Space Flight Vehicles Research Articles

Comparison of the acoustical emissions of multiple full-scale rocket motors

Development of the next-generation space flight vehicles has prompted a renewed focus on rocket sound source characterization and near-field propagation modeling. Improved measurements of the sound near the rocket plume are critical for direct determination of the acoustical environment both in the near and far-fields. They are also crucial inputs to empirical models and to validate computational aeroacoustics models. Preliminary results from multiple measurements of static horizontal firings of Alliant Techsystems motors including the GEM-60, Orion 50S XLG, and the Reusable Solid Rocket Motor (RSRM) performed in Promontory, UT, are analyzed and compared. The usefulness of scaling by physical parameters such as nozzle diameter, velocity, and overall sound power is demonstrated. The sound power spectra, directional characteristics, distribution along the exhaust flow, and pressure statistical metrics are examined over the multiple motors. These data sets play an important role in formulating more realistic sound source models, improving acoustic load estimations, and aiding in the development of the next generation space flight vehicles via improved measurements of sound near the rocket plume.

Tolerance of centrifuge-simulated suborbital spaceflight by medical condition.

We examined responses of volunteers with known medical disease to G forces in a centrifuge to evaluate how potential commercial spaceflight participants (SFPs) might tolerate the forces of spaceflight despite significant medical history. Volunteers were recruited based upon suitability for each of five disease categories (hypertension, cardiovascular disease, diabetes, lung disease, back or neck problems) or a control group. Subjects underwent seven centrifuge runs over 2 d. Day 1 consisted of two +G(z) runs (peak = +3.5 G(z), Run 2) and two +G(x), runs (peak = +6.0 G(x), Run 4). Day 2 consisted of three runs approximating suborbital spaceflight profiles (combined +G(x) and +G(z), peak = +6.0 G(x)/+4.0 G(z)). Data collected included blood pressure, electrocardiogram, pulse oximetry, neurovestibular exams, and post-run questionnaires regarding motion sickness, disorientation, grayout, and other symptoms. A total of 335 subjects registered for participation, of which 86 (63 men, 23 women, age 20-78 yr) participated in centrifuge trials. The most common causes for disqualification were weight and severe and uncontrolled medical or psychiatric disease. Five subjects voluntarily withdrew from the second day of testing: three for anxiety reasons, one for back strain, and one for time constraints. Maximum hemodynamic values recorded included HR of 192 bpm, systolic BP of 217 mmHg, and diastolic BP of 144 mmHg. Common subjective complaints included grayout (69%), nausea (20%), and chest discomfort (6%). Despite their medical history, no subject experienced significant adverse physiological responses to centrifuge profiles. These results suggest that most individuals with well-controlled medical conditions can withstand acceleration forces of launch and re-entry profiles of current commercial spaceflight vehicles.

Intensity-based approach to characterize near-field acoustic environments of space flight vehicles

An intensity-based measurement probe has been developed to measure the magnitude, directivity, and spectral content of near-field rocket source noise. An array of the intensity-based measurement probes was deployed in a static test firing of the GEM-60 at Alliant Techsystems in Promontory, UT, in 2012. The probes were positioned along the shear layer of the rocket motor plume to enable a comparison of the resultant source characterization obtained via sound power type measurement approaches to traditional acoustic measurement methodologies. The measurement results demonstrate that the intensity-based probes advance the measurement and characterization of the near-field acoustic environment of rockets. Moreover, intensity-based acoustic data provides an important role in formulating more realistic sound source models, improving acoustic load estimations, and aiding in the development of the next-generation space flight vehicles via improved measurements of noise near the rocket plume.

Crew exploration vehicle (CEV) attitude control using a neural–immunology/memory network

This paper addresses the problem of the crew exploration vehicle (CEV) attitude control. CEVs are NASA's next-generation human spaceflight vehicles, and they use reaction control system (RCS) jet engines for attitude adjustment, which calls for control algorithms for firing the small propulsion engines mounted on vehicles. In this work, the resultant CEV dynamics combines both actuation and attitude dynamics. Therefore, it is highly nonlinear and even coupled with significant uncertainties. To cope with this situation, a neural–immunology/memory network is proposed. It is inspired by the human memory and immune systems. The control network does not rely on precise system dynamics information. Furthermore, the overall control scheme has a simple structure and demands much less computation as compared with most existing methods, making it attractive for real-time implementation. The effectiveness of this approach is also verified via simulation.

