Advanced Launch System Research Articles

Simulation of Startup Process of Air Turbine with Load

Air turbine is the power unit of the hydraulic balanced torpedo launch system which is the most advanced launch system in active service.In order to evaluate the performance of the air turbine,models of the start process for air turbine and supporting system are modeled on the basis of theories of thermodynamics and aerodynamics,the simulation software is developed,and the simulation results are analyzed.The simulation results show that the startup performance of the air turbine can match the air turbine pump torpedo launch system.These models not only can be a theoretical basis in the process of designing and manufacturing this launch system,but also can be used to analyze the operation principles of the air turbine pump torpedo launch system.

RADEM: An air launched, rocket demonstrator for future advanced launch systems

Critical features associated with future reusable launch vehicles include reduction of turn around effort, use of integral liquid hydrogen tanks, advanced structures and thermal protection, and re-usable LOx-hydrogen propulsion with low maintenance overheads. Many doubts associated with such designs could be removed by a sub-orbital demonstrator. An air launched vehicle would fulfil many of the objectives for such demonstration. British Aerospace, NPO Molnija, TsAGI and DB Antonov have made an initial study for ESA for such a demonstrator (RADEM), using earlier studies of operational launch systems with the An-225 /Hotol and MAKS proposals. The paper describes the results of this study, including the selection of two potential vehicle designs, and an approach to sub-system design and vehicle development to minimize the costs. It appears that such a vheicle, capable of flying to Mach 12 or beyond using currently available technology, could have a cost an order of magnitude less than that required for development of an operational vehicle.

Neighboring optimal control based feedback law for the advanced launch system

In this paper a robust feedback algorithm is presented for a near-minimum-fuel ascent of a generic two-stage launch vehicle operating in the equatorial plane. The development of the algorithm is based on the ideas of neighboring optimal control and can be divided into three phases. In phase 1 the formalism of optimal control is employed to calculate fuel-optimal ascent trajectories for a simple point-mass model. In phase 2 these trajectories are used to numerically calculate gain functions of time for the control(s), for the total flight time, and possibly for other variables of interest. In phase 3 these gains are used to determine feedback expressions for the controls associated with a more realistic model of a launch vehicle. With the advanced launch system in mind, all calculations in this paper are performed on a two-stage vehicle with fixed thrust history, but this restriction is by no means important for the approach taken. Performance and robustness of the algorithm is found to be excellent. cg ycg *TB yxB JCTC

Techniques for developing approximate optimal advanced launch system guidance

In this paper an extension to our previous technique used to develop a real-time guidance scheme for the Advanced Launch System is presented. Our approach is to construct an optimal guidance law based upon an asymptotic expansion associated with small physical parameters, ?. The problem is still to maximize the payload into orbit subject to the equations of motion of a rocket over a nonrotating spherical Earth. The trajectory of a rocket modeled as a point mass is considered with the flight restricted to an equatorial plane while reaching an orbital altitude at orbital injection speeds. The dynamics of this problem can be separated into primary effects due to thrust and gravitational forces, and perturbation effects which include the aerodynamic forces and the remaining inertial forces. An analytic solution to the reduced-order problem represented by the primary dynamics is possible. The Hamilton-Jacobi-Bellman or dynamic programming equation is expanded in an asymptotic series where the zeroth-order term (? = 0) can be obtained in closed form. The neglected perturbation terms are included in the higher-order terms of the expansion. These higher-order terms are determined from the solution of first-order linear partial differential equations requiring only integrations which are quadratures. These quadratures can be performed rapidly with the emerging computer capability so that real-time approximate optimization can be used to construct the launch guidance law. Here ? is chosen as the ratio of the atmospheric scale height to the radius of the Earth. It is important that the perturbation effects remain small.

General adaptive guidance using nonlinear programming constraint-solving methods

An adaptive, general-purpose, constraint-solving guidance algorithm has been developed by the authors in response to the requirements for the advanced launch system. The algorithm can be used for all mission phases for a wide range of space transportation vehicles without code modification because of the general formulation of the nonlinear programming problem, and the general trajectory simulation used to predict constraint values. The approach allows onboard retargeting for severe weather and changes in payload or mission parameters, increasing flight reliability and dependability, while reducing the amount of preflight analysis that must be performed. The algorithm is described in general in this paper. Three-degree-of-freedom closed-loop simulation results are presented for application of the algorithm to advanced launch system ascent, re-entry of a low lift-todrag vehicle, and Mars aerobraking. Flight processor throughput requirement data are shown for each of these applications.

