2 Redstone/Mercury, 4 Atlas/Mercury, 13 B-52/X-15, 1 Titan II/Gemini, 13 Saturn/Apollo, 3 Saturn/Skylab, 3 White Knight/SS1, and 1 STS/Shuttle missions. Table 1 lists all the U.S. human space missions. For the U.S., the human-cost of access to space includes one X-15 pilot during near-space flight in 1967, seven STS crew members during launch in 1986, and seven STS crew members during reentry in 3. In addition to these casualties, three astronauts died in 1967 when a fire swept through the Apollo 1 crew module on the launch pad in a pre-launch test. The Apollo 1 mishap is also included in Table 1 as the failure occurred in an attempt to carry out an orbital mission. A comprehensive database has been developed at The Aerospace Corporation to log the entire space launch and flight history. Data is collected from multiple sources including journal papers, public access sites, publications and an assortment of other historical data references published by The Aerospace Corporation and other organizations 15)-43). A significant part of the database compilation process consists of reviewing and comparing the various sources, identifying conflicts and resolving inconsistencies. The data entries have been populated for the small launch vehicles 9)-1), heavy launch vehicles 13), and human space transportation vehicles 11). The database for human space transportation has been expanded to comprise crew module, service module, re-entry module, lunar module, and lunar rover of space transportation systems, in addition to solid motor stages, liquid engine stages, hybrid motor stages, payload fairing, and ground equipment of space launch systems. For each system, mission failures and major anomalies are identified and examined. As mentioned previously, the database also includes entries for space station, docking module, fueling module, extravehicular unit, and uncrewed support missions. These data will be incorporated into future papers and in the overall project report. The following sections will analyze the U.S. human space mission failures and anomalies. 5. U.S. Mission s and Major Anomalies A space mission failure is an unsuccessful attempt to place a payload in the intended orbit or to perform a planned space activity or mission. A major anomaly is a near miss in launch or flight even when the mission was considered successful. Out of 168 U.S. human space missions since 1961, there were 1 pre-launch, 1 launch and 8 in-flight mission failures. s are categorized Table 1. U.S. human space launch log No. Launch Date LV SC No. Launch Date LV SC No. Launch Date LV SC No. Launch Date LV SC Near-Space Flights ( miles altitude) STS- 1 Columbia STS- 42 Discovery STS- 89 Endeavour NS B-52/X-15 X STS- 2 Columbia STS- 45 Atlantis STS- 9 Columbia NS B-52/X-15 X STS- 3 Columbia STS- 49 Endeavour STS- 91 Discovery NS B-52/X-15 X STS- 4 Columbia STS- 5 Columbia STS- 95 Discovery NS B-52/X-15 X STS- 5 Columbia STS- 46 Atlantis STS- 88 Endeavour NS B-52/X-15 X STS- 6 Challenger STS- 47 Endeavour STS- 96 Discovery NS B-52/X-15 X STS- 7 Challenger STS- 52 Columbia STS- 93 Columbia NS B-52/X-15 X STS- 8 Challenger STS- 53 Discovery STS-13 Discovery NS B-52/X-15 X STS- 9 (41A) Columbia STS- 54 Endeavour STS- 99 Endeavour NS B-52/X-15 X STS- 11 (41B) Challenger STS- 56 Discovery STS-11 Atlantis NS B-52/X-15 X STS- 13 (41C) Challenger STS- 55 Columbia STS-16 Atlantis NS B-52/X-15 X STS- 16 (41D) Discovery STS- 57 Endeavour STS- 92 Discovery STS- 17 (41G) Challenger STS- 51 Discovery STS- 97 Endeavour Suborbital Flights STS- 19 (51A) Discovery STS- 58 Columbia STS- 98 Atlantis S Redstone Mercury 7 MR STS- (51C) Discovery STS- 61 Endeavour STS-12 Discovery S Redstone Mercury 11 MR STS- 23 (51D) Discovery STS- 6 Discovery STS-1 Endeavour S B-52/X-15 X-15 Flight STS- 24 (51B) Challenger STS- 62 Columbia STS-14 Atlantis S B-52/X-15 X-15 Flight