Specifications for the Design of a Low Cost Portable ...

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White Sands Complex. Scientific Community. Figure 1. Communications Architecture Concept Diagram. SMALL TERMINAL (TASTE). The step in the design of ...
98 Specifications for the Design of a Low Cost

Portable Earth Terminal

and Rafael Partnership for Space Telecommunications Education Electrical and Computer Engineering Department University of Puerto Rico, Campus PO Box 5000, Puerto Rico 00681-5000 Tel. (787)834-7620 Ext. 2263 or 2264- Fax (787)832-2485

INTRODUCTION Antarctica provides an incredibly rich variety of unspoiled settings for the installation and operation of scientific to study both our planet as well as the cosmos. The lack of spectral pollution, as well as unique atmospheric and environmental conditions, provide a great setting for earth-based experiments. The international scientific community has recognized Antarctica’s potential and is increasing its presence. One of these organizations, the Center for Astronomical Research in Antarctica under the sponsorship of the National Science Foundation has established the Automated Astronomical Site-Testing at the South Pole. The is a self-contained observatory, currently located at the South Pole, and proposed to be moved to the high plateau of Antarctica. Its purpose is to collect atmospheric and environmental data for the determination of the optimum location for a permanent multinational astronomical observatory. The itself is derived from the successful US Automated Geophysical Observatory (AGO) program. The same conditions that make Antarctica attractive for an observatory pose a significant challenge in the establishing of communication links to allow command and control of the instruments, as well as the gathering of data in a timely fashion. Currently, personnel must use low data rate links with some satellites or travel to the South Pole to retrieve the data for later analysis at their home institutions. A high data rate two-way communication link between the scientists and the would greatly enhance the productivity and efficiency of these projects. This issue is being addressed for other South Pole experimenters at Goddard Space Flight Center by the South Pole Relay Project. SOUTH POLE

RELAY

The South Pole Relay Project is a Proof-Of-Concept activity will provide high data rate communications links to the South Pole via the to allow Antarctica experimenters interactive Internet-type connectivity to and their scientific experiments. It will provide fill duplex communications channel at a 1.024 Megabit/second data rate in both directions while allowing the experimenters to utilize standard protocol. Also to be provided will be a simplex communications channel from the South Pole to White Sands Complex for data rates between I and 50 Megabits/second. Initial capability for file transfers will be constrained by the processors to 10 Megabit/second. The highly inclined (9.5 degrees) geosynchronous 1 spacecraft, currently located at longitude, will be used on a daily basis to open up a 2-2.5 hour window of communications with the South Pole when it is at its most southerly inclination each day. Its inclination will increase over the years, thus increasing the access time for the South Pole. It should be noted that is the only capable of covering the South Pole but a large part of Antarctica is in view of at least one The will apply the lessons learned from It will have a similar communications and operational architecture (see Figure 1). An earth terminal will be designed to provide the access to and NASA’s Space Network. It will be called the Small Terminal (TASTE).

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TAST E

White Sands Complex

Scientific Community

Figure 1

Communications Architecture Concept Diagram SMALL TERMINAL (TASTE)

The step in the design of TASTE is to determine the technical, operational, and economic requirements, constraints and options of the project. This sounds much simpler than what it really is since the process is an iterative one; requiring input potential customers, engineers, and managers spread out throughout all the world. At the moment of writing this report, input of various types had been received Antarctica, Australia, Canada, Belgium, and the United States. Most of the communications has been via thus making this a worldwide project from the beginning. REQUIREMENTS AND CONSTRAINTS Communication Links At present there is no communication link from the scientists to the There is only a Housekeeping and Status Report that is periodically relayed via the low-earth-orbit (LEO) satellite. This is a low bit rate, packet store-and-forward mode, method which does not provide much timeliness in data acquisition. A full-duplex link of only 300 baud would be a significant operational improvement over current capabilities and a maximum daily transfer of around 500 is projected. TASTE will provide data rates from 9.6 up to 150 rate for the transfer of 500 The upper limit, 150 comply with future service plans.

The lower limit, 9.6 should provide a reasonable was selected so as to have sufficient flexibility to

TASTE will only use the S-Band Multiple Access Mode for both Forward and Return links. Multiple Access allows for easier scheduling of Space Network time and will provide compatibility with the Demand Access Service Concept to be implemented in the Low Power Consumption Electrical power is a very scarce resource. A propane thermoelectric generator provides all the power for heating the as well as for electrical power. A total of regulated to is available for all the instrumentation. The resulting power budget is very tight, allowing for about to be available for the TASTE. Since current transceivers can consume over when transmitting, a group of batteries ( 12 AH) will

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be supplied to configure a regulating/charging power subsystem. A 1/20 duty cycle seems to be adequate for reliable operation. Reliable and Autonomous Operation instruments have been designed to in an autonomous mode and this standard must also be applied to TASTE. It should be extremely reliable and have the capability to work independently. Sufficient “intelligence” should be incorporated to allow continuous operation and recuperation from potential anomalies (discharged batteries, temporary loss of communications, etc.). Low Costs If TASTE is to become a viable alternative for operations it must be cost effective, both in the initial expenses as well as in daily operations. Current transceivers are too expensive (over $ for and other scientific observatories. A judicious selection of specifications and requirements for TASTE should improve the probability of designing an acceptable product. TASTE PRELIMINARY SPECIFICATIONS Enough information has been gathered to permit the publication of a reasonable set of TASTE Specifications with a conceptual block diagram. TASTE General Features and Specifications Return Link Transmitter Characteristics Operating Frequency RF Power Output Antenna Gain Total Antenna 3 Carrier Modulation Selectable Code Chip Rate Data Format Encoding Rate Data Rates Stability On/off Forward Link Receiver Characteristics Operating Frequency Antenna Gain Antenna 3 Carrier Demodulation Selectable Code Chip Rate Date Format Decoding Rate Data Rates Acquisition Threshold Noise Figure Implementation Loss

2287.5 MHz (Multiple Access) 1.0/5.0 W (Computer controlled) 26.5 26.5 33.5 8.1 degrees Compatible 3.08 1/2 9.6

Encoding (Computer controlled) to 150 (300

Computer controlled 2106.40625 MHz (Multiple Access) 26.5 8.1 degrees Compatible 3.08 1/2 to 150 >45

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Decoding (Computer controlled) (300 in

TASTE General Features and Specifications (cont.) S-Band Antenna Interface to Antenna

50 Ohms, N-type

Personal Computer / LAN Interface Interface Type Protocol

and Ethernet Asynchronous rate for Ethernet and Coax

Connector Type Physical and Environmental Temperature Supply Voltage DC Power Consumption

for

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