ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Providing normal telemetry behavior predictions prior to and post launch will help to stop surprise catastrophic satellite and spacecraft equipment failures. In-orbit spacecraft fail from surprise equipment failures that can result from not having normal telemetry behavior available for comparison with actual behavior catching satellite engineers by surprise. Some surprise equipment failures lead to the total loss of the satellite or spacecraft. Some recovery actions as a consequence of a surprise equipment failure are high risk and involve decisions requiring a level of experience far beyond the responsible engineers.

The plasma environment of an active comet provides a unique setting for plasma physics research. The complex interaction of newly created cometary ions with the flowing plasma of the solar wind gives rise to a plethora of plasma physics phenomena, that can be studied over a large range of activity levels as the distance to the sun, and hence the influx of solar energy, varies. In this thesis, we have used measurements of the spacecraft potential by the Rosetta Langmuir probe instrument (LAP) to study the evolution of activity of comet 67P/Churyumov-Gerasimenko as it approached the sun from 3.6 AU in August 2014 to 2.1 AU in March 2015. The measurements are validated by cross-calibration to a fully independent measurement by an electrostatic analyzer, the Ion Composition Analyzer (ICA), also on board Rosetta. The spacecraft was found to be predominantly negatively charged during the time covered by our investigation, driven so by a rather high electron temperature of ~5 eV resulting from the low collision rate between electrons and the tenuous neutral gas. The spacecraft potential exhibited a clear covariation with the neutral density as measured by the ROSINA Comet Pressure Sensor (COPS) on board Rosetta. As the spacecraft potential depends on plasma density and electron temperature, this shows that the neutral gas and the plasma are closely coupled. The neutral density and negative spacecraft potential were higher in the northern hemisphere, which experienced summer conditions during the investigated period due to the nucleus spin axis being tilted toward the sun. In this hemisphere, we found a clear variation of spacecraft potential with comet longitude, exactly as seen for the neutral gas, with coincident peaks in neutral density and spacecraft potential magnitude roughly every 6 h, when sunlit parts of the neck region of the bi- lobed nucleus were in view of the spacecraft. The plasma density was estimated to have increased during the investigated time period by a factor of 8-12 in the northern hemisphere and possibly as much as a factor of 20-44 in the southern hemisphere, due to the combined effects of seasonal changes and decreasing heliocentric distance. The spacecraft potential measurements obtained by LAP generally exhibited good correlation with the estimates from ICA, confirming the accuracy of both of these instruments for measurements of the spacecraft potential.

International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada / PC technology has progressed to the point that it can very effectively support commercial geostationary spacecraft design, manufacture, test, launch, ground station, and on-orbit mission control activities. Many of the manufacturers that provide VME spacecraft test hardware and software are now providing the same functions and performance for the PC. A PC workstation equipped with single and multiple Pentium processors and Windows NT software can support single and multiple uplinks/downlinks and provide client/server capabilities that perform traditional UNIX client/server operations. Such a PC workstation can provide the functionality, features, and performance necessary for commercial spacecraft board-level test, unit-level test, subsystem-level test, spacecraft bus and payload integration, and ground station monitoring and control, as well as on-orbit mission control activities.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / A ground based intelligent agent and operations network is being created to handle all aspects of spacecraft command and control. This system will have the dual purpose of enabling cost efficient operation of a number of small satellites and serving as a flexible testbed for the validation of space system autonomy strategies. The system is currently being targeted to include over a dozen globally distributed amateur radio ground stations and access to nearly ten spacecraft. The use of distributed computing systems and virtual interaction schemes are significantly contributing to the creation of this system. The Internet is used to link the network's control centers and ground stations. In addition, a World Wide Web (WWW) based user and operator interface is being developed to permit high level goal specification of spacecraft experiments and actions. This paper will describe the operating network being developed, the use of the Internet as an integral part of the system's architecture, the design of the WWW interface, and the future development of the system.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / NASA Marshall Space Flight Center’s Bantam Robust Guidance Navigation & Control Project is investigating off the shelf navigation sensors that may be inexpensively combined into Kalman filters specifically tuned for launch and orbital vehicles. For this purpose, Marshall has purchased several GPS receivers and is evaluating them for these applications. The paper will discuss the receiver selection criteria and the test equipment used for evaluation. An overview of the analysis will be presented including the evaluation used to determine their success or failure. It will conclude with goals of the program and a recommendation for all GPS users.