STS- 25 (51G) Discovery STS- 59 Endeavour STS-15 Discovery S White Knight/SS1 SS1 F STS- 26 (51F) Challenger STS- 65 Columbia STS-18 Endeavour S White Knight/SS1 SS1 F STS- 27 (51I) Discovery STS- 64 Discovery STS-19 Columbia S White Knight/SS1 SS1 F STS- 28 (51J) Atlantis STS- 68 Endeavour STS-11 Atlantis STS- 3 (61A) Challenger STS- 66 Atlantis STS-111 Endeavour Orbital Flights STS- 31 (61B) Atlantis STS- 63 Discovery STS-112 Atlantis Atlas LV-3B Mercury 13 MA STS- 32 (61C) Columbia STS- 67 Endeavour STS-113 Endeavour Atlas LV-3B Mercury 18 MA STS- 33 (51L) Challenger STS- 71 Atlantis STS-17 Columbia Atlas LV-3B Mercury 16 MA STS- 26R Discovery STS- 7 Discovery STS-114 Discovery Atlas LV-3B Mercury MA STS- 27R Atlantis STS- 69 Endeavour STS-121 Discovery Titan II Gemini STS- 29R Discovery STS- 73 Columbia STS-115 Atlantis Titan II Gemini STS- 3R Atlantis STS- 74 Atlantis STS-116 Discovery Titan II Gemini STS- 28R Columbia STS- 72 Endeavour STS-117 Atlantis Titan II Gemini STS- 34 Atlantis STS- 75 Columbia STS-118 Endeavour Titan II Gemini STS- 33R Discovery STS- 76 Atlantis STS-1 Discovery Titan II Gemini STS- 32R Columbia STS- 77 Endeavour Titan II Gemini STS- 36 Atlantis STS- 78 Columbia Titan II Gemini STS- 31R Discovery STS- 79 Atlantis Lunar Flights Titan II Gemini STS- 41 Discovery STS- 8 Columbia L Saturn V Apollo Titan II Gemini STS- 38 Atlantis STS- 81 Atlantis L Saturn V Apollo Saturn IB Apollo STS- 35 Columbia STS- 82 Discovery L Saturn V Apollo Saturn IB Apollo STS- 37 Atlantis STS- 83 Columbia L Saturn V Apollo Saturn V Apollo STS- 39 Discovery STS- 84 Atlantis L Saturn V Apollo Saturn IB Skylab STS- 4 Columbia STS- 94 Columbia L Saturn V Apollo Saturn IB Skylab STS- 43 Atlantis STS- 85 Discovery L Saturn V Apollo Saturn IB Skylab STS- 48 Discovery STS- 86 Atlantis L Saturn V Apollo Saturn IB Apollo 18-ASTP STS- 44 Atlantis STS- 87 Columbia L Saturn V Apollo 17 launch failure in-flight failure on-pad failure The date is Greenwich Mean Time (GMT). 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4 Trans. JSASS Space Tech. Japan Vol. 7, No. ists26 (9) as catastrophic (5), mission abort (3), and unsuccessful satellite delivery (2). The causes of the human space mission failures are listed in Table 2, which includes the Apollo 1 on-pad catastrophic failure. The large number of anomalies prevents all causes to be listed in the present paper. Research has identified 273 U.S. human space flight major anomalies (not including space habitation events). The major anomalies are distributed: X-15 (7), Mercury (11), Gemini (17), Apollo (33), Space Shuttle (3), and SS1 (2). Analysis of space mission failures is critical to a space program s future success. A systematic look at mission successes as well as failures, including scrutiny of various launch vehicle and spacecraft subsystems, can shed light on precise areas that might be at the root of many problems. This type of study can also help suggest what actions to take to address those problems. Where data is available, failures and anomalies are further identified by the defective part. Table 3 shows failures and anomalies by part for U.S. human space missions. Thermal protection, thruster, and case joint seal defects appear to be major sources of anomaly. The database is developed to assess launch vehicle failure and anomaly data and to understand causes and trends of flight failures and anomalies. Table 4 defines the legends used in the database and in the figures of this paper. No. Launch Date Date Orbit LV SC Mission LEO Titan II Gemini 9 Gemini SC None Saturn IB Apollo 1 AS-4; Apollo CSM NS B-52/X-15A X-15A Atm. Sample; Solar Astro Lunar Saturn V Apollo 13 Apollo CSM 19/LM LEO STS-11 (41B) Challenger Westar 6; Palapa B LEO STS-23 (51D) Discovery Leasat LEO STS-33 (51L) Challenger TDRS 2; Spartan-Halley LEO STS-75 Columbia TSS-1R LEO STS-83 Columbia Spacelab MSL LEO STS-17 Columbia Spacehab DM; FreeStar No. Table 2. U.S. human space mission failures Cause 1 Docking with the target was cancelled, because the augmented target docking adapter (ATDA) failed to separate. 