• Application of GPS to Hybrid Integrated Ranges and Simulations

      Van Wechel, R. J.; Jarrell, R. P.; Interstate Electronics Corp. (International Foundation for Telemetering, 1995-11)
      GPS user equipment has matured and is now available to support the use of live players in integrated ranges and simulations. P-code GPS provides true WGS-84 based coordinate information anywhere in the world at any time and to accuracies at the 5 ft (1s) level (demonstrated in high dynamic aircraft using differential P-code GPS). C/A code GPS shows lower accuracy and is especially vulnerable to multipath degradation over water. In supporting networked ranges with simulations, GPS is directly applicable to the dead reckoning requirements of the Distributed Interactive Simulation (DIS) community. DIS dead reckoning provides the capability of much reduced data rates in recovering TSPI information from platforms. The on-board state vector for an integrated GPS/Inertial Reference Unit provides accurate position, velocity and acceleration as well as attitude and attitude rate information so that dead reckoning thresholds can be both position and attitude driven. A simplified analysis is presented in the paper to derive dead reckoning update rates from the G loading levels of various player dynamics. Also, information is provided which results in word length requirements for GPS-based state vector information for transmission over minimum word length DIS Field Instrumentation Protocol Data Units (PDUs, which are the data block formats). The coordinate frame problem in use of GPS-based state vector information from fixed ranges is also addressed, showing that the use of a local geodetic frame is preferable to the use of an earth centered earth fixed frame, in that it is more efficient of network PDU word length.

      Mitchell, B. J.; The Johns Hopkins University (International Foundation for Telemetering, 1995-11)
      Recent narrow band imagery of the surface of Titan reveals a very non-uniform surface. While there are no global oceans of liquid ethane/methane as once conjectured, the imagery does suggest the possibility of seas or lakes of liquid ethane, methane, and other organic materials. If these exist, Titan could be considered a gigantic analog model of the Earth's climate system complete with land masses, moderately thick atmosphere, and large bodies of liquid. By studying the climate of Titan, we could gain further understanding of the processes and mechanisms that shape the Earth's climate. Reuse of existing technology and methods may be a way to speed development and lower costs for the global study of Titan. Surprisingly, one of the key technologies could be a Transit or Global Positioning System (GPS) descendant for use in tracking probes wandering the surface of Titan.
    • A GPS-Based Autonomous Onboard Destruct System

      Alves, Daniel F., Jr.; Keith, Edward L.; Alpha Instrumentation and Information Management; Microcosm Inc. (International Foundation for Telemetering, 1995-11)
      This paper examines the issues involved in replacing the current Range safety infrastructure with an autonomous range safety system based on GPS (Global Positioning Satellite) integrated navigation system solutions. Range safety is required in the first place because current launch vehicle navigation systems cannot meet a level of trust needed to determine if the mission is really under control and on course. Existing launch vehicle navigation is generally based on attitude and acceleration sensing instrumentation that are subject to drift, initialization errors and failures. Thus, a launch vehicle can easily be under the control of a seemingly operating navigation system, yet be steering the launch vehicle along an incorrect and dangerous flight path. Inertial-based navigation systems are good, but they cannot be trusted. The function of Range safety is to assure that untrustworthy navigation is backed up with a trusted system that has positive knowledge of the launch vehicle location, and the intelligence to decide when and where a launch vehicle must be destroyed. Combining inertial navigation, GPS derived position information and knowledge-based computer control has the potential to provide trusted and autonomous Range safety functions. The issues of autonomous Range safety are addressed in this paper.
    • Lessons Learned from Operating C/A-Code COTS GPS Receivers on Low-Earth Orbiting Satellites for Navigation

      Wiest, Terry; Nowitzky, Thomas E.; Grippando, Steven A.; Space & Missile Systems Center; Loral Space & Range Systems (International Foundation for Telemetering, 1995-11)
      Since June of 1993, an experimental GPS receiver system has been orbiting the earth aboard a small, low-altitude, polar-orbiting satellite called RADCAL. The purpose of the experiment was to prove the concept of using GPS for satellite navigation. If successful, the system would also provide a backup to the satellite's primary navigation beacon. The goal: provide position and velocity data to an accuracy of three to five meters, and provide attitude data to within a degree. The configuration of the RADCAL GPS experiment precluded realtime feedback loops for navigation; the data was stored and downloaded after a designated collection period. On the ground, a lengthy process was used to yield the position and attitude data days after the collection event. The GPS receivers and ground equipment were configured in several modes; they ultimately yielded a position accuracy of five meters, and attitude of two degrees. This was the original goal, and the experiment was considered successful. However, one of the receivers failed in November 1993, and the other failed in January 1995. The GPS receivers were commercially available and not spaceflight proven; they were suspected of being vulnerable to single-event upsets and latchups. This turned out to be the cause of the failure of both receivers. The interface between the GPS receivers and RADCAL's other subsystems proved to be the area which could not tolerate corrupt data. The single-event latchups problems would ultimately lead to the failure of the receivers. These difficulties, as well as other lesser obstacles, provide a host of lessons learned for future satellite navigation systems.
    • Talking GPS Locating System

      Buchwitz, Guy R. (International Foundation for Telemetering, 1995-11)
      The Talking GPS Locating System (TGLS) was developed to facilitate recovery of airborne targets by vocalizing and transmitting their Global Positioning System (GPS) coordinates to surface recovery teams following target splashdown. The airborne portion of the TGLS includes an off-the-shelf five-channel GPS receiver board, a GPS antenna, a microcontroller board with voice sample/playback circuitry, and a transmitter with antenna. Also part of the TGLS is a Record/Test Unit (RTU) which is used for pre-launch voice recording and ground tests. Upon splashdown, the TGLS is energized, the GPS receiver is initialized, and an optional homing tone burst -- periodically interrupted by a voice message relaying target and GPS receiver status -- is transmitted. Once the receiver has output valid longitude and latitude information to the microcontroller, this position is vocalized as the GPS status portion of the broadcast message. Just one intelligible reception of this message by any inexpensive, properly-tuned voice receiver will allow recovery teams to vector to within 25 to 100 meters of the target regardless of weather conditions or the time of day.
    • A Vehicle Tracking System Based on GPS

      Yongqian, Wang; Xianliang, Li; Qishan, Zhang (International Foundation for Telemetering, 1995-11)
      Vehicle tracking system based on GPS has been paid more and more attention. The system consists of GIS (Geological Information System), master station, movable station and communication network. Movable stations installed on automobiles transmit their position and status messages to the master station. All vehicles' tracks are drawn on the electrical map displayed by the master station's computer screen in real time. Vehicles' alarming signals can also be transmitted to the master station simultaneously. This paper presents a whole designing scheme of the vehicle tracking system, then it makes a thorough introduction to the system's performance and working procedure. The key technologies employed by the system and the relations between them are also discussed in details in the paper.