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / Spacecraft on-board time keeping, to an accuracy better than 1 millisecond, is a requirement for many satellite missions. Scientific satellites must precisely "time tag" their data to allow it to be correlated with data produced by a network of ground and space based observatories. Multiple vehicle satellite missions, and satellite networks, sometimes require several spacecraft to execute tasks in time phased fashion with respect to absolute time. In all cases, mission systems designed to provide a high accuracy on-board clock must necessarily include mechanisms for the determination and correction of spacecraft clock error. In addition, an approach to on-orbit verification of these mechanisms may be required. Achieving this accuracy however need not introduce significant mission cost if the task of maintaining this accuracy is appropriately distributed across both the space and ground mission segments. This paper presents the mission systems approaches taken by two spacecraft programs to provide high accuracy on-board spacecraft clocks at minimum cost. The first, NASA Goddard Space Flight Center's (GSFC) Extreme Ultraviolet Explorer (EUVE) program demonstrated the ability to use the NASA Tracking and Data Relay Satellite System (TDRSS) mission environment to maintain an on-board spacecraft clock to within 100 microseconds of Naval Observatory Standard (NOS) Time. The second approach utilizes an on-board spacecraft Global Positioning System (GPS) receiver as a time reference for spacecraft clock tracking which is facilitated through the use of Fairchild's Telemetry and Command Processor (TCP) spacecraft Command & Data Handling Subsystem Unit. This approach was designed for a future Shuttle mission requiring the precise coordination of events among multiple space-vehicles.

This dissertation addresses the problem of rigid-body attitude tracking control under three scenarios of high relevance to many aerospace guidance and control applications: adaptive attitude-tracking control law development for a spacecraft with time-varying inertia parameters, velocity-free attitude stabilization using only vector measurements for feedback, and smooth angular velocity observer design for attitude tracking in the absence of angular velocity measurements. Inertia matrix changes in spacecraft applications often occur due to fuel depletion or mass displacement in a flexible or deployable spacecraft. As such, an adaptive attitude control algorithm that delivers consistent performance when faced with uncertain time-varying inertia parameters is of significant interest. This dissertation presents a novel adaptive control algorithm that directly compensates for inertia variations that occur as either pure functions of the control input, or as functions of time and/or the state. Another important problem considered in this dissertation pertains to rigid-body attitude stabilization of a spacecraft when only a set of inertial sensor measurements are available for feedback. A novel gyro-free attitude stabilization solution is presented that directly utilizes unit vector measurements obtained from inertial sensors without relying on observers to reconstruct the spacecraft's attitude or angular velocity. As the third major contribution of this dissertation, the problem of attitude tracking control in the absence of angular velocity measurements is investigated through angular velocity observer (estimator) design. A new angular velocity observer is presented which is smoothed and ensures asymptotic convergence of the estimation errors irrespective of the initial true states of the spacecraft. The combined implementation of a separately designed proportional-derivative type controller using estimates generated by the observer results in global asymptotic stability of the overall closed-loop tracking error dynamics. Accordingly, a separation-type property is established for the rigid-body attitude dynamics, the first such result to the author's best knowledge, using a smooth (switching-free) observer formulation. / text

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / A Communication Subsystem has been developed capable of 25 Megasymbol per Second (MSPS) data rates. The unit operates in the 8300 to 8400 MHz band and uses shaped QPSK for excellent spectral containment properties. The Communication Subsystem (CSS) has a number of features which make it attractive for many applications: (1) Data is convolutionally encoded inside the transmitter resulting in excellent link performance without using external hardware. (2) Data is encrypted inside the transmitter. The DES standard is currently implemented, however, military encryption is an option which requires minimal changes in the CSS design. (3) Frame Synchronization Sequences and Block Identification Numbers are inserted into the data by the CSS. (4) Cyclic Redundancy Checked Codes for each data block are generated within the CSS. (5) Health and Status of the CSS is formatted into digital words. (6) Mode Control, Key Maintenance, and Health and Status Reporting is easily handled through an RS-422 interface. (7) The CSS is ruggedized for launch environments and is highly reliable for space applications.

The Composite Infrared Spectrometer (CIRS) instrument onboard the Cassini spacecraft will be used to probe the atmosphere and surface of Saturn's giant moon Titan. This thesis describes an investigation of the capabilities of CIRS as a remote sounding instrument. To enable infrared spectra to be computed, a radiative transfer code has been adapted for Titan's atmosphere. The atmospheric model, including gases and aerosol particles, was refined by comparison of synthetic spectra with results from the IRIS instrument of the Voyager 1 spacecraft. Characteristics of the instrument have been deduced from laboratory measurements. The size and shape of the field of view was found for the mid-infrared detectors. A Fourier code was developed to transform the raw data (interferograms). Blackbody spectra taken with the flight instrument were analysed to calculate the noise equivalent radiance for the detectors of all three focal planes. Finally, the data regarding instrument performance was used in combination with the predictive radiative transfer code to consider in detail the extent to which gaseous bands and other spectral features will be observable for a variety of limb and nadir viewing modes. Current observing strategies are reviewed and recommendations for scientific emphasis in the light of the actual instrument performance are made.

The aim of this study is to outline circumstances and reasons which caused a birth of an ambitious plan which enabled the USA to land a man on the Moon and return him safely to the Earth. The impact of this thesis is to chart individual pilot expeditions also from the eyes of real participants. One part of this study is a chapter dealing with astronauts' preparation and training. The thesis also reminds the fact that among people who landed on the Moon was also the astronaut of the Czech origin, Eugene A. Cernan. In the end the study deal with technology that helped to include program Apollo among the greatest events of the 20th century.