Commercial Spaceflight Participant G-Force Tolerance During Centrifuge-Simulated Suborbital Flight

Medical knowledge of the human body in microgravity and hypergravity is based upon studies of healthy individuals well-conditioned for such environments. Little data exist regarding the effects of spaceflight on untrained commercial passengers. We examined the responses of potential spaceflight participants (SFP) to centrifuge G-force exposure. There were 77 individuals (65 men, 12 women), 22-88 yr old, who underwent 6 centrifuge runs over 48 h. Day 1 consisted of two +Gz runs (peak = 3.5+Gz, run 2) and two +Gx runs (peak = 6.0+Gx, run 4). Day 2 consisted of two runs approximating a suborbital spaceflight profile. Data included blood pressure, electrocardiogram, and postrun questionnaires regarding motion sickness, disorientation, greyout, and other symptoms. Of the 77 participants, average age was 50.4 +/- 12.7 yr. Average heart rate (HR) varied by sex and direction of G-exposure (+Gz: F 150 +/- 19, M 123 +/- 27; +Gx: F 135 +/- 30, M 110 +/- 27). Age and peak HR were inversely related (HR < 120 bpm: 60.2 +/- 12.2 yr, HR > 120: 47.1 +/- 10.9 yr). HR during peak G-exposure for the final run was associated with post-run imbalance (no imbalance: HR 126 +/- 26, imbalance: HR 145 +/- 21); no other significant hemodynamic change, sex, or age variation was associated with imbalance. Age and greyout were inversely associated; there was no association between greyout and vital sign change, sex, or G-force magnitude. Baseline/pretrial mean arterial pressure (MAP) was not associated with any symptoms. The results suggest that most individuals with well-controlled medical conditions can withstand acceleration forces involved in launch/landing profiles of commercial spaceflight vehicles. Further investigation will help refine which conditions present significant risk during suborbital flight and beyond.

Full-scale rocket motor acoustic tests and comparisons with models: Updates and comparisons with SP-8072

Development of the next-generation space flight vehicles has prompted a renewed focus on rocket sound source characterization and near-field propagation modeling. Measurements taken during a static horizontal firing of Alliant Techsystems Orion 50S XLG are compared to the predicted levels produced from NASA’s SP-8072 Distributed Source Methods (DSM-1 and DSM-2). Two modifications to the SP 8072 prediction model are considered in regards to the source directivity and the source power spectral distribution. All models considered provide a good first-order approximation given an appropriate total acoustic sound power. However, a more physical model is needed to adequately map out the critical near-field region as well as the far-field propagation. A new intensity-based measurement system and corresponding procedures are currently being developed for determining this near field energy flow and for achieving source characterization capabilities beyond traditional pressure measurements. These advances are believed to be a step toward improved measurements and modeling of the rocket plume.

Full-scale rocket motor acoustic tests and comparisons with models: Revisiting the empirical curves

Development of the next-generation space flight vehicles has prompted a renewed focus on rocket sound source characterization and near-field propagation modeling. Improved measurements of the noise near the rocket plume are critical for direct determination of the noise environment. They are also crucial in providing inputs to empirical models and in validating computational aeroacoustics models. NASA’s SP 8072 acoustic load prediction model is a widely used method for predicting liftoff acoustics. SP-8072 implements two Distributed Source Methods (DSM-1 and DSM-2), which predict the loading as the sum of the radiated field from each source distributed along the plume. The prediction model depends largely on empirical curve fits computed from historical data to determine the source power and frequency content at distances along the plume. Preliminary results from measurements of a static horizontal firing of Alliant Techsystems Orion 50S XLG performed in Promontory, UT are analyzed with respect to the historical data that drives the SP-8072 prediction model.

Human Spaceflight and Hypersonic Re-entry Vehicles: Looking Backward to Step Forward

Human Spaceflight and Hypersonic Re-entry Vehicles: Looking Backward to Step Forward

Human Systems Integration in the Federal Government

Human Systems Integration principles and methods can be used to help integrate people, technology, and organizations in an effective and efficient manner. Over the past decade, a wide range of tools, techniques, and technologies have been developed by federal agencies to achieve significant cost and performance benefits. In this discussion, we will explore trends in military human systems integration and learn about the critical role being played by human performance and effectiveness research. We will also examine case studies on the planning and design of future human space flight vehicles, the national air space system and the first nuclear reactors to be built in the United States in over 30 years. And with an eye toward sustaining the discipline's principles and methods, we'll take a look at educating and training the next generation of human systems integration practitioners.

Aerodynamic design and computational analysis of a space flight vehicle cabin ventilation fan.

