AO-40 Future Rests on Reducing Spin, Regaining Attitude Control

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    Space Bulletin 004 ARLS004

    From ARRL Headquarters

    Newington, CT February 6, 2001

    To all radio amateurs




    SB SPACE ARL ARLS004


    ARLS004 AO-40 Future Rests on Reducing Spin, Regaining Attitude Control



    The key to a successful AO-40 recovery effort continues to be a
    matter of reducing the satellite's spin and regaining the ability to
    adjust its attitude from the ground. ''The current problem is the
    lack of accurate AO-40 attitude data,'' AMSAT News Service said.
    Accurate data are not available because AO-40's sun sensor is not
    seeing the sun because of the satellite's attitude.



    Only when ground controllers can accurately determine the
    satellite's attitude will it be possible to change it and correctly
    aim AO-40's high-gain antennas for optimal reception on Earth--and
    that's assuming the transmitters are functioning on bands other than
    2.4 GHz. Ground controllers have had no luck hearing AO-40's
    transmitters on the omnidirectional antennas on 2 meters, 70 cm or
    1.2 GHz. Since the satellite's computer was reset and telemetry
    resumed December 25, the AO-40 ground team has been analyzing
    telemetry sent via the 2.4 GHz beacon--the only transmitter now
    operating.



    AMSAT-Germany described AO-40 as ''in the fog'' because its high
    angle with respect to the sun temporarily prevents the sun sensors
    from providing attitude data.



    Ground controllers have been pinning their hopes on a previously
    announced ''de-spinner'' programming routine that would permit AO-40
    spin control without having to rely on the sun sensors. The
    satellite's current spin rate is reported to be 17.7 RPM. But even
    if the programming fix fails, ''it's no cause for panic,'' AMSAT-DL
    said. By April, controllers reason, the satellites sensors will
    again see the sun and ''thanks to magnetorquing, spin and attitude
    can be actively improved upon the rising tide.'' Once the spin is
    reduced, sun angle improved, and antennas pointed, testing can
    resume. Still outstanding are tests of the VHF and UHF transmitters,
    the arc-jet motor, and the reaction wheels, among others.



    Both AMSAT-DL President and AO-40 Project Leader Karl Meinzer,
    DJ4ZC, and AMSAT-NA President Robin Haighton, VE3FRH, have continued
    to be optimistic that AO-40 will have a useful life of Amateur Radio
    service. Command stations James Miller, G3RUH, Stacey Mills, W4SM,
    made a long-term prediction of AO-40's new orbit. They say that even
    after last year's incident--which silenced the satellite for nearly
    two weeks--and the resulting decrease of perigee, AO-40's orbit will
    be stable, although perigee will oscillate by several hundred
    kilometers.



    AMSAT-DL says the recovery effort has been slowed somewhat because
    of limited access time on the part of the command team, due to
    AO-40's current orbital parameters.



    Discussions of the future of AO-40 are expected to dominate the
    eighth AMSAT-DL Symposium on March 17, AMSAT-DL said.
     
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