A computer network with SCADA and case tools for on-line process control in greenhouses.

Climate control computers in greenhouses are used to control heating and ventilation, supply water and dilute and dispense nutrients. They integrate models into optimally controlled systems. This paper describes how information technology, as in use in other sectors of industry, is applied to greenhouse control. The introduction of modern software and hardware concepts in horticulture adds power and extra oppurtunities to climate contol in greenhouses.     

Galileo probe battery system

NASA's pair of Galileo spacecraft arrived at Jupiter on 7 December 1995. The Probe descended into the upper Jovian atmosphere, performing its planned sequence of scientific measurements of the properties of that medium for about an hour. This Probe has been the most ambitious planetary entry vehicle to date. It evolved over several years of planning and construction, its launch was postponed many times, for a variety of reasons; and it required more than 6 years of travel after launch to reach the planet. Its electrical power was provided by a primary Li-SO₂ battery, supplemented with two thermal batteries (CaCrO₄-Ca) used for firing pyrotechnic initiators during the atmospheric entry. These power sources were designed to be robust, to assure they would perform their intended function after surviving several years in space. This paper discusses the final production, qualification, and the systems testing of these batteries prior to and following launch. Their excellent performance at Jupiter confirmed their life enhancement design features     

The message and the experience of the site project

The Satellite Instructional Television Experiment (SITE) was a unique effort aimed at studying the possibilities of satellite broadcasting for education and national development. This one-year joint India-USA project was carried out in 1975–1976 using the ATS-6 spacecraft. This paper briefly describes the experiment and its major findings. It goes on to distill the learning experiences derived from SITE and analyses the extent to which these have influenced the design and configuration of India's domestic satellite system, INSAT. INSAT-1B, which will serve as a replacement for the short-lived INSAT-1A, will be launched shortly and will be operational by the end of 1983. Its payload includes two S-band TV transponders capable of broadcasting directly to augmented TV sets. The paper examines which lessons of SITE are being applied in the planning and operationalisation of the TV system and discusses why others are not being taken account of. Major issues confronting TV system planners in developing countries like India are highlighted and the possible role of satellite broadcasting discussed in this context. The paper concludes by outlining an “ideal scenario” for a large, multilingual country like India, towards which TV planners could attempt to strive.     

Statistical study of inverted-V events: A comparison between experiment and theory

We present a detailed study of the distribution and of the internal structure of the inverted-V electron precipitation commonly detected in the 500 – 2000 km altitude range aboard the AUREOL-3 satellite. These structured precipitations are statistically observed inside the auroral oval with a maximum occurence in the nightside sector. They correspond to primary electron fluxes peaked at energies generally below 10 keV. It is shown that, as predicted by kinetic theories, most inverted-V structures present a clear relationship between the field-aligned current density carried by the 1 – 20 keV primary electrons and the potential drop inferred from particle distribution functions. Furthermore the study demonstrates the existence of strong electron heating, related to the energy gain, when the current density exceeds some threshold of about 1 – 5 μA(m)^?2.     

EXOSAT observations of NGC 1399 and NGC 1404: Two elliptical galaxies in the center of the Fornax cluster

Imaging X-ray observations of the Fornax cluster of galaxies centered on NGC 1399 and NGC 1404 are presented. NGC 1399 and NGC 1404, which are separated by about 10 arc minutes, are found to have an unusually high ratio of x-ray to optical flux. We consider the possibility that the x-radiation is produced by hot gas in the cores of the galaxies. Weak X-ray emission is also detected from a point almost exactly mid-way between NGC 1399 and NGC 1404. The combined emission from the galaxies is insufficient by over an order of magnitude to account for the the low-energy X-ray emission detected from this region by the HEAO-l satellite. It is suggested that the bulk of the HEAO-1 source is diffuse gas associated with the cluster as a whole, rather than individual galaxies.     

