A wireless ad hoc network is introduced that enables inter-robot communication and shared computation among multiple robots with PC/104-based single board computers running the real-time application interface patched Linux operating system. Through the use of IEEE 802.11 ad hoc technology and User Datagram Protocol, each robot is able to exchange data without the need of a centralized router or wireless access point. The paper presents three key aspects of this novel architecture to include: 1) procedures to install the real-time application interface patched operating system and wireless ad hoc communication protocol on a multiple robot system; 2) development of a Simulink ® library to enable intercommunication among robots and provide the requisite software-hardware interfaces for the onboard sensor suite and actuator packages; 3) methods to rapidly generate and deploy real-time executables using Mathwork's Real-Time Workshop™ to enable an autonomous robotic system. Experimental test results from the Spacecraft Robotics Laboratory at the Naval Postgraduate School are presented which demonstrate negligible network latencies and real-time distributed computing capability on the Autonomous Spacecraft Assembly Test Bed. A complete manual is also included to replicate the network and software infrastructures described in this work. Also, the developed Simulink ® library can be requested from the authors.
The Petite Amateur Navy Satellite (PANSAT) was launched aboard the STS-95 Discovery Shuttle on 29 October 1998. PANSAT was inserted into a circular, low-Earth orbit at an altitude of 550 km and 28.45°i nclination on 30 October 1998. PANSAT continues to operate and support the educational mission at NPS even after reaching its two-year design life. The research aspect also continues with the analysis of the accumulated telemetry data, in terms of how well the spacecraft operated over the mission design life. However, the store-and-forward mission using direct sequence spread spectrum was never realized. This paper describes the successes of the PANSAT project in developing a functional, low-cost, small satellite; and the lessons learned in designing largely with industrial components. Specifically, the use of commercial, off-the-shelf (COTS) nickel-cadmium batteries, sparse, yet judicious use of radiation-tolerant devices, error-detection-and-correction (EDAC) system RAM, and software design issues are discussed. The inability to realize the spread spectrum communications aspect is also presented.
PANSAT Mission DescriptionPANSAT will be a low-Earth orbit, free-tumbling satellite providing digital, store-and-forward communication using spread spectrum modulation. The satellite structure is composed of aluminum in a spherical configuration with a diameter of about 19 inches. PANSAT can be launched from a Shuttle Get Away Special (GAS) canister, which provides a typical orbit of 480 km at 28.5 o inclination. An average of 6 minutes of communication per pass is possible with this orbit, providing brief communication possibilities throughout the day. The satellite is expected to remain operational for two years.A general user on Earth will be able to connect with the orbiting PANSAT. While connected, the user may send and receive mail that is stored on-board PANSAT, upload and download files, and read spacecraft telemetry. Multiple users will have the capability of communicating with PANSAT during the same window of time over the one physical communication channel. The use of sophisticated protocols allows users to interleave their activities with PANSAT.The NPS ground station will be used to command PANSAT. It will also be used to gather telemetry not destined for the ordinary user, and to command any one of the spacecraft's subsystems. Furthermore, the NPS ground station will be able to communicate with an on-board experiment module, or future software programs, all of which are still unspecified or not selected. These features give PANSAT the ability to evolve and also correct deficiencies in software. Amateur Packet RadioAmateur packet radio is a communication technique that allows high speed and error-free digital data exchange. The amateur radio community has developed a data link layer protocol that fits within the seven layer Open Systems Interconnection (OSI) Reference Model. The data link layer is considered the second level protocol that communicates with the physical level. This protocol layer is responsible for taking a transmission facility (such as a spread spectrum modem attached to a radio transmitter) and producing an error-free link. This is accomplished by sending and This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States AbstractThe Naval Postgraduate School (NPS) is developing a small satellite for digital store-and-forward communication using spread spectrum techniques. NPS is looking toward the amateur radio community in an effort to utilize costeffective engineering and proven means of radio message relay. This cooperative initiative between NPS and the amateur radio community provides numerous benefits for the education of NPS officer students. The spacecraft will provide for amateur radio enthusiasts a new space communication mode utilizing spread spectrum modulation for packet radio. It also offers a means of evaluating spread spectrum in the increasingly congested frequency bands.
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