Ground and on-orbit command and data handling architectures for the Active Rack Isolation System microgravity flight experiment

The Active Rack Isolation System [ARIS] International Space Station [ISS] Characterization Experiment, or ARIS-ICE for short, is a long duration microgravity characterization experiment aboard the ISS. The objective of the experiment is to fully characterize active microgravity performance of the first ARIS rack deployed on the ISS. Efficient ground and on-orbit command and data handling [C&DH] segments are the crux in achieving the challenging objectives of the mission. The objective of the paper is to provide an overview of the C&DH architectures developed for ARIS-ICE, with the view that these architectures may serve as a model for future ISS microgravity payloads. Both ground and on-orbit segments, and their interaction with corresponding ISS C&DH systems are presented. The heart of the on-orbit segment is the ARIS-ICE Payload On-orbit Processor, ARIS-ICE POP for short. The POP manages communication with the ISS C&DH system and other ISS subsystems and payloads, enables automation of test/data collection sequences, and provides a wide range of utilities such as efficient file downlinks/uplinks, data post-processing, data compression and data storage. The hardware and software architecture of the POP is presented and it is shown that the built-in functionality helps to dramatically streamline the efficiency of on-orbit operations. The ground segment has at its heart special ARIS-ICE Ground Support Equipment [GSE] software developed for the experiment. The software enables efficient command and file uplinks, and reconstruction and display of science telemetry packets. The GSE software architecture is discussed along with its interactions with ISS ground C&DH elements. A test sequence example is used to demonstrate the interplay between the ground and on-orbit segments.     

One year old and growing: a status report of the International Space Station and its partners.

The International Space Station (ISS), as the largest international science and engineering program in history, features unprecedented technical, cost, scheduling, managerial, and international complexity. A number of major milestones have been accomplished to date, including the construction of major elements of flight hardware, the development of operations and sustaining engineering centers, astronaut training, and eight Space Shuttle/Mir docking missions. International partner contributions and levels of participation have been baselined, and negotiations and discussions are nearing completion regarding bartering arrangements for services and new hardware. As ISS is successfully executed, it can pave the way for more inspiring cooperative achievements in the future.     

Solar particle events and the International Space Station

The high inclination orbit for the International Space Station poses a risk to astronauts on EVA during occasional periods of enhanced high energy particle flux from the sun known as Solar Particle Events. We are currently unable to predict these events within the few-hour lead time required for evasive action. Compounding the threat is the fact that station construction occurs during increasing solar activity and through the peak of the solar cycle. In this paper we present an overview of the risk, the current methods to provide forecasts of SPEs, and potential risk mitigation options.     

Control-structure interaction study of the proposed space station freedom

A relatively general formulation for studying the dynamics and control of an arbitrary spacecraft with interconnected flexible bodies has been developed accounting for transient system properties, shift in the center of mass, shear deformations, rotary inertias and geometric nonlinearities. This self-contained, comprehensive, numerical algorithm using system modes is applicable to a large class of spacecraft configurations of contemporary and future interests. Here, versatility of the approach is demonstrated through the dynamics and control studies aimed at the evolving Space Station Freedom.     

Remote sensing of planetary properties and biosignatures on extrasolar terrestrial planets

The major goals of NASA's Terrestrial Planet Finder (TPF) and the European Space Agency's Darwin missions are to detect terrestrial-sized extrasolar planets directly and to seek spectroscopic evidence of habitable conditions and life. Here we recommend wavelength ranges and spectral features for these missions. We assess known spectroscopic molecular band features of Earth, Venus, and Mars in the context of putative extrasolar analogs. The preferred wavelength ranges are 7-25 microns in the mid-IR and 0.5 to approximately 1.1 microns in the visible to near-IR. Detection of O2 or its photolytic product O3 merits highest priority. Liquid H2O is not a bioindicator, but it is considered essential to life. Substantial CO2 indicates an atmosphere and oxidation state typical of a terrestrial planet. Abundant CH4 might require a biological source, yet abundant CH4 also can arise from a crust and upper mantle more reduced than that of Earth. The range of characteristics of extrasolar rocky planets might far exceed that of the Solar System. Planetary size and mass are very important indicators of habitability and can be estimated in the mid-IR and potentially also in the visible to near-IR. Additional spectroscopic features merit study, for example, features created by other biosignature compounds in the atmosphere or on the surface and features due to Rayleigh scattering. In summary, we find that both the mid-IR and the visible to near-IR wavelength ranges offer valuable information regarding biosignatures and planetary properties; therefore both merit serious scientific consideration for TPF and Darwin.     

The applications of lower power satellites for direct television broadcasting

The use of 12 GHz satellites for TV broadcasting directly to individual homes and small communities has been the subject of analysis and design study by groups in many countries. Implementation of the concept has been slow to follow because of the high satellite transmitter powers of from 100 to 450 W that have usually been determined to be necessary. Accumulated experience in Canada with 12 GHz operation and the evolution of technology are leading to changes in the concept of direct broadcasting such that lower power satellites may be capable of meeting the requirements.

