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At least 631 records · Page 35

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NASA NTRS1992

A case of poor substructure diagnostics

The NASTRAN Manuals in the substructuring area are all geared toward instant success, but the solution paths are fraught with many traps for human error. Thus, the probability of suffering a fatal abort is high. In such circumstances, the necessity for diagnostics that are user friendly is paramount. This paper is written in the spirit of improving the diagnostics as well as the documentation in one area where the author felt he was backed into a blind corner as a result of his having committed a data oversight. This topic is aired by referring to an analysis of a particular structure. The structure, under discussion, used a number of local coordinate systems that simplified the preparation of input data. The principle features of this problem are introduced by reference to a series of figures.

Butler, Thomas G.↗

NASA NTRS1992

Numerical methods for the simulation of complex multi-body flows with applications for the integrated Space Shuttle vehicle

This project forms part of the long term computational effort to simulate the time dependent flow over the integrated Space Shuttle vehicle (orbiter, solid rocket boosters (SRB's), external tank (ET), and attach hardware) during its ascent mode for various nominal and abort flight conditions. Due to the limitations of experimental data such as wind tunnel wall effects and the difficulty of safely obtaining valid flight data, numerical simulations are undertaken to supplement the existing data base. This data can then be used to predict the aerodynamic behavior over a wide range of flight conditions. Existing computational results show relatively good overall comparison with experiments but further refinement is required to reduce numerical errors and to obtain finer agreements over a larger parameter space. One of the important goals of this project is to obtain better comparisons between numerical simulations and experiments. In the simulations performed so far, the geometry has been simplified in various ways to reduce the complexity so that useful results can be obtained in a reasonable time frame due to limitations in computer resources. In this project, the finer details of the major components of the Space Shuttle are modeled better by including more complexity in the geometry definition. Smaller components not included in early Space Shuttle simulations will now be modeled and gridded.

Chan, William M.↗

NASA NTRS1990

Optimal trajectories and guidance trajectories for aircraft flight through windshears

The research on the optimization and guidance of flight trajectories in the presence of windshear performed by the Aero-Astronautics Group of Rice University is summarized. This research refers to windshear recovery systems and covers three areas of investigation: take-off, abort landing, and penetration landing. Determination of optimal trajectories and development of near-optimal guidance schemes are outlined.

Miele, A.↗

NASA NTRS1990

Aircraft control in a downburst on takeoff and landing

Aircraft takeoff and landing in the presence of downbursts are addressed. Dynamic optimization and feedback control system design techniques are used to determine proper guidance laws for aircraft in the presence of downbursts, and insensitivity to downburst structures is emphasized. Avoidance is the best policy. If an inadvertent encounter occurs when the aircraft is already close to or even in the downburst, the pilot should concentrate on vertical flight, unless he is sure which direction to turn for winds of less intensity. If such an encounter happens on takeoff, maximum thrust should be used aggressively and a lower climb rate or even descending flight is recommended. Similar strategy is applicable for abort landing. If an encounter happens on landing and encounter height is low, landing should proceed. It is recommended that the nominal horizontal and vertical velocities w.r.t the ground should be maintained, subject to a minimum airspeed constraint. A landing control logic is designed to accomplish this.

Zhao, Yiyuan↗

NASA NTRS1991

Mission design strategies for the human exploration of Mars

Conventional mission planning for piloted flights to Mars has been confined to comparing the round-trip energy and flight time requirements of several trajectory classes. This paper addresses these trades in the context of acceptable operational flight characteristics including abort considerations and crew exposure to the interplanetary environment. Quantitative estimates of crew radiation exposure, both during transit and on the surface of Mars, are made and compared to established NASA standards. Time periods spent in zero-gravity during mission transit legs for the various mission options are compared, along with the recovery times in the Mars gravity field. Finally, an integrated mission/abort strategy is proposed, consistent with the expected performance of first-generation nuclear propulsion systems.

Joosten, B. K.↗

NASA NTRS1991

Logistics impacts on lunar and Mars lander design

The results of trade studies and evaluations done to determine the impact of accommodation and unloading of cargo on spacecraft design are reviewed. It is concluded that the effectiveness of the surface mission to moon or Mars is best accomplished by providing for undivided cargo delivery and for cargo unloading indirectly to earth surface without the aid of a surface system unloader, for immediate cargo drop during descent abort to orbit, for immediate cargo drop in case of need for an emergency ascent from the surface, and for contiguous placement of cab and surface habitat modules. For exploration architectures that include multiple site visits within as much as several hundred km of each other, use of excursion vehicles capable of short suborbital hops to secondary sites is much less expensive in terms of IMLEO than a strategy of using multiple landers or multiple missions.

