Future Space Systems Research Articles

Space debris mitigation and space systems design

The necessity to implement space debris mitigation measures in present and future space systems and missions has been generally identified by all space faring agencies and nations. On the long term, this will lead to noticeable design changes for rocket upper stages and satellites. Technical solutions will have to be found by a dialogue between the debris research groups and the hardware designers taking account of the feasibility, cost and mission limitations of such measures. The paper reviews the fields in which spacecraft design changes would be effective to improve the future debris situation. The classical fields are passivation (i.e. fuel venting, battery discharging etc.) and orbital lifetime limitation (de-orbiting, re-orbiting to disposal orbits etc.). De-orbiting or lifetime-reduction of rocket upper stages can be accomplished by depletion burn, extra retrothrusters, drag enhancement and electrodynamic tethers. To facilitate lifetime reduction of rocket stages on GTO, time and thrust direction of retromanoeuvres shortly after perigee passage can be considered (trade-off between propellant mass and battery power). The de-orbiting or lifetime reduction of satellites can be accomphlished by an existing attitude/orbit control system. Since for circular orbits of 1300 km and higher the propellant mass fraction for lifetime reduction would become a sensitive cost burden, there is a strong incentive to look into high specific impulse systems as arcjets etc.

Evaluating Future Military Space Technologies

In a major Air Force study of future space systems, SPACECAST 2020, study teams produced a set of system concepts for 21st century military space operations. Our goal was to assess the potential operational utility of these systems in an objective, traceable, and robust manner, so that we could compare the systems and identify the most important. An additional goal was to determine the technologies whose advancement will do the most to make the high-priority systems a reality. To do this, we developed a hierarchical value model based on Department of Defense policy documents and the operational judgments of Air University faculty and students (senior and mid-level managers who will be future Air Force leaders). We completed the study within an extremely tight deadline, and it was widely accepted within the Air Force.

Skill maintenance in extended spaceflight: A human factors analysis of space and analogue work environments

This paper discusses the implications of increasing mission lengths of manned spaceflight for the design of future space systems from a human factors point of view. It is argued that the increase in mission duration has brought about a number of new problems, which have not been sufficiently addressed in space research. Therefore, a review of analogue work environments is carried out to make up for the paucity of space research found in the area of human performance in long-duration spaceflight. This resulted in an evaluation of seven analogue environments concerning their similarity to space with industrial process control and nuclear submarines coming out as the closest match on the technical dimension. Finally, some recommendations are given from the lessons learnt in spaceflight, simulation studies and appropriate analogue environments.

SPACE SYSTEMS PRELIMINARY DESIGN

AbstractAs in all other industries, the space industry is evolving in three primary areas: technology, costs and socio‐organisational approaches.A project conducted in CNES aims to revise the definition of future space systems with the introduction of global methods and computer‐aided tools. One of the main goals is the definition and the development of a cooperative workbench for missions and space systems design. It will be composed of a certain number of design and simulation tools dealing with unique and coherent information shared between different view points. Operated in CNES, this computer‐based workbench will focus on the early stages of projects but will also treat first order or “simplified” models which are managed daily during the projects' life span, in accordance with the detailed models from industry.

High performance, accelerometer-based control of the Mini-MAST structure

Many large space system concepts will require active vibration control to satisfy critical performance requirements such as line of sight pointing accuracy and constraints on rms surface roughness. In order for these concepts to become operational, it is imperative that the benefits of active vibration control be shown to be practical in ground based experiments. The results of an experiment shows the successful application of the Maximum Entropy/Optical Projection control design methodology to active vibration control for a flexible structure. The testbed is the Mini-Mast structure at NASA-Langley and has features dynamically traceable to future space systems. To maximize traceability to real flight systems, the controllers were designed and implemented using sensors (four accelerometers and one rate gyro) that are actually mounted to the structure. Ground mounted displacement sensors that could greatly ease the control design task were available but were used only for performance evaluation. The use of the accelerometers increased the potential of destabilizing the system due to spillover effects and motivated the use of precompensation strategy to achieve sufficient compensator roll-off.