2 During pre-launch test, a electrical short in oxygen rich environ. resulted in crew module fire. The crew was killed. 3 Pilot killed when X-15A deviated in heading from distraction, yawed out of control at 15G, and broke up at Mach 5. 4 LOX tank ruptured during translunar flight due to heater circuit wiring overstressed. The crew returned safely. 5 Failed to deliver two satellites (Westar VI and Palapa B2) to GEO because the two PAM-D AKMs failed to ignite. 6 Satellite was delivered to low-earth orbit when Perigee Kick Motor failed to ignite. 7 Hot gas leaked through O-ring at SRM joint & vehicle exploded during launch. All 7 crew members perished. 8 Tethered Satellite System connecting tether broke during deployment. Satellite was lost. 9 Shuttle returned 12 days early due to fuel cell failure; Reflight as STS Orbiter broke up during reentry due to breach of thermal protection system. Vehicle and crew perished. Table 3. U.S. human space mission failures and anomalies by part Part Anomaly Part Anomaly Part Anomaly Case joint seal 1 16 Yawdamper 2 Laser attack 1 Exit cone 1 1 Acoustic overpressure system 1 Lightning strike 1 Fuel Cell 1 4 Actuator 1 Limit switch 1 LO2 Tank 1 Autopilot 1 Motor performance 1 Motor controller 1 Ball nose servo 1 Multiplexer 1 Pilot 1 Ballon seam 1 Navigation system 1 Target vehicle 1 Cable damage 1 Nozzle 1 Tether 1 Cabling 1 Nozzle ablative ring 1 TPS 1 6 Circuit breaker 1 Ordnance firing circuit 1 Wiring 1 1 Compressor 1 Position counter 1 Thruster 42 Connector 1 Power supply 1 Igniter joint seal 8 Control software 1 Propellant utilization 1 Window 8 Coolant valve 1 Quick disconnect 1 WSB 6 Cooling loop 1 Radar 1 Brakes 5 Cooling tubes 1 Reaction wheels 1 APU 4 Crew sickness 1 Relay 1 Hatch 4 CRT 1 Response timing 1 Unkown 4 Dump line 1 Rudder sevo 1 Valve 4 Electrical motor 1 Sensor 1 Wing RCC 4 End flap 1 Software upload 1 Condenser 3 EVA Restraints 1 Solenoid valve 1 Docking system 3 Feed valve 1 Squib valve 1 Nozzle joint seal 3 Fender 1 Steering 1 Switch setting 3 Fluid valve 1 Structural dynamics 1 Wiring 3 General pupose computer 1 Switch 1 Computer 2 Gimbal joint seal 1 Thermal paint 1 Environmental pressure 2 Guidance computer 1 Tire 1 Fitting 2 Heater 1 Transmitter 1 Insulation 2 Horizon scanner 1 Umbilical 1 Management software 2 IMU 1 Umbilical connector 1 MDM 2 Initiator 1 Umbilical door 1 Parachutes 2 Injector 1 Vent fitting 1 RMS 2 Inverter 1 Visor 1 Suit mobility 2 Lanyard 1 Water spray boiler 1 Tg_4

5 E. J. TOMEI and I-S. CHANG: U.S. Human Space Transportation s Table 4. Human space transportation database legends Element Component Outcome -H Strap-on - Hybrid motor A/E Avionics/Electronic B Breakup -L Strap-on - Liquid engine C Crew De Death -S Strap-on - Solid motor E Electrical DP Damaged Payload 1-H First stage - Hybrid motor EC Environmental control E Explosion 1-L First stage - Liquid engine EN Engine EL Emergency Landing 1-S First stage - Solid motor FP Fluid/Pneumatic F Fire 2-H Second stage - Hybrid motor H Hydraulic I Impact 2-L Second stage - Liquid engine M Mechanical In Injury or Illness 2-S Second stage - Solid motor O Ordnance MF Mission 3-H Third stage - Hybrid motor P Propellant N No Launch 3-L Third stage - Liquid engine S Structural NR No Recovery 3-S Third stage - Solid motor SM Solid motor O Wrong Orbit or Trajectory 4-H Fourth stage - Hybrid motor SWA Software computational algorithm R Reentry 4-L Fourth stage - Liquid engine SWD Software data input RD Range Safety Destruct 4-S Fourth stage - Solid motor SWL Software timing/memory control logic SD Self Destruct 5-H Fifth stage - Hybrid motor T Thermal protection U