Magnesium-neutralized propellant

Conventional solid rocket motors, which utilize ammonium perchlorate as the propellant oxidizer, produce hydrochloric acid (HC1) as an exhaust product. A low-acid propellant has been developed which substantially reduces the HCl content of the solid rocket exhaust. The predominant mechanism for HC1 exhaust reduction is a neutralization of the acid by the base magnesium hydroxide which is generated in the exhaust plume from the combustion of magnesium (Mg) fuel. Experimental analysis of the Mg-propellant combustion products has shown that HCl levels of less than 1 % are achievable. The Mg-neutralized propellant exhibits properties that are compatible with the reliability, cost, performance, ballistic, and mechanical properties as well as the safety dictates of an advanced launch system (ALS). Predictions for propellant variability and sensitivity suggest that the Mg-neutralized propellant reliability will compare favorably with the current state-of-the-art hydroxy terminated polybutadiene (HTPB) propellants. The range of ballistic tailorability is broad and the low-volumetric solids loading of the Mg propellant results in outstanding mechanical properties and simple processing. The Mg propellant also exhibits DoD zero cards class 1.3 hazards properties which suggests that no compromise in safety will be encountered relative to current propellants used in large booster applications.

Use of approximate gradients in trajectory optimization

Introduction T HE nonlinear programming approach has proven quite successful in solving optimal control problems, especially for highly nonlinear complicated systems. It does not usually require a very good initial estimate of the solution and offers great flexibility when the system model changes. Also, considerably less programming efforts are needed when all gradient information is generated by finite differences. In some problems, such as trajectory optimization for multistage launch vehicles where discontinuities in the system are inherent, the application of the necessary conditions in the function space is almost prohibitive. For those problems, the nonlinear programming approach has demonstrated great superiority over other methods. On the other hand, the efficiency of the nonlinear programming approach is not as good because additional n +1 (n = dimensionality of the problem) integrations of the system equations are required to compute the gradients in each iteration by finite differences. As a result, the dominant portion of computational time is spent on the gradient evaluations. There are situations where it is essential to obtain quickly a trajectory that satisfies all terminal constraints and any other imposed constraints when a slight penalty on the performance index is tolerable. Such a trajectory serves all of the practical purposes well even if it is just near optimal. In this Note, we shall explore the possibility of using approximate gradients to enhance the efficiency of the nonlinear programming approach. A formula for approximate gradients is derived that is more accurate than a well known result. The method is tested on trajectory optimization for an advanced launch system.

The advanced launch system: Application of total quality management principles to low-cost space transportation system development

Recognizing that a major inhibitor of man's rapid expansion of the use of space is the high cost (direct and induced) of space transportation, the U.S. has embarked on a major national program to radically reduce the cost of placing payloads into orbit while, at the same time, making equally radical improvements inlaunch system operability. The program is entitled “The Advanced Launch System” (ALS) and is a joint Department of Defense/National Aeronautics and Space Administration (DoD/NASA) program which will provide launch capability in the post 2000 timeframe. It is currently in Phase II (System Definition), which began in January 1989, and will serve as a major source of U.S. launch system technology over the next several years. The ALS is characterized by a new approach to space system design, development, and operation. The practices that are being implemented by the ALS are expected to affect the management and technical operation of all future launch systems. In this regard, the two most significant initiatives being implemented on the ALS program are the practices of Total Quality Management (TQM) and the Unified Information System (Unis). TQM is a DoD initiative to improve the quality of the DoD acquisition system, contractor management systems, and the technical disciplines associated with the design, development, and operation of major systems. TQM has been mandated for all new programs and affects the way every group within the system currently does business. In order to implement the practices of TQM, new methods are needed. A program on the scale of the ALS generates vast amounts of information which must be used effectively to make sound decisions. Unis is an information network that will connect all ALS participants throughout all phases of the ALS development. Unis is providing support for project management and system design, and in following phases will provide decision support for launch operations, computer integrated manufacturing, automated ground operation systems, and any other computer applications. Unis is providing information to a dynamic computerized ALS Model (ALSYM) which is a decision aiding tool, supporting the ALS design efforts. ALSYM will evolve to support operations decision making as the program matures. These efforts are expected to serve as a model for other DoD and NASA large-scale system developments.

A view toward future launch vehicles: A civil perspective

New launch capabilities are needed to support the evolving U.S. civil space activities. Requirements are materializing for unmanned cargo vehicles and manned systems to effectively support a balanced aggressive space activity, including the Space Station Freedom and planetary exploration. Needs include larger lift, better assured access, lower operating costs, and operating flexibility. The set of logical, complementing new cargo vehicles are a mid-1990s Shuttle cargo vehicle for delivery of 45,400–68,000 kg (100 K–150 K lb) to low Earth orbit (LEO) with limited flight rates; the modular Advanced Launch System with 45,000–90,700 kg (100 K–200 K lb) by the year 2000, and a very large heavy lift capability system of 90,700–181,400 kg (200 K–400 K lb) by 2010. Manned access must be sustained and broadened by improvements to the Space Shuttle operations, the use of a personnel launch vehicle in the late 1990s, and consideration of a Space Shuttle replacement in 2005–2015. Designs must and are embracing modularity, ruggedness, recoverability, new manufacturing techniques, and selected technologies to achieve necessary reliabilities, operability, and cost effectiveness. The result is a logical time-phased integrated set of effective capabilities.

Advanced concepts for launch vehicle control

The objective of the advanced launch system (ALS) program is to develop a family of launch vehicles which provides a substantial improvement in reliability, operability, and economy over existing systems. This requires that autopilot design and verification procedures be of minimum sensitivity to recurring costs while providing adequate, but not necessarily optimal, vehicle performance. One approach to accomplishing this task, namely, the utilization of advanced control design and analysis techniques, is considered. It is shown that the techniques, which represent a cross-section of developments in control theory, attempt to solve the ALS control problem in one of two ways: given increased knowledge of the launch vehicle and its environment, through greater model fidelity and additional sensor data; and autopilot design in the presence of quantified model/disturbance uncertainties and less stringent sensing requirements. It is concluded that the methods are promising and cost effective. >

Advanced Launch System (ALS) actuation and power systems impact operability and cost

A brief status review of the Advanced Launch System (ALS) is given. The use of electrical actuation integrated with a single-vehicle electrical power system and controls for all actuation and avionic requirements is highlighted. This technology will help attain the ALS primary goals of reduced costs ($300/lb Earth to LEO (low Earth orbit)) and improved operability by significantly reducing the launch operations and servicing requirements relative to current vehicle designs and practices. Six candidate government-supported programs that are involved in the relevant technologies or that could have significant applications for electric actuators and an integrated power-distribution and control system are listed with a brief explanation and description of noteworthy technology.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

NASA launch vehicles: The next 20 years

Low cost, reliable access to low Earth orbit and the pursuit of our nation's goal to further explore the moon and Mars are the foci for NASA advanced transportation development programs. The space infrastructure projected to evolve over the next two decades will be deployed and maintained by the Shuttle and its derivatives, by commercial expendables, and by new vehicles such as the Advanced Launch System. One Shuttle derivative currently being studied is the Shuttle-C, an unmanned cargo version in which the Orbiter is replaced by a cargo element. At first, manned access to the Space Station and other low Earth orbiting platforms and spacecraft will be via the Shuttle as now configured. Later, improvements aimed at increased reliability and operational cost reduction will be implemented. Major “block” changes such as the introduction of reusable liquid rocket boosters may further reduce the costs. When NASA transportation needs for the operational Space Station and for lunar and Mars exploration are better defined, Shuttle II and/or the Advanced Launch System and other vehicles now only being conceptualized will be needed. The Advanced Development Program of the Office of Space Flight has structured its requirements analyses, concept definition studies and advanced technology development projects to satisfy the evolutionary launch vehicle needs of NASA and to transition technological improvements to the military and commercial segments of the aerospace industry as well.

The joint DoD/NASA advanced launch system: Pathway to low-cost, highly operable space transportation

In response to changing needs, a major change in U.S. space transportation policy has occurred in the last few years. The joint Department of Defense/National Aeronautics and Space Administration Advanced Launch System program (ALS) intends to respond to this change in policy. The program, initiated in July 1987, completed Phase I at the end of August 1988 and is currently in Phase II. The ALS is cost optimized, rather than performance optimized, and will utilize advanced technology and innovative management and design approaches to achieve an ambitious congressionally mandated cost goal of $300/lb to low Earth orbit by the year 2005. The technological innovations will directly benefit other U.S. space transportation programs, such as the commercial programs and the National Aero Space Plane (NASP).