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Results of the telstar radiation experiments

The data from the particle experiments of the Telstar satellite have been analyzed to provide maps of the distribution of electrons and protons as measured in three of the Telstar detectors during the period from July through October, 1962. For the protons between 26 and 34 Mev and >50 Mev, the particle distributions are stable in time, but for the electron distribution there is a time decay of the electron flux over most of the region explored by the Telstar orbit. The connection of these observations to the high-altitude nuclear explosion of July 9, 1962, is discussed. The introduction of additional electrons by Russian tests at the end of October was also observed. The particle maps have been used to derive the integral particle exposure of the satellite, which is found to account quantitatively quite well for the radiation damage observed in the main solar power plant and in the radiation damage experiments on solar cells and special damage transistors carried by the satellite. In the main power plant the proton and electron contributions to damage are found to be equal. The integral particle exposure has also been used to compute the level of ionization in different depths of material in order to evaluate the degradation of semiconductor devices in the Telstar canister.

RADIATION EXPOSURE

Digital equipment for the antenna pointing system

This paper describes the digital control and data processing portions of the antenna pointing system used to track the Telstar satellite. The description is functional in nature, giving the form of the inputs, the functions performed, and the outputs produced. A general description of the digital equipment is followed by a discussion of the functions performed by the subsystems, the operational modes provided, the equipment features, and the operating experience.

DIRECTIONAL CONTROL

A high power travelling wave tube for satellite communications

This paper describes the CW travelling wave tube used by the Genera Post Office in their ground transmitter for Project Telstar. It operatcs in the 6000 Mc/s band with a maximum power output of about 5 kw and a bandwidth of great than 100 Mc/s. The factors influencing the design of the valve and its performance are discussed in some detail.

GROUND STATION

The autotrack system

The autotrack system accurately senses the direction of arrival, at the horn-reflector antenna, of the microwave beacon signal from the communications satellite. When this direction does not coincide with the horn-reflector pointing direction, error correcting voltages are automatically generated to enable the antenna direction system to steer the antenna toward the satellite. This paper presents a simple analysis of error voltage generation, a description of the system, and a brief discussion of system performance. Measurements at Andover, Maine, have shown that an angular pointing error of less than 0.005 degree is maintained by the antenna when using the autotrack system to follow the Telstar communications satellite.

SATELLITE COMMUNICATION

The satellite traveling-wave tube

The traveling-wave tube amplifier described provides a minimum output power of 3.5 watts at 4.0 to 4.2 gc. Design aspects that lead to lifetimes in excess of 10 years and to tube efficiencies between 35 to 40 per cent are discussed. The tube is focused by an improved version of the single-reversal magnetic circuit. Performance data pertinent to this particular satellite operation are shown. Highlights from the final production run and the subsequent life test serve to illustrate the care with which this TWT has been built.

TELSTAR SATELLITE

New Developments and Research Findings: NASA Hydrazine Arcjets

In 1984, the market for commercial geosynchronous communications satellites (comsats) was expanding and there was strong competition between spacecraft builders for market share. The propellant required for the north-south stationkeeping (NSSK) function was a major mission limiter, and the small chemical and resistojet systems then in use were at or near their physical limits. Thus, conditions were right for the development of a high performance NSSK system, and after an extensive survey of both propulsion technologies and the aerospace community, the NASA program chose hydrazine arcjets for development. A joint government/industry development program ensued which culminated in the acceptance of arcjet technology. NASA efforts included fundamental feasibility assessments, hardware development and verification, and multiple efforts aimed at the demonstration of critical operational characteristics of arcjet systems. Throughout the program, constant contact with the user community was maintained to determine system requirements. Both contracted and cooperative programs with industry were supported. First generation, kW-class arcjets are now operational for NSSK on the Telstar 401 satellite launched in December of 1993 and are baselined for use on multiple future satellite series (Intelsat 8, AsiaSat, Echostar). Arcjet development efforts are now focusing on the development of both high performance (600 s), 2 kW thrusters for application on next generation comsats and low power (Pe approximately 0.5 kW) for a variety of applications on power limited satellites. This paper presents a review of the NASA's role in the development of hydrazine arcjets with a focus on approaches, lessons learned, and the future.