Unknown 5-L Fifth stage - Liquid engine U Unknown 5-S Fifth stage - Solid motor CM Crew Module DM Docking Module ER Escape Rocket Domain Mode EV Extravehicular Unit ENV Environment CO Checkout test FM Fueling Module H/W Hardware F Fallback G Ground system S/W Software L Landing LM Lunar Module U Unknown MFT Malfunction turn O Operations OO On orbit failure PAF Payload Attach Fitting OT On trajectory failure PLF Payload Fairing P On pad failure RM Re-entry Module PF Failed to program (flies straight up) RoV Rover Vehicle SO Surface operation SM Service Module U Unknown SP SpacePlane SS Space Station SV Space Vehicle U Unknown Root Cause A Analysis: An engineering error or flaw in the definition of the system design characteristics (hardware and/or software), or incorrect/insufficient analysis of system behavior that becomes the primary cause of a failure/anomaly. D Design: An engineering error or flaw in the definition of the system design characteristics (hardware and/or software), other than incorrect/insufficient analysis of system behavior that becomes the primary cause of a failure/anomaly. P Process: An engineering error or serious omission in the definition of manufacturing, installation, test, or operating procedures or criteria, or inaccurate communication of engineering intent that becomes the primary cause of a failure/anomaly. Or: A manufacturing/assembly error or misapplication of the system of checks and balances designed to screen out errors. R W U Random: An undectable fault that occurs randomly due to the inherent reliability characteristics of the hardware. Workmanship: Hardware or software technicians missapply or ignore proper procedures by commission or omission resulting in error or defect that is the primary cause of a failure/anomaly. Can occur in manufacture, assembly, installation, inspection and test. Includes software data entry and pilot errors. Unknown Function C&C ECLSS ENV EPDC GN&C GSE LAND MECH PROP SEP STRU T&FS TLM TV&AC U Ground command and control system: elements designed to command and control the launch vehicle operations prior to and during flight. Environmental control: crew cabin, life support systems and equipment, flight suits, space suits, manned maneuvering units. Environmental protection: elements designed to control or protect from launch or reentry induced environments; includes vibration, shock,acoustic, aerodynamic and thermal environments protection. Electrical: elements designed to provide electrical power generation, conditioning and distribution; includes power supplies, batteries, converters, inverters, sequencers, switches, relays, diodes, cabling and harnesses for carrying electrical power. Guidance, navigation and control: elements designed to measure position, velocity and attitude, determine motion necessary to reach desired positon or attitude, and issue steering and attitude commands; includes gyros, inertial measurement and navigation units, computers and associated software. Ground support equipment: elements designed to support, interface, service, supply, restrain and release the vehicle prior to flight. Landing systems: parachutes, drag brakes, impact bags, floats, tires. Mechanism: docking adapters, holddown and release arms, remote manipulator system, landing gear. Propulsion: elements designed to produce thrust and manage propellant supply; includes liquid engines, solid motors, propellant conditioning, feed and pressurization, propellant utilization, engine conditioning, controllers and igniters. Separation: elements designed to perform vehicle staging and jettison; includes separation ordnance, springs, thrusters, motors, clamp bands, tiedowns, connecting devices and controllers. Structures: elements design to carry or react vehicle loads or environments, provide mounting interfaces and environmental protection; includes skirts, thrust