The Development of Rendez-Vous and Docking Technology for Japanese Future Space Systems

The Development of Rendez-Vous and Docking Technology for Japanese Future Space Systems

The Advanced Onboard Signal Processor (AOSP)

The Advanced Onboard Signal Processor (AOSP) address the onboard processing requirements of future space systems. In this context, a unique multiprocessor architectural concept has evolved, envisioning a distributed array of loosely coupled programmable processors interconnected by a packet-based high-speed bus local area network. Sophisticated fault recovery and reconfiguration capabilities achieve the desired degrees of autonomy and system availability. Processing tasks are partitioned and mapped onto the resources of, the AOSP in the form of a generalized series-parallel pipeline, with processor interactions synchronized by data flow. The AOSP architectural concept is extremely flexible. Without change to the fundamental operating system, AOSP can be configured to perform a wide range of processing applications. Moreover, the design is not restricted to any particular topology or number of processors. Novel at its conception [1], [2], AOSP's major design features are becoming increasingly popular, and the literature on loosely coupled and data-flow-synchronized multiprocessors is expanding rapidly [3]---[8]. In this article we describe the architecture of the AOSP, its embedded survivable local area network (LAN), its operating system software, and its fault tolerance features; discuss the issues associated with partitioning and programming of applications; and, finally, summarize the program phases.

NASDA's Long-Range Plan and Automatic Control

A long-range plan of NASDA's space development, until the beginning of the 21st century and thereafter, is outlined, and automatic control-related features and technologies of the space systems appearing in this long-range plan are described. Currently, NASDA is developing world-level rockets and satellites such as the H-II rocket and the Engineering Test Satellite-VI (ETS-VI). And, NASDA is about to develop the Japanese Experiment Module (JEM) participating in the International Space Station (ISS) program. In the future, NASDA intends to place emphasis on the development of the space infrastructure including such future space systems as the H-II Orbiting Plane (HOPE), the H-II derived rockets, the Rocket Plane (RP), space-to-space transportation systems, the Data Relay and Tracking Satellite (DRTS), manned space facilities, various platforms, etc. And, the space infrastructure around the earth will be extended to the moon and planets. The space infrastructure will be developed economically by employing unmanned systems as much as possible, safely by employing fully-automatic, manned systems, and efficiently by promoting international cooperation with autonomy.

The NASA technology push towards future space mission systems

As a result of the new Space Policy, the NASA technology program has been called upon to a provide a solid base of national capabilities and talent to serve NASA's civil space program, commercial, and other space sector interests. This paper describes the new technology program structure and its characteristics, traces its origin and evolution, and projects the likely near- and far- term strategic steps. It addresses the alternative “push-pull” approaches to technology development, the readiness levels to which the technology needs to be developed for effective technology transfer, and the focused technology programs currently being implemented to satisfy the needs of future space systems.

Microgravity research and user support in the Space Station era: The Microgravity User Support Centre

Future space systems, such as Columbus, the planned European contribution to the International Space Station, offer ample possibilities for microgravity research and application. These new opportunities require adequate user support on ground and novel operational concepts in order to ensure an effective utilization. Extensive experience in microgravity user support has been accumulated at DFVLR during the past Spacelab 1 and D1 missions. Based on this work, a Microgravity User Support Centre (MUSC) has been built and is active for the forthcoming EURECA-A1 and D2 missions, to form an integrated support centre for the disciplines life sciences and material sciences in the Space Station era. The objective of the user support at MUSC is to achieve: • easy access to space experiments for scientific and commercial users, • efficient preparation of experiments, • optimum use of valuable microgravity experimentation time, • cost reduction by concentration of experience. This is implemented by embedding the MUSC in an active scientific environment in both disciplines, such that users can share the experience gained by professional personnel. In this way, the Space Station system is operated along the lines established on ground for the utilization of large international research facilities, such as accelerators or astronomical observatories. In addition, concepts are developed to apply advanced telescience principles for Space Station operations.

Intelligent, autonomous systems in space

Systems autonomy will be an important ingredient of future space systems. The Space Station, in particular, is expected to be equipped with intelligent, autonomous capabilities. To achieve and incorporate these capabilities, the required technologies need to be identified, developed and validated within realistic application scenarios. The critical technologies for the development of intelligent, autonomous systems are discussed in the context of a generalized functional architecture. The present state of this technology implies that it be introduced and applied in an evolutionary process which must start already during the Space Station design phase. An approach is proposed to accomplish design information acquisition and management for knowledge base development.

Shuttle orbit flight control design lessons: Direction for space station

The Space Shuttle orbit flight control system, which operates during all exo-atmospheric flight phases, has successfully met operational requirements. Many design integration and operational issues that required resolution during development and testing provide an experience base that will benefit the development of future space systems, particularly the Space Station. To this end, the applicable Shuttle and Space Station hardware/software is reviewed with some perspective provided on how current design groundrules were derived and how issues that affected the Shuttle orbit control system design are a pathway for the Space Station. Some of the most significant lessons learned from the Shuttle are summarized, with a discussion of the effect of performance and design of hardware, including the data processing system, on software structures and usage procedures. Crew interface issues and important results from man-in-the-loop tests are summarized. Problems resulting from trying to meet difficult orbital operational objectives, including some sophisticated payload operations are characterized. Several proposed Shuttle flight control design improvements, developed in response to some of the lessons learned so far, are identified. Potential application of the Shuttle design lessons and new control technologies to the Space Station are discussed.