Quieter working environments for astronauts are needed if future long-duration space exploration missions are to be safe and productive. Ventilation and payload cooling fans are known to be dominant sources of noise, with the International Space Station being an important case in point. To address this issue in a cost effective way, early attention to fan design, selection, and installation has been recommended. Toward that end, NASA has begun to investigate the potential for small-fan noise reduction through improvements in fan aerodynamic design. Using tools and methodologies similar to those employed by the aircraft engine industry, the aerodynamic design of a new cabin ventilation fan has been developed, and its aerodynamic performance predicted using computational fluid dynamics (CFD) codes. The design, intended to serve as a baseline for future work, is discussed along with selected CFD results.

Fuel Cell Development for NASA’s Human Exploration Program: Benchmarking With “The Hydrogen Economy”

The theoretically high efficiency and low temperature operation of hydrogen-oxygen fuel cells have motivated them to be the subject of much study since their invention in the 19th century, but their relatively high life cycle costs have kept them as a “solution in search of a problem” for many years. The first problem for which fuel cells presented a truly cost effective solution was that of providing a power source for NASA’s human spaceflight vehicles in the 1960s. NASA thus invested, and continues to invest, in the development of fuel cell power plants for this application. This development program continues to place its highest priorities on requirements for minimum system mass and maximum durability and reliability. These priorities drive fuel cell power plant design decisions at all levels, even that of catalyst support. However, since the mid-1990s, prospective environmental regulations have driven increased governmental and industrial interest in “green power” and “the hydrogen economy.” This has in turn stimulated greatly increased investment in fuel cell development for a variety of commercial applications. This investment is bringing about notable advances in fuel cell technology, but as these development efforts place their highest priority on requirements for minimum life cycle cost and field safety, these advances are yielding design solutions quite different at almost every level from those needed for spacecraft applications. This environment thus presents both opportunities and challenges for NASA’s Human Exploration program.

Frictional Ignition Testing of Composite Materials

Abstract The space flight community has been investigating lightweight composite materials for use in propellant tanks for both liquid and gaseous oxygen for space flight vehicles. The use of these materials presents some risks pertaining to ignition and burning hazards in the presence of oxygen. Through the hazard analysis process, some ignition mechanisms have been identified as being potentially credible. One of the ignition mechanisms was reciprocal friction; however, test data do not exist that could be used to clear or fail these types of materials as “oxygen compatible” for the reciprocal friction ignition mechanism. Therefore, testing was performed at the NASA Johnson Space Center White Sands Test Facility to provide data to evaluate this ignition mechanism. This paper presents the test system, approach, data results, and findings of the reciprocal friction testing performed on composite sample materials being considered for propellant tanks.

Upgrades to the Caution and Warning System of the Space Shuttle

During a Space Shuttle mission, astronauts are alerted to off-nominal conditions via a Caution and Warning System that often generates a myriad of auditory and visual alerts. A key component of this system is the Fault Summary display, which contains text messages describing the malfunctions. The display often becomes cluttered with extraneous messages, increasing the difficulty of diagnosing a malfunction. In an effort to improve the crew's diagnostic performance, increase their situational awareness and reduce their workload, the Caution and Warning System is being improved as part of the Cockpit Avionics Upgrade. In the first phase of the upgrade, the Fault Summary display is being redesigned with a more logical task-oriented graphical layout and multiple text fields for malfunction messages. In the second phase, the text fields will indicate only the source (i.e., root-cause) of the malfunction to prevent non-operationally useful messages from appearing on the display. These and other aspects of the upgrades are based on extensive collaboration among astronauts, engineers, and human factors scientists. This paper describes the human factors principles applied to upgrading the Caution and Warning System in the presence of inherent limitations associated with legacy manned spaceflight vehicles.

Limiting stationary motions of a body on a string

A string suspension is suggested as an experimental arrangement for examining new samples of air flight and space flight vehicles or their components. The dynamics of a rigid body on a string suspension is considered. Stationary motions of an axisymmetric body on a string are studied at high angular velocities of the system rotation. In the case where the suspension point is on the axis of symmetry, all limiting permanent rotations and regular precessions are determined, the domains of their existence are obtained and also the system' equilibria evolution when its parameters are changed is examined. In the case of the displaced suspension point the exact upper bound of the number of possible permanent rotations of the system is given and all types of limiting equilibrium configurations are determined as well as the domains of their existence. The domain in the space of dimensionless parameters of the system is found where the maximal number of different permanent rotations exist at sufficiently high angular velocity.