structures, bulkheads, interstages, adapters, shrouds, shields, covers, tanks and pressure vessels. Tracking and flight safety: elements designed to track, safe and destroy vehicle for public safety; includes transponders, receivers, ordnance, antennas and destruct and thrust termination devices. Telemetry: elements designed to measure vehicle activity, condition data and transmit to ground stations; includes sensors, transducers, signal conditioners, instrumentation converters, multiplexers, combiners, transmitters and antennas. Controls: elements designed to control direction, position and attitude; includes thrust vector control, engine gimbals, position actuators, position controllers, attitude control systems and devices, spin, despin and nutation damping elements. Unknown Tg_5

6 Trans. JSASS Space Tech. Japan Vol. 7, No. ists26 (9) For this study, human space transportation failure and anomaly data are combined into a single analysis. Due to the large quantity, the anomaly data dominates the results. The anomalies addressed in this paper are those determined to be significant enough to be considered major. In the database each major anomaly is weighted as an estimate of severity but for the purposes of this paper all anomalies are treated equally. In addition, those considered minor or out-of-family anomalies are not addressed. Judgment and historical evidence are used in assigning anomaly weight. s and anomalies can have their roots in any phase of launch vehicle and spacecraft development. The root causes (design, analysis, process, random, or workmanship) of mission failure and anomaly are shown in Fig. 2. The figure shows that 35.% of all human space mission failures and anomalies are attributable to engineering process errors with design defects next highest at 34.3%. The 17.3% unknown root causes are associated with the mission failure of the STS/Shuttle on and 2 Redstone/Mercury, 1 Atlas (target launch for Gemini), 3 B-52/X-15, 5 Titan II/Gemini, 5 Saturn/Apollo, and 32 STS/Shuttle mission anomalies. s and anomalies can occur at any stage of launch and flight. Fig. 3 shows failures and anomalies by element. The number on the abscissa stands for the stage number, S is for solid motor stage, H for hybrid stage, L for liquid engine stage, CM for crew module, EV for extravehicular unit, G for ground system, LM for lunar module, O for operations, PAF for payload attach fitting, RoV for rover vehicle, SM for service module, SP for spaceplane (orbiter), SS for space station (docking system in this case), and SV for space vehicle. Because of Shuttle s frequent flights, failures and anomalies for the spaceplane (46.64%) stand out among all the others, followed by solid motor booster (14.49%), liquid rocket first stage (11.31%), and crew module (8.83%). s and anomalies are usually attributable to problems associated with a functional subsystem. The sources of launch vehicle failures are defined into a comprehensive set of functional areas in order to determine the distribution of failures and anomalies due to various sources. Fig. 4 shows failures and anomalies by function. In the figure C&C stands for command and control, ECLSS for environmental control and life support, ENV for environmental protection, EPDC for electrical power, GN&C for guidance, navigation and control, LAND for landing system, MECH for mechanical, PAF for payload attach fitting, PROP for propulsion, SEP for separation, STRU for structures, TLM for telemetry, TV&AC for thrust vector and attitude control, and Unk for unknown. Overall, ENV (29.33%) caused the greatest number of human space mission failures and anomalies, followed by TV&AC (23.67%) and propulsion (16.25%). The unknown is for an STS/Shuttle anomaly. Fig. 5 shows failures and anomalies by domain (hardware, software, or environment). Problems in hardware caused the majority