Hermes, the Canadian/U.S. 12/14 GHz Communications Technology Satellite, has been in use for over 3 years in a program of experiments and measurements. This program has included an extensive six month experiment in direct broadcasting to 7 small communities. Experience with Hermes has shown that the signal strength is stable over long periods of time and that in Canada, significant precipitation attenuation at 12 GHz is of relatively short duration and typically occurs only during certain seasons. Operation with low propagation margins is feasible if some picture degradation and some outages at these times are acceptable. The frequency and duration of occurrence of outages can be controlled by the Earth station G/T which is cost sensitive. An individual may choose to use a low cost system with a small antenna and accept a degraded picture and outages at some times. A small community may choose to pay more for a larger antenna and lower noise receiver to achieve better performance.

Developments in technology are reducing the noise figure of mass-producible receivers from more than 6 dB to as low as 4 dB. Another technology contribution is the use of reduced bandwidth and other signal processing techniques in low-cost receivers. While use of such techniques may introduce distortions that would be unacceptable in rebroadcasting systems, there is little impact for individual and community reception. Use of both technologies reduce the required satellite EIRP or ground terminal G/T.

A field trial was begun in April 1979 to test these concepts for use in television program delivery. One hundred Earth stations capable of being tuned across a 500 MHz band and having antennas with diameters of either 1.2 m or 1.8 m are being installed for a test in Canada to receive TV signals from the 20 W transponders of ANIK-B (peak EIRP of 51 dBw) on an experimental basis. The acceptability of the video signals and the technical performance of the low-cost terminals in the bands of non-technical users are being evaluated.

The paper will summarize the concept of TV broadcasting with lower power satellites and describe the results to date of the ANIK-B field trials.     

On the dynamics of a novel manipulator with slewing and deployable links

Using a novel space platform-based manipulator with slewing and deployable links, the paper addresses two issues of considerable importance: (a) How important is it to model flexibility of the system? (b) How many modes are needed to adequately represent the elastic character? Results suggest that the fundamental mode is able to capture physics of the response quite accurately. Due to its massive character, the platform dynamics is virtually unaffected, even by severe maneuvers of the manipulator. Hence, treating the platform as rigid would save the computational cost without affecting the accuracy. Although the link flexibility does affect the manipulator's tip vibration, the joint and platform vibrations remain negligible. The revolute joint flexibility appears to be an important parameter affecting both the joint as well as tip responses. The information should prove useful in the design of this new class of manipulators.     

RLV economics: fiscal evaluation of NASA''s reusable launch vehicle effort

The US RLV program aims to stimulate commercial development of a next-generation heavy-lift launcher and lower launch costs by one order of magnitude from the Space Shuttle. This paper discusses the incentives needed to encourage private investment — income tax relief, investment mitigation, financing assistance — in the venture and uses a specifically developed case study model to evaluate their effectiveness. It finds that an R&D tax credit would be the most practical incentive. Directions for future work are provided.     

Bubble detector characterization for space radiation

In light of the importance of the neutron contribution to the dose equivalent received by space workers in the near-Earth radiation environment, there is an increasing need for a personal dosimeter that is passive in nature and able to respond to this neutron field in real time. Recent Canadian technology has led to the development of a bubble detector, which is sensitive to neutrons, but insensitive to low linear energy transfer (LET) radiation. By changing the composition of the bubble detector fluid (or “superheat”), the detectors can be fabricated to respond to different types of radiation. This paper describes a preliminary ground-based research effort to better characterize the bubble detectors of different compositions at various charged-particle accelerator facilities, which are capable of simulating the space radiation field.     

Raman imagery: a new approach to assess the geochemical maturity and biogenicity of permineralized precambrian fossils

Laser-Raman imagery is a non-intrusive, non-destructive analytical technique, recently introduced to Precambrian paleobiology, that can be used to demonstrate a one-to-one spatial correlation between the optically discernible morphology and kerogenous composition of permineralized fossil microorganisms. Made possible by the submicron-scale resolution of the technique and its high sensitivity to the Raman signal of carbonaceous matter, such analyses can be used to determine the chemical-structural characteristics of organic-walled microfossils and associated sapropelic carbonaceous matter in acid-resistant residues and petrographic thin sections. Here we use this technique to analyze kerogenous microscopic fossils and associated carbonaceous sapropel permineralized in 22 unmetamorphosed or little-metamorphosed fine-grained chert units ranging from approximately 400 to approximately 2,100 Ma old. The lineshapes of the Raman spectra acquired vary systematically with five indices of organic geochemical maturation: (1) the mineral-based metamorphic grade of the fossil-bearing units; (2) the fidelity of preservation of the fossils studied; (3) the color of the organic matter analyzed; and both the (4) H/C and (5) N/C ratios measured in particulate kerogens isolated from bulk samples of the fossil-bearing cherts. Deconvolution of relevant spectra shows that those of relatively well-preserved permineralized kerogens analyzed in situ exhibit a distinctive set of Raman bands that are identifiable also in hydrated organic-walled microfossils and particulate carbonaceous matter freed from the cherts by acid maceration. These distinctive Raman bands, however, become indeterminate upon dehydration of such specimens. To compare quantitatively the variations observed among the spectra measured, we introduce the Raman Index of Preservation, an approximate measure of the geochemical maturity of the kerogens studied that is consistent both with the five indices of organic geochemical alteration and with spectra acquired from fossils experimentally heated under controlled laboratory conditions. The results reported provide new insight into the chemical-structural characteristics of ancient carbonaceous matter, the physicochemical changes that accompany organic geochemical maturation, and a new criterion to be added to the suite of evidence by which to evaluate the origin of minute fossil-like objects of possible but uncertain biogenicity.