Curren, Francis M.

4-gc parametric amplifier for satellite communication ground station receiver

This paper describes the design and performance of a 4-gc parametric amplifier which meets the stringent requirements of a satellite ground station receiver. It consists of two cascaded stages of similar design: the first of these is operated at liquid nitrogen temperature and the second at room temperature. One 23-gc pump source is used for both amplifier stages. The combination of the two amplifier stages provides 38-db over-all gain, 45°K over-all system input noise temperature, 60-mc bandwidth, 0.1-db short-term gain stability and 0.3-db long-term gain stability. A carefully designed cryogenic system maintains the amplifier refrigerated with only infrequent refilling of the dewar, i.e., once every 10 days.

MASER

A general description of the telstar spacecraft

The Telstar spacecraft design is discussed with emphasis on the electronics system. The description includes early planning, starting with frequency allocation considerations, and carries the program through electrical and mechanical design, construction and evaluation of the electronics system. The content is aimed at a broad introduction, depending on companion papers for many details of the spacecraft design.

TELSTAR SATELLITE

The spacecraft communications repeater

This paper describes the electrical characteristics of the waveguide components, the solid-state circuits and the traveling-wave tube used in the microwave communications repeater. The reflex-circuit method of obtaining local oscillator signals for the modulators and certain circuit stability problems are discussed.

MICROWAVE APPARATUS

The spacecraft antennas

The spacecraft employs two microwave antennas for communications and a single VHF antenna for telemetry, beacon, and command functions. One microwave antenna centered at 6 gc is used to receive broadband signals from a ground transmitter while the other microwave antenna centered at 4 gc is used to transmit signals to a ground receiver. Each microwave antenna is composed of a large number of circularly polarized radiating elements equally spaced around the equator of the spacecraft and connected to the electronic receiver and transmitter by a complex precision feed system. The VHF antenna is a small multi-element helix mounted at the pole of the spacecraft and radiates a linearly polarized signal. All antennas provide nearly isotropic antenna patterns with the axis of symmetry corresponding to the spin axis of the spacecraft. The antenna systems were constructed of light, but rugged, materials and passed extensive electrical, mechanical, and thermal tests.

ANTENNA

The ground transmitter and receiver

Ground station equipment for the Telstar experiment includes a 6-kmc transmitter and a 4-kmc receiver used for television and telephone channels. This paper describes the over-all transmitting and receiving arrangements and presents detailed accounts of the RF and power-supply subsystems. Information is also presented on protection, control and equipment features, and on receiver noise performance.

TRANSMITTER

Components for the telstar project

The Telstar project required a variety of components and structures of high reliability. The program for obtaining these components was essentially that originated for submarine cable devices, in which designs of proven integrity were manufactured under controlled conditions, screened and aged to remove defectives, and then life tested and certified using techniques for selecting the most stable components. This program summary illustrates in principle the techniques described in detail in the body of this components section of the issue.

SUBMARINE CABLE

The ground station high-power traveling-wave tube

The M4040 is a 2-kw CW traveling-wave tube developed specifically for communications applications. It was used as the power amplifier in the Project Telstar ground transmitter. Analytic methods employed in the design of the electron gun, the beam collector, the RF circuit and the output match are presented. Typical performance characteristics and drawings of the tube subassemblies serve to describe the electrical and physical features of the M4040 traveling-wave tube. Methods used to inhibit oscillation and the effects of ion drainage and collector depression on tube performance are also discussed.

TRAVELING WAVE TUBE

Telstar I, volume 4

Volume IV of NASA Special Publication SP-32 was originally intended to contain only those papers published outside of the Bell System Technical Journal that were pertinent to the Telstar I project. However, since that time, the results of Telstar II have been reported to NASA by the Bell Telephone Laboratories. It was then decided that this report should also be included.

PERFORMANCE CHARACTERISTICS