of the failures and anomalies for human space missions. Overall, at least 96.11% of all failures and anomalies have been caused by hardware. The 5 unknowns are associated with 1 Titan II/Gemini and 4 STS/Shuttle mission anomalies. s and anomalies caused by hardware and software malfunctions have also been categorized by component type shown in Fig. 6. In the figure, A/E stands for Avionics/Electronic, C for crew, E for electrical, EC for environmental control, EN for engine, FP for fluid/pneumatic, H for hydraulic, M for mechanical, O for ordnance, P for propellant, S for structures, SM for solid motor, SWD for software data input, SWL for software timing/memory control logic, T for thermal protection, WE for weather, and Unk for unknown. While thermal protection (22.61%) defects have the greatest single impact on human space mission failures and anomalies, engine (15.9%), mechanical (15.55%) and solid motor (12.72%) malfunctions are also major contributors to failures and anomalies. The 3 unknowns are associated with 1 STS/Shuttle and 2 SS1 mission anomalies. 6. Flight Safety Data Flight safety analysis uses failure outcome, failure mode, time of failure, and mission reliability to assess future potential risk of like systems. In addition to data for mission failure and anomaly analysis shown in the previous section, data relevant to flight safety analysis is included in the study. Fig. 7 shows the outcomes of U.S. human space mission failure. In the figure, failure outcomes are categorized as breakup (B), explosion (E), fire (F), impact (I), mission unaccomplished (MF), no launch (N), wrong orbit (O), reentry (R), range safety destruct (RD), self destruct (SD), damaged payload (DP), and unknown (Unk). Overall, mission unaccomplished (3%), wrong orbit (%), and reentry failures (%) constitute most of the observed outcomes. Fig. 8 shows the modes of failure. In the figure, failure modes are defined as fallback (F), landing (L), malfunction turn (MFT), on-orbit (OO), on-trajectory (OT), on-pad (P), and unknown (Unk) failure. On-trajectory failures (5%) are observed to be the most commonly occurring failure mode, followed by on-orbit failures (3%). Fig. 9 shows the times of failure. Eight out of 1 failures occurred near the end of mission. One failure (Apollo 1) occurred on-pad, and the other within the first 1 sec of the mission. The yearly mission success and failure data and the demonstrated mission reliability of all U.S. human space missions are shown in Fig. 1. It can be seen from the figure that no human space missions were conducted from 1976 through 198 during the development of STS/Shuttle system. The U.S. human space programs attained an impressive 93.7% mission reliability with 158 successes out of 168 attempts as of Summary and Conclusions The results of investigation of human space Tg_6

7 E. J. TOMEI and I-S. CHANG: U.S. Human Space Transportation s 14 Number of s/anomalies Anomaly Process Design Unknown Wmanship Random Analysis 6.71% 17.3% 5.65% 1.6% 34.3% 35% Process Design Unknown Wmanship Random Analysis Root Cause F+A Fig. 2. U.S. human space mission failures and anomalies by root cause 14 Number of s/anomalies S 1-H 1-L Anomaly 2-L 3-L 3-S CM EV G LM O Element PAF RoV SM SP SS SV 46.64% 1.6% 2.47% 14.49%.71% 11.31%.71%.71% 1.6% 8.83% 2.47% 1.6% 2.12% 1.41%.35% 4.24%.35% -S 1-H 1-L 2-L 3-L 3-S CM EV G LM O PAF RoV SM SP SS SV Fig. 3. U.S. human space mission failures and anomalies by element 14 Number of s/anomalies C&C ECLSS ENV EPDC GN&C LAND MECH PAF PROP Function SEP STRU Anomaly TLM TV&AC Unk 2.83% 1.6% 1.6%.71%.35% 3.18% 23.67% 16.25%.35% 9.89% percent 29.33% 6.1% 4.59%.71% C&C ECLSS ENV EPDC GN&C LAND MECH PAF PROP SEP STRU TLM TV&AC Unk Fig. 4. U.S. human space mission failures and anomalies by function 28 Number of s/anomalies Anomaly Environment Hardware Software Unknown 1.77% 1.77%.35% 96.11% Environment Hardware Software Unknown Domain percent Fig. 5. U.S. human space mission failures and anomalies by domain Tg_7

