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    Within the nest two days, the Flight One ESRO II Satellite will be despatched to the U.

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    Background: Within the nest two days, the Flight One ESRO II Satellite will be despatched to the U.S.A. At TRW Systems, Los Angeles, it will undergo a solar simulation test in vacuum to confirm finally the thermal characteristics, before being moved to the Western Test Range in prepartation for the launch, due to take place on the 1st March, 1967.

    The ESRO II Satellite is the first of a series of satellites which are to be launched as part of a joint co-operative programme between the National Aeronautics and Space Administration of America and the European Space Research Organisation.

    The Satellite will measure the energy levels and spectral distribution of solar and cosmic radiation. It carries seven experiments which have been designed and developed by research groups in England, France and Holland. The experimentors and their intentions are shown in Table I.

    The timing of the launch has been chosen so that the atellite will spend a full year in space during the period of solar maximum. This will be the first time a satellite has been in orbit during a period of peak solar acitivity. The orbit has been chosen to be slightly elliptical, the perigee being at 350 km. and the apogee at 1100 km. The inclination of the orbit is retrograde at 98.22(degrees). At this inclination, the orbit plane rotates about the earth at the same rate as the sun and the satellite will be continuously in sunlight. Requirements of the orbit automatically define the maximum satellite weight which, at the beginning of the project, was specified at 80 kg. including the boost vehicle-to-satellite adaptor section.

    Certain experiments require to sample alternatively radiation from the sun and background radiation from space. It is, therefore, convenient to acheive this requirement by providing a spinning satellite with the spin axis perpendicular tot he sun line and the experiments veiwing radially perpendicular to the spin axis. A viewing accuracy of ??? 10(degrees) is required and it is therefore necessary to provide an attitude control system to maintain the spin axis perpendicular tot he sun line to within this tolerance. The attitude control system uses a magnetorquer, reference being made to the direction of the sun and the earth's magnetic field which, by use of suitable logic, causes the magnetorquer to operate as necessary.

    Since errors of launch time, dat and injection conditions can affect the attitude of the satellite spin axis, the attitude control system must be capable of removing any such initial errors.

    Some of the experiments also require that the sensors traverse the solar disc at a specific rate. This, therefore, dictates that a spin rate control system be employed. ESRO II is equipped with the capability of being spun-up from the minimum spin rate to the maximum, that is 15-40 r.p.m., three times during its lifetime. The spin up is achieved by dry nitrogen gas being discharged through an expansion nozzle, initiation being commanded from the ground.

    The R.F. system of the satellite consists of a command receiver with a capacity of 36 commands, a highpower transmitter which transmits data stored on a tape recorder which is caused to transmit by a ground command and a low power continuously operating telemetry which transmits real time data.

    Four antennae are provided. The antenna system includes a hybrid and dyplexor for frequency separation to the various transmitters and recievers.

    The power supplies are derived form body mounted solar cells and the solar array is capable of providing power to the system under the worst exlipse conditions.

    The structure consists basically of a central thrust tube carrying two equipment mounting floors. The two floors are of bonded honeycomb panels with aluminum skins and are joined together with six vertical diaphragms giving a stiff platform. The floors have additional support struts attached to the central cylinder which provide attenuation of low frequency vibrations. The solar cell panels are of aluminium faced honeycomb and are carried on six extruded magnesium alloy longerons which are stabilised at each end by frames. The frames also carry the thermal control end covers. Thermal control is achieved passively.

    The Sattelite also carries a nutation damping system of the ball and tube type which will minimise the coning angle which may occur from various perturbations in flight.

    A de-spin system,a yo-yo or bolas, is also carried as, at injection, in order to achieve stability, the 4th stage rocket will be spinning at 170 r.p.m. It is necessary to reduce this rotaiton rate to that required by the Satellite design.

    A housekeeping system is provided which enables various technological measurments to be made and enables the operation of the satellite when in orbit to be monitored. The separation sequence is also initiated by this system.

    Hawker Siddley Dynamics have been mainly contractors for the ESRO II Satellite and have been responsible for Project Management, Structure and Integration. Engins Matra of France have been the main associates with H.S.D. and have designed and developed the bulk of the electronic systems, antennae and ground equipment. The solar cells were produced by Ferranti Limited, the magnetometer by Sperry Gyroscope and the battery was manufactured by Gulton Industries of the U.S.A.

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