Donahue, Benjamin↗

NASA NTRS1989

Liquid Rocket Boosters for Shuttle

The Liquid Rocket Booster study was initiated by NASA to define an alternative to the Solid Rocket Boosters used on the STS. These studies have involved MSFC, JSC and KSC and their contractors. The prime study contractors, Martin Marietta Corporation and General Dynamics Space Systems, have identified Liquid Booster configurations which would replace the SRB's in the Shuttle stack. The Liquid Rocket Booster increases Shuttle performance to 70 K LBS, provides improved reliability, hold down and verification prior to vehicle release, engine out and improved abort capability, and is phased into the STS launch operations without adversely affecting flight rate.

Hughes, James E.↗

NASA NTRS1992

Manned transportation systems design considerations

Manned transportation mission and programmatic requirements and how they affect spacecraft size, mass and complexity are presented. Some of these requirements include fundamental issues such as the degree of separation of cargo and people, abort requirements and the issue of man rating. Attention is given to design considerations, crew size and mission requirements, payloads, crew physiologic considerations, and a vehicle health monitoring and emergency detection system.

Teixeira, Charles↗

NASA NTRS1992

The HL-20 Personnel Launch System

A lifting-body approach to the design of a personnel launch system spacecraft for Space Station crew rotation missions is presented. Recent study findings in the areas of wind tunnel tests, landing dynamics, handling qualities, and abort are summarized. HL-20, which is designed for safe and reliable operations, has improved operability, maintainability, and affordability as compared to current manned transportation operations. The high lift-to-drag ratio of the HL-20 provides significant advantages in reduced g-loads during entry, high crossrange capability, ability to fly to landing sites over an extensive part of the earth, and multiple landing opportunities per day at specific landing sites. Pilot ratings of the flying qualities are at level 1 on the Cooper-Harper scale. Attention is also given to a streamlined management approach to HL-20 PLS development and operations which are presently under study.

Talay, Theodore A.↗

NASA NTRS1992

Mars trajectory options for the Space Exploration Initiative

The Mission Definition Office within the Lunar and Mars Exploration Program Office at the NASA/Johnson Space Center has the responsibility for leading the Space Exploration Initiative mission design activities across the Agency. In support of the Synthesis Group architecture analyses, a mission concept that includes fast one-way transits to and from Mars, a powered flyby abort, and an early return option has been developed. This paper will describe this integrated approach to Mars mission planning.

Soldner, John K.↗

NASA NTRS1992

Atmospheric entry of nuclear-powered vehicles due to accidental/inadvertent termination of operations

The entries of the radioactive components into earth's atmosphere resulting from an accident or inadvertent abort of a space vehicle powered by nuclear-thermal-rockets are investigated. The study is made for a typical piloted Mars mission vehicle incapacitated by an accident or malfunction during the trans-Mars-injection maneuver due to simultaneous multiple failures of its component systems. The three different accident/abort modes considered are the following: (1) a constant-rate angular pitching motion of the vehicle, (2) a constant-acceleration angular pitching motion of the vehicle, and (3) the rocket engine breaks away from the rest of the vehicle with a finite relative (dispersion) velocity. The speeds and angles of the atmospheric entries are calculated for each mode for different values of the time of the accident, pitching rate, acceleration, and dispersion velocity. For the most severe entry speeds and flight-path angles, the stagnation-point pressures, heat transfer rates, thickness, and mass per unit area of the heat shields necessary to protect the radioactive components from disintegrating, deceleration g-loads, and high ground-impact velocities are calculated. The study points out that the high g-loads and high ground-impact velocities are the most serious problems that must be addressed.

Menees, Gene P.↗

NASA NTRS1992

Trajectory design and navigation analysis for Cargo Transfer Vehicle proximity operations

The paper documents an investigation of alternative (or off-nominal) final approach trajectories and terminal guidance algorithms for Cargo Transfer Vehicle (CTV) automated rendezvous and proximity operation in the vicinity of Space Station Freedom (SSF). Ten candidate trajectory designs, representing a survey of all approaches that reasonably satisfy the mission constraints, are compared qualitatively and quantitatively. It is shown that several fundamentally different types of approach strategies are feasible in the CTV application and enjoy more favorable passive collision avoidance and plume impingement properties than the nominal. They are, however, generally more costly in propellant. The extent to which an alternative approach is more costly is determined largely by the abort (or specifically the 'hold' or 'wave-off') requirements. These approach techniques are verified in a software simulation using a parametrically defined candidate navigation system, and proximity sensor accuracy requirements are derived.

Marsh, S. M.↗

NASA NTRS1992

Takeoff Performance Monitoring System display options

The development of displays for the Takeoff Performance Monitoring System (TPMS) is described with attention given to the three concepts prepared for commercial applications. The TPMS algorithm is described and related to the display requirements for pilots of two-engine airplanes. Head-up and -down displays are considered for displaying the simple advisory data which indicate whether the takeoff is a 'Go' or 'No-go' based on engine failure, acceleration error, and runway length. Six pilots are shown the three display options which include: (1) basic information; (2) basic data with 'Go/No-go' advisory flags; and (3) basic data, advisory flags, and an abort-warning symbol. The pilots tended to select the option with the most advisory data available, but the inconclusive preference study led to the concept of presenting all three configurations as possible display options for the TPMS.