8 Trans. JSASS Space Tech. Japan Vol. 7, No. ists26 (9) 14 Number of s/anomalies T EN Anomaly M SM A/E FP E EC C O Component SWL S Unk H P SWD 1.41% 1.6%.35% 1.41% 1.6%.35%.35% 1.77% 3.89% 5.3% 22.61% 7.42% 8.83% 15.9% 12.72% 15.55% T EN M SM A/E FP E EC C O SWL S Unk H P SWD Fig. 6. U.S. human space mission failures and anomalies by component % Number of s % % 1% 1% B E F MF O R 2 3% B E F I MF N O R RD SD Unk Outcome percent Fig. 7. U.S. human space mission failure outcome % 1% Number of s % 3% MFT OO OT P 2 F L MFT OO OT P Unk Mode percent Fig. 8. U.S. human space mission failure mode % Number of s % P -1 End/Mission 4 2 8% P above 3 End/Mission Unknown Time (sec) percent Fig. 9. U.S. human space mission time of failure Tg_8

9 E. J. TOMEI and I-S. CHANG: U.S. Human Space Transportation s transportation history shown in this paper helps to reveal the most common causes of U.S. human space mission failures and anomalies and should be useful to implement strategies to avoid similar failures in the future both for new and existing programs. The study shows that engineering design and process errors are the greatest threat to U.S. human space mission success, which requires engineering checks and balances with additional mission assurance and flight test. Human spaceflight data reviewed in this paper covers a wide span of years and vehicle types. The earliest missions were flown nearly 5 years ago, were of short duration, and used fairly primitive flight systems compared to today s vehicle, the Space Shuttle. A review of the human space mission failure and anomaly trends suggest the following lessons can be learned for future applications: First: Complex missions, such as the Apollo moon landing and return, or complex human space vehicles, such as the reusable Space Shuttle, can be expected to encounter numerous unexpected events. Results of this paper clearly suggest that fault tolerant, redundant systems with backup capabilities are necessary for crew safety and mission success. The study also shows that catastrophic failures have occurred in different flight phases so there is no evident trend, but system redundancy and back-up capabilities have clearly kept flight anomalies from propagating to failures. Second: The rate of occurrence of major anomalies is approximately 1.6 per flight on average. This reduces to 1.1 per flight when the repeated Space Shuttle thermal protection system (TPS) and solid motor leak anomalies (which did not involve crew action) are not included. This rate of occurrence appears manageable based on the success rate of the US human space missions. Pre-flight training of the flight and ground crews and flight testing of the vehicles can also help enhance mission success. Lastly: Ignoring clear evidence of a design defect on otherwise successful flights can be catastrophic to human space missions. For example, process and design errors resulted in many observed Shuttle TPS anomalies, but were not corrected, before the reentry failure of Shuttle Columbia on Moreover, SRB joint gas leaks had been a recurring problem with the large segmented solid motors, but less prevalent after the design changes following the Shuttle Challenger failure on Additional analysis of this data is planned to investigate flight results as a function of vehicle type and trends over time, but this will be the subject of a future report. An accompanying paper 44) will address non-u.s. human space transportation failures U.S Mission Reliability (%) Country Reliability Success Rate U.S. 93.7% 158 / 168 = 94.5% U.S. failure U.S. success Number of Launches Calendar Year Fig. 1. U.S. human space mission reliabilities Tg_9

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