Extremally steered singular thrust-arcs for space flight in an atmosphere

This paper advances prior results on the problem of time-free, Mayer-optimal control of a blunt space vehicle's flight in an atmosphere. The extremally steered, first order, singular arc is partially singular and the Lie-bracket formalism employed previously for the totally singular case is not quite applicable. However, by differentiating the switching function, a relationship is obtained between the totally and partially singular arcs. For the special case of coplanar flight, the singular thrust control is expressed in a nonlinear state feedback form. This form indicates that the singular thrust magnitude is separable as the sum of five types of forces: one due to gravity alone, another due to centrifugal effects, a third due to drag alone, a fourth due to atmospheric density gradient, and finally a fifth due to a coupling between these forces. The extremal steering angle along the singular arc is obtained as an implicit function of the states. An explicit solution is obtained for the special case of a low-density atmosphere. For proper combinations of steering and rocket exhaust speed, the singular arc satisfies the generalized Legendre-Clebsch condition and the Goh-Robbins condition making it a strong candidate for Mayer optimality.

Collection, compaction and storage of solid waste for space missions

Efficient trash collection and volume reduction becomes very important during extended, manned space flight missions because of the high rate of crew member generated trash and the limited volume available to store this trash. Trash management in manned space flight vehicles requires that the following considerations be addressed: definition of the trash model including quantities/rates of generation and the physico-chemical characteristics of the trash; methods of collection and temporary stowage prior to treatment or processing; the method of treatment/processing to affect biochemical stabilization and volume reduction; and storage of treated/ processed trash prior to final disposition. This paper discusses trash management design approaches with focus on trash collection, compaction and storage. This paper also discusses the trash compactor design currently being developed for the Space Station Freedom program.

Measurements of the spectral emissivity of surfaces used in jet engines and space technology

Three relevant thermal radiation problems are identified and commented with reference to own experimental data: (1) The chance to optimize the spectral emissivity behavior for radiation cooling in space flight vehicles by purposely prepared coatings, (2) to evaluate the influence of a hydrocarbon-flame emission spectrum on the walls of the combustion chamber, and (3) to clarify the reliability of the pyrometric thermometry, especially used in air-breathing jet engines for power control. At present, only experiments made up for accurate radiative material properties offer key data for items (1)–(3). Appropriate devices are explained.

Collection, compaction and storage of solid waste for space missions.

Efficient trash collection and volume reduction becomes very important during extended, manned space flight missions because of the high rate of crew member generated trash and the limited volume available to store this trash. Trash management in manned space flight vehicles requires that the following considerations be addressed: definition of the trash model including quantities/rates of generation and the physico-chemical characteristics of the trash; methods of collection and temporary stowage prior to treatment or processing; the methods of treatment/processing to affect biochemical stabilization and volume reduction; and storage of treated/processed trash prior to final disposition. This paper discusses trash management design approaches with focus on trash collection, compaction and storage. This paper also discusses the trash compactor design currently being developed for the Space Station Freedom program.

Space Shuttle Solid Rocket Motor Testing for Return to Flight: Transient Pressure Test Article Test Program

The Transient Pressure Test Article (TPTA) test program is being conducted at a new test facility located in the east test area at the National Aeronautics and Space Administration's (NASA's) Marshall Space Flight Center (MSFC) in Huntsville, Alabama. This facility, along with the special test equipment (STE) required for facility support, was constructed specifically to test and verify the sealing capability of the redesigned solid rocket motor's (RSRM) field, igniter, and nozzle joints. The test article consists of full scale RSRM hardware loaded with inert propellant and assembled in a short stack configuration. The TPTA is pressurized by igniting a propellant cartridge capable of inducing a pressure rise rate that simulates the ignition transient that occurs during launch. Dynamic loads are applied during the pressure cycle to simulate external tank attach (ETA) strut loads present on the ETA ring. Sealing ability of the redesigned joints is evaluated under joint movement conditions produced by these combined loads since joint sealing ability depends on seal resilience velocity being greater than gap opening velocity. Also, maximum flight dynamic loads are applied to the test article which is either pressurized to 600 psia using gaseous nitrogen (GN2) or applied to the test article as the pressure decays inside the test article on the down cycle after the ignition transient cycle. This paper will present the uniqueness of this new test facility with respect to its capabilities. It will also touch on both the topic of test effectiveness versus space vehicle flight performance and new aerospace test techniques, as well as presenting a comparison between the old SRM design and the RSRM.

Navigation simulator for the space tug vehicle

A general simulation program (GSP) for state estimation of a nonlinear space vehicle flight navigation system is developed and used as a basis for evaluating the performance of a Space Tug navigation system. An explanation of the iterative guidance mode (IGM) guidance law, derivation of the dynamics, coordinate frames and state estimation routines are given in order to clarify the assumptions and approximations made. A number of simulation and analytical studies are used to demonstrate the operation of the Tug system. Included in the simulation studies are (1) initial offset vector parameter study; (2) propagation time vs accuracy; (3) measurement noise parametric study and (4) reduction in computational burden of an on-board implementable scheme. From the results of these studies, conclusions and recommendations concerning future areas of practical and theoretical work are presented.