SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS

A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 43, ISSUE 19 - SEPTEMBER 23, 2006

17 SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
Includes space systems telemetry; space communications networks; astronavigation and guidance; and spacecraft radio blackout.

For related information see also 04 Aircraft Communications and Navigation; and 32 Communications and Radar.

20050212230 Defence Science and Technology Organisation, Edinburgh, Australia

Using Rotations to Build Aerospace Coordinate Systems

Koks, Don; June 2005; 48 pp.; In English Report No.(s): DSTO-TN-0640; AR-013-424; Copyright; Avail: Other Sources

Presented here are the main techniques necessary to understand rotations in three dimensions, for use with global visualisation and aerospace simulations. Relevant techniques can be extremely difficult to find in textbooks, so some useful examples are collected here to highlight these techniques. The three standard aerospace coordinate systems are described and built using rotations. The mathematics of rotations is described. using both matrices and quaternions. The necessary calculations are given for analysing standard scenarios that involve the Global Positioning Satellite system for finding lineof-sight directions on Earth. as well as for visualizing the world from a cockpit. and for converting to and from the standard software protocol for distributed interactive simulation environments. Appendices then discuss combining rotations. conversions with a particular type of Euler angle convention. the dangers of confusing Euler angles with incremental rotations for software writers, and finally there is a short discussion of interpolation of rotations in computing. Author

Coordinates; Aerospace Systems; Global Positioning System; Computerized SIMulation; Distributed Interactive SIMulation; Line of Sight; Rotation

20050212422 NASA Goddard Space Flight Center, Greenbelt, MD, USA

Introduction to Global Navigation Satellite System

Moreau, Michael; [2005]; 76 pp.; In English; NIST/30th Annual Time and Frequency Metrology Seminar, 9 Jun. 2005, Boulder, CO, USA; No Copyright; Avail: CASI; A05, Hardcopy

This viewgraph presentation reviews the fundamentals of satellite navigation, and specifically how GPS works. It presents an overview and status of Global Positioning System, for both the current GPS, and plans to modernize it in the future. There is also a overview and status of other Global Navigation Satellite System (GNSS), specifically GLONASS, Galileo, and QZSS. There is also a review of Satellite based time transfer techniques. The topic is of interest to the Time and Frequency Community, because the Global Positioning system has become the primary system for distributing Time and frequency globally, and because it allows users to synchronize clocks and calibrate and control oscillators in any location that has a GPS antenna. CASI

Frequencies; Navigation Satellites; Time Synchronization; Frequency Synchronization; Time Signals; Clocks; Global Positioning System

20050214128 NASA Goddard Space Flight Center, Greenbelt, MD, USA

A Model-based Approach to Controlling the ST-5 Constellation Lights-Out Using the GMSEC Message Bus and Simulink

Witt, Kenneth J.; Stanley, Jason; Shendock, Robert; Mandl, Daniel; [2005]; 7 pp.; In English; SERP 2005, 27-30 Jun. 2005, Las Vegas, NV, USA; Copyright; Avail: CASI; A02, Hardcopy

Space Technology 5 (ST-5) is a three-satellite constellation, technology validation mission under the New Millennium Program at NASA to be launched in March 2006. One of the key technologies to be validated is a lights-out, model-based operations approach to be used for one week to control the ST-5 constellation with no manual intervention.

The ground architecture features the GSFC Mission Services Evolution Center (GMSEC) middleware, which allows easy plugging in of software components and a standardized messaging protocol over a software bus. A predictive modeling tool built on MatLab’s Simulink software package makes use of the GMSEC standard messaging protocol to interface to the Advanced Mission Planning System (AMPS) Scenario Scheduler which controls all activities, resource allocation and real-time re-profiling of constellation resources when non-nominal events occur.

The key features of this system, which we refer to as the ST-5 Simulink system, are as follows: Original daily plan is checked to make sure that predicted resources needed are available by comparing the plan against the model. As the plan is run in real-time, the system re-profiles future activities in real-time if planned activities do not occur in the predicted timeframe or fashion. Alert messages are sent out on the GMSEC bus by the system if future predicted problems are detected. This will allow the Scenario Scheduler to correct the situation before the problem happens. The predictive model is evolved automatically over time via telemetry updates thus reducing the cost of implementing and maintaining the models by an order of magnitude from previous efforts at GSFC such as the model-based system built for MAP in the mid-1990’s.

This paper will describe the key features, lessons learned and implications for future missions once this system is successfully validated on-orbit in 2006. Author

Prediction Analysis Techniques; Satellite Constellations; Mission Planning; Autonomous Navigation; Formation Flying

20050214220 NASA Glenn Research Center, Cleveland, OH, USA, DYNACS Engineering Co., Inc., Cleveland, OH, USA

Radio Frequency (RF) Micro-Electromechanical Systems (MEMS) Switches for Space Communications

Simons, Rainee N.; Ponchak, George E.; Scardelletti, Maximillian C.; Varaljay, Nicholas C.; [2000]; 1 pp.; In English; International Conference on Integrated Nano/Microtechnology for Space Applications, 23-28 Jan. 2000, Houston, TX, USA Contract(s)/Grant(s): NAS3-98008; RTOP 632-50-58; No Copyright; Avail: Other Sources; Abstract Only

Micro-electromechanical systems (MEMS) is an emerging technology for radio frequency (RF) systems because it has the potential to dramatically decrease loss and improve efficiency. In this paper, we address the design and fabrication of novel MEMS switches being developed at NASA Glenn Research Center.

Two types of switches are being developed: a microstrip series single pole single throw (SPST) switch and a coplanar waveguide (CPW) series SPST and single pole double throw (SPDT) switches. These are being fabricated as an integral part of 50 Ohm microstrip and CPW RF integrated circuits using microfabrication techniques.

The construction of the switch relies on a cantilever beam that is partially supported by a dielectric post. The cantilever beam is electro-magnetically actuated. To decrease stiction, a Si3N4 thin film is deposited over the contact area. Thus, when the switch is closed, the ON-state insertion loss is governed by the parallel plate capacitance formed by the two contacts. The isolation in the OFF-state is governed by the parasitic capacitance when the cantilever is in the up position.

RF MEMS switches have been demonstrated with 80% lower insertion loss than conventional solid state devices (GaAs Metal Semiconductor Field Effect Transistors (MESFETs) and Silicon PIN diodes) based switches. For example, a conventional GaAs five-bit phase shifter which is required for beam steering in a phased array antenna has approximately 7 dB of insertion loss at 26.5 GHz where as a comparable MEMS based phase shifter is expected to have only 2 dB of insertion loss. This translates into 56% lower power dissipation and therefore decreases the thermal load on the spacecraft and also reduces the power amplifier requirements.

These benefits will enable NASA to build the next generation of deep space science crafts and micro/nano satellites. Author

Microelectromechanical Systems; Switches; Telecommunication; Radio Frequencies; Space Communication

Source: NASA.