Characterization of Good Teleoperators: What Aptitudes, Interests, and Experience Correlate with Measures of Teleoperator Performance

Since teleoperation will be a required feature of future space systems, it will be necessary to select and train individuals to operate these remotely controlled manipulator systems. Training for this type of activity will be extremely time-consuming and costly; consequently, it would be advantageous to train only those individuals who are best-suited for the task. A study conducted at NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, attempted to construct a selection instrument composed of aptitude tests and questionnaire items that could be used for identifying individuals with an aptitude for teleoperation. Seventeen engineers from MSFC were given a 16-item questionnaire and three psychological aptitude tests designed to measure basic intelligence and spatial abilities. The aptitude test scores and the questionnaire responses were then correlated with actual teleoperator performance. The results of a multiple regression analysis revealed that the eight predictor variables individually were not significant with respect to operator performance, but as a whole, the regression model accounted for 49 percent of subject variance on the criterion task.

Navigating Low Altitude Satellites Using the Current Four NAVSTAR/GPS Satellites

A greater degree of survivability is a significant requirement of future space systems. Toward this end, an important aspect is an autonomous navigation capability. For many space systems, an obvious choice is the use of the Navstar/Global Positioning System (GPS). With the operational 18-satellite GPS constellation (plus three active spares), low altitude user satellites will have continuous tracking data available for navigation. On the other hand, with the current constellation of four satellites, there is less available data and, consequently, the accuracy of navigation varies a great deal throughout the user satellite orbit. This paper discusses the navigational performance that can be achieved with this constellation. Last summer, the Ladsat 4 satellite was placed into a near circular, sun synchronous, orbit at an altitude of 705 km, and at an inclination angle of 98.3 deg. This satellite contains a Navstar GPS receiver (called GPSPAC), and is the first user satellite to employ GPS. Using this satellite as an example, an error analysis was performed of the navigation accuracy that can be obtained for a low altitude satellite. During the course of a Landsat 4 orbit, it will be able to observe from none to four Navstar/GPS satellites. When four satellites are available, the three-dimensional accuracy can be expected to be about 11 m. Since Landstat 4 is sun synchronous, i.e., its orbit plane rotates in longitude with the sun, there will be times during the year when this satellite and the GPS satellites simultaneously come together over the continental United States. This is where Landsat 4 is primarily used, and is the ideal geometric relationship between Landsat 4, the GPS satellites, and the earth. This favorable condition occurred last November. This paper discusses the use of Navstar/GPS to navigate Landsat 4 under this ideal geometric situation, as well as at other times during the year. The paper presents the results of a theoretical accuracy analysis. The actual on-orbit experience with Landsat 4 is not covered here.

Development of advanced composite materials and geodetic structures for future space systems

The results of recent work accomplished under a NASA Johnson Space Center contract to develop an advanced composite geodetic beam and beam fabrication machine for the on-orbit construction of large space structures are given in this paper. Testing to determine mechanical, physical, thermal and electrical property characteristics of a near thermally inert advanced composite material for fabrication of geodetic structures is described and results are presented. Development testing of full-scale segments of geodetic structures fabricated with this material is discussed, along with results of a test to demonstrate structural feasibility of the cylindrical geodetic beam's end attachment design. Future tests of a long geodetic beam with conical end attachments are described. These latter tests are to verify the ability of geodetic structures to withstand mechanical and thermal loading environments of space.

