Time-Optimal Control of a Bounded Phase-Coordinate Process II: High-Order Systems with Multiple Control Inputs

This paper considers the problem arising from the design of an autopilot for a large booster. The motion-controlling actuators of the booster have both position and rate limits. The problem is formulated as a bounded phase-coordinate problem and analyzed by the ``backing out of the target' procedure. A method of constructing the optimal control is presented. An example of an oscillatory system with two control inputs is given, and the optimal control is expressed as an explicit time function.     

The FAST Satellite Fields Instrument

We describe the electric field sensors and electric and magnetic field signal processing on the FAST (Fast Auroral SnapshoT) satellite. The FAST satellite was designed to make high time resolution observations of particles and electromagnetic fields in the auroral zone to study small-scale plasma interactions in the auroral acceleration region. The DC and AC electric fields are measured with three-axis dipole antennas with 56 m, 8 m, and 5 m baselines. A three-axis flux-gate magnetometer measures the DC magnetic field and a three-axis search coil measures the AC magnetic field. A central signal processing system receives all signals from the electric and magnetic field sensors. Spectral coverage is from DC to 4 MHz. There are several types of processed data. Survey data are continuous over the auroral zone and have full-orbit coverage for fluxgate magnetometer data. Burst data include a few minutes of a selected region of the auroral zone at the highest time resolution. A subset of the burst data, high speed burst memory data, are waveform data at 2×10⁶ sample s^–1. Electric field and magnetic field data are primarily waveforms and power spectral density as a function of frequency and time. There are also various types of focused data processing, including cross-spectral analysis, fine-frequency plasma wave tracking, high-frequency polarity measurement, and wave-particle correlations.     

Space Weather applications with CDPP/AMDA

AMDA (Automated Multi-Dataset Analysis), a new data analysis service, recently opened at the French Plasma Physics Data Center (CDPP). AMDA is developed according to the Virtual Observatory paradigm: it is a web-based facility for on-line analyses of space physics. Data may come from its own local database as well as remote ones. This tool allows the user to perform classical manipulations such as data visualization, parameter computation and data extraction. AMDA also offers innovative functionalities such as event searches on the content of the data in either visual or automated ways, generation, use and management of time tables (event lists). The general functionalities of AMDA are presented in the context of Space Weather with example scientific use cases.     

Crew autonomy for deep space exploration: Lessons from the Antarctic Search for Meteorites

Future piloted missions to explore asteroids, Mars, and other targets beyond the Moon will experience strict limitations on communication between vehicles in space and control centers on Earth. These limitations will require crews to operate with greater autonomy than any past space mission has demonstrated. The Antarctic Search for Meteorites (ANSMET) project, which regularly sends small teams of researchers to remote parts of the southern continent, resembles a space mission in many ways but does not rely upon a control center. It provides a useful crew autonomy model for planners of future deep space exploration missions. In contrast to current space missions, ANSMET gives the crew the authority to adjust competing work priorities, task assignments, and daily schedules; allows the crew to be the primary monitor of mission progress; demands greater crew accountability for operational errors; requires the crew to make the most of limited communication bandwidth; adopts systems designed for simple operation and failure recovery; and grants the crew a leading role in the selection and stowage of their equipment.     

Flare build up: 21 May 1980

The decaying solar active region that crossed the central meridian on May 20, 1980 at latitude S13° produced a major flare (2B/X1) at 2054 on May 21. This region was a target of the international Flare Buildup Study and was well observed. The buildup was characterized by little flare activity during two days prior to the major flare but a great deal of activity in the filament that separated the opposite magnetic polarities of the active region. Large proper motions of sunspots and magnetic fields suggest that the magnetic field was stressed prior to the flare. The immediate trigger of the flare appears to have been an eruption of new magnetic flux in the center of the active region. The new flux erupted in a configuration that decreased the net flux of the active region and contributed to the decay of the region.     

Vehicular Positioning System

There is a US Army vehicular positioning program under way called MAFIS (Mobile Automated Field Instrumentation System). Though its use is intended for full scale battlefield operational testing of mobile ground units and aircraft systems, the implications for extending this technology toward commercial aplications are the thrust of this paper.     

Space exploration policy: Towards an operational vision

This article examines the historical and social context of space exploration policy. It seeks to reconcile a contradiction between the visionary grandeur of space and public perceptions of space exploration as the province of a narrowly-focused political interest group. The author argues that perceptions of the space age are artificially restricted by dating its origins to Sputnik and Apollo and allowing it to be dominated by science and technology objectives devoid of a more encompassing social framework. Guiding principles for developing space exploration activities in a broader conceptual and operational framework are offered.     

The critical satellite technical issues of future pervasive broadband low-cost communication networks

Using a baseline design for a 30/20 GHz system, this paper addresses the critical technical issues of signal waveform design, projected spacecraft technology, satellite launch options and satellite cost. With DPCM (differential pulse-coded modulation) video signal encoding, 32 Mb/s user-to-user data rate per channel, 10% overhead, two orthogonal polarizations, and crosstalk loss limited to 1 dB, TFM (tamed frequency modulation—a type of QPSK) permits about 75 channels/GHz of frequency allocation, i.e. about twice the capacity possible with MSK or SFSK (types of QPSK). The BOM (beginning of mission) weight and power of a baseline 400-channel multi-beam satellite is about 1800 kg and 5000 W. Each 35 Mb/s channel can support 1–10 video channels depending on the signal processing at the ground terminals. These weight and power estimates assume hardened digital logic, composite material for a multibeam antenna structure, high-efficiency solar cells (45 W/kg), NiH₂ batteries and 10W/20 GHz power amplifiers. If more speculative late-1980s solar cell technology is assumed, then the BOM weight decreases about 10–15%. Using the Space Transportation System being developed by NASA, geosynchronous deployment options are shown as a function of communications capacity. Based on a cost model for large communication satellites, the total space segment cost of two active satellites and one spare would be about $485M. This system would have a peak capacity of 14 Gb/s or 400-35 Mb/s simultaneous one-way channels. Demonstration and/or initial system (ground plus space) costs would be significantly less. It is concluded that the above baseline satellite appears to be technically feasible in the late-1980s.