Wireless power transmission: the key to solar power satellites

Maturing of the enabling technologies has provided much of the infrastructure to support the development of a commercial Solar Power Satellite program. Solar Space Industries was formed to accomplish this goal. The basis of their development plan is to build a Ground Test Installation that will duplicate, in small scale on the Earth, all aspects of the power generating and power transmission systems except for the space environment and the range and size of the energy beam. Space operations issues will be separated from the power generation fixation and verified by testing. Doing the developmental testing on the ground instead of in space will result in a low cost program that can be accomplished in a very short time. The concept is to build a Ground Test Installation that couples an existing 100 kW terrestrial solar cell array to a phased-array wireless power transmitter based on a subarray. Power will be transmitted over a 1-¼ mile range to a receiving antenna and then fed into a commercial utility power grid. The objective is to demonstrate the complete function of the Solar Power Satellites, with the primary issue being the validation of practical wireless power transmission. The key features to demonstrate are: beam control, stability, steering, efficiency, reliability, cost, and safety     

Landsat-4 orbit determination using TDRSS

This paper presents the results of a study to compare the orbit determination accuracy for a Tracking and Data Relay Satellite (TDRS) System (TDRSS)-user spacecraft, Landsat-4, obtained using a Prototype Filter Smoother (PFS), with the accuracy of an established batch-least-squares system, the Goddard Trajectory Determination System (GTDS). The results of Landsat-4 orbit determination provide useful experience for the Earth Observing System (EOS) series of satellites. The filtered and smoothed PFS orbit solutions were compared with the definitive GTDS orbit solutions for Landsat-4; the root-mean-square (RMS) solution difference was 6.6 meters.     

Application of ISFETs in closed-loop systems for greenhouses.

In horticulture, growing in artificial substrates such as rockwool is more and more considered to be a sound alternative to growing in soil. This development enables the opportunity to create closed-loop systems which lower the waste of raw materials and reduce pollution of the environment. Applying closed-loop systems needs precise knowledge of the composition of the recirculating nutrient solution. This paper presents basic principles of a measuring system, which can monitor continuously the concentration of nutrients in water. The system is based on ion-selective field effect transistors (ISFETs). By appropriate calibration, a high accuracy is achieved for pH and potassium measurements in the nutrient solution. An accuracy of better than 10% (mMol/l) has been achieved.     

A methodology to determine the sociopolitical forces influencing lunar development policies

The rate of progress in any particular program is primarily dependent on the annual resources committed for the specific program. Soon after the turn of the century, the question of returning to the Moon will probably be raised again among political decision makers. At that time the positive and negative arguments will have to be weighed again. A simple method to analyse the relevant force-field was developed comprising the following steps: (1) Definition of positive and negative forces; (2) cross-impact analysis between the individual forces producing relative weights; (3) probability analysis of the current relevance of the individual forces; (4) estimating resulting negative and positive partial force-fields as functions for selected years between 1960 and 2030; and (5) determination of the strength of the resulting force influencing a decision. An example is presented.     

On algebraic compilers and planetary fly-by orbits

This paper reports on two major technology events of great significance in the field of Astronautics which were conceived and developed at the MIT Instrumentation Laboratory during the decade of the fifties. It is a personal memoir by the author on two important topics which should be a part of the written history of our field.Part one details the conception and development by Dr J. Halcombe Laning, Jr of “George”, the world's first algebraic compiler for use on Project Whirlwind—MIT's first experimental all-digital computer. This was indeed challenging since Whirlwind at that time had but 1024 sixteen-bit words. Dr Laning began work in the summer of 1952 and the first version of the George compiler was finished in March of 1953.In the early fifties many people were debating the feasibility of a system for translating algebraic formulae into computer programs which would allow the engineer to avoid the all too painstaking and error-prone task of writing programs using basic computer code. But Hal Laning was the first to do it.In part two of this paper, the author explores the early concepts of energy exchange between a spacecraft and a planet during a close encounter of these two celestial objects. The fact that this energy transfer could be exploited for useful purposes in the development of interplanetary orbits was first documented in an MIT Instrumentation Laboratory report published in April of 1958. The topic has been the subject of recent papers at several IAF congresses, but they failed to recognize the early work at MIT. As a part of this important history, the author describes his own work to develop a round-trip orbit to Mars using the planet Venus for a gravity assist to shorten the flight time from three years to one and a quarter years. The first orbit of this type was obtained by the author on 26 January 1961. To the author's knowledge, no one has even suggested that practical three-dimensional multiple fly-by orbits had been constructed at an earlier date.