Problems of Nuclear Rockets

In man's effort to conquer space, he has relied on the same type of propulsion that powers cars, lawn mowers, jet planes, Piper Cubs, battleships and motor boats: chemical propulsion. For a long time to come, burning a fuel and controlling its combustion energy will be the way to boost a rocket into space. This may do for manned missions to the moon. But scientists and engineers at the National Aeronautics and Space Administration and the Atomic Energy Commission regard this method already as antiquated and uneconomical when it comes to missions deep in space. Over the last decade, AEC and NASA have spent $1.2 billion in developing the basic technology of the nuclear rocket; another $1 billion is needed to complete the project. It looks like it's around the corner, says Sen. John D. Pastore (D-R.I.) of the Joint Congressional Committee on Atomic Energy. We've been working on it for years, but where is it? The nuclear rocket, called NERVA (Nuclear Engine for Rocket Vehicle Application), has gone through all its preliminary design and testing stages, and the time from now until 1978-the current project completion date-will be taken up with getting it ready for flight. The rocket is expected to be ready in time to power a shuttle for ferrying men and cargo from low earth orbit to the space stations in high earth (geosynchronous) or lunar orbit, or to send payloads deeper into space on such missions as a trip to Mars for either a manned landing, an unmanned fly-by oI an instrumented sampling mission. Because of the trip time and the heavy payloads involved, NERVA is not only ideally suited for such a job but is considered critical to its success (SN: 9/20, p. 233). In all of these missions, a chemically powered shuttle rocket (SN: 1/3, p. 22) would first place the NERVA and its companion vehicle in low earth orbit. Then the rocket would blast off for its mission. When done it would return to low earth orbit, waiting for another payload tc be launched and docked to it. The nuclear engine, like other future space systems, is being designed with reusability as a guiding principle. Simply stated, the aim of reusability is to make a nuclear rocket engine that can be used a number of times. The idea is motivated by economics. Just as it would be uneconomical to build a car that could only make one round tripwhich is in essence what the present Apollo rockets do-NASA and the AEC want a nuclear engine that can be flown on several round trips. In no case in the foreseeable future is it envisioned for earth liftoff. The main reason is that chemically propelled rockets are adequate for that job, and present nuclear rocket capability would not provide significant advantages. Another reason is radioactivity, which could escape in small amounts to the launch area or in large amounts if an accident occurred. A nuclear rocket can carry heavier payloads on less fuel than a chemical rocket because of the nuclear engine's greater propulsion efficiency, or specific impulse. This is the tiube period in which one pound of thrust is produced by one pound of fuel. For the best chemical rocket using liquid hydrogen and oxygen, the specific impulse is about 450 seconds; NERVA'S specific impulse is nearly double that, 825 seconds, which means that one pound of propellant producing the same thrust as one pound of chemical fuel will last almost twice as long. The saving in fuel can go into carrying extra payload. As it now stands, NERVA iS comKlein: It's still a breadboard engine.

Speech Sounds in Atypical Environments

Unusual breathing environments such as those containing helium are being considered for future manned space systems. In the study reported herein, the physical acoustic characteristics of speech generation were investigated for helium concentrations of 0%–70% at pressures from sea level to 258 mm Hg. An electromechanical-acoustical model of the vocal tract for the sustained phonetic vowel sounds of [i] (eat), [o] (lost), and [u] (boot) was utilized to determine the shift in formant frequency and the change in acoustic power radiated relative to that for normal air. For comparison purposes, the relative acoustic powers were calculated for the sss and th fricatives, some simple ideal acoustic generators and moving voice coil-type loudspeakers; in addition, loudspeaker directivity characteristics and power output were experimentally measured. Previously noted impaired communication capability in these environments can be attributed to speech spectrum changes due to the nonuniform power reduction of vowels and consonants and changes in formant frequency and directivity.

Maintainability Design Requirements for Future Space Systems

Design requirements which consider maintenance capability can be expected to be quite different for space system application when compared to those currently in use for today's weapon systems. Needs will vary, as will the base for the definition of quantized criteria. Maximum urgency is placed on crew safety, mission success, and meeting a launch window. The expressions for quantitative maintainability design criteria will shift from the familiar ``Meantime'' base to one of ``Allowable Time,'' ``Probability of Repair Within Time Limits,'' and ``Expenditure of Human Energy.'' This paper explores the operational requirements for maintainability in future space systems, discusses interface problems, and defines quantized maintainability objectives for the different applications of 1) spacecraft, 2) space stations, 3) boosters, and 4) support equipment.

Human Output Characteristics during Specific Task Performance in Reduced Traction Environments

Alterations in the force and work producing characteristics of unbraced operators performing in reduced traction environments have been reported. Data descriptive of the capabilities and requirements of man in such environments would prove invaluable in designing future space systems. To facilitate the acquisition of such data, a study was executed which examined the effects of varying levels of instability upon the amplitude, rate and efficiency with which manual work was produced. Ten subjects exercised in a special suspensory system. Work output/metabolic input ratios were determined at varying levels of stability. Data were subjected to analyses via Duncan's Multiple correlation test. Significant increases, of up to 70 per cent in oxygen consumption per horsepower developed were found. The ratio increased in non-linear fashion as instability was increased. Decreases in output capability were also found.

Determination of Human Operator Functions in a Manned Space Vehicle

Man's participation in limited space travel is imminent. Attention must be focused now upon the nature and extent of his participation in future manned space systems. It is imperative that the human not be assigned functions as an afterthought. Rather, functions must be assigned in a manner that will optimize system performance with respect to the mission requirements. This paper describes a practical methodology for determining the human operator functions within the context of a specific mission. A space ferry mission is used to illustrate the approach.