Middleton, David B.↗

NASA NTRS1992

Database recovery using redundant disk arrays

Redundant disk arrays provide a way for achieving rapid recovery from media failures with a relatively low storage cost for large scale database systems requiring high availability. In this paper a method is proposed for using redundant disk arrays to support rapid-recovery from system crashes and transaction aborts in addition to their role in providing media failure recovery. A twin page scheme is used to store the parity information in the array so that the time for transaction commit processing is not degraded. Using an analytical model, it is shown that the proposed method achieves a significant increase in the throughput of database systems using redundant disk arrays by reducing the number of recovery operations needed to maintain the consistency of the database.

Mourad, Antoine N.↗

NASA NTRS1992

NSPWG-recommended safety requirements and guidelines for SEI nuclear propulsion

An interagency Nuclear Safety Policy Working Group (NSPWG) was chartered to recommend nuclear safety policy, requirements, and guidelines for the Space Exploration Initiative (SEI) nuclear propulsion program to facilitate the implementation of mission planning and conceptual design studies. The NSPWG developed a top-level policy to provide the guiding principles for the development and implementation of the nuclear propulsion safety program and the development of safety functional requirements. In addition, the NSPWG reviewed safety issues for nuclear propulsion and recommended top-level safety requirements and guidelines to address these issues. Safety requirements were developed for reactor start-up, inadvertent criticality, radiological release and exposure, disposal, entry, and safeguards. Guidelines were recommended for risk/reliability, operational safety, flight trajectory and mission abort, space debris and meteoroids, and ground test safety. In this paper the specific requirements and guidelines will be discussed.

Marshall, Albert C.↗

NASA NTRS1992

Thermal issues at the SSC

A variety of heat transfer problems arise in the design of the Superconducting Super Collider (SSC). One class of problems is to minimize heat leak from the ambient to the SSC rings, since the rings contain superconducting magnets maintained at a temperature of 4 K. Another arises from the need to dump the beam of protrons (traveling around the SSC rings) on to absorbers during an abort of the collider. Yet another category of problems is the cooling of equipment to dissipate the heat generated during operation. An overview of these problems and sample heat transfer results are given in this paper.

Ranganathan, Raj P.↗

NASA NTRS1991

Space transfer vehicle concepts and requirements. Volume 1: Executive summary

The objectives of the Space Transfer Vehicle (STV) Concepts and Requirements studies were to provide sensitivity data on usage, economics, and technology associated with new space transportation systems. The study was structured to utilize data on the emerging launch vehicles, the latest mission scenarios, and Space Exploration Initiative (SEI) payload manifesting and schedules, to define a flexible, high performance, cost effective, evolutionary space transportation system for NASA. Initial activities were to support the MSFC effort in the preparation of inputs to the 90 Day Report to the National Space Council (NSC). With the results of this study establishing a point-of-departure for continuing the STV studies in 1990, additional options and mission architectures were defined. The continuing studies will update and expand the parametrics, assess new cargo and manned ETO vehicles, determine impacts on the redefined Phase 0 Space Station Freedom, and to develop a design that encompasses adequate configuration flexibility to ensure compliance with on-going NASA study recommendations with major system disconnects. In terms of general requirements, the objectives of the STV system and its mission profiles will address crew safety and mission success through a failure-tolerant and forgiving design approach. These objectives were addressed through the following: engine-out capability for all mission phases; built-in-test for vehicle health monitoring to allow testing of all critical functions such as, verification of lunar landing and ascent engines before initiating the landing sequence; critical subsystems will have multiple strings for redundancy plus adequate supplies of onboard spares for removal and replacement of failed items; crew radiation protection; and trajectories that optimize lunar and Mars performance and flyby abort capabilities.

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NASA NTRS1993

Thirty years together: A chronology of U.S.-Soviet space cooperation

The chronology covers 30 years of cooperation between the U.S. and the Soviet Union (and its successor, the Commonwealth of Independent States, of which the Russian Federation is the leading space power). It tracks successful cooperative projects and failed attempts at space cooperation. Included are the Dryden-Blagonravov talks; the UN Space Treaties; the Apollo Soyuz Test Project; COSPAS-SARSAT; the abortive Shuttle-Salyut discussions; widespread calls for joint manned and unmanned exploration of Mars; conjectural plans to use Energia and other Russian space hardware in ambitious future joint missions; and contemporary plans involving the U.S. Shuttle, Russian Mir, and Soyuz-TM. The chronology also includes events not directly related to space cooperation to provide context. A bibliography lists works and individuals consulted in compiling the chronology, plus works not used but relevant to the topic of space cooperation